Solidification Mechanisms and Microstructure of Bi-Alloyed Sn–Cu Solder at Low Cooling Rate
Abstract
Microstructural evolution in silver-free, Sn-based lead-free solder alloys can be tailored through bismuth alloying. In this study, an Sn-0.7Cu-0.05Ni-1.5Bi solder was examined and compared with a reference Sn-0.7Cu-0.05Ni alloy. The microstructural modifications induced by Bi addition promote solid-solution strengthening, a mechanism independent of intermetallic compound growth and the associated coarsening effects. The results show that introducing 1.5 wt% Bi significantly decreases both the number and total volume of primary (Cu,Ni)6Sn5 phases. Thermal and microstructural analyses were conducted using differential scanning calorimetry (DSC), energy-dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), and X-ray computed tomography (XCT), and were supported by phase-transformation simulations.
Fields of Study & Subjects
Electronic Packaging and Soldering Technologies
Solidification and crystal growth phenomena
Metallurgical and Alloy Processes
Publication details
- Journal / source
- IEEE Transactions on Components Packaging and Manufacturing Technology
- Publisher
- Institute of Electrical and Electronics Engineers (IEEE)
- Volume
- 16
- Issue
- 4
- Pages
- 674–681
- Publication date
- 23 February 2026