Research On Precision Gold Plating Process Based On Commutation Pulse

Gold has the characteristics of high chemical stability,excellent corrosion resistance and soft.The gold coatings as the surface protective layer of the component is thin,requiring low porosity and high thickness uniformity.Pulse plating is a common method for obtaining a gold coating.The pulse reverse current is to increase the reverse pulse on the basis of the forward pulse.It has the advantages of strong cathode magnetization,fine grain in the forward pulse plating.It also has the advantages of dissolving the convex portion and reducing the concentration polarization during reverse pulse plating.Its many adjustable parameters have different effects on gold plating.The overall performance of the gold plating layer can be improved by exploring suitable pulse reverse current parameters.In this paper,the method of pulse reverse electroplating and the citrate plating solution with high polarization and stability were used.The research goal is to optimize the pulse reverse gold plating process,which further improves the compactness,thickness uniformity,plating rate and grain refinement of the gold coatings compared with the existing forward pulse gold plating process.The main research contents are as follows:According to the research goal,it is determined by mechanism analysis that the reverse pulse can further improve the deposition rate of metal ions,the compactness and the thickness uniformity of the coating.It is verified by the plating forming simulation that the reverse pulse can significantly improve the thickness uniformity of the coating compared with the forward pulse.The larger forward pulse average current density and the reverse pulse peak current density help to increase the plating rate.The shorter reverse pulse on-time and high reverse pulse peak current density help to increase the thickness uniformity of the coating.The pulse reverse current waveform applied to the process experiment was determined.Based on the pulse reverse plating forming simulation,the single factor experiment and the orthogonal experiment were designed.Multiple detection methods were determined to estimate the technological parameter.The experimental system was constructed by using the self-developed pulse reverse current power supply.The pretreatment process of the sample was determined.Based on the experimental system,the experiments were carried out on the parameters of the pulse reverse gold plating process.Based on the results of single factor experiment,the effects of forward and reverse pulse parameters on the gold coating microstructure,plating rate,thickness uniformity,porosity,corrosion resistance and grain size were analyzed.The suitable ranges of pulse parameters are determined as follows:forward pulse average current density[0.273-0.455]A/m~2,forward pulse width[40-200]μs,forward pulse duty cycle[1:5-1:15],forward pulse number[5-15],reverse pulse peak current density[2.07-6.21]A/m~2 and reverse pulse width[40-220]μs.The orthogonal experiment range analysis results show that among the optimization objectives,the plating rate is mainly affected by the forward pulse average current density;the thickness uniformity of the coating is mainly affected by the reverse pulse peak current density;the coating porosity is mainly affected by the forward pulse average current density and the reverse pulse width;the grain size is mainly affected by the forward pulse number and the the reverse pulse width.The optimized pulse parameters are as follows:forward pulse average current density 0.455 A/m~2,forward pulse width 160 μs,forward duty ratio 1:15,forward pulse number 9,reverse pulse peak current density 4.14 A/m~2 and the reverse pulse width 100 μs.The experiment compares the gold plating effect of the pulse reverse electroplating optimization parameters with the existing forward pulse electroplating parameters,and verifies the superiority of the pulse reverse electroplating optimization process parameters.The optimized pulse reverse electroplting process parameters has higher plating rate 0.165 um/min(forward pulse current 0.09 um/min),the gold plating layer is dense and non-porous(forward pulse current 1.6/cm2),the corrosion resistance is strong Ecorr 0.17V(forward pulse current Ecorr-0.14V),the thickness uniformity is higher 0.117(forward pulse current 0.162)and the grain size is smaller 52.2 nm(forward pulse current 71.4 nm).