Title of Invention: Compliant contact integrator
Abstract: A contact integrator for supporting a die in a semiconductor package and for providing an electrical pathway from the semiconductor package to one or more bonding pads on the die is provided. The contact integrator includes a substrate that has one or more conductor trace for interconnection to the semiconductor package. A Z-elastomer member is disposed on the substrate. An insulating member is disposed on the Z-elastomer member. One or more conductor rods are coupled to the insulating member. Each of the conductor rods has a first end adapted to contact one of the bonding pads and a second end adapted to contact the Z-elastomer member. The conductor rods are respectively substantially vertically aligned with the bonding pads and the conductor traces, and are capable of longitudinal movement relative to the insulating member.
Detailed Description: Part PAC: DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS
Part PAR: Referring now to the figures, and particularly to FIGS. 1-3, there is shown an exemplary embodiment of a compliant contact integrator 10 that is adapted to facilitate placement and electrical connection of a bare die 12 in a semiconductor package (shown in FIGS. 4-6 and discussed below). The compliant contact integrator 10 includes a relatively rigid insulating substrate 14, a selectively conducting Z-elastomer member 16, and a sheet of insulating material 18 assembled into a stack suitable for placement in a semiconductor package as discussed below. The die 12 is supported above the insulating sheet 18 by a plurality of vertically disposed cylindrical contact rods 20. Note that the die 12 has a number of conducting regions or bonding pads 21 (shown in phantom in FIGS. 1-2) spaced about the perimeter of the die 12. The contact rods 20 are respectively disposed in a corresponding plurality of holes or vias 22 extending vertically through the insulating sheet 18. As shown in FIG. 3, which is a cross-sectional view of FIG. 1 taken at section line 3--3, the contact rods 20 are aligned to contact the bonding pads 21 and the Z-elastomer member 16.
Part PAR_2: The substrate 14 has a size and peripheral outline that generally correspond to the peripheral outline of the semiconductor die 12, though with a proportionately larger upper surface area than the die 12, to provide for electrical interconnection with a semiconductor package as discussed more below. The substrate 14 is advantageously formed of a material that has a coefficient of thermal expansion (CTE) that approximates the CTE of the silicon die 12. In this embodiment, materials for the substrate 14 may include silicon, silicon-on-sapphire, silicon-on-glass, germanium and ceramic materials. Glass-filled plastics, e.g. (FR-4) and metals may also be used to form the substrate 14. The substrate 14 may be about 4 to 30 mils thick and is advantageously about 28.5 mils thick.
Part PAR_3: The substrate 14 includes a centrally located passage 24. There are similarly located and sized passages 26 and 28, respectively, in the Z-elastomer member 16 and the insulating sheet 18. When the substrate 14, the Z-elastomer member 16, and the insulating sheet 18 are assembled into a stack as shown in FIGS. 1 and 3, the passages 24, 26 and 28 are aligned to form a conduit. A vacuum source (not shown) may then be attached to the lower end of the passage 24 to urge the die 12 to seat snugly against the conductor rods 20 and the insulating sheet 18 during assembly.
Part PAR_4: To provide an electrical pathway from the conductor rods 20, one or more conductor members or traces 30 are formed on the upper surface of the substrate 14. The conductor traces 30 are composed of a conductive metal such as aluminum, copper, nickel or alloys thereof. The conductor traces 30 may be formed from a metal layer that is deposited on the substrate 14 and then patterned. For example, the conductor traces 30 may be electroplated to the substrate 14 through a mask. Alternatively, the conductor traces 30 may be created by laminating a metal layer to the substrate 14 by molding or other process, followed by a wet or a dry etch of the metal laminate to form the conductor traces 30. Thin film formation may also be used to form the conductor traces 30 using deposition techniques such as chemical vapor deposition, followed by photolithography and etching. As noted above, the area of the upper surface of the substrate 14 is proportionately larger than the die 12 so that when the compliant contact integrator 10 is assembled, a sufficient amount of the conductor traces 30 proximate the ends of the substrate 14 are exposed to facilitate subsequent interconnection with bonding wires or other such connections when the compliant contact integrator 10 is placed in a semiconductor package.
