Failure analysis of VDMOS in DC/DC converter

In this paper, the failure mechanism of VDMOS in DC/DC converter was analyzed in detail. The result was gained by the reliability project that included reliability experiment and reliability analysis. The VDMOS devices were used in the circuit of DC/DC converter which can achieve the function of 28 V into 15 V. The accelerated life test was imposed on the VDMOS of the circuit, which has the temperature stress 5degC/day and the electrical stress. The test was began at 75degC, and the VDMOS devices failed at 215degC. Then the failure analysis which recurred to the failure analysis tools such as the photon emission analysis (PEM) and the physical failure analysis (PFA) to the failed device showed the failure mechanism which is junction-break-down leakage inside source contact, under source wire bond. And the possible root cause of failure probably is Al spiking / diffusion into source contact causing junction leakage under reliability test condition of bias and temp. So in this way, the reliability of VDMOS in DC/DC converter can be tested and evaluated effectively.