Research On Electrodeposition And Welding Technology Of SnAgCu Solderable Alloy

Surface Mounted Technology(SMT)is a technology that solders electronic components on the surface of a printed circuit board(PCB)by reflow soldering or wave soldering.Sn-Pb alloy has been widely used as a solderable layer for its many advantages in the field of SMT.However,due to the toxicity of metal Pb,it may seriously threatens human health and environmental safety.The Ro HS and WEEE directives strictly restrict the use of metal Pb.Therefore,it is necessary to find a alloy replacement of Sn-Pb.SnAgCu ternary alloy has low melting temperature,good compatibility with lead-free solder,excellent soldering performance,and can inhibit tin whisker growth.It is currently recognized in the field as the most excellent and promising alternative to Sn-Pb alloy Product.This paper proposes a new SnAgCu ternary alloy electroplating coordination system using ammonium citrate as the main complexing agent,which is used to produce the ternary alloy solderable coating conrains of 96.5% tin,3.0% silver and 0.5% copper on the PCB surface.The specific research content includes:1)The composition of the ternary alloy electroplating solution and the proportion and concentration of each composition are determined through experiments.Through the Hall cell experiment,stability experiment and cathode current efficiency experiment,the three systems of ammonium citrate,ammonium citrate-MPS and ammonium citrate-thiourea were tested respectively,the superiority of ammonium citrate thiourea was proved and the ratio of main coordination agent to main salt ion was determined.By observing the surface morphology of the coating and determining the composition of the plating solution,suitable additives were selected from a variety of electroplating additives — benzylidene acetone + polyethylene glycol as brightener,poly propylene glycol as dispersant,and ascorbic acid as Stabilizer.The optimal concentration of stannous methanesulfonate,silver methanesulfonate,copper methanesulfonate and brightener in the ternary alloy electroplating bath was determined by four-factor three-level orthogonal experiment to be 0.10mol/ L,7mmol/L,0.5mmol/L,30ml/L(containing benzylidene acetone 27mg/L,containing polyethylene glycol 1.5g/L).2)The effects of temperature,p H value and current density on ternary alloy electroplating solution were determined.The optimum temperature was 30 ?,and the optimum p H value was 5.0.And using the method of electrochemical test,the electrochemical reaction process of the ternary alloy electroplating solution was analyzed,and it was found that the three metal ions were co-deposited at-1.05 V.3)The properties of SnAgCu ternary alloy coating were analyzed and compared with pure tin coating.The results showed that the melting temperature of SnAgCu ternary alloy coating was low,and the adhesion,wettability,corrosion resistance,solderability,reflow property and tin whisker growth resistance of the coating were excellent.In summary,this article proposes a new SnAgCu ternary alloy electroplating system,and successfully obtained a ternary alloy coating with a composition close to96.5% tin,3.0% silver,and 0.5% copper.The various weldability properties of the obtained coating have been analyzed,and they all perform well and can be applied in actual production.