Product Description and Features

Electroless nickel plating fundamentally involves depositing a nickel alloy coating through self-catalyzed redox reactions on the metal surface without the application of an external electric current.

1. Core Principle: Autocatalytic Reduction Reaction

Unlike electroplating, electroless plating requires no external power source or anode. Its driving force originates from the chemical energy within the solution. The fundamental principle involves two simultaneous reactions occurring on the workpiece surface:

Reduction reaction (cathodic reaction): Nickel ions (Ni²⁺) in the solution are reduced to metallic nickel by electrons supplied from a reducing agent (such as sodium hypophosphite) at the catalytic active surface.

Oxidation reaction (anodic reaction): The reducing agent (e.g., sodium hypophosphite NaH₂PO₂) is oxidized at the catalytic surface, releasing electrons.

The key point is "autocatalysis": The deposited nickel layer itself (typically containing phosphorus or boron) acts as a catalyst for subsequent reactions. This means that once the reaction begins, as long as the workpiece remains in contact with the solution and the solution composition and temperature are maintained, the deposition process will continuously proceed on the newly grown nickel layer, resulting in a uniform coating.

2. Formation of Alloy Coatings

Chemical nickel plating does not produce pure nickel but rather nickel alloys, most commonly nickel-phosphorus (Ni-P) alloys and nickel-boron (Ni-B) alloys.

Nickel-Phosphorus Alloy: When sodium hypophosphite is used as the reducing agent, some hypophosphite ions decompose and incorporate phosphorus atoms into the deposit.

Phosphorus Content: Classified by phosphorus content:

Low Phosphorus (1-3% P): High hardness, excellent wear resistance, strong alkali resistance.

Medium Phosphorus (6-9% P): Optimal overall performance, most widely used, with excellent corrosion resistance, weldability, and non-magnetic properties.

High-Phosphorus (10-12% P): Exceptional corrosion resistance, particularly against hydrochloric acid; non-magnetic coating.

Nickel-Boron Alloy: Uses sodium borohydride or dimethylamine borane as reducing agents. Produces higher coating hardness and superior wear resistance, but at a higher cost.

3. Technical Features

Excellent uniform plating capability: As long as the solution can contact and continuously renew itself, the coating thickness remains highly uniform across all surfaces without edge effects, making it ideal for complex shapes, parts with internal holes, and blind holes.

Unique coating properties: The coating is dense with low porosity, offering outstanding corrosion resistance and wear resistance.

No electrical current required: Non-metallic substrates (e.g., plastics, ceramics) can also undergo electroless nickel plating after appropriate activation treatment.

Process Requirements for Electroless Nickel Plating Line

The electroless nickel plating production line is a system with extremely stringent process control requirements. Its complete workflow and core requirements are as follows:

 Process Requirements for Electroless Nickel Plating (Core Control Points)

The stability of the electroless nickel plating bath solution is directly related to coating quality and requires precise control.

Plating Solution Composition and Maintenance:

Main salt: Nickel sulfate or nickel chloride, providing nickel ions.

Reducing agent: Sodium hypophosphite (most commonly used) or boron-based reducing agents.

Chelating Agent: One of the core components. Used to chelate nickel ions, prevent nickel hydroxide precipitation, stabilize the plating solution, and control deposition rate and phosphorus content. Commonly used are lactic acid, citric acid, malic acid, etc.

Buffering Agent: Stabilizes pH. Commonly used are boric acid, sodium acetate.

Stabilizer: Trace component. Inhibits spontaneous decomposition of the plating bath on catalytic impurities (e.g., solid particles). However, excess amounts can hinder normal deposition.

Accelerator: Increases deposition rate.

Maintenance Requirements:

Continuous Filtration: Must be continuously filtered 24 hours a day (typically 1-5 micron precision) to remove solid particles and prevent spontaneous decomposition of the plating bath.

Periodic Analysis: Regularly titrate and analyze nickel ion concentration, hypophosphite concentration, and pH. Replenish consumed chemicals accordingly.

Load Ratio: Strictly control the surface area of workpieces treated per unit volume of plating solution (dm²/L), typically between 0.5–1.5 dm²/L. Excessively high ratios cause solution instability; excessively low ratios are uneconomical.

Process Parameter Control:

Temperature: One of the most critical parameters. Typically maintained between 85-95°C. Temperature fluctuations must be controlled within ±2°C; otherwise, deposition rate, phosphorus content, and bath stability will be severely affected. Too low a temperature prevents reaction, while too high a temperature causes bath decomposition.

pH: Another most critical parameter. Monitored using a precision pH meter, it must be strictly maintained within the process range (typically 4.5-5.2 for acidic systems). pH affects deposition rate, phosphorus content, and coating stress. Adjust regularly using ammonia solution or dilute sodium hydroxide/dilute sulfuric acid.

Agitation: Employ gentle air agitation or mechanical stirring to ensure uniform composition and temperature. Promptly remove hydrogen gas generated on the workpiece surface to minimize pinholes.

Product Specifications

Scope of Application