High Thermal Dissipation Ceramics and Composite Materials for Microelectronic Packaging

Abstract

Upcoming microwave device power requirements are increasing from 1–2 W to 100 W, in some cases resulting in waste heat flux higher than 3–5 kW/cm² under the hot die. As operating frequency climbs from microwave to millimeter wave, the required power also increases and the device efficiency falls. Recently, the incorporation of IGBT’s built on SiC substrates packaged on Al/Diamond/Graphite heat sinks have allowed power levels reaching 50 kW used for 3-phase motor inverters. Traditionally, high thermal conductivity (TC) electrical insulator ceramics have been used to package bi-polar devices, while electrically conductive metal matrix composites (MMCs) have been used to package grounded dies such as LDMOS FETs or GaAs FETs. The TC of traditional oxide ceramics has been expanded to 325 W/mK with the introduction of advanced beryllia formulations. Diamond or cubic boron nitride (cBN) will allow attainment of TC levels as high as 1200–1300 W/mK. When these materials are integrated into advanced MMCs, the thermal performance is improved to levels approaching 500–600 W/mK. Other carbon based compounds like single-wall carbon nanotubes have been reported with TCs reaching 3000 W/mK although no practical applications have yet been reported. MMCs such as aluminium/diamond, copper/diamond, and copper/cubic boron nitride, have been reported at 500–1000 W/mK. Traditional ceramics are compared to high performance advanced ceramics such as diamond, cubic boron nitride, carbon fiber, and carbon nano tubes. Upcoming advanced MMCs such as copper/diamond, aluminium/diamond, copper/cubic boron nitride, silicon carbide/diamond, aluminium/silicon carbide, copper/silicon carbide, and beryllium/beryllia are compared to traditional existing metallic alloys. Experimental data gathered during the last three years while developing some of these low-weight, high thermal dissipation MMCs is presented. Details of the technologies, applications, and cost considerations are provided. Packaging applications for both microelectronics and optoelectronics using these new materials, which are designed based on point-to-point discrete functionality to better utilize material properties and reduce cost, are included. Discussion also includes associated necessary technologies such as metallization, plating, brazing, net shaping, and machining.