Study On Cyanide-free Immersion Gold Technology With Gold Potassium Citrate

In the electroless gold plating technology, a new type of cyanide-free electroless gold plating technology, gold potassium citrate electroless plating, was studied more and more in order to reduce to environment pollution of the waste plating liquid, ensure worker safety operation and provide convenient management of production line. This technology is environmental friendly for the cyanogen and nitriles free gold potassium citrate and the complexing agent. The performances of the gold layer obtained by cyanide and cyanide-free process are at the same level. So the gold potassium citrate electroless plating is able to replace the existing gold potassium cyanid electroless plating in the actual production.In this peper, pretreatment process for gold potassium citrate electroless plating was studied. The surface profiler step tester and Scanning Electron Microscope were used to analysis the copper surface after different single pretreatment processes. In addition, different combination pretreatment processes was adopted to roughen the copper surface. The roughness of copper surface and the appearance of the electroless plating gold layer was also analysized to compare the performances of different combination pretreatment processes. The test result showed that micro etching pretreatment and sand blasting + micro etching combination pretreatment were the best pretreatment process for the electroless gold plating.In this detail, a cyanide.free gold plating process with gold potassium citrate as basic salt and RW.905 as cyanide.free additive was studied. The X-ray coating thickness measuring instrument, Scanning Electron Microscope, Energy Dispersive Spectrometer, 3M adhesive tape peel testing, sulfur dioxide corrosion testing, hydrochloric acid corrosion testing and wetting balance testing were adopted to evaluate the performance of the plating layer and the stability of the plating solution is aslo researched.In the non.cyanide immersion gold plating bath, the single factor experiments were designed to study the effects on the gold plating layer and glod ion deposition rate. Temperature, pH, gold ions concentration, additive concentration and by.product (Ni2+, Cu2+) were chosen as the single factor. After experiments, the process parameters of these factors were determined for the actual operation. Further more, an orthogonal experimen was designed to get the optimization parameters of temperature, pH, gold ions concentration and additive concentration. The optimized technology parameters are as follows: temperature 90℃, PH 5.3, Rw-905 additive concentration 200mL/L, gold concentration at 1.0g/L. The quality of gold plating layer prepared by the cyanide.free process was tested. And the test results showed that the quality was the same as the gold plating layer prepared by the cyanide process. Through gold ion deposition rate and gold and nickel surface texture as the nickel coating thickness, deposition time and phosphorus content changes in cyanide-free and cyanide technology was compared, the reaction of replacement mechanism of cyanide.free gold plating was proved.On the basis of reaction of replacement mechanism, reducing agents such as ascorbic acid, thiourea, sodium phosphate, sodium gluconate were added to influence the performances of plating solution. The reducing agents aslo change the properties of the gold plating layer and accelerate the gold ion deposition rate. And the gold ion deposition rate would be at a high level, when thiourea concentration was 1.5g/L while the gold plating layer retained good performance. In comparison with gold plating layer prepared by the solution without thiourea, thickness of the plating layer added 83% in the same deposition time.The experimental research and theoretical analysis results show that the cyanide-free immersion gold plating techonlogy is feasibile and reliabile in the practical application.