# Patent

## Title
Flip chip interconnection with double post

## Abstract

A microelectronic assembly includes a substrate having a first surface, a plurality of first conductive pads exposed thereon, and a plurality of first metal posts. Each metal post defines a base having an outer periphery and is connected to one of the conductive pads. Each metal post extends along a side wall from the base to ends remote from the conductive pad. The assembly further includes a dielectric material layer having a plurality of openings and extending along the first surface of the substrate. The first metal posts project through the openings such that the dielectric material layer contacts at least the outside peripheries thereof. Fusible metal masses contact the ends of some of first metal posts and extend along side walls towards the outer surface of the dielectric material layer. A microelectronic element is carried on the substrate and is electronically can be connected the conductive pads.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This invention is a continuation of U.S. patent application Ser. No. 12/286,102, filed Sep. 26, 2008, which claims the benefit of U.S. Provisional Patent Application No. 60/995,849 filed Sep. 28, 2007, the disclosures of which is hereby incorporated herein by reference.


BACKGROUND OF THE INVENTION
The present invention relates to microelectronic apparatuses and packaging microelectronic components for microelectronic packages and assemblies.
Microelectronic devices generally comprise a thin slab of a semiconductor material, such as silicon or gallium arsenide, commonly called a die or a semiconductor chip. Semiconductor chips are commonly provided as individual, prepackaged units. In some unit designs, the semiconductor chip is mounted to a substrate or chip carrier, which is in turn mounted on a circuit panel, such as a printed circuit board.
In one face of the semiconductor chip is fabricated the active circuitry. To facilitate electrical connection to the active circuitry, the chip is provided with bond pads on the same face. The bond pads are typically placed in a regular array either around the edges of the die or, for many memory devices, in the die center. The bond pads are generally made of a conductive metal, such as gold or aluminum, around 0.5 μm thick. The size of the bond pads will vary with the device type but will typically measure tens to hundreds of microns on a side.
Flip-chip interconnection is a commonly used scheme for conductively connecting bond pads on the semiconductor chip to contact pads on a substrate. In flip-chip interconnection, lumps of metal are typically placed on each bond pad. The die is then inverted so the metal lumps provide both the electrical pathway between the bond pads and the substrate as well as the mechanical attachment of the die to the substrate.
There are many variations of the flip-chip process, but one common configuration is to use solder for the lumps of metal and fusion of the solder as the method of fastening it to the bond pads and the substrate. When it melts the solder flows to form truncated spheres.
Despite the advances that have been made in flip chip interconnections, there is still need for improvements in order to minimize the package thickness, while enhancing joint reliability. These attributes of the present invention are achieved by the construction of the microelectronic packages as described hereinafter.
SUMMARY OF THE INVENTION
According to an embodiment of the invention, there is a packaged microelectronic element that includes a microelectronic element having a front surface and a plurality of first solid metal bumps extending away from the front surface. Each of the posts has a width in a direction of the front surface and a height extending from the front surface, wherein the height is at least half of the width. There is also a substrate that has a top surface and a plurality of second solid metal posts extending from the top surface and joined to the first solid metal posts with a fusible metal. The second posts have top surfaces and edge surfaces extending abruptly away from said top surface of the substrate.
The posts of this embodiment may be etched and comprised essentially of copper. Additionally, underbump metallizations may underly the first bumps. A ratio of a diameter of the first posts to a pitch between the first posts may be no more than 3:4. Furthermore, a diameter of the first posts may be less than one-half of a pitch between each of the first posts.
In another embodiment, a packaged microelectronic element comprises a microelectronic element having a front surface and a plurality of first solid metal posts extending away from the front surface. Each post has a width in a direction of the front surface and a height extending from the front surface, wherein the height is at least half the width. There is also a substrate having a top surface and a plurality of second solid metal posts extending from the top surface and joined to the first solid metal posts. In this embodiment, the first and second posts are diffusion-bonded together.
The ratio of a diameter of the first posts to a pitch between the first posts may be no more than 3:4. The distance between the front surface of the microelectronic element and the top surface of the substrate may be greater than 80 microns. Furthermore, each of the first posts may have a diameter that is equal to a diameter of each of the second metal posts. Finally, an underfill material may be deposited between the front surface of the microelectronic element and the top surface of the substrate.
In still another embodiment, a packaged microelectronic element includes a microelectronic element having a front surface and a plurality of first solid metal posts extending away from the front surface. Each post has a width in a direction of the front surface and a height extending from the front surface. The posts consist essentially of metal other than solder, lead, or tin. There is also a substrate that has a top surface. A plurality of second solid metal posts extend from the top surface and are joined to the first solid metal posts with a fusible metal. A ratio of a diameter of the first or second solid metal posts to a pitch between the plurality of the first or second solid metal posts is no more than 3:4.
In an alternative to this embodiment, the substrate may be a multilayer substrate. Additionally, a diameter of the first posts may be less than one-half of a pitch between each of the first posts. Furthermore, each of said first posts may have a diameter that is equal to a diameter of the second metal posts.
