The Effects of Copper Particles on the Microstructure of Sn58Bi Soldered Joints

In the light of the effect of copper particles(2 μm) on the microstructure and mechanical properties of sn58Bi welded joints. The results show that when the content of copper particles in the Sn58Bi solder was ω(Cu)=0.3%~1.0%, the fine particles are pinned near the grain boundaries, which inhibits the pure Bi and pure Sn phase segregation of the Sn58Bi system. At the same time, copper particles and the intermetallic compound Cu₆Sn₅ around particles can effectively promote the nucleation of Bi phase and refine the microstructure of Bi phase. But when ω(Cu)>1.0%, because the fine particles are pinned near the grain boundaries, the contact area of the copper particles and the Sn in the solder multiply. It makes the amount of Cu₆Sn₅ increased and lead to the increase of the molar volume. In order to achieve the balance of the system, Bi phase structure which is extremely thin and easy to break occurs in the rich Bi region, it makes that the mechanical properties of the joints caused by brazing are decreased. In the experimental data range, the mechanical properties of the nonageing Cu containing solders are much better than those without copper. When ω(Cu)=0.5%, the maximum value of the joint tensile shear strength of five kinds is finally achieved.