Study On Tin-Plating Of PCB Process And Electrochemical Behavior

In this research, by large number of experiments, the process formula of electroplating and electroless plating tin in methane sulfonic acid bath was studied, the effect of bath composition and process conditions on coating and plating solution was analysed. And then, got a new tin-plating technology can reach the different requirement of PCB. meanwhile, function and electrodeposition mechanism of addtives was disscussed.A new process of electroplating tin in methane sulfonic acid bath was established, which process contained that:Stannous methanesulfonate 8.0ml/L～10.0ml/L,methanesulfonate 96ml/L-112ml/L,hgll 0.16g/L-0.24g/L,phenolphthalein 0.8ml/L～1.2ml/L,stablizing agent 0.8g/L-1.5g/L,dispersing agent 1.0ml/L～1.4ml/L,temperature 15℃-30℃,current density 1.0A/dm2～3.0A/dm2,mechanical agitation. Tested by SEM,AFM,Metalloscope,electrochemical measurement and other methods, the results showed the dispersion ability and coverage ability of the bath were well, the thickness of coating can reach 3μm, fine grained and smooth & compact electrodeposits were obtained, with high binding power, and the process met to the requirements of Pattern Plating. Then, electrodepositon mechanism of methanesulfonate,hg11,phenolphthalein and dispersing agent were discussed also.A new process of electroless plating tin in methane sulfonic acid bath was established. Firstly, by single factor experiment, the effect of every factor on coating thickness and surface microstructure were disscussed, and the the role of the various components was described, afterwards, through analyzing orthogonal test result, make sure the complete composition of plating bath. The properties of bath was stable and the coating was a silvery-white & smooth deposits, with high binding power, the thickness of coating can reach 0.8μm, it could reach the requirement of solderability coating. The results showed that the coating thickness will become increase with increase of time and temperature by AFM&SEM, but the grain sizes and surface roughness of the deposits increase also; in addition, the PH of bath(methanesulfonate content) could influence the thickness and surface quality of the deposits too.Then, studied the functon of additives by Polarization curves and SEM. The reduction of stannous ions at the pointed sites (protrusions) of the substrate. was suppressed by hg22, at the same time, the thickness of the MIDL(metal-ion denuted layer) above the substrate surface was decreased, and improved the dispersion ability and the surface quality, accordingly,obtained deposits with brightness surfaces. What is more, XRD analysis indicated that time and temperature had nothing influence on the crystal texture of tin deposits that exhibited growth orientation of crystal face (220) and (211), while the sodium hypophosphite was conducive to form crystal faces of Sn (101).