In another embodiment, a packaged microelectronic element includes a microelectronic element having a front surface and a plurality of first solid metal posts extending away from the front surface. Each post has a width in a direction of the front surface and a height extending from the front surface. There is a substrate that has a top surface. A plurality of second solid metal posts extend from the top surface and are joined to the first solid metal posts. A pitch of the first posts ranges between 50 and 200 microns and a distance between the bottom surface of the microelectronic element and the top surface of the substrate is greater than 80 microns.
In an alternative of this embodiment, a fusible metal may be used to join the second posts to the first posts. Each of the first posts may have a diameter that is equal to a diameter of the second metal posts. Furthermore, a diameter of the first posts may be less than one-half of a pitch between each of the first posts.
In another embodiment, a packaged microelectronic element includes a microelectronic element, a substrate, and a plurality of pillars extending between the microelectronic element and the substrate. Each of the plurality of pillars comprise a first metal post portion attached to the microelectronic element, a second metal post portion attached to the substrate, and a metal fusion portion, wherein the first and second metal portions are joined together. The plurality of pillars having a length not less than 50 microns. The height of the first and second metal post portions is at least half of the width.
In an alternative of this embodiment, a distance between the front surface of the microelectronic element and the top surface of the substrate is greater than 80 microns. The substrate may also be a multilayer substrate.
Each of the first posts may have a diameter that is equal to a diameter of the second metal posts. A diameter of the first posts may be less than one-half of a pitch between each of the first posts. Additionally, the first or second posts may be etched.
A method of fabricating a packaged microelectronic element assembly includes providing a microelectronic element having a plurality of conductive posts extending away from a first surface of a microelectronic element. The posts have top surfaces and edge surfaces extending abruptly away from the top surfaces. A fusible metal cap is attached to an end of each of the plurality of conductive posts. Another next step includes at least substantially aligning the posts of the microelectronic element with a plurality of posts extending from a first surface of a substrate. The last step includes joining the posts of the microelectronic element with the posts of the substrate.
In an alternative method, step (c) includes heating the fusible metal to a melting temperature, wherein the fusible metal flows onto exposed portions of the edge surfaces of the posts.
In another alternative method, a passivation layer and an underbump metallization layer are deposited over the microelectronic element.
A further embodiment relates to a microelectronic assembly including a substrate having a first surface, a plurality of first conductive pads exposed on the first surface, and a plurality of first metal posts. Each metal post defines a base having an outer periphery and is connected to a respective one of the first conductive pads. Each metal post extends along a side wall from the base to ends remote from the first conductive pad. The assembly further includes a dielectric material layer having an inner surface, an outer surface, and a plurality of openings. The inner surface extends along the first surface of the substrate, the outer surface being remote from the substrate. Respective ones of the first metal posts project through the openings such that the dielectric material layer contacts at least the outside peripheries of the first metal posts. A plurality of fusible metal masses contact the ends of at least some of first metal posts and extend along side walls of the first metal posts towards the outer surface of the dielectric material layer. A microelectronic element is carried on the substrate and is electronically connected to at least some of the first conductive pads.
The microelectronic element can include a first side facing the first surface of the first substrate and can have a plurality of contacts exposed thereon. Further, the contacts can be electrically and mechanically connected to at least some of the first fusible metal masses. Additionally, the first surface of the substrate can include a first region and a second region. At least two fusible metal masses can be located within the first region and at least two of the fusible metal masses can be located within the second region. The plurality of contacts on the microelectronic element can be connected to the fusible metal masses located within the second region such that the microelectronic region overlies the second region. The substrate can further include a plurality of second metal posts extending from the second region of the first surface thereof. In such an instance, the microelectronic element can include a first surface and a plurality of second metal posts extending away from the first surface thereof that can be joined to the second metal posts of the substrate with a fusible metal.
Each of the plurality of openings in the dielectric material layer can define an inside surface that extends along a portion of the sidewall of a respective one of the first metal posts in substantial contact therewith. Further, the side walls of the first posts are substantially straight along a cross-sectional portion thereof and can taper inward from the bases to the ends thereof or be substantially perpendicular to the faces of the conductive pads. Alternatively, each of the first metal posts can include a substantially straight portion extending from the end thereof and a transition portion extending from the outer periphery of the base. In such an arrangement, the transition portion can be substantially arcuate along a cross-sectional profile of the first metal post. At least one of the first conductive posts can include a plating layer forming the end surface and at least a portion of the side wall thereof.
In a further embodiment, a microelectronic assembly, as described above is included in stacked microelectronic assembly along with at least a second microelectronic assembly. The second microelectronic assembly includes a substrate having an outer surface with a plurality of second conductive pads exposed thereon. The plurality of second conductive pads are affixed to respective ones of the plurality of fusible metal masses, thereby electronically connecting the plurality of second conductive pads to respective ones of the first metal posts.



BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A and 1B are sectional views of the components of a microelectronic assembly in accordance with one embodiment.
FIG. 1C is a sectional view illustrating FIGS. 1A and 1B being joined together.
FIG. 2 is a sectional view illustrating a microelectronic assembly in accordance with the embodiment of FIGS. 1A-1C.
FIG. 2A is an exploded sectional view of a portion of FIG. 2.
FIG. 3 is a sectional view illustrating a completed microelectronic assembly in accordance with a variation of the embodiment shown in FIG. 2.
FIG. 4 is a sectional view illustrating a completed microelectronic assembly in accordance with in accordance with a variation of the embodiment shown in FIG. 2.
FIG. 5 is a sectional view illustrating the components of a microelectronic assembly in accordance with another embodiment.
FIG. 6 is a sectional view illustrating components of a microelectronic assembly in accordance with a variation of the embodiment shown in FIG. 5.
FIG. 7 is a sectional view illustrating a completed microelectronic assembly in accordance with one embodiment.
FIG. 8 is a sectional view illustrating a completed microelectronic assembly in accordance with another embodiment.
FIG. 9 is a sectional view illustrating a completed microelectronic assembly in accordance with another embodiment.
FIG. 10 is a sectional view illustrating a completed microelectronic assembly in accordance with another embodiment.
FIG. 11 is a sectional view illustrating a completed microelectronic assembly in accordance with another embodiment.
FIG. 12 is a sectional view illustrating a completed microelectronic assembly in accordance with another embodiment.
FIG. 13 is a sectional view illustrating a completed microelectronic assembly in accordance with another embodiment.



