Guide
Should Machined Electrical Contacts Be Plated With Tin, Silver or Nickel?
Machined electrical contacts are the turned or milled copper-alloy terminals, lugs, studs, pins and blades that carry current across a mating surface, and the plating on that surface decides how they behave over years of connection cycles: how well they conduct, what film forms on them, how they wear and what can grow on them.
By Saola Manufacturing engineering team · Published · Updated
Short answer: choose by the job of the contact. Silver is the usual choice where current is high, tin is the economical choice for ordinary mating contacts if whiskers and fretting are controlled, and nickel is mostly an underplate, with limited use as a final finish in battery and high-temperature contacts. Whichever you pick, write each layer on the drawing as its own callout and name the standard that sets its thickness and quality.
On this page
How do you choose between tin, silver and nickel for a contact?
Start from the current, the number of mating cycles and the environment. High-current, wiping contacts point to silver; ordinary connectors with low cost targets point to matte tin over nickel; battery and high-temperature contacts are where nickel shows up as the surface.
A component maker's overview of contact finishes, published by Passive Components (Würth Elektronik, 2025), is a good neutral starting point. It says silver is chosen for high-current contacts because of its conductivity and arc resistance compared with tin or gold, that tin forms a self-limiting oxide film that breaks up on mating, and that nickel is used in battery and high-temperature contacts. The page also notes that the contact spring material carries the constriction resistance, which is a reminder that the base metal and the contact force matter at least as much as the plating.
Cost is a third axis. MCL Industries describes tin as a very affordable option for contacts. Silver is the dearer metal, and its price moves with the market, so ask the plating supplier to quote the layer on your actual surface area rather than assuming a ratio.
At production volume the decision is less about the plating metal and more about repeatability: layer thickness, adhesion and contamination have to be the same on the last lot as on the first. That favors a clear callout and an agreed inspection over a clever finish.
How do tin, silver and nickel compare on a copper-alloy contact?
Each finish trades something: tin gives you cost but whiskers and fretting, silver gives you conductivity but tarnish, and nickel gives you hardness and a barrier but is rarely the contact surface.
The table summarizes what the sources above say, together with the standard that governs each plating. It is qualitative on purpose: the sources give no like-for-like resistance or hardness figures, and neither does this guide.
| Plating | Best at | Main risk | Governing specification |
|---|---|---|---|
| Tin | Low cost; self-limiting oxide protects the contact until mating breaks it | Whiskers on pure tin; fretting corrosion under small movements | ASTM B545 (electrodeposited tin) |
| Silver | High-current contacts; conductivity; arc resistance | Tarnish films, mainly sulfides, which are displaced on mating | ASTM B700 (silver for engineering use) |
| Nickel | Underplate for wear resistance and as a barrier; surface use in battery and high-temperature contacts | Thin oxide layer; not usually the first choice as the contact surface | ASTM B689 (engineering nickel) |
Why does tin grow whiskers, and what controls them?
Whiskers are single-crystal fibers that grow from pure tin plating and can short adjacent conductors. The usual controls are matte instead of bright tin, a nickel underplate, or a non-tin finish.
The Würth overview says whiskers are single-crystal fibers when pure tin plating is used, that they can cause electrical failures, and that prevention options are matte tin instead of bright tin, a non-tin finish such as gold, or a nickel underplate beneath the tin. The NASA tin whisker pages collect research on whiskers from pure tin and on mitigation, including a study of nickel underlayers and another of conformal coatings; they also document failures of electrical systems traced to whiskers. This guide has not reviewed those papers, so read them before relying on any single mitigation.
For a power contact with generous spacing between conductors, whiskers are a smaller concern than for a fine-pitch connector, but they are still a risk where the contact is enclosed. Whiskers are a reliability risk to disclose in the RFQ, not a reason to dismiss tin; write the tin type (matte or bright) on the drawing.
The second tin problem is fretting. Small movements, from vibration or thermal cycling, wear through the oxide and let it re-form, which the Würth overview calls fretting corrosion. Contacts that sit in a vibrating machine need either a higher contact force, a different finish or a design that stops the movement; see the guide on fretting corrosion.
Why does silver tarnish, and does it need a nickel underplate?
Silver reacts with sulfur in the air to form a tarnish film that is mostly sulfide. On a wiping contact the film is displaced when the contact mates, so tarnish matters most on contacts that rarely move.
The Würth overview describes silver surface films as primarily sulfides, which are readily displaced on connector mating, and gives silver's high-current and arc-resistance advantages. By inference, a bolted lug that is closed once and never wiped does not get that cleaning, so the same film sits in the joint. For static joints in sulfur-bearing air, ask the plating supplier about an anti-tarnish treatment and say so on the drawing.
