IC packaging interposer having controlled impedance or optical interconnections and an integral heat spreader

Disclosed are embodiments of an integrated circuit die interconnection interposer suited to controlled high performance transmission of electronic or optical signals or combinations thereof. The various embodiments are designed to provide direct path interconnections away from the surface of one or more integrated circuit die. The structures are amenable to improved thermal management and can be fabricated on at semiconductor wafer.

FIELD OF THE INVENTION

The present invention relates to the field of IC packaging for high speed signal transmission and the thermal management of the energy associated therewith.

BACKGROUND

IC packages serve to space transform the I/O of an IC chip to a pattern and pitch which is more suitable to the needs of a next level interconnection device. The next level device may be another IC package, an electronic module or an interconnection substrate such as a printed circuit board (PCB). IC packages are thus created in a wide variety of different constructions based on the requirements of the application ands the number of input/output (I/O) terminals on the die. The package constructions themselves vary from chip scale and wafer level packages created near or at the size of the IC die, to leadframe type structures, to highly complex multi layer interconnection structures all of which serve to translate the I/O on the chip from a fine pitch to a more useful pitch.

IC package substrate structures, especially those used for high performance applications, are designed with great care in an effort to precisely control the characteristic impedance of the electronic signal from the chip to the next level interconnection device. Due to the complexities of the traditional approach to design, manufacture and assembly, signal quality is often degraded or compromised by the intrinsic frailties and inefficiencies of those same design and interconnection manufacturing technologies employed in the creation of higher performance IC packages. Some relief can be obtained by use of more exotic materials which provide a more acceptable signal quality, however, those gains are achievable only at costs that often exceed in multiples the cost of IC they are packaging. While solutions continue to be developed to solve the electrical problems, optical interconnections will be similarly challenged as optical IC solutions come of age. Moreover, it is anticipated that both electrical and optical solutions will be required on a common IC in the near future.

In general, transmission of high speed signals, whether achieved electrically using metal or other conductive materials or optically using optical fiber, requires that precise control of the structure and materials be maintained at every point along the transmission path, starting at the chip itself, to ensure the quality of the transmitted signal. Any disruptions along the transmission path will degrade signal quality. Thus there is present and future need for improved IC package and interconnection structures and alternative interconnection methods that will meet the needs of both high speed electrical and optical interconnections both separately and together and in doing so meet the performance and cost demands of next generation electronic products.

DETAILED DESCRIPTION

In the following description and in the accompanying drawings, specific terminology and drawings are set forth to provide a thorough understanding of the present invention. In some instances, the terminology or drawings may imply need for specific details that are not required to practice the invention in its fundamental form.

Among signal path constructions, impedance controlled structures such as coaxial connections are considered by electronic signal integrity experts to be ideal. Thus making coaxial connections to I/O on the IC die by extension can also be considered to be an optimal or ideal connection. The present invention is intended to provide a direct, impedance controlled pathway, such as a coaxial connection from the chip to either the body of a package or an interconnection substrate. In addition to providing an electrical path, the structure is well suited to facilitating making optical interconnection to the surface of the chip as well. For electrical signals, the structure allows for impedance control of the signal to begin immediately upon the signal exiting the chip.

Disclosed herein are embodiments of an integrated circuit die interconnection interposer suited to controlled high performance transmission of electronic or optical signals or combinations thereof. The various embodiments are designed to provide direct path interconnections away from the surface of one or more integrated circuit die. The optimal path is orthogonal (i.e. at right angles) to the chip, for shortest path. However, other angles of attachment may be used without departing from the spirit and scope of the present invention.

The structure provides a special translation element that facilitates routing I/O either into a suitably designed package or onto a suitably designed interconnection substrate. In one embodiment, the structure includes a substrate of a suitable material such as a metal (e.g. copper, molybdenum, etc.) or alloy (iconel, invar, etc.) or an insulating material (e.g. ceramic or organic filled or unfilled sheet or laminate) coated with metal. Openings, such as holes, are drilled, etched or otherwise created into the substrate with a pattern that aligns with features of interest on the IC chip to which it is to be interconnected. If an insulating material is used, the structure is plated with metal (e.g. copper). An insulating coating can be applied over the metal to prevent shorting to the conductive material surfaces when the interposer is attached to the chip. The insulation could also be a suitable adhesive pre-applied to the metal before holes are drilled. Moreover, the adhesive may have a thermally conductive material within it to provide an improved thermal path from the surface of the IC die to the metal, which can serve as both ground and thermal spreader.

