Non-cyanide Alkaline Copper Plating

As to conform the policy of replacing cyanide electroplating, and to protect environment, this paper chooses non-cyanide copper electroplatig as our research object. We try to develop a low-cost, practical and environment friendly non-cyanide copper electrolyte. Considering the phosphorous wastewater such as wastewater containing pyophosphate and HEDP is hard to treat, and considering the Cu⁺ is easy to form in the copper electrolyte containing -NH₂ complexing agent, this paper chooses citrate as the major complex agent, which can complexes well with cupric in the alkaline environment. With citrate as our research object, and we do the job of electrolyte developing and some testing.With our research, from an alkaline bath which is only containing citrate, cupric and alkali, we ofen get a multicolored copper coating. Adding boric acid, sodium gluconate or aminosulfonic acid can eliminate the multicolored copper coating, and make the coating on the Hull-trough testing pattern change regularly. The effect of eliminating multicolored coating through adding aminosulfonic acid or sodium gluconate is very obvious, and the efficiency is better than adding boric acid series. But adding excess sodium gluconate may give a bad effect to the coating. There is very few literatue systematically researchs on multicolored copper coating. Through literatue search, we find very few reports of adding aminosulfonic acid in copper eletroplating bath, and we did not find any report of the effect of amidosulphonic acid in copper eletroplating bath.The auxiliary complex agent FL can improve the quality of copper coating. The auxiliary complex agent changes the structure of the dimer Cu₂(OH)₂(H_-1Cit)₂^6-, which is dominant in our alkaline electrolyte. And the auxiliary complex agent also changes the electrochemical process of copper electrodeposition. Adding the mulripe electroplating addtives TJ can obvious increase cathode polarization, and make the copper electrodiposition slower. The adding of TJ make the coating brighter, and improve the adhesion with the substrate too. The main component of TJ has not found being used as electroplating addtive in the electroplating industry. Through our test, we found soya peptone can adsorb on the surface of cathode, and improve the quality of the coating, especially in the high current density zone. From the voltammetric curves, we find the electrode process is under electrochemistry control and diffusion control.Through the Hull-trough test, we determine a good formula for copper electroplating which based on citrate as the major complex agent. The formula and the elctroplating process conditions is copper(add to electrolyte by the cupric salt:Cu₂(OH)₂CO₃) 20g/L～30g/L, citric acid monohydrate 160g/L～200g/L, auxiliary complex agent FL 12g/L～24g/L, aminosulfonic acid 2g/L～6g/L, soya peptone 0.1g/L～0.2g/L, the mulripe electroplating addtives TJ 2g/L～3g/L, pH9.5, 30℃～40℃, current density of 0.1A/dm²～1.4A/dm².