| Copper-tin alloy electroplating is a traditional nickel plated electroplating process, thisprocess is very extensive. At present, the Cu-Sn alloy plating bath has three types: cyanide,low cyanide and free-cyanide. The electroplating process in the cyanide bath was mature. TheCu-Sn coatings got in the cyanide bath had meticulous crystallization, excellent adhesion, lowporosity and strong corrosion resistance. The quality of the product was easy to control.However, the working temperature was high, the environment was contaminated and theworkers healthy were threatened. The free-cyanide electroplating bath has pyrophosphate, citricacid and stannate, HEDP, etc. Copper-tin coating have three kinds, according to the tincontent, there are low tin （6%-15%）, middle tin （15%-45%） and high tin （>45%）. Becauseof tin content increase, the color of the Copper-tin coating became from shallow red intogolden brown finally into silver white. Cupronickel tin coating belongs to high tin coating,low tin copper-tin alloy coating has a color-for golden brown.This article is based on the study in phosphate solution of cupronickel tin coating system;feasibility of low tin copper-tin alloy coating in phosphate solution system has been discussed.The low tin Cu-Sn alloy in focal phosphate was studied by Hull slot and dc electrolyticexperiment. The results showed that solution composition, temperature, pH, cathodic currentdensity and so on were affected to the appearance, thickness and alloy composition. Theoptimal bath formulation and operation conditions were as follows: Cu2P2O7·3H2O25g/L;Sn2P2O71.0g/L; K4P2O7·3H2O250g/L; K2HPO4·3H2O60g/L; pH8.5; cathodic currentdensity0.5-1.5A/dm2; temperature25℃; stir the plating bath, under this given processconditions, we could get a golden Cu-Sn alloy with copper85%-95%, which deposit wasuniform and bright. The Cu-Sn alloy deposit has the advantages of high diacolorationresistance and good adhesion to the substrate.In the best solution formulation and process conditions, the function of auxiliarycomplexing agent and additives is discussed about copper-tin alloy （low tin） electroplating incoke phosphate solution system. An effective auxiliary complexing agent has not beenfounded in the process of research. Organic amine additive can restrain the exhalation of tin,and make copper content increased. When the use of additives increase, the content of tin isdecreased in alloy coating, and alloy plating is density and uniform, corrosion resistantperformance is improve. After adding additives, the best solution formulation and processconditions is: Cu2P2O7·3H2O20-25g/L；Sn2P2O71-3g/L；K4P2O7·3H2O250-300g/L； K2HPO4·3H2O60g/L-80g/L；pH=8.0-9.0；temperature25℃-30℃; additive A0.5-0.8mL/L; cathodic current density0.3A/dm2-2.0A/dm2.Through the roll plating and hang plating experiment, the practical of this technology isproved. The effect of the composition, Appearance, corrosim resistance and microscopicmorphology was studied by scanning electron microscopy （SEM）, X-ray diffraction （XRD）,energy-dispersive spectroscopy （EDS）. The result of SEM test indicated that the deposit hadmeticulous crystallization and regular lattice arrangement at cathodic current density1.0A/dm2. The XRD test showed that thecrystal structure of deposit was primarily Cu13.7Sn.The EDS text showed that the coatings compostion was89%-95%Cu,95%-11%Sn. Thecoatings performance showed that the microhardness of the coatings was300–400HV. Thecorrosion resistance of the Cu-Sn coatings was better than the nickel coatings in the sameconditions. It was indicated that the copper-tin alloy coatings were binding strongly with baseby bending test, scratches experiment and thermal shock test. The bath performance textproved that the bath were stable. |
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