Overview

A shim etching process is the photochemical workflow used to make precision spacers, gap shims, washers, shim packs and stepped adjustment plates where thickness and flatness are the functional dimensions. Rather than stamping, which rolls a burr and work-hardens the edge, a resist image of the shim outline is laminated to the sheet, the unwanted metal is dissolved away, and the part leaves the bath flat, burr-free and at the as-supplied temper. Materials span 304/316L stainless, spring steel, brass, copper, beryllium copper C17200 and nickel, from 0.02 mm to 2.0 mm, and thickness is held to ±0.005 mm with profile tolerances of ±0.01 mm on the outline. The route also allows half-etched steps and peelable laminated shim stacks that stamping cannot produce economically.

For a manufacturing engineer, the shim etching process is a tolerance chain, not a single cut. Final thickness is set by incoming foil plus the small, uniform amount removed during etching, so incoming gauge, etch rate uniformity across the panel and dwell time all have to be logged. Lateral undercut shifts the outer profile inward as the part is cut, so artwork is oversized by the etch factor to hold the outline; spray pressure, FeCl3 or CuCl2 concentration, temperature, ORP and conveyor speed govern that undercut. Flatness is protected by avoiding mechanical force and by stress-relief annealing where the service needs it. This article follows the eight-step workflow, the parameter window and the design rules that keep precision shims repeatable from sample to production.

Parameter Window

• Available Materials: 304/316L stainless steel, spring steel, brass, copper, beryllium copper C17200, nickel
• Material Thickness Range: 0.02–2.0 mm, with step or peelable stacks built by half-etch lamination
• Tolerance: ±0.005 mm on thickness, ±0.01 mm on outline profile, ±0.02 mm on step depth
• Minimum Feature: 0.15 mm slot, 0.2 mm hole, 0.2 mm web, 0.05 mm half-etch step
• Surface Options: passivated, electropolished, tumbled, black oxide, plated Ni, bonded peelable shim pack
• Compliance: ISO 9001 process control, RoHS/REACH material traceability

Manufacturing Process / Workflow (8 Steps)

1. Artwork & Compensation — Oversize the shim outline by the expected etch factor so lateral undercut brings the finished profile onto the nominal dimension.
2. Gauge Selection — Certify incoming foil thickness and temper, since finished shim thickness is built on the as-received gauge.
3. Cleaning & Lamination — Degrease and hot-roll dry-film resist on both faces; uniform adhesion is needed so the outline etches evenly across the panel.
4. UV Exposure — Expose the outline, holes and half-etch step regions through registered tooling, keeping stepped and through areas in one image.
5. Development — Open the waste-metal areas and inspect step boundaries; residual resist here would leave an unetched step or a ragged outline.
6. Controlled Etching — Spray matched etchant while logging Baumé, temperature, ORP, spray pressure and conveyor speed to hold uniform removal and wall straightness.
7. Stripping & Finishing — Strip resist, neutralize, then passivate, electropolish or tumble; stress-relief anneal is added where flatness must be restored.
8. Inspection & Packaging — Measure thickness at multiple points, profile and flatness against the approved sample, then pack flat with interleave to protect the gauge.

Core Advantages

1. Tight thickness control: Finished gauge is built from certified foil and uniform chemical removal, holding ±0.005 mm without grinding or skiving.
2. Burr-free flat parts: No punching force or rolled edge means shims stack flush and seat without a burr lifting the assembly.
3. No hard tooling: Each shim geometry is a new film, so gap sets, prototypes and frequent thickness revisions carry no die cost.
4. Stepped and peelable shims: Half-etch steps and laminated peelable packs are imaged in one workflow, replacing multi-piece bonded assemblies.
5. Stress-free temper: Cold-work-free edges keep spring steel and beryllium copper at their supplied hardness and flatness.
6. Full-panel consistency: All shims on a sheet etch at the same rate, so thickness and profile match across a batch and against the signed sample.

Typical Applications

• Precision gap shims: Stainless or spring steel spacers that set bearing preload and gear backlash in gearboxes and spindles.
• Peelable shim packs: Laminated, layer-by-layer adjustable shims for alignment and leveling of heavy machinery.
• Stepped adjustment plates: Half-etched shims with two thickness zones for valve and pump clearance setting.
• Flat washers and spacers: Burr-free 304/316L washers for corrosion-resistant assemblies and clean stacking.
• Tooling and fixture shims: Thin brass or steel shims for mold, die and jig height adjustment.
• Optical and semiconductor spacers: Nickel or stainless shims holding controlled standoff in lens and wafer fixtures.

Design Notes & Process Considerations

1. Thickness budget: State whether tolerance applies to foil gauge or finished part, and allow for the small uniform removal during the shim etching process itself.
2. Etch factor on profile: Give foil thickness and expected undercut so artwork is oversized correctly, or the outline finishes undersize.
3. Web and hole limits: Keep minimum webs at or above material thickness; narrow ligaments can break through during development and handling.
4. Flatness callout: Specify flatness per 100 mm and request stress-relief annealing for spring materials that will be clamped in assembly.
5. Half-etch step definition: Define step depth and boundary clearly, since depth is time-controlled and drifts with bath age and temperature.
6. Chemistry log: Hold Baumé, temperature, ORP, spray pressure and conveyor speed per lot; drift changes both undercut and removal rate, moving profile and gauge together.