Semiconductor device manufacturing: process – Packaging or treatment of packaged semiconductor – Metallic housing or support
Reexamination Certificate
2000-02-04
2001-06-26
Picardat, Kevin M. (Department: 2823)
Semiconductor device manufacturing: process
Packaging or treatment of packaged semiconductor
Metallic housing or support
C438S108000, C438S121000
Reexamination Certificate
active
06251709
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to cooling structures that cool down integrated circuit devices mounted on multichip modules by using heat sinks as well as methods of manufacturing those structures. This application is based on patent application No. Hei 9-174143 filed in Japan, the content of which is incorporated herein by reference.
2. Description of the Related Art
According to the conventional cooling structure of the multichip module, heat-radiation surfaces of devices of LSI (an abbreviation for “Large Scale Integration”) mounted on a board of the multichip module are forced to come in contact with a single heat sink. Thus, it is possible to radiate heat from each of the LSI devices. In some cases, however, the LSI devices differ from each other in standards. Or, even if all of the LSI devices are manufactured in the same standard, the LSI devices differ from each other due to manufacture error, which occurs when they are mounted on the board, or due to a bend of the board and the like. In that case, uniform mount height cannot be secured for all of the LSI devices, whose mount heights may disperse. For this reason, the LSI devices may have different slopes in upper surfaces thereof. The dispersion in mount heights of the LSI devices may frequently reach 0.5 mm or so. The dispersion in mount heights and slopes of the LSI devices may cause dispersion in heat-radiation surfaces and slopes of the LSI devices. So, there exist LSI devices whose heat-radiation surfaces cannot come in contact with the heat sink. As a result, there occurs a problem that those LSI devices cannot radiate heat.
To solve the above problem, a heat-transfer sheet having flexibility is provided in a gap between the heat-radiation surface of the LSI device and a lower surface of the heat sink so as to absorb (or cancel) dispersion in heights and slopes of the heat-radiation surfaces. Such a technique will be called “prior art 1”.
The paper of Japanese Patent Publication No. Sho 62-59887 discloses another technique (called “prior art 2”) that provides bond having good thermal conduction in a gap between the heat-radiation surface of the LSI device and the lower surface of the heat sink so as to absorb dispersion in heights and slopes of the heat-radiation surfaces.
However, the prior arts 1 and 2 have a problem because they cannot be applied to the case where the LSI devices mounted on the multichip module have great heating values.
The aforementioned heat-transfer sheet and thermal conductive bond, used by the prior arts 1 and 2, contain thermal conductive particles such as alumina-filler. In order to achieve heat radiation of the LSI device having a great heating value, a number of the thermal conductive particles is increased to increase thermal conductivity. In that case, however, flexibility could be damaged in the heat-transfer sheet and the thermal conductive bond before hardening, because, the density of the thermal conductive particles is increased. If the flexibility is damaged, it should be necessary to impart excessive stress to the heat-radiation surfaces to absorb dispersion in mount heights of the heat-radiation surfaces. That is, sufficient flexibility should be required for the heat-transfer sheet and the thermal conductive bond before hardening. For this reason, it is difficult to increase the number of the thermal conductive particles. So, there is a limit in thermal conductivity, which corresponds to 1 W/m·K or so. As described above, the heat-transfer sheet and thermal conductive bond of the prior arts 1 and 2 cannot reduce thermal resistance.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a cooling structure that provides improvements in thermal conductivity from heat-radiation surfaces of LSI devices, mounted on a multichip module, to a single heat sink.
It is another object of the invention to provide a cooling structure that can absorb (or cancel) dispersion in heights and slopes of LSI chips with respect to a heat sink.
It is a further object of the invention to provide a method of manufacturing the above cooling structure of the multichip module.
According to a cooling structure of this invention provided for a multichip module on which integrated circuit devices (i.e., LSI devices) having heat-radiation surfaces are mounted, there are provided a heat sink, thermal conduction blocks and thermal compounds. Recess portions are formed at a surface of the heat sink in connection with the integrated circuit devices of the multichip module. Low melting point metal material such as solder is supplied to interiors of the recess portions of the heat sink. The thermal conduction blocks are partially inserted into the interiors of the recess portions under the condition where the low melting point metal material is heated and melted, so that the thermal conduction blocks temporarily float in the melted material. Herein, the thermal conduction blocks are made of material which is smaller in specific gravity than the low melting point metal material. To avoid heat transfer toward the LSI devices, a heat insulating sheet is provided on the thermal conduction blocks.
Then, the low melting point metal material is solidified, so the heat insulating sheet is removed. The thermal compounds are placed on the thermal conduction blocks, wherein the thermal compounds are made of silicon oil mixed with alumina-filler, for example. Thus, the integrated circuit devices and the thermal conduction blocks are connected together by means of the thermal compounds.
Because of temporary floating of the thermal conduction blocks in the melted material, it is possible to absorb dispersion in heights and slopes of the heat-radiation surfaces of the integrated circuit devices.
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Collins D. B.
NEC Corporation
Picardat Kevin M.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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