# Patent

## Title
Method of assembling a ball grid array package with patterned stiffener layer

## Abstract

Electrically, mechanically, and thermally enhanced ball grid array (BGA) packages are described. An IC die is mounted in a centrally located cavity of a substantially planar first surface of a stiffener. The first surface of a substrate is attached to a substantially planar second surface of the stiffener. The second surface of the stiffener is opposed to the first surface of the stiffener. A centrally located protruding portion on the second surface of the stiffener is opposed to the centrally located cavity. The protruding portion extends through an opening in the substrate. A wire bond is coupled from a bond pad of the IC die to a contact pad on the first surface of the substrate through a through-pattern in the stiffener. The through-pattern in the stiffener is one of an opening through the stiffener, a recessed portion in an edge of the stiffener, a notch in an edge of the recessed portion, and a notch in an edge of the opening.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This is a divisional of application Ser. No. 10/284,340 filed Oct. 31, 2002, now U.S. Pat. No. 6,906,414, which claims the benefit of U.S. Provisional Application No. 60/352,877, filed Feb. 1, 2002, which is herein incorporated by reference in its entirety, and is a continuation-in-part of pending U.S. application “Enhanced Die-up Ball Grid Array Packages and Method for Making the Same,” Ser. No. 09/984,259, filed Oct. 29, 2001 Now U.S. Pat. No. 7,132,744, which is a continuation-in-part of pending U.S. application “Enhanced Die-Up Ball Grid Array and Method for Making the Same,” Ser. No. 09/742,366, filed Dec. 22, 2000, now abandoned which are incorporated herein by reference in their entirety.
The following applications of common assignee are related to the present application, have the same filing date as the present application, and are herein incorporated by reference in their entireties:
“Ball Grid Array Package Enhanced With a Thermal And Electrical Connector,”, Ser. No. 10/284,312;
“Ball Grid Array Package with Stepped Stiffener Layer,”, Ser. No. 10/284,371;
“Ball Grid Array Package Fabrication with IC Die Support Structures,”, Ser. No. 10/284,349, now U.S. Pat. No. 6,825,108;
“Ball Grid Array Package with Multiple Interposers,”, Ser. No. 10/284,166; and “Ball Grid Array Package with Separated Stiffener Layer,”, Ser. No. 10/284,366.


BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to the field of integrated circuit (IC) device packaging technology and, more particularly, to substrate stiffening and heat spreading techniques in ball grid array (BGA) packages.
2. Background Art
Integrated circuit (IC) dies are typically mounted in or on a package that facilitates attachment to a printed circuit board (PCB). One such type of IC package is a ball grid array (BGA) package. BGA packages provide for smaller footprints than many other package solutions available today. A BGA package has an array of solder balls located on a bottom external surface of a package substrate. The solder balls are reflowed to attach the package to the PCB. The IC die is mounted to a top surface of the package substrate. Wire bonds typically couple signals in the IC die to the substrate. The substrate has internal routing which electrically couples the IC die signals to the solder balls on the bottom substrate surface.
A number of BGA package substrate types exist, including ceramic, plastic, and tape (also known as “flex”). In some BGA package types, a stiffener may be attached to the substrate to supply planarity and rigidity to the package. In such packages, the IC die may be mounted to the stiffener instead of the substrate. Openings in the stiffener may be used to allow the IC die to be wire-bonded to the substrate.
Die-up and die-down BGA package configurations exist. In die-up BGA packages, the IC die is mounted on a top surface of the substrate or stiffener, opposite of the side to which the solder balls are attached. In die-down BGA packages, the IC die is mounted on a bottom surface of the substrate or stiffener, on the same side as which the solder balls are attached.
Existing BGA packages are subject to high thermal stresses that result from the heat given off during operation of the mounted IC die. The thermal stresses are primarily imposed on the IC die and solder balls due to the mismatch of the thermal expansion coefficient (CTE) between the semiconductor die and the metal stiffener. As a result, existing flex BGA packages have difficulty in meeting reliability requirements for die sizes larger than about 9 mm. See, e.g., Thompson, T., et al., Reliability Assessment of a Thin (Flex) BGA Using a Polyimide Tape Substrate, International Electronics Manufacturing Technology Symposium, IEEE, pp. 207–213 (1999).
The tape substrate used in flex BGA packages is typically polyimide, which has a low value of thermal conductivity. Consequently, the IC die is separated from the PCB internally by the tape substrate which acts as a thermal barrier. The lack of direct thermal connection from IC die to PCB leads to relatively high resistance to heat transfer from IC die-to-board (theta-jb).
A stiffener attached to a substrate can enhance heat spreading. However, the openings on the stiffener for wire bond connections tend to reduce the thermal connections between the IC die and the edges of the stiffener. As a result, heat spreading is limited largely to the region of the IC die attach pad, while areas at the stiffener periphery do not contribute effectively to heat spreading.
Furthermore, because of the high density of the substrate routing circuitry, it is difficult to bond each power and ground pad on the IC die to the substrate by a corresponding bond finger. As a result, the distribution of ground and power signals connecting to the IC die is frequently compromised in conventional BGA packages.
Ball grid array packages that use plastic substrates (for example, BT or FR4 plastic) are commonly known as plastic BGAs, or PBGAs. See, e.g., Lau, J. H., Ball Grid Array Technology, McGraw-Hill, New York, (1995). A PBGA package, for example, may add solder balls to the bottom substrate surface under the IC die to aid in conducting heat to the PCB. Solder balls such as these are referred to as thermal balls. The cost of the PBGA package, however, will increase with the number of thermal balls. Furthermore, a large array of thermal balls may be necessary for heat dissipation into the PCB for high levels of IC device power.
Hence, what is needed are BGA packages with improved heat spreading capabilities, while also providing for high levels of IC electrical performance.
BRIEF SUMMARY OF THE INVENTION
Ball grid array (BGA) packages having enhanced electrical and thermal characteristics are described herein. In an aspect of the present invention, a stiffener for use in a ball grid array (BGA) package is described. The stiffener includes a substantially planar first surface having a centrally located cavity, and a substantially planar second surface opposed to the first surface. The second surface has a centrally located protruding portion that opposes the centrally located cavity.
In an aspect, the protruding portion has a height such that the protruding portion is capable of extending through an opening in a BGA package substrate when the stiffener is present in a BGA package. In one aspect, a surface of the protruding portion is capable of being attached to a surface of a printed circuit board (PCB) when the BGA package is mounted to the PCB. In another aspect, the surface of the protruding portion is capable of extending into a cavity formed in a surface of a printed circuit board (PCB) when the BGA package is mounted to the PCB.
In a further aspect, the stiffener further includes a plurality of openings through the stiffener that are open at the first surface and the second surface.
In an aspect, the plurality of openings includes a substantially rectangular shaped opening proximate to each of first, second, third, and fourth edges of the cavity.
In another aspect, the plurality of openings includes a plurality of substantially rectangular shaped openings arranged in series proximate to an edge of the cavity.
In another aspect, the plurality of openings includes a substantially rectangular shaped opening adjacent to an edge of the cavity. The substantially rectangular opening is bridged by at least one stiffener stud.
In another aspect, the plurality of openings includes a first opening having an edge that coincides with the first edge of the cavity.
In another aspect, the plurality of openings includes an opening adjacent to an edge of the cavity. The opening has at least one notch formed in at least one edge of the opening.
In a still further aspect of the present invention, the stiffener includes at least one recessed portion in at least one edge of the first and second surfaces.
In an aspect, the at least one recessed portion includes a substantially rectangular shaped recessed portion in a first edge of the first and the second surfaces, a second substantially rectangular shaped recessed portion in a second edge of the first and the second surfaces, a third substantially rectangular shaped recessed portion in a third edge of the first and the second surfaces, and a fourth substantially rectangular shaped recessed portion in a fourth edge of the first and the second surfaces.
In another aspect, the at least one recessed portion includes a first recessed portion that is substantially rectangular shaped and has an edge that coincides with a first edge of the cavity.
In another aspect, the at least one recessed portion includes a first recessed portion that has at least one notch formed in at least one edge of the first recessed portion.
In a further aspect of the present invention, a BGA package incorporates a patterned stiffener. An IC die is mounted in a centrally located cavity of a substantially planar first surface of a stiffener. The first surface of a substrate is attached to a substantially planar second surface of the stiffener. The second surface of the stiffener is opposed to the first surface of the stiffener. A centrally located protruding portion of the second surface of the stiffener is opposed to the centrally located cavity. The protruding portion extends through an opening in the substrate. A wire bond is coupled from a bond pad of the IC die to a contact pad on the first surface of the substrate through a through-pattern in the stiffener.
In aspects of the present invention, the through-pattern in the stiffener is an opening through the stiffener, a recessed portion in an edge of the stiffener, a notch in an edge of the recessed portion, a notch in an edge of the opening, and/or additional through-patterns described herein.
Further aspects, features, and advantages of the present invention, as well as the structure and operation of the various embodiments of the present invention, are described in detail below with reference to the accompanying drawings.



BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES
The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention.
FIGS. 1A and 1B illustrate conventional flex BGA packages.
FIG. 2A shows a top view of a stiffener.
FIG. 2B shows a temperature distribution for a stiffener during operation of an IC device in a flex BGA package.
FIG. 2C shows an top view of an alternative stiffener configuration.
FIG. 3 shows a cross-sectional view of a conventional die-up plastic BGA package.
FIG. 4 illustrates a cross-sectional view of a die-up flex BGA package with heat spreader, according to an embodiment of the present invention.
FIG. 5 show a cross-sectional view of an alternative BGA package, according to embodiments of the present invention, where the heat spreader is internal to the BGA package.
FIG. 6 illustrates a cross-sectional view of a die-up flex BGA package with stiffener ground plane, according to an embodiment of the present invention.
FIG. 7 illustrates a cross-sectional view of a die-up flex BGA package with patterned stiffener, according to an embodiment of the present invention.
FIG. 8 illustrates a cross-sectional view of a die-up flex BGA package with ground/thermal connector, according to an embodiment of the present invention.
FIG. 9A illustrates a cross-sectional view of a die-up tape BGA package with metal ring, according to an embodiment of the present invention.
FIG. 9B illustrates a top view of the die-up tape BGA package with metal ring of FIG. 9A, according to an embodiment of the present invention.
FIG. 10A illustrates a stiffener that includes one or more thermal studs, according to an embodiment of the present invention.
FIG. 10B illustrates an IC die that is wire bound to a substrate through openings in the stiffener of FIG. 10A, according to an embodiment of the present invention.
FIG. 11 illustrates a cross-sectional view of a die-up PBGA package with ground/thermal connector, according to an embodiment of the present invention.
FIG. 12A illustrates a cross-sectional view of a die-up BGA package.
FIGS. 12B and 12C illustrate exemplary solder ball arrangements for the die-up BGA package of FIG. 12A.
FIG. 13 shows exemplary routing in a substrate layer.
FIG. 14 shows a flowchart related to FIGS. 4 and 5, that provides operational steps of exemplary embodiments of the present invention.
FIG. 15 shows a flowchart related to FIG. 6 that provides operational steps of exemplary embodiments of the present invention.
FIGS. 16A–D show flowcharts related to FIGS. 7 and 8 that provide operational steps of exemplary embodiments of the present invention.
FIG. 17 shows a flowchart related to FIGS. 9A and 9B that provides operational steps of exemplary embodiments of the present invention.
FIG. 18 shows a flowchart related to FIGS. 10A and 10B that provides operational steps of exemplary embodiments of the present invention.
FIGS. 19A–C show flowcharts related to FIG. 11 that provide operational steps of exemplary embodiments of the present invention.
FIG. 20 illustrates a substrate that has a central window opening, according to an embodiment of the present invention.
FIG. 21 illustrates a side view of a stiffener that has a downward protruding portion, according to an embodiment of the present invention.
FIG. 22 illustrates a cross-sectional view of a portion of a die-up PBGA package, according to an embodiment of the present invention.
FIG. 23 shows an example ground/thermal connector attached to a bottom surface of a substrate, according to an embodiment of the present invention.
FIG. 24 shows first and second ground/thermal connectors attached to a bottom surface of a substrate, according to an exemplary embodiment of the present invention.
FIG. 25 shows first, second, third, and fourth ground/thermal connectors attached to a bottom surface of a substrate, according to an exemplary embodiment of the present invention.
FIG. 26 shows a flowchart providing operational steps for assembling one or more embodiments of the present invention.
FIG. 27 shows first and second ground/thermal connectors attached to a bottom surface of a substrate, according to an exemplary embodiment of the present invention.
FIG. 28 shows a bottom view of a corner portion of a substrate with potential via locations.
FIGS. 29 and 30 show an example bottom views of a corner portion of a substrate, according to embodiments of the present invention.
FIG. 31 shows a bottom view of an example BGA package, according to an embodiment of the present invention.
FIG. 32 shows a bottom view of the example BGA package of FIG. 31, with electronic devices attached, according to an embodiment of the present invention.
FIG. 33 shows a portion of a printed circuit board for mounting a BGA package, according to an exemplary embodiment of the present invention.
FIG. 34 shows the printed circuit board portion of FIG. 33 with electronic devices attached, according to an embodiment of the present invention.
FIG. 35 shows an cross-sectional view of the BGA package of FIG. 32 mounted to the printed circuit board of FIG. 34, according to an embodiment of the present invention.
FIGS. 36A and 36B show flowcharts providing operational steps for assembling embodiments of the present invention.
FIG. 37 illustrates a cross-sectional view of a stiffener, according to an embodiment of the present invention.
FIG. 38 illustrates a cross-sectional views of die-up BGA package with patterned stiffener, according to an example embodiment of the present invention.
FIGS. 39A and 39B illustrate top and bottom views of the patterned stiffener shown in FIG. 38, according to an embodiment of the present invention.
FIG. 39C illustrates a top view of a patterned stiffener with trapezoidal openings, according to an embodiment of the present invention.
FIG. 40 illustrates a cross-sectional views of die-up BGA package with patterned stiffener, according to an example embodiment of the present invention.
FIGS. 41C–41F illustrate top and bottom views of stiffeners with recessed edge portions wherein these recessed edges are not substantially rectangular shaped.
FIGS. 42 and 43 show flowcharts providing steps for forming a stiffener, according to example embodiments of the present invention.
FIG. 44 shows a flowchart providing steps for assembling one or more BGA packages, according to embodiments of the present invention.
FIGS. 45A, 45B, 46A, 46B, 47A, 47B, 48A, 48B, 49A, and 49B show views of PCBs with example land patterns for attaching patterned stiffeners, according to embodiments of the present invention.
FIGS. 50A and 50B show views of PCBs with example openings for accommodating patterned stiffeners, according to embodiments of the present invention.
FIG. 51 shows a BGA package with seal ring, according to an embodiment of the present invention.



