Failure Mechanisms in Chip-Metallization in Power Applications

Degradation of the chip-metallization layer in power electronic packages under Active Power Cycling is still a major reliability concern. During Active Power Cycling tests, the chip acts as a heat source and temperature gradients develop within the package inducing stress and plastic deformation in aluminum metallization. This study is conducted on a power module using a copper clip soldered on the top side of the chip, instead of aluminum wire bonds. Both experiments and simulations are performed, to better understand mechanisms of chip-metallization degradation. In this paper, experimental Power Cycling tests are performed on power packages and a 2D Finite Elements model of MOSFET is used for thermo-mechanical simulation. Modules are monitored during tests and metallographic specimens are made at the end of tests in order to examine changes in the metallization layer. Thermo-mechanical analysis allows us to monitor the evolution of stress and strain in aluminum during power pulses. A study of the sensitivity of various test parameters is also simulated and the influence of those parameters on the mechanical behavior of power metallization is quantified. Knowledge of degradation phenomena gained with simulation helps to improve product design.