Study On PSA Tin Plating Of Composite Anode System

Phenol sulfonic acid high speed tin electroplating solution （PSA） is a kind ofplating solution with high production efficiency, good performance and environmentprotection. Both soluble anode and insoluble anode can be used in PSA system, butthere are some shortcomings in soluble anode, such as the large variation of tin ionconcentration, complex operation and the existence of anode striation. Theshortcomings of the insoluble anode are the production of large quantities of tin mudand large investment. This paper studied the anode of PSA tin plating system anddeveloped a kind of composite anode system in order to improve the problem of PSA tinplating system.Firstly experiments were conducted to test the basic performance of PSA tinplating solution. The conductivity of the solution is128ms/cm and C.P is74.1%andT.P is91.2%when the working temperature is50℃.The results shows that the platingsolution has good conductivity and excellent capability of dispersing and covering.Secondly single-factor comparative experiments were conducted to study thefactors that influenced the chemical dissolution and electrochemical dissolution of tinanode in the plating solution when the soluble anode was used in the PSA tin platingsystem. The changing law of Sn²⁺，Sn⁴⁺and the gross of tin was analyzed by the methodof chemical titration. The results shows that the longer the standing time, the higher thetemperature and the severer the solution agitation, the more Sn²⁺will transform intoSn⁴⁺. The concentration of Sn²⁺、Sn4and the gross of tin gradually increases asprolonging the plating time under the electrochemical action of tin anode.The pH value and volume of oxygen are the mainly contributing factors that affectthe dissolution of the tin particles when the insoluble anode is used. In the process ofdissolution of tin, the reduction of pH value can result in the decrease of Sn²⁺and theincrease of Sn⁴⁺; The concentration of Sn²⁺and Sn⁴⁺in the solution increases gradually with the increase of the oxygen content. When the oxygen content exceeds75L/h, theconcentration of Sn²⁺decreases while the concentration of Sn⁴⁺increases. The evolutionpotential of the insoluble anode is0.85V in the use of insoluble anode whenelectroplating. In the solution, the decline rate of Sn²⁺is4.1g/（Lï¹’h）and the increaserate of Sn⁴⁺is3.056/（Lï¹’h） without the addition of tin ions.Finally, according to the research results of the soluble anode and the insolubleanode in the PSA tin plating system,a kind of was designed. Contrast experiments wereconducted to study the area ratio of the composite anode, soluble anode and theinsoluble anode, the current distribution and anodic polarization. The results shows thatthe content of Sn²⁺in the solution stays steady in the use of composite anode with thecurrent of tin anode is0.25A and Ti anode is0.1A when the area ratio of tin anode andTi anode is1:3and PH value is1.05. Hole rate,corrosion resistance and other indexesof the coating are equal to the coatings which are obtained from the soluble anode andthe insoluble anode in the PSA tin plating system.