The present invention will now be described with reference to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements. Additionally, the left-most digit(s) of a reference number identifies the drawing in which the reference number first appears.
DETAILED DESCRIPTION OF THE INVENTION
Overview
The present invention is directed to a method and system for improving the mechanical, thermal, and electrical performance of BGA packages. The present invention is applicable to all types of BGA substrates, including ceramic, plastic, and tape (flex) BGA packages. Furthermore the present invention is applicable to die-up (cavity-up) and die-down (cavity-down) orientations.
Numerous embodiments of the present invention are presented herein. In a first embodiment, BGA package thermal stress at the IC die/stiffener interface is released or altered with the introduction of a heat spreader on the top surface of the IC die, enabling large size dies with high input and output (I/O) counts to be packaged using BGA technology. In a second embodiment, BGA package thermal resistance and the length of the current return path are reduced by introducing thermal/ground balls underneath or within close proximity of the IC die. In a third embodiment, the package thermal resistance and ground inductance are reduced by removing center solder balls, and enabling the attachment of a die pad to the PCB. The die pad is attached to the PCB with novel patternings of the metal stiffener, or by positioning a thermal/ground connector in between the IC die pad and the PCB. In a fourth embodiment, the package thermal resistance is reduced by attaching a metal ring to the top surface of a stiffener. In a fifth embodiment, the package thermal resistance is reduced by bridging the die pad to the outer regions of the stiffener with metal studs.
In further embodiments according to the present invention, the electrical performance of the BGA package is improved. In a sixth embodiment, electrical performance is improved by connecting ground bonds from the IC die to the stiffener. In such a configuration, the stiffener operates as a package ground plane. The package ground plane may be connected to PCB ground through either thermal/ground balls or thermal/ground connectors mentioned in embodiments above, and further described herein. In a seventh embodiment, package power distribution is enhanced by using a layer in a tape substrate as a power or ground plane.
In still further embodiments according to the present invention, plastic ball grid array (PBGA) package thermal and electrical performances are improved. In an eighth embodiment, replacing the center solder balls with a solid conductor reduces the package junction-to-board thermal resistance and package ground inductance of a PBGA package.
Ball grid array package types are described below. Further detail on the above described embodiments, and additional embodiments according to the present invention, are presented below. The embodiments described herein may be combined as required by a particular application.
Ball Grid Array (BGA) Package
A ball grid array (BGA) package is used to package and interface an IC die with a printed circuit board (PCB). BGA packages may be used with any type of IC die, and are particularly useful for high speed ICs. In a BGA package, solder pads do not just surround the package periphery, as in chip carrier type packages, but cover the entire bottom package surface in an array configuration. BGA packages are also referred to as pad array carrier (PAC), pad array, land grid array, and pad-grid array packages. BGA packages types are further described in the following paragraphs. For additional description on BGA packages, refer to Lau, J. H., Ball Grid Array Technology, McGraw-Hill, New York, (1995), which is herein incorporated by reference in its entirety.
Die-up and die-down BGA package configurations exist. In die-up BGA packages, the IC die is mounted on a top surface of the substrate or stiffener, in a direction away from the PCB. In die-down BGA packages, the IC die is mounted on a bottom surface of the substrate or stiffener, in a direction towards the PCB.
A number of BGA package substrate types exist, including ceramic, plastic (PBGA), and tape (also known as “flex”) (for example, refer to Hayden, T. F., et al., Thermal &Electrical Performance and Reliability Results for Cavity-Up Enhanced BGAs, Electronic Components and Technology Conference, IEEE, pp. 638–644 (1999), which is incorporated herein by reference). FIG. 1A illustrates a conventional flex BGA package 100. Flex BGA package 100 includes an IC die 102, a tape substrate 104, a plurality of solder balls 106, and one or more wire bonds 108. Tape or flex BGA packages are particularly appropriate for large IC dies with large numbers of inputs and outputs, such as application specific integrated circuits (ASIC) and microprocessors.
Tape substrate 104 is generally made from one or more conductive layers bonded with a dielectric material. For instance, the dielectric material may be made from various substances, such as polyimide tape. The conductive layers are typically made from a metal, or combination of metals, such as copper and aluminum. Trace or routing patterns are made in the conductive layer material. Substrate 104 may be a single-layer tape, a two-layer tape, or additional layer tape substrate type. In a two-layer tape, the metal layers sandwich the dielectric layer, such as in a copper-Upilex-copper arrangement.
IC die 102 is attached directly to substrate 104, for example, by an epoxy. IC die 102 is any type of semiconductor integrated circuit.
One or more wire bonds 108 connect corresponding bond pads 118 on IC die 102 to contact points 120 on substrate 104.
An encapsulate, mold compound, or epoxy 116 covers IC die 102 and wire bonds 108 for mechanical and environmental protection.
As shown in FIG. 1A, flex BGA package 100 does not include a stiffener. In some BGA package types, particularly in flex BGA packages, a stiffener can be attached to the substrate to add planarity and rigidity to the package. FIG. 1B illustrates a flex BGA package 110, similar to flex BGA package 100, that incorporates a stiffener 112. Stiffener 112 may be laminated to substrate 104. Stiffener 112 is typically made from a metal, or combination of metals, such as copper, tin, and aluminum, or may be made from a polymer, for example. Stiffener 112 also may act as a heat sink, and allow for greater heat spreading in BGA package 110. One or more openings 114 in stiffener 112 may be used to allow for wire bonds 108 to connect IC die 102 to substrate 104. Stiffener 112 may be configured in other ways, and have different opening arrangements than shown in FIG. 1B.
The use of a stiffener in a flex BGA package requires additional considerations when attempting to manage heat spreading. FIG. 2A shows a top view of a stiffener 112. Stiffener 112 includes an opening 114 adjacent to all four sides of an IC die mounting position 202 in the center of stiffener 112. FIG. 2B shows a temperature distribution 204 of a stiffener, such as stiffener 112, during operation of an IC die in a flex BGA package. Temperature distribution 204 shows that heat transfer from IC die mounting position 202 to the edges of stiffener 112 is substantially limited by openings 114. Openings 114 act as thermal barriers to heat spreading in stiffener 112.
FIG. 2C shows a top view of an alternative configuration for stiffener 112, according to an embodiment of the present invention. Stiffener 112 includes an opening 206 adjacent to all four sides of an IC die mounting position 202 in the center of stiffener 112. Openings 206 are similar to openings 114 of FIG. 2A, but have a different shape. Further alternatively shaped openings in stiffener 112 are applicable to the present invention.
FIG. 3 shows a cross-sectional view of a conventional die-up PBGA package 300. PBGA package 300 includes a plastic substrate 302, an IC die 304, a plurality of solder balls 306, a plurality of wire bonds 308, a die pad 310, one or more vias 314, a solder mask 318, and one or more thermal/ground vias 316.
Plastic substrate 302 includes one or more metal layers formed on an organic substrate. For example, plastic or organic substrates may include materials such as “BT”, which includes a resin called bis-maleimide triazine, and/or “FR-4,” which is a fire-retardant epoxy resin-glass cloth laminate material, and/or other similar materials. IC die 304 is mounted to die pad 310. IC die 304 may be attached to die pad 310 with an epoxy, such as a silver-filled epoxy. Wire bonds 308 connect signals of IC die 304 to substrate 302. For instance, gold bonding wire is bonded from aluminum bond pads on IC die 304 to gold-plated contact pads on substrate 302. The contact pads on substrate 302 connect to solder balls 306 attached to the bottom surface of substrate 302, through vias 314 and routing within substrate 302 using copper conductors 312. Thermal/ground vias 316 connect die pad 310 to one or more thermal/ground balls 322 on the center bottom surface of substrate 302. An encapsulate, mold compound, or epoxy 320 covers IC die 304 and wire bonds 308 for mechanical and environmental protection.
As described above, a BGA package includes an array of solder balls located on a bottom external surface of the package substrate. FIG. 12A illustrates a cross-sectional view of a die-up BGA package 1200. FIGS. 12B and 12C illustrate exemplary solder ball arrangements for die-up BGA package 1200. As shown in FIG. 12A, BGA package 1200 includes an IC die 1208 mounted on a substrate 1212. IC die 1208 is electrically connected to substrate 1212 by one or more wire bonds 1210. Wire bonds 1210 are electrically connected to solder balls 1206 underneath substrate 1212 through corresponding vias and routing in substrate 1212. The vias in substrate 1212 can be filled with a conductive material, such as solder, to allow for these connections. Solder balls 1206 are attached to substrate 1212, and are used to attach the BGA package to a PCB.
Note that although wire bonds, such as wire bonds 1210, are shown and described herein, IC dies may be mounted and coupled to a substrate with solder balls located on the bottom surface of the IC die, by a process commonly referred to as “C4” or “flip chip” packaging.
As shown in FIG. 12B, solder balls 1206 may be arranged in an array. FIG. 12B shows a 14 by 14 array of solder balls on the bottom surface of BGA package 1200. Other sized arrays of solder balls are also applicable to the present invention. Solder balls 1206 are reflowed to attach BGA package 1200 to a PCB. The PCB may include contact pads to which solder balls 1206 are bonded. PCB contact pads are generally made from a metal or combination of metals, such as copper, nickel, tin, and gold.
FIG. 12C shows a bottom view of BGA package 1200, with an alternative solder ball array arrangement. BGA package 1200 attaches an array of solder balls 1206 on a bottom surface of substrate 1212. As shown in FIG. 12C, solder balls 1206 are located in a peripheral area of the bottom surface of substrate 1212, away from a substrate center 1224. For example, solder balls 1206 on the bottom surface of substrate 1212 may be located outside an outer profile area of an IC die mounted on the opposite surface of substrate 1212. The solder ball array may be organized in any number of ways, according to the requirements of the particular BGA package application.
The solder ball arrangement shown in FIG. 12C is particularly applicable to embodiments of the present invention described below, such as for attaching a heat spreader or ground/thermal connector to a bottom surface of a BGA package. The heat spreader or ground/thermal connector may be connected in substrate center 1224.
As described above, the BGA package substrate provides vias and routing on one or more layers to connect contact pads for wire bonds on its upper surface to solder balls attached to the bottom substrate surface. For illustrative purposes, FIG. 13 shows solder ball pads and routing 1304 in an example bottom substrate layer 1302.
The present invention is applicable to improving thermal and electrical performance in the BGA package types described herein, and further BGA package types.
BGA Embodiments According to the Present Invention
Further details of structural and operational implementations of ball grid array packages of the present invention are described in the following sections. These structural and operational implementations are described herein for illustrative purposes, and are not limiting. For instance, the present invention as described herein may be implemented in both die-up and die-down BGA package types, as well as other IC package types. Furthermore, each of the embodiments presented below are applicable to tape substrate BGA packages, plastic substrate BGA packages, and ceramic substrate BGA packages. The description below is adaptable to these and other package types, as would be understood to persons skilled in the relevant art(s) from the teachings herein. For instance, in plastic substrate BGA packages, and some tape BGA packages, a stiffener may not be required in the BGA package.
Features of each of the embodiments presented below may be incorporated into BGA packages independently, or may be combined in any manner, as would be apparent to persons skilled in the relevant art(s) from the teachings herein.
Drop-In Heat Spreader Embodiments
According to an embodiment of the present invention, a heat spreader may be used in a BGA package to provide for thermal stress relief and heat dissipation. In a preferred embodiment, a drop-in heat spreader is attached to the top surface of an IC die in a flex BGA package to provide for thermal stress relief and heat dissipation.
FIG. 4 illustrates a cross-sectional view of a die-up flex BGA package 400, according to an embodiment of the present invention. BGA package 400 includes IC die 102, substrate 104, plurality of solder balls 106, one or more wire bonds 108, stiffener 112, epoxy 116, a drop-in heat spreader 402, and an epoxy 404. Refer to the discussion above related to FIGS. 1A–1B for additional detail on the structure and operation of some of these elements.
Substrate 104 has a top surface to which a bottom surface of stiffener 112 is mounted. A bottom surface of substrate 104 attaches the plurality of solder balls 106. The plurality of solder balls 106 connect to vias and/or points on the bottom surface of substrate 104 to which signals internal to substrate 104 are routed and exposed.
Stiffener 112 has a top surface to which IC die 102 is mounted. In alternate embodiments, BGA package 400 does not require a stiffener, and does not include a stiffener 112. In such an alternate embodiment, IC die 102 is mounted to substrate 104.
One or more wire bonds 108 connect corresponding bond pads 118 on IC die 102 to contact points 120 on substrate 104. When a stiffener 112 is present, as shown in FIG. 4, wire bonds 108 extend through one or more openings 114 in stiffener 112 to form connections with substrate 104.
Heat spreader 402 is attached to the top surface (active surface) of IC die 102 using epoxy 404. The epoxy 404 may be the same substance as epoxy 116, or may be a different substance. Silver filled epoxies may be used for epoxy 404 to enhance heat extraction from IC die 102.
As shown in FIG. 4, heat spreader 402 is smaller in area than the upper surface of IC die 102. Alternative sizes for heat spreader 402 are also applicable to the present invention, including sizes equal to the area of IC die 102, or larger areas. Heat spreader 402 is shaped and configured to spread heat from IC die 102, as is required by the application.
As shown in FIG. 4, the top surface of heat spreader 402 forms a portion of a top surface of BGA package 400. Heat dissipation to the environment can be improved by exposing the top surface of heat spreader 402. Furthermore, in such a configuration, additional heat sinks may be attached to heat spreader 402. FIG. 5 show a cross-sectional view of an alternative BGA package 500, according to embodiments of the present invention, where a heat spreader 502 is internal to BGA package 500. Heat spreader 502 is completely encapsulated by epoxy 116.
By attaching heat spreader 402 to the top surface of IC die 102, the mechanical structure of BGA package 400 becomes more symmetrical in its center region, particularly when ground/thermal solder balls do not exist on the bottom surface of substrate 104 underneath the outer profile of IC die 102. Thermal stress at the interface of IC die 102 and stiffener 112 is substantially released or altered by heat spreader 402. Deformation caused by thermal stress in stiffener 112 and substrate 104 is substantially reduced through the use of heat spreader 402. Drop-in heat spreader 402 allows for even larger sizes for IC die 102 and greater I/O counts by providing for greater heat spreading capacity in BGA package 400.
FIG. 14 shows a flowchart 1400 providing operational steps for assembling one or more embodiments of the present invention. The steps of FIG. 14 do not necessarily have to occur in the order shown, as will be apparent to persons skilled in the relevant art(s) based on the teachings herein. Other structural embodiments will be apparent to persons skilled in the relevant art(s) based on the following discussion. These steps are described in detail below.
Flowchart 1400 begins with step 1402. In step 1402, a substrate that has a first surface and a second surface is provided. For example, the substrate is flex substrate 104, or another substrate type suitable for a BGA package. For example, an IC die mounting position and/or contact points are provided on a first, upper surface, and solder ball pads are provided on a second, bottom surface.
In step 1404, a first surface of a stiffener is attached to the first substrate surface. For example, the stiffener is stiffener 112, which is attached to substrate 104. In alternative embodiments, a stiffener is not required.
In step 1406, an IC die is mounted to the second stiffener surface. For example, the IC die is IC die 102, which is mounted to stiffener 112. In alternative embodiments, when a stiffener is not used, IC die 102 is mounted directly to the substrate.
In step 1408, a heat spreader is mounted to the IC die, wherein the heat spreader dissipates heat from the IC die. For example, the heat spreader is heat spreader 402 or 502, which is mounted with epoxy 404 or other attachment means to the upper surface of IC die 102. Heat spreader 402 or 502 typically is mounted to the center of the upper surface of IC die 102, and covers less than the entire upper surface of IC die 102. For instance, the smaller area of heat spreader 402 or 502 allows for bond pads 118 to be exposed on the upper surface of IC die 102 for wire bond connections. In alternative embodiments, heat spreader 402 or 502 is of the same size, or comprises a larger area than the upper surface of IC die 102.
In step 1410, a plurality of solder balls are attached to the second substrate surface. For example, the plurality of solder balls are plurality of solder balls 106, which connect to vias and/or solder ball pads on the bottom surface of substrate 104. The solder balls may be arranged on the bottom surface of substrate 104 as shown in FIGS. 12B and 12C, or in alternative arrangements. The solder balls are used to attach a BGA package to a PCB.
A benefit of performing the steps of flowchart 1400 is that the heat spreader relieves thermal stress at an interface of the IC die and the first stiffener surface.
Flowchart 1400 may include the additional step where the second stiffener surface is encapsulated. For instance, the second stiffener surface may be encapsulated by a resin or molding compound, that also encapsulates the IC die, heat spreader, and wire bonding.
Stiffener Ground Plane Embodiments
According to an embodiment of the present invention, electrical performance of an IC die, and thermal performance of a corresponding BGA package may be improved by allowing a stiffener to act as a ground plane. In a preferred embodiment, a stiffener in a die-up tape BGA (Flex BGA) package is coupled to PCB ground through one or more vias to ground solder balls. Ground contact pads of the IC die are connected to the stiffener by ground wire bonds. In a further aspect, one or more metal layers of a flex tape substrate may be coupled to a ground or power potential, to operate as a ground or power plane.
FIG. 6 illustrates a cross-sectional view of a die-up flex BGA package 600, according to an embodiment of the present invention. BGA package 600 includes IC die 102, substrate 104, plurality of solder balls 106, one or more wire bonds 108, stiffener 112, epoxy 116, one or more ground bonds to stiffener 602, one or more ground/thermal vias 604, one or more ground/thermal balls 606, one or more ground contact pads 608, one or more power contact pads 610, and one or more power vias 612.
Substrate 104 has a top surface to which a bottom surface of stiffener 112 is mounted. A bottom surface of substrate 104 attaches the plurality of solder balls 106. The plurality of solder balls 106 connect to vias and/or points on the bottom surface of substrate 104 to which signals internal to substrate 104 are routed and exposed.
Stiffener 112 has a top surface to which IC die 102 is mounted.
One or more wire bonds 108 connect corresponding bond pads 118 on IC die 102 to contact points 120 on substrate 104. Wire bonds 108 extend through one or more openings 114 in stiffener 112 to form connections with substrate 104.
IC die 102 has a top surface that includes at least one ground pad 608. Ground pad 608 is coupled to a ground potential signal in IC die 102. A ground wire bond 602 connects ground pad 608 to stiffener 112. The bottom surface of stiffener 112 is coupled to a ground potential signal in the PCB to which BGA package 600 is attached, to cause stiffener 112 to operate as a ground plane. Stiffener 112 is coupled to PCB ground through one or more of ground/thermal via 604 that extend through substrate 104. The one or more of ground/thermal vias 604 are located in substrate 104, underneath IC die 102, and can be filled with a conductive material, such as solder. A ground/thermal solder ball 606 is attached to each ground/thermal via 604 on the bottom surface of substrate 104. Ground/thermal solder ball 606 forms the connection to PCB ground, when reflowed to attach to the PCB. Each ground/thermal via 604 connects the respective ground/thermal solder ball 606 to stiffener 112 both electrically and thermally.
