Toward defects-free in lead-free micro-soldering

Many works have been continued to replace Sn-Pb solder alloys by lead-free solder. The lead-free solders to be used in electronics assembly should be compatible for micro-soldering, which means the alloys should have adequate melting temperature range and excellent wettability. No lead-free solder has superior wettability to Sn-Pb, therefore, to secure sound joints without defects is important not only from the reliability but also from the environmental aspects, because sound joints usually offer long life, high reliability and repair free operation. This work aims to develop a strategy for obtaining defects-free joints in micro-soldering with lead-free solder from an environmentally conscious viewpoint. Especially, the work focuses on the appropriate selection of lead-free solders and soldering atmosphere to reduce soldering defects.