Whether silver on a copper alloy needs a nickel underplate depends on the service temperature and life, and the sources here do not settle it. The safe course is to write the underplate as a separate layer, with its own thickness, when the supplier recommends one, and to ask for the reason. The ASTM specification for silver for engineering use, B700, sets the quality of the silver layer; it is a paid standard, so this guide quotes only its scope and edition.
Where does nickel belong: as the surface or as an underplate?
Mostly as an underplate. Nickel hardens the stack and protects the layers above it, and as a final finish it appears mainly in battery and high-temperature contacts.
The Würth overview says the hardness of the nickel underplate improves the wear resistance of the system and that the underplate protects the contact surface from external corrosion; it also lists battery and high-temperature contacts as the places nickel is used as the surface, where the oxide on nickel is thinner than the oxide on tin. If your contact is a connector for a battery pack or an enclosure that runs hot, nickel on its own can be the correct finish. For a general plug or terminal, treat nickel as the layer under the tin or silver.
Nickel specifications split by type. ASTM B689 covers electroplated nickel coatings for engineering applications; at the time of writing the ASTM store lists the 2023 reapproval as the active edition. Ask the plating supplier which nickel they apply, and write it on the drawing if hardness or stress matters.
What goes on the drawing, and which standard sets the thickness?
List the layers from the base up, each with its specification, type and minimum thickness, and say where on the part thickness is measured. The thickness values themselves come from ASTM B545 for tin, B700 for silver and B689 for nickel.
ASTM B545 covers electrodeposited coatings of tin applied to metallic articles; the store lists the 2022 edition as active. ASTM B700 covers electrodeposited silver for engineering use, and the store shows a 2026 edition as the active one, with the 2020 edition marked historical. Check the edition when you cite one. None of the values from these documents are reproduced here, because they are paid standards; take the thickness classes from the edition you reference.
A good plating note has four parts. The stack, for example nickel underplate then silver. The specification and type for each layer. The minimum thickness and the significant surface where it applies, since thickness varies across a part. And the post-plate requirements: no peeling in a bend or adhesion test as you define it, and a note on whether baking is required for hardened parts. The guide on measuring coating thickness explains how a supplier verifies the callout.
What does the machined contact need before it goes to plating?
A clean, consistent surface with broken edges and allowance for the layer build-up. Plating follows the surface it is put on, so scratches, burrs and tool marks come through.
Saola's lead CNC plant turns and mills parts before they go to plating (CNC turning and CNC milling), and those pages list the materials it runs today; name the copper alloy of the contact in the RFQ so the quote can confirm the route and hold the surface finish and edge breaks the plater needs. Plating itself is a step done at a partner plant Saola manages. The finishing menu lists electroplating in general terms, so whether a given tin, silver or nickel stack can be supplied is confirmed in the quote, which also names the production site. Say on the drawing whether dimensions apply before or after plating; the guide on surface finish before or after coating explains the choice.
Sharp edges on a contact tend to plate unevenly, so ask for a defined edge break before plating. Keep cutting oil off the surface; a part that arrives with residue gives poor adhesion. If the contact has threads or a bore that must fit, state whether the tolerance is before or after plating, because even a thin layer can matter on a close fit.
Frequently asked
Should I use matte or bright tin on a contact?
The Würth overview lists matte tin instead of bright tin as one way to reduce whisker risk, so matte is the usual specification for contacts. Write the tin type on the drawing.
Is silver better than tin for high current?
That is the common practice: the same source says silver is chosen for high-current contacts because of its conductivity and arc resistance. Tin can still be right for lower-current mating contacts where cost drives the decision.
Can nickel be the final finish on a contact?
Yes in some cases. Nickel appears as the surface in battery and high-temperature contacts, and as a general rule it is more often the underplate beneath tin or silver.
Who decides the plating thickness?
The drawing does. Cite the specification and the class or minimum thickness you need, and let the plating supplier confirm that the layer can be deposited on your geometry. Thickness values come from the edition of ASTM B545, B700 or B689 you reference.
Sources
- Noble and non-noble metal finishes, Würth Elektronik via Passive Components, October 2025
- Tin whisker research and mitigation pages, NASA Electronic Parts and Packaging program, accessed 2026
- ASTM B545-22, Standard Specification for Electrodeposited Coatings of Tin, ASTM International, 2022
- ASTM B700, Standard Specification for Electrodeposited Coatings of Silver for Engineering Use, ASTM International, 2020 edition (superseded; store lists 2026 edition as active)
- ASTM B689, Standard Specification for Electroplated Engineering Nickel Coatings, ASTM International, 1997 (reapproved 2013 shown; 2023 reapproval active)
- How to choose the right plating for contacts on your electrical assembly, MCL Industries, accessed 2026