Part PAR_5: The Z-elastomer member 16 is placed on top of the substrate 14. The Z-elastomer member 16 has a size and peripheral outline that generally correspond to the peripheral outline of the semiconductor die 12. Although the inherent tackiness of the Z-elastomer member 16 will generally hold the Z-elastomer member 16 in place, a Z-axis adhesive may also be used, such as Scotch 9703 double-sided tape, or an epoxy matrix with conducting particles supplied by Zymet, Inc. of East Hannover, N.J. The Z-elastomer member 16 may be about 4 to 20 mils thick and is advantageously about 10 mils thick.
Part PAR_6: The Z-elastomer member 16 provides a selectively conducting path between the conductor rods 20 and the conductor traces 30. It also provides a degree of compliance to reduce the stresses imparted on the die 12 by the conductor rods 20. To provide such a conducting path between the conductor rods 20 and the conductor traces 30 on the substrate 14, the Z-elastomer member 16 is advantageously composed of a Z-axis anisotropically conductive elastomeric material (otherwise known as a Z-elastomer). A Z-elastomer is selectively conductive along the Z-axis. The selectively conductive character is achieved by impregnating an elastomer matrix with a plurality of tiny conducting particles, such as gold coated polymer, glass, or nickel spheres. When the Z-elastomeric material is in an uncompressed state, the conducting particles are dispersed within the elastomeric material such that the Z-elastomer behaves like an insulating material. However, when a compressive force is applied to the Z-elastomeric material at a given point along a Z-axis, the dispersion of the conducting particles at that point will decrease, thereby forming a path of conductive material through which current may flow at that point along a Z-axis. However, the Z-elastomer retains dielectric properties along the X and Y axes. Exemplary Z-elastomers are manufactured by A.I. Technology, Inc., AT&T Corp. and Zebra Strip Corp.
Part PAR_7: As shown in FIGS. 1 and 3, the Z-elastomer member 16 is disposed on top of the substrate 14 so that a portion of each conductor trace 30 is in physical contact with the Z-elastomer member 16. When the compliant contact integrator 10 is assembled, and a vacuum is applied to the passages 24, 26, and 28, the die 12 is urged downward toward the substrate 14. As the die 12 moves downward, it contacts and moves the conductor rods 20 downward through the vias 22 until the lower ends of the conductor rods 20 depress into the Z-elastomer member 16. At the point where each conducting rod 20 depresses into the Z-elastomer member 16, a conducting path along the Z-axis is established through the Z-elastomer member 16. Since the conductor rods 20 are spatially aligned with their respective conductor traces 30, a conductive path is established from the bond pads 21 to each respective conductor trace 30.
Part PAR_8: The insulating sheet 18 is placed over the Z-elastomer member 16 and held in place by the inherent tackiness of the Z-elastomer member 16, or alternatively, by an adhesive, such as an epoxy, that may be applied between the Z-elastomer member 16 and the insulating sheet 18. The insulating sheet 18 functions to isolate the die 12 electrically from the Z-elastomer member 16 and to provide an alignment structure for placement of the conductor rods 20. The insulating sheet 18 is advantageously composed of a relatively rigid dielectric material, such as aluminum oxide. Other advantageous materials include chemical etchable glass, such as Foturan.RTM. by Schott Glass Technology of Duryea, Pa. The insulating sheet 18 may be about 5 to 45 mils thick and is advantageously about 10 mils thick.
