Study of microstructures and mechanical properties of lead-free solder joints

Abstract

Reliability of solder joints is a most critical issue in electronic packaging. There is the urgent need to understand reliability of lead-free solder joints because lead-free solders are replacing the conventional tin-lead solders due to environmental concerns and legislation to ban use of lead in electronic products. In soldering process, formation of thin intermetallic compounds (IMC) due to reaction between the solder and substrate is essential to achieve a good metallurgical bond. However, excessive IMC growth in service could cause premature failure of the joint. Therefore, the primary objective of the project was to understand IMC growth in lead-free solder joints. Bulk solders were studied but special attention was paid to the solder-substrate interface. The project aimed to study 95.5Sn-3.8Ag-0.7Cu solder because it is a type of lead-free solder especially recommended by the National Electronic Manufacturing Initiative, but 99.3Sn-0.7Cu solder was also studied because the binary alloy contains single type of 1IMC and thus makes it easier to monitor the IMC growth quantitatively.