Joint properties and reliability of Cu/Sn-Ag pillar bumps via low-temperature thermo-compression bonding

Abstract

The joint properties and reliability of Cu/SnAg pillar joints via a low-temperature thermo-compression bonding (LT-TCB) process below the melting temperature of SnAg solder were investigated in this study. The bonding temperature was 150 °C. The pitches of the Cu/SnAg pillar bumps were 40 and 60 μm. The LT-TCB process was conducted using a non-conductive adhesive (NCA) and the post-curing of the NCA was conducted at 150 °C for 30 s. The SnAg solder was not melted but deformed to contact with the Cu pad following the LT-TCB. As the bonding time of the LT-TCB increased from 3 to 5 s, the gap between the SnAg and the Cu pad decreased and some areas showed an interfacial intermetallic compound (IMC) indicating that bonding had occurred. The electrical resistance of the LT-TCB samples increased after a temperature and humidity (TH) test and a thermal cycle (TC) test. The gap between the SnAg and the Cu pad decreased and interfacial IMCs formed in some regions following the reliability tests. The electrical resistance of the 3-s bonding sample was higher than that of the 5-s sample following the reliability tests. The bonding pressure also affected the joint properties. The electrical resistance after the TH and TC tests decreased with increasing bonding pressure. Without post-curing of the NCA, a crack occurred after the reliability test. The NCA did not fully cure during the LT-TCB; thus, the NCA did not play a role as a stress reliever.