2022 年 63 巻 7 号 p. 1021-1027
In this study, the microstructure and the thermal fatigue life of Sn–3.0 mass%Ag–0.5 mass%Cu–6.0 mass%In–1.0 mass%Sb (SAC305–6In–1Sb) were investigated and they were compared with those of Sn–3.0 mass%Ag–0.5 mass%Cu (SAC305). As the test pieces, chip resistors were joined on a printed wiring board by reflow soldering with each solder. Although precipitates of Ag and Cu were present in both solder joints, the precipitation state and size of Ag precipitates were different for each solder joint. In the solder joint with SAC305–6In–1Sb, the precipitate of In and Sb was also confirmed. In addition, In and Sb were solid-soluted in Sn. Solder joints with SAC305–6In–1Sb were polycrystal with approximately 20 crystal grains per cross section of the joint. On the other hand, the joint of SAC305 was consisted of a single crystal. Average of thermal fracture life of SAC305–6In–1Sb was approximately 4.3 times longer than that of SAC305. In addition, the variation in the life of SAC305–6In–1Sb was smaller.
