Investigation on the Solidification and Phase Transformation in Pb-Free Solders Using In Situ Synchrotron Radiography and Diffraction: A Review

It is widely accepted that further development of Pb-free solder alloys for improved processing and in-service properties of next-generation electronics, can be accelerated through a fundamental understanding of phase transformation and microstructure control in Pb-free solder joints. Advanced characterization techniques including synchrotron radiation provide a comprehensive toolset to measure the composition, crystallography, morphology, and properties of the major components of solder alloys. The research using such techniques is reviewed in detail including the characterization of the effects of micro-alloy additions on the microstructure and properties of Pb-free solder joints, especially those on the intermetallic phases. The discoveries outlined are of scientific and industrial relevance and have implications for new solder alloy composition design and the reliability of lead-free solder joints.