Analyses of thermo-mechanical reliability issues for power modules designed in planar technology

Theoretical analyses on the thermo-mechanical behavior of power modules designed in a new buildup and interconnection technology based on silver sintering and electroplated copper interconnects have been made. The characteristic difference to other technologies can be seen in the replacement of bonding wires by planar copper interconnects and the high voltage applicability of the resulting modules. A high voltage and temperature resistant polymeric foil provides the insulation in this high voltage planar interconnect technology. Electrical connection is made by structured electro-deposited copper structures, which allow additional heat spreading from top of the dies. This interconnection technology is raising new questions concerning the constitutive behavior of the materials involved in the power stack as well as the closely linked questions concerning their thermo-mechanical reliability. Investigations on characteristics of dielectric materials and copper plated interconnects are reported. For the latter, a significant dependence on microstructure is seen. FE-analyses were made to study the thermal and mechanical loadings. Both passive and power cycling were investigated for a prototype converter module substrate designed by HVPT. Transient power cycling induced loading was studied using electric-thermal-mechanical coupling. Significant change in the potential failure modes of such an assembly are to be expected, in particular metallization delamination failure at different interfaces can occur.