In a further embodiment, a tape substrate is configured such that a metal layer is used as a package power or ground plane. For instance, with a two-layer tape substrate, the bottom metal layer may be used as a power or ground plane.
In FIG. 6, PCB package 600 includes a bottom metal layer 614 of a two-layer tape substrate 104 that is coupled to a potential to operate as a power plane, according to an embodiment of the present invention. One or more power contact pads 610 on IC die 102 are coupled to a power potential signal in IC die 102. Power contact pad 610 on IC die 102 is connected to a corresponding power via 612 by a power wire bond 616. When a stiffener 112 is present, power wire bond 616 extends through opening 114. Power via 612 extends through substrate 104. Power via 612 can be filled with a conductive material, such as solder. Each power via 612 is coupled to the bottom metal layer 614 of substrate 104.
Furthermore, one or more power vias 612 may be connected to corresponding solder balls on the bottom of substrate 104, to connect bottom metal layer 614 to PCB power pads when the solder balls are reflowed.
The introduction of a stiffener ground plane, and/or a power/ground plane using a metal layer of a tape substrate allows for very short power and ground connections. Current return path lengths are shortened, voltage drop across planes is reduced, and power/ground inductance is reduced. The shorter power and ground paths are also significant in reducing a power/ground path resistance, which advantageously reduces required IC device power levels.
For further description of the use of a thermal vias in a flex tape substrate, and of the use of a thermal ball coupled to a heat spreader in a die-down TBGA package, refer to U.S. Pat. No. 6,020,637, which is incorporated by reference in its entirety herein. For further description of the use of a thermal via and a thermal ball in a plastic substrate BGA package, refer to U.S. Pat. No. 5,894,410, which is incorporated by reference in its entirety.
FIG. 15 shows a flowchart 1500 providing operational steps for assembling one or more embodiments of the present invention. The steps of FIG. 15 do not necessarily have to occur in the order shown, as will be apparent to persons skilled in the relevant art(s) based on the teachings herein. Other structural embodiments will be apparent to persons skilled in the relevant art(s) based on the following discussion. These steps are described in detail below.
Flowchart 1500 begins with step 1502. In step 1502, a substrate that has a first surface and a second surface is provided. For example, the substrate is flex substrate 104, or another substrate type suitable for a BGA package. For example, an IC die mounting position and/or contact points are provided on a first, upper surface, and solder ball pads are provided on a second, bottom surface.
In step 1504, at least one opening in a stiffener from a first surface of the stiffener to a second surface of the stiffener is provided. For example, the at least one opening includes openings 114 in stiffener 112. In a preferred embodiment, an opening 114 is located on each of the four edges of IC die 102.
In step 1506, the first stiffener surface is attached to the first substrate surface. For example, the stiffener is stiffener 112, which is attached to substrate 104. In alternative embodiments, a stiffener is not required, and is not attached to the substrate.
In step 1508, an integrated circuit (IC) die is mounted to the second stiffener surface, wherein a first surface of the IC die includes a contact pad. For example, the IC die is IC die 102, which is mounted to stiffener 112. In alternative embodiments, when a stiffener is not used, IC die 102 is mounted directly to the substrate. For example, the contact pad is ground contact pad 608.
In step 1510, the contact pad is coupled to the second stiffener surface. For instance, contact pad is ground contact pad 608, which is connected to stiffener 112 by ground wire bond 602. Ground wire bond 602 may be soldered, or otherwise attached to stiffener 112.
In step 1512, a plurality of solder balls is attached to the second substrate surface, inside an outer dimensional profile of the IC die. For example, the plurality of solder balls include one or more ground/thermal balls 606, which are arranged on the bottom surface of substrate 104 in the region of substrate center 1224, shown in FIG. 12C. The outer dimensional profile of the IC die is the area bounded by the edges of IC die 102.
In step 1514, the plurality of solder balls are coupled through corresponding vias in the substrate to the first stiffener surface. For example, the vias include ground/thermal via 604. The vias can be filled with a conductive material, such as solder, to allow the electrical connection of the solder balls to stiffener 112.
In a further embodiment according to flowchart 1500, the substrate includes a metal layer, wherein the metal layer is coupled to a second potential. The stiffener has at least one opening extending from the first stiffener surface to the second stiffener surface. The second IC die surface includes a second contact pad. The second contact pad is coupled to the metal layer through one of the openings in the stiffener and through a corresponding via that extends through the substrate. The second contact pad may be coupled to a power or ground potential in the IC die. For example, the second contact pad is power contact pad 610, the metal layer is metal layer 614, and the corresponding via is power via 612.
In an embodiment, flowchart 1500 may include an additional step, where the contact pad is coupled to a ground potential in the IC die. For example, the contact pad may be connected to a ground plane or ground signal in IC die that is routed to the contact pad.
Flowchart 1500 may include the additional step where the second stiffener surface is encapsulated. For instance, the second stiffener surface may be encapsulated by a resin or molding compound, that also encapsulates the IC die and wire bonding.
Flowchart 1500 may include the additional step where a second plurality of solder balls is attached to the second substrate surface, outside an outer dimensional profile of the IC die. For example, the second plurality of solder balls are plurality of solder balls 106, which connect to vias and/or solder ball pads on the bottom surface of substrate 104. The solder balls are arranged on the bottom surface of substrate 104 as shown in FIG. 12B, outside of substrate center 1224. The solder balls are used to attach a BGA package to a PCB.
Embodiments with Stiffener Coupled to a PCB
According to an embodiment of the present invention, electrical performance of the IC device, and thermal performance of a BGA package is improved by enabling an IC die pad to attach to a PCB. In an embodiment, the IC die pad is attached to the PCB by a novel patterning of the metal stiffener in a die-up tape BGA package. In an alternate embodiment, the IC die pad is attached to the PCB by placing a thermal/ground connector between the IC die pad and PCB in a die-up tape BGA package.
A BGA package junction-to-board thermal resistance can be substantially reduced by the attachment of a metal die-attach pad directly to a PCB. Metal die-attach pads are coupled to a PCB for package junction-to-board thermal resistance minimization in an exposed pad quad flat pack (QFP), a QFP with exposed heat sink at bottom, and a leadless plastic chip carrier (i.e. LPCC, QFN, SON, QLP) package, for instance. All existing such designs that involve an exposed die pad or an exposed heat sink at package bottom are “lead frame” packages. The present invention provides for an exposed die-attach pad or heat sink at the bottom of flex BGA packages.
FIG. 7 illustrates a cross-sectional view of a die-up flex BGA package 700, according to an embodiment of the present invention. BGA package 700 includes IC die 102, substrate 104, plurality of solder balls 106, one or more wire bonds 108, stiffener 112, epoxy 116, ground wire bond to stiffener 602, ground contact pad 608, and a stiffener cavity 702.
Substrate 104 has a top surface to which a bottom surface of stiffener 112 is mounted. A bottom surface of substrate 104 attaches the plurality of solder balls 106. The plurality of solder balls 106 connect to vias and/or points on the bottom surface of substrate 104 to which signals internal to substrate 104 are routed and exposed. Substrate 104 in FIG. 7 has a central window-shaped opening 704, under which solder balls are preferably not connected. FIG. 20 illustrates a bottom view of a substrate 104 that has a central window opening 704, according to an embodiment of the present invention.
Stiffener 112 has a top surface to which IC die 102 is mounted. Stiffener 112 in FIG. 7 is patterned with a cavity 702, which protrudes downward for attachment of IC die 102. As described above, a central window-shaped opening 704 exists in substrate 104. This opening 704 exists to allow stiffener 112 to protrude through, and make contact with soldering pads on a PCB to which BGA package 700 is to be mounted. The bottom exposed surface of cavity 702 can be plated with solder to facilitate surface mount to solder plated metal pads on a PCB to which BGA package 700 is mounted. Hence, stiffener 112 may act as a conduit for heat to be transferred from IC die 102 to the PCB.
Stiffener 112 may optionally be configured to operate as a ground plane. One or more ground pads 608 may be coupled to a ground potential signal in IC die 102. A ground wire bond 602 connects each ground pad 608 to stiffener 112. With one or more ground wire bonds 602 coupled to stiffener 602, the bottom exposed surface of cavity 702 may function both as an exposed ground pad of BGA package 700, and as an exposed heat spreader. As described above, the bottom exposed surface of cavity 702 may be plated with solder to allows stiffener 112 to be surface mounted to one or more soldering pads on the PCB. The pads on the PCB can be connected to a PCB ground plane to shorten the length of electrical current return paths, as well as to form a conductive heat dissipation path from BGA package 700 to the PCB.
Direct electrical and thermal connection from BGA package ground to a PCB ground plane is also possible by attaching a heat spreader between the stiffener and PCB. FIG. 8 illustrates a cross-sectional view of a die-up flex BGA package 700, according to an embodiment of the present invention. Substrate 104 in FIG. 8 has a central window-shaped opening, under which no solder balls are connected. A portion of the bottom surface of stiffener 112 is exposed through the central window-shaped opening 704 of substrate 104. A heat spreader (for example, manufactured from copper or aluminum), shown as ground/thermal connector 802, is coupled to the exposed portion of stiffener 112. Ground/thermal connector 802 can be made from the same material as stiffener 112. Material different from stiffener 112 may be used for ground/thermal connector 802 to compensate for the mismatch of thermal expansion coefficient between the die 102 and stiffener 112. Ground/thermal connector 802 may be laminated to the exposed portion of stiffener 112 using conductive epoxy or solder. In FIG. 8 the ground thermal connector is laminated to the exposed portion of stiffener 112 using epoxy 804. The bottom surface of ground/thermal connector 802 may be plated with solder to facilitate its surface mount to soldering pads on the PCB. Metal pads on the PCB may be connected to a PCB ground plane to shorten the length of electrical current return paths, as well as enhance the conductive heat dissipation path from IC die 102 to the PCB. An advantage of this design is a high efficiency in the metal connector lamination process.
In a further embodiment, stiffener 112 and ground/thermal connector 802 may be manufactured from a single piece of metal, and hence consist of a single metal piece. FIG. 21 illustrates a side view of stiffener 112 that has a downward protruding portion 2102, according to an embodiment of the present invention. When stiffener 112 shown in FIG. 21 is attached to substrate 104, portion 2102 extends partially or entirely through window-shaped opening 704. Portion 2102 may be directly connected to the PCB, or may be connected to a ground/thermal connector 802 that is connected to the PCB. Because of the thermal and electrical improvement enabled by the coupling of stiffener 112 to a PCB, length of wire bonds can be reduced by moving opening 114 closer to the proximity of die 102 without compromising thermal performance significantly.
FIG. 16A shows a flowchart 1600 providing operational steps for assembling one or more embodiments of the present invention. FIGS. 16B–D provide operational steps according to further embodiments. The steps of FIGS. 16A–D do not necessarily have to occur in the order shown, as will be apparent to persons skilled in the relevant art(s) based on the teachings herein. Other structural embodiments will be apparent to persons skilled in the relevant art(s) based on the following discussion. These steps are described in detail below.
Flowchart 1600 begins with step 1602. In step 1602, a substrate that has a first surface and a second surface is provided. For example, the substrate is flex substrate 104, or another substrate type suitable for a BGA package. For example, an IC die mounting position and/or contact points are provided on a first, upper surface, and solder ball pads are provided on a second, bottom surface.
In step 1604, a first surface of a stiffener is attached to the first substrate surface. For example, the stiffener is stiffener 112, which is attached to substrate 104.
In step 1606, a portion of the first stiffener surface is exposed through a window opening in the substrate. For example, substrate 104 has a window opening 704 in its center. A portion of the bottom surface of stiffener 112 is exposed through window opening 704.
In step 1608, an IC die is mounted to a second surface of the stiffener, wherein a surface of the IC die includes at least one contact pad. For example, the IC die is IC die 102, which is mounted to stiffener 112.
In step 1610, a plurality of solder balls are attached to the second substrate surface. For example, the plurality of solder balls are plurality of solder balls 106, which connect to vias and/or solder ball pads on the bottom surface of substrate 104. The solder balls are arranged on the bottom surface of substrate 104 as shown in FIG. 12B, exclusive of the area of window opening 704. The solder balls are used to attach a BGA package to a PCB.
In step 1612, the exposed portion of the first stiffener surface is configured to be coupled to a printed circuit board (PCB), whereby electrical and thermal performance of the BGA package is improved.
FIG. 16B provides exemplary steps for performing step 1612:
In step 1614, a heat spreader is coupled to the exposed portion of the first stiffener surface. For example, the heat spreader is ground/thermal connector 802, which is coupled to stiffener 112 through window opening 702.
In step 1616, a surface of the heat spreader is configured to be coupled to the PCB. In an embodiment, step 1612 further includes the step where the heat spreader surface is plated with solder to allow the heat spreader surface to be surface mounted to soldering pads on the PCB.
In an alternate embodiment, step 1612 comprises the step where the stiffener is shaped to have a centrally-located cavity shaped portion that protrudes through the window opening. In an embodiment, step 1612 further includes the step where a surface of the cavity shaped portion is plated with solder to allow the stiffener to be surface mounted to soldering pads on the PCB. For example, stiffener 112 is patterned with a cavity 702, which protrudes downward in window opening 704. The bottom surface of cavity 702 is plated with solder.
FIG. 16C provides additional exemplary steps for flowchart 1600 of FIG. 16A:
In step 1618, the stiffener is coupled to a potential. For example, the stiffener may be coupled to ground or power on the PCB. The bottom surface of cavity 702 may be coupled to the ground or power potential on the PCB, or ground/thermal connector 802 may make the connection to the PCB.
In step 1620, each of the at least one contact pads are coupled to the second stiffener surface with corresponding wire bonds.
FIG. 16D provides exemplary steps for performing step 1618:
In step 1622, the stiffener is coupled to a ground potential.
In step 1624, the stiffener allowed to serve as a ground plane.
Flowchart 1600 may include the additional step where the second stiffener surface is encapsulated. For instance, the second stiffener surface may be encapsulated by an epoxy, that also encapsulates the IC die and wire bonding.
Further Detail of BGA Package Embodiments with Patterned/Shaped Stiffener
This section provides further embodiments and description of the shaped stiffener shown in FIG. 7, and described above. Example stiffener and BGA package embodiments are provided. The invention described herein improves the thermal, electrical, and mechanical performances of a die-up BGA package with the integration of the shaped stiffener.
FIG. 37 shows a perspective view of an example stiffener 112, according to an embodiment of the present invention. Stiffener 112 provides mechanical support and stiffness for the BGA package in which it resides. Stiffener 112 may also be referred to as an “interposer.” Furthermore, in embodiments, stiffener 112 is thermally conductive. Stiffener 112 conducts heat away from an IC die centrally mounted to stiffener 112. Hence, stiffener 112 may also be referred to as a heat sink or heat spreader.
As shown in FIG. 37, stiffener 112 has a substantially planar top surface 3702 that has a centrally located cavity 702. Stiffener 112 further has a substantially planar bottom surface 3704, which is opposed to top surface 3702. Bottom surface 3704 has a centrally located protruding portion 3714 that opposes cavity 702.
As shown in the example embodiment of FIG. 37, cavity 702 may be substantially rectangular in shape, having a first edge 3706, a second edge 3708, a third edge 3710, and a fourth edge 3712. In alternative embodiments, cavity 702 may have other shapes, including round, elliptical, a combination of rectangular and elliptical, and additional shapes.
Protruding portion 3714 has a height that may have various values. For example, protruding portion 3714 may have a height such that protruding portion 3714 is capable of extending through an opening formed in a BGA package substrate to be attached to a surface of a PCB when the BGA package is mounted to the PCB. In another example, protruding portion 3714 has a height such that protruding portion 3714 is capable of extending through the opening formed in the BGA package substrate to extend into a cavity formed in a surface of the PCB when the BGA package is mounted to the PCB. By coupling to the PCB, protruding portion 3714 enhances the mechanical attachment of the BGA package to the PCB, and enhances thermal and/or electrical connectivity of the BGA package to the PCB.
Note that the present invention also improves electrical routing design and performance for the BGA package substrate. When the opening through which protruding portion 3714 extends is cut or punched through the substrate, a “de-bussing” operation occurs. For example, for electrolytically plated substrates, the de-bussing operation removes unwanted metal traces in the substrate that exist in the portion of the substrate that is removed by the de-bussing operation.
In embodiments, stiffener 112 can be shaped/patterned in various forms to improve BGA package assembly yields, mechanical, thermal, and electrical performances and reliability. In an embodiment, one or more edges and/or corners of stiffener 112 are formed so that they do not contact the top surface of the BGA package substrate to which stiffener 112 is attached. Openings, cutouts, recessed portions, notches, and steps can be patterned through/into stiffener 112 to provide numerous advantages. For example, these patternings can reduce the length of wire bonds coupled between the IC die and package substrate, improve substrate routability, and improve the overall manufacturing process for the BGA package. Example embodiments for such patterning of stiffener 112 are further described below.
For example, as shown in FIG. 37, stiffener 112 includes a plurality of openings 114 through stiffener 112 that are open at top surface 3702 and bottom surface 3704 of stiffener 112. Openings 114 allow for wire bonds 108 to pass through stiffener 112 to form connections with the BGA package substrate. The dimensions of openings 114 can be varied to allow for reduced wire bond lengths, for improved routability of the BGA package substrate, and for improved manufacturability of the BGA package. As will be described below, stiffener 112 may include any combination of one or more through-patterns such as openings 114, recessed edge portions, and other through-patterns described herein, according to embodiments of the present invention.
As shown in FIG. 37, each of openings 114 in stiffener 112 is substantially rectangular shaped. In alternative embodiments, openings 114 may have other shapes, including elliptical or round, rectangular and any other quadrilateral including trapezoidal, irregular, other polygons and shapes, and combinations thereof. Hence, openings 114 may be regular in shape (e.g., rectangular, trapezoidal) or irregular.
As shown in the example of FIG. 37, four openings 114 are present in stiffener 112. One of the four openings 114 is located proximate to each of first, second, third, and fourth edges 3706, 3708, 3710, and 3712 of cavity 702.
