Effect of Cooling Rate on the Microstructures and Mechanical Properties of Sn-Ag-Cu Lead-free Solder Joints on Cu Substrate

摘要

Environmentally friendly unleaded solder alloys instead of Pb-Sn alloy have been researched extensively. Among the candidate Pb-free alloys, Sn-3.5wt%Ag (numbers are in wt% unless specified otherwise) alloys have lately attracted considerable attention since they have good mechanical properties and tolerable wetting properties. In this study, a small amount of Cu was added to Sn-3.5Ag solder alloy and the cooling rate after soldering on Cu substrate was variously changed. Microstructures of solder joints were observed by an optical microscopy and are discussed along with the variation of mechanical properties.