Research on the reliability of vacuum welding of IGBT modules

The reliability of the soldering layer of an IGBT module directly affects its thermal performance and long-term service life. In this study, the reliability of the ceramic copper-clad substrate connected with the base plate is investigated by a vacuum welding process combined with Sn-Ag3.0-Cu 0.5 solder (SAC 305). The results show that the number of vacuum pumping operations and the soldering temperature greatly affect the soldering void fraction, while the extension of the vacuum holding time has a smaller effect. The lowest voiding rate (about 1%) is found in the solder layer when 2 vacuum operations (vacuum ≤ 10 m bar) are performed, the vacuum state is maintained for 30 s, and the soldering temperature is 260 °C~280 °C. In addition, the Ni layer on the substrate surface can inhibit the reaction between Sn and Cu at the interface between the solder and the substrate, reducing the thickness of the intermetallic compound (IMC) layer on the nickel-plated substrate (7.6 μm) to that on the copper substrate. This phenomenon can effectively reduce the risk of solder layer cracking caused by excessive IMC layer thickness and improve the long-term reliability of the solder layer.