Plating Q&A: Copper Buffing Prior to Nickel-Chrome Plating

What are some options to reduce this plating time and increase my throughput?

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Q. I am currently electroplating metal parts that get copper buffed prior to nickel-chrome plating. I have to reduce my amperage, 10–15 amps per square foot, so I don’t burn the “high current density” areas in my acid copper plating bath. I am also experiencing low thickness in some areas as well. This is extending my immersion time to almost two hours. I have ample time in my nickel baths, which are currently running 50 percent utilization with the long acid copper immersion times. What are some options to reduce this plating time and increase my throughput?

A. This is not an easy answer because there are several factors to consider. Burning typically takes place when the solution temperature is cold, the chloride levels are low, sulfuric acid levels are low, the anode to cathode distance is short and the part design has some difficult geometry. A typical acid copper plating solution is operated between 25–50 amps per square foot of surface area. Since you are running much lower than this range, I would suggest some potential resolutions:

Part Shielding

Agitation Enhancement

Placement of Anodes

Chemistry Modifications

Part shielding can be successful, but requires some trial and error. Distance from the cathode to the anode may be a restriction when using shields.

Agitation Enhancement such as higher air, cathode agitation and eductors can all help replenish the cathode film with ions and organic additives to reduce burning. There are limitations to this method with regards to hydraulic actions and tank size/design.

The anode placement may be another option if your tank can accommodate the added spacing. Typically you will find that larger anode to cathode distance will help to reduce variation I the metal distribution. However, this may also require additional voltage from your rectifier.

Maybe the easiest thing to try first is a chemistry adjustment. 

Inorganic Additives and Their Functions

Copper sulfate—provides the copper ions necessary to reduce at the cathode to copper metal

Sulfuric acid—enhances solution conductivity and prevents the formation of cuprous oxide at the cathode surface, which causes roughness. Higher sulfuric acid concentrations enable higher current densities while plating.

Chloride ion—assists with anode dissolution and grain refinement. The cathode will “burn” if this level is too low. If the chloride level is too high, >150 mg/l, then the formation of cuprous chloride at the anode surface restricts the dissolution of the anode and increases the required voltage necessary to achieve amperage. This reduces the overall efficiency of the bath and can be seen easily as a white film on the copper anodes.

Organic Additives

Grain refiners—typically improve the deposit with regards to overall finish.

Wetting agents—assist with preventing burning

Leveler—assist with overall deposit leveling and low current brightness

I have seen where certain types of dye-based acid copper solutions with higher sulfuric acid content are able to run at elevated temperatures. These two factors enable better current distribution and reduced burning particularly in the high current density areas. Additives that are designed to run at elevated temperatures will not deplete as quickly as those that are typically used in acid copper processes. This is a viable option with no capital investment to increase throughput. At one location, they were able to reduce the overall acid copper immersion time by 50 percent while improving the deposit and eliminated burning.

Originally published in the January 2016 issue.

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