Coupling effect between two pads in Ni(Au/Ni/Cu)-SnAg-Cu sandwich solder joints during reflow and thermal aging

摘要

The coupling effect of interfacial reactions between the two pads in Ni(Au/Ni/Cu)-SnAg-Cu solder joints was investigated in this paper. After reflow soldering, a large amount of Cu can diffuse across the solder bulk to the opposite Ni pad to form (Cu,Ni)_6Sn_5 intermetallic compound (IMC) in the Ni-SnAg-Cu solder joint. For as-reflowed Au/Ni/Cu-SnAg-Cu solder joint, (Cu,Ni)_6Sn_5 and Cu_6Sn_5 were formed on the Au/Ni/Cu and Cu pad, respectively. A small amount of Au was detected in the (Cu,Ni)_6Sn_5 and Cu_6Sn_5 during the subsequent thermal aging. It is interesting to note that some (Cu,Au)_6Sn_5 with lower Au concentration was always surrounded by (Cu,Au)_6Sn_5 with higher Au concentration at the interfaces or in the solder bulk. Compared with the Ni-SnAg-Cu solder joint, the IMCs formed on both interfaces in Au/Ni/Cu-SnAg-Cu solder joint were much thinner. Au may play an important role in inhibiting the growth of interfacial IMCs. In addition, Cu dissolved from Cu pad inhibits the redeposition behavior of (Au,Ni)Sn_4.