Study Of Non-cyanide Copper Plating Process Using Hydantoin As Complexing Agent

Copper has good thermal conductivity, electrical conductivity and ductility, always worked as intermediate coating of gold, silver, nickel and other metals, and excellent coating to prevent carburizing and nitriding. Electroplated copper is widely used in the field of printed circuit boards, its application in the through-hole plating of printed circuit board greatly improves the integration of PCB. Cyanide copper plating system can plate directly in iron and steel, zinc alloy surface without generating displacement plating, and its plating is bright and dense. However, cyanide is highly toxic, so it’s urgent to develop an alternative system of cyanide copper plating.This paper compares different auxiliary complexing agent, determines the potassium pyrophosphate worked as auxiliary complexing agent in the DMH and potassium pyrophosphate complex system of non-cyanide copper plating process. The effect on the stability of the bath, the appearance of the co ating, the coating microstructure, current efficiency of the bath components, process conditions was studied by single factor experiment. The results show that the concentration of main salt, potassium pyrophosphate and temperature, stirring intensity have a great impact on the appearance of the coating, current efficiency, the upper limit of the current density. Optimized bath composition and process to read as follows: Copper sulfate 25 g·L^-1, DMH 100 g·L^-1, potassium pyrophosphate 60 g·L^-1, potassium carbonate 30 90 g·L^-1, p H is 9 10, temperature is 50 ℃, stirring rate is 600 rpm, current density is 1.5 5 A·dm-2. The appearance of the coating obtained under these condition is smooth, bright, dense. Additive could be used in the present system is selected by Hull tank experiment. The coating appearance is improved significantly, the range of light density is wider, but current efficiency decreased with the addition of additive.Experiments show that the stability, dispersion capacity, coverage ability of the bath are excellent, current efficiency is greater than 80%, the electrodeposition speed reach 32 μm·h^-1. The coating has an excellent adhesion with substrate, porosity is less and continue to decrease with the extension of plating time. The microstructure of the coating is characterized by SEM, shows that grains are very fine. The electrodeposition process and the effect on it with potassium pyrophosphate and additive by cathodic polarization curves, cyclic voltammetry and other electrochemical test. The results show that the electrodeposition process of copper ions in DMH and potassium pyrophosphate complex system is diffusion controlled irreversible process, cathode transfer coefficient α is 0.8548, the diffusion coefficient of Cu²⁺ is 3.79 × 10-9 cm2·s^-1 in bath contains 25 g·L^-1 Cu²⁺. The addition of potassium pyrophosphate increases the cathodic polarization, suppresses the hydrogen evolution reaction, improves the current efficiency. The addition of additive decreases the cathodic polarization, therefore the additive needs further exploration.