Photochemical Machining
Photochemical machining masks sheet metal photographically and etches away the unmasked areas, cutting burr-free flat parts with no hard tooling.
- Part
- Cutting
- Revised
- 2026-08-11
At a glance
- Family
- Chemical
- Typical tolerances
- ±10% of material thickness as standard (±0.001 in / ±0.025 mm on 0.010 in / 0.25 mm stock); ±20% of thickness for conservative planning; ±0.0005 in (±0.013 mm) on thin foil
- Surface finish
- Unetched faces retain the mill finish of the incoming sheet; etched faces are matte and lightly textured. Edges are entirely burr-free with a characteristic cusp at mid-thickness where the two etch fronts meet
- Typical volumes
- 1–1,000,000+; economical at both extremes because there is no hard tooling
- Lead time
- Phototools in 1–3 days; prototypes in 1–2 weeks; production 2–4 weeks
- Materials
- Metal
What it is
Photochemical machining — also called chemical etching or photo etching — masks sheet metal photographically and dissolves away everything the mask does not protect. There is no punch, no cutting force and no heat, so parts come out completely burr-free, stress-free and free of any heat affected zone or work hardening. That combination is why it is the standard process for shims, lead frames, encoder discs, EMI shields, fine mesh screens, flexures and precision springs.
Stock runs 0.0005–0.060 in (0.013–1.5 mm), with most work between 0.001 and 0.030 in (0.025–0.75 mm). Tolerance scales with thickness at roughly ±10% of material thickness, so 0.010 in (0.25 mm) stock holds about ±0.001 in (±0.025 mm).
Complexity is free. A part with a thousand holes etches in exactly the same time as a plain rectangle, and the only tooling is a piece of film.
How it works
- Phototool generation. The CAD outline is plotted at high resolution onto film or glass, in two halves that register front to back. Tooling cost is trivial compared with a die, and a revised design means a new plot rather than new steel.
- Cleaning and lamination. The sheet is chemically cleaned and a photoresist — usually dry film — is laminated to both faces. Any contamination here becomes a defect later.
- Exposure and development. UV light through the phototool cures the resist in the pattern; developing washes away the uncured resist and exposes bare metal exactly where material is to be removed.
- Etching. The sheet passes through a spray etcher that floods both faces. Ferric chloride is the workhorse etchant for steels, stainless, copper alloys and nickel, run at controlled concentration (commonly around 42–45° Baumé) and temperature (roughly 120–130 °F / 49–54 °C). Aluminum and titanium use different chemistries.
- Isotropic attack. Etching removes material in all directions at once, so it undercuts the resist as it goes down. Etching from both sides simultaneously halves the depth each front must travel and leaves the characteristic cusp where the two fronts meet at mid-thickness.
- Stripping and rinsing. Resist is stripped, the sheet is rinsed and dried, and parts are broken out of the retaining tabs that hold them in the panel.
- Optional half-etching. Etching one side only produces fold lines, counterbores, recesses and part marking. Depth is targeted at 30–60% of thickness and controlled to roughly ±10% of the stock thickness.
Design guidelines
Feature size is governed by thickness
The minimum hole diameter, slot width and web between features is about 1.0–1.2× material thickness. This is a direct consequence of isotropic etching: the etch spreads sideways as fast as it goes down, so no feature can be much narrower than the sheet is thick.
Tolerance scales with thickness, not with part size
Plan on ±10% of material thickness as the standard tolerance, with ±20% as a conservative figure for large panels. On 0.005 in (0.13 mm) foil that is ±0.0005 in (±0.013 mm); on 0.040 in (1 mm) stock it is ±0.004 in (±0.1 mm). Thin stock is where the process is most precise. Specify stock as a decimal thickness rather than a gauge number, and cross-check the two against the sheet metal gauge chart.
Do not draw sharp internal corners
Etched corners come out radiused. Specify a radius of at least 0.5× material thickness on internal corners rather than a sharp corner the process cannot make.
The edge is not square
Etching from both faces leaves an hourglass profile with a cusp at mid-thickness. Where a square edge is functionally required — a bearing surface, a precise slot width for a mating tongue — dimension to the narrowest point and state it, or choose a different process.
Use half-etching deliberately
Half-etched fold lines let a flat part be bent by hand into a formed shape without tooling. Half-etched pockets make counterbores and recesses. Depth control of about ±10% of stock thickness is the practical limit, so do not use a half-etch where the residual thickness is structurally critical.
