Thermomigration suppression in Sn3.5Ag solder joints by hot-end FeCoNiMn alloy

Temperature gradient is inevitable in solder joints in advanced electronic packaging; it induces thermomigration (TM), critically affecting the reliability of micro solder joints. Although a FeCoNiMn alloy (FCNM) can resist thermal aging in solder joints, its TM resistance has seldom been examined. Thus, this study investigated the TM in Cu/Sn3.5Ag (SA3.5)/FCNM solder joints between a cold end (50 degrees C) and a hot end (200 degrees C) at different times. A multielement intermetallic compound (MEIMC), (Cu, Mn, Fe, Co, Ni)6Sn5, is formed at the SA3.5/FCNM interface in the reflowed and aged solder joints. A (Fe, Co, Ni, Mn)Sn2 MEIMC also formed, but it was very thin. The (Cu, Mn, Fe, Co, Ni)6Sn5 was completely decomposed by TM from the hot-end FCNM. In contrast, the (Cu, Mn, Fe, Co, Ni)6Sn5 MEIMC thickened as the rapid TM flux of Cu from the hot-end Cu cap; however, the low chemical flux from FCNM hindered its formation, which was replaced by Cu6Sn5 formation near the Cu/SA3.5 interface. The findings demonstrate that FCNM providing a very low chemical flux is a remarkably promising diffusion barrier for TM in micro solder joints.

Automated summary

Temperature gradient leads to thermomigration in solder joints, which greatly affects their reliability. This study investigates the thermomigration in Cu/Sn3.5Ag/FeCoNiMn solder joints at different temperatures and times. The results show the formation of a multielement intermetallic compound (MEIMC) at the joint interface, which is decomposed by thermomigration from the hot-end FCNM. However, a thickened MEIMC is observed due to rapid thermomigration flux from the hot-end Cu cap. This study suggests FCNM as a promising diffusion barrier for thermomigration in micro solder joints.