Residual stress in copper paste films on alumina substrates

The mechanical properties of metal conductor layers strongly influence the reliability of high-power electrical modules. In this study, the microstructure, elastic modulus, and residual stress during temperature cycling of screen-printed sintered paste films were evaluated to develop guidelines for designing metal conductor layers to the module. The number of pores decreased and the elastic modulus increased for paste films sintered at higher temperatures. These films deformed plastically at lower temperatures when heated from room temperature; those that had been sintered at the highest temperature of 800 °C showed the highest maximum compressive stress, which was still approximately one third smaller than that of copper electroplated films. All films developed creep deformation above 200 °C during both heating and cooling processes. The substrate under the film was considered to affect the residual stress in the elastic-deformation area owing to its coefficient of linear thermal expansion and to not affect the residual stress in the creep-deformation area.