The Study Of Palladium Free Activation And Electroless Nickel Plating For PCB Copper Circuit Surface

Electroless nickel plating is required for copper circuit on the surface of printed circuit board.The process of electroless nickel plating usually carries out smoothly by the way of palladium activation.However,the palladium is pretty expensive,which greatly increases the production cost of printed circuit board.What's more,the method of palladium activation in industry is easy to cause the phenomenon of overflow plating.Therefore,it is very significant that develop a palladium free activation method of electroless nickel plating.In this article,we first deposited a thin nickel layer on the copper surface of printed circuit board.Due to the catalytic effect of nickel,which will enable electroless nickel plating to carry on continuously to instead of palladium activation method.In this article,the influence factors of activation process were analyzed by single factor experiment and orthogonal optimization test,and obtain the suitable activation process conditions.Besides,the instability of activation solution was studied.Then electroless nickel plating was studied,the structure and properties of the final electroless nickel plating coating were characterized and compared with the one by the method of palladium activation in industry.By single factor experiment,the influences of relevant factors on the time required for activation to begin and the thickness of preplating layer were studied.The main impact factors include concentration of the dimethlamine borane,the concentration triammonium citrate tribasic,temperature,pH and so on.Then the effects of the concentration of dimethylamine borane,the concentration of trimmonium citrate tribasic,temperature and pH on the time required for activation and the thickness of preplating layer were analyzed by orthogonal optimization test.The optimum activation conditions were obtained as follows:the temperature was 70?,the pH value was 9.0,the activation time was 20 ~ 180 seconds,and the activation bath comprised nickel sulfate 40 g/L,boric acid 30 g/L,ammonium chloride 30 g/L,dimethlamine borane 5 g/L and ammonium citrate tribasic 20 g/L.The effects of the concentration of thiourea,potassium iodide and ammonium persulfate on the stability of activation solution were studied.The ammonium persulfate of special stabilizer carried out the kinetic study.The result showed that the activation energy of thereaction between ammonium persulfate and dimethylamine borane was relatively high,which was 89.75 kJ/mol;Besides,by studying the influence of thiourea and ammonium persulfate on the stability of activation solution,it was found that the stabilization effect was better.Finally,the suitable stabilizer of activation solution was determined as follows: 1mg/L thiourea and 9 g/L ammonium persulfate.Electroless nickel plating was carried out under the optimum activation condition.The structure and properties of the final electroless nickel plating coating were characterized and compared with those by industrial palladium activation method.The results of SEM and EDS show that the electroless nickel plating layer obtained by nickel activation is more dispersed and the particles are smaller.In addition to the presence of Ni and P elements,there is B element in the electroless nickel plating layer,which content is 1.91%.By analyzing Tafel polarization curve and EIS curve of electroless nickel plating coating in 3.5%NaCl solution.The results showed that the electroless nickel plating coating obtained by nickel activation has better corrosion resistance than that by palladium activation.The microstructure of the final electroless nickel plating coating was preliminarily determined by XRD test.The result proved that the electroless nickel plating coating is amorphous structure.Besides,we can know the electroless nickel plating coating had good adhesion and porosity by related tests.The experiment used preplating nickel coating as a protective nickel plating coating on copper surface.The effects of concentration of DMAB,concentration of triammonium citrate tribasic,temperature and pH value on the corrosion resistance of the coating were analyzed by electrochemical methods.The preplating process with excellent corrosion resistance is obtained: the temperatue was 60?,the pH value was controlled 9.5,the preplating time was 5 minutes,and the preplating bath comprised DMAB 0.9 g/L,triammonium citrate tribasic 30 g/L,nickel sulfate 40 g/L and ammonium chloride 30 g/L.