Overview

Shim photo etching is a lithographic process, not a mechanical one, and that distinction explains why it suits thin gauge work. A dry film or liquid photoresist is applied to a cleaned strip, exposed through a film tool carrying the shim outline, then developed so that only the areas to be removed remain unprotected. The strip passes through a spray etchant that dissolves metal from both faces at once, and the resist is stripped afterwards. The shim never sees a punch, a laser or a grinder, so the sheet stays flat and the thickness chosen from the mill is the thickness delivered.

The lithographic sequence matters most on shims because the part is often defined by two numbers: overall thickness and local step height. Etching controls both, and a second exposure-and-etch pass can produce a recessed pocket, a locating step or a half-etched relief without any secondary machining. Registration between the two passes is what determines whether the step sits where the drawing says. Shims from 0.02 mm to 2.0 mm in stainless, brass, copper and beryllium copper run through the same line, and because the artwork is digital, a revision costs a new film rather than a new tool.

Parameter Window

• Available Materials: stainless steel 301/304/316L, brass H62/H65, copper C1100, beryllium copper, nickel silver
• Material Thickness Range: 0.02–2.0 mm
• Tolerance: ±0.05 mm on cut profile, ±0.02 mm on step depth, flatness 0.02 mm per 100 mm
• Minimum Feature: 0.05 mm slot and 0.08 mm hole at 0.05 mm stock
• Surface Options: stress-relief anneal, passivation, nickel or gold plating, adhesive backing, laser marking
• Compliance: ISO 9001 process control, RoHS/REACH material traceability

Manufacturing Process / Workflow (8 Steps)

1. Film Tool Preparation — Plot the shim layout to high-resolution film at 1:1, add registration targets and step-feature layers, and verify line width against the artwork.
2. Substrate Cleaning — Degrease, micro-etch and rinse the strip so the resist bonds uniformly and no pinhole opens during etching.
3. Resist Application — Laminate dry film or coat liquid resist to a controlled thickness; coating uniformity sets the achievable edge definition.
4. Exposure — Expose under collimated light with the film held in hard contact, so the wall angle stays near-vertical instead of undercut.
5. Development — Dissolve unexposed resist in a developer matched to the coating, then rinse and dry without leaving residue in narrow slots.
6. Etching — Spray etchant from both sides at controlled pressure, temperature and dwell so the cut proceeds evenly and side-etch stays predictable.
7. Step Etching — Re-mask and re-expose for pockets or reliefs, holding registration to the first layer within the stated step tolerance.
8. Stripping and Inspection — Remove resist, neutralize, anneal if required, then check thickness, step depth, flatness and hole size against the drawing.

Core Advantages

1. Lithography holds fine detail: Because the pattern is transferred optically, slots and holes far smaller than the strip thickness remain practical, which punching cannot achieve.
2. No stress, no distortion: There is no mechanical force, so thin shims stay flat and do not bow after trimming, which matters when a shim sets a bearing preload.
3. Thickness is the function: Mill thickness tolerance is preserved across the part, so a 0.05 mm shim is 0.05 mm everywhere rather than thinning at the edges.
4. Steps in one part: Multi-level shims are made by repeated exposure and etch, replacing stacked loose shims with a single part that cannot be assembled out of order.
5. Tooling-free revisions: Because shim photo etching is driven by digital artwork, a changed slot position is a film change, and prototype quantities stay affordable.
6. Burr-free by nature: Metal is dissolved rather than sheared, so edges arrive clean and no deburring step can round the face that must sit flat.

Typical Applications

• Bearing and gearbox shims: Preload and end-play adjustment shims in 0.1–0.5 mm stainless with etched thickness markings.
• Laminated adjustment stacks: Multi-layer peelable shims etched to stepped outlines so layers can be removed on site.
• Electrical insulation shims: Slotted insulating washers and spacers in nickel silver or brass for connector and busbar assemblies.
• Optical and sensor spacers: Thin apertures and standoff shims that set a fixed gap between lens, filter and sensor.
• Spring and contact shims: Beryllium copper shims etched with integral fingers for light spring loading in small mechanisms.
• Step shims for assembly: Single-piece shims with a half-etched pocket that locates over a boss or a fastener head.

Design Notes & Process Considerations

1. Thickness tolerance first: Buy strip to a controlled thickness tolerance, since etching does not correct gauge variation and the shim's function depends on it.
2. Etch allowance on outlines: Add roughly one material thickness per side to the finished outline when the cut is through, so the finished size lands on nominal.
3. Step registration: Two-level shims need a registration target on both film layers; without it the pocket drifts and the step wall thins.
4. Minimum slot versus thickness: Keep slot width at least 1.2 times the material thickness in through-cut areas, or the etchant cannot refresh inside the channel.
5. Flatness after anneal: If stress-relief annealing is required, specify flatness after heat treatment, not before, and state the temperature range.
6. Edge and surface condition: Since shim photo etching leaves no burr, the remaining risk is handling, and scratches show on soft brass, so specify protective film and pack face-to-face.