Study of highly accelerated thermal cycling test for DC/DC converter

DC/DC converter often undergoes the severest thermal stress and most likely to be damaged. The purpose of the paper is to introduce the method of highly accelerated thermal cycling test for DC/DC converter. Firstly, in order to identify the operating limits and failure of DC/DC converters, an on-line monitoring system was established for some key parameters monitoring, such as output voltage, input current and efficiency. Low temperature limits test and high temperature limits test were performed at first. The temperature was decremented and incremented until the device under test failed or the chamber maximum temperature was reached. The low and high temperature operating limits were obtained and failure mechanisms were identified. Based on the results of low and high temperature limits test, the profile of highly accelerated thermal cycling test was designed, and then the test was performed. The failure modes during highly accelerated thermal cycling test was burn-out of MOSFET. We also investigated the failure mechanisms and found the root causes by using some conventional methods of failure analysis such as optical inspection and SEM&EDS analysis. The burn-out of MOSFET is mainly driven by the degradation of heat dissipation performance. The root cause is the degradation of bond performance between the chip and solder, which was due to solder creep and re-melting under the influence of accelerated thermal cycling stress. The solder crack which would affect the reliability was also found. Finally, for reliability improvement, several suggestions were given.