Electroless Nickel Plating, also known as EN or E/Ni, can be plated over a wide variety of metals including aluminum, titanium, mild steels, stainless steel, hardened steel, copper, brass and zinc die-cast.
Electroless nickel provides :
Introduction
- Uniform coating on most complex,and/or Irregular surfaces
- Improves resistance to galling
- Provides a hard, wear resistant surface
- Electroless Nickel is an auto-catalytic chemical reduction coating requiring no electricity to process.
- The phosphorus content of the bath determines the hardness and corrosion resistance of the coating as well as the matte, semi-bright or bright finish.
- With the addition of a baking operation following the plating, hardness of coating is enhanced
Industry Standards of Electroless Nickel Plating
ASTM B733-97 ASM 2404E
ASM 2404B Mil-C-26074E
Corrosion Resistant
Because of its excellent corrosion resistance, nickel plating is used as deposited when the plated part is intended for a corrosive environment, such as brine, acids, etc. The plated part should not be hardened after coating because hardening significantly reduces its corrosion resistance
Electroless Nickel Plating Specifications
This report conforms to Aerospace Material Specification AMS 2404C for Electroless Nickel Plating
Quality Control
In addition to the surface cleaning and activation processes described above, there are several strict quality control requirements necessary during electroless nickel plating. The electroless nickel-plating process is more sensitive to variations than electrodeposited chrome plating in which fewer parameters must be as strictly controlled. It is essential to select a plating vendor with a high level of quality control to assure positive results when using the electroless nickel process
Properties
Electroless nickel plating has several properties, which change when the plating is heat -treated. It is important to select the proper plating condition to suit the application.
Recommended Plating Thickness
Generally, the most desirable plating thickness is from 0.0005 inch to 0.0008 inch (0,01 mm to 0,02 mm). Thicker plating could leave a wavy or rougher surface that might require refinishing
Purpose of Plating
Electroless nickel plating improves corrosion resistance, increases the surface hardness of the material, provides a uniform and dense coating, and, in many cases, maintains the same surface finish the material had before plating
Pretreatment
Before performing electroless nickel plating, the material to be plated must be cleaned by a series of chemicals, this is known as the pre-treatment process. Failure to remove unwanted “soils” from the part’s surface result in poor plating. Each pre-treatment chemical must be followed by water rinsing (normally two to three times) to remove chemicals that may adhere to the surface. De-greasing removes oils from surfaces, whereas acid cleaning removes scaling.
Activation is done with a weak acid etch, or nickel strike or, in the case of non-metallic substrate, a proprietary solution. After the plating process, plated materials must be finished with an anti-oxidation or anti-tarnish chemical such as trisodium phosphate or chromate, followed by water rinsing to prevent staining. The rinse object must then be completely dried or baked to obtain the full hardness of the plating film.
The pre-treatment required for the deposition of nickel and cobalt on a non-conductive surface usually consists of an initial surface preparation to render the substrate hydrophillic. Following this initial step, the surface is activated by a solution of a noble metal, e.g., palladium chloride. Silver nitrate is also used for activating ABS and other plastics. Electroless bath formation varies with the activator.
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%.[6] 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 as electroless nickel immersion gold.
Due to the high hardness of the coating it can be used to salvage worn parts. Coatings of 25 to 100 micrometres 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 a way of providing an atomically smooth coating to the aluminium disks, the magnetic layers are then deposited on top of this film, usually by sputtering and finishing with protective carbon and lubrication layers; these final two layers 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 End of Life Vehicles Directive or RoHS compliant process types (free from heavy metal stabilizers) may be used for these applications
Standards
AMS-2404 AMS-C-26074 ASTM B-733 ASTM-B-656 MIL-DTL-32119