Gold Plating for Electronics — Contacts and Connectors

Gold is the only practical contact metal that stays electrically clean forever. That single fact explains why the electronics industry — from consumer USB connectors to satellite RF assemblies — deposits more gold than any other market. This deep-dive covers the electrical engineering behind gold plating for electronics: contact physics, solderability, wire bonding, and how to specify the deposit.

Why is gold used in electronics at all?

Gold is used because it forms no oxide or sulfide film, so a gold contact surface presents bare metal to its mate every single time, keeping contact resistance low and stable for the life of the device. Every alternative — copper, silver, tin, nickel — grows an insulating or semi-conducting film that degrades the connection.

The numbers behind the choice: gold's bulk conductivity is about 70 percent of copper's, which sounds unimpressive until you realize bulk conductivity is not the problem in a connector — the interface is. A tarnished tin or silver film can add milliohms to ohms of unstable resistance; a gold interface holds steady in the low-milliohm range across years, humidity, and temperature cycling. Gold is also immune to fretting corrosion oxide buildup that plagues tin contacts under vibration, which is why anything that must work after a decade in the field — avionics, medical, industrial control — specifies gold.

How does gold plating improve connector reliability?

A hard gold layer over nickel gives a connector three things: stable low contact resistance, wear life across hundreds or thousands of mating cycles, and corrosion protection at the contact interface. The standard engineered stack is copper alloy, then 50 to 200 microinches of nickel, then 30 to 50 microinches of cobalt-hardened gold.

Each layer has a job. The copper alloy spring provides contact normal force. The nickel underplate blocks copper diffusion into the gold, supports the gold against the mating wipe, and stops corrosion creep at pores — the mechanics are detailed in our nickel underplating guide. The hard gold (Type II, 130 to 200 Knoop) takes the sliding wear. Durability scales with thickness: light-duty consumer connectors run 10 to 15 microinches, standard industrial contacts 30, and high-cycle or high-reliability designs 50 and up, per MIL-G-45204 and ASTM B488 Class callouts.

What role does gold play on printed circuit boards?

On PCBs, gold appears in two distinct forms: thin immersion gold (ENIG) that protects solderable pads, and thick electrolytic hard gold on edge connectors and keypads that must survive repeated contact. Confusing the two is a classic specification error.

• ENIG (electroless nickel, immersion gold) deposits 2 to 8 microinches of gold over electroless nickel. Its job is purely to keep the nickel solderable until assembly; the gold dissolves into the solder joint at reflow.
• Electrolytic hard gold ("gold fingers") is plated to 15 to 50 microinches on card-edge contacts, test points, and membrane switch pads — surfaces that mate and wear rather than get soldered.

A pad that will be soldered needs only ENIG-level gold; a surface that will slide needs hard gold thickness. Boards often carry both, with selective plating separating the areas.

Is gold plating solderable and wire-bondable?

Yes — clean gold is one of the most solderable and bondable surfaces in electronics, but purity and thickness rules apply. Soft, high-purity gold (Type III, 99.9 percent) is required for gold wire bonding, while soldering to gold requires managing the gold's dissolution into the joint.

For soldering, the gold layer dissolves into molten solder almost instantly. In thin layers this is by design (ENIG), but gold content above roughly 3 to 5 percent of the joint embrittles tin-lead and tin-based solders by forming AuSn4 intermetallics — which is why very thick gold is stripped or tinned before soldering in high-reliability assembly. For thermosonic gold wire bonding, the pad wants 30 to 50 microinches or more of soft Type III gold; the cobalt in hard gold poisons bond formation. This is why semiconductor packaging and hybrid microelectronics specify soft gold while connector manufacturers specify hard — same element, different deposit.

What about RF, microwave, and high-frequency applications?

At high frequencies, current flows only in the outer skin of a conductor — so the plated surface effectively is the conductor, and gold's conductivity plus permanence make it the standard finish for RF hardware. At 10 GHz, the skin depth in gold is under 1 micron (about 31 microinches).

That means an RF cavity, waveguide flange, or coaxial pin plated with 50 to 100 microinches of gold carries virtually all the signal in gold, with insertion loss that never degrades because the surface never tarnishes. One design note: nickel is ferromagnetic and lossy at microwave frequencies, so RF stacks sometimes replace or minimize the nickel underplate on critical surfaces — a detail to resolve with your plating lab at quoting time.

How should you specify gold plating for an electronic part?

Specify five things: deposit type (hard vs soft), purity Type per ASTM B488, thickness Class on the significant surface, the nickel underplate, and any selective or masking requirements. A complete callout looks like "ASTM B488, Type II, Code C, Class 1, over 100 microinches low-stress nickel, contact area only."

Common recipes:

• Separable contacts: Type II hard gold, 30 to 50 microinches over nickel
• Wire-bond pads: Type III soft gold, 50 microinches minimum over nickel
• RF surfaces: 50 to 100 microinches 24K gold, underplate per electrical review
• Bus bars and grounding hardware: 20 to 50 microinches per corrosion environment

For the standards matrix behind these callouts, see MIL-SPEC gold plating standards; for who typically needs them, our electronics industry page covers connector, PCB, and instrument work.

Where can you get electronics-grade gold plating done?

Electronics work demands a lab with XRF thickness verification, controlled bath chemistry, and selective plating capability — not a decorative shop with a gold tank. Our Vista, CA lab plates connectors, bus bars, RF components, and PCB hardware to commercial and MIL-type callouts, with high-volume capacity and fast turnaround for OEMs from San Diego to Los Angeles.

Have contacts, connectors, or RF parts that need gold? Send photos and your spec — request a free quote or call (760) 458-3299. $500 minimum, $100 per square inch, certification available on request.