ELECTRONIC SURFACE TREATMENT MATERIAL SUPPLIER

Full Detailed Process Flow

1. Pre‑cleaning: Alkaline degreasing and ultrasonic cleaning remove oil, grease and fingerprints from copper substrate. Followed by cascade DI‑water rinsing.
2. Acid activation: Dilute sulphuric acid pickling removes copper surface oxide and tarnish, exposing active pure‑copper surface. Rinse thoroughly.
3. Nickel barrier plating: Deposit controlled‑thickness nickel underlayer. Good agitation ensures uniform thickness across complex geometry.
4. Intermediate rinse: Multi‑stage DI‑water rinse to drag‑out nickel bath chemicals and avoid contamination of tin plating tank.
5. Tin electroplating: Deposit bright or matte tin topcoat according to component specification. Strictly control current density to prevent tin burning or uneven thickness.
6. Post‑rinse & passivation: DI‑water cascade rinse, followed by weak chromate‑free passivation for anti‑tarnish protection of tin surface.
7. Drying: Hot‑air low‑temperature drying (60‑70 °C). Avoid over‑heating to prevent premature inter‑metallic growth.
8. Inspection: Verify coating thickness, adhesion, surface appearance, solderability and contact resistance; whisker risk assessment for 

Nickel‑tin on copper is a multi‑layer electroplating system widely used for copper and copper‑alloy substrates for connectors, busbars, terminal pins and electronic hardware. The standard stack is copper substrate → nickel barrier underlayer → bright/matte tin top layer. A nickel underlayer is electroplated first, followed by electrolytic tin plating. This layered architecture blocks copper‑tin inter‑diffusion, delivers solderability, low contact resistance, wear performance and corrosion protection without sacrificing base‑metal conductivity.
Core Functions

1. Diffusion barrier function (nickel underlayer) Nickel acts as a dense barrier layer that suppresses mutual diffusion between copper and tin. It slows the growth of brittle Cu‑Sn intermetallic compounds and greatly reduces tin whisker risk during long‑term storage and thermal cycling, preventing short‑circuit failure in electronic assembliesPMC.

1. Corrosion protection Nickel provides mechanical strength and barrier‑type corrosion resistance; the outer tin layer sacrificially protects nickel and copper. The combined stack improves salt‑spray performance against humidity, sulphide and atmospheric oxidation, avoiding copper tarnish and green‑rust formation.

1. Solderable surface (tin topcoat) Pure tin surface offers excellent solder wetting ability for wave soldering, reflow soldering and crimp connections, supporting mass electronic assembly. It maintains stable low contact resistance for electrical signal and power transmission.

1. Mechanical performance improvement Nickel increases hardness and wear resistance for mating cycles in connectors; soft tin supplies ductility for contact deformation under clamping pressure. The composite balances wear resistance and contact compliance.

1. Surface defect covering The double‑layer plating conceals minor copper surface scratches, tool marks and texture variations, delivering uniform appearance for decorative and functional parts.

Typical Bath Formulations & Operating Parameters

1. Nickel Under‑layer (Watts nickel, barrier layer)

• Nickel sulphate: 220‑280 g/L
• Nickel chloride: 40‑60 g/L
• Boric acid: 30‑45 g/L (pH buffer)
• Brightener / leveller / stress‑reducer: proprietary trace additives
• Operating: pH 3.8‑4.8; temperature 50‑60 °C; current density 2‑5 A/dm²; air agitation
• Thickness specification: 1‑3 μm for electronic connectors; 3‑8 μm for busbar heavy‑duty applications.

2. Bright Acid Tin Top‑layer (sulphate‑based)

• Stannous sulphate: 40‑70 g/L
• Sulphuric acid: 120‑180 g/L (conductive medium, inhibits Sn⁴⁺ precipitation)
• Anti‑oxidant stabilizer for Sn²⁺
• Brightener, leveller and non‑ionic wetting agent
• Operating: temperature 15‑25 °C; current density 1‑4 A/dm²; moderate cathode movement
• Thickness specification: 1‑5 μm for most electronic components.

Note: For post‑plating reflow process, parts go through thermal reflow oven (230‑270 °C) to produce smooth reflowed tin surface with enhanced solderability.