Electroless Nickel Plating

 Electroless nickel plating is an auto-catalytic reaction used to deposit a coating of nickel on a substrate. Unlike electroplating, it is not necessary to pass an electric current through the solution to form a deposit. This plating technique is to prevent corrosion and wear. EN techniques can also be used to manufacture composite coatings by suspending powder in the bath.

Electroless nickel plating has several advantages versus electroplating. Free from flux-density and power supply issues, it provides an even deposit regardless of workpiece geometry, and with the proper pre-plate catalyst, can deposit on non-conductive surface.

Advantages of EN
Hard deposits
Very uniform thickness  
Superior corrosion protection
Lower porosity
Non-magnetic
Less prone to staining
Pit-free deposits

Applications
The most common form of Electroless nickel plating produces a nickel phosphorus alloy coating. The phosphorus content in electroless nickel coatings can range from 2% to 13%[1] It is commonly used in engineering coating applications where wear resistance, hardness and corrosion protection are required. Applications include oil field valves, rotors, drive shafts, paper handling equipment, fuel rails, optical surfaces for diamond turning, door knobs, kitchen utensils, bathroom fixtures, electrical/mechanical tools and office equipment. It is also commonly used as a coating in electronics printed circuit board manufacturing, typically with an overlay of gold to prevent corrosion. This process is known by the acronym ENIG, which stands for "Electroless Nickel, Immersion Gold".

Due to the high hardness of the coating it can be used to salvage worn parts. Coatings of .001" to .004" can be applied and machined back to final dimensions. Its uniform deposition profile mean it can be applied to complex components not readily suited to other hard wearing coatings like hard chromium.

It is also used extensively in the manufacture of hard disk drives, as the final top coat on the aluminium disks (or platters), after the magnetic alloy (usually an alloy of Cobalt-Platinum-Chromium, CoPtCr) is deposited. It is used here for its wear resistance to protect the underlying magnetic layer (media layer) from damage should the read / write head lose its cushion of air, and contact the surface.

Its use in the automotive industry for wear resistance has increased significantly, however it is important to recognise that only EOLVD or RoHS compliant process types (free from heavy metal stabilizers) may be used for these applications.

Specifications
AMS-2404
AMS-C-26074
ASTM B-733
ASTM-B-656
MIL-DTL-32119