Development of high reliability lead-free solder joint dispersed IMC pillar

The aim of this study is to create a high reliability solder joint for automotive applications by actively utilizing IMC formation in the joint. The method to disperse pillar-shaped IMCs in the solder joint with Cu was examined with four types of lead-free solder. In the joint with Sn-0.7Cu-0.05Ni (mass%), growth of pillar shaped (Cu, Ni)6Sn5 IMCs which connect Cu plates on both sides was observed when bonding was conducted at 300°C for 30 min. In the joint with Sn-3.0Ag-0.7Cu-5.0In (mass%), coarsen columnar CueSn5 IMCs which include a few mol % In grow in relatively random directions in bonding at 300°C for 30 min. The growth rate of IMCs in bonding is the largest among solder investigated. In the joint with Sn-5.0Sb (mass%), thick columnar CueSn5 IMCs grow from both Cu sides although there are no IMCs to connect Cu plates on both sides in bonding at 300°C for 30 min. For joints with Sn-3.0Ag-0.7Cu-5.0In and Sn-5.0Sb, an effectively IMC dispersed joint is expected to be fabricated by optimization of bonding conditions. In the joint with Sn-3.0Ag-0.5Cu (mass%), a thick scallop shaped IMC layer forms at the joint interface and thus it is difficult to fabricate pillar shaped IMCs to connect Cu plates on both sides.