THERMALLY AND ELECTRICALLY ENHANCED BALL GRID ARRAY PACKAGING

Abstract: Electrically and thermally enhanced die-up ball grid array (BGA) packages are described. A BGA package includes a stiffener, substrate, a silicon die, and solder balls. The die is mounted to the top of the stiffener. The stiffener is mounted to the top of the substrate. A plurality of solder balls are attached to the bottom surface of the substrate. A top surface of the stiffener may be patterned. A second stiffener may be attached to the first stiffener. The substrate may include one, two, four, or other number of metal layers. Conductive vias through a dielectric layer of the substrate may couple the stiffener to solder balls. An opening may be formed through the substrate, exposing a portion of the stiffener. The stiffener may have a down-set portion. A heat slug may be attached to the exposed portion of the stiffener. A locking mechanism may be used to enhance attachment of the heat slug to the stiffener. The heat slug may be directly attached to the die through an opening in the stiffener.

Description: Thermally and Electrically Enhanced Ball Grid Array Packaging THERMALLY AND ELECTRICALLY ENHANCED BALL GRID ARRAY PACKAGING Background of the Invention Field of the Invention The invention relates generally to the field of integrated circuit (IC) device packaging teclmology, and more particularly to substrate stiffening and heat spreading techniques in ball grid array (BGA) packages. Background Art Integrated circuit (IC) dies are typically mounted in or on a package that is attached to a printed circuit board (PCB). One such type of IC die 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 reflo wed 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. It would be advantageous to provide a thermally and electrically enhanced ball grid array (BGA) package that is smaller, cheaper, customizable and capable of superior performance when compared with conventional BGA packages. More specifically, it would be advantageous to provide an advanced BGA package that achieves: 1) enhanced thermal and electrical performance; 2) reduced package size; 3) increased flexibility of die configuration; 4) reduced ball pitch; 5) increased flexibility in circuit routing density; and 6) configurations with greater thermal spreading capabilities. XL- Summary of the Invention Electrically and thermally enhanced die-up ball grid array (BGA) packages are described. In an embodiment, a BGA package includes a stiffener, substrate, a silicon die, and solder balls. The die is mounted to the top of the stiffener. The stiffener is mounted to the top of the substrate. A plurality of solder balls are attached to the bottom surface of the substrate. A top surface of the stiffener may be patterned. A second stiffener may be attached to the first stiffener. The substrate may include one, two, four, or other number of metal layers. Conductive vias through a dielectric layer of the substrate may couple the stiffener to solder balls. An opening may be formed through the substrate, exposing a portion of the stiffener. The stiffener may have a down-set portion. A heat slug may be attached to the exposed portion of the stiffener. A locking mechanism may be used to enhance attachment of the heat slug to the stiffener. The heat slug may be directly attached to the die through an opening in the stiffener. Further embodiments, features, and advantages of the present inventions, 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 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. FIG. 1 is a cross-sectional representation of a BGA package design in accordance with one embodiment of the disclosed method and apparatus. FIG.2 is a cross-sectional representation of another BGA package design in accordance with one embodiment of the disclosed method and apparatus. FIG. 3 is a cross-sectional representation of another BGA package design in accordance with one embodiment of the disclosed method and apparatus. FIG.4 is a cross-sectional representation of another BGA package design in accordance with one embodiment of the disclosed method and apparatus. FIG. 5 is a cross-sectional representation of another BGA package design in accordance with one embodiment of the disclosed method and apparatus. FIG. 6 is a cross-sectional representation of another BGA package design in accordance with one embodiment of the disclosed method and apparatus. FIG. 7 is a cross-sectional representation of another BGA package design in accordance with one embodiment of the disclosed method and apparatus. FIG. 8 is a cross-sectional representation of another BGA package design in accordance with one embodiment of the disclosed method and apparatus. FIG. 9 is a cross-sectional representation of another BGA package design in accordance with one embodiment of the disclosed method and apparatus. FIG. 10 is a cross-sectional representation of another BGA package design in accordance with one embodiment of the disclosed method and apparatus. FIG. 11 is a cross-sectional representation of another BGA package design in accordance with one embodiment of the disclosed method and apparatus. FIG. 12 is across-sectional representation of anotherBGA package design in accordance with one embodiment of the disclosed method and apparatus. FIG. 13 is a cross-sectional representation