DETAILED DESCRIPTION
Reference is now made to FIGS. 1A-1C, which illustrate cross-sectional views of the components of the packaged microelectronic assembly 100 shown in FIG. 2. As shown, the packaged microelectronic assembly 100 includes a substrate 102, a microelectronic element 104 in a face down or flip chip position, and conductive columns 106 joining the substrate with the microelectronic element. The conductive columns include conductive bumps or posts 108 which protrude above a fact 105 of the substrate 102 that are aligned with conductive bumps or posts 110 protruding above a face 107 of the microelectronic element 104. The conductive columns 106 provide for increased height for chip-on-substrate packaging by increasing the standoff or vertical distance between the microelectronic element 104 and substrate 102, while at the same time allowing for a decrease in the center-to-center horizontal distance or pitch P between conductive columns 106. As will be discussed in further detail below, the ability to increase the distance between the substrate 102 and the microelectronic element 104 may help reduce stress at the conductive columns, may help ease the application of underfill material 112 (see FIG. 2A), and allow for a greater variety of underfills to be used.
With reference to FIG. 1A, the substrate 102 preferably includes a dielectric element 102A. The dielectric element 102A having a top surface 101 and an oppositely facing bottom surface 103. A plurality of conductive traces 109 may extend along the top or bottom surfaces or both. The dielectric element 102A may be rigid or flexible. The dielectric element 102 may be comprised of a polyimide or other polymeric sheet. Although the thickness of the dielectric element 102 may vary, the dielectric element 102A most typically up to 2 millimeters. The substrate 102 may include other conductive elements such as external contacts (not shown) exposed at the bottom surface 103. The bond traces may be created using the methods illustrated in commonly assigned U.S. Published application Ser. No. 11/014,439, the disclosure of which is hereby incorporated by reference herein. In the particular embodiment illustrated, the conductive elements (not shown) are disposed on the top surface 101 of substrate 102. However, in other embodiments, the conductive elements may also extend along the bottom surface 103 of substrate 102; on both the top and bottom surfaces 101, 103 or within the interior of the substrate 102. Thus, as used in this disclosure, a statement that a first feature is disposed “on” a second feature should not be understood as requiring that the first feature lie on a surface of the second feature. Additionally, descriptive words such as “top,” “bottom,” “upper,” and “lower” are used only for illustration purposes.
Solid metal bumps or conductive posts 108 also extend from the top surface 101 of the substrate 102 to form the first portion of the conductive columns 106 (FIGS. 2 and 2A). The conductive posts 108 have top surfaces 111 and edge surfaces 113 extending abruptly away from the top surface of the substrate 102 such that a distinct angle is created where the edge surfaces 113 meet the top surfaces 101 of the substrate 102. For example, in the embodiment shown, an angle greater than 90 degrees is created between the top surfaces 101 of the substrate 102 and the edge surfaces 113 of the conductive posts 108. The angle will differ based upon the shape of the conductive post 108. For example, a cylindrical post may have an angle of 90 degrees between the top surface 101 of the substrate 102 and the conductive post 108. Exemplary processes and posts are described in Provisional Applications Nos. 60/875,730, filed on Dec. 19, 2006, and entitled Chip Capacitor Embedded PWB; 60/964,916, filed on Aug. 15, 2007, and entitled Multilayer Substrate with Interconnection Vias and Method of Manufacturing the Same; 60/964,823 filed on Aug. 15, 2007, and entitled Interconnection Element with Posts Formed by Plating; the disclosures all of which are incorporated herein by reference. For example, the conductive posts 108 may be formed by etching processes, as described in more detail herein. Alternatively, conductive posts 108 may be formed by electroplating, in which posts 108 are formed by plating a metal onto a base metal layer through openings patterned in a dielectric layer such as a photoresist layer.
The dimensions of the conductive posts 108 can vary over a significant range, but most typically the height H1 of each conductive post 108 extending from the top surface 103 of dielectric element 102A is at least 50 microns and can extend up to 300 micrometers. These conductive posts 108 may have a height H1 that is greater than its diameter or width W1. However, the height H1 may also be smaller than the width W1, such as at least half the size of the width W1.
The conductive posts 108 may be made from any electrically conductive material, such as copper, copper alloys, gold and combinations thereof. The conductive posts 108 may include at least an exposed metal layer that is wettable by solder. For example, the posts may be comprised of copper with a layer of gold at the surfaces of the posts. Additionally, the conductive posts 108 may include at least one layer of metal having a melting temperature that is greater than a melting temperature of the solder to which it will be joined. For example, such conductive posts 108 would include a layer of copper or be formed entirely of copper.
The conductive posts 108 may also take on many different shapes, including frustoconical. The base 114 and tip 116 of each of the conductive posts 108 may be substantially circular or have a different sha+pe, e.g. oblong. The bases 114 of the conductive posts 108 typically are about 50-300 μm in diameter, whereas the tips 116 typically are about 25-200 μm in diameter. Each conductive post 108 may have a base 114 adjacent the dielectric substrate 102 and a tip 116 remote from the dielectric substrate. Additionally, the height H1 of the conductive posts from the top surface 101 of the dielectric element 102A (excluding any solder mask) typically ranges from as little as 30 μm up to 200 μm.
As shown, solder mask 118 (FIG. 2) may be disposed over the substrate 102 and adjacent the conductive posts 108. The solder mask 118 helps to prevent solder overflow and bridging between adjacent columns 106 during the reflow phase.
Referring to FIG. 1B, the microelectronic element 104 has a front surface 122 and a rear surface 124. The microelectronic element 104 is preferably a semiconductor chip or the like prior to its packaging and interconnection with another element. For example, the microelectronic element is a bare die.
