Photochemical machining dissolves a part out of a metal sheet instead of cutting, punching, or melting it. The sheet is cleaned, laminated with a light-sensitive resist, exposed through a photographic tool on both faces, developed, and then sprayed with an etchant — usually ferric chloride — that eats away everything the resist did not protect. What falls out the other end is a flat part with no burr, no work hardening, no heat-affected zone, and no residual stress from forming.

For some components that combination is the only way to get the part at all: shielding cans, encoder discs, spring contacts, filter screens, lead frames, flexures, and shims thin enough that a punch would deform them before it cut them.

What the Process Can and Cannot Hold

Etching is a bulk chemical process, so its capability scales with material thickness rather than with machine precision.

  • Thickness range: roughly 0.0005 in to 0.060 in (0.013 mm to 1.5 mm). Below that the sheet is hard to handle; above it, undercut becomes unmanageable.
  • Minimum feature size: a hole or slot no smaller than about 1.0 to 1.2 times material thickness — roughly 0.012 in on 0.010 in stock.
  • Tolerance: typically ±10 to 20 percent of thickness, so ±0.001 in on 0.010 in stock. Tighter is available and costs more.
  • Edge profile: the etchant attacks sideways as well as down, giving a cusped edge rather than a square one, at an etch factor around 2:1 to 3:1.
  • Flatness: excellent, since nothing mechanically stresses the sheet.

The burr-free result is the headline benefit. Stamped thin parts carry a burr on the die-break side that must be tumbled or lived with, and on a contact spring or a fluidic orifice that burr is a functional defect. Laser cutting leaves a recast layer and a heat-affected edge; etching leaves neither.

Materials That Etch Well

The common list is austenitic and spring-temper stainless (301, 302, 304, 316), beryllium copper, phosphor bronze, brass, copper, nickel and nickel-iron alloys including Kovar and Invar, molybdenum, and titanium. Aluminum etches but holds looser tolerances; specify 5052 or 1100 rather than the high-copper aerospace grades.

Because there is no mechanical work, the temper of the incoming sheet survives untouched — a full-hard stainless strip stays full hard, which is why etching is the standard route for flat springs and contact fingers. Post-etch plating or passivation is normally added by the same shop, following the same logic as any other corrosion protection decision for metal parts.

Tooling Cost Is the Real Argument

The economics are lopsided in etching's favor at the front end. The only tooling is a phototool: a film or glass plate carrying the artwork, produced in a day or two for roughly $100 to $600 depending on size and precision. A progressive stamping die for the same part starts around $8,000 and easily reaches $60,000, with an eight to sixteen week build. The volume-versus-tooling logic that governs the choice is spelled out in metal stamping and progressive die economics.

That gap means:

  1. Design changes are nearly free. Move a hole, reissue the phototool, run parts the same week. A die change is a machining operation on hardened steel.
  2. Prototype and production parts come off the same process, so nothing changes when you scale — unlike prototyping in one process and tooling in another, the trap described in sheet metal prototypes.
  3. Multiple part variants can be nested on one panel, which is how families of shims and spacers get made economically.

Per-part cost, though, barely falls with volume. Etching is priced by panel area and etch time, so a part costs roughly the same each whether you buy five hundred or fifty thousand, while stamping drops toward pennies once the die is paid for. The crossover typically lands between ten thousand and two hundred thousand annual pieces, depending on how much panel your part wastes.

Etching Against the Other Flat-Cutting Processes

Versus laser cutting

Fiber lasers work well down to about 0.020 in with no tooling either, but they cut serially, so a part with four hundred holes is expensive by laser and effectively free by etch, since the whole panel etches at once. Lasers also leave heat effects that matter on springs and foils.

Versus waterjet and plasma

Neither competes at these thicknesses. Waterjet kerf is around 0.030 in and abrasive jets tear thin foil; plasma is a thick-plate process. Their proper domains are covered in waterjet cutting and plasma versus laser cutting.

Versus wire EDM

Wire EDM holds far tighter tolerances, around ±0.0002 in, with square edges through stacked plates — but an order of magnitude slower and dearer per part, so it belongs on precision one-offs and hardened tooling, as discussed in EDM machining.

Design Rules That Make Etched Parts Cheaper

Two tricks are worth knowing. Half-etching exposes one face only, removing material to a controlled partial depth — used for counterbores, recessed pockets, part-number legends, and forming lines. A groove etched to 50 to 60 percent depth gives a repeatable bend line, letting a flat blank be folded into a bracket without a form die. Tab retention keeps parts attached to the panel by breakaway tabs so they can be plated and shipped as a sheet, solving handling on parts too small to pick individually.

Beyond that the usual flat-part discipline applies: avoid sharp internal corners, keep webs at least as wide as the material is thick, allow generous edge distance around holes, and dimension from a single datum. Broader guidance, including what changes once bending enters the picture, is in the sheet metal design guide.

Sourcing and Lead Times

The US has a healthy base of photochemical machining shops, concentrated in the Northeast, upper Midwest, and California, most serving medical and aerospace customers with quality systems to match. Prototype turnaround is typically five to ten business days from approved artwork; production lots run two to four weeks. Send a flat DXF with a separate layer for half-etch features, a note on material and temper, and tolerances only on the dimensions that matter.

Not Sure Etching Is Your Process?

The decision usually depends on annual volume, edge quality requirements, and whether the part needs forming after cutting. Projects House evaluates that tradeoff for US clients and takes the part through detailed design and sourcing across a global manufacturing network. Send your part concept and volume through our contact form.