Radiation-Induced Alterations in the Eutectic Microstructure and Hardness of Lead-Free Solder

Abstract

In this study, the effect of high-dose gamma radiation on the hardness and the eutectic phase area of SAC305 solder was characterized. The solder paste was applied to the printed circuit board via stencil printing and reflow soldering, then subjected to gamma radiation doses (5, 50, 500, 5000 and 50000 Gy). After the exposure, the samples underwent a metallographic procedure prior to the indentation test. The hardness, intermetallic compound (IMC) thickness, and phase area before and after irradiation were observed via nanoindentation, optical microscope and analysed via ImageJ. It was found that when exposed to gamma radiation, the hardness decreased to 0.12 GPa at 500 Gy from 0.26 GPa before exposure and suddenly increased to 0.18 GPa for 5000 Gy due to disturbance in the atomic arrangements of materials in the solder. Gamma radiation altered the microstructure of SAC305 solder resulting in a change in IMC thickness as the radiation increased. The phase area was analysed for SAC305 by using  ImageJ. This phenomenon may be correlated with changes in the structure and atomic arrangement within the SAC305 solder alloy. It is believed that the heat generated by gamma rays initiates the coarsening of the microstructure and the evolution of intermetallic compounds, consequently affecting the hardness of the solder joint. Therefore, when testing solders intended for radiation-related applications, the effect of radiation should be considered when testing solders to be used in radiation-related applications.