Microscopic observation of Pb-free solder joint interface

Amid the growing concern about global environmental problems, there is a positive movement to reduce the amount of lead contained in the solder that is used for mounting printed circuit boards. Although many researchers have studied alternative solder materials and evaluated their reliability, there are few reports on a minute examination of the interface of solder joint. We considered that in order to evaluate the reliability of solder joint, it was indispensable to study the mechanism of alloy formation at the joint interface. Therefore, we made a microscopic observation of cross sections of solder joint specimens and examined the segregation of Pb from SnPb plating at the joint interface.