Copper-diamond composite substrates for electronic components

The application of high power density electronic components such as fast microprocessors and power semiconductors is often limited by an inability to maintain the device junctions below their maximum rated operating temperature. The junction temperature rise is determined by the thermal resistance from junction to the ambient thermal environment. Two of the largest contributions to this thermal resistance are the die attach interface and the package base. A decrease in these resistances can allow increased component packing density in MCMs, reduction of heat sink volume in tightly packed systems, enable the use of higher performance circuit components, and improve reliability. The substrate for a multichip module or device package is the primary thermal link between the junctions and the heat sink. Present high power multichip module and single chip package designs use substrate materials such as silicon nitride or copper tungsten that have thermal conductivity in the range of 200 W/m/spl middot/K. We have developed a copper-diamond composite material, named Dymalloy, with a thermal conductivity of 420 W/m/spl middot/K, better than copper, and an adjustable coefficient of thermal expansion, nominally 5.5 ppm//spl deg/C at 25/spl deg/C, compatible with silicon and gallium arsenide. Because of the matched coefficient of thermal expansion it is possible to use low thermal resistance hard die attach methods. Dymalloy is a composite material made using micron size Type I diamond powder that has a published thermal conductivity of 600 to 1000 W/m/spl middot/K in a metal matrix that has a thermal conductivity of 350 W/m/spl middot/K. Besides having exceptional thermal properties, the mechanical properties of this material also make it an attractive candidate as an electronic component substrate material.