Due to the interfacial reaction between the solder and substrate, either during manufacturing or in service, the solder joints may contain one or more intermetallic layers at the interface. While such intermetallic layers may provide strong bonding, they may also be responsible for problems associated with solderability and reliability of joints. Certain physical and mechanical properties of the intermetallic may determine the integrity and reliability of solder assembly. So far detailed analysis, modelling, and testing of simulated and actual joints have been performed with Pb-Sn solders. However, in view of the increasing environmental and legislative concerns, lead-free solders are currently being developed and designed for microelectronics applications. As the solder joints in high-performance electronic circuits are expected to carry increasing mechanical, electrical and thermal burdens, it is essential to address the technological and reliability issues for lead-free solders. Among the lead-free solders, tin-zinc based alloys can be designed to achieve melting and solidification behavior similar to those of lead-tin eutectic or near eutectic alloys.
The liquid structure of Sn-based lead-free solders and the correlative effect in liquid-solid interfacial reaction