However, any number of openings 114 may be present in stiffener 112. Openings 114 are typically located proximate to edges of cavity 702 in order to be close to IC die 102, to allow for relatively short lengths for wire bonds 108, but may be located anywhere in stiffener 112.
According to embodiments of the present invention, stiffener 112 can be made from a variety of materials. For example, stiffener 112 can be made from a metal. For example, the metal may be copper, a copper based alloy, aluminum, an aluminum based alloy, as well as other types of metals and alloys. Stiffener 112 can also be made from ceramic materials, thermally conductive dielectric materials, organic materials, plastics, and combinations of these materials, as would be apparent to one skilled in the relevant art(s) based on the teachings described herein. In embodiments, stiffener 112 is made from an electrically conductive material to enhance its electrical properties. Additionally or alternatively, stiffener 112 may be made from thermally conductive materials to enhance its thermal characteristics.
The surfaces of stiffener 112 are not required to be finished with physical or chemical treatment. However, one or more surfaces of stiffener 112 may be finished with additional treatment processes. For example, surfaces of stiffener 112 may be finished using processes such as micro-etch or oxidation to promote adhesion of an encapsulating material to stiffener 112. In embodiments, a surface plating of silver, solder, nickel, gold, or other metals and alloys thereof, may be applied on one or more surfaces of stiffener 112 to create spot, strip, bar, ring, and other shape contact areas for wire bond attachment to stiffener 112.
FIG. 38 shows an example BGA package 3800, according to an embodiment of the present invention. BGA package 3800 includes an example stiffener 112, according to an embodiment of the present invention. FIGS. 39A and 39B show top and bottom views, respectively, of stiffener 112 of FIG. 38. As shown in FIGS. 38, 39A, and 39B, stiffener 112 includes an example plurality of openings 114, shown as a first opening 114a, a second opening 114b, a third opening 114c, a fourth opening 114d, and a fifth opening 114e. First and second openings 114a and 114b are positioned proximate to first edge 3706, third opening 114c is positioned proximate to second edge 3708, fourth opening 114d is positioned proximate to third edge 3710, and fifth opening 114e is positioned proximate to fourth edge 3712.
As shown in FIG. 38, IC die 102 is mounted in cavity 702 on the top surface of stiffener 112 by an adhesive material. For example, the adhesive material may be a thermally conductive adhesive material, to enhance transfer of heat from IC die 102 to stiffener 112.
Bottom surface 3704 of stiffener 112 is coupled to a top surface of substrate 104. Protruding portion 3714 of the bottom surface of stiffener 112 extends through opening 704 in substrate 104. A plurality of solder ball pads 3810 on the bottom surface of substrate 104 have a respective plurality of solder balls 106 attached thereto. The solder ball pads 3810 are electrically coupled through substrate 104 to contact pads/lands on the top surface of substrate 104. Conductive areas/lands/traces/etc. on the top surface of substrate 104 that are wire bond attachable are referred to herein as “contact pads.” Substrate 104 can be BT plastic, tape, organic, ceramic, glass, laminated, build-up, and/or any other substrate type.
One or more wire bonds 108 are coupled from bond pads on IC die 102 to contact pads on the top surface of substrate 104. In an embodiment, one or more wire bonds 602 are coupled from bond pads on IC die 102 to stiffener 112. For example, wire bonds 602 may couple to bond pads on IC die 102 that are coupled to power, ground, or some other signal internal to IC die 102. In such an embodiment, stiffener 112 may operate as a ground, power, or signal plane to enhance electrical performance of BGA package 3800. Furthermore, protruding portion 3714 may be coupled to a conductive area of the PCB to provide an enhanced electrical connection for the ground, power, or other signal to the PCB.
An encapsulate 3802 is used to encapsulate IC die 102 and wire bonds 108/602 on the top surfaces of stiffener 112 and substrate 104. In the example of BGA package 3800, encapsulate 3802 is in the form of a “glob top.” In a glob top encapsulation embodiment, an encapsulating material is applied in a cavity formed by top surface 3702 of stiffener 112 and a dam 3806. Dam 3806 may be a material, such as an epoxy, that is formed in a ring to contain the encapsulating material when it is applied. However, in the embodiments described herein, encapsulate 3802 may be any form and type of encapsulation/encapsulating material, including glob top, molding compound, saw singulation, and/or epoxy, for example.
In embodiments, a plurality of openings 114 may be arranged in series proximate to a single edge of cavity 702, such as shown for openings 114a and 114b along first edge 3706 in FIGS. 39A and 39B. Such an arrangement provides multiple openings for wire bond connections. This arrangement also allows for greater thermal transfer from IC die 102 to the outer regions of stiffener 112 than when a single opening 114 is positioned along the length of the cavity edge. This is because with a plurality of openings 114 arranged in series, heat can conduct across the portion of stiffener 112 between the openings 114. The portions of stiffener 112 that bridge between openings 114 that are arranged in series along an edge of cavity 702 may be referred to as studs, which are further described elsewhere herein. For example, FIG. 10A illustrates a stiffener 1000 that includes one or more studs 1002. Stiffener 1000 with studs 1002 is further described below. As shown in FIGS. 39A and 39B, a stud 1002 bridges stiffener 112 between openings 114a and 114b. 
All of openings 114a, 114b, 114c, 114d, and 114e are substantially rectangular in shape in the example of FIGS. 39A and 39B. Note, however, that opening 114c has a notch 3902 formed in an edge. Notch 3902 allows for a wire bond 108 (not shown in FIGS. 39A and 39B) to pass through opening 114c to couple to the top surface of substrate 104 at a point further away from IC die 102 than when notch 3902 is not present. One or more notches may be formed in any one or more edges of an opening 114. For example, a notch may be formed in an edge of an opening 114 that is closest to IC die 102. Such a notch may provide for greater clearance for a wire bond 108 to avoid contacting the respective edge of the opening when passing through the opening. Notches may have any desired shape, including rectangular, triangular, round, elliptical, combinations thereof, and other shapes, such as irregular. Note that opening 114c may be considered to be an irregular shaped opening, due to the combination of a rectangular opening and a notch.
Openings 114 may be formed in stiffener 112 by any applicable process. For example, openings 114 may be formed during the same step in which stiffener 112 is formed, such as when stiffener 112 is formed in a mold. Alternatively, openings 114 may be formed after stiffener 112 has already been formed, by cutting, stamping, or etching openings 114 through an existing stiffener 112, for example. Furthermore, notches similar to notch 3902 in openings 114 may also be formed during the same step as stiffener 112, or during a subsequent step. For example, a notch may be formed in an opening 114 during the same step in which the opening 114 is formed, or during a prior or subsequent step. For instance, a notch 3902 may be cut, stamped, or etched into opening 114 after opening 114 has been formed. The present invention is not limited to these processes for forming openings 114 and notches 3902, which may be formed in any way known by persons skilled in the relevant art(s).
As described above, openings 114 may be located anywhere in stiffener 112. As shown in FIG. 38, opening 114e has an edge that coincides with fourth edge 3712 of cavity 702. Because the edge of opening 114e coincides with fourth edge 3712 of cavity 702, a step or ridge 3804 is present in stiffener 112, next to cavity 702. The space above ridge 3804 that exists due to the coinciding edges allows for greater clearance for wire bonds 108. Furthermore, a wire bond 602 may be coupled between IC die 102 and ridge 3804. Note that a step or ridge 3804 may be formed next to cavity 702 without an opening 114 being present.
In the embodiment shown in FIG. 38, protruding portion 3714 has a height 3808 that allows the bottom surface of protruding portion 3714 to be attached to a PCB when BGA package 3800 is mounted to the PCB. In an alternative embodiment, height 3808 may be increased to allow protruding portion 3714 to extend into a cavity in a PCB, to enhance the mechanical, thermal, and/or electrical coupling of BGA package 3800 to the PCB. In such embodiments, a thermally and/or electrically conductive adhesive material may be used to attach protruding portion 3714 to the PCB.
FIG. 39C illustrates a top view of a stiffener 112 with trapezoidal openings 206a–d, according to an alternative embodiment of the present invention. Stiffener 112 of FIG. 39C is applicable to BGA package 3800 shown in FIG. 38, for example. As shown in FIG. 39C, openings 206a–d in stiffener 112 are substantially trapezoidal shaped. Stiffener studs or “tie bars” 3910 separate openings 206a–d. Furthermore, one or more of openings 206a–d have one or more notches 3902. A first opening 206ahas a first notch 3902a and a second opening 206b has a second notch 3902b. Notches 3902a and 3902b may be used to accommodate wire bonds, as described above. Note that one or more plated areas, such as a conductive ring 3912, may be plated on stiffener 112 to enhance wire bond connections to stiffener 112. Conductive ring 3912 may be a plating of silver, gold, other metal, or combination/alloy thereof. Note that openings 206a and 206b may also be considered to be irregular shaped openings, due to each having the combination of a trapezoidal opening and a notch.
FIG. 40 shows an example BGA package 4000, according to a further embodiment of the present invention. BGA package 4000 includes an example stiffener 112, according to an embodiment of the present invention. FIGS. 41A and 41B show top and bottom views, respectively, of stiffener 112 of FIG. 40. As shown in FIG. 40, BGA package 4000 is substantially similar to BGA package 3800 of FIG. 38. However, stiffener 112 of FIGS. 40, 41A and 41B includes a plurality of recessed portions 4002 in outer edges of the top and bottom surfaces 3702 and 3704 of stiffener 112, according to an example embodiment of the present invention. As shown in FIGS. 41A and 41B, stiffener 112 has a first recessed portion 4002a in a first edge 4004, a second recessed portion 4002b in a second edge 4006, a third recessed portion 4002c in a third edge 4008, and a fourth recessed portion 4002d in a fourth edge 4010.
Each recessed portion 4002 allows one or more wire bonds 108 to be coupled between IC die 102 and the top surface of substrate 104. Recessed portions 4002 also can allow for reduced wire bond lengths, for improved routability of substrate 104, and for improved overall manufacturability of the BGA package.
In embodiments, stiffener 112 may have any number of one or more recessed portions 4002 in one or more outer edges. Furthermore, the recessed portions may have any shape. As shown in FIGS. 41A and 41B, first, second, third, and fourth recessed portions 4002a, 4002b, 4002c, and 4002d are substantially rectangular shaped. However, recessed portions 4002 may have other shapes, including elliptical or round, triangular, rectangular and any other quadrilateral including trapezoidal, irregular, other polygons and shapes, and combinations thereof as shown in FIGS. 41C–41F.
In embodiments, recessed portions 4002 may be of any size. For example, as shown in FIGS. 40, 41A, and 41B, recessed portion 4002d is of a size such that an edge of recessed portion 4002d coincides with fourth edge 3712 of cavity 702. Because the edge of recessed portion 4002d coincides with fourth edge 3712 of cavity 702, a step or ridge 4012 is present in stiffener 112, next to cavity 702. The space above ridge 4012 that exists due to the coinciding edges allows for greater clearance for wire bonds 108. Furthermore, a wire bond 602 may be coupled between IC die 102 and ridge 4012. Note that a step or ridge 4012 may be formed next to cavity 702 without a recessed portion 4002 being present.
All of recessed portions 4002a, 4002b, 4002c, and 4002d are shown to be substantially rectangular in shape in the example of FIGS. 41A and 41B. However, recessed portion 4002c has a notch 4102 formed in an edge. Notch 4102 allows for at least one wire bond 108 (not shown) to pass through recessed portion 4002c and couple to the top surface of substrate 104 at a closer point than when notch 4102 is not present. Furthermore, notch 4102 may provide for greater clearance for a wire bond 108 to avoid contacting the edge when passing through the recessed portion 4002c. Note that any number of notches may be formed in any of one or more edges of one or more recessed portions 4002. Furthermore, a notch may have any applicable shape, including rectangular, triangular, round, elliptical, combinations thereof, and/or other shapes.
Note that recessed portions 4002 may be formed in stiffener 112 by a variety of processes. For example, recessed portions 4002 may be formed during the same step in which stiffener 112 is formed, such as when stiffener 112 is formed in a mold. Alternatively, recessed portions 4002 may be formed in an existing stiffener 112, by cutting, etching, or stamping recessed portions 4002 into the stiffener 112, for example. Furthermore, notches similar to notch 4102 in recessed portions 4002 may also be formed during the same step as stiffener 112, or during a subsequent step. For example, a notch may be formed in a recessed portion 4002 during the same step in which the recessed portion 4002 is formed, or during a prior or subsequent step. For example, a notch 4102 may be cut, etched, or stamped into recessed portion 4002 after recessed portion 4002 has been formed.
Methods and processes for forming and assembling embodiments of the present invention are provided below. Flowcharts are provided showing steps for forming stiffeners of the present invention. Then, a flowchart is provided showing steps for assembling a BGA package that incorporates a stiffener of the present invention.
FIG. 42 shows a flowchart 4200 providing steps for forming a stiffener having openings therethrough, according to one or more embodiments of the present invention. The steps of FIG. 42 do not necessarily have to occur in the order shown, as will be apparent to persons skilled in the relevant art(s) based on the teachings herein. Other operational and structural embodiments will be apparent to persons skilled in the relevant art(s) based on the following discussion. These steps are described in detail below.
Flowchart 4200 begins with step 4202. In step 4202, a cavity is formed in a first surface of a body such that an opposed second surface of the body has a protruding portion that opposes the cavity. For example, in an embodiment, the body of the stiffener 112 is formed from a substantially planar metal piece. A cavity such as cavity 702 may be formed in a central region of the body, such as is shown in FIG. 37. As shown in FIG. 37, cavity 702 is formed in top surface 3702 of stiffener 112. Protruding portion 3714 is formed in bottom surface 3704 of stiffener 112 as a result of cavity 702 being formed in stiffener 112. Bottom surface 3704 is opposed to top surface 3702 of stiffener 112.
In step 4204, a plurality of openings are formed through the body. For example, the openings are openings 114 formed in stiffener 112, such as shown in FIGS. 39A and 39B. Openings 114 are open at top surface 3702 and bottom surface 3704 of stiffener 112.
In an embodiment, steps 4202 and 4204 may be performed simultaneously by forming the stiffener according to a mold process. For example, stiffener 112 may be formed in a mold that shapes both of cavity 702 and openings 114 in stiffener 112.
For example, in another embodiment, the cavity may be formed in step 4202 by stamping the cavity into the body. In embodiments, cavity 702 may be formed in stiffener 112 by stamping, pressing, or otherwise forming the cavity shape into stiffener 112.
In an embodiment, flowchart 4200 may include the additional step where the body is separated from a metal sheet as a metal piece. For example, multiple stiffeners 112 may be formed in a single metal sheet. The individual metal pieces may be separated from the metal sheet before or after the individual metal pieces have been formed into stiffeners 112.
In an embodiment, step 4204 may include the step where the plurality of openings are stamped through the body. In embodiments, openings 114 may be stamped, cut, etched, or otherwise formed through stiffener 112.
FIG. 43 shows a flowchart 4300 providing steps for forming a stiffener having recessed edge portions, according to one or more embodiments of the present invention. The steps of FIG. 43 do not necessarily have to occur in the order shown, as will be apparent to persons skilled in the relevant art(s) based on the teachings herein. Other operational and structural embodiments will be apparent to persons skilled in the relevant art(s) based on the following discussion. These steps are described in detail below.
Flowchart 4300 begins with step 4302. In step 4302, a cavity is formed in a first surface of a body such that an opposed second surface of the body has a protruding portion that opposes the cavity. For example, in an embodiment, the body of the stiffener 112 is formed from a substantially planar metal piece. A cavity such as cavity 702 may be formed in a central region of the body, such as is shown in FIG. 37. As shown in FIG. 37, cavity 702 is formed in top surface 3702 of stiffener 112. Protruding portion 3714 is formed in bottom surface 3704 of stiffener 112 as a result of cavity 702 being formed in stiffener 112. Bottom surface 3704 is opposed to top surface 3702 of stiffener 112.
In step 4304, at least one recessed portion is formed in an edge of the body. For example, the at least one recessed portion may be one or more of recessed edge portions 4002–4002d, as shown in FIGS. 41A and 41B.
In an embodiment, steps 4302 and 4304 may be performed simultaneously by forming the stiffener according to a mold process. For example, stiffener 112 may be formed in a mold that shapes both of cavity 702 and one or more recessed portions 4002 in stiffener 112.
For example, in an embodiment, the cavity may be formed in step 4302 by stamping the cavity into the body. Cavity 702 may be formed in stiffener 112, such as by stamping, pressing, or otherwise forming the cavity shape into stiffener 112.
In an embodiment, flowchart 4300 may include the additional step where the body is separated from a metal sheet as a metal piece. For example, multiple stiffeners 112 may be formed in a single metal sheet. The individual metal pieces may be separated from the metal sheet before or after the individual metal pieces have been formed into stiffeners 112.
For example, in an embodiment, step 4304 may include the step where the at least one recessed portion is cut out of the edge. In embodiments, one or more recessed edge portions 4002 may be stamped, cut, etched, or otherwise formed in the edge of stiffener 112.
FIG. 44 shows a flowchart 4400 providing steps for assembling a BGA package according to one or more embodiments of the present invention. The steps of FIG. 44 do not necessarily have to occur in the order shown, as will be apparent to persons skilled in the relevant art(s) based on the teachings herein. Other operational and structural embodiments will be apparent to persons skilled in the relevant art(s) based on the following discussion. These steps are described in detail below.
Flowchart 4400 begins with step 4402. In step 4402, an IC die is mounted in a cavity in a stiffener. For example, the IC die is IC die 102, which is mounted in cavity 702 in top surface 3702 of stiffener 112, as shown in FIGS. 38 and 40.
In step 4404, a substrate is attached to the stiffener such that a protruding portion of the stiffener opposed to the cavity extends through an opening in the substrate. For example, the substrate is substrate 104, which is attached to bottom surface 3704 of stiffener 112, as shown in FIGS. 38 and 40. The centrally located protruding portion is protruding portion 3714 located on bottom surface 3704 of stiffener 112. As shown in FIGS. 38 and 40, protruding portion 3714 extends through opening 704 in substrate 104.
In step 4406, a wire bond is coupled from a bond pad of the IC die to a contact pad on the substrate through a through-pattern in the stiffener. For example, the through-pattern may be an opening 114 through stiffener 112 as shown in FIGS. 39A and 39B, a recessed portion 4002 in an edge of stiffener 112 as shown in FIGS. 41A and 41B, or any other opening or recess.
For example, in an embodiment, the through-pattern is a recessed edge portion of the stiffener, such as a recessed portion 4002 shown in FIGS. 41A and 41B. In such an embodiment, step 4406 may include the step where the wire bond is coupled through the recessed edge portion of the first and second surfaces of the stiffener.
In another example, in an embodiment, the through-pattern is a rectangular shaped recessed edge portion of the stiffener, such as one of recessed portions 4002–4002d, as shown in FIGS. 41A and 41B. In such an embodiment, step 4406 may include the step where the wire bond is coupled through the rectangular shaped recessed edge portion of the first and second surfaces of the stiffener.
In another example, in an embodiment, the through-pattern is a rectangular shaped recessed edge portion of the stiffener that has a notch formed therein. For example, the rectangular shaped recessed edge portion having a notch formed therein is recessed portion 4002c with notch 4102, as shown in FIGS. 41A and 41B. In such an embodiment, step 4406 may include the step where the wire bond is coupled through the notch formed in the recessed edge portion of the first and second surfaces of the stiffener.
