This invention relates to thermal management materials that conduct heat from a heat source to a heat-sinking component and, more particularly, components that interface between a heat source and a heat switch.
During operation, IC devices produce heat. Efficient cooling systems are sometimes necessary to prevent the failure of IC devices due to this heat. Certain types of cooling systems work by transferring heat from the surface of a heat source to a heat-sinking component that dissipates the heat. Heat sinking components typically are metal, for example aluminum, and have expanded surface areas to transfer heat to the environment or may have other mechanical cooling means. When the surface of a heat source, such as an integrated circuit or a module or package containing such components, is directly engaged with the surface of a heat-sinking component, surface irregularities may prevent optimum contact and result in air spaces located in the interface between the surfaces. These air spaces can reduce the rate of heat transfer from the heat source to the heat-sinking component to unacceptable ranges.
A key aspect of efficiently and effectively transferring heat from a heat source to a heat-sinking component, therefore, is maximizing heat transfer between the surfaces. To this end, an interface of thermally conductive material or a component formed from such thermally conductive material can be placed between the heat source and heat sink. Preferably, the material or compound should reduce or eliminate gaps or air spaces that resist heat transfer by maximizing contact with the surfaces of the heat source and heat-sinking components.
One such material that may be used to facilitate heat transfer between a heat source and heat-sinking components is a viscous, thermally conductive paste or grease extending between the contact surfaces of the components. Such pastes or greases function by increasing surface area contact between the heat-dissipating and heat-sinking components. Furthermore, thermally conductive pastes and greases are difficult to apply and messy, and often bond to the surfaces to which they have been applied or may melt and flow under elevated temperatures.
Products have been developed to avoid some of the problems associated with thermally conductive pastes and greases and still facilitate heat transfer through an interface. For example, thermal pads are now made from an elastomeric or foam matrix material loaded with a material that has favorable thermally conductive characteristics. Thermal pads, including those loaded with such materials, are further described in U.S. Pat. Nos. 6,054,198; 5,679,457; 5,545,473; 5,510,174; 5,309,320; 5,298,791; 5,213,868; 5,194,480; 5,137,959; 5,151,777; 5,060,114; 4,979,074; 4,869,954; 4,782,893; 4,685,987; 4,606,962; and 4,602,678. These patents are incorporated herein by reference.
By combining the elastomeric-conforming properties of one material with the favorable thermally conductive properties of another, thermal pads loaded with a thermally conductive material can significantly reduce air spaces and facilitate heat transfer between the surfaces of a heat source and heat-sinking components. Silicone-based materials have come into favor in thermal management materials due to their excellent heat transfer capabilities and their high conformability under compression. Such compression can cause many of these silicone-based materials to effectively flow rather than to simply be compressed, essentially maintaining the original volume of the pad. Especially when used under conditions of continuous elevated temperatures, these silicone-loaded pads have a tendency to exude fluids, for example, silicone and other fluids and may out-gas. These fluids and gases, in turn, may contaminate the IC devices or other components or portions of the equipment. In some applications, this is not a concern, but in many applications, such exudation and/or outgassing is not acceptable.
It is considered by many in the field that thermal pad materials based on or loaded with a non-silicone material are not as effective as other materials in transferring heat and in conformability.
Thus, there is a need for an effective thermal interface component that has the performance characteristics of silicone-based or silicone-loaded thermal pad material but that does not exude silicone or oils under operating conditions.