The openings (e.g., holes) in the interposer substrate serve as conduits for either electrical or optical signals. The body of the structure, being either metal or metallized insulation, can be constructed so as to create a coaxial interconnection path from the surface of one side to the surface of the second side. The coaxial interconnection pathways can be created in several ways. For example, it is possible to fill the holes in the metal or metallized insulator with a suitable dielectric material, drill holes through the center of the fill and then either plating the opening or placing a metal pin in the drilled hole. In another example of method, insulated wires may be placed or fitted into the holes. In yet another example of method, wires may be bonded leaving vertical tails and the metal or metallized interposer substrate having holes in it placed over the matching pattern of vertical wires. In the latter case, a liquid, dielectric may be used to first flood the surface of the die and wires and capillary action employed to fill the holes, followed by a cure step. For optical interconnection application, the wires can be replaced with optical fibers positioned in the chosen openings. Moreover, combinations of the two may be desired and are possible. The body of the interposer can be fully planar but can also be provided with stair steps to facilitate in egress of signals from the interposer to a package or substrate, which has as part of its design, mating stair steps, which are more easily mated and interconnected to in order to make the desired higher performance connectors.

As stated earlier, because the body of the structure can be all metal if desired, it is possible that the interposer could serve as a heat spreader and provide an auxiliary thermal path for heat removal. Moreover, the invention relates to IC interposer structures suited to either high-speed electrical connections, optical connections or a combination thereof in either

InFIG. 1is illustrated an embodiment of an interposer100having stair step interconnections104on a first side with the opposite side having a planar array of coaxial I/O terminals101disposed for subsequent interconnection to I/O terminals on an IC die and further disposed to follow the general contours of a stair stepped IC package to which it is to be joined. The body of the structure can be constructed from all metal or from a suitable insulator plated with metal on the surfaces and through the holes (not shown). The holes are desirably filled with an insulator102to support and space coaxial conductors101away from the hole walls. In fabricating the structure the filled holes may be drilled and filled with metal pins which or other suitably conductive material such as compactable or sinterable metal paste which serve as conductors101. Alternatively the holes may be filled with insulated wires pressed into them. Terminations on the bottom side of the device can be provided with a joining material103(e.g., solder, conductive adhesive or non conductive adhesive). Alternatively the coaxial connections could extend slightly beyond the surface and interconnected to the IC die by means of an anisotropic conductive adhesive.

While both sides of the structure can be fully planar and parallel, the terminations on the side opposite the chip can be made planar, rise above or set below the various plane levels of a mating IC package. In other words, the body of the structure can be provided with stair steps104to facilitate egress of the signals from the package with out using traditional unshielded vias.

In one embodiment, the upper surface of the device is designed to provide selected interconnection circuits on the top side105to facilitate cross-chip interconnections or interconnections to other devices either in stacked form or edge connected such as by wire bonds or other suitable interconnection methods. This can be accomplished by increasing the size of the interposer substrate to support the requirements of the design.

The terminations to the chip can be dual path and exit from a common terminal (e.g. twin axial) if desired and interconnected both through the interposer and off of its surface. In addition, because in certain embodiments, the body of the structure can be all metal, the interposer device can desirably serve also as a heat spreader and provide an auxiliary thermal path for heat removal. Moreover, the body of the device may be extended laterally to increase its surface area for increased heat spreading if desired (not shown). A keying feature can be provided to assure proper alignment of the interposer to the assembly.

InFIG. 2is illustrated the interposer substrate with coaxial connections with an IC die mounted to it in a flip chip fashion200. While only one die is shown, more than one IC die can be mounted to the surface if desired.