In another example, in an embodiment, the through-pattern is an opening through the stiffener, such as opening 114 shown in FIG. 37. In such an embodiment, step 4406 may include the step where the wire bond is coupled through the opening through the stiffener.
In another example, in an embodiment, the through-pattern is an opening through the stiffener that has a notch formed therein. For example, the opening having a notch formed therein is opening 114c with notch 3902, as shown in FIGS. 39A and 39B. In such an embodiment, step 4406 may include the step where the wire bond is coupled through the notch formed in the opening in the stiffener.
In another example, in an embodiment, the through-pattern is a rectangular shaped opening in the stiffener, such as one of openings 114–114e shown in FIGS. 39A and 39B. In such an embodiment, step 4406 may include the step where the wire bond is coupled through the rectangular shaped opening in the stiffener.
In another example, in an embodiment, the through-pattern is an opening in the stiffener that has an edge that coincides with an edge of the cavity. For example, the opening that has an edge coinciding with an edge of the cavity is opening 114e, which has an edge coinciding with edge 3712 of cavity 702, as shown in FIG. 39A. In such an embodiment, step 4406 may include the step where the wire bond is coupled through the opening in the stiffener that has the edge that coincides with an edge of the cavity.
Further steps for the processes of flowcharts 4200, 4300, and 4400 will be understood to persons skilled in the relevant art(s) from the teachings herein.
PCB Land Patterns for Connection of Patterned Stiffener to the PCB
This section describes PCB land patterns and configurations for attaching to a PCB a BGA package having a stiffener patterned with a cavity, according to embodiments of the present invention. The PCB land patterns and configurations are applicable to mounting all types of patterned stiffeners described herein. For example, applicable patterned stiffeners include stiffener 112 shown in FIG. 7, stiffener 112 shown in FIG. 21, and stiffener 112 shown in FIG. 37.
FIG. 45A shows a cross-sectional view of a portion of a PCB 4500 that has a land pattern 4502 thereon, according to an embodiment of the present invention. FIG. 45B shows a top view of a portion of PCB 4500. As shown in FIG. 45B, land pattern 4502 is substantially rectangular shaped, and is adapted to allowing a rectangular surface of a protruding portion of a patterned stiffener to be mounted to PCB 4500, such as protruding portion 3714 of BGA package 3800, as shown in FIG. 38. Protruding portions with shapes other than rectangular may also be mounted to PCB 4500 via land pattern 4502.
As shown in FIG. 45A, land pattern 4502 is an opening that allows access to a portion of a conductive land 4504 through a solder mask 4506 on the top surface of PCB 4500. FIG. 45B shows an outline of conductive land 4504 under solder mask 4506. A protruding portion of a stiffener may be attached to conductive land 4504 through land pattern 4502 by solder or other adhesive material. Conductive land 4504 may be rectangular, as shown in FIG. 45B, or may be formed in another shape, including round, elliptical, irregular, and other polygons. Conductive land 4504 may be electrically and/or thermally conductive.
Conductive land 4504 may be electrically conductive in order to couple an attached stiffener to a ground, power, or other signal in PCB 4500. Conductive land 4504 may be thermally conductive in order to enhance transfer of heat from the stiffener attached to land pattern 4502. For example, conductive land 4504 may be made from copper, copper-based alloys, aluminum, aluminum-based alloys, other metals, or alloys/combinations thereof.
FIG. 46A shows a cross-sectional view of a portion of a PCB 4600 that has a land pattern 4602 thereon, according to an embodiment of the present invention. FIG. 46B shows a top view of a portion of PCB 4600. Land pattern 4602 of PCB 4600 is similar to land pattern 4502 of PCB 4500 shown in FIGS. 45A and 45B, subject to at least the following discussion.
As shown in FIG. 46B, land pattern 4602 includes an array or matrix of substantially rectangular shaped openings 4604. Openings 4604 allow access to a portion of conductive land 4504 through solder mask 4506 on the top surface of PCB 4600. Land pattern 4602 may include any number of openings 4604 arranged in an array or matrix. Land pattern 4602 is adapted to mounting a protruding portion of a patterned stiffener in a BGA package, such as protruding portion 3714 of BGA package 3800, shown in FIG. 38.
Note that for illustrative purposes, the present description illustrates “solder mask defined land openings,” (SMDs) such as land pattern 4602. For SMDs, a portion of the conductive land that is exposed through openings in the solder mask has a smaller area than the entire conductive land. The present invention, however, is also applicable to “non-solder mask defined land openings” (NSMDs). For NSMDs, the entire conductive land is exposed. For example, in an NSMD embodiment for PCB 4600, conductive land 4504 may be formed as a plurality of rectangular conductive lands arranged in an array or matrix, so that solder mask 4506 is not required to define the array or matrix, and/or is not required to define the rectangular shapes of openings 4604. Any of the land patterns described herein may be formed as SMDs or NSMDs.
FIG. 47A shows a cross-sectional view of a portion of a PCB 4700 that has a land pattern 4702 thereon, according to an embodiment of the present invention. FIG. 47B shows a top view of a portion of PCB 4700. Land pattern 4702 of PCB 4700 is similar to land pattern 4602 of PCB 4600 shown in FIGS. 46A and 46B, except that land pattern 4702 of PCB 4700 has an array or matrix of substantially round or elliptical shaped openings 4704, rather than rectangular shaped openings.
FIG. 48A shows a cross-sectional view of a portion of a PCB 4800 that has a land pattern 4802 thereon, according to an embodiment of the present invention. FIG. 48B shows a top view of a portion of PCB 4800. Land pattern 4802 of PCB 4800 is similar to land pattern 4702 of PCB 4700 shown in FIGS. 47A and 47B, except that land pattern 4802 of PCB 4800 has a staggered array or matrix of substantially round or elliptical shaped openings 4704, rather than a regular, or non-staggered array or matrix, as in land pattern 4702.
FIGS. 49A and 49B provide additional internal detail for example PCBs, according to embodiments of the present invention. The description related to FIGS. 49A and 49B is provided below for illustrative purposes, and is applicable to all PCBs described herein, including PCBs having any number of layers.
FIG. 49A shows a cross-sectional view of PCB 4600 of FIGS. 46A and 46B. As shown in the example of FIG. 49A, PCB 4600 is a multi-layer (five conductive layers shown) PCB. In embodiments, conductive land 4504 may be coupled to any number of conductive planes, layers, and/or traces in a PCB. For example, in FIG. 49A, a first electrical potential plane 4904 and a second electrical potential plane 4906 in PCB 4600 are coupled to conductive land 4504 by a plurality of vias 4902. Plurality of vias 4902 may be electrically conductive in order to electrically couple conductive land 4504 to first electrical potential plane 4904 and second electrical potential plane 4906. Plurality of vias 4904 may be thermally conductive in order to enhance heat transfer from conductive land 4504 to first electrical potential plane 4904 and second electrical potential plane 4906. In embodiments, any number of one or more vias 4902 may be present.
FIG. 49B shows a cross-sectional view of PCB 4500 of FIGS. 45A and 45B. As shown in the example of FIG. 49B, PCB 4500 is a two-layer PCB, and conductive land 4504 is coupled to electrical potential plane 4910 by plurality of vias 4902.
FIG. 50A shows a cross-sectional view of a PCB 5000 that has an opening 5002 through PCB 5000. Opening 5002 is open at a top surface 5006 and a bottom surface 5008 of PCB 5000. A protruding portion of a patterned stiffener may extend or protrude into/through opening 5002, to be coupled to a conductive land 5004 on an inner surface around opening 5002. For example, the protruding portion may be attached to conductive land 5004 by a solder or other adhesive material. As shown in FIG. 50A, conductive land 5004 is electrically and/or thermally coupled to one or more electrical potential planes 5006 in PCB 5000. As shown in the example of FIG. 50, PCB 5000 is a multi-layer (five conductive layers shown) PCB. FIG. 50B shows a PCB 5010 with opening 5002 therethrough for accommodating a protruding portion, similar to PCB 5000. PCB 5010 is shown as a two-layer PCB, for illustrative purposes.
Seal Ring Embodiments
This section describes a seal ring for a protruding portion of a patterned stiffener in a BGA package, according to embodiments of the present invention. The seal ring as described herein is applicable to all configurations of BGA packages having stiffeners with protruding portions. For example, applicable protruding portions include cavity 702 of stiffener 112 shown in FIG. 7, protruding portion 2102 of stiffener 112 shown in FIG. 21, and protruding portion 3714 of stiffener 112 first shown in FIG. 37.
FIG. 51 shows a cross-sectional view of BGA package 5100, according to an embodiment of the present invention. BGA package 5100 is substantially similar to BGA package 4000 shown in FIG. 40, subject to the following discussion. As shown in FIG. 51, IC die 102 is encapsulated using a molding compound 5104. Furthermore, a sealant material 5102 fills a gap between protruding portion 3714 and substrate 104 in opening 704. Sealant material 5102 is formed in a ring around protruding portion 3714, and therefore is also referred to as a seal ring. In an embodiment, sealant material 5102 is a dielectric sealant, an epoxy, or other electrically non-conductive sealing material. The seal ring formed by sealant material 5102 improves a BGA package resistance to moisture, BGA package manufacturing yields, BGA package reliability, as well as additional BGA package thermal and mechanical performances.
In an alternative embodiment, sealant material 5102 is an electrically conductive material that can electrically couple protruding portion 3714 to one or more electrically conductive traces, rings, and/or planes of substrate 104, that are coupled to an electrical potential. Such an embodiment provides additional flexibility for routing of substrate 104, and an improvement in BGA package electrical performance.
Overview of Some Features of the Present Invention
The following paragraphs list some notable features of the present invention:
(1) A window opening 704 is patterned in the package substrate 104 to facilitate thermal and electrical connection from IC die 102 to an application PCB.
(2) A thermal/electrical connector (protruding portion 3714) is exposed at the bottom of the BGA package.
(3) Designs can use conventional substrate types for substrate 104 (such as organic, tape, and ceramic, etc.) as well as advanced types of substrate (high density substrate, build-up substrate, Teflon substrate, etc.); a substrate with one, two, or more routing layers can be used.
(4) Glob-top, over-mold, saw-singulation and further encapsulation processes for IC die 102 can be used.
(5) Stiffener/interposer 112 can be patterned in different forms (openings, cutouts, steps, etc.) or shapes (square, rectangular, circular, spoke-like, cutouts or notches and steps on one or more edges, etc.) for wire bond connection, and for BGA package mechanical, thermal, electrical, reliability, substrate design, and manufacturing process enhancement
(6) One or more surfaces of stiffener/interposer 112 may be finished using a variety of processes, materials, and methodologies at various spots and locations.
(7) The stiffener/interposer 112 and protruding portion 3714 are constructed in one-piece.
(8) Cavity 702 is formed in stiffener 112 for attachment of IC die 102.
(9) Protruding portion 3714 may be extended to protrude under the sitting plane of the BGA package.
(10) A cavity may be formed on a surface of the PCB to allow protruding portion 3714 to be more easily attached to the PCB, and/or be exposed to the backside of the PCB, and/or make connection to heat sinking devices from the backside of the PCB.
(11) Rigid support is provided for IC die 102 for rigorous BGA package assembly processes.
Overview of Some Advantages of the Present Invention
The following paragraphs list some notable advantages of the present invention:
(1) Protruding portion 3714 of stiffener 112 provides a low impedance path for heat flow and current flow between IC die 102 and an application PCB.
(2) Opening 704 in substrate 104 facilitates thermal and electrical connection from IC die 102 to the PCB.
(3) Various processes may be used for die encapsulation, including glob-top, over-mold, saw-singulated, and others to meet requirement of various applications and provide the BGA package with various forms and appearances.
(4) Different forms (openings, cutouts, steps, etc.) or shapes (square, rectangular, circular, spoke-like, cutouts or notches and steps on one or more edges, etc.) in a stiffener/interposer 112 can reduce length of wire bonds 108 for critical nets, reduce risks of wire short during assembly of the BGA package, provide flexibility for the routing design of substrate 104, and enhance BGA package mechanical, thermal, electrical, and reliability performances.
(5) A black-oxidized surface treatment may be applied on top surface 3702 of stiffener/interposer 112. This promotes adhesion between a molding compound used for IC die encapsulation and stiffener 112. A surface coating or plating on a bottom surface of protruding portion 3714 of silver, solder, or other metals and alloys promotes adhesion between the bottom surface of protruding portion 3714 of the BGA package and a PCB during a surface mount process.
(6) A one-piece construction for stiffener/interposer 112 with protruding portion 3714 reduces an electrical and thermal interface impedance present in two-piece versions.
(7) Cavity 702 in stiffener 112 that allows attachment of IC die 102 reduces length of wire bonds 108 and improves BGA package electrical and thermal performances.
(8) Extension of protruding portion 3714 under the sitting plane of the BGA package allows connection of heat sinking devices from the backside of a PCB to the BGA package.
Metal Ring Embodiments
According to an embodiment of the present invention, the mechanical and thermal performance of a BGA package is enhanced by attaching a metal ring to the top surface of the stiffener. In a preferred embodiment, a metal ring is attached to the top surface of the stiffener in a die-up tape BGA package.
FIG. 9A illustrates a cross-sectional view of a die-up tape BGA package 900, according to an embodiment of the present invention. BGA package 900 includes IC die 102, substrate 104, plurality of solder balls 106, one or more wire bonds 108, stiffener 112, epoxy 116, and a ring 902. FIG. 9B illustrates a top view of die-up tape BGA package 900, with ring 902.
Substrate 104 has a top surface to which a bottom surface of stiffener 112 is mounted. A bottom surface of substrate 104 attaches the plurality of solder balls 106. The plurality of solder balls 106 connect to vias and/or points on the bottom surface of substrate 104 to which signals internal to substrate 104 are routed and exposed.
One or more wire bonds 108 connect corresponding bond pads 118 on IC die 102 to contact points 120 on substrate 104. Wire bonds 108 extend through one or more openings 114 in stiffener 112 to form connections with substrate 104. Stiffener 112 has a top surface to which IC die 102 is mounted. Furthermore, ring 902 is attached to the top surface of stiffener 112. Ring 902 may be laminated to stiffener 112, after wire bonding is completed. Epoxy 116 is filled in and flushed to ring 902 after the attachment of ring 902. Ring 902 is preferably made of a metal, such as copper or aluminum, or a combination thereof, but may be constructed from other applicable materials. Preferably, ring 902 is made from the same material as stiffener 112, to minimize the mismatch of the thermal expansion coefficient. Ring 902 is preferably flush with the outer edges of stiffener 112 to form an outer edge of BGA package 900, but may also reside entirely within an outer profile of stiffener 112.
A primary benefit of attaching ring 902 to stiffener 112 is an increase in stiffness of BGA package 900. Ring 902 also aids in reducing the amount of warp of BGA package 900. Furthermore, ring 902 promotes heat dissipation from stiffener 112, reduces junction-to-case thermal resistance, and facilitates the attachment of an external heat spreader to BGA package 900.
Furthermore, ring 902 enhances the process of encapsulation of the BGA package. Ring 902, with stiffener 112, creates a cavity that may be filled with a dispensed glob top or encapsulating material, that locks IC die 102 and surrounding elements in place.
FIG. 17 shows a flowchart 1700 providing operational steps for assembling one or more embodiments of the present invention. The steps of FIG. 17 do not necessarily have to occur in the order shown, as will be apparent to persons skilled in the relevant art(s) based on the teachings herein. Other structural embodiments will be apparent to persons skilled in the relevant art(s) based on the following discussion. These steps are described in detail below.
Flowchart 1700 begins with step 1702. In step 1702, a substrate that has a first surface and a second surface is provided. For example, the substrate is flex substrate 104, or another substrate type suitable for a BGA package. For example, an IC die mounting position and/or contact points are provided on a first, upper surface, and solder ball pads are provided on a second, bottom surface.
In step 1704, a first surface of a stiffener is attached to the first substrate surface. For example, the stiffener is stiffener 112, which is attached to substrate 104. In alternative embodiments, a stiffener is not required, and is not attached to the substrate.
In step 1706, an IC die is mounted to the first stiffener surface. For example, the IC die is IC die 102, which is mounted to stiffener 112. In alternative embodiments, when a stiffener is not used, IC die 102 is mounted directly to the substrate.
In step 1708, a plurality of solder balls are attached to the second substrate surface. For example, the plurality of solder balls are plurality of solder balls 106, which connect to vias and/or solder ball pads on the bottom surface of substrate 104. The solder balls may be arranged on the bottom surface of substrate 104 as shown in FIGS. 12B and 12C, or in alternative arrangements. The solder balls are used to attach a BGA package to a PCB.
In step 1710, a metal ring is attached to the first stiffener surface. Attaching the metal ring enhances heat dissipation from the stiffener. For example, the metal ring is ring 902. In alternative embodiments, when a stiffener is not used, ring 902 is attached directly to the substrate.
Flowchart 1700 may include the additional step where the second stiffener surface within the volume encompassed by the ring is encapsulated. For example, such a filled upper surface may be called a “glob top”. For instance, this volume may be encapsulated by a resin or molding compound, that also encapsulates the IC die and wire bonding.
Embodiments Using Metal Studs to Bridge Stiffener Openings
According to an embodiment of the present invention, the thermal performance of a BGA package is improved by bridging an IC die pad to which the IC die is mounted to the outer regions of the stiffener. In a preferred embodiment, one or more metal studs are used as thermal bridges, to bridge the openings in the stiffener that surround the IC die, in a die-up tape BGA package.
The openings on a stiffener surface allow for wire bond connections between an IC die and a substrate. These openings have the additional effect of reducing the amount of heat that can spread to the outer surface regions of the stiffener, hampering the ability of the stiffener to act as a heat spreader. This effect is illustrated in FIG. 2B, which is further described above. To promote heat spreading according to the present invention, the stiffener is patterned such that one or more short studs run across each wire bond opening. More than one stud may be used to bridge each wire bond opening to promote heat spreading. The manufacturing process used for lead frame patterning may be adapted to pattern a stiffener with studs across the wire bond openings. The use of the studs, however, may reduce space for wire bonds, and may reduce BGA package I/O capability, in some situations.
FIG. 10A illustrates a stiffener 1000, that includes one or more studs 1002, according to an embodiment of the present invention. Stiffener 1000, having one or more studs 1002, may be incorporated into a BGA package in the same manner as is described elsewhere herein for stiffener 112. As shown in FIG. 10A, a stud 1002 bridges each opening 114 in stiffener 1000. In alternative embodiments, more than one stud 1002 per opening 114 may be used. Furthermore, each opening 114 may be bridged by a different number of studs 1002. Some of openings 114 may be bridged by one or more studs 1002, while other openings 114 may not be bridged at all.
FIG. 10B provides an illustration where IC die 102 is wire bound to substrate 104 through stiffener 1000, according to an embodiment of the present invention. One or more wire bonds 108 connect corresponding bond pads 118 on IC die 102 to contact points 120 on substrate 104. Wire bonds 108 avoid studs 1002 when making connections to substrate 104.