of another BGA package design in accordance with one embodiment of the disclosed method and apparatus. FIG. 14 is a cross-sectional representation of another BGA package design in accordance with one embodiment of the disclosed method and apparatus. FIG. 15 is a cross-sectional representation of another BGA package design in accordance with one embodiment of the disclosed method and apparatus. FIG. 16 is a cross-sectional representation of another BGA package design in accordance with one embodiment of the disclosed method and apparatus. FIG. 17 is a cross-sectional representation of another BGA package design in accordance with one embodiment of the disclosed method and apparatus. FIG. 18 is a cross-sectional representation of another BGA package design in accordance with one embodiment of the disclosed method and apparatus. 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 Preferred Embodiments The present invention provides a thermally and electrically enhanced ball grid array (BGA) packaging that is smaller, cheaper, customizable and capable of superior performance when compared with conventional BGA packages. More specifically, the present invention offers advanced BGA packages that achieve: 1) enhanced thermal and electrical performance; 2) reduced package size; 3) increased flexibility of die configuration; 4) reduced ball pitch; 5) increased flexibility in circuit routing density; and 6) optional configurations with or without the attachment of a heat sink. Embodiments of the present invention may be used in a variety of electronic devices, including telecommunication devices, mobile phones, camcorders, digital cameras, network systems, printers, and testers. Advantages of the various embodiments of the invention include: 1) an embedded heat spreader in the package for the silicon die to adhere onto, and a connection between the die and the heat spreader to provide thermal and electrical performance enhancement; 2) an option of a fully populated ball grid array assignment for circuit routing; 3) an option of multi-layer heat spreader structure to provide split and isolated ground; 4) an option of utilizing single, double or multi-layer metal circuitry substrate with or without plating traces and with or without conductive via connections to accommodate different thermal, electrical and design requirements; 5) exposed die attach pad for enhanced thermal performance; 6) drop-in heat slug for direct thermal and electrical conduction; 7) flexible range of ball pitch from 0.3 mm to 1.5 mm; 8) active ground connection capability from silicon die to motherboard through conductive slug attachment or through solder ball connects to the heat spreader; 9) high thermal conductive path; 10) low package profile compared with plastic ball grid array (PBGA) and other conventional BGA packages; and 11) wafer saw or punch format for maximized material utilization. Embodiments of the present invention are described in detail below, and are designated as Designs 1 through 18. Design 1 - Fully Populated Package with Solid Grounding FIG. 1 shows a BGA package 100, according to an embodiment of the present invention. BGA package 100 incorporates a substrate 130 with a single metal layer, and a heat spreader/stiffener 112 with selective plating. BGA package 100 includes substrate 130, stiffener 112, an integrated circuit die 114, a mold/glob top 120, a plurality of solder balls 122, a first wire connection 124, and a second wire connection 126. Substrate 130 includes a base material/dielectric layer 102, a conductive metal layer 106, and a circuit mask 108. Metal layer 106 is attached to the bottom surface of dielectric layer 102 by an adhesive 104. Metal layer 106 is a conductive layer that is patterned with traces. Circuit mask 108 is applied to the top surface of dielectric layer 102. Dielectric layer 102 may be any one of PCB, FR4, polyimide, and ceramic dielectric materials. Stiffener 112 is attached to the top surface of substrate 130 by an adhesive 110. Die 114 is attached to the top surface of stiffener 112 by a die attach epoxy 116. First wire connection 124 is coupled from a pin on die 114 to stiffener 112. A bondable plating surface 118 is formed on the top surface of stiffener 112 to enhance attachment of first wire connection 124 to stiffener 112. Second wire connection 126 is coupled from a pin on die 114 to a trace of metal layer 106. Mold/glob top 120 is formed over the top surface of stiffener 112 to encapsulate die 114 and first and second wire connections 124 and 126. Preferably, copper is used to make metal layer 106, although other metals may also be used. Similarly, stiffener 112 is preferably made from copper so that it may provide a substantially rigid and planar surface, enhance the coplanarity of the different layers of substrate 130, and, at the same time, act as a heat spreader to help dissipate heat. Alternatively, other materials, such as aluminum or ceramic, may also be used to make the stiffener. Preferably, bondable surface 118 is selectively plated, chemically deposited or electro-deposited on stiffener 112 for solid or float grounding purposes. Otherwise, stiffener 112 may be fully plated. Dielectric layer 102, preferably a polyimide tape, is patterned with openings or vias for accepting solder balls 122 so that solder balls 122 make