Optimizing defect detection in connections of power electronics by laser speckle photometry

Abstract For reliable structures in power electronics, it is crucial to guarantee the proper quality of their interconnection layers. At the moment, most of these joints are made by a solder process. Like every joining process, irregularities such as cracks or voids can impair their thermal and structural resilience. In the context of power electronics, one of the most important factors is the heat path from semiconductor devices into the substrates they are soldered onto. A disturbed heat path can, in the worst case, lead to failure of an entire (safety-relevant) system. Recent investigations have shown that the Laser Speckle Photometry (LSP) is a promising method to detect such impurities. Therefore, the specimen is illuminated by coherent monochromatic light. The interfering effects can then be recorded and analysed, since their behaviour can be correlated with the sample’s state. Additionally, due to its easy setup and its non-contact, non-destructive manner, the LSP could be well suited even for inline applications. The previous publication presented a simulation that showed the underlying physical processes and the transmission of these into a real setup, testing on synthetically provoked voids. This paper will concentrate on improving the system to analyse real samples, optimize measurement times and provide an outlook for further development steps.