Overview

Spring chemical etching forms flat springs, contact fingers and leaf elements by dissolving the outline out of tempered strip, so the spring is never sheared, bent or struck. The material is laminated, exposed through a film carrying the spring profile, developed, and etched from both faces, which leaves an edge that is square, burr-free and free of the work-hardened zone that punching leaves along a cut. For a part that flexes millions of times, that edge condition matters more than the outline tolerance: fatigue cracks start at burrs and at the micro-cracks a shear edge carries, and neither exists after chemical machining.

Spring rate is set by geometry and by the temper of the strip, not by the process, which is why the process suits springs that must be identical in a batch. Etching removes a uniform amount of material from each face, so a cantilever 0.2 mm thick stays 0.2 mm thick along its length, and the deflection calculated from the drawing is the deflection measured on the part. Common substrates are spring steel 301, 17-7PH, beryllium copper C17200, phosphor bronze C5210 and stainless 304/316L, from 0.05 mm to 0.8 mm.

Parameter Window

• Available Materials: spring steel 301, 17-7PH, beryllium copper C17200, phosphor bronze C5210, stainless steel 304/316L
• Material Thickness Range: 0.05–0.8 mm
• Tolerance: ±0.05 mm on profile, ±0.01 mm on strip thickness, ±10% on calculated spring rate after heat treatment
• Minimum Feature: 0.12 mm arm width and 0.15 mm slot at 0.1 mm stock; 0.3 mm at 0.5 mm stock
• Surface Options: as-etched, passivation, nickel or gold plating, black oxide, stress-relief anneal, age hardening
• Compliance: ISO 9001 process control, RoHS/REACH material traceability

Manufacturing Process / Workflow (8 Steps)

1. Spring Design Review — Check arm width against thickness, root radii, travel and the load point, and confirm the target rate is reachable in the chosen alloy.
2. Alloy & Temper Selection — Match temper to the required rate and fatigue life; 301 for general purpose, 17-7PH where corrosion and stress relaxation both matter.
3. Film Set & Prototype — Produce the film and a prototype lot so the rate can be measured on real parts before batch release.
4. Cleaning & Lamination — Degrease and laminate resist on both faces without tensioning the strip, since stretched foil changes the finished rate.
5. Exposure & Development — Expose both faces with registered artwork and develop fully; a partly opened root radius becomes a stress riser.
6. Etching — Etch in chemistry matched to the alloy, controlling time and temperature so arm width and thickness both land in window.
7. Strip & Heat Treatment — Remove resist, then stress-relieve or age harden as specified; this step sets the final rate and removes etch-induced residual stress.
8. Rate Test & Packing — Measure load at deflection on a sample, check flatness and burr, then pack so springs are not pre-loaded in transit.

Core Advantages

1. No burr at the fatigue-critical edge: A chemically machined edge has no roll-over and no micro-crack, so crack initiation at the tensile edge is delayed and life cycles rise.
2. No work-hardened shear zone: Punching hardens the cut edge and leaves residual stress; etching leaves the metallurgy of the strip intact along the profile.
3. Rate that repeats: Thickness and arm width are controlled independently of tool wear, so the tenth thousand spring deflects like the first.
4. Geometry without a die: Spiral, meander, multi-arm and tapered profiles are film features, so a new spring design costs a film rather than a progressive die.
5. Stress relief built into the route: Anneal or age hardening after etching sets the final rate and relaxes the stress the etch itself introduces.
6. Thin stock handled well: Etching holds 0.05 mm spring steel flat where stamping would distort it. Spring chemical etching therefore covers the thin, high-cycle parts that are hardest to punch.

Typical Applications

• Contact fingers and leaf contacts: Multi-finger contacts in connectors, etched as one strip with uniform finger force.
• Battery and terminal springs: Flat springs that hold a cell or a contact in place under vibration.
• Snap and latch springs: Detent arms and latch fingers where the root radius controls both force and life.
• Flat spiral springs: Clock-type and constant-force spirals etched from 0.1 mm strip without a forming die.
• Valve and diaphragm reeds: Thin reeds that seal or modulate flow and must sit flat on their seat.
• Shield and grounding fingers: Spring fingers that maintain contact between shielding cans and board ground.

Design Notes & Process Considerations

1. Arm width versus thickness: Keep the narrowest arm at 1.2 × thickness or more; thinner arms etch with a rounded section and the rate drops below calculation.
2. Root radius: Use a radius of at least 0.5 × arm width at every bend or transition; a sharp internal corner is where the spring will eventually break.
3. Rate tolerance: State the rate as load at a defined deflection, not as a thickness, and allow ±10% unless the design has been characterised.
4. Heat treatment callout: Say whether the part is stress-relieved or age hardened, and at what condition; skipping it leaves the rate drifting after assembly.
5. Edge condition: Specify burr-free edges and avoid tumbling, which rounds the edge and changes the effective section of a thin spring.
6. Grain direction: Spring strip is anisotropic, so state whether the flexing arm should run along or across the rolling direction. A spring chemical etching supplier should confirm this before the film is made.