Inline solution for characterization of chip substrate connections by Laser Speckle Photometry

In the production of power electronics, quality, and reliability is an important factor. Especially, the connection layer between the chip and the ceramic based substrate often includes defects which can reduce the heat dissipation in these areas. This can lead to overheating and furthermore reduce the lifetime of the component. In the worst case, failures like this can have a huge impact on safety relevant systems. Therefore, a quality control within the production line or at least before the packaging of the components is very important.The Laser Speckle Photometry (LSP) provides a promising solution to this problem. Speckle patterns are generated by interfering light waves that are reflected by the illuminated surface.In this paper, a quality control concept based on the LSP in the production process of power electronic chips for the automotive industry is presented. The aim is to find and evaluate the voids in the solder connection, and furthermore determine the porosity in sintered connections. Especially, the size and location of these voids are of great interest. First investigations have shown promising results, finding defects with the size of less than 15 % (v/v) of the actual connection layer of the chips. This proves that the LSP has a big potential to inspect the connection quality of chips during the manufacturing of power electronics.