Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
2002-06-25
2004-09-14
Tucker, Philip (Department: 1712)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C361S704000, C361S707000, C361S708000, C361S709000, C156S327000, C428S332000, C428S339000, C523S400000, C523S440000, C523S457000, C523S459000, C523S460000, C524S403000, C524S408000, C524S413000, C524S860000, C524S861000, C524S862000, C524S866000
Reexamination Certificate
active
06791839
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a thermal interface material (TIM). More particularly, this invention relates to a TIM comprising a curable matrix and a low melting metal filler.
BACKGROUND
Electronic components such as semiconductors, transistors, integrated circuits (ICs), discrete devices, and others known in the art are designed to operate at a normal operating temperature or within a normal operating temperature range. However, the operation of an electronic component generates heat. If sufficient heat is not removed, the electronic component will operate at a temperature significantly above its normal operating temperature. Excessive temperatures can adversely affect performance of the electronic component and operation of the device associated therewith and negatively impact mean time between failures.
To avoid these problems, heat can be removed by thermal conduction from the electronic component to a heat sink. The heat sink can then be cooled by any convenient means such as convection or radiation techniques. During thermal conduction, heat can be transferred from the electronic component to the heat sink by surface contact between the electronic component and the heat sink or by contact of the electronic component and heat sink with a TIM.
Surfaces of the electronic component and the heat sink are typically not completely smooth, therefore, it is difficult to achieve full contact between the surfaces. Air spaces, which are poor thermal conductors, appear between the surfaces and impede the removal of heat. Inserting a TIM between the surfaces of the electronic component and heat sink can fill these spaces to promote efficient heat transfer. The lower the thermal impedance of the TIM, the greater the heat flow from the electronic component to the heatsink.
Most TIMs are based on thermosetting or thermoplastic polymeric matrices. However, the thermal conductivity of conformable polymers is rather low, typically in the range of 0.15 to 0.30 W/mK. To increase the thermal conductivity of the TIM, thermally conductive fillers can be added to the polymeric matrices. The thermal conductivity of these filled TIMs depends on various factors including the thermal conductivity of filler and the packing of filler in the polymeric matrix as dictated by filler particle size and filler particle size distribution.
The effectiveness of the heat transfer between two substrates through the TIM is expressed in terms of thermal impedance or thermal resistance. The thermal impedance or thermal resistance is the summation of bulk resistance of the TIM and interfacial resistance between the TIM and the substrates. At thin TIM bondlines, contributions from interfacial resistance can dominate the total resistance. Since the fillers in these TIM do not make intimate contact with the substrates, interfacial resistance can be high. Consequently, this can translate into higher overall thermal impedance at thin bondlines.
SUMMARY OF THE INVENTION
This invention relates to a composition that can be used as a thermal interface material. The composition comprises:
A) a curable matrix having a curing temperature,
B) a low melting metal filler having a softening temperature, and
C) a spacer.
The temperature at which component B) commences softening is less than the curing temperature of component A). The average particle size of component B) is greater than the average particle size of component C).
This invention further relates to a method for preparing a thermal interface material. The method comprises:
1) interposing a composition between a first substrate and a second substrate to form a bondline having a bondline thickness, where the composition comprises
A) a curable matrix having a curing temperature,
B) a low melting metal filler having a softening temperature, and
optionally C) a spacer, and
with the provisos that
i) the softening temperature of component B) is less than the curing temperature of component A), and
ii) the average particle size of component B) is greater than or equal to the bondline thickness; and
2) heating the composition.
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Brown Catherine U.
Dow Corning Corporation
Feely Michael J
Tucker Philip
LandOfFree
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