Aavid Engineering, Inc.

Thermal Associates, Inc.

Ralph I Larson, Jr

Richard F Kiley

Efficient dissipation and uniform spreading of heat from electronic solid-state devices by their associated heat-sink structures is promoted by thin broad-area thermally-conductive mountings built up from layers of a special form of substantially pure flexible and compressible flat graphite sheet material and a bonding-and-filling coating. At least one such 5-10 mil thickness layer of Grafoil flexible sheet, involving a crushable compressed mass of expanded graphite particles which are plate-like and oriented essentially parallel with the sheet surfaces, is intimately connected with a very thin bonding-and-filling coating substantially fully along its broad-area surfaces, and the latter coating is bonded at elevated temperature and pressure into a self-adhering relationship with surfaces of a heat-sink device intended to be disposed opposite surfaces of an electronic semiconductor device from which excess heat is to escape. The coating is applied while in a liquid condition, in quantity sufficient to be effective to fill minute interstitial spaces appearing along the heat-sink surfaces and yet not so thickly as to prevent numerous point contacts from being made at sites of minute surface irregularities of the graphite sheet material and the heat-sink device. Mechanical fastening of a semiconductor device atop the prepared mounting layers of the heat-sink device compresses the crushable graphite sheet material so that voids are minimized and low thermal impedance can be realized between the heat sink and semiconductor device.

Graphite heat-sink mountings

A semiconductor element is positioned between opposing faces of two thermally and electrically conductive members. An external force is then applied to the two members to move the opposing faces of the members toward each other and against the sides of the element. While this external force is maintained, the members are fixed in a housing by means of bonding means, and are separated from the housing by an electrically insulating, thermally conducting material, which may itself be the bonding means. Upon removal of the external force from the members, the members are held by the bonding means and the housing in thermal and electrical contact with the semiconductor element, and the assembly has been pre-stressed. During the operation of the semiconductor element the pressure is controlled by thermally responsive elements.

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North Reading, MA, United States of America

Ralph I Larson, Jr