Part PAR_9: The vias 22 in the insulating sheet 18 are formed in vertical alignment with the bonding pads 21 of the die 12. Each via 22 is provided with an elastomeric bushing 32 retains one of the conductor rods 20 therein and provides additional Z-axis compliance to accommodate for structural variations in the die 12. The elastomeric bushings 32 are advantageously composed of a silicone rubber that vulcanizes, such as Zymet TC-101 and Sumitomo KE1830. The vias 22 may be formed in the insulating sheet 18 by laser ablation, chemical etching, or mechanical punch-out. For example, an excimer laser having a laser fluence in the range of 250-350 mJ may be used to drill the vias 22. The vias 22 are advantageously formed with a diameter that is approximately twice that of the conductor rods 20 in order to accommodate the placement of the elastomeric bushings 32.
Part PAR_10: The conductor rods 20 are advantageously composed of a relatively low ductility conducting metallic material, such as nickel or a nickel alloy. Other materials include tungsten, titanium, chromium or vanadium. The conductor rods 20 are advantageously formed into cylindrical segments by cutting cold drawn wire. The ends of the rods 20 may be lapped flat or rounded by machining. The specific length and diameter of the conductor rods 20 will be a matter of discretion on the part of the designer. However, designers often limit the amount of bonding pad area that may be deformed by a contact member to approximately 40% of the bonding pad area. In this regard, the diameter of an exemplary conductor rod 20 with flat ends may be approximately 1 to 2.5 mils and is advantageously about 2 mils. The diameter of a conductor rod 20 with rounded ends may be approximately 1 to 5 mils and is advantageously about 2 mils. The conductor rods 20 should be longer than the thickness of the insulating sheet 18 so that when the compliant contact integrator 10 is assembled, the lower ends of the conductor rods 20 will depress into the Z-elastomer member 16 without bottoming out in the Z-elastomer member 16. In an exemplary embodiment, the conductor rods 20 should project approximately 2.5 to 5 mils above the insulating sheet 18 and may have a total length of approximately 9.5 to 65.5 mils.
Part PAR_11: The assembly and integration of the compliant contact integrator 10 into a semiconductor package may be understood by reference to FIGS. 1-6. FIG. 4 depicts a plan view of an exemplary semiconductor package 38 following complete integration of the contact integrator 10. FIG. 5 is a cross-sectional view of FIG. 4. FIG. 6 depicts a cross-sectional view of the package 38 prior to complete integration, and with a force distribution mechanism in place. The package 38 may be a test package or a package designed for permanent integration of the die 12. The semiconductor package 38 includes a lid 40, which is shown partially cut away to reveal the details of the interior of the package 38. As is evident from FIGS. 4 and 5, the semiconductor package 38 is adapted to be plugged into a circuit board socket via a plurality of pins 42 emanating from the bottom of the test package 38. An electrical path from the pins 42 is provided via a plurality of leads 44 formed in the body 46 of the package 38. The package body 46 is provided with an internal cavity 48 that is adapted to receive the die 12 and any supporting structure therefore. The package body 46 includes a vacuum passage 50 for facilitating the application of a vacuum to the structure supporting the die 12 within the cavity 48.
Part PAR_12: During the assembly and integration procedure, a suitable insulating adhesive (not shown), such as, for example, double-sided tape, is applied to the bottom of the cavity 48. The substrate 14 is placed on the adhesive. The Z-elastomer member 16 is placed on the substrate 14 so that a portion of each trace 30 that will carry current to or from the die 12 is covered by the Z-elastomer member 16. Next, the elastomeric bushings 32 and conductor rods 20 are installed in the insulating sheet 18, and the insulating sheet 18 is applied to the Z-elastomer member 16. The vias 22 must be carefully aligned with the traces 30 to ensure establishment of proper electrical pathways. This alignment may be accomplished using the optical alignment technique described in U.S. Pat. No. 5,483,174, the whole of which is incorporated herein by reference. The passages 24, 26, and 28 should also be substantially aligned. Following placement of the insulating sheet 18, the die 12 is placed on the conductor rods 20. Alignment of the bond pads 21 of the die 12 may be accomplished by the optical technique discussed above. After the die 12 has been properly aligned, a vacuum source (not shown) is applied to the passages 24, 26, 28, and 50 to seat the die 12. The vacuum should seat the die 12 sufficiently so that the entire assembly may be handled without the die 12 moving out of alignment.