FIG. 18 shows a flowchart 1800 providing operational steps for assembling one or more embodiments of the present invention. The steps of FIG. 18 do not necessarily have to occur in the order shown, as will be apparent to persons skilled in the relevant art(s) based on the teachings herein. Other structural embodiments will be apparent to persons skilled in the relevant art(s) based on the following discussion. These steps are described in detail below.
Flowchart 1800 begins with step 1802. In step 1802, a substrate that has a first surface and a second surface is provided. For example, the substrate is flex substrate 104, or another substrate type suitable for a BGA package. For example, an IC die mounting position and/or contact points are provided on a first, upper surface, and solder ball pads are provided on a second, bottom surface.
In step 1804, a wire bond opening is created along each edge of an IC die mount position on a stiffener, wherein each wire bond opening extends through the stiffener. For example, the wire bond openings are wire bond openings 114 in stiffener 1000. The IC die mount position is IC die mounting position 202, shown in FIG. 10A.
In step 1806, a first surface of the stiffener is attached to the first substrate surface. For example, the stiffener is stiffener 1000, which is attached to substrate 104.
In step 1808, an IC die is mounted to a second surface of the stiffener. For example, the IC die is IC die 102, which is mounted to stiffener 1000, in IC die mounting position 202.
In step 1810, at least one of the wire bond openings are bridged with at least one stud. For example, one or more of wire bond openings 114 are bridged with one or more studs 1002. Studs 1002 allow for increased heat spreading across corresponding wire bond openings 114 to the outer edges of stiffener 1000.
In step 1812, a plurality of solder balls are attached to the second substrate surface. For example, the plurality of solder balls are plurality of solder balls 106, which connect to vias and/or solder ball pads on the bottom surface of substrate 104. The solder balls may be arranged on the bottom surface of substrate 104 as shown in FIGS. 12B and 12C, or in alternative arrangements. The solder balls are used to attach a BGA package to a PCB.
The flowchart 1800 may include the further step where a contact pad on the IC die is coupled to the substrate with a wire bond, wherein the wire bond passes through one of the wire bond openings in the stiffener.
Flowchart 1800 may include the additional step where the second stiffener surface is encapsulated. For instance, the second stiffener surface may be encapsulated by a resin or molding compound, that also encapsulates the IC die and wire bonding.
PBGA Thermal/Ground Connector Embodiments
According to an embodiment of the present invention, the electrical and thermal performance of a plastic BGA (PBGA) package is improved by attaching a thermal/ground connector to the bottom surface of a PBGA package. The thermal/ground connector couples the bottom center of a plastic substrate of a die-up PBGA to the PCB. Heat from an IC die is more easily spread to the PCB through the thermal/ground connector, which is attached to the plastic substrate underneath the IC die.
In the discussion above regarding FIG. 8, embodiments were described that used a ground/thermal connector to couple a flex BGA package to a PCB, to reduce package junction-to-board thermal resistance. Aspects of this discussion above are adaptable to other die-up BGA package types. These include BGA packages having an organic substrate, such as PBGA and fine pitch ball grid array (FBGA) packages. Further detailed description is provided in the following discussion that is applicable to BGA packages with organic substrates.
FIG. 11 illustrates a cross-sectional view of a die-up PBGA package 1100, according to an embodiment of the present invention. PBGA package 1100 includes plastic substrate 302, IC die 304, plurality of solder balls 306, plurality of wire bonds 308, die pad 310, one or more vias 314, one or more thermal/ground vias 316, epoxy 320, a ground/thermal connector 1102, adhesive material 1104, a plurality of ground bonds 1106, and a plurality of ground bond pads 1108.
IC die 304 is mounted to die pad 310. Wire bonds 308 connect signals of IC die 304 to contact pads on substrate 302. The contact pads on substrate 302 connect to solder balls 306 attached to the bottom surface of substrate 302, through vias 314 and routing within substrate 302.
Thermal/ground vias 316 connect die pad 310 to an exposed metal plane 1110 at the bottom center of substrate 302. For instance, die pad 310 and metal plane 1110 may be exposed copper pads of plastic substrate 302.
Solder balls are not attached to the bottom region of substrate 302 covered by metal plane 1110. Ground/thermal connector 1102 is attached to metal plane 1110. For instance, ground/thermal connector 1102 may be a metal piece (copper or aluminum, for example) that is laminated to metal plane 1110 at the bottom center of substrate 302 using a conductive adhesive material 1104, such as a conductive epoxy, solder, or other adhesive material. A bottom surface 1112 of ground/thermal connector 1102 may be plated with solder for surface mount to soldering pads on the PCB.
BGA package 1100 provides a thermal path of IC die 304, to die pad 310, to thermal/ground vias 316, to metal plane 1110, to adhesive material 1104, to ground thermal connector 1102 (and bottom surface 1112) to the PCB soldering pads. Heat spreading is improved by a direct thermal path from IC die 304 to the PCB.
Metal pads on the PCB can be connected to a PCB ground plane to advantageously shorten the length of electrical current return paths, as well shorten the conductive heat dissipation path from device junctions of IC die to the PCB.
Ground bonds 1106 may be used to couple ground bond pads 1108 on IC die 304 to die pad 310, when die pad 310 is coupled to ground. This provides for very short ground connections for signals in IC die 304.
FIG. 19A shows a flowchart 1900 providing operational steps for assembling one or more embodiments of the present invention. FIGS. 19B–C provide operational steps according to further embodiments. The steps of FIGS. 19A–C do not necessarily have to occur in the order shown, as will be apparent to persons skilled in the relevant art(s) based on the teachings herein. Other structural embodiments will be apparent to persons skilled in the relevant art(s) based on the following discussion. These steps are described in detail below.
Flowchart 1900 begins with step 1902. In step 1902, a substrate that has a first surface and a second surface is provided. For example, the substrate is plastic substrate 302, or another substrate type suitable for a BGA package. For example, an IC die mounting position and contact points are provided on a first, upper surface, and solder ball pads are provided on a second, bottom surface.
In step 1904, an IC die is mounted to the first substrate surface. For example, the IC die is IC die 304, which is mounted to substrate 302. IC die 304 may be mounted to a die pad 310 attached to substrate 302.
In step 1906, a plurality of solder balls are attached to the second substrate surface. For example, the plurality of solder balls are plurality of solder balls 306, which connect to vias and/or solder ball pads on the bottom surface of substrate 302. The solder balls may be arranged on the bottom surface of substrate 302 as shown in FIG. 12B, or in other arrangements. The solder balls are used to attach a BGA package to a PCB.
In step 1908, a first surface of a heat spreader is coupled to the second substrate surface. For example, the heat spreader is ground/thermal connector 1102, which is coupled to substrate 302 with adhesive material 1104. Ground/thermal connector 1102 may be mounted to metal plane 1110 on substrate 302 by adhesive material 1104.
In step 1910, a second surface of the heat spreader is configured to be coupled to a printed circuit board (PCB). Second heat spreader surface is bottom surface 1112. In an embodiment, step 1910 may include the step where the second surface of the heat spreader is plated with solder.
Flowchart 1900 may comprise the additional step where the first substrate surface is coupled to the heat spreader through at least one via that extends through the substrate. For example, the first substrate surface may be coupled to the heat spreader by one or more ground/thermal vias 316.
FIG. 19B provides exemplary steps for performing step 1904:
In step 1912, a copper plated die-attach pad is exposed in the center of the first substrate surface. The copper plated die-attach pad, die pad 310, may be an exposed portion of a metal layer of plastic substrate 302.
In step 1914, the IC die is mounted to the copper plated die-attach pad. For example, the IC die may be mounted with an epoxy.
FIG. 19C provides exemplary steps for performing step 1908:
In step 1916, a copper plated plane is exposed in the center of the second substrate surface. The copper plated plane, metal plane 1110, is an exposed portion of a metal layer of plastic substrate 302.
In step 1918, the die-attach pad is coupled to the copper plated plane with at least one via.
Flowchart 1900 may include the additional step where the first substrate surface is encapsulated. For instance, the first substrate surface may be encapsulated by a resin or molding compound, that also encapsulates the IC die and wire bonding.
Example PBGA Thermal/Ground Connector Embodiments
Additional description for exemplary embodiments of die-up PBGA package 1100 are described in this section. FIG. 22 illustrates a cross-sectional view of a portion of die-up PBGA package 1100, according to an embodiment of the present invention. PBGA package 1100 includes plastic substrate 302, IC die 304, plurality of solder balls 306, one of the plurality of wire bonds 308, epoxy 320, ground/thermal connector 1102, adhesive material 1104, metal plane 1110, a connector plating 2202, and plurality of solder ball contact pads 2224 (vias 314 and 316, ground bonds 1106, and pads 310 and 1108 are not shown in FIG. 22). PBGA package 1100 is substantially configured as described above, and as further described below. Also shown in FIG. 22 is a cross-sectional view of a portion of an exemplary printed circuit board (PCB) 2222, according to an embodiment of the present invention. PCB 2222 includes a PCB substrate 2212, a PCB metal pad plating 2214, a PCB metal pad 2216, and plurality of solder ball contact pads 2226. Under normal operating conditions, PBGA package 1100 is attached to PCB 2222 in order for IC die 304 to be interfaced with an electronic circuit system.
In the configuration of package 1100 shown in FIG. 22, IC die 304 is mounted to substrate 302. Wire bond 308 connects one or more signals of IC die 304 to contact pads (not shown) on the top surface of substrate 302. These contact pads connect through substrate 302 to solder ball contact pads 2224 exposed through the solder mask on the bottom surface of substrate 302. Solder balls 306 attach to solder ball contact pads 2224.
Ground/thermal connector 1102 is attached to metal plane 1110. Metal plane 1110 is a portion of a metal layer of substrate 302 exposed though the solder mask on the bottom surface of substrate 302. As described above, ground/thermal connector 1102 may be a metal piece or slug (copper or aluminum, for example) similar to the heat spreaders described elsewhere herein, that is laminated to metal plane 1110 at the bottom center of substrate 302 using a conductive adhesive material 1104, such as a conductive epoxy, solder, or other adhesive material. A bottom surface 1112 of ground/thermal connector 1102 may be plated with a metal (including a metal alloy), such as a solder, which may include palladium, nickel, tin, gold, silver, lead and/or further related substance(s), to form connector plating 2202. Connector plating 2202 enhances the surface mounting of connector 1102 to PCB 2222.
The top surface of PCB substrate 2212 includes solder ball contact pads 2226 for surface mount of solder balls 306 to PCB 2222, and includes PCB metal pad 2216 for surface mount of connector 1102 to PCB 2222. PCB metal pad plating 2214 may be attached to PCB metal pad 2216 to enhance the surface mounting of connector 1102 to PCB metal pad 2216. For example, PCB metal pad 2216 may be screen printed with a solder paste to form PCB metal pad plating 2214. PCB metal pad plating 2214 also may be formed in other known manners from processes and substances described herein or elsewhere.
Heat spreading is improved in package 1100 by a direct thermal path from IC die 304 through connector 1102 to PCB 2222. Furthermore, PCB metal pad 2216 on PCB 2222 can be connected to a PCB ground plane to advantageously shorten the length of electrical current return paths, as well shorten the conductive heat dissipation path from device junctions of IC die 304 to PCB 2222. As described above, vias may be created in substrate 302, and filled with a conductive material, to enhance thermal and electrical performance by coupling IC die 304 to connector 1102 more directly.
Example implementations for package 1100 and PCB 2222 according to the present invention will now be described. These implementations are provided for purposes of illustration, and are not intended to limit the scope of the invention. Alternate implementations, differing slightly or substantially from those described herein, will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein. Such alternate implementations fall within the scope and spirit of the present invention.
FIG. 22 illustrates various dimensions of package 1100 and PCB 2222. For package 1100, the following dimensions are shown: an adhesive material height 2204, a connector height 2206, a connector plating height 2208, a solder ball height 2218, and a ball pitch 2220. For PCB 2222, a PCB metal pad plating height 2210 is shown. These dimensions of package 1100 and PCB 2222 may have a variety of values, according to the present invention.
In an example implementation, ground/thermal connector 1102 may be attached to metal plane 1110 on substrate 302 by adhesive material 1104 that has an adhesive material height 2204 in the range of 1 to 1.5 mil (0.025 to 0.0375 mm). Connector 1102 has a connector height 2206 equal to 0.38 mm. Connector plating 2202 has a connector plating height 2208 equal to 1 mil (0.025 mm). According to these example height values, the sum of adhesive material height 2204 (using a value of 0.025 mm), connector height 2206, and connector plating height 2208 is 0.43 mm.
Furthermore, prior to attachment to substrate 302, solder balls 306 may have a height of 0.6 mm, for example. Ball pitch 2220, which represents the distance from the center of a solder ball mounted to substrate 302 to the center of an adjacent solder ball, is equal to 1 mm, for example. When attached to substrate 302, the height of solder balls 306 may decrease slightly, to have a solder ball height 2218 equal to 0.5 mm, for example. This decrease in height is due to the spreading of solder of the solder ball onto a solder ball pad 2224 to which it is attaching. In this example configuration, therefore, the difference in height between the solder ball height 2218 (0.5 mm) and the sum of adhesive material height 2204, connector height 2206, and connector plating height 2208 (0.43 mm) is equal to 0.07 mm, which is the value of a gap distance. When package 1100 is attached to PCB 2222, this gap distance appears between connector plating 2202 and PCB 2222. In this example implementation, the gap distance may vary between 2.0 to 4.0 mils (0.05 to 0.1 mm), or even outside of this range, due to variations in the actual height values recited above that occur during the manufacturing process.
As described above, the dimensions shown in FIG. 22 and described above may have values that are different from those presented above. In an embodiment, solder ball height 2218 is greater than the height of the attached connector 1102 (including connector height 2206, adhesive material height 2204, and connector plating height 2208, when present), although in alternative embodiments, the attached connector 1102 may have an equal height.
As described above, PCB metal pad plating 2210 may be formed on PCB metal pad 2216. PCB metal pad plating 2210 substantially bridges the above described gap distance, and enhances the connection of connector 1102 to PCB 2222. For example, PCB metal pad plating 2214 may be formed such that PCB metal pad plating height 2210 is in the range of 4 to 6 mil (0.1 to 0.15 mm) to substantially fill the gap distance.
In another example configuration, ball pitch 2220 may be equal to 1.27 mm and solder ball height 2218 may be equal to 0.75 or 0.76 mm. In further implementations, these dimensions may have other values. As described above, the dimension values provided in the section are examples, and are not limiting to the present invention.
Furthermore, ground/thermal connector 1102 may be shaped in additional ways, to enhance the operation and manufacturability of package 1100. FIG. 23 shows ground/thermal connector 1102 attached to a bottom surface of substrate 302, according to an exemplary embodiment of the present invention. Connector 1102 is attached to metal plane 1110, and is plated with connector plating 2202. As shown in FIG. 23, connector 1102 may be rectangular in shape. Ground/thermal connector 1102 may be formed in other shapes, such as an ellipse, polygon, star-shaped, and irregular.
Furthermore, in the example embodiment shown in FIG. 23, connector 1102 is smaller in area than metal plane 1110. In alternative embodiments, connector 1102 may have the same area, or a greater area than metal plane 1110.
Ground/thermal connector 1102 may also include two or more separate sub-sections that are attached to package 1100. FIG. 24 shows first and second ground/thermal connectors 2402 and 2404 attached to a bottom surface of substrate 302, according to an exemplary embodiment of the present invention. Connector plating, which may be present on first and second ground/thermal connectors 2402 and 2404, is not shown in FIG. 24. First ground/thermal connector 2402 is attached to first metal plane 2406 on substrate 302. Second ground/thermal connector 2404 is attached to second metal plane 2408 on substrate 302. In alternative embodiments, first and second metal planes 2406 and 2408 may be combined into a single metal plane, or may be each divided into any number of metal planes, for attachment of first and second ground/thermal connectors 2402 and 2404 to substrate 302. Furthermore, one or more PCB metal pads may be present on PCB substrate 2212 (shown in FIG. 22) to attach first and second ground/thermal connectors 2402 and 2404 to PCB 2222.
The use of more than one ground/thermal connector, as shown in FIG. 24, may enhance the functionality, thermal performance, electrical performance, mechanical performance, and the manufacturability of package 1100. For example, electrical performance may be enhanced by electrically isolating first and second connectors 2402 and 2404, and coupling them to separate potentials (i.e., ground or other potentials) of IC die 304 (through vias in substrate 302).
First and second connectors 2402 and 2404 may then be coupled to the separate potential signals in PCB 2222.
Any number of additional ground/thermal connectors may be used, according to the present invention. FIG. 25 shows first, second, third, and fourth ground/thermal connectors 2502, 2504, 2506, and 2508 attached to a bottom surface of substrate 302, according to a further exemplary embodiment of the present invention. Connector plating, which may be present on first, second, third, and fourth ground/thermal connectors 2502, 2504, 2506, and 2508, is not shown in FIG. 25. First, second, third, and fourth ground/thermal connectors 2502, 2504, 2506, and 2508 are attached to first, second, third, and fourth metal planes 2510, 2512, 2514, and 2516, respectively, on substrate 302.
According to the present invention, ground/thermal connectors may be shaped and arranged in a variety of configurations. For example, one or more ground/thermal connectors may be formed around a portion of, or all of one or more other ground/thermal connectors. FIG. 27 shows first and second ground/thermal connectors 2702 and 2704 attached to a bottom surface of substrate 302, according to a further exemplary embodiment of the present invention. First and second ground/thermal connectors 2702 and 2704 are attached to first and second metal planes 2706 and 2708. As shown in FIG. 27, first ground/thermal connector 2702 is formed in a substantially rectangular shape, and second ground/thermal connector 2704 is formed in a substantially rectangular ring shape that surrounds first ground/thermal connector 2702 on the bottom surface of substrate 302. First metal plane 2706 is correspondingly formed in a rectangular-shaped metal plane, and second metal plane 2708 is formed in a rectangular ring-shaped metal plane. As shown in FIG. 27, a portion of the bottom surface of substrate 302 is present between first and second metal planes 2706 and 2708.
Vias through a package substrate may be located in a variety of places in a substrate. One example pattern for locating vias in a substrate is shown in FIG. 28. FIG. 28 shows a bottom view of a corner portion of substrate 302 with potential via locations. Substrate 302 of FIG. 28 is divided into a peripheral region 2804 and a central region 2806. The central region 2806 corresponds to the portion of the substrate adjacent to a mounted IC die 102 (and corresponding metal pad) and/or a mounted ground/thermal connector. The peripheral region 2804 corresponds to the portion of the substrate that is not adjacent to the mounted IC die 102. As shown in FIG. 28, a plurality of potential vias 2802 may be located in substrate 302 in an array configuration. In the peripheral region 2804 of substrate 302, the plurality of solder balls 306 are arranged in an array. In this region, each via of the plurality of potential vias 2802 is located between surrounding solder balls 306. In the central region 2806 of substrate 302, solder balls are not attached. In the central region 2806, potential vias 2802 continue to be arranged in the array configuration as they are in the peripheral region 2804.
