The thermal stress in metal conductor layers strongly influences the reliability of high-power electrical modules. We evaluated the stress behavior of copper paste films, which were sintered on alumina substrates, during repeated thermal cycles. The thermal cycle tests were performed from room temperature to 500 °C, which was lower than the sintering temperature. As the number of cycles increased, there was an increase in the temperature at which the compressive stress reached a maximum during heating and there was an increase in the tensile stress during cooling. However, the magnitude of increase reduced as the number of thermal cycles increased. On the other hand, the stress-change rates in the elastic region remained unchanged though the films were subjected to the thermal cycles. We surmised that these changes were owing to an increase in the dislocation density due to plastic deformation, grain refinement due to the increase in the dislocation density, and restoration processes in the copper paste films.
Thermal Stress Dislocation Density Sinter Temperature Thermal Cycle Creep Deformation
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This work was supported by Council for Science, Technology and Innovation (CSTI), Cross-ministerial Strategic Innovation Promotion Program (SIP), “Next-generation power electronics/Consistent R&D of next-generation SiC power electronics” (funding agency: NEDO).
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