Plating Stamped Contacts: Gold, Tin and Nickel Where Each Belongs
Short answer: gold goes where the contact must stay reliable for tens of thousands of cycles at low voltage; tin goes where cost rules and the connection is made once or occasionally; nickel sits under both as the barrier that stops copper migrating to the surface. The three metals are not rivals — they are a stack, and the engineering is choosing the right thickness of each for the duty: contact force, cycles, temperature and environment.
A stamped contact made of brass or phosphor bronze works fine for a day. Bare copper alloys oxidize within weeks in air, and the oxide film is an insulator that turns a connector into a resistor or an open circuit. Plating exists to keep the mating interface conductive over the part's real life. Which metal, how thick, and where on the part — selective or full coverage — is a cost-versus-reliability decision you can make before ever sending the drawing.
What Each Metal Actually Does
Every plating metal has one job it does better than the others, and choosing by "what is the standard" instead of by mechanism is how connectors fail in the field.
| Plating | Primary job | Fails when |
|---|---|---|
| Gold (hard gold typical) | Low, stable contact resistance over many cycles | Cost, or used where tin would do |
| Tin (matte or bright) | Cheap solderable, low-cost stable surface | Fretting at low force, cold welding, creep |
| Nickel | Barrier + hard underlayer | Used alone on a critical low-voltage contact |
| Silver | Lowest resistance, high current | Tarnishes in sulfur air; needs force to break film |
| Palladium / palladium-nickel | Gold alternative for long-life dry circuits | Cost, special processes |
Takeaway: the mechanism matters more than the metal name. Gold and palladium are noble — they do not oxidize, so low-force, low-voltage circuits stay reliable. Tin protects by being sacrificial and is fine where mating force is high enough to break its oxide. Silver conducts superbly but tarnishes, which is why it is a power-contact metal, not a signal-contact metal.
Where Each Belongs
Application decides the plating more than preference does. A battery contact that mates once a year does not need gold. A connector pin rated for 10,000 insertions carrying 5 V logic signals cannot survive on tin alone. The table below is the practical map we use when reviewing drawings on the stamping terminals and contacts line.
| Application | Typical plating | Why |
|---|---|---|
| Battery contacts, low cost | Tin, 2–5 µm, or nickel | Few cycles, high force, cost-driven |
| Signal connector pins | Gold 0.1–0.76 µm over nickel | Low voltage, many cycles, no oxide allowed |
| Power terminals, crimp | Tin over nickel, 2–8 µm | Solderable, corrosion-resistant joint |
| Relay and switch contacts | Silver or gold flash over silver | Current-carrying with stable resistance |
| EMI spring fingers | Gold flash or tin over nickel | Wear plus corrosion on flexing contacts |
| High-temperature contacts | Nickel or palladium-nickel | Gold migrates/softens above ~150 °C use |
The takeaway column is the rule: cycle count and voltage decide nobility, current decides thickness, and temperature rules out the wrong choices. Specify plating by function per contact zone, not by "gold-plated everything."
Reading a Plating Spec
Plating thickness is stated in micrometres (µm) or microinches (µin), and the numbers are small — 0.76 µm gold is 30 µin and looks like nothing to the eye, yet it is a serious industrial spec. What the drawing must state: metal, thickness range, underplate, hardness grade, and which areas are plated if selective. A bare "gold plated" callout is a guess, and the factory will price the guess at the top of the range.
| Plating | Typical thickness | Typical underplate |
|---|---|---|
| Hard gold, connector grade | 0.1–0.76 µm (4–30 µin) | Nickel 1–3 µm |
| Tin, matte | 2–8 µm | Nickel 1–2 µm optional |
| Nickel alone | 1–5 µm | None |
| Silver | 2–10 µm | Nickel or copper flash |
| Palladium-nickel | 0.4–1.5 µm | Nickel 1–3 µm |
Takeaway: the underplate is not optional padding. Nickel stops copper and zinc from the base alloy diffusing through the gold, which would oxidize at the surface and recreate the exact problem the plating was meant to solve. Gold without nickel underplate is a corrosion time bomb on brass.
