An Alternative Junction-to-Case Thermal Resistance Test Method for High Power Press-Pack IGBTs

Press-pack insulated gate bipolar transistors (PP IGBTs) is well suited for high-voltage, high-power applications due to their double-side cooling, ease of series connection, and higher power density. It is very important to measure the junction-to-case thermal resistance (R-thjc) for evaluating thermal performance, with high accuracy. However, the existing thermal resistance test methods will have the problem of low accuracy when it is used in PP IGBTs. In this article, a new thermal resistance test method is proposed based on the transient dual-interface method (TDIM), different from traditional TDIM, which can obtain two transient thermal impedance (Z(th)) curves without disassembling the fixture, and determine the R-thjc through the separation point. The 4500 V 3000 A StakPak PP IGBTs is used as the measurement object. The results show that compared with the traditional TDIM, the new method is very simple to operate, and the test results are more accurate than thermocouples, which is more suitable for PP IGBTs. The single-side thermal resistance of the PP IGBTs is analyzed, and the emitter side is even worse due to the disc spring. The R-thjc calculated by single-side thermal resistance is close to the proposed method, but fluctuates widely.