Microstructural Coarsening and Mechanical Properties of Eutectic Sn-58Bi Solder Joint During Aging

Abstract

With miniaturization and heterogeneous integration in packaging, there has been a drive toward developing lower temperature solders. Sn-58Bi eutectic solder provides an attractive alternative with its meting point at 138°C. Due to the lower melting temperature of Sn-Bi solder, Bi coarsening may occur even at room temperature. In this paper, the microstructural evolution in Sn-58Bi joints was observed during room temperature storage. Room temperature aging induced the dissolution and coarsening of Bi phases in the solder matrix, especially in the primary Sn phases and Sn-Bi dendrites. The mechanical properties of individual Sn-rich and Bi-rich phases were measured by nanoindentation. The results showed that the Sn-rich phases had higher Young's modulus and hardness than Bi-rich phases in aged solder joints due to solution strengthening. Bi phases were more compliant and had lower hardness than Sn.

Long-Term Microstructural Stability of Sn-40Bi and Sn-40Bi-10In Alloys

“…Extensive research has been conducted on the influence of element doping on the microstructural stability of Sn-Cu alloys at high temperatures. [13][14][15] Despite some research on the precipitation of Bi in Snrich solder alloys aged at room temperature in the literature, [16][17][18][19][20] there remain limited data on the coarsening of Biphase at higher temperatures. Few studies have investigated the coarsening of Bi particles in SAC-Bi/Cu, Sn-Ag-Bi/Cu, and Sn-Bi/Cu joints aged at room temperature.…”