Advanced packaging for GaN high power electronics

Devices based on wide-bandgap semiconductors such as SiC or GaN allow high power densities and elevated working temperatures. Here we present an innovative package for high-power electronics, within the framework of an ESA-contracted project. The housing concept, design study, materials selection, manufacturing method and first test results are the parameters to be followed in order to get this innovative electronic package. Materials are selected for their high thermal conductivity (TC) and low coefficient of thermal expansion (CTE). Several materials were selected: A1N was selected as substrate material, and novel metal-matrix composites (MMCs) based on Cu-Diamond were evaluated as heat-sink materials. Determination of the final dimensions of the housings according to the new design was required to get a complete bonding. This new heat sink geometry has been validated and the new components fabrication has been already started. An improved surface quality has been achieved, which will increase the contact between the heat sink and the aluminum spreader for electrical characterization. Subsequently, a complete bonding study between ceramic materials and the MMCs was performed. Determination of the final dimensions of the housings according to the new design was required to get a complete bonding. This new MMCs heat sink geometry has been validated and the new components fabrication has been selected. An improved surface quality has been achieved, which will increase the contact between the heat sink and the aluminum spreader for high temperature electrical characterization. In order to obtain fully dense materials A1N was manufactured by pressureless sintering, while the MMCs parts were manufactured by hot-pressing. The MMCs powders were obtained by an electroless plating process. Preliminary characterization of the housing and its parts show encouraging results as a solution for high-power devices working at temperatures up to 400 °C. TC near 500W/mK and CTEs of around 10 ppm/K have been obtained. These are comparable to the stateof-the-art materials. Out-gassing, thermal cycling and hermeticity tests of the packages and high temperature electrical characterization of the electronic paths and global package were performed. The presented new packaging solutions are showing great promise for space applications such as high-frequency power amplifiers for satellite communications and for radar transmitters, and have started to generate an interest from commercial space-system manufacturers.