The IC die201is provided with a suitable underfill material202to protect the terminations203which are made directly to the end surfaces of the coaxial wires which traverse from a first side to opposite side within and through the body of the interposer. Ground terminations (not shown) may be made to the surface of the interposer at locations positioned between the coaxial contacts on its surface to improve signal integrity if desired.

InFIG. 3is illustrated an interposer assembly embodiment300disposed to make both coaxial electric102and optical interconnections301to one or more IC die. The optical fiber terminations can be made to recede from, stay planar with or protrude from the body of the interposer device302. The protruding fibers can cut square relative to the length302or alternatively can be pre or post processed in a manner suitable for making directional changes to the optical signals by chamfering the fibers303and304at desired angle and rotation thus creating a prism which directs the optical signal to a predetermined path. Alternatively, the receiving substrate can be fitted with prisms to accomplish directional change at the next interconnection level.

FIG. 4illustrates an embodiment suited to accepting multiple stacked chips inside a single assembly400. I/O terminations on the assembly designed for IC die connections can be stepped internally401to accept die of different dimensions. The number and size of stair steps on first and second sides need not be identical. For example, a three die internal stair step stack can be terminated on the side opposite with an equal or lesser number of stair steps down to a single common plane of contacts.

FIG. 5illustrates an embodiment of an inner and outer stair stepped package interposer with IC die assembled within500. Terminations from two or more stacked IC die can exit the package at one common level (501band501c) or at multiple levels as required by the design. The final structure may be considered as an integrated die assembly that may be packaged again at a next level if desired.

FIG. 6illustrates various useful terminations that can be employed for interconnections signal pathways traversing the interposer600. A typical coaxial structure is presented at601. 90 degree offset configurations of twin axial structures are represented by602and603. A tri-axial structure having three leads for use as, for example, power, ground and signals is represented by604. A quad lead triangular structure is illustrated by605and an alternative quad lead structure is represented by606. Although the number of separate conductors captured within an insulating material as shown is limited for purposes of this illustration to four, there are no limits to the number of signal conductors which may be grouped to traverse thorough an insulating interposer structure.

FIG. 7shows a perspective view with a cutaway of a partial structure of an embodiment having surface conductors and passive devices700. The structure700has, for purposes of example, differential pair conductors701which traverse the body and which are surrounded by insulating material702that supports and separates the conductors from the supporting structure. Circuit paths704are provided on the surface of the assembly to provide connections to discrete devices703. The discrete devices can be resistors, capacitors, or voltage switchable materials suitable for providing ESD (electro-static discharge) protection. This embodiment is useful due to the fact that in many integrated circuit designs, it is difficult to implement resistive, inductive or electrostatic protection circuits which meet the precision or specification levels necessary to achieve the desired performance. By removing these elements from the integrated circuit and making them part of the IC die interposer assembly, it is often possible to lower the cost and increase the performance of the overall system. Embodiments having included discrete devices on any face of the interposer thus offer additional value. In the embodiment shown the face of interposer can be milled or etched to create “reliefs” in the surface706creating room for the addition of discrete components703so that the discrete components do not rise higher than the surface of the interposer. The surface of the relief areas and the entire face of the interposer excepting contact termination surfaces can then be coated with a non-conductive material upon which conductive pathways may be placed to provide for connections to the conductors704. The embodiment illustrates, by way of example, pull-up resistors703connected to a differential signal pair701. Pull-up resistors703are connected to coaxial connector707, which has the pull-up power supply source voltage. Connections705provide connections to ground.

Discrete ESD components can also connect to the twin-axial conductors, if desired, to provide integrated circuit ESD protection via their path to ground705. The discrete components are not limited to separately mounted, individual components. Component functions may be constructed by the use of thin films or other deposition processes on the surface of the interposer.