Exemplary conductive posts and methods of making conductive posts capable of extending from a microelectronic element or the like are described on the website of Advanpak Solutions Pte. Ltd. (“Advanpak”), as well as in U.S. Pat. Nos. 6,681,982; 6,592,109; and 6,578,754 that are assigned to Advanpak, and the disclosures of which are incorporated herein by reference. For example, the conductive posts 110 may be formed by etching processes. Alternatively, conductive posts 110 may be formed by electroplating, in which posts 110 are formed by plating a metal onto a base metal layer through openings patterned in a photoresist layer. Like the conductive posts 108 extending from the substrate, the posts 110 extending from the microelectronic element 104 may have top surfaces 111 and edge surfaces 113 extending abruptly away from said top surface 122 of the microelectronic element such that a distinct angle is created between the microelectronic element and the conductive posts.
To provide a metal contact between the conductive posts 110 and the microelectronic element 104, an underbump metallization layer 120 may be provided on the front surface 122 of the microelectronic element 104. The underbump metallization layer 120, is typically composed of a material including titanium, titanium-tungsten, chromium. The underbump metallization layer 120 operates as the conducting metal contact for the conductive columns 106. A passivation layer 119 may also be provided on the front surface 122 of the microelectronic element 104 between the microelectronic element 104 and the underbump metallization layer 120 using known methods in the art.
Referring to FIGS. 1B, 1C, and 2, the dimensions of the conductive posts 110 extending from the microelectronic element 104 may also vary over a significant range, but most typically the height H2 of each conductive post 110 is not less than 50 microns. The conductive posts 110 may have a height H2 that is greater than its width W2. However, the height may also be smaller than the width W2, such as at least half the size of the width.
The conductive posts 110 are preferably made from copper or copper alloys, but may also include other electrically conductive materials, such as gold or combinations of gold and copper. Additionally, the conductive posts 110 may include at least one layer of metal having a melting temperature that is greater than a melting temperature of the solder to which it will be joined. For example, such conductive posts would include a layer of copper or be formed entirely of copper.
In a particular embodiment, the conductive posts 110 can be cylindrical, so that the diameter of the bases 126 of the post and tips 128 of the posts are substantially equal. In one embodiment, the bases 126 and tips 128 of the conductive posts can be about 30-150 μm in diameter. Each conductive post 110 may have a base 126 adjacent the substrate 102 and a tip 128 remote from the substrate 102. Alternatively, the conductive posts 110 may take on a variety of shapes, such as frustroconical, rectangular, or bar-shaped.
A coating or cap of solder 130 may be attached to the tips 128 of the conductive posts 110 or the portion of the conductive posts that are not attached to the microelectronic element 104. The cap of solder 130 can have the same diameter or width W2 of the conductive posts 110 so that it becomes an extension of the conductive post 110. In one example, the cap of solder 130 can have a height H3 ranging from approximately 25-80 μm.
It should be appreciated that the height H2 of the conductive posts 110 extending from the front surface 122 of the microelectronic element 104 can be equal to the height H1 of the conductive posts 108 extending from the top surface 101 of the dielectric element 102A (FIG. 1A). However, the heights may alternatively differ, such that the height H2 of the conductive posts 110 can be less than or greater than the height H1 of the conductive posts 108. In a particular illustrative example, the conductive posts 110 extending from the microelectronic element 104 may have a height H2 of 50 μm in length, whereas the conductive posts 108 extending from the substrate may have a height H1 of 55 μm (FIG. 2).
To conductively connect the microelectronic element 104 and substrate 102 together, the conductive posts 110 on the microelectronic element 104 must be connected to the conductive posts 108 on the substrate 102. Referring to FIG. 1C, the microelectronic element 104 is inverted so that the conductive posts 110 of the microelectronic element 104 and the conductive posts 108 of the substrate 102 are aligned with one another and brought into close proximity. The cap of solder 130 on the microelectronic element 104 is reflowed to allow the solder to wet the surfaces of the conductive posts 110 on the microelectronic element 104 and the conductive posts 108 on the substrate 102. As shown in FIGS. 2-2A, the solder will wet to the exposed surfaces of the conductive posts and create a conductive column 106 that extends from the microelectronic element to the substrate. The increased surface areas of the conductive columns 108, 110 on the microelectronic element 104 and substrate 102 to which the solder is joined can help reduce the current density at the solder interface. Such decrease in current density may help reduce electromigration and provide for greater durability.
As shown, the conductive columns 106 include solder conductively interconnecting the conductive posts. The standoff or height H of the conductive columns extending between the base of the conductive post extending from the microelectronic element and the exposed portions of the base extending from the substrate in one example ranges 80-100 μm.
As shown in FIGS. 2, 2A, the walls 132 of the conductive columns 106 can be convex or barrel shaped, wherein the midpoint region M of the conductive column (i.e., between the conductive posts 110 of the microelectronic element and conductive posts 108 of the substrate) has a width W that is greater than the widths W1, W2 of the portions of the conductive columns 106 respectively adjacent the top surface 101 of the substrate 102 and front surface 102 of the microelectronic element 104.
