Study On Bath Property And Electroplating Process Of Non-cyanide Au-Sn Co-deposition

With the size of bump continued to decrease in high-power light-emitting diode?LED?,Au-30 at.%Sn alloy as one of the most promising lead-free solders has been widely used in LED packaging,owing to its excellent mechanical properties and thermal conductivity.Nowadays,with the improvement of national environmental protection requirements and the enhancement of people's environmental awareness,the development of electroplating has changed from cyanide electroplating to non-cyanide electroplating,and almost all non-cyanide system Au-Sn plating bath have poor stability.Therefore,its great practical significance to develop a highly stable and environmentally friendly non-cyanide Au-Sn plating to prepare Au-30 at.%Sn alloy bumps.In the present work,a non-cyanide Au-Sn plating bath with high stability was developed.The mechanism of Au-Sn co-deposition was analyzed electrochemically,and the influence of plating bath composition and electroplating process parameters on the composition and morphology of Au-Sn alloy films were studied.The Au-30at.%Sn eutectic alloy films were obtained.Finally,the plating speed,bonding force and phase structure of Au-Sn eutectic films were tested and analyzed.The main conclusions are drawn as follows:1.The study obtained a non-cyanide Au-Sn co-deposition electroplating bath with high stability.It can be stably remained at room temperature for 3 months and still maintain a clear state,and no precipitation or turbidity occurs when heated to 50?.The composition of the non-cyanide Au-Sn electroplating bath include:Au-DMH?5,5-dimethylhydantoin?,potassium pyrophosphate,stannous pyrophosphate,sodium sulfite,sodium stannate,EDTA,catechol.The cathodic polarization curve indicated that the addition of Na₂SO₃ made the potential of Au deposition shifted negatively.With the plating bath temperature increased,the plating deposition rate and cathode current efficiency increased.The initial deposition potential of Au-Sn alloys occurred at-797 mV,there was a sharp increase of cathodic current with the scanning area exceeding-1.33 V?vs.SCE?,and the hydrogen evolution occurred on the cathode.2.By studying the influence of plating bath composition and electroplating process parameters on the composition and morphology of Au-Sn alloy films,the appropriate plating bath composition concentration:0.03 mol/L Sn₂P₂O₇,0.025⁰.04 mol/L EDTA,0.03 mol/L Na₂SnO₃.3H₂O,0.03 mol/L catechol,and the suitable electroplating pH of the electroplating bath was 7.5,electroplating temperature was 40?,stirring speed was 300 rpm,peak current density was 25³0 mA/cm² of Au-Sn alloy.Among them,EDTA has a significant effect on the Sn content in the films due to its strong complexing ability.The catechol that act as antioxidant and brightener in the plating bath can significantly increase the cathodic polarization rate.The peak current density has a significant effect on the morphology and Sn content of the Au-Sn alloy films.3.The orthogonal experiment optimization results showed that when the catechol concentration was 0.026 mol/L,the concentration of EDTA was 0.025 mol/L,and the peak current density was 26 mA/cm²,the bright silver surface and fine crystal grains of co-electrodeposited Au-30 at.%Sn films were obtained.The plating speed of Au-30at.%Sn eutectic alloy can reach 11.4?m/h.Moreover,the eutectic alloy films have great adhesion strength with the substrate.The results of XRD experiments on Au-Sn alloy films with different compositions show that the phase composition of the films obtained by co-deposition electroplating was consistent with the Au-Sn phase diagram.