Reliability Analysis of Large-Area, Low-Pressure-Assisted Silver Sintering for Medium-Voltage Power Modules

Multi-layer insulating ceramic substrates can enable medium-voltage (MV) power modules with reduced peak electric field. This benefit is particularly important for MV silicon carbide (SiC) MOSFETs due to their higher operating voltages. Large-area, low-pressure-assisted silver sintering is a potential solution for bonding substrates to create a multi-layer structure. The voiding content and defect density of the bond used to create the multi-layer substrate stack-up are critical to the reliability of the power module and thermal performance, as this bond is in the primary path for heat dissipation in the power module structure. Samples of two-layer direct bonded aluminum (DBA) stacks have been fabricated and subjected to thermal cycling to analyze their reliability. Passive thermal cycling from −40 °C to 200 °C was performed. Cross sections were cut at pre-determined intervals and imaged with scanning electron microscopy (SEM). After 1000 thermal cycles, adhesive failures are observed between the sintered silver and DBA surface. Cross sections were cut and imaged via optical microscope and SEM. Thermal analyzer measurements are recorded on a 10-kV SiC power module using the sintered DBA substrate stacks.