QLQ zinc alloy surface finishing equipment and process QLQ zinc alloy surface finishing equipment and process

Professional Zinc Alloy Surface Finishing Solutions

Industrial Gold Plating

Industrial Gold Plating — Connectors, PCB Gold Fingers & Precision Contacts

Functional gold for electronics: hard gold vs. soft gold, selective plating, barrel vs. rack, and the critical salt spray / contact resistance specifications that govern electronic reliability.

Why Gold in Electronics?

Gold does not oxidize. One atomic layer of oxide on a copper contact = a failed connection. Gold guarantees < 10 mΩ contact resistance for the life of the product.

Gold Fingers

PCB edge connectors

Connector Pins

Miniature contacts

Barrel vs Rack

Choice by part geometry

Salt Spray

24–96 h requirement

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The Industrial Gold Plating Process

From base metal prep through hard/soft gold deposition to final QC

1Gold Thickness Selection (0.5–5.0 μm)

Contact resistance and wear life scale with thickness. 0.5–1.0 μm: low-cycle connectors (1K–5K mate cycles). 2.0–5.0 μm: high-reliability (10K+ cycles, MIL-spec). IPC-4552 defines gold finger thickness standards.

Key Parameters
Low-cycle: 0.5–1.0 μm
Standard: 1.0–2.0 μm
High-reliability: 2.0–5.0 μm
Standard: IPC-4552

2Hard Gold (Cobalt / Nickel Hardened)

Gold alloyed with 0.1–0.5% Co or Ni. Hardness 150–250 HV vs. 50–90 HV for soft gold. Much better wear resistance for repeated mating. Preferred for connector pins, edge card fingers, and relay contacts.

Key Parameters
Hardness: 150–250 HV
Alloy: Au + 0.1–0.5% Co/Ni
Wear: Excellent — 10K+ cycles
Best for: Connectors, relays

3Soft Gold (Pure, 99.9% Au)

Pure gold for thermal compression bonding and soldering. Soft gold deforms under thermode pressure for void-free bonds. Lower hardness (50–90 HV) but superior weldability. Used for semiconductor die attach and wire bonding.

Key Parameters
Purity: 99.9% Au
Hardness: 50–90 HV
Best for: Die attach, wire bonding
Thickness: 0.5–3.0 μm

4Barrel vs. Rack Plating Selection

Barrel plating (small parts in rotating drum): efficient for mass-production connector pins, terminals, and stampings. Rack plating (fixtured): for PCB panels, odd-shaped housings, and parts needing selective plating.

Key Parameters
Barrel: Small loose parts, 1000s per load
Rack: PCB panels, selective plating
Selective: Rack with masked areas
Cost: Barrel < Rack for small parts
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Hard Gold vs. Soft Gold — Selection Guide

Both have their place in electronics manufacturing

PropertyHard Gold (Co/Ni)Soft Gold (Pure)
Hardness (HV)150–25050–90
Wear cycles10,000–50,000+500–2,000
Contact resistance< 10 mΩ< 5 mΩ
SolderabilityGood (with flux)Excellent (no flux)
Wire bondingPossible (high force)Standard (low force)
Thickness typical1.0–5.0 μm0.5–3.0 μm
Cost (per μm)Same as soft + alloySame

📌 Industrial Gold Plating Quick Reference

Thickness range0.5–5.0 μm
Hard gold (Co/Ni)150–250 HV
Soft gold (pure)50–90 HV
Contact resistance< 10 mΩ
Barrel max loadup to 15 kg
IPC standardIPC-4552
💡 Selective gold plating saves costYou don't need gold on the whole part. Selective rack plating (masked areas) plates gold only on contact surfaces — the rest stays nickel or tin. Typical saving: 40–60% of gold cost. We offer precision mask tooling for custom patterns.

FAQ

What is the minimum gold thickness for reliable connectors?
IPC-4552 specifies minimum 0.5 μm for gold fingers (Class 1) and 1.27 μm for Class 3 (high-reliability). For connector pins with 10K+ mate cycles, we recommend 2.0–3.0 μm hard gold.
Can you plate gold on stainless steel contacts?
Yes — stainless steel needs an intermediate nickel strike to activate the surface before gold. Without it, gold adhesion on stainless is unreliable. Our process: Wood's nickel strike → sulfamate Ni → hard gold.
Barrel vs. rack — which gives better gold thickness distribution?
Rack plating gives ±10% thickness uniformity across the part. Barrel plating is ±25–30% due to random contact. For critical contact resistance (e.g. 0.5 μm minimum requirement), rack or selective rack is mandatory.
How is contact resistance tested?
4-wire Kelvin method at 10–100 mA, 20 mV max open circuit. Typical spec: < 10 mΩ initial, < 20 mΩ after environmental testing (heat/humidity). We test per batch on a Caltech CR-100 or equivalent.
What salt spray rating does industrial gold plating achieve?
Gold itself is inert. The corrosion resistance comes from the nickel underlayer. Our standard process: 2 μm Ni + 1 μm Au passes 48 h neutral salt spray. With thicker Ni (5 μm): 96+ h. MIL-G-45204 Type II requires 24 h minimum.

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Industrial vs decorative gold

AspectDecorativeIndustrial
Thickness0.03-0.3 um0.5-5 um
AlloySoft 24K lookHard gold with cobalt or nickel
RequirementColour and appearanceContact resistance, wear life
TestVisual against chipThickness, porosity, contact resistance

FAQ

When is hard gold required?

Wherever the surface sees wiping or mating cycles - connectors, slip rings, contact pads. Soft gold wears through quickly.

How is porosity checked?

Nitric acid vapour or electrographic test on a sample per lot.