Difference Between 85 °C/85 %RH Accelerated Life Test and Pressure Cooker Test on Copper/Epoxy Bonding

The reliability of copper/epoxy bonding is crucial for the performance of power modules used in high-demand applications such as electric vehicles and renewable energy systems. This study investigates the degradation mechanisms and failure modes of copper/epoxy bonding under two accelerated life testing conditions: 85 °C/85 %RH and pressure cooker test (PCT). The bonding strength was measured at 0 hours, 240 hours, 500 hours, and 1000 hours for the 85 °C/85 %RH test, and at 0 hours and 96 hours for the PCT. Results showed a gradual decline in bonding strength for the 85 °C/85 %RH test, with values decreasing from 14.90 MPa to 13.34 MPa over 1000 hours. In contrast, the PCT conditions led to a more pronounced reduction in bonding strength from 14.90 MPa to 10.70 MPa in just 96 hours. SEM analysis of the fracture surfaces revealed that before any reliability tests, fractures primarily occurred within the epoxy layer. After the reliability tests, fractures shifted to the interface, indicating the weakening of the bonding interface. These findings indicate that the 85 °C/85 %RH test and PCT have distinct effects on copper/epoxy bonding, with the PCT causing significantly greater degradation. Therefore, industries should not regard these two tests as equivalent.