Two rules of thumb
Before any quoting, two numbers get you 90% of the way:
- Minimum feature ≈ metal thickness. The smallest hole, slot or thin web you can hold is about the same as the sheet thickness.
- Tolerance ≈ ±10% of thickness. A 0.2 mm sheet sits around ±0.02 mm; a 1 mm sheet around ±0.05 mm and up.
They're approximations, not promises — alloy, feature shape and how the part is laid out all nudge the real figure. But they're close enough that an experienced engineer can sanity-check a drawing in a few seconds.
Why thickness sets the limit
Etching is isotropic — the etchant goes down into the metal and outward under the resist at much the same rate. That sideways bite is undercut, and the deeper you have to etch, the more of it you accumulate. We measure how well it's controlled with the etch factor:
Etch factor = etch depth ÷ undercut. The higher the number, the more vertical the wall and the tighter the part.
Precision work runs an etch factor of about 3 to 4. Because undercut scales with depth, a thin sheet clears before it can wander far — so you hold fine features and tight tolerances. A thick sheet takes a long etch, undercut builds, and both the minimum feature and the tolerance open up. That's the whole reason the numbers track thickness. The mechanism is the same one described in how photochemical etching works.
What you can hold, by thickness
A practical reference for common metals. Treat it as a starting point and send us the drawing for anything near the edge of these figures:
| Metal thickness | Smallest feature (hole / slot / web) | Typical tolerance |
|---|---|---|
| 0.05 mm | ~0.05 mm | ±0.01 mm |
| 0.10 mm | ~0.08–0.10 mm | ±0.01–0.02 mm |
| 0.20–0.30 mm | ~0.15–0.25 mm | ±0.02–0.03 mm |
| 0.50 mm | ~0.4–0.5 mm | ±0.03–0.05 mm |
| 1.0 mm | ~0.8–1.0 mm | ±0.05 mm |
| 2.0 mm | ~1.6–2.0 mm | ±0.08–0.10 mm |
How we hold tighter tolerances
Most of the precision is in the machine, not the chemistry. To keep the etch factor high and the spread low, the things that matter are:
- Even, high-pressure spray on both faces, so the etch rate is the same across the sheet and top-to-bottom.
- Tight temperature control on the etchant, so the rate doesn't drift mid-run.
- Good film and resist with clean exposure, so the mask edges are sharp to begin with.
- Two-sided etching on through-features, halving the depth each side has to travel and so halving the undercut.
- Sensible layout — etch-compensated artwork that allows for the undercut you know is coming.
That's what separates a precision etching machine from a basic one, and it's why machine choice shows up directly in the parts. If you're specifying equipment, the cost guide covers what that precision adds, and the FAQ answers the quick ones.
Send us the tight feature, not just the part
When you ask for a quote, point us at the one or two features that worry you — the finest slot, the closest tolerance, the thinnest web. We'll tell you straight whether it etches as drawn, needs a tweak, or wants a thinner gauge. Start on the contact page.
Common questions
As a rule the smallest reliable feature — hole, slot or remaining web — is about the metal thickness. On 0.1 mm foil you can hold features near 0.08–0.10 mm; on 1 mm sheet the realistic minimum is closer to 0.8–1.0 mm. Thinner metal lets you go finer.
On thin material, yes. Our precision horizontal and vertical machines hold about ±0.02 mm down to ±0.01 mm — fine enough for SMT stencils, encoder discs and gratings. As the metal thickens the achievable tolerance opens up, because undercut grows with etch depth.
Etch depth divided by sideways undercut. The higher it is, the more vertical the wall and the more precise the part. Precision etching typically runs an etch factor of about 3 to 4, held with even high-pressure spray, fresh etchant and good temperature control.
Yes. Etching removes metal sideways as well as down, so the longer the etch — i.e. the thicker the metal — the more undercut builds up and the wider the tolerance. The same machine can hold ±0.01 mm on foil but around ±0.05 mm on 1 mm plate.