Effect of Zn and in to microstructure of aged SAC305/Cu joint

In this project, Sn-3.0Ag-0.5Cu (SAC305) solder was alloyed with Indium (In) and Zinc (Zn) at 0.5-1.5 wt%, and the aim was to reduce growth rate of IMC layer at interface of solder joint during thermal exposure. Five samples were prepared via casting; SAC305, SAC/1In, SAC/1In-0.5Zn, SAC/1In-1Zn and SAC/1In-1.5Zn. Solders were characterized via SEM equipped with EDX for the bulk microstructure, and the IMC layer after reflow and aging at 150 degrees C for 100 h. Reflow was done on bare copper (Cu) substrate at 270 degrees C for 10 s. Among the percentages evaluated, microstructural analysis revealed that addition of 1.0% Zn not only refined the Ag3Sn and Cu6Sn5 particles, but also increased the eutectic area and promoted the formation of small (Cu,Ag)(5)Zn-8 intermetallic compound (IMC). This would potentially increase the strength of solder, and at the same time, provide blocking mechanism for atomic diffusion during thermal aging and could lead to lower IMC growth. With increasing Zn content up to 1.0 wt%, the reaction phase (Cu,Ag)(5)Zn-8 becomes larger and its morphology changed from a strip-like shape into flower-like or dendritic shape. Highest addition of Zn at 1.5 wt% gave slowest growth indicating that addition of Zn did suppress growth of IMC in SAC305. This could be because Cu was being used to form (Cu,Ag)(5)Zn-8 which was observed at vicinity of the Cu6Sn5 layer. The results showed great potential of Zn alloying to suppress growth of IMC layer during thermal aging of solder joint, and this could lead to higher reliability of solder joint in electronic packaging.Copyright (C) 2022 Elsevier Ltd. All rights reserved.