electrical contact with the patterned conductive metal layer 106. The distance between centers of adjacent solder balls 122 is shown as ball pitch 128 in FIG. 1. Table 1 shows example dimensions and ranges for some of the elements shown in FIG. 1: Table 1 Design 2 - Fully Populated Package with Solid Grounding FIG. 2 shows a BGA package 200, according to an embodiment of the present invention. As shown in FIG. 2, BGA package 200 is basically the same as BGA package 100, except that it does not have an adhesive layer 104 between patterned dielectric layer 102 and patterned conductive metal layer 106. Furthermore, a first and second dimple design 202 and 204 are shown on stiffener 112 in FIG. 2. First and/or second dimple designs 202 and 204 on stiffener 112 (e.g., a protrusion or indention) are preferably introduced to enhance the adhesiveness of the molding compound or encapsulant material (i.e., mold/glob top 120) to the surface of stiffener 112 by increasing the total contact surface area. First and second dimple designs 202 and 204 may have any applicable dimensions. Design 3 - Fully Populated Package with Two Stiffeners and Symmetrical Segment Grounding FIG. 3 shows a BGA package 300, according to an embodiment of the present invention. As shown in FIG. 3, BGA package 300 incorporates first stiffener 112 and a second stiffener 302, each with selective plating, to achieve split grounding. In BGA package 300, die 114 is mounted to the top surface of second stiffener 302. A third wire connection 306 is coupled from a pin on die 114 to bondable plating surface 118 on second stiffener 302. In an example embodiment, bondable plating surface 118 on the top stiffener, second stiffener 302, may be used for digital grounding, and bondable plating surface 118 on the bottom stiffener, first stiffener 112, may be used for analog grounding. A dielectric adhesive layer 304 is incorporated between first and second stiffeners 112 and 302 to ensure separated grounding. Other features of BGA package 300 are similar to the corresponding features in BGA package 200. Design 4 - Fully Populated Package with Two Stiffeners and Asymmetrical Segment Grounding FIG. 4 shows a BGA package 400, according to an embodiment of the present invention. As shown in FIG. 4, BGA package 400 is similar to BGA package 300 shown in FIG. 3, except that split solid grounding is done asymmetrically. In other words, bondable plating surfaces 118 are placed on the respective first and second stiffeners 112 and 302 asymmetrically. Other features of BGA package 400 are similar to the corresponding features in aforementioned designs. Design 5 - Fully Populated Package with Enhanced Routability FIG. 5 shows a BGA package 500, according to an embodiment of the present invention. As shown in FIG. 5, a substrate 502 of BGA package 500 incorporates two conductive layers, first metal layer 106 and second metal layer 504, that include traces. First circuit mask 108 is formed over the top surface of substrate 502, and a second circuit mask 506 is formed over the bottom surface of substrate 502. First and second metal layer 106 and 504 are separated by dielectric layer 102, which is preferably a polyimide tape. Dielectric layer 102 includes selective conductive vias 508 between first and second metal layers 106 and 504. By selectively connecting the metal layers through conductive vias 508, enhanced routing flexibility as well as enhanced electrical and thermal performance is provided. Other features of BGA package 500 are similar to the corresponding features in aforementioned designs. Design 6 - Fully Populated Package with Enhanced Routability FIG. 6 shows a BGA package 600, according to an embodiment of the present invention. As shown in FIG. 6, BGA package 600 is similar to BGA package 500 shown in FIG. 5 except that BGA package 600 includes a substrate 616 that has four conductive trace layers: a first metal layer 602, a second metal layer 604, a third metal layer 606, and a fourth metal layer 608. The metal layers are separated by dielectric layers with conductive vias. A first dielectric layer 610 separates first metal layer 602 and second metal layer 604. A second dielectric layer 612 separates second metal layer 605 and third metal layer 606. A third dielectric layer 614 separates third metal layer 606 and fourth metal layer 608. For example, second dielectric layer 612 may be a prepeg organic material. Solder balls 122 are attached to portions of fourth metal layer 608 exposed through second circuit mask 506. As such, BGA package 600 provides superior routing flexibility to BGA package 500, and offers excellent electrical and thermal performance. Note that more conductive layers may be used. In that case, however, both the manufacturing cost and the package size (thickness) would increase accordingly. Other features of BGA package 600 are similar to the corresponding features in aforementioned designs. Design 7 - Fully Populated Package with Enhanced Signal Integrity FIG. 7 shows a BGA package 700, according to an embodiment of the present invention. As shown in FIG. 7, BGA package 700 uses conductive paths 702 to connect and ground selected solder balls 122 to stiffener 112. As such, BGA package 700 provides enhanced noise reduction, thus improved signal integrity, by grounding the discharge current through the