Plan tabs and nesting
Parts are held in the panel by small tabs and broken out, and each tab leaves a witness mark. Say where tabs are acceptable. Since price is per panel area, nesting drives cost — panels are typically in the 12 × 18 in to 24 × 36 in (300 × 450 mm to 600 × 900 mm) range depending on the shop.
| Material | Etchability | Notes |
|---|---|---|
| 301 / 302 / 304 / 316 stainless | Excellent | The most common PCM material; ferric chloride |
| Copper, brass, phosphor bronze | Excellent | Fast etching; standard for shields and lead frames |
| Beryllium copper | Excellent | Springs and contacts; etch then heat treat |
| Nickel, Inconel, Kovar, Invar | Good | Slower etch rates; common in electronics packaging |
| Spring steel, shim steel | Excellent | Burr-free shims are a signature application |
| Molybdenum, tungsten | Specialty | Not every shop runs the chemistry |
| Aluminum | Good | Different chemistry, coarser minimum features |
| Titanium | Specialty | Requires aggressive chemistry and specific handling |
| Plastics, glass, ceramics | Not possible | No etchant chemistry in this process |
| Feature | Recommended | Limit | Why |
|---|---|---|---|
| Material thickness | 0.001–0.030 in (0.025–0.75 mm) | 0.0005–0.060 in (0.013–1.5 mm) | Feature size and tolerance scale with thickness |
| Hole diameter | ≥ 1.2× thickness | 1.0× thickness | Etch spreads sideways as fast as down |
| Slot width | ≥ 1.2× thickness | 1.0× thickness | Same isotropic limit |
| Web between features | ≥ 1× thickness | 0.8× thickness | Undercut from both sides |
| Internal corner radius | ≥ 0.5× thickness | Sharp corners not achievable | Isotropic etch rounds corners |
| Half-etch depth | 30–60% of thickness | ±10% of thickness control | Depth control limit |
| Standard tolerance | ±10% of thickness | ±20% on large panels | Undercut variation across the panel |
Cost drivers
Photochemical machining is priced by panel area and by the number of panels, which produces an unusual cost structure: complexity is free, and area is everything.
Panel area and nesting. You pay for sheet processed, not features produced. A part that nests at 90% yield costs a fraction of one that nests at 50%, and adding features to the part changes nothing.
Material. Thin precision-rolled stainless, beryllium copper and nickel alloys are a real share of the panel cost, particularly at production volumes.
Thickness. Thicker stock etches longer, holds looser tolerance and needs coarser minimum features, so thickness pushes cost up in two directions at once.
Phototooling. A one-time charge measured in hundreds rather than thousands, with a lead time of days. This is what makes the process viable for prototypes and for designs that are still changing.
Secondary operations. Forming half-etched fold lines, plating, and passivation are separate steps priced separately.
Four ways to take cost out:
- Send the part outline to the shop for nesting before finalizing dimensions — panel yield dominates price.
- Use the thinnest stock that meets the functional requirement; it etches faster and holds tighter tolerance.
- Combine multiple part numbers onto one panel when they share material and thickness.
- Add features freely — holes, text, patterns and half-etched fold lines cost nothing extra, so consolidate parts rather than adding assembly steps.
Questions
6 questionsWhat tolerance can photochemical machining hold?
Roughly ±10% of the material thickness as a standard, with ±20% as a conservative planning figure on large panels. On 0.010 in (0.25 mm) stock that is about ±0.001 in (±0.025 mm), and on 0.005 in (0.13 mm) foil about ±0.0005 in (±0.013 mm). The process is most precise on thin material, which is the opposite of most cutting processes.
What is the minimum feature size for chemical etching?
About 1.0–1.2× the material thickness for hole diameter, slot width and the web between features. Etching is isotropic, so the etchant spreads sideways as fast as it works down, and no feature can be much narrower than the sheet is thick. That is why thin stock gives fine features and thick stock does not.
Why are photochemically machined parts burr-free?
Nothing mechanical touches the part. Material is dissolved rather than sheared, cut or melted, so there is no plastic deformation to raise a burr, no work hardening, no heat affected zone and no residual stress. For thin springs, shims and flexures this matters as much as the dimensional accuracy.
What thickness range can be photochemically machined?
About 0.0005–0.060 in (0.013–1.5 mm), with most production between 0.001 and 0.030 in (0.025–0.75 mm). Above that range, etch times get long, features get coarse relative to the part, and laser or water jet cutting becomes the better option.
What is half-etching used for?
Etching from one side only, typically to 30–60% of the thickness, creates fold lines that let a flat part be bent by hand into a formed shape, as well as counterbores, recesses and permanent part marking. Depth control is roughly ±10% of stock thickness, so half-etching should not be used where the residual thickness carries a critical load.
Does photochemical machining need tooling?
Only a phototool — a high-resolution plot on film or glass, costing a small fraction of a die and produced in 1–3 days. That is why the process suits prototypes and evolving designs as well as million-piece production runs, and why adding features to a part costs nothing.