Electroless Nickel Coating on Copper Parts
Copper is an excellent conductor but a rather soft metal which tarnishes easily and does not take solder well once it has oxidised. In order to use copper for components which are to be soldered later it is necessary to coat it properly.
Why Copper Gets Plated This Way
Copper parts are frequently plated in order to protect the copper against corrosion. It also provides a surface for subsequent soldering and protects the part against wear and abrasion. In terms of coating a copper part, an Electroless Nickel Coating is often used as it produces an even coating, ideal for items with complicated geometries such as recesses, threads and fine details. These types of articles would likely produce an uneven coating using conventional plating techniques as the electrical current would find it difficult to reach all areas.
Preparing Copper Before Plating
If copper is left prior to plating to be exposed to the atmosphere, it will quickly oxidise. Any oxide will prevent the nickel from bonding properly with the base metal. Therefore the part must be cleaned and etched prior to plating to remove any oxide. However, there is also a risk of immersion deposits forming. These occur when the copper has reacted with the plating bath to form a very thin layer of nickel on the surface of the part. This will not be strongly bonded and can start to flake off when the part is subject to normal use.
Why a Strike Step Matters
Bare copper is very reactive and in contact with nickel plating bath solutions can deposit nickel on the copper surface. This can give poor and patchy adhesion and flake off later in service. This type of damage is not always visible prior to use. A strike or catalyst coat is needed to give the nickel a surface to bond to.
Getting the Thickness Right
Thick nickel coatings provide excellent wear resistance, but also have the negative effect of increasing weight. Also important is the influence on the parts’ electrical and thermal conductivity. Most copper parts are coated with a layer of nickel in the range of 5 – 25 microns.
Typical Copper Parts That Get Coated
Other typical applications of plated copper are connectors of RF-cables, waveguides, heat sinks, contacts and busbars. Parts plated with metal plating solutions need to be handled with care. If a plating line is to be set up or is operated by someone, they should seek information from documented sources on safe handling of chemicals used in metal plating.
Looking After Coated Parts Afterwards
Remember that coated parts must be treated with care after plating and that damage to the coating will expose the copper beneath. In addition, consideration must be given to soldering of plated parts, and the plated finish/thickness must not interfere with joint solderability.
As long as you select a suitable thickness and have the part prepared for plating correctly then it should last for years to come and give the user of the part all the benefits of using copper in the first place.
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