The present invention is applicable to the via configuration shown in FIG. 28, and to other via configurations. According to an embodiment of the present invention, the potential vias located in the central region may be located relatively closer to each other than in the peripheral region, allowing for the use of a greater number of vias in a given area in the central region. The resulting increased density of vias allows for more connections by vias between IC die 102 and a ground/thermal connector attached to the bottom surface of substrate 302. This will allow for a greater heat transfer from IC die 102 to the PCB through the vias and ground/thermal connector. Furthermore, if the ground/thermal connector is used as a ground potential (or other potential), additional vias will enhance the ground connection, reduce ground bounce and other types of unwanted circuit noises.
FIG. 29 shows an example bottom view of a corner portion of substrate 302, according to an embodiment of the present invention. As shown in FIG. 29, the spacing of potential vias 2904 in central region 2806 is denser than the spacing of potential vias 2902 in peripheral region 2804. A variety of possible via arrangements are applicable to the present invention. FIG. 30 shows another example of a bottom view of a corner portion of substrate 302, according to an embodiment of the present invention. As shown in FIG. 30, the spacing of potential vias 3004 in central region 2806 is denser than the spacing of potential vias 3002 in peripheral region 2804. However, central region vias 3004 are not located adjacent to solder balls 306 as they are in FIG. 29. Furthermore, although central region vias 2904 and 3004 are arranged in columns and rows, central region vias may be arranged in any other applicable arrangement.
Referring to the example shown in FIG. 29, an example via 2902 may have a via diameter of 0.2 mm. The invention is applicable to alternative via diameters. In peripheral region 2804, a solder ball pitch (i.e., spacing between solder ball centers) 2906 may be equal to 1.0 mm. In peripheral region 2804, a peripheral region via pitch 2908 may be equal to 1.0 mm. In central region 2806, a central region via pitch 2910 is smaller than peripheral region via pitch 2908. For example, central region via pitch 2910 may be equal to 0.4 mm, 0.45 mm, 0.5 mm, or any other value in this range, or less than peripheral region via pitch 2908. These solder ball/via pitch values are provided for exemplary purposes, and are not limiting to the present invention.
Note that in FIGS. 29 and 30, the distances between adjacent vias in central region 2806 and peripheral region 2804 are shown to be uniform. These distances are not required to be uniform in a particular region. In an alternative embodiment, in either the central or peripheral region, a distance between a first pair of adjacent vias may differ from a distance between a second pair of adjacent vias. However, taken as a whole, the distances between adjacent vias in central region 2806 may still on average be less than the distances between adjacent vias in peripheral region 2804. In other words, in such an embodiment, a via density in central region 2806 will be greater than a via density in peripheral region 2804, even if the distances between via pairs differ.
FIG. 26 shows a flowchart 2600 providing operational steps for assembling one or more embodiments of the present invention. The steps of FIG. 26 do not necessarily have to occur in the order shown, as will be apparent to persons skilled in the relevant art(s) based on the teachings herein. Other structural embodiments will be apparent to persons skilled in the relevant art(s) based on the following discussion. These steps are described in detail below.
Flowchart 2600 begins with step 2602. In step 2602, a substrate that has a first surface is provided. For example, the substrate is plastic substrate 302, or another substrate type suitable for a BGA package. The first surface is the bottom surface of substrate 302 shown in FIG. 22, for example.
In step 2604, an array of contact pads and a metal plane on the first surface of the substrate are exposed. For example, the contact pads are solder ball contact pads 2224, and the metal plane is metal plane 1110. The contact pads and metal plane are portions of a metal layer of substrate 302 that are completely or partially exposed through a solder mask on the bottom surface of substrate 302.
In step 2606, a solder ball is attached to each of the exposed contact pads on the first surface of the substrate. For example, the solder balls attached to each contact pad are plurality of solder balls 306, which attach to solder ball contact pads 2224.
In step 2608, a first surface of a thermal connector is coupled to the exposed metal plane. For example, the thermal connector is ground/thermal connector 1102, which is coupled to metal plane 1110.
In an embodiment, step 2608 may include a step wherein the first surface of the thermal connector is coupled to the exposed metal plane, wherein the thermal connector has a height that is less than a height of a solder ball attached to one of the exposed contact pads. For example, as shown in FIG. 22, ground/thermal connector height 2206 is less than solder ball height 2218. In alternative embodiments, ground/thermal connector height 2206 may be equal to or greater than solder ball height 2218. Step 2608 may include a further step wherein the first surface of the thermal connector is coupled to the exposed metal plane by a conductive adhesive material. For example, the conductive epoxy is adhesive material 1104, which may be a silver-filled epoxy, solder, or other similar substance.
Flowchart 2600 may include the additional step wherein the second surface of the thermal connector is plated with a metal. For example, as shown in FIG. 22, a bottom surface 1112 of ground/thermal connector 1102 is plated with connector plating 2202. The second surface of the thermal connector 1102 may be plated with a metal, wherein a combined height of the thermal connector, the conductive adhesive material, and the metal plating is less than a height of a solder ball attached to one of the exposed contact pads. As shown in FIG. 22, connector height 2206, adhesive material height 2204, and connector plating height 2208 are less than solder ball height 2218. In alternative embodiments, this combined height may be equal to or greater than solder ball height 2218.
Flowchart 2600 may include the additional step wherein the second surface of the thermal connector is configured to be coupled to a second metal plating formed on a metal plane on the PCB. As shown in FIG. 22, PCB 2222 has a PCB metal pad 2216, with a PCB metal pad plating 2214 formed thereon. Ground/thermal connector 1102 is configured to be coupled to PCB metal pad plating 2214 during surface mount of package 1100 to PCB 2222. For example, connector 1102 may be shaped and sized to conform to being surface mounted to PCB 2222. The second surface of the thermal connector 1102 may be configured to be coupled to the second metal plating, wherein the second metal plating has a height. For example, PCB metal pad plating 2214 has a PCB metal pad plating height 2210. The second surface of the thermal connector 1102 may be coupled to the PCB metal pad 2216 through PCB metal pad plating 2214. This may occur during the surface mount process, where package 1100 is attached to PCB 2222. Connector 2206 may be configured such that when package 1100 is attached to PCB 2222, a combined height of the thermal connector (e.g., connector height 2206), the conductive adhesive material (e.g., adhesive material height 2204), the first metal plating (e.g., connector plating height 2208), and the second metal plating (e.g., PCB metal pad plating height 2210) may be substantially equal to a height of a solder ball (e.g., solder ball height 2218) attached to one of the exposed contact pads (e.g., solder ball contact pad 2224) and attached to a contact pad (e.g., PCB contact pad 2226) on PCB 2222.
In an embodiment, the thermal connector of step 2608 may include a plurality of separate thermal connectors. For example, as shown in FIG. 24, a first and second ground/thermal connector 2402 and 2404. Step 2608 may include a step wherein a first surface of the plurality of separate thermal connectors is coupled to the exposed metal plane. The exposed metal plane of step 2604 may include a plurality of separate exposed metal planes. For example, FIG. 24 shows first and second metal planes 2406 and 2408. Step 2608 may further include the step wherein the first surface of each one of the plurality of separate thermal connectors is coupled to a corresponding one of the plurality of separate exposed metal planes. FIG. 24 shows first and second ground/thermal connectors 2402 and 2404 attached to first and second metal planes 2406 and 2408, respectively, on the bottom surface of substrate 302. Alternatively, the plurality of thermal connectors may include first and second ground/thermal connectors 2702 and 2704, and the exposed metal planes may include first and second metal planes 2706 and 2708, for example.
In an embodiment, step 2602 may include the step wherein an organic substrate that has a first surface is provided. For example, the organic substrate may be plastic substrate 302, which includes one or more metal layers formed on an organic substrate (for example, BT resin or FR4 epoxy/glass).
In an embodiment, flowchart 2600 may include the additional step wherein an IC die is mounted to a second surface of the substrate. For example, the IC die may be IC die 304. IC die 304 may be mounted to a die pad 310 attached to substrate 302, as shown in FIG. 3. Furthermore, flowchart 2600 may include the additional step wherein the IC die is coupled to the exposed metal plane by at least one via that extends through the substrate. For example, IC die 304 may be coupled to metal plane 1110 by one or more ground/thermal vias 316, as shown in FIG. 11. This step may include the step wherein the at least one via is filled with a conductive material, such as a solder.
In an example embodiment, substrate 302 has a central portion that is defined by the metal plane to which an IC die may be mounted. In an embodiment, flowchart 2600 may include the additional steps where a plurality of vias are located in the substrate in the central region, and a plurality of vias are located in the substrate outside of the central region. For example, the central region may be central region 2806, and an area outside of the central region may be peripheral region 2804. In an embodiment, a first via density for the plurality of vias in the central portion is greater than a second via density for the plurality of vias outside of the central portion.
Embodiments Allowing Attachment of Additional Electronic Devices
According to an embodiment of the present invention, the electrical performance of a BGA package is improved by configuring the BGA package to allow the attachment of electronic devices to the bottom surface of a BGA package. In an example BGA package, a thermal/ground connector couples the bottom center of the package substrate to a PCB. According to the present invention, electronic devices are attached to the bottom surface of the BGA package, in a region between the thermal/ground connector and the array of solder balls. This configuration allows for enhanced electrical performance, by allowing additional electronic devices to be present in the BGA package. Furthermore, the electronic devices are mounted closely to the thermal/ground connector, and hence may have shorter ground current paths. Further benefits may be realized, as would be understood by persons skilled in the relevant art(s) from the teachings herein.
Embodiments allowing the attachment of electronic devices to the bottom surface of the BGA package are adaptable to any BGA package types, including any of those described elsewhere herein. These BGA package types include tape and organic substrate BGA packages, and include die-up and die-down BGA package configurations. For exemplary purposes, the present invention is described below in relation to a die-up BGA package similar to BGA package 800 shown in FIG. 8, but the present invention is also applicable to other BGA package configurations, as would be understood by persons skilled in the relevant art(s) from the teachings herein.
FIG. 31 shows a bottom view of an example BGA package 3100, according to an embodiment of the present invention. BGA package 3100 is configured similarly to BGA package 800 described above. Attached to substrate 104 on the bottom of BGA package 3100 are plurality of solder balls 106 and ground/thermal connector 802. Additional or fewer solder balls 106 may be present. Ground/thermal connector 802 may be attached directly to the bottom surface of substrate 104, or may be attached to a stiffener in BGA package 3100 through a central opening formed in substrate 104. Ground/thermal connector 802 may be relatively larger or smaller, or differently shaped than as shown in FIG. 31, and may be centrally located, or located off-center of the bottom surface of substrate 104.
As shown in FIG. 31, a substrate region 3102 exists on the bottom surface of substrate 104, bounded on an outer edge 3104 by solder balls 106, and on an inner edge 3106 by thermal connector 802. According to the present invention, electronic devices may be attached/mounted to the bottom surface of substrate 104 in substrate region 3102.
FIG. 32 shows a bottom view of BGA package 3100, with first and second electronic devices 3202 and 3204 attached to the bottom surface of substrate 104, according to an embodiment of the present invention. First and second electronic devices 3202 and 3204 may be any applicable type of electronic device that would be useful to include in an integrated circuit package, that meet applicable size constraints. For example, first and second electronic devices 3202 and 3204 may be passive or active components. For instance, first and second electronic devices 3202 and 3204 may be any passive component type, including resistors, capacitors, and/or inductors. Furthermore, first and second electronic devices 3202 and 3204 may be leaded and/or leadless devices. Any number of one or more electronic devices may be attached/mounted to the bottom surface of substrate 104 in substrate region 3102.
Electronic devices may be attached to the bottom surface of substrate 104 adjacent to ground/thermal connector 802. In some configurations, electronic devices may be attached more closely to ground/thermal connector 802 than in others. For example, as described above, ground/thermal connector 802 may be coupled to a stiffener in BGA package 3100 through a central opening in substrate 104. When ground/thermal connector 802 is directly coupled to the bottom surface of substrate 104, no central opening in substrate 104 is required. The structural integrity of substrate 104 near ground/thermal connector 802 when a central opening is present may be less than when a central opening is not present. Hence, in some embodiments, electronic devices may be attached in substrate region 3102 more closely to ground/thermal connector 802 when a central opening is not present in substrate 104, than when a central opening is present.
FIG. 33 shows a PCB portion 3300 for mounting a BGA package such as BGA package 3100, according to an exemplary embodiment of the present invention. PCB portion 3300 includes PCB contact pads 3302 and a PCB metal pad 3304. When BGA package 3100 is attached to PCB portion 3300, solder balls 106 attach to PCB contact pads 3302, and ground/thermal connector 802 attaches to PCB metal pad 3304. For example, solder balls 106 may be reflowed to attach to PCB contact pads 3302, and ground/thermal connector 802 may be attached by solder to PCB metal pad 3304. The present invention is applicable to additional ways of attaching BGA package 3100 to PCB portion 3300.
As shown in FIG. 33, a PCB region 3306 exists on PCB portion 3300, bounded on an outer edge 3308 by PCB contact pads 3302, and on an inner edge 3310 by PCB metal pad 3304. According to the present invention, electronic devices attached/mounted to the bottom surface of substrate 104 in substrate region 3102, as shown in FIG. 32, will be present above PCB region 3306 when BGA package 3100 is attached to PCB portion 3300. Furthermore, according to additional embodiments of the present invention, electronic devices may be attached/mounted to PCB portion 3300 in PCB region 3306.
FIG. 34 shows PCB portion 3306 with third and fourth electronic devices 3402 and 3404 attached, according to an embodiment of the present invention. Third and fourth electronic devices 3402 and 3404 may be any applicable type of electronic device that would be useful to attach to a PCB, that meet applicable size constraints. For example, third and fourth electronic devices 3402 and 3404 may be passive or active components. For instance, third and fourth electronic devices 3402 and 3404 may be any passive component type, including resistors, capacitors, and/or inductors. Furthermore, third and fourth electronic devices 3402 and 3404 may be leaded and/or leadless devices. Any number of one or more electronic devices may be attached/mounted to PCB portion 3300 in PCB region 3306.
When BGA package 3100 is mounted on PCB portion 3306, either or both of substrate region 3102 and PCB region 3306 may have electronic devices attached/mounted on them. For example, FIG. 35 shows an cross-sectional view of a portion of BGA package 3100 mounted to PCB portion 3300, according to an embodiment of the present invention. The portion of BGA package 3100 shown in FIG. 35 includes substrate 104, respective bottom substrate surface contact pads, solder balls 106a–c, and ground/thermal connector 802. Solder balls 106-c, which are attached to solder ball contact pads 3502 on substrate 104, are attached to PCB contact pads 3302. Ground/thermal connector 802 attaches to a metal plane 3506 on the bottom surface of substrate 104 by an epoxy or other adhesive material (not shown). Ground/thermal connector 802 attaches to PCB metal pad 3304 by solder or other attachment material (not shown).
As shown in FIG. 35, first electronic device 3202 is attached to the bottom surface of substrate 104 between ground/thermal connector 802 and solder ball 106b. First electronic device 3202 attaches to one or more substrate contact pads 3504 by solder or other attachment material (not shown). Furthermore, third electronic device 3402 is attached to PCB portion 3306, between ground/thermal connector 802 and solder ball 106c. Third electronic device 3402 attaches to one or more PCB contact pads 3508 by solder or other attachment material (not shown). The present invention is applicable to any number of electronic devices attached to BGA package 3100 and/or PCB 3300.
As described above, FIG. 26 shows a flowchart 2600 providing operational steps for assembling one or more embodiments of the present invention. FIGS. 36A and 36B show additional steps for flowchart 2600, according to embodiments of the present invention. These steps do not necessarily have to occur in the order shown, as will be apparent to persons skilled in the relevant art(s) based on the teachings herein. Other structural embodiments will be apparent to persons skilled in the relevant art(s) based on the following discussion. These steps are described in detail below.
In an embodiment, step 2604 includes the step where the array of contact pads are arranged in at least one ring to surround the metal plane on the first surface of the substrate. For example, as shown in FIG. 31, solder balls 106, which are attached to an array of contact pads such as solder ball contact pads 3502 shown in FIG. 35, are arranged in three rectangular rings around ground/thermal connector 802. Ground/thermal connector 802 is attached to metal plane 3506. The invention is applicable to any number of such solder ball rings.
As shown in FIG. 36A, flowchart 2600 may include step 3602. In step 3602, at least one passive electronic device is attached to the first surface of the substrate in a region bounded on a first edge by the metal plane and on a second edge by the array of contact pads. For example, as shown in FIG. 32, first and second electronic devices 3202 and 3204 are attached to the bottom surface of substrate 104 in substrate region 3102. Substrate region 3102 is bounded on an inner edge 3106 by ground/thermal connector 802, and on an outer edge 3104 by solder balls 106. Ground/thermal connector 802 is attached to metal plane 3506.
As shown in FIG. 36B, flowchart 2600 may include additional steps. In step 3604, a second metal plane is exposed on a first surface of a PCB that corresponds to the first metal plane. For example, as shown in FIG. 33, PCB metal pad 3304 is exposed on PCB portion 3300. PCB metal pad 3304 corresponds to metal plane 3506 on the bottom surface of substrate 104. Ground/thermal connector 802 attaches to PCB metal pad 3304 when BGA package 3100 is mounted to PCB portion 3300.
In step 3606, a second array of contact pads are exposed arranged in at least one ring that corresponds to the first array of contact pads. For example, as shown in FIG. 33, array of PCB contact pads 3302 are exposed on PCB portion 3300. Solder balls 106 are attached to PCB contact pads 3302 when BGA package 3100 is mounted on 3300. PCB contact pads 3302 are arranged in three rectangular rings, that correspond to the three rectangular rings formed by solder balls 106 and their respective contact pads on substrate 104, as shown in FIG. 31.
In step 3608, at least one passive electronic device is attached to the first surface of the PCB in a region bounded on a first edge by the second metal plane and on a second edge by the second array of contact pads. For example, as shown in FIG. 34, third and fourth electronic devices 3402 and 3404 are attached to PCB portion 3300 in PCB region 3306. PCB region 3306 is bounded on an inner edge 3310 by PCB metal pad 3304, and on an outer edge 3308 by PCB contact pads 3302.
CONCLUSION 
While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

