Reactive diffusion at the interface between Cu and Sn–Ag alloys

Abstract

This study investigates the microstructural evolution and growth behavior of intermetallic compound (IMC) layers in the Cu/(Sn-yAg, y = 0.29–2.00 wt%) system during isothermal aging within the temperature range of 433–473 K. Through systematic variations in Ag content, aging temperature, and time, the fundamental mechanisms governing IMC formation and growth in Cu/(Sn–Ag) solder joints are elucidated. The results demonstrate that IMC growth kinetics follow a power-law relationship, with IMC layer thickness increasing systematically with annealing time. The addition of Ag significantly influences IMC nucleation and growth, with higher Ag content correlating with faster growth rates. Furthermore, the temperature dependence of IMC growth rates is investigated, revealing higher temperatures leading to increased growth rates, indicative of boundary diffusion-controlled growth. By calculating activation enthalpies, values of 36.4 kJ/mol for Sn-2.00Ag and 30.2 kJ/mol for Sn-0.50Ag were obtained, providing quantitative insights into the faster growth rate of intermetallic compound thickness in the Cu/(Sn-2.00Ag) diffusion couple within the experimental temperature range. These findings offer valuable insights into factors affecting the reliability and performance of solder joints in electronic packaging applications.

Keywords

• Sn–Ag
• Grain boundary diffusion
• Cu6Sn5 morphology
• Grain growth
• Intermetallic compound