Improving Monitoring of Parallel Ageing of IGBT Bond-Wires and Solder Layers by Temperature Compensation

Two failure mechanisms can generally be identified by means of accelerated power cycling tests on IGBT power modules: bond-wire lift-off and die-solder delamination. Aging associated to bond-wire lift-off is detected by monitoring the increase of collector-emitter voltage while aging linked to die-solder delamination is detected by observing the increase of thermal resistance. This paper presents experimental results demonstrating the possible effect on the bond-wire end-of-life detection due to concurrent ageing of the solder layer. Solder layer degradation leads to a larger thermal impedance, and consequently, the voltage drop of the IGBT chip increases due to the increased operating temperature. This temperature-driven increase might falsely be interpreted as bond-wire degradation and end-of-life could be stated prematurely. This paper introduces a graphical representation of the power cycling results that gives an overview of the parameter development throughout the test. Based on this representation, the paper proposes a method for temperature compensation that can improve monitoring of bond-wire degradation in the case of parallel aging. Finally, the feasibility and usability of this method is demonstrated.