Base solder voids identification of IGBT modules using case temperature

Abstract

Solder voids has an important impact on healthy operation of insulated-gate bipolar transistor (IGBT) modules, but voids damage is difficult to be estimated accurately by conventional methods due to the lack of calculation in mutual thermal effect between chips. So this paper proposes a base solder voids identification method by using case temperature, takes into account both self-thermal diffusion and coupling inside module, and adopts case temperature distribution on bottom of baseplate to assess voids damage indirectly. Firstly, finite element method (FEM) of IGBT module with base solder voids was established to study junction and case temperature response with different voids distribution, the practicability of base solder voids identification based on case temperature is verified. Then the influence mechanism of voids on case temperature was discussed theoretically, voids identification is extended to dynamic load conditions, temperature-to-thermal resistance conversion and dynamic thermal resistance reference calibration with different power loss ratio were realized by improved thermal network, recursive least square (RLS) algorithm was designed for dynamic identification of real-time identifiable thermal resistance, the difference between RLS results and thermal resistance reference was compared to confirm the severity of base solder voids, two or more groups of comparison results with different power conditions are used to complete the voids analysis. Finally, validity of proposed method is demonstrated by simulation. Compared with conventional method, it shows better ability in dynamic identification.