| The process of tin plating is one of the key techniques for printed circuit board manufacture,the quality of the coating directly affected the quality of etching circuits and reliability of components soldering.In recent years,the application and status of tin-plating technology was further improved by using the tin coating as a binding-force enhancement layer for multilayer boards with the appearance of whitening technique.In the tin electroplating solution,the electrochemical method was used to study the tin electrodeposition mechanism on copper surface in sulfuric acid systems,the mechanism of additives were discussed during tin electro-deposition by analyzing the effects of the cathodic polarization curve.In the range of 0.010.05 A·cm-2,the best technology parameters of Sn plating process in sulfuric acid system were obtained by the effects of current density on cathodic overpotential,current efficiency and coating morphology:seignette salt was 80 g·dm-3,octylphenol-10 was 1.5ml·dm-3,2-mercaptohenzothiazole was 0.4 g·dm-3,formaldehyde was 8 ml·dm-3 and current density was 0.03 A·cm-2.Compared to electroplating tin,electroless tin has the advantages of good dispersion,uniform coating and it doesn't require an external power supply,and it could meet the weldability requirement when the thickness is 0.51.2?m.In this paper,the composition of electroless tin bath was studied by optimizing test design method and the best formula of electroless tin plating process in sulfuric acid system was obtained:thiourea was 80 g·dm-3,hypophosphite was 100 g·dm-3,octylphenol-10 was 0.5ml·dm-3,stannous sulfate was 20 g·dm-3,concentrated sulfuric was 40 ml·dm-3 and citric acid was 90 g·dm-3.The influence of plating time and annealing on the corrosion resistance of the coating were studied by Tafel curve,the tests indicated that the corrosion resistance of the tin coating was mainly related to the content of the copper-tin intermetallic compounds,and annealing could increase the content of Cu6Sn5 metallic compounds and effectively improve the corrosion resistance of the coating.Improving the rout densities for printed circuit boards by the single-layer laminated is the main stream technology of industry,and the adhesion strength of inner-layer is one of pivotal factors affecting the quality of printed circuit board.To solve the poor bonding-force between layers as the hetero atoms of prepreg and brown oxide layer are prone to formed hydrogen bonds with water molecules in the air,surface of no-flow prepreg was modified by the O2/CF4 plasma,the relationships between technical parameters of plasma treatment and hydrophilicity,roughness and adhesion of prepreg surface were investigated using 3D microscope,contact angle measurement,and pe el strength tester.The results showed prepreg surface exhibited the highest roughness and the lowest contact angle and thus peel strength reached the maximum in the condition of20 min plasma modification.In terms of improving adhesion performance between prepreg and copper layer,a new technology to improve the adhesion between prepreg and copper,the electroless tin layer was used as an inner layer to replace the traditional brown oxide layer was presented in this paper,and the influence of tin plating process on adhesion of coating was studied.The results showed that electroless tin plating could effectively improve the adhesion of coating surface and its degree of improvement mainly depends on the oxide content of surface,annealing could increase the content of oxide and improve the adhesion to a certain extent. |
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