Now, the development of lead-free solder alloys and soldering technology using them is pushed forward by global scale. Among them, the examination for the Sn-Ag-Cu solder is pushed forward mainly for the reason of being superior in joint reliability although the melting point is higher. And products using this solder are already on the market partly. However, in flow soldering with Sn-Ag-Cu solder, peculiar defects called shrinkage cavity, fillet-lifting and land-lifting occur at solder joints. And these defects become one of a problem toward full-scale practical use. In this study, we investigated the influence that shrinkage cavities occurred on the solder joint surface in flow soldering with Sn-3.5 mass%Ag-0.75 mass%Cu lead-free solder on reliability. Furthermore, we added examination about prevention of shrinkage cavity. As a result, the shrinkage cavity understood not to become a fatal defect and not to largely decrease reliability of solder joints. We understood also, that shrinkage cavities are prevented by water cooling just after soldering or increasing the silver content.
