Plating Thickness on Copper: What to Write and Where
September 26, 2026
Plating thickness is the line on a copper drawing that most often reads “tin plated” and nothing else. Every shop then assumes a different number, every plater applies a different amount, and the quotes are not comparable. This is what to write.
Two numbers, not one
Plating serves a purpose on the contact face and a different, lesser purpose everywhere else. The contact face needs full thickness for contact resistance, wear and corrosion at the joint. The rest of the part needs enough to stop tarnish and no more.
So the specification has two thicknesses:
- Contact areas: the full functional thickness
- Non-contact areas: a minimum, or masked and bare
Writing one number for the whole part either over-plates the body, which costs money and changes fit, or under-plates the contact face, which is the only place it mattered.
Typical ranges
These are common specification ranges rather than rules. The standard your assembly is built to governs.
| Finish | Contact areas | Elsewhere |
|---|---|---|
| Tin | A few micrometres up to around 10 to 15 | Minimum, or masked |
| Nickel, as a finish | Around 5 to 10 | Minimum, or masked |
| Nickel, as a barrier under silver | A few micrometres | Same as the silver area |
| Silver over nickel | A few micrometres up to around 10 | Masked |
Where on the part it is measured
Plating is not uniform. Edges and corners plate thicker, recesses and holes plate thinner. A thickness with no location is not a specification.
Name the measurement point: “minimum [x] micrometres measured at the centre of the contact pad” is a statement a plater can meet and an inspector can check.
Before or after plating
Plating adds material. On a tight fit, a stacked assembly or a threaded feature it changes whether the part fits. State it, once, on every plated drawing:
Dimensions apply before plating.or
Dimensions apply after plating.Most machined copper parts are dimensioned before plating, with the plater told which fits are critical. Threads are usually masked or the plating allowance is accounted for.
Masking
Masking is a real operation at the plater with its own cost. Mark the plated and masked areas on the drawing, not in a note. On a busbar the usual answer is contact pads plated and the rest masked, which reduces both the plating cost and the silver bill. See tin, nickel and silver plating on copper busbars.
The full callout
Plating: silver, minimum 5 micrometres,
over nickel, minimum 2 micrometres,
on contact pads marked P.
All other surfaces masked.
Thickness by XRF at centre of pad.
Adhesion per [standard].
Dimensions apply before plating.Six lines. Every one of them prevents a specific dispute. The RFQ builder writes the outline and you fill the numbers.
What plating does not fix
A tool mark, a smear or a scratch on the contact pad is still there under the plating and often looks worse. Finish the pad, then plate it. Copper surface finish covers what to specify.
Frequently asked questions
Is thicker plating always better?
No. Past what the corrosion, wear and contact requirement needs, thicker plating adds cost, changes fit, can crack on bends and is harder to inspect. Specify what the function needs, and specify it separately for contact and non-contact areas.
Do drawing dimensions include the plating?
Only if the drawing says so. This is the single most common plating dispute. Write 'dimensions apply before plating' or 'after plating' on every plated copper drawing.
How is plating thickness verified?
Commonly by X-ray fluorescence on the finished part, sometimes by cross section on a sample. State the method and where on the part it is measured, because thickness varies across a part.
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