Application of Gold-Tin Solder Paste for Fine Parts and Devices

Au-Sn solder paste can be applied by various providing methods, such as printing, dispense, pin transfer, etc.. These methods also make it possible to reduce the production cost. However, in the case of using solder paste, the occurrence of void is one of the most undesirable problems. In this study, we have tried to identify the mechanism of void generation and to reduce voids. We found that the most important factor was to prevent both the gases generated during the reflow process and the generation of Au and/or Sn rich phase in molten Au-Sn solder. For details, it was indicated that for the former it is practical to optimize the pre-heat temperature and holding time in reflow process, to make O2 contents of the powder lower, to control the amount of activator in flux, etc.. For the latter it is important to optimize the composition of the Au-Sn alloy for the reduction of Au and/or Sn rich phases in molten solder.