Volume 43 (2002) Issue 8 Pages 1808-1815
This paper presents the mechanical properties and microstructure of Sn–Ag–Bi Pb-free solder. We evaluated the effects of Bi content on the mechanical properties of Sn–Ag–Bi solder such as tensile strength, elongation and deformation behavior at cross-head speeds of 0.1 mm/min and 500 mm/min. The experimental results show that at low cross-head speeds, the addition of Bi to Sn–Ag solder initially increases the tensile strength and decreases elongation due to solid-solution hardening of Sn-phase. As the Bi content is increased to 10 mass% and more, however, elongation increases to a maximum at Sn–Ag–Bi solder containing 57 mass%Bi. Deformation of Sn–Ag solder is governed by slip within the Sn phase, and for high-Bi solders (about 57 mass%Bi) deformation occurs due to slip at Sn–Bi grain boundaries. Intermediate-Bi solders, on the other hand, do not slip in either the Sn phase or at Sn–Bi grain boundaries. At high cross-head speeds, the elongation of both intermediate-Bi solders and high-Bi solders was low and almost constant, indicating slip at Sn–Bi grain boundaries becomes difficult. The impact resistance of these solders was investigated through charpy impact tests, and it is found that Bi has a marked effect on impact resistance. The impact absorption energy of Sn–Ag solder decreases rapidly with the addition of Bi.