Part PAR_13: FIG. 6 shows the package 38 and the contact integrator 10 following application of the vacuum but prior to complete integration. Following application of the vacuum source, a force distribution mechanism is applied to the package 38 to temporarily hold the contact integrator 10 in place, pending installation of the more permanent lid 40. In this embodiment, the force distribution mechanism consists of a temporary lid 52, a foam layer 54 to gently engage the die 12, and two C-clips 56 to hold the temporary lid 52 in place. Other conventional force distribution mechanisms may also be used.
Part PAR_14: To complete the integration of the contact integrator 10, the force distribution mechanism is removed and electrical connections between the contact integrator 10 and the leads 44 of the package 38 are established via a plurality of bonding wires 58. The bonding wires 58 are coupled between each trace 30 and a corresponding trace 60 that is coupled to the package body 46 and in ohmic contact with the leads 44. After the contact integrator 10 is disposed in the package 38, the lid 40 may be placed on the top of the package to enclose the cavity 48. The lid 40 may be temporarily attached to the package body 46 in the case of a testing mode, or the lid 40 may be permanently fixed to the test body 46 in the case of a permanent integration.
Part PAR_15: An alternate embodiment of a compliant contact integrator 10' is depicted in FIGS. 7 and 8, which show respectively, a pictorial of the compliant contact integrator 10' and a cross-sectional view of FIG. 7 taken at section 8--8. To the extent the same or similar elements from the previously described embodiment are used in this embodiment, like reference numerals will be used. This alternative embodiment of the compliant contact integrator 10' includes the relatively rigid dielectric substrate 14, the conductor rods 20, and the conductor traces 30 depicted in FIGS. 1-3. However, in this alternate embodiment, the insulating sheet 18 depicted in FIGS. 1-3 is eliminated from the final structure as shown in FIGS. 4 and 5. To afford the positional stability and vertical alignment that would ordinarily be facilitated by the placement of the insulating sheet 18, the conductor rods 20 are bonded to the Z-elastomer member 16a during the curing process. The Z-elastomer member 16a is composed of a two-stage Z-elastomer material that is deposited on the substrate 14 and exposed to a two-stage curing process. In the initial stage of the two-stage cure, a liquid phase Z-elastomer material is subjected to a low temperature cure of about 50 to 60.degree. C. The rods 20 are then depressed into the Z-elastomer member 16a, and a higher temperature second curing stage of between about 130 and 500.degree. C. is applied to set the Z-elastomer and bond the lower ends of the conductor rods 20 to the Z-elastomer member 16a. When the conductor rods 20 are depressed into the upper surface of the Z-elastomer member 16a subsequent to the first curing stage, dimples 64 will typically form in the upper surface of the Z-elastomer member 16a. The dimples 64 will typically survive the higher temperature curing process.
Part PAR_16: The Z-elastomer member 16a may be about 2 to 30 mils thick and is advantageously about 10 mils thick. Exemplary two-stage Z-elastomers are available from A.I. Technology, of Princeton N.J.
Part PAR_17: During the formation of the compliant contact integrator 10', an insulating sheet 18 of the type depicted in FIGS. 1-3, though without elastomeric bushings 32, is temporarily placed on the upper surface of the Z-elastomer member 16a subsequent to the initial curing step. The insulating sheet (not shown) provides the initial vertical and spatial alignment of the conductor rods 20. Subsequent to the higher temperature curing step, the insulating sheet (not shown) is removed, leaving the configuration shown in FIGS. 7 and 8. Although the term insulating sheet is used to describe the member used to provide the initial vertical and spatial alignment of the conductor rods 20 in this alternative embodiment, the skilled artisan will appreciate that the transient nature of the insulating sheet suggests that the types of materials used to form the insulating sheet spacer are not limited to dielectrics. Indeed, the insulating sheet may be formed from a conducting material, such as stainless steel. It is envisioned that the insulating sheet may be repeatedly used. Consequently, it is advantageous that the material used to form the insulating sheet have a low enough ductility such that the holes through which the conductor rods 20 are placed are not subject to rapid wear which might degrade the dimensional tolerances of the holes.
