Technical Basics: Electroless Nickel Plating Bath

Electroless plating is a method of obtaining a metal alloy by using an oxidation-reduction reaction on a plated part having a catalytic surface in the absence of electricity. It is a newly developed new technology. The United States, Britain, Japan, Germany and other countries, their industrial output value is increasing at a rate of 15% per year. It is widely used in machinery, electronics, plastics, molds, metallurgy, petrochemicals, ceramics, hydraulics, aerospace and other industrial sectors, and is one of the most promising new technologies. Electroless nickel plating bath is described as follows:

1. The composition of the bath:

The composition of electroless nickel plating solution includes:

Nickel ions, complexing agents, buffers, accelerators, reducing agents, stabilizers, wetting agents, brighteners, stress relieving agents, pH regulators, etc.

(1) Nickel ion: It is the source of plating metal, mainly including nickel sulfate, nickel chloride, nickel acetate, and nickel sulfonate.

(2) Complexing agent: Nickel complex or chelate is formed to prevent excessive nickel ion concentration, thereby stabilizing the solution and preventing precipitation of nickel phosphite. It also acts as a pH buffer. For example, glycolic acid (glycolic acid), aminoacetic acid, lactic acid, hydroxysuccinic acid, citric acid, alcoholic acid and salts thereof.

(3) Buffer: Long-term control of pH makes it stable. Such as acetic acid, sodium acetate, boric acid and so on.

(4) Accelerator: Activation of hypophosphite ions accelerates the deposition reaction. For example, some 1- and 2-carboxylic acid anions, fluorides, borate, etc.

(5) Reducing agents: There are mainly sodium hypophosphite, sodium borohydride, dimethylamine borane, diethylamine borane, hydrazine, and the like.

(6) Stabilizer: Contains the catalytically active core by adsorption to prevent decomposition of the plating solution. Such as Pb, Sn, molybdenum, Cd or cesium ions, urine and so on.

(7) Wetting agent (surfactant): Improves the wettability of the surface of the plated part, such as ionic or non-ionic surfactants.

(8) Brightener: Enhances the brightness of the chemical nickel layer and enhances the decorative effect. There are mainly butynediols, propargyl alcohols,,,, and the like.

(9) Stress relieving agent: reduce the internal stress (tensile stress) of the coating and increase the binding force between the coating and the substrate. Such as saccharin.

(10) PH adjuster: continuously adjust the PH value. Such as H2SO4, HCl, NaOH, ammonia and so on.

2. Some acid, alkaline chemical nickel bath examples:

(1) Acid bath solution:

Nickel sulfate: 23 g/l, sodium hypophosphite: 18 g/l, lactic acid: 20 g/l

Malic acid: 15g/l, Pb: 1mg/l, PH: 5.2 (NaOH regulation)

Temperature: 85-90°C.

(2) Alkaline bath:

Nickel sulfate: 32g/l; sodium hypophosphite: 15g/l; sodium citrate: 84g/l;

Ammonium chloride: 50g/l; NH4OH: 60g/l; pH: 9.3

Temperature: 89°C.

Posted on