Describes the electroless plating process (electroless plating of Nickel over copper), mechanism and reactions. Advantages of electroless plating over electroplating. Applications. It describes the plating bath solution and the function of each component is also explained. The reactions involved in the process is also explained.
Electroless plating, also known as chemical plating or autocatalytic plating. Electroless plating of Ni is explained in detail with all the ingredients of the electrolytic bath solutions and all steps involved.
Electroless plating/Electroless deposition
You will be able to define electroless plating.
You will be able to describe the process of electroless plating with an example.
You will be able to list out the objectives of electroless plating.
You will be able to mention the role of each reagent used in the electroless plating bath solution.
You will be able to enumerate the advantages of this method.
You will be able to compare this method with electroplating.
Electroless plating is a process of coating a superior metal over the base metal (inferior metal) by catalytic reduction using a reducing agent in the electrolyte containing the soluble salt of the coating metal without the use of electricity.
Objectives of electroless plating
To improve the corrosion resistance of the metal.
e.g chromium and nickel coated components in automotive applications.
For the aesthetic appearance of the metals/reduce the cost.
e.g gold covering ornaments.
To increase the thermal conductivity of the metal.
e.g copper bottomed vessels.
To increase the tensile strength of the metals.
e.g aluminum (Al) coatings.
Electroless plating bath solution
Soluble salt of coating metal – gets reduced and deposited on the surface of the article eg. sulphates and chloride salts
Reducing agent – gets oxidised by reducing the metal ions eg. Formaldehyde, hypophosphites
Complexing agent– improves the quality of the deposit eg. citrates, phosphates and succinates.
Exhaltant –enhances the plating rate. eg. fluorides, glycinates and succinates.
Stabilizer – prevents the decomposition of plating bath solution eg. Thiourea, cations of lead, Calcium, Thalium
Buffer – controls the pH and to obtain thin and uniform plating. eg. Sodium acetate, sodium hydroxide and rochelle salt
Electroless plating bath solution for Nickel
Soluble salt of coating metal NiCl2.6H2O
Reducing agent sodium hypophosphite (NaH2PO2.H2O)
Complexing agent and exhaltant sodium succinate
Buffer sodium acetate
pH 6.5 to 6.7 (Adjusted with NaOH & HCl)
Temperature 70 to 72 o C
Time to get 5 to 6 microns of Nickel 25 to 30 minutes
on Copper
Anodic reaction
The reducing agent gets oxidized
Cathodic reaction
Ni2+ ions gets reduced to Ni and gets deposited on the article
Advantages of electroless plating
Why Electroless plating is superior to electroplating?
Uniform deposition even in complex and intricate shapes such as recesses, bents, sharp edges, cleavages and blind holes.
High corrosion resistance, as it forms a less porous coating.
Does not require electricity.
Deposits are hard.
Metallic anodes are not required, hence reduces cost.
Can be plated even on insulators such as plastics, semiconductors, glasses, ceramics etc.
Applications of electroless plating
Food Service Industry: molds and food processing machine parts.
Electronic appliances : heat sinks, semiconductor packages, microwave components and battery components
Oil & Gas Industry: valves, heat exchangers, pumps balls and plugs to barrels, pipe fittings.
Automotive Industry:  brake pistons, gears, fuel injection systems, aluminum fuel filter, sand bleed valves, car parts like shock absorbers, cylinders, etc.
Aerospace Industry: valves, pumps, engine assemblies, landing gears, turbine blades, pistons, rocket components.
Chemical Industry: pumps, mixing blades, heat exchangers, filter units, valves and flanges etc.
Plastics and Textiles: Molds, dies, machine parts, spinnerets, extruders etc.