Semiconductor device manufacturing: process – Including control responsive to sensed condition – Electrical characteristic sensed
Reexamination Certificate
1999-05-04
2001-05-29
Niebling, John F. (Department: 2822)
Semiconductor device manufacturing: process
Including control responsive to sensed condition
Electrical characteristic sensed
C438S015000, C438S106000
Reexamination Certificate
active
06238938
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to mounting and connection devices and techniques for use with microelectronic elements such as semiconductor chips.
BACKGROUND OF THE INVENTION
Complex microelectronic devices such as modern semiconductor chips require numerous connections to other electronic components. For example, a complex processor chip may require hundreds of connections to external devices.
Typically, microelectronic components such as chips are mounted on substrates such as circuit panels having electrical contacts, and the contacts on the chip are electrically connected to the contacts of the substrate. The substrate may be a circuit panel with internal circuitry connected to the contacts. The substrate may be adapted to accommodate other components, including additional chips. Also, the substrate may have pins or other connectors adapted to connect the contacts or internal circuitry of the substrate to a larger assembly, thereby connecting the chip to the larger assembly.
Connections between microelectronic elements and substrates must meet several demanding and often conflicting requirements. They must provide reliable, low-impedance electrical interconnections. They must also withstand stresses caused by thermal effects during manufacturing processes such as soldering. Other thermal effects occur during operation of the device. As the system operates, it evolves heat and the components of the system, including the chip and the substrate expand. When operation ceases, the components cool and contract. When the assembly is heated and cooled during manufacture or in operation, the chip and the substrate expand and contract at different rates, so that portions of the chip and substrate move relative to one another. Also, the chip and the substrate can warp as they are heated and cooled, causing further movement of the chip relative to the substrate. These and other effects cause repeated strain on electrical elements connecting the chip and the substrate. The interconnection system should withstand repeated thermal cycling without breakage of the electrical connections. The interconnection system should provide a compact assembly, and should be suitable for use with components having closely-spaced contacts. Moreover, the interconnection should be economical.
Various solutions have been proposed to meet these needs. In particular, as disclosed in U.S. Pat. Nos. 5,148,265; 5,148,266; 5,455,390 and in International Publication WO 96/02068, flexible leads may be provided between the contacts on a chip or other microelectronic element and the contact pads of a substrate. According to preferred embodiments taught in these documents, a compliant layer, such as an elastomer or a gel may be provided between the chip and the substrate. Flexible leads connecting the chip and substrate may extend through the compliant layer. In these preferred arrangements, the chip is mechanically decoupled from the substrate, so that the chip and substrate can expand and move independently of one another without excessive stress on the electrical connections between the chip contacts and the contact pads of the substrate. Moreover, the assemblies disposed in these patents and publications meet the other requirements discussed above. In certain preferred embodiments according to these documents, the chip and the interconnections to the substrate can occupy an area of the substrate about the same size as the chip itself.
Nonetheless, still further improvement would be desirable. For example, it would be desirable to provide additional connection components and methods which provide effective mechanical decoupling and high resistance to thermally induced stresses, while also providing low cost and high reliability.
SUMMARY OF THE INVENTION
The present invention addresses the foregoing needs.
One aspect of the present invention provides microelectronic assemblies. Assemblies according to this aspect of the invention desirably include first and second microelectronic elements having contacts thereon, and further include a compliant dielectric material having cavities therein. Masses of a conductive material are disposed in the cavities so that the masses of the fusible conductive material are electrically interconnected between contacts on the first microelectronic element and contacts on the second microelectronic element. Thus, each mass forms part or all of a conductor extending between contacts on the two elements. The conductive material may be a liquid or may be a fusible material adapted to liquify at a relatively low temperature, typically below about 125° C. Preferably, the conductive material in each mass is contiguous with the compliant material and is contained by the compliant material, so that the conductive material remains in place when liquid. The compliant layer keeps the liquid masses associated with different sets of contacts separate from one another, and electrically insulates the masses from one another. The elements may have confronting surfaces bearing the contacts, and the compliant material may be in the form of a compliant layer disposed between the confronting surfaces. In this case, the masses of conductive material are also disposed between the confronting surfaces of the elements. Most preferably, the liquid masses are contiguous with contacts of one or both of the microelectronic elements, so that the liquid masses are contiguous with the microelectronic elements and contained by the microelectronic elements in conjunction with the compliant layer.
When the masses of conductive material are liquid, essentially no forces will be transmitted between the elements through the electrical conductors. Stated another way, the electrical conductors have spring constants at or close to zero and do not resist movement of the contacts on the microelectronic elements relative to one another. Preferably, the compliant dielectric layer also allows confronting portions of the microelectronic element surfaces to move relative to one another. Thus, the dielectric layer desirably is formed from a material such as an elastomer, gel, foam or other material having relatively low resistance to deformation. Preferred assemblies according to this aspect of the invention thus allow portions of the contact-bearing surfaces on the microelectronic elements to move relative to one another and thus compensate for movement and distortion. As further discussed below, the compliant connection between the microelectronic elements also helps to compensate for tolerances encountered during manufacturing. The compliant, flexible connection between the microelectronic elements can be provided even where each conductor has substantial cross-sectional area. Thus, low resistance, low impedance conductors can be utilized without impairing the flexible connection.
The conductive material desirably is liquid at temperatures within the range of temperatures encountered during normal operation of the microelectronic elements. Where the conductive material is a fusible material, it may have a melting temperature within or below the range of operating temperatures of the microelectronic elements. The fusible material may be in its solid state or in its liquid state when the assembly is inactive. During operation, the fusible material is wholly or partially liquid, and mechanical stress on the electrical connections is relieved. Moreover, when the fusible material melts, cracks or other defects in the conductive masses are repaired. Alternatively, the conductive material may be a fusible material which melts at temperatures slightly above the range of temperatures encountered during normal operation. In this case, the assembly relieves mechanical stress in the electrical connections, and repairs defects in the connections, when the assembly is exposed to high temperatures during abnormal operating conditions or during processing operations.
The first and second elements may be rigid or flexible. For example, the first element may include one or more semiconductor chips and the second element may
Jones Josetta
Lerner David Littenberg Krumholz & Mentlik LLP
Niebling John F.
Tessera Inc.
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