FIG. 8provides surface8A and cross section views of embodiments both pre-assembled,8B and8C, and after assembly,8B′ and8C′, respectively.FIG. 8Ashows a surface view of circuits and interconnections of a die having center bond pads800.FIG. 8Aalso has an area of magnification801that provides detail of interconnection areas of the assembly. In the magnified detail area, the hole in the interposer is filled with insulation material802and the conductor803is centered within it. Connection is made from the center conductor803or circuit terminations on the redistribution circuits804. For illustration purposes, one termination,804a, is shown with the termination bent away to show the termination on the interposer. The circuits from the interposer are routed to distal termination points that are on a courser pitch805. The circuit layer generally resides on an insulating material that may have an adhesive layer.806. Finally,FIG. 8Ahas a section Z-Z that defines an area of cross section viewing forFIGS. 8B and 8B′ and FIGS.8C and8C′

InFIG. 8Bshown in cross section, defined by the Z-Z inFIG. 8A, are shown an IC die807having an insulating/adhesive layer806and bumped contacts808of a suitable material (e.g., solder, conductive adhesive, etc.). Above the chip is shown an assembly comprising a conductive core of the general types described earlier809and having openings with insulating material802through which passes a conductor (e.g. a bond wire)803which is bonded to a circuit trace lead804. The insulating material802can be used to cover all surfaces of the conductive core if desired. Openings can be left in the conductive core as well to allow for electrical connection to it if desired. The circuit traces are bonded to the core with an insulator/adhesive layer806. FIG.8B′ shows the elements ofFIG. 8Bin an assembled embodiment form.

InFIG. 8C, shown in cross section defined by the Z-Z inFIG. 8A, are shown an embodiment of an IC die807having an insulating/adhesive layer806to which bond wires803have been bonded and project up from the surface of the chip. A conductive core of the general types described earlier809and having openings with insulating material802is positioned on the chip and adhered with an insulator/adhesive. The insulating material802can be used to cover all surfaces of the conductive core if desired. Openings can be left in the conductive core as well to allow for electrical connection to it if desired. The conductor wires to pass though the conductive core with the termination ends, distal from the surface of the IC die, exposed and disposed to attachment. Positioned above the just described assembly shown inFIG. 8Cis a circuit layer with circuit traces804on an insulator/adhesive806and having bumped contacts808of a suitable material (e.g., solder, conductive adhesive, etc.) for joining and interconnecting to the exposed conductor contacts of the assembly below it in the figure. FIG.8C′ shows the elements ofFIG. 8Cin an assembled embodiment form.

FIG. 9provides a perspective view of a method for making an embodiment directly on a wafer. In the figure a silicon wafer having a plurality of ICs901and termination bond pads for the ICs902is processed by wire bonding bond wires to the bond pads and terminating the wires at a desired vertical length903, such as by flaming off the wires with an electrical spark. The conductive core structure904with apertures905can then be placed on the wired bonded assembly. The holes can be filled by coating the assembly with a liquid polymer and drawing a vacuum to expel trapped air. Alternatively a thin layer of liquid polymer can be first applied to the wafer assembly and the metal core placed on the assembly relying on capillary action to fill the holes. This of course, can be assisted by vacuum as well. The cured assembly can then be surface lapped to expose the wire bond wire end contacts.

Though not specifically shown inFIG. 9, it should be noted that it is also possible to bond the wires to a substrate having shielding features and then attach the substrate to a prepared wafer in a manner such as shown inFIG. 8C

FIG. 10provides close up perspective view of a wafer level assembly embodiment1000comprising an IC semiconductor wafer1001bonded to a core1003by means of a suitable insulator1002. In the image, while most wire termination ends1004are shown planar with the surface certain wires1005rise vertically from the surface. A discrete core piece1006designed to placed atop the free standing wires is shown. The resulting structure is a stair step structure that is suitable for use and attachment to mating stair step structures. While this approach is possible for wafer level, it is also possible to create a structure that has all terminations at a common level to start and then machine the full assembly to create stair step structures in situ by cutting into the core with wires to different levels.

While the full wafer assembly embodiment described may offer the best economy of scale, the staking method described for the second layer can be employed for the entire structure while still in wafer form by stacking layers of cores of decreasing dimensions which result in a layered stair step interposer.

Although the invention has been described with reference to specific exemplary embodiments thereof, it will be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention. The specification and drawings are, accordingly, to be regarded in an illustrative rather than in a restrictive sense.