As further shown in FIG. 2A, contact pads 117 may be formed on the microelectronic element 104 and substrate 102 using known methods. In one embodiment, the lower post 108 that extends away from the substrate 102, as well as the lower contact pad 117 may be formed by separate etching steps, such as disclosed in International Application PCT No. WO 2008/076428, which published on Jun. 28, 2008 and the disclosure of which is incorporated herein by reference. For example, a tri-metal substrate with top and bottom metal layers 123 and in intermediate etch stop layer or interior metal layer 121 may be utilized to create the conductive post 108 and contact pad 117. In one such process, an exposed metal layer of a three-layer or more layered metal structure is etched in accordance with a photolithographically patterned photoresist layer to form the conductive post 108, the etching process stopping on an interior metal layer 121 of the structure. The interior metal layer 121 includes one or more metals different from that of the top and bottom metal layers 123, the interior metal layer being of such composition that it is not attached by the etchant used to etch the top metal layer 123. For example, the top metal layer 123 from which the conductive posts 108 are etched consists essentially of copper, the bottom metal layer 123 may also consist essentially of copper, and the interior metal layer 121 consists essentially of nickel. Nickel provides good selectivity relative to copper to avoid the nickel layer from being attached with the metal layer is etched to form conductive posts 108. To form the contact pad 117, another etching step may be conducted in accordance with another photolithographically patterned photoresist layer. The post 108 may be further interconnected with other conductive features such as a via 115, which is, in turn, further interconnected to other conductive features (not shown).
Referring to FIG. 3, the walls 232 of the conductive columns 106 may also be straight, such that the width W5 is about equal to the widths W4, W4′ of the conductive columns 106′ respectively adjacent the top surface 101′ of the substrate 102′ and front surface 122′ of the microelectronic element 104′. It should be appreciated that the widths W4, W4′ do not need to be equal. Alternatively, the walls 232 of the conductive columns 106 may be concave (see FIG. 4), depending on the desired standoff to be achieved.
The conductive columns 106 in accordance with the present invention allow for a greater standoff height between the dielectric element and the microelectronic element while permitting a significant reduction in the pitch P (see FIGS. 1B, 2) between each of the conductive posts 110 exposed at the front surface 122 of the microelectronic element 104, as well as the pitch P between each of the conductive posts 108 exposed at the top surface 101 of the substrate 102. In one embodiment, the pitch P may be as small as 50 μm or as large as 200 μm. It should be appreciated that by virtue of the fact that the conductive columns 108, 110 are aligned with one another, the pitch P between each of the conductive posts 108, 110 will be equal.
The pitch P may also be a function of the diameter or width W1, W2 of the conductive posts 108, 110, such that the diameter W1, W2 of the base of the conductive posts is up to 75% of the pitch P. In other words, the ratio of the diameter W1, W2 to the pitch P can be up to 3:4. For example, if the pitch P is 145 μm, the diameter W1, W2 of the conductive posts 108, 110 may range up to 108 μm or 75% of the pitch P.
The increased standoff height reduces the strain on Low-k dielectric materials which can be present in the microelectronic element. Additionally, the increased standoff helps to minimize the problems typically associated with small pitches, such as electromigration and crowding. This is due to the fact that the conductive columns 106 are able to wet the surfaces of the conductive posts 108, 110.
Referring to FIGS. 5-6, alternative arrangements for joining the conductive bumps on the microelectronic element with the conductive bumps on the substrate are shown. With reference to FIG. 5, instead of the solder cap 230 being placed at the tip 228 of the conductive post 210 extending from the microelectronic element 204, the solder cap 230 can be placed at the tip 216 of the conductive post 208 extending from the substrate 202. In one embodiment, the width or diameter W5 of the solder cap 230 is roughly equal to the diameter W6 of the base 214 of the conductive post 208. The solder cap 230 therefore extends beyond the tip 216 of the conductive post 208 extends from the substrate 202. Once the solder is reflowed, however, the conductive column will preferably take the shape of the conductive column shown in FIG. 2.
Referring to FIG. 6, in yet another alternative arrangement, solder caps 330 may be placed onto the conductive posts 310, 308 extending from both the microelectronic element 304 and the substrate 302. The conductive posts 308, 310 are placed in close proximity to one another. Heat is applied causing the solder caps 330 to reflow, wet, and fuse to the conductive posts 308, 310. Once reflowed, the conductive column 306 will preferably be similar to the conductive column 306 shown in FIG. 2.
With reference to FIG. 7, an alternative arrangement for a microelectronic package is shown. The arrangement is similar to the one shown in FIG. 2, the only difference being the absence of a solder mask adjacent the conductive posts extending from the substrate. In this alternative arrangement, vias 307 can be used to conductively connect the conductive columns 406 to electronic circuitry (not shown) exposed at the bottom surface of the substrate 402, as opposed to the top surface 401 of the substrate 402. The use of vias 307 obviates the need for the solder mask.
Referring to FIG. 8, an alternative embodiment is shown, wherein a metal-to-metal bond between the conductive posts is made without the use of solder. Instead, a bond may be formed between the conductive posts 508, 510 by deforming them into engagement with each other. The conductive posts 508, 510 are preferably formed from a malleable material with minimal resilience or spring-back as, for example, substantially pure gold. Furthermore, the conductive posts 508, 510 may be bonded together by eutectic bonding or anodic bonding between the posts and the material of the cover. For example, the tips 516, S17 of the conductive posts 508, 510 may be coated with a small amount of tin, silicon, germanium or other material which forms a relatively low-melting alloy with gold, and the posts may be formed entirely from gold or have a gold coating on their surfaces. When the conductive posts 508, 510 are engaged with one another and then heated, diffusion between the material of conductive posts 508, 510 and the material on the tips 516 of the conductive posts forms an alloy having a melting point lower than the melting points of the individual elements at the interfaces between the posts and walls. With the assembly held at elevated temperature, further diffusion causes the alloying element to diffuse away from the interface, into the bulk of the gold of the posts, thereby raising the melting temperature of the material at the interface and causing the interface to freeze, forming a solid connection between the parts.
