Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
2001-06-07
2002-11-19
Tolin, Gerald (Department: 2835)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C156S346000, C165S080300, C174S252000, C361S703000, C428S209000, C428S343000
Reexamination Certificate
active
06483707
ABSTRACT:
BACKGROUND OF THE INVENTION
Interface systems for use in transferring heat produced from a heat-dissipating electronic component to a heat dissipator or heat sink are well-known in the art. In this regard, such electronic components, the most common being computer chip microprocessors, generate sufficient heat to adversely affect their operation unless adequate heat dissipation is provided. To achieve this end, such interface systems are specifically designed to aid in the transfer of heat by forming a heat-conductive pathway from the component to its mounting surface, across the interface, and to the heat sink.
In addition to facilitating the transfer of heat, certain applications further require electrical insulation. Accordingly, such interface systems are frequently further provided with materials that are not only effective in conducting heat, but additionally offer high electrical insulating capability. Among the materials frequently utilized to provide such electrical insulation are polyimide substrates, and in particular KAPTON (a registered trademark of DuPont) type MT.
Exemplary of such contemporary thermal interfaces are THERMSTRATE and ISOSTRATE (both trademarks of Power Devices, Inc. of Laguna Hills, Calif.). The THERMSTRATE interface comprises thermally conductive, die-cut pads which are placed intermediate the electronic component and the heat sink so as to enhance heat conduction therebetween. The THERMSTRATE heat pads comprise a durable-type 1100 or 1145 aluminum alloy substrate having a thickness of approximately 0.002 inch (although other aluminum and/or copper foil thickness may be utilized) that is coated on both sides thereof with a proprietary thermal compound, the latter comprising a paraffin base containing additives which enhance thermal conductivity, as well as control its responsiveness to heat and pressure. Such compound advantageously undergoes a selective phase-change insofar the compound is dry at room temperature, yet liquifies below the operating temperature of the great majority of electronic components, which is typically around 51E° C. or higher, so as to assure desired heat conduction. When the electronic component is no longer in use (i.e., is no longer dissipating heat), such thermal conductive compound resolidifies once the same cools to below 51E° C.
The ISOSTRATE thermal interface is likewise a die-cut mounting pad that utilizes a heat conducting polyimide substrate, namely, KAPTON (a registered trademark of DuPont) type MT, that further incorporates the use of a proprietary paraffin based thermal compound utilizing additives to enhance thermal conductivity and to control its response to heat and pressure. Advantageously, by utilizing a polyimide substrate, such interface is further provided with high dielectric capability.
Additionally exemplary of prior-art thermal interfaces include those disclosed in U.S. Pat. No. 5,912,805, issued on Jun. 15, 1999 to Freuler et al. and entitled THERMAL INTERFACE WITH ADHESIVE. Such patent discloses a thermal interface positionable between an electronic component and heat sink comprised of first and second generally planar substrates that are compressively bonded to one another and have a thermally-conductive material formed on the outwardly-facing opposed sides thereof. Such interface has the advantage of being adhesively bonded into position between an electronic component and heat sink such that the adhesive formed upon the thermal interface extends beyond the juncture where the interfaces interpose between the heat sink and the electronic component.
The process for forming thermal interfaces according to contemporary methodology is described in more detail in U.S. Pat. No. 4,299,715, issued on Nov. 10, 1981 to Whitfield et al. and entitled METHODS AND MATERIALS FOR CONDUCTING HEAT FROM ELECTRONIC COMPONENTS AND THE LIKE; U.S. Pat. No. 4,466,483, issued on Aug. 21, 1984 to Whitfield et al. and entitled METHODS AND MEANS FOR CONDUCTING HEAT FROM ELECTRONIC COMPONENTS AND THE LIKE; and U.S. Pat. No. 4,473,113, issued on Sep. 25, 1984 to Whitfield et al. and entitled METHODS AND MATERIALS FOR CONDUCTING HEAT FROM ELECTRONIC COMPONENTS AND THE LIKE, the contents of all three of which are expressly incorporated herein by reference.
In addition to the construction of thermal interfaces, there have further been advancements in the art with respect to the thermal compositions utilized for facilitating the transfer of heat across an interface. Exemplary of such compounds include those disclosed in U.S. Pat. No. 6,054,198, issued on Apr. 25, 2000 to Bunyan et al. and entitled CONFORMAL THERMAL INTERFACE MATERIAL FOR ELECTRONIC COMPONENTS, and U.S. Pat. No. 5,930,893, issued on Aug. 3, 1999 to Eaton and entitled THERMALLY CONDUCTIVE MATERIAL AND METHOD OF USING THE SAME, the teachings of which are expressly incorporated by reference.
In addition to being able to facilitate the transfer of heat and provide electrical insulation, many interface systems additionally employ a grounded substrate formed from a conductive material, such as copper, to suppress radiated emissions, namely electromagnetic interference (EMI), generated in high frequency transistor applications. In this regard, such grounded substrate is utilized to minimize capacitance to the heat sink to which it is attached, as well as to provide shielding effectiveness and attenuation of radiated EMI. With respect to the latter, it has been shown that electrically grounded copper substrates can provide shielding effectiveness to 60 dB at 1000 KHz, which is an attenuation percentage of 99.9%.
One such commercially-available thermal interface incorporating a grounded conductive substrate is EMI-STRATE (a registered trademark of Power Devices, Inc. of Laguna Hills, Calif.). Such interface comprises a grounded copper substrate sandwiched between two polyimide film substrates, the latter being comprised of KAPTON-type MT. The exterior sides of such interface are further coated with a proprietary thermal compound to thus facilitate the transfer of heat away from the electronic component to a heat sink.
Notwithstanding the effectiveness of thermal interfaces currently in use, a substantial need exists in the art for an interface that provides greater EMI attenuation, shielding effectiveness, and thermal conductivity. In this regard, newer electronic componentry continues to have ever increasing power dissipation and EMI emission. While such electronic componentry typically is constructed and/or packaged to be electrically isolated, the aforementioned increases in power dissipation and EMI emission currently present drawbacks that must be addressed if such componentry is to perform optimally. Additionally, as such advances are made in such componentry, it is certain that the aforementioned concerns regarding radiated emission and power dissipation will continue to create a demand for an interface system that can adequately address the same.
Prior art interface systems, however, are ill-suited to meet such needs insofar as such interface systems, because of their multiple-layer construction, substantially reduces the flow of heat thereacross. In this regard, it has been found that the use of thermal interface systems having six layer construction does not provide desirable heat transfer from a given electronic component to a heat sink. Moreover, not only does each individual layer impede heat flow, but, as those skilled in the art will appreciate, each interface of adjacent layers additionally inhibits heat flow. In this respect, each layer contributes three distinct impediments to heat flow, namely, each layer introduces the material of which the layer itself is comprised, as well as the two interfaces at either surface of the layer. Thus, it will be appreciated that it is highly desirable to minimize the number of layers, and consequently the number of interfaces, comprising such interface system. In addition to the foregoing, it should be noted from a practical standpoint that manufacturing such interface systems having multiple layers is expensive.
In
Flynn Gary E.
Freuler Raymond G.
Loctite Corporation
Stetina Brunda Garred & Brucker
Tolin Gerald
LandOfFree
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