Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
1997-12-08
2001-06-12
Young, Lee (Department: 3729)
Metal working
Method of mechanical manufacture
Electrical device making
C029S837000, C029S843000, C029S593000, C228S180220, C228S234100, C228S122100, C228S191000, C324S760020
Reexamination Certificate
active
06243944
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to electromechanical assemblies in which heat is conducted between two components, such as an integrated circuit module and a temperature regulating unit, which are pressed together.
In the prior art, various electromechanical assemblies have been disclosed which maintain an integrated circuit chip at a certain temperature while the chip is operating. For a general background of such assemblies, see U.S. Pat. No. 4,791,983 by E. Nicol and G. Adrian entitled “Self-Aligned Liquid Cooling Assembly”, and U.S. Pat. No. 4,879,629 by J. Tustaniwskyj and K. Halkola entitled “Liquid Cooled Multi-Chip Integrated Circuit Module Incorporating a Seamless Compliant Member for Leakproof Operation”.
In such assemblies, heat flows between an integrated circuit chip and a temperature regulating unit along a thermal conduction path which includes one or more joints. In the case where the components of each joint are rigidly fused together, then the task of taking the joint apart in order to remove a chip is made difficult. On the other hand, in the case where a joint consists of two components that are merely pressed together, then the thermal resistance through the joint is increased.
To reduce the thermal resistance through a pressed joint, thermal greases and metal pastes have been developed. When a layer of these materials is placed in the joint, microscopic air gaps between the joined components are reduced which in turn reduces thermal resistance through the joint. Such greases and pastes are described in U.S. Pat. No. 5,056,706 by T. Dolbar, C. McKay, and R. Nelson which is entitled “Liquid Metal Paste for Thermal and Electrical Connections”.
However, one drawback of a thermal grease is that its thermal conductivity is still relatively low, in comparison to the conductivity of a metal. See U.S. Pat. No. 5,056,706 at column 2, lines 24-29.
Also, another problem with the thermal grease and the metal paste is that they stick to both of the components which are pressed together in the joint. Thus, when those components are subsequently separated in order to remove a chip from the assembly, a residue portion of the grease or paste from the joint stays on both of the separated components.
If the electromechanical assembly is used to test hundreds or thousands of integrated circuit chips which are subsequently put into an end product, any grease or paste which is retained by a chip presents a problem. Specifically, the task of cleaning the residue grease/paste from each chip before the chip is put into an end product adds to the time and cost of producing the end product.
Also in the prior art, a novel pressed joint is disclosed in U.S. Pat. No. 5,323,294 by W. Layton, et al. entitled “Liquid Metal Heat Conducting Member and Integrated Circuit Package Incorporating Same.” In this patent, two components are pressed together with a thin compliant body lying between them which has microscopic voids like a sponge, and a liquid metal alloy is absorbed by the compliant body and partially fills the voids.
However, one drawback of this joint is that it requires the compliant body as a carrier for the liquid metal, and this compliant body is an extra component which adds to the cost of the joint. Also, if the joint is taken apart, a portion of the liquid metal can adhere to the components that were pressing against the compliant body, and that is a residue which must, be cleaned up. Further, the liquid metal in patent '294 will chemically attack aluminum and copper, and those metals often are in the electromechanical assembly. See U.S. Patent 5,658,831 by W. Layton, et al, at column 7, lines 8-42. Thus, extreme care must be used to insure that no residue liquid metal is inadvertently squeezed out of the compliant body and put in contact with any aluminum or copper.
Accordingly, a primary object of the present invention is to provide a novel method of assembling and disassembling a pressed joint with a low thermal resistance that overcomes the above drawbacks of the prior art.
BRIEF SUMMARY OF THE INVENTION
In accordance with the present invention, a novel method of assembling a joint between an integrated circuit module and a temperature regulating unit includes the steps of: 1) providing the integrated circuit module with a contact surface of a first material and providing the temperature regulating unit with a contact surface of a second material; 2) selecting a metal alloy which adheres in a solid state to the second material but not the first material; 3) heating the metal alloy to a slurry/liquid state; and 4) squeezing the slurry/liquid alloy between the contact surfaces.
To maintain the integrated circuit module at a predetermined temperature while it operates, it is important that microscopic air gaps be minimized in the joint between the contact surfaces of the integrated circuit module and the temperature regulated unit. This is achieved by the step of heating the alloy to a slurry/liquid state while the alloy is squeezed in the joint between the contact surfaces of the integrated circuit module and the temperature regulating unit.
Also, it is important that the joint between the integrated circuit module and the temperature regulating unit can be dissassembled, without any residue of a foreign material being transferred from the joint to the integrated circuit module. This is achieved, with the present invention, by the steps of cooling the alloy to a solid state, and then separating the integrated circuit module from the temperature regulating unit with the alloy adhered in the solid state to just the second material on the contact surface of the temperature regulating unit.
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Miller, L., Elongated Flexible Chip Joint, IBM Technical Disclosure, vol. 10, No. 11, p. 1670, Apr. 1968.*
Chip with Lengthened Solder Joints using Shape Memory Alloy, IBM Technical Disclosure, vol. 29, No. 12, p. 5213, May 1987.
Babcock James Wittman
Tustaniwskyj Jerry Ihor
Fassbender Charles J.
Rode Lisa A.
Starr Mark T.
Tugbang A. Dexter
Unisys Corporation
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