Power Module Using Ceramic Heat Sink and Multilayers Silver Sintering

Abstract

A new packaging technology allowing the development of high-performance power modules for harsh environments and the optimization of the manufacturing process is presented. The assembly is achieved using an aluminum nitride ceramic heat sink and multilayer silver sintering to make both current track and die attach layers. In order to control the properties of silver sintered layers, a focus on the pressureless sintering process parameters at conventional and unusually high temperatures was performed. Depending on the sintering temperature and the dwell time, the relative density of the sintered layers was evaluated in the range of 56%–88%. The electrical resistivity was measured in a large temperature range for various densities, and the latter can only be 30% higher than the one of bulk silver once the paste is sintered at 500 °C for 1 h. Finally, the mechanical and microstructure properties of assemblies using several metal adhesion layers on the ceramic heat sink and silver sintered multilayers were investigated. Assemblies using Ti/Ni/Ag sputtered layers and silver ink sintered layer as adhesion layers on the AlN ceramic show acceptable shear stress values of about 20 MPa, while the values less than 10 MPa are obtained for W/Ni/Au and W/Ni/Ag adhesion layers. For W/Ni/Au adhesion layers, Ag–Au solid solution was formed at the interface between the sintered silver and the Au finish, leading to a depletion zone at the sintered silver interface and, hence, low shear stress. For W/Ni/Ag adhesion layers, the low shear stress value is mainly due to the oxidation of the Ni layer.