Interaction of solder balls containing Cu with Au/Ni plated Cu pads

摘要

Interaction of the eutectic Sn-37mass%Pb or Sn-3.5mass%Ag based solder balls with Ni/Au electroplated or electroless plated Cu has been investigated. Changes in the joint microstructure during reflow and the subsequent heat exposure at 423K were observed and their effects on the shear strength of BGA were discussed. While a metastable (Au, Ni) Sn3 reaction layer was formed on the interface between the solder and the pad for joints using both Cu free Sn-Pb and Sn-Ag solder balls, stable η'- (Au, Cu, Ni){sub}6Sn{sub}5 reaction layer was formed for the joints using Cu containing solder balls. The growth rate during heat exposure was much slower for η' reaction layer than that for (Au, Ni) Sn3 reaction layer. All the joints after a heat exposure fractured on the lower shear load than as reflowed joints, but the shear strength of the joint using Cu containing ball was less degraded than that using Cu free solder balls, because η' reaction layer grows slower and plays a roll as a good barrier layer to suppress the Ni-Sn interaction. Almost the same effect was confirmed for the BGA joints using Cu cored solder balls, since Cu dissolves into the solder during reflow soldering.