Research On HEDP Bright Copper Plating And Chromium-free Passivation

The HEDP system copper plating bath has stable performance and long service life.It can directly obtain a good electroplating copper layer on the steel substrate,which is a promising non-cyanide copper plating system.At present,research reports on copper plating in HEDP systems mainly involve the selection of main salts,optimization of process conditions,electrochemical behavior of copper electrodeposition,etc.There are few reports on the dissolution mechanism of anode copper during HEDP copper plating;The copper coating obtained by the copper plating of the HEDP system is not bright enough,and the workpiece needs to be polished before acid bright copper plating;the passivation treatment of the copper plating mostly uses hexavalent chromate passivation.In this paper,the dissolution of copper anode in HEDP system was studied by cyclic voltammetry and steady-state polarization curves.It was found that there were five main stages in the process of copper anode dissolution:the formation of Cu₂O in low potential area,the normal dissolution of Cu²⁺,the concentration polarization blocking dissolution after electrode reaction,the formation of Cu（OH）₂ and Cu CO₃ in high potential area,and the oxygen precipitation.When the current density of HEDP copper plating system is high or low,it is not conducive to the normal dissolution of copper.The area ratio of anode and cathode should be well controlled in the practical application process.The dissolution rate of phosphor copper is slow,and the surface is easy to be passivated;the dissolution rate of electrolytic copper is fast,and it is easy to produce"copper powder",which affects the quality of cathode coating.Cold rolled red copper is more suitable as anode of copper plating in HEDP system.The effects of additives ATMP and H on the bright performance of copper plating in HEDP system were studied by Hull cell experiment,polarization curve,cyclic voltammetry curve and other methods.Hull cell experiments and cathodic polarization curves show that ATMP acts in the mid-to-high current density region and has the effect of increasing cathodic polarization and improving the brightness of the coating.Appropriate amount of additive H can increase the upper limit of the current density in the bright area,and obtain a full-bright coating on the Hull groove test piece.When the amount of additive H is more than 0.8 m L/L,the deposition potential of Cu²⁺can be negatively shifted from-1.0 V to-1.3 V,which greatly increases the overpotential during copper deposition.The cyclic voltammetry curve shows that the position and shape of the nucleation ring with the additive H is completely different from that without the additive H.The additive H will be adsorbed and reduced on the surface of the cathode,which has a large inhibitory effect on the electrodeposition process of copper.Addition of the additive H makes the grain size of Cu close to the nanometer size,and improves the microscopic flatness of the coating.A chromium free passivation process of copper plating layer with simple composition and good corrosion resistance was proposed by using the method of BTA and MBT.The passivation process of BTA+MBT was compared with that of hexavalent chromate by means of nitric acid drop test,saltwater immersion and electrochemistry.The experimental results show that the passivation film formed by BTA+MBT（60℃）passivation is complete and dense,and its corrosion resistance is close to that of hexavalent chromate passivation.XPS showed that the surface layer of passivation film was MBT-Cu（Ⅰ）and Cu₂O,and the inner layer of passivation film was BTA-Cu（Ⅰ）and MBT-Cu（Ⅰ）.BTA and MBT can promote the interface interaction,increase the corresponding film-forming ability,and make BTA and MBT penetrate deeper into the copper layer.