Part PAR_18: The skilled artisan will appreciate that the conductor rods 20 in the compliant contact integrator 10' provide the sole support of a die 12 placed thereon. Consequently, in this embodiment, the compliant contact integrator 10' uses a minimum of three conductor rods 20 spaced apart in a triangular arrangement. The number of conductor rods 20 will generally be a matter of discretion on the part of the designer.
Part PAR_19: In the assembly procedure for the compliant contact integrator 10', the substrate is placed in the cavity 48 of the package 38 shown in FIGS. 4-6, and the Z-elastomer member 16a is disposed on the substrate 14 using the aforementioned staged curing process. The remainder of the integration process is carried as described above.
Part PAR_20: An alternate embodiment of the compliant contact integrator 10" is depicted in FIG. 9. To the extent the same or similar elements from the previously described embodiment are used in this embodiment, like reference numerals will be used. The compliant contact integrator 10" includes a relatively rigid dielectric substrate 14, an insulating sheet 18, conductor rods 20, and elastomeric bushings 32 of the types described above. However, in this alternative embodiment, the Z-elastomer member 16 and the conductor traces 30 depicted in FIGS. 1-3 are replaced with a layer of insulating elastomer 66 disposed on the substrate 14, a layer of polymeric material 68 disposed on the insulating elastomer layer 66, and one or more metallic conductor traces 30a formed on the upper surface of the polymeric layer 68. The conducting path from the die 12 passes through the conductor rods 20 to the conductor traces 30a.
Part PAR_21: The insulating elastomer layer 66 is composed of a silicone or like elastomer, such as polyimide siloxane manufactured by Dow Chemical Co. or Rogers Corporation. To provide a conducting path to the conductor rods 20, the conductor traces 30a may be formed on the polymeric layer 68, as shown in FIG. 9, or directly on the upper surface of the insulating elastomer layer 66 without an intervening polymeric layer 68. In the former situation, the polymeric layer 68 is advantageously formed from polyimide or similar material that is usually in the form of a tape that may be attached to the insulating elastomer layer 66 with an adhesive, such as an epoxy. The conductor traces 30a may be formed on polymeric layer 68 using techniques described above in conjunction with the discussion of conventional bare die integration schemes.
Part PAR_22: The compliant contact integrator 10" is assembled using the same procedure described with regard to the embodiment depicted in FIGS. 1-3. When the compliant contact integrator 10" is assembled, the lower ends of the conductor rods 20 deform the conductor traces 30a as shown in FIG. 9. Compliant contact between the die 12 and the conductor rods 20 is provided by the insulating elastomer layer 66 and by the elastomeric bushings 32.
Part PAR_23: Although particular detailed embodiments have been described herein, it should be understood that the invention is not restricted to the details of the disclosed embodiments and that changes in design, configuration, and dimensions may be possible without departing from the spirit and scope of the invention as defined by the appended claims.


{'bibliographic_information': "{'Patent Number': '058937650', 'Series Code': '8', 'Application Number': '7910398', 'Application Type': '1', 'Art unit': '283', 'Application Filing Date': '19970129', 'Title of Invention': 'Compliant contact integrator', 'Issue Date': '19990413', 'Number of Claims': '29', 'Exemplary Claim Number(s)': '1', 'Assistant Examiner': 'Davis; Katrina', 'Primary Examiner': 'Abrams; Neil', 'Number of Drawing Sheets': '5', 'Number of figures': '9'}", 'source_file': './grant/1999/pftaps19990413_wk15.txt', 'source_data': 'USPTO-Grant'}