Inhibiting growth of the Au0.5Ni0.5Sn4 intermetallic layer in Pb-Sn solderjoints reflowed on Au/Ni metallization

Au/Ni metallization has become increasingly common in microelectronic packa ging when Cu pads are joined with Pb-Sn solder. Recent work has shown that a ternary compound with stoichiometry Au0.5Ni0.5Sn4 redeposits onto the int erface during aging, compromising the strength of the joint. In the present work the growth of the Au0.5Ni0.5Sn4 layer is documented and methods for i nhibiting its growth were investigated. It was determined that multiple ref lows, both with and without additional aging, can substantially limit the t hickness of the ternary layer.