Junction-to-Case Thermal Resistance Measurement and Analysis of Press-Pack IGBTs Under Double-Side Cooling Condition

Junction-to-case thermal resistance R thjc measurement under a double-side cooling condition of press-pack IGBTs (PP IGBTs) is a great challenge since the heat flow through the two heat paths is hard to be accurately extracted. In this article, an indirect method determining the proportion of heat dissipation on both sides only by temperature measurement is proposed to simultaneously measure two single-sided R thjc of PP IGBTs under the double-side cooling condition, and it is performed with 4500 V/3000 A PP IGBTs. The test results show that the measured R thjc is not a fixed value but is related to the load current used in the test, it increases as the load current increases, which is different from the traditional wire-bonded IGBT module. A thermomechanical bidirectional coupling finite element model is built to explain the impact mechanism that the deformation of the device causes the change of internal heat flow distribution since the components will be properly separated. In addition, a simpler double-sided R thjc definition method that directly takes the average value of the case temperature on both sides as the case temperature to calculate the thermal resistance is developed, and the equivalence of the two methods are discussed based on the theoretical analysis and experiment.