Novel cyanide free electroless Au plating with an excellent bath stability and the reliable joint with solder was developed. Although the Au plating solution was based on sulfurous acid, the solution’s stability turned out to be excellent by the effective complexing force of the novel additives. The bath stood working without any precipitations for more than 3 metal turnovers. Since the displacement reaction between Ni-P and Au took place in the mild and the uniform way by the aid of the additives involved, resulting in the uniform and the fine grain structure of the plated film, almost no pinholes on the Au plating layer and no pitting corrosion in the ground Ni-P layer could be observed. The joint strength between the BGA pad plated with this novel Ni-P/Au plating and Sn-Ag-Cu based lead free solder ball was found to be much higher than that obtained by the conventional cyanide process. The excellent joint reliability of this process was probably due to the fact that the uniform Au layer with almost no pinholes effectively suppressed the oxidation of the Ni-P surface and eventually almost no pitting corrosion was produced in the Ni-P layer without forming any fatal voids.

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