Identification of solder layer defects in power modules using short pulse heating

The thermal impedance is a key characteristic of an IGBT power module that is crucial for the performance and lifetime of a power electronic inverter system. In order to detect defects, such as solder voids or delamination in the packaging of the power module during manufacturing, a suitable thermal characterization test should be deployed. This paper investigates a fast transient thermal characterization method for the detection of voids in the solder layers that can be easily implemented in end-of-line test equipment. The measurement is realized by pure electrical means and does not require additional temperature measurement equipment. It uses short electrical load pulses to heat the semiconductor chip and measures the transient thermal response by utilizing a temperature sensitive electrical parameter of the chip. The optimization of the required heating and waiting times during measurement can aid to reduce the duration of the test while maintaining sufficient resolution to detect significant solder defects. Numerical simulations were performed to accelerate the selection of optimal timing parameters and to adapt these for alternative module packages with different thermal constants due changes in layout or materials.