ground bond (i.e., wire connection 124), stiffener 112, conductive paths 702, and solder balls 122, and discharge to a connecting motherboard (not shown). Other features of BGA package 700 are similar to the corresponding features in aforementioned designs. Design 8 - Fully Populated Package with Enhanced Signal Integrity and Routability FIG. 8 shows a BGA package 800, according to an embodiment of the present invention. As shown in FIG. 8, BGA package 800 is basically a combination of BGA package 500 shown in FIG. 5 and BGA package 700 shown in FIG. 7, providing enhanced routing flexibility and signal integrity. In other words, BGA package 800 is BGA package 700 with two conductive layers, first and second metal layers 106 and 504, instead of a single metal layer. Other features of BGA package 800 are similar to the corresponding features in aforementioned designs. Design 9 - Partially Depopulated Package with Partially Exposed Stiffener FIG. 9 shows a BGA package 900, according to an embodiment of the present invention. As shown in FIG. 9, substrate 130 of BGA package 900 has a "punched" opening or window that exposes a part of stiffener 112, shown as exposed stiffener portion 902. BGA package 900 improves thermal performance because heat may be readily dissipated via exposed stiffener portion 902 of stiffener 112. In addition, plating trace routability is also enhanced through the debussing window punched opening. It should be readily apparent to those of ordinary skill in the art that the size of the opening may vary depending on, for example, the desired size of an optional heat slug to be attached to stiffener 112 via the opening (as described in embodiments in the sections below related to Designs 11-14). Other features of BGA package 900 are similar to the corresponding features in aforementioned designs. Design 10 - Partially Depopulated Package with Partially Exposed Stiffener FIG. 10 shows a BGA package 1000, according to an embodiment of the present invention. As shown in FIG. 10, BGA package 1000 is similar to BGA package 900 shown in FIG. 9, except that BGA package includes substrate 502, which has two patterned conductive layers (first and second metal layers 106 and 504), instead of one metal layer, for enhanced routing flexibility. Substrate 502 has a punched opening or window, similar to that shown in substrate 130 in FIG. 9. Other features of BGA package 1000 are similar to the corresponding features in aforementioned designs. Design 11 - Partially Depopulated Package with Drop-In Heat Slug FIG. 11 shows a BGA package 1100, according to an embodiment of the present invention. As shown in FIG. 11 , BGA package 1100 is similar to BGA package 900 shown in FIG. 9, but with an additional drop-in heat slug 1102 attached to the bottom surface of stiffener 112 by adhesive 1104. Adhesive 1104 is a conductive adhesive, epoxy, or solder. Heat slug 1102 allows direct conductive heat dissipation from die 114 through die attach epoxy 116, stiffener 112, adhesive 1104, and heat slug 1102 to an attached motherboard (not shown). Other features of BGA package 1100 are similar to the corresponding features in aforementioned designs. Design 12 - Partially Depopulated Package with Drop-In Heat Slug FIG. 12 shows a BGA package 1200, according to an embodiment of the present invention. As shown in FIG. 12, BGA package 1200 is similar to BGA package 1000 shown in FIG. 10, but with the addition of drop-in heat slug 1102. Heat slug 1102 allows direct conductive heat dissipation from the die 114 through die attach epoxy 116, stiffener 112, adhesive 1104, and heat slug 1102 to an attached motherboard (not shown). Other features of BGA package 1200 are similar to the corresponding features in aforementioned designs. Design 13 - Partially Depopulated Package with Drop-In Heat Slug FIG. 13 shows a BGA package 1300, according to an embodiment of the present invention. As shown in FIG. 13, BGA package 1300 is similar to BGA package 1100 shown in FIG. 11. The difference is that BGA package 1300 has an added locking mechanism for attaching drop-in heat slug 1102 to stiffener 112. The locking mechanism includes a bump 1302 on heat slug 1102 that fits into a slot 1304 in stiffener 112. The locking mechanism allows easy attachment and alignment of heat slug 1102 to stiffener 112. An adhesive 1306 is used to adhere bump 1302 in slot 1304. Adhesive 1306 may be a conductive adhesive, epoxy, or solder. Other features of BGA package 1300 are similar to the corresponding features in aforementioned designs. Design 14 - Partially Depopulated Package with Drop-In Heat Slug FIG. 14 shows a BGA package 1400, according to an embodiment of the present invention. As shown in FIG. 14, BGA package 1400 is similar to BGA package 1300 shown in FIG. 13, except it includes a substrate 502 that has two conductive layers (first and second metal layers 106 and 504) instead of a single conductive layer. Other features of BGA package 1400 are similar to the corresponding features in aforementioned designs. Design 15 - Partially Depopulated Package with Partially Exposed Down-Set Stiffener FIG. 15 shows a BGA package 1500, according to an embodiment of the present invention. As shown in FIG. 15, BGA package 1500 has a stiffener 112 with a lowered and exposed stiffener portion 1502. This "down-set" stiffener