Referring to FIG. 9, which is identical to FIG. 8, except that the conductive posts 608, 610 are both preferably comprised of copper and are fused directly to one another without the presence of a low melting temperature metal such as a solder or tin between the conductive posts. Preferably, in order to achieve a strong bond, the joining surfaces of the conductive posts 608, 610 must be clean and substantially free of oxides, e.g., native oxides, before the conductive posts 608, 610 are joined to the terminals. Typically, a process characterized as a surface treatment of etching or micro-etching can be performed to remove surface oxides of noble metals such as copper, nickel, aluminum, and others, the surface etching process being performed without substantially affecting the thicknesses of the bumps or metal layer which underlies them. This cleaning process is best performed only shortly before the actual joining process. Under conditions in which the component parts are maintained after cleaning in a normal humidity environment of between about 30 to 70 percent relative humidity, the cleaning process can usually be performed up to a few hours, e.g., six hours, before the joining process without affecting the strength of the bond to be achieved between the bumps and the capacitor terminals.
As illustrated in FIGS. 10-11, during a process performed to join the conductive posts 608, 610, a spacer structure 726 is placed on the top surface 601 of the substrate 602. The spacer structure 626 can be formed of one or more materials such as polyimide, ceramic or one or more metals such as copper. The microelectronic element 604 from which conductive posts 610 extend are placed above the spacer structure 626, such that the tips 628 of the conductive posts 610 of the microelectronic element 604 overlie the tips 616 of the conductive posts 608 of the substrate 602. Referring to FIG. 10, the spacer structure 626, microelectronic element 604 and substrate 602 are inserted between a pair of plates 640 and heat and pressure are simultaneously applied to the conductive posts in the directions indicated by arrows 636. As illustrated in FIG. 9, the pressure applied to plates 640 has an effect of reducing the height of the conductive posts to a height H6 lower than an original height H5 of the conductive posts 608, 610 as originally fabricated (FIG. 10). An exemplary range of pressure applied to during this step is between about 20 kg/cm2 and about 150 kg/cm2. The joining process is performed at a temperature which ranges between about 140 degrees centigrade and about 500 degrees centigrade, for example.
The joining process compresses the conductive posts 608, 610 to an extent that metal from below the former top surfaces of the conductive posts 608, 610 comes into contact and joins under heat and pressure. As a result of the joining process, the height of the conductive posts 608, 610 may decrease by one micron or more. When the conductive posts 608, 610 consist essentially of copper, the joints between the conductive posts also consist essentially of copper, thus forming continuous copper structures including the bumps and terminals. Thereafter, as illustrated in FIG. 9, the plates and spacer structure are removed, leaving a subassembly 250 having conductive columns 606 formed from the conductive joinder of the conductive posts 608, 610.
Referring to FIG. 12, another alternative embodiment in accordance with the present invention is shown. The only difference here is that instead of a single layer substrate, a multilayer substrate may be used, such as the multilayer substrates described in U.S. Appln. No. 60/964,823, filed on Aug. 15, 2007, and entitled Interconnection Element with Posts Formed by Plating; U.S. Appln. No. 60/964,916 filed Aug. 15, 2007, and entitled Multilayer Substrate With Interconnection Vias and Method of Manufacturing the Same; and U.S. patent application Ser. No. 11/824,484, filed on Jun. 29, 2007, and entitled Multilayer Wiring Element Having Pin Interface, the disclosures of which are incorporated herein. As shown, the multilayer substrate 702 is joined in flip-chip manner with a microelectronic element 704, e.g., a semiconductor chip having active devices, passive devices or both active or passive devices thereon. The tips 716 of the conductive posts 710, which protrude from the top surface 701 of the multilayer substrate, are joined as described herein to conductive posts 710 extending from the microelectronic element. As shown, the conductive posts 708 of the multilayer substrate 702 can be joined directly to the conductive posts 710 extending from the front surface microelectronic element, such as through a diffusion bond formed between a finished metal at the tips 160 of the posts, e.g., gold, and another metal present in the conductive pads and the posts. Alternatively, the conductive posts 708, 710 posts can be joined together through a fusible metal such as a solder, tin or a eutectic composition, the fusible metal wetting the posts and the pads to form wetted or soldered joints. For example, the fusible metal can be provided in form of solder bumps (not shown), exposed at a front surface 722 of the microelectronic element 704, the bumps being provided at the ends of either or both of the tips of the conductive posts.
The conductive columns may also be utilized in stacked packaging, such as those packages described in commonly owned applications U.S. Appln. No. 60/963,209, filed Aug. 3, 2007, and entitled Die Stack Package Fabricated at the Wafer Level with Pad Extensions Applied To Reconstituted Wafer Elements; U.S. Appln. No. 60/964,069, filed Aug. 9, 2007, and entitled Wafer Level Stacked Packages with Individual Chip Selection; U.S. Appln. No. 60/962,200, filed Jul. 27, 2007, and entitled Reconstituted Wafer Stack Packaging with After-Applied Pad Extensions; and U.S. Appln. No. 60/936,617, filed Jun. 20, 2007, and entitled Reconstituted Wafer Level Stacking.
For example, with reference to FIG. 13, in an alternative embodiment, a stacked package assembly includes a first subassembly 800 and a second subassembly 802. The first and second subassemblies are virtually identical to the packaged microelectronic element shown in FIG. 2, except for the fact that the substrates 806, 806′ extend further out to accommodate conductive columns 808 extending between the substrates 806, 806′ of the first and second subassemblies. The conductive columns 808 also include a conductive post 812 extending from the substrate that connects to vias 814 extending through the top and bottom surfaces of the substrate on the second subassembly. As shown in FIG. 13, solder mask layer 818 can extend upwardly along and in contact with edge surface 813 of conductive post 812. This arrangement keeps conductive columns 808 out of contact from substrate 806 in the area around post 812, which as shown in previously-discussed Figures, such as FIG. 2A, can have conductive elements, such as contact pad 117, disposed thereon. Accordingly, the arrangement between solder mask layer 818 and conductive post 812 can further serve to keep conductive column 808 out of contact with a contact pad (or another conductive element such as a trace) that can be formed on substrate 806 and having post 812 affixed thereon.
Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.

