Overview

Stainless steel spring etching is the photochemical route to flat elastic parts cut from spring-temper stainless foil. Instead of shearing a blank in a die, the process coats the sheet with photoresist, images the part outline and dissolves the exposed metal from both faces at once. The result is a burr-free, stress-free component whose flexures, slots and locating holes all form in one bath, on 301, 304, 316L, 17-7PH or 430 stock between 0.03 mm and 0.80 mm. Because the spring is not work-hardened at the bend root, its force-deflection curve stays close to the calculated value.

What a process engineer needs to understand about stainless steel spring etching is that the chemistry is isotropic. Etchant attacks sideways as well as downward, so every edge is compensated in the artwork by an etch factor that depends on alloy, thickness and spray pressure. Passivation films on stainless also resist attack, which makes cleaning and etchant activation a controlled step rather than a rinse. Temper, rolling direction and post-etch stress relief then decide the final spring rate and fatigue life as much as the outline itself, so process windows are qualified on a coupon before a production film is cut.

Parameter Window

• Available Materials: stainless steel 301/304/316L spring temper, 17-7PH, 430
• Material Thickness Range: 0.03–0.80 mm
• Tolerance: ±0.02 mm on profile at 0.20 mm stock, ±10% on half-etched depth
• Minimum Feature: 0.08 mm line, 0.12 mm slot at 0.10 mm stock
• Surface Options: passivation, electropolish, bright anneal, stress-relief, formed and pre-loaded
• Compliance: ISO 9001 process control, RoHS/REACH material traceability

Manufacturing Process / Workflow (8 Steps)

1. Spring Requirement Review — Define force, deflection, cycle life, environment and assembly envelope before layout.
2. Alloy & Temper Choice — Select strength level and corrosion resistance, then fix the rolling direction of the flexure.
3. Artwork Compensation — Apply the empirically measured etch factor to every edge and half-etch boundary.
4. Cleaning & Activation — Degrease and lightly activate the passive film, then laminate dry-film resist on both faces.
5. Exposure & Development — Expose through registered film and develop, inspecting narrow slots for resist residue.
6. Two-Sided Etching — Spray from both faces under logged temperature and conveyor speed to balance undercut.
7. Stripping & Stress Relief — Strip resist, passivate or electropolish, then stress-relieve and form to free height.
8. Verification — Measure force-deflection, flatness, half-etch depth and fatigue sample, then pack to the drawing.

Core Advantages

1. No sheared edge: Chemical removal avoids the burr, roll-over and work-hardened zone of a stamped spring.
2. Predictable spring rate: Because the bend root is not hardened, measured force tracks the design calculation.
3. Half-etch zoning: Reduced-thickness flexures are made in the same bath as the through-cut outline.
4. Fine, complex outlines: Slots, micro-holes and asymmetric arms need no secondary machining.
5. Whole-sheet uniformity: All parts on a panel see identical chemistry, so force scatter is narrow.
6. Low-cost iteration: With stainless steel spring etching, a force revision is a compensated film, not a new die.

Typical Applications

• Switch and relay flexures: Thin blades that cycle millions of times between electrical contacts.
• Battery and holder contacts: Pre-loaded springs that maintain pressure through shock and vibration.
• Connector retention clips: Flat springs that latch a mating half without a separate fastener.
• EMI grounding fingers: Compliant contacts along enclosure seams that tolerate repeated opening.
• Valve and pump reeds: Corrosion-resistant flexing elements in fluid-control assemblies.
• Instrument suspension arms: Low-hysteresis springs for meters, sensors and optical adjustments.

Design Notes & Process Considerations

1. Slot width versus thickness: Keep narrow slots at 1.5 × stock thickness or wider, or sidewalls thin and warp.
2. Etch factor validation: Measure undercut on a coupon for each alloy and thickness before final artwork is released.
3. Passive film management: Inconsistent activation shows up as ragged edges, so specify the cleaning and activation method.
4. Temper and rolling direction: Lock both at qualification; reversing the grain direction changes spring rate and fatigue life.
5. Stress relief after forming: State temperature and time, since residual forming stress drifts the free height over time.
6. Fatigue acceptance criteria: Define the cycle count, deflection amplitude and allowable force loss; a controlled stainless steel spring etching line will test to that criterion rather than to a visual check.