portion 1502 provides for a thinner package design. For example, as shown in FIG. 15, die 114 can sit lower in BGA package 1500 than in other BGA packages. The exposed stiffener 112 also enhances thermal performance similar to BGA package 900 shown in FIG. 9. Other features of BGA package 1500 are similar to the corresponding features in aforementioned designs. Design 16 - Partially Depopulated Package with Partially Exposed Down-Set Stiffener FIG. 16 shows a BGA package 1600, according to an embodiment of the present invention. As shown in FIG. 16, BGA package 1600 is similar to BGA package 1500 shown in FIG. 15, except that substrate 502 in BGA package 1500 includes two conductive layers (first and second metal layers 106 and 504) instead of a single conductive layer. Other features of BGA package 1600 are similar to the corresponding features in aforementioned designs. Design 17 - Partially Depopulated Package with a One-Piece Stiffener/Die Paddle/Heat Slug FIG. 17 shows a BGA package 1700, according to an embodiment of the present invention. As shown in FIG. 17, BGA package 1700 incorporates a one- piece stiffener/die paddle/heat slug 1702 such that die 114 sits directly on top of stiffener/die paddle/heat slug 1702. BGA package 1700 provides excellent thermal performance, as heat directly dissipates from die 114 through die attach epoxy 116 and stiffener/die paddle/heat slug 1702 to an attached motherboard (not shown). Other features of BGA package 1700 are similar to the corresponding features in aforementioned designs. Design 18 - Partially Depopulated Package with a One-Piece Stiffener/Die Paddle/Heat Slug FIG. 18 shows a BGA package 1800, according to an embodiment of the present invention. As shown in FIG. 18, BGA package 1800 is similar to BGA package 1700 shown in FIG. 17, except that substrate 502 of BGA package 1800 includes two conductive layers (first and second metal layers 106 and 504) instead of a single conductive layer. Other features of BGA package 1800 are similar to the corresponding features in aforementioned designs. Note that all of the above designs may be manufactured in wafer saw format for maximized material utilization. Refer to Table 2 below, which provides a brief overview of the above described embodiments/designs. Table 2 Conclusion Although the invention herein has been described with reference to particular embodiments, it is to be understood that the embodiments are merely illustrative of the principles and application of the present invention. It is therefore to be understood that various modifications may be made to the above mentioned embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention. For example, Design 5 could be modified to incorporate two stiffeners to achieve split grounding. In fact any of the above mentioned designs may be combined with any other design or designs to produce a new package.

Claims: What Is Claimed Is: 1. A ball grid array (BGA) package, comprising: a substrate; a stiffener that has a surface attached to a first surface of said substrate; and a plurality of solder balls attached to a second surface of said substrate'. 2. The package of claim 1 , wherein at least a portion of a second surface of said stiffener is patterned. 3. The package of claim 1, further comprising: a second stiffener coupled to a second surface of said first stiffener. 4. The package of claim 3, further comprising: an adhesive dielectric layer coupled between said first stiffener and said second stiffener. 5. The package of claim 1, wherein said substrate includes at least one metal layer. 6. The package of claim 1, wherein said substrate includes at least one conductive via coupling at least one of said plurality of solder balls to said surface of said stiffener. 7. The package of claim 1, wherein said substrate has an opening through said second surface of said substrate, wherein a portion of said surface of said stiffener is exposed through said opening. 8. The package of claim 7, wherein said exposed portion of said surface of said stiffener includes a down-set portion. 9. The package of claim 7, further comprising: a heat slug coupled to said exposed portion of said surface of said stiffener. 10. The package of claim 9, wherein said heat slug includes a surface bump, wherein said exposed portion of said surface of said stiffener includes a surface slot, wherein said surface bump and said surface slot form a locking mechanism. 11. The package of claim 1 , wherein said substrate has a first opening through said second surface of said substrate, wherein said stiffener has a second opening though said surface of said stiffener, the package further comprising: a heat slug that resides at least partially in said first and said second openings, wherein a surface of said heat slug is exposed through a second surface of said stiffener. 12. The package of claim 11, further comprising: a semiconductor die mounted to said exposed surface of said heat slug. 13. The package of claim 1 , further comprising: a semiconductor die mounted to a second surface of said stiffener.

Inventors: KHAN REZA-UR RAHMAN, LAW EDWARD, PAPAGEORGE MARC, ZHAO SAM ZIQUN, KHAN, REZA-UR, RAHMAN, LAW, EDWARD, PAPAGEORGE, MARC, ZHAO, SAM, ZIQUN
Applicants: BROADCOM CORP, BROADCOM CORPORATION
Application year: 2001
Main classification: H01L23
IPC codes: H01L23