## Claims

1. A microelectronic assembly, comprising:
a substrate having a first surface, a plurality of first conductive pads exposed on the first surface and defining a face, and a plurality of first metal posts, each defining a base connected to a respective one of the first conductive pads and having an outer periphery, each of the first metal posts extending along a side wall from the base to an end remote from a respective one of the first conductive pads, wherein the side walls of the first metal posts taper continuously inward from the bases to the ends thereof, and wherein the first metal posts are frustoconical throughout the entirety of first heights thereof;
a plurality of copper spacers surrounding the first metal posts on the outer periphery of the first surface of the substrate;
a solder mask layer, having an inner surface, an outer surface, and a plurality of openings, the inner surface extending along the first surface of the substrate, the outer surface being remote from the substrate, and respective ones of the first metal posts projecting through the openings, the solder mask layer contacting at least the outside peripheries of the first metal posts;
a plurality of fusible metal masses contacting the ends of at least some of first metal posts and extending along the continuously tapered side walls of the first metal posts towards the outer surface of the solder mask layer; and
a microelectronic element carried on the substrate and electronically connected to at least some of the first conductive pads.

2. The microelectronic assembly of claim 1, wherein the microelectronic element includes a first side facing the first surface of the first substrate and having a plurality of contacts exposed thereon, and wherein the contacts are electrically and mechanically connected to at least some of the first fusible metal masses.

3. The microelectronic assembly of claim 1, wherein the first surface of the substrate includes a first region and a second region, at least two of the first metal posts being located within the first region and at least two of the first metal posts being located within the second region, and wherein the microelectronic element includes a plurality of contacts connected to the first metal posts located within the second region such that the microelectronic region overlies the second region, the first metal posts within the first region being available for connection with an external component.

4. The packaged microelectronic assembly of claim 1, wherein the first surface of the substrate includes a first region and a second region, wherein the fusible metal masses are located within the first region, wherein the substrate further includes a plurality of second metal posts extending from the second region of the first surface thereof, and wherein the microelectronic element includes first surface and a plurality of third metal posts extending away from the first surface thereof and joined to the second metal posts of the substrate with a fusible metal.

5. The microelectronic assembly of claim 1, wherein at least one the faces of the first conductive pads defines a first width therealong, wherein a corresponding one of the bases of the first metal posts defines a second width therealong, wherein a corresponding one of the plurality of openings defines a third width thereacross at the outer surface of the solder mask layer, wherein the third width is less than the second width, and wherein the first width is greater than the second width and the third width.

6. The microelectronic assembly of claim 5, wherein each of the at least one first face, the corresponding base and the corresponding opening are substantially circular, and wherein the respective widths thereof are diameters.

7. The microelectronic assembly of claim 1, wherein each of the plurality of openings in the solder mask layer defines an inside surface, and wherein the inside surface extends along a portion of the sidewall of a respective one of the first metal posts in substantial contact therewith.

8. The microelectronic assembly of claim 1, wherein the side walls of the first metal posts are substantially straight along a cross-sectional portion thereof.

9. The microelectronic assembly of claim 8, wherein the side walls of the first metal posts are substantially perpendicular to the faces of the first conductive pads.

10. The microelectronic assembly of claim 1, wherein each of the first metal posts includes a substantially straight portion extending from the end thereof and a transition portion extending from the outer periphery of the base, the transition portion being substantially arcuate along a cross sectional profile of the first metal post.

11. The microelectronic assembly of claim 1, wherein at least one of the first metal posts includes a plating layer forming the end surface and at least a portion of the side wall thereof.

12. A stacked microelectronic assembly comprising:
a first microelectronic assembly according to claim 1,
a second microelectronic assembly including a substrate having an outer surface with a plurality of second conductive pads exposed thereon;
wherein the plurality of second conductive pads are affixed to respective ones of the plurality of fusible metal masses, thereby electronically connecting the plurality of second conductive pads to respective ones of the first metal posts.

13. The microelectronic assembly of claim 1, wherein at least some of the plurality of fusible metal masses further contact the outer surface of the solder mask layer adjacent respective ones of the openings therein.

14. The microelectronic assembly of claim 1, wherein the first metal posts define abrupt transitions from the ends to the side walls thereof.

15. A microelectronic assembly, comprising:
a substrate having a first surface, a plurality of first conductive pads exposed on the first surface and defining a face, and a plurality of first metal posts, each defining a base connected to a respective one of the first conductive pads and having an outer periphery, each of the first metal posts extending along a substantially straight side wall that is continuously tapered from the base to an end of the post remote from a respective one of the first conductive pads, and each of the first metal posts being frustoconical;
a plurality of copper spacers surrounding the first metal posts on the outer periphery of the first surface of the substrate;
a solder mask layer, having an inner surface, an outer surface, and a plurality of openings, the inner surface extending along the first surface of the substrate, the outer surface being remote from the substrate, and respective ones of the first metal posts projecting through the openings, the solder mask layer contacting at least the outside peripheries of the first metal posts;
a plurality of fusible metal masses contacting the ends of at least some of first metal posts and extending along side walls of the first metal posts towards the outer surface of the solder mask layer; and
a microelectronic element carried on the substrate and electronically connected to at least some of the first conductive pads.

16. The microelectronic assembly of claim 15, wherein the first metal posts define abrupt transitions from the ends to the side walls thereof.