Electroless Nickel Plating

Electroless nickel, EN, plating utilizes a chemical reaction to deposit a nickel phosphorous alloy onto a variety of substrates. This is a different process than electrolytic plating in that it is an autocatalytic reaction. Deposition occurs in electroless nickel chemical baths which contain a solution of metal ions, chelates, reducing and complexing agents, and stabilizers. Since the process is a chemical reaction, the resulting thickness and coverage of the part is more easily controlled, as long as the surface is sufficiently prepared to allow for the EN adhesion. “Electroless nickel is preferred for irregularly shaped parts when a uniform thickness is required (NASA-STD-6012).” In addition, EN is capable of deposing uniformly on internal and external configurations regardless of the complexity of the shape.

The electroless nickel baths used at Electro-spec vary based on the amount of phosphorus in the deposit. The concentration of phosphorus can determine the mechanical, thermal and electrical properties of the plated deposit. Below is a table which summarizes some of the key properties of the electroless nickel plating solutions offered at Electro-Spec;

EN Type Hardness As Plated
(HK100)		 Thermal
Conductivity
(CAL/CM/SEC/°C)		 Tensile Strength
(MPa)		 Electrical Resistivity
(mOHM-CM)
High Phosphorus 450 - 525 0.01 650 - 900 75 - 110
Mid Phosphorus 500 - 600 0.012 800 - 1000 40 - 70

The two EN deposits offered at Electro-spec will be suitable for different applications:

  • Medium Phosphorus alloys provide high-speed deposit rates and appealing bright or semi-bring finishes.
  • High Phosphorus alloys provide superior corrosion protection and are most resistant to harsh environments.

 

Resulting Properties
  • Corrosion Resistance
  • Wear Resistance (due to a hardened deposit)
  • Uniformity in Thickness of Deposits
  • High Solderabilty and Weldability of Parts
  • Bright and Reflective Finish (depending on substrate finished)
Applications
  • Aerospace Components
  • Electrical Equipment
  • Packaging & Handling Machinery
  • Chemical Manufacturing and Transport Equipment
  • Molds & Dies
  • Food Service Equipment
  • Plastics Manufacturing Equipment
  • Oil & Gas Components
  • Printing Industry EquipmentAutomotive Components

Electroless nickel plating follows industry standards ASTM B733-97, ASM 2404E, ASM 2404B, and MIL-C-26074E.

Electrolytic Nickel Plating

Electrolytic nickel plating involves the use of a flow of current and a complex of ions in solution to allow a transfer of electrons from the power supply to the base metal. The transfer of electrons causes a charge to be present across the bath and creates the attraction for the deposition of the metal onto the substrate. This plating is different than the electroless plating because it is both an electrical and chemical process. Electrolytic nickel baths utilize different ions and additives to achieve the properties of the deposit which are requested by the customer.

Electroless nickel plating offers the following advantages:

  • Ability to achieve high throwing power to allow for a uniform surface coating Superior resistance to a range of chemicals
  • Wear resistance and increase product life cycles
  • An alternative to pricey stainless steel when using a Nickel coated steel instead
  • Complex filtration methods are not needed
  • An aesthetically pleasing surface finish based on customer specifications
  • Increased corrosion resistance due to the application of a sacrificial coating
  • Electrolytic Nickel Plating follows industry standards QQ-C-320, ASTM B456, and AMS 2406.

One of the additives to a nickel plating bath is a brightener. The amount and type of brightener will result in varying deposit brightness:

  • Carrier brighteners, such as paratoluene sulfonamide and benzene sulphonic acid, contain sulfur to provide uniform grain structure of the nickel plating.
  • Leveler or second class brighteners, such as allyl sulfonic acid and formaldehyde chloral hydrate, produce bright deposits (when used with carrier brighteners)
  • Inorganic brighteners, such as cobalt and zinc, provide a coating with added luster

Types of Nickel baths used include:

  • Nickel Sulfamate, used typically as an underplate for tin, gold, palladium, or silver deposits. Ideal for solderability applications and offers good ductility if forming is needed after plating.
  • Nickel Chloride, the chloride helps with anode corrosion and brighness/leveling ability.

Nickel Plating follows industry standards AMS-QQ-N-290, ASTM B689, QQ-N-290, and MIL-P-81728.