Fast power cycling protocols implemented in an automated test bench dedicated to IGBT module ageing

Abstract

This paper presents fast test protocols for ageing IGBT modules in power cycling conditions, and a monitoring device that tracks the on-state voltage VCE and junction temperature TJ of IGBTs during ageing test operations. This device is implemented in an ageing test bench described in previous papers, but which has since been modified to perform fast power cycling tests.The fast test protocols described here use the thermal variations imposed on IGBT modules by a test bench operating under Pulse Width Modulation conditions. This test bench reaches the maximal values of power cycling frequencies attainable with a given module packaging in order to optimize test duration.The measurement device monitors VCE throughout the ageing test that is needed to detect possible degradations of wire bonds and/or emitter metallization. This requires identifying small VCE variations (a few dozen mV). In addition, the thermal swing amplitude of power cycling must be adjusted to achieve a given ageing protocol. This requires measuring junction temperature evolution on a power cycle, which is carried out by means of VCE measurement at a low current level (100mA).Experimental results demonstrate the flexibility of this test bench with respect to various power cycling conditions, as well as the feasibility of the proposed on-line monitoring methods.