Electroless Nickel Plating

Electroless Nickel Plating, what is that? Electroless plating is an auto catalytic chemical technique used to deposit a layer of nickel phosphorous or nickel boron alloy on a solid work piece, such as metal or plastic. On this process is no need additional electric current because the electric charge is merging from the substance itself. The principle of work of this process is the present of reducing agent, for example hypophospite react with metal ions to deposit metal.

Electroless nickel plating often use in various type of parts to protect against wear and corrosion. Uniform deposit of nickel useful for hydraulic cylinders, worm feeds, gears, bellows, shafts, chain belts and other close filling components.

Nickel plating on subject can be doing in two kind of process, using electroplating method and can do by electroless nickel plating. For electroless nickel plating or coating then be classified in accordance with the thermal treatment applied:

• Class 1 = no subsequent heat treatment: A bake for hydrogen belittlement relief is not considered a heat treatment.
• Class 2 = using heat treated to obtain required hardness: this can be applied to all metals not affected by heating up to 260° C or above.
• Class 3 = by non heat-treatable, and use beryllium alloys to improve adhesion nickel plating deposit.
• Class 4 = heat-treatable, use aluminum alloy and heat applied to improve adhesion nickel deposit.

Quality of Plating Thickness

Beside divide into the class on the process do, electroless nickel plating also divide into the grade of coating thickness. There are three thickness class:

• Grade A = 0.127 mm
• Grade B = 0.254 mm
• Grade C = 0.381 mm

Hard Electroless Nickel Plating

If use alloy with low phosphorous, plating utilizes a unique bath providing coating hardness up to 60 Rockwell. This result can be similar with hard crome Hard, with the advantage of a uniform thickness inside complex configurations, as well as outside. Low contain of phosporous have excellent result and resistance to corrosive and high pH chemicals.

The quality of electroless nickel plating may not stronger as using Nickel electroplating, but electroless nickel plating will improves the quality of components. Tight manufacturing tolerance can be achieved as the electroles nickel is deposited evenly on the surface of the parts. It can be also used to improve the surface of a component so that it is back within the specific tolerance, and provide a surface that allows post finishes to be carried out effectively produce bright surface coating.

Some example product of Electroless Nickel Plating as on the picture below:

Electroless plating product

Reaction on Electroless Nickel Bath

Electroless nickel bath contain of nickel ions, reducing agent, complexant, neutralizer, buffer, stabilizer and brighteners.

The reation on bath as follows:

1) NiSO4 + H2O → Ni2+ + SO42 - + H2O
2) NaH2PO2 + H2O → Na+ + H2PO2- + H2O
3) Ni2+ + H2PO2- + H2O → Ni + H2PO3- + 2H+
4) H2PO2- + H2O → H2PO3- + H2 (by catalist)

Next articles:

• Electroplating Process Flow Diagram
• Electroplating service
• Nickel plating brighteners 

Bright Electroless Plating

To make a bright electroless plating can do by simple technique to process by immersion technique. Deposit metal can cover onto copper, brass, copper based alloy, gold and lead tin electroplate.

Description:
The process is based on the reduction characteristics of chelated tin in divalent state. Under certain condition, reduction process to pure tin occur readily. On this process use grain-refining agent, free of phosporus, is present as well as an activator and buffer for pH control. Bright electroless plating can use to provide corrosion protection to copper and lead tin electroplate, minimum plate thick about 25 millionths of an inch of tin deposit required.

Bright Electroless Tin is recommended to preserve solderability of printed boards, either copper or lead-tin electroplate. This is also use for plating electronic parts such as diodes or leads and for corrosion protection of die stampings and machined copper or brass parts.

Formula Use:
Prepare electroless plating solution use 5 lbs Tin Powder with one half gallon water and add 4 gallons water. Mix all material will dissolved at about 180 oF.

Yield:
Bright electroless Tin will deposit about 25 millionths of an inch over 100 sq ft of copper/gallon of plating solution.

Electroless Copper

Electroless copper is a coating process of copper with no electrical involved on this coating method. Electroless has been applied for coating to metal and non metal materials, but operator often exposed to formaldehyde and difficult to remove waste stream of this process, so they often seek other alternative of better process. The deficiency of this process is as follows:

• Use of formaldehyde as reducing agent.
• The process is unstable, requiring stabilizing additives to avoid copper precipitation.
• Many complex agents are non Environmental friendly, such as EDTA, are used.
• The large number of process and rinse tanks causes high water consumption.

There are four basic process of copper electroless; cleaning, activation, acceleration and deposition. Only micro etch, that is associated with sulfuric dip, and anti tarnish baths are likely to be non proprietary chemistries. Usually all shop purchase a series of proprietary chemistries from single vendor that use for several process bath line.





Cleaning.
To cleaning segment begins with a cleaner conditioner to remove organics and condition the hole barrels for the subsequent uptake of catalyst, followed by micro-etch step. Cleaner conditioner mostly consist of common alkaline solutions.

Activation and Acceleration.
Activation process is to make the metal surface active to be coated, for this process usually use hydrochloric acid and possibly tin or sodium chloride. The activation bath itself consists of hydrochloric acid and possibly tin or sodium chloride.

Copper Deposition.
Electroless copper bath can divided into two types. Heavy deposition baths and light deposition bath. Heavy deposition bath will produce copper coating for about 75 to 125 micro inches and light deposition bath will produce about 20 to 40 micro inches.

On the light deposition process must be followed by electrolytic copper plating immediately. The main constituent of electroless copper chemistry are sodium hydroxide, formaldehyde, EDTA and copper salt.