Elimination of the Corrosion of Ni-P Substrates During Electroless Gold Plating
N. Shaigan, S.N. Ashrafizadeh, M.S.H. Bafghi, S. Rastegari
In conventional galvanic displacement gold plating, the Ni-P substrates used as the diffusion barrier between the gold film and the copper substrate are severely corroded or etched. This corrosion weakens the shear strength of the solder joints, subsequently applied on such gold films. In this research, the effect of incorporation of two additives, hydrazine and tetraethylenepentamine, in a neutral gold plating solution on the elimination of the corrosion of Ni-P substrates was examined. The examination took place by means of microscopic investigations of the surface of the Ni-P substrates, as well as electrochemical polarization measurements. In addition, the effect of the concentration of free excess cyanide in the bath solution on the maximum obtainable thickness of the gold film was studied. The results demonstrate that hydrazine in the presence of tetraethylenepentamine is capable of providing the required electrons for the electrochemical deposition at a neutral pH condition and thus protecting the Ni-P substrate against the corrosion. In this way, a uniform and compact gold film on the surface of the Ni-P substrate was deposited. Also, although the maximum obtainable thickness of the gold film through this process is intrinsically limited, a maximum gold film thickness of 0.66 µm was achieved, when a free excess cyanide concentration of 35 m mol.dm-3 was employed.