The Research Of Non-Cyanide Electroless Gold Plating

Non-cyanide is an important development direction of electroless gold plating. Non-cyanide type plating bath is now strongly demanded from the standpoint of safety, waste water treatment and environmental concern.A non-cyanide electroless gold plating bath using Na3Au(SO3)2 as gold source and sulfite-thiosulfate together as complexing agents is studied. The thickness and S content are measured by X-ray fluorescence spectrum(XRF); surface morphology is observed by stereomicroscope; Ni/Au adhesion is tested by tape test and thermal shock test; corrosion resistance is analyzed by sulfur dioxide test; besides, bath stability is also studied.The performance of plating bath and coating for the basic non-cyanide immersion gold plating process is tested, and an excellent non-cyanide immersion gold plating bath and process condition is given out. NiSO4 is added into the bath to simulate the aging of the bath and the tolerance capability of Ni2+ in this bath is studied. The addition of adequate metallic shielding agent can improve the appearance of gold coating to a certain extent. The working range of Au+ concentration is measured by atomic absorption spectroscopy and the replenishment method is confirmed according to the periodic experiment.Based on the non-cyanide immersion gold plating process, four reducing agent are added: thiourea, ascorbic acid, sodium gluconate and sodium hypophosphite. According to the performance of the bath and coating, together with the anodic polarization curves, thiourea is chosen as reducing agent while hydroquinone is chosen as additive. Orthogonal test is carried out, and an optimizational non-cyanide electroless gold plating process is given out. Design experiments, the mechanism of this plating bath is researched. With the stereomicroscope photoes of gold coatings under different plating time compared, variation of surface morphology with plating time is studied.