## Claims

1. A method of assembling a ball grid array (BGA) package, comprising the steps of:
(A) mounting an IC die in a centrally located cavity of a substantially planar first surface of a stiffener;
(B) attaching the first surface of a substrate to a substantially planar second surface of the stiffener that is opposed to the first surface of the stiffener, such that a centrally located protruding portion on the second surface of the stiffener opposed to the centrally located cavity extends through an opening in the substrate; and
(C) coupling a wire bond from a bond pad of the IC die to a contact pad on the first surface of the substrate through a recessed edge portion of the first and second surfaces of the stiffener.

2. A method of assembling a ball grid array (BGA) package, comprising the steps of:
(A) mounting an IC die in a centrally located cavity of a substantially planar first surface of a stiffener;
(B) attaching the first surface of a substrate to a substantially planar second surface of the stiffener that is opposed to the first surface of the stiffener, such that a centrally located protruding portion on the second surface of the stiffener opposed to the centrally located cavity extends through an opening in the substrate: and
(C) coupling a wire bond from a bond pad of the IC die to a contact pad on the first surface of the substrate through a rectangular shaped recessed edge portion of the first and second surfaces of the stiffener.

3. A method of assembling a ball grid array (BGA) package, comprising the steps of:
(A) mounting an IC die in a centrally located cavity of a substantially planar first surface of a stiffener:
(B) attaching the first surface of a substrate to a substantially planar second surface of the stiffener that is opposed to the first surface of the stiffener, such that a centrally located protruding portion on the second surface of the stiffener opposed to the centrally located cavity extends through an opening in the substrate; and
(C) coupling a wire bond from a bond pad of the IC die to a contact pad on the first surface of the substrate through a notch formed in a recessed edge portion of the first and second surfaces of the stiffener.

4. A method of assembling a ball grid array (BGA) package, comprising the steps of:
(A) mounting an IC die in a centrally located cavity of a substantially planar first surface of a stiffener;
(B) attaching the first surface of a substrate to a substantially planar second surface of the stiffener that is opposed to the first surface of the stiffener, such that a centrally located protruding portion on the second surface of the stiffener opposed to the centrally located cavity extends through an opening in the substrate; and
(C) coupling a wire bond from a bond pad of the IC die to a contact pad on the first surface of the substrate through a notch formed in an opening in the stiffener.

5. The method of claim 4, wherein step (C) includes the step of:
coupling a wire bond from a bond pad of the IC die to a contact pad on the first surface of the substrate through a rectangular shaped notch formed in an opening in the stiffener.

6. The method of claim 4, wherein step (C) includes the step of:
coupling a wire bond from a bond pad of the IC die to a contact pad on the first surface of the substrate through a circularly shaped notch formed in an opening in the stiffener.

7. The method of claim 4, wherein step (C) includes the step of:
coupling the wire bond through a notch in an opening in the stiffener that is bridged by a stud.

8. A method of assembling a ball grid array (BGA) package, comprising the steps of:
(A) mounting an IC die in a centrally located cavity of a substantially planar first surface of a stiffener;
(B) attaching the first surface of a substrate to a substantially planar second surface of the stiffener that is opposed to the first surface of the stiffener, such that a centrally located protruding portion on the second surface of the stiffener opposed to the centrally located cavity extends through an opening in the substrate; and
(C) coupling a wire bond from a bond pad of the IC die to a contact pad on the first surface of the substrate through an opening in the stiffener that has an edge that coincides with an edge of the cavity.

9. The method of claim 8, wherein step (C) includes the step of:
coupling the wire bond through a rectangular shaped opening in the stiffener that has an edge that coincides with an edge of the cavity.

10. The method of claim 8, wherein step (C) includes the step of:
coupling a wire bond from a bond pad of the IC die to a contact pad on the first surface of the substrate through a recessed edge portion that has an edge that coincides with an edge of the cavity.

11. The method of claim 8, wherein step (C) includes the step of:
coupling a wire bond from a bond pad of the IC die to a contact pad on the first surface of the substrate through a rectangular shaped recessed edge portion that has an edge that coincides with an edge of the cavity.

12. The method of claim 8, further comprising the step of:
substantially filling a gap around the protruding portion between the protruding portion and the substrate with a sealant material.

13. The method of claim 8, wherein step (C) includes the step of:
coupling a wire bond from a bond pad of the IC die to a contact pad on the first surface of the substrate through a notch formed in an opening in the stiffener that has an edge that coincides with an edge of the cavity.

14. A method of assembling a ball arid array (BGA) package, comprising the steps of:
(A) mounting an IC die in a centrally located cavity of a substantially planar first surface of a stiffener;
(B) attaching the first surface of a substrate to a substantially planar second surface of the stiffener that is opposed to the first surface of the stiffener, such that a centrally located protruding portion on the second surface of the stiffener opposed to the centrally located cavity extends through an opening in the substrate;
(C) coupling wire bond from a bond pad of the IC die to contact pad on the first surface of the substrate through a through-pattern in the stiffener; and
(D) substantially filling a gap around the protruding portion between the protruding portion and the substrate with a sealant material.

15. The method of claim 14, wherein step (C) includes the step of:
coupling the wire bond through a through pattern in the stiffener that is bridged by a stud.

16. The method of claim 14, wherein step (C) comprises the step of:
coupling the wire bond through a trapezoidal shaped opening in the stiffener.