Effect of Multiple Reflows on the Interfacial Reactions and Mechanical Properties of an Sn-0.5Cu-Al(Si) Solder and a Cu Substrate

In this study, the interfacial reactions and mechanical properties of solder joints after multiple reflows were observed to evaluate the applicability of the developed materials for high-temperature soldering for automotive electronic components. The microstructural changes and mechanical properties of Sn-Cu solders regarding Al(Si) addition and the number of reflows were investigated to determine their reliability under high heat and strong vibrations. Using differential scanning calorimetry, the melting points were measured to be approximately 227, 230, and 231 degrees C for the SC07 solder, SC-0.01Al(Si), and SC-0.03Al(Si), respectively. The cross-sectional analysis results showed that the total intermetallic compounds (IMCs) of the SC-0.03Al(Si) solder grew the least after the as-reflow, as well as after 10 reflows. Electron probe microanalysis and transmission electron microscopy revealed that the Al-Cu and Cu-Al-Sn IMCs were present inside the solders, and their amounts increased with increasing Al(Si) content. In addition, the Cu6Sn5 IMCs inside the solder became more finely distributed with increasing Al(Si) content. The Sn-0.5Cu-0.03Al(Si) solder exhibited the highest shear strength at the beginning and after 10 reflows, and ductile fracturing was observed in all three solders. This study will facilitate the future application of lead-free solders, such as an Sn-Cu-Al(Si) solder, in automotive electrical components.

Automated summary

This study investigated the microstructural changes and mechanical properties of Sn-Cu solders with Al(Si) addition after multiple reflows to evaluate their reliability under high heat and strong vibrations. It was found that the Sn-0.03Al(Si) solder exhibited the least growth of intermetallic compounds after reflows, with Al-Cu and Cu-Al-Sn IMCs present inside the solders in increasing amounts with higher Al(Si) content. The Sn-0.5Cu-0.03Al(Si) solder showed the highest shear strength and ductile fracturing in all three solders, indicating its potential application in automotive electronic components.