Effect of Composition on Structural, Mechanical, and Wetting Properties of Sn-40Bi-xAg Lead-Free Solder Alloys for Green Electronics

This study investigates the impact of Ag on the structural, mechanical, wettability, and electrical properties of alloys Sn-40Bi-xAg lead-free solder for electronic applications. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were carried out to identify the crystalline phases and the morphology features of the solders. Thermal parameters were investigated using differential scanning calorimetry (DSC). Elastic factors, such as tensile strength (S), Young's modulus (E), yield strength (Y), and toughness (T), were investigated by using the tensile test machine (TTM). Hardness and creep resistance of the (Sn-40Bi-xAg) lead-free solder ribbons were tested using a Vickers microhardness tester. Sessile drop method (SDM) was used to measure the wettability properties. The results obtained from the study showed that the microstructure is made up of tetragonal beta-Sn, rhombohedral Bi-rich phases, and Ag3Sn intermetallic compound (IMC). The addition of Ag increased the strength and effectively reduced the electrical resistivity. The elastic modulus of solders containing Ag was enhanced to about 39.61 GPa with 5 wt. % of Ag addition. The higher elastic modulus can be attributed to the solid solution strengthening effect, solubility extension, microstructure refinement, and precipitation hardening of uniformly distributed Ag3Sn IMC particles. These modifications can reasonably alter the microstructure, inhibit segregation, and impede the motion of dislocations.