Preapplicable phase change thermal interface pad

Details Preapplicable phase change thermal interface pad Preapplicable phase change thermal interface pad

2000-05-17

2003-09-09

Pyon, Harold (Department: 1772)

Stock material or miscellaneous articles

Layer or component removable to expose adhesive

C428S041400, C428S192000, C428S343000, C428S344000, C174S016300, C174S13800J, C361S697000, C257S712000, C257S717000, C257S718000, C257S719000, C165S104190, C165S185000

Reexamination Certificate

active

06616999

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 by forming a heat-conducted pathway from the components to its mounting surface, across the interface, and to the heat sink.
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 there between. The THERMSTRATE heat pads comprise a durable Type 1100 or 1145 aluminum alloy substrate having a thickness of approximately 0.002 inches (although aluminum and/or copper foil thicknesses 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 as the compound is dry at room temperature yet liquifies below the operating temperature of the great majority of electronic components, which is typically around 51° C. or higher, so as to assure desired heat conduction. When the electronic component is no long in use (i.e., is no longer dissipating heat), such thermal conductive compound re-solidifies once the same cools below 51° 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.
The process for forming interfaces according to contemporary methodology is described in more detail in U.S. Pat. No. 4,299,715 issued on Nov. 10, 1991 to Witfield 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 Witfield 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 Witfield et. al. entitled METHODS AND MATERIAL FOR CONDUCTING HEAT FROM THE ELECTRONIC COMPONENTS AND THE LIKE, the contents of all three of which are expressly incorporated herein by reference.
The prior art of adhesively bonding a thermal interface to either the electronic component or the heat sink is likewise well-known. Such practice facilitates handling and expedites installation of the interface, as well as allows the heat conductive interface to be sold along with either the electronic component or the heat sink already in place there upon. According to contemporary practice, however, the use of an adhesive material to attach the heat conductive interface to either the electronic component or the heat sink is generally undesirable. In this regard, by introducing an additional layer to the interface system, namely in the form of adhesive, the ability of the interface to conduct the flow of heat thereacross is substantially reduced. As those skilled in the art will appreciate, the addition of a layer of material to an interface system, which is already typically compromised by virtue of its multi-layered construction, contributes three distinct impediments to heat flow, namely, each layer introduces the material of which the layer itself is comprised—across which the heat must be conducted—as well as creates two (2) interfaces at either surface of the adhesive layer.
Thus, it will be appreciated that it is highly desirable to minimize the number of layers, and consequently the number of interfaces, comprising an interface system. Along these lines, it has been found that the use of a thermal interface having six or more layers do not provide desirable heat transfer from a given electronic component to the heat sink coupled therewith. The use of an adhesive, and more particularly a layer thereof for affixing an interface system between and electronic component and heat sink further contributes to such inefficiency by introducing yet another layer at the electronic component/heat sink interface. Accordingly, there has been and continues to exist a recognized problem of finding methods to securably mount such interface systems in fixed position between an electronic component and a heat sink, particularly through the use of adhesives, without such adhesive layer extending across or otherwise obtruding upon the interface mating surface across which heat is conducted. Additionally, it should further be noted that from a practical standpoint, the manufacture of interface systems having multiple layers is known in the art to be expensive, and adding yet another layer of adhesive further compounds the expense and complexity associated with such interface fabrication processes.
As such, there is a considerable need in the art to provide a thermal interface having a minimal number of layers that provides adequate heat dissipation from an electronic component to a heat sink, but further utilizes an adhesive to attach the interface to either one of the electronic component or the heat sink coupled therewith. There is a further need in the art to provide a thermal interface which is adhesively bondable to either an electronic component or the heat sink coupled therewith which further does not substantially increase the manufacturing cost thereof, as opposed to contemporary interface pads. There is yet an additional need in the art for a thermal interface that, through the use of novel heat conductive compositions, is more effective in transferring and, hence, dissipating heat generated from an electronic component than prior art interfaces.
SUMMARY OF THE INVENTION
The present invention specifically addresses and alleviates the above-identified deficiencies. In this regard, the present invention is directed to a thermal interface that more effectively facilitates the transfer of heat from an electronic component to a heat sink than prior art interfaces that can further be adhesively bonded to such componentry without diminishing the ability of the interface to transfer heat thereacross. According to a preferred embodiment, the interface comprises a generally planar substrate, which preferable comprises a layer of foil having excellent thermal conductivity, such as aluminum. Formed upon the opposed sides of the substrate are layers of a heat-conducting material formulated to enhance heat transfer from the electronic component to the heat sink. Preferably, such heat-conducting material comprises a graphitic allotrope composition formulated in accordance to those graphitic allotrope compositions disclosed in Applicants' co-pending patent application entitled GRAPHITIC ALLOTROPE COMPOSITION INTERFACE AND METHOD OF FABRICATING THE SAME, Serial No. not yet assigned, the teachings of which are expressly incorporated herein by reference. In this regard, such heat-conducting material is comprised of a base of paraffin having quantities of graphite particles suspended therewithin such that the material exists in a solid phase at normal temperature, but melts when subjected to temperatures of approximately 51° C. or higher (which approximates the threshold temperature at which most electronic componentry operates).
To enable the interface of the present invention to be adhesively bonded to into position, the substrate is sized to over

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