Overview

Thin aperture etching produces knife-edge optical stops and pinholes from 304/316L stainless or nickel foil between 0.02 and 0.10 mm, where the edge itself must be almost zero thickness. A resist mask defines the opening and the metal is dissolved from both faces so the aperture rim tapers to a few micrometres rather than a blunt cut wall. Hole diameter is held to ±0.005 mm with roundness inside 0.005 mm, and the edge is left free of burrs, roll-over and recast layer. Because the finished rim is a true knife edge, a knife-edge stop avoids the diffraction and stray-light scatter that a thick, square-cut hole would add to an optical path.

Optical performance, not mechanical strength, drives every setting here. Dual-side etching is balanced so the two tapers meet at the centre of the foil, and spray pressure is kept low to keep a 0.02 mm web from fluttering. The artwork is compensated for the etch factor, and after stripping the parts can be blackened by black oxide or a light-absorbing coating to kill reflections off the rim. Thin aperture etching is specified for confocal pinholes, beam stops, spatial filters and encoder masks, where a burr or a 10 um flat on the edge would raise the background signal.

Parameter Window

• Available Materials: stainless 304/316L, nickel, nickel-iron, blackened copper on request
• Material Thickness Range: 0.02–0.10 mm, with 0.025–0.05 mm typical for knife-edge stops
• Tolerance: hole diameter ±0.005 mm, roundness <=0.005 mm, position ±0.01 mm
• Minimum Feature: 0.03 mm pinhole, rim edge thickness below 10 um, 0.05 mm ligament
• Surface Options: bare, black oxide, light-absorbing coating, electropolished, framed or ring-mounted
• Compliance: ISO 9001 process control, RoHS/REACH material traceability

Manufacturing Process / Workflow (8 Steps)

1. Optical Review — Set hole diameter, roundness and rim thickness from the diffraction and stray-light budget, then build compensated artwork.
2. Foil Selection — Choose gauge and alloy, and verify thickness uniformity, since gauge drift moves where the two tapers meet.
3. Cleaning & Lamination — Laminate dry film on both faces without bubbles, keeping the aperture field perfectly clean.
4. Dual-Side Exposure — Expose registered front and back artwork so the opening is imaged identically from both sides.
5. Development — Develop both faces and inspect the pinhole field for scumming before the fragile foil reaches etchant.
6. Balanced Knife Etching — Spray at fixed Baume and low pressure from both faces until the tapers meet, leaving a micrometre-scale rim.
7. Stripping & Blackening — Strip resist, rinse gently, then apply black oxide or an absorbing coating to the rim.
8. Optical Inspection — Measure diameter, roundness and edge thickness under magnification, check for burrs, then mount in a ring if specified.

Core Advantages

1. True knife edge: Two-sided tapering leaves a rim of only a few micrometres, minimising diffraction and stray-light scatter.
2. Round, burr-free holes: ±0.005 mm diameter and 0.005 mm roundness with no roll-over or recast layer.
3. No thermal distortion: Chemical removal adds no heat, so 0.02 mm foil stays flat and the hole stays circular.
4. Balanced tapers: Front and back etch rates are matched so the knife edge lands at mid-gauge, not off to one face.
5. Absorbing finish: Black oxide or a light-absorbing coating can be added to suppress reflections from the rim itself.
6. Repeatable optics: A controlled thin aperture etching line holds the same edge geometry across every aperture on a panel.

Typical Applications

• Confocal pinholes: Micrometre-scale stops for confocal microscopy and laser scanning systems.
• Spatial filters: Knife-edge apertures that clean a beam profile in optical benches.
• Beam stops and masks: Light-blocking apertures for lithography alignment and detector shielding.
• Optical encoder discs: Fine slot arrays with clean edges for rotary and linear encoders.
• Spectrometer slit plates: Precision entrance and exit slits, blackened to reduce internal stray light.
• Astronomical and sensor masks: Calibrated aperture arrays for imaging calibration and detector testing.

Design Notes & Process Considerations

1. Rim from light budget: Fix edge thickness and roundness from the stray-light target first, then choose foil gauge.
2. Gauge uniformity: Hold incoming thickness tightly, because the two tapers must meet near the mid-plane of the foil.
3. Dual-side balance: State the front-to-back etch ratio, or the knife edge will sit closer to one face and scatter asymmetrically.
4. Roundness callout: Give roundness as well as diameter, since an oval pinhole changes the point-spread function.
5. Blackening allowance: Reserve a small diameter allowance for black oxide, which builds a few micrometres on the rim.
6. Handling and mounting: Keep a solid border and mount in a ring before removing it; a 0.02 mm knife edge folds at a touch.