This dissertation investigates the reliability of assembly and interconnection technologies in silicon carbide power modules, specifically focusing on top-side interconnections using aluminum and copper bond wires. Driven by the increasing demand for robust and high-performance silicon carbide modules for applications in electric mobility and power electronics requiring high power densities, switching frequencies, and operating temperatures, two module types—aluminum modules (aluminum bond wires, aluminum metallization) and copper modules (copper bond wires, copper metallization)—were designed, fabricated, and tested using active power cycling. Modules were subjected to varying temperature cycles (110 - 170 Kelvin) under two environmental conditions: uncapped and nitrogen flooded, to assess the impact of oxidation on reliability. Experimental lifetime data were compared with established lifetime models (CIPS 08, SKiM 63) and literature data. Finite element method simulations complemented the experimental analysis to investigate stress and strain distribution in the bond interconnections and to better understand degradation mechanisms. In the Al module, thermomechanical stresses led to bond wire lift-off, with cracks starting at the bond foot and spreading along the bond interface due to the coefficient of thermal expansion (CTE) mismatch between aluminum and SiC. Microscopic analyses showed recrystallization and grain coarsening, which weakened the material strength. In the Cu modules, the increase in thermal resistance led to the degradation of the Ag-sinter die-attach connection. Oxidation in non-encapsulated modules promoted brittle crack formation, while nitrogen-flooded modules exhibited longer lifetimes. Oxidation in non-encapsulated Cu modules caused brittle, vertical cracks in the Cu metallization, extending close to the SiC semiconductor structures. Compared to the Al module, this is a new failure mechanism. In nitrogen-flooded Cu modules with minimal oxidation, a horizontal crack formed below the bond interface in the Cu metallization. Prolonged APC stress may lead to delamination of the metallization from the bond, which also degrades heat dissipation and represents a failure mechanism similar to that observed in the Al module. Finite element method simulations corroborated the experimental findings, showing that the highest plastic strains occur in the aluminum bond feet and the copper bond wire foot near the metallization interface. For both aluminum and copper, thinner bond wires and thicker metallizations resulted in reduced plastic strain and thus increased lifetime. The simulations underscore the importance of optimized assembly and interconnection technologies design, particularly metallization thickness, for the reliability of silicon carbide power modules. This work elucidates the influence of material, oxidation, and metallization thickness on the lifetime of bond interconnections in silicon carbide power modules, providing insights for the development of highly reliable assembly and interconnection technologies concepts. Copper proves to be a promising bond wire material for silicon carbide chips. Future research should focus on optimizing copper metallization, the influence of encapsulation materials, investigating the impact of aging and humidity under realistic operating conditions, and refining simulation models to improve lifetime predictions and understanding of the complex failure mechanisms.
Rasched Sankari (Wed,) studied this question.