Effect of Addition of Small Amount of Zinc on Microstructural Evolution and Thermal Shock Behavior in Low-Ag Sn–Ag–Cu Solder Joints during Thermal Cycling

Abstract

The effects of adding small amounts of Zn on the microstructural evolution of low-Ag Sn–Ag–Cu solders and thermal shock behavior during thermal cycling between −40 and 125°C were investigated. Observation of the visual appearance of the solder joints revealed that the probability of solder deformation and crack initiation in the solder fillets after thermal cycling was lower in Sn–1Ag–0.3Cu–1Zn than in Sn–3Ag–0.5Cu. Microstructural observation of the interface of the solder joints revealed that the addition of Zn to a low-Ag Sn–Ag–Cu solder inhibited the growth of the intermetallic compound layer between the solder and the Cu pad in printed circuit boards. The addition of small amounts of Zn improved the thermal shock behavior of the low-Ag Sn–Ag–Cu solder.