Strip Plating vs Selective Plating
How the plating is applied matters as much as what is applied. For stamped parts there are three routes: plate the strip before stamping, plate the finished parts in bulk, or selectively plate only the contact zones in the strip process. Strip plating before stamping is the norm for high-volume stamped electrical contacts: the plating is uniform, and the die never sees plating chemicals.
Selective plating cuts cost hard, because gold is priced per area. A reel-to-reel line can plate a 0.5 mm band of gold exactly where the contact wipes, leaving the rest of the strip bare or tin-plated. Gold usage drops to a fraction of full coverage, which on a 100,000-piece order is a five-figure saving. Barrel plating after stamping is cheapest but covers everything, plates unevenly in corners, and can damage delicate stamped geometry in the tumbling.
| Route | Coverage | Cost | Typical use |
|---|---|---|---|
| Full strip plate | All surfaces | Moderate | Simplicity, corrosion protection everywhere |
| Selective strip plate | Contact band only | Lowest gold use | High-volume gold contacts |
| Barrel after stamping | All surfaces | Cheap per part | Tin/nickel on robust parts |
| Rack after stamping | All surfaces | Higher | Large parts, controlled thickness |
Takeaway: for gold, always ask for selective plating before assuming full coverage is cheaper. The die and the plating line must be coordinated — the strip is plated where the future contact area sits — which is why plating is designed into the strip layout, not bolted on at the end.
Common Field Failures and Their Fixes
Most plating complaints trace to three causes. First, too-thin gold over a porous surface: porosity lets the base metal corrode through pinholes, and the fix is adequate thickness plus nickel underplate. Second, tin fretting: low-force vibration rubs tin oxide into a high-resistance surface, so tin contacts need high mating force or a different metal. Third, hydrogen embrittlement or contamination from plating chemistry on spring materials, which shows up as cracked or failed stamped spring contacts after assembly.
Because plating is a chemical process on a mechanical part, the part maker and the plater must both own the spec. Under our ISO9001 system at BQUQ, plated batches ship with coating-thickness records traceable to the strip lot, so when a contact misbehaves in the field you can check the actual plating, not the intention.
Email sc@bquq.com or WhatsApp +86 137 1315 7787 with your PDF/DXF/STEP file. An engineer reviews it and replies with price, lead time and DFM notes on working days.
Frequently Asked Questions
Q: Why put nickel under gold on a stamped contact?
Nickel is the diffusion barrier. Without it, copper and zinc from the brass base migrate through thin gold and oxidize at the surface, raising contact resistance. Nickel also adds hardness, so the gold wears less in sliding contacts.
Q: When is tin plating good enough for a contact?
When the connection is made rarely or once, mating force is high, and cost rules — battery contacts, crimp terminals, power lugs. Tin oxide breaks down under high contact force, so low-force signal contacts should not rely on it.
Q: How thick does gold plating need to be?
For connector-grade dry circuits, 0.1–0.76 µm (4–30 µin) hard gold over 1–3 µm nickel covers most needs. Thicker gold buys wear life, not lower resistance — beyond about 1 µm you are paying for cycles, not for conductivity.
Q: Does stamping after plating damage the plating?
Plating is applied to strip before stamping in the high-volume route, and the die can crack or smear plating at tight bends and shear edges. That is why plating thickness and hardness are specified together, and why edge quality is inspected at the contact zones.
Q: What plating should a battery contact spring use?
Tin over nickel is the economical answer for most battery contacts, with silver for high-current versions. If the spring must survive many insertions at low force, move to gold flash over nickel — the extra cost buys cycle life.
Authored by the BQUQ Engineering Team. BQUQ is an ISO9001-certified source factory in Dongguan, China, running CNC machining, metal stamping, custom springs, heat sink and collet lines under one roof. Send drawings to sc@bquq.com or WhatsApp +86 13713157787 for a quote within 12 working hours. www.bquq.com
