Chemistry

Copper Electroplating



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Copper electroplating is the process of adding a thin layer of copper to a metal base part using an electric current.  Copper is often plated over other metals to improve electrical conductivity or appearance.  Due to the high cost of copper, many parts that were traditionally solid copper are now manufactured using a less expensive zinc base material and electroplated with copper.  Pennies currently in circulation in the United States have a zinc base and are plated with copper.

The electroplating process requires several components:

- A metal base component (cathode) that will be plated

- A copper anode.  The anode provides the copper ions that will be transferred to the outer surface of the cathode.

- A electrolytic solution to facilitate the electric current.  The solution contains metal salts and ions that help the copper ions leave the anode and move to the cathode.  Electrolytic solutions for electroplating often contain cyanide and can be dangerous if not handled and disposed of properly.

- A power supply and wiring.  A constant direct current is most often used for electroplating copper, but a cyclic process called "pulse plating" can also be used to allow for higher input currents while avoiding overheating the parts.

The part to be plated (cathode) is connected to the negative terminal of the power supply and immersed in the electrolytic solution.  The copper anode is connected to the positive terminal of the power supply and also immersed in the electrolytic solution near the cathode, but not touching it.

When the power supply is turned on, the current causes copper ions to leave the anode, dissolving into the electrolytic solution.  The ions are attracted to the cathode and bond to the outer surface of the part.  As the electroplating process continues, the anode is consumed.  The thickness of the copper coating on the cathode depends on the amount of current used and the amount of time the part remains in the solution.

The copper ions are most attracted to flat and convex features of the part being plated, so interior corners and concave features may have thinner plating.  The design of the part to be plated and the plating process itself can be tailored to minimize this effect.

Copper is often used as an intermediate layer between materials that do not actively plate well.  A very thin layer of copper, called a "strike" layer is often electroplated onto zinc parts that then receive a more substantial nickel coating.

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