Overview

Test spring etching uses photochemical machining to cut fine, flat contact springs out of thin spring alloy rather than forming them from drawn wire. A photoresist is laminated, exposed with the spring outline and developed, then the unprotected metal is dissolved in a matched etchant to leave the cantilever arms, tips and mounting tabs in one flat piece. Springs are usually made from beryllium copper (C17200) or 300-series stainless steel, supplied between 0.03 mm and 0.3 mm thick. Because the profile is chemically removed rather than die-stamped, the etched edges are smooth and stress-free, with none of the micro-cracks or burrs that shorten fatigue life.

For test probe and socket applications, the spring must deliver a repeatable contact force over millions of cycles while keeping electrical resistance low. Etching lets designers tune the beam width, length and thickness precisely, so the force and travel of every spring in a batch match the drawing. The stress-free edge also improves fatigue life, and the flat surface plates uniformly for stable contact resistance. This is why test spring etching is specified for pogo-pin springs, test-socket contacts and battery contacts where wire-formed or stamped springs cannot hold the same dimensional control.

Parameter Window

• Available Materials: beryllium copper (C17200), stainless steel 301/304
• Material Thickness Range: 0.03–0.3 mm
• Tolerance: ±0.01 mm on beam width, ±0.05 mm on overall length
• Minimum Feature: 0.03 mm beam width, 0.05 mm slot width
• Surface Options: gold plating, nickel plating, passivation, electropolish
• Compliance: ISO 9001 process control, RoHS/REACH material traceability

Manufacturing Process / Workflow (8 Steps)

1. Spring Design — Convert the spring profile to vector artwork and check beam width, length and bend radius against the target force.
2. Material Selection — Choose beryllium copper for low resistance and high fatigue strength, or stainless for corrosion resistance.
3. Cleaning & Lamination — Degrease the sheet and laminate dry film with no bubbles so the beam edges etch clean and straight.
4. UV Exposure — Expose the spring outline registered to the sheet for accurate tab-to-tip length across the panel.
5. Development — Wash out the unexposed resist to open the spring profile, then inspect for under-developed narrow slots.
6. Etching — Spray etch at controlled temperature; beam width is set by time, pressure and conveyor speed.
7. Stripping & Finishing — Remove resist, neutralize, then plate gold or nickel where the contact touches the pad.
8. Inspection & Packaging — Verify beam width, length and flatness on a vision system, then pack on trays to protect the arms.

Core Advantages

1. Controlled force: Beam width, length and thickness are held to microns, so contact force and travel repeat across every part.
2. High fatigue life: The stress-free etched edge has no micro-cracks, letting the spring survive millions of deflection cycles.
3. Low contact resistance: The flat, smooth surface plates uniformly and makes a consistent electrical contact.
4. Fine geometry: Beams down to 0.03 mm wide are routine, finer than wire-formed or stamped springs can hold.
5. No tooling cost: Each spring revision is a new film, so prototype and low-volume runs stay economical.
6. Batch consistency: Every spring on a sheet etches at the same rate, so force characteristics stay uniform.

Typical Applications

• Pogo-pin springs: Micro cantilever springs for test probes and spring-loaded pins.
• Test-socket contacts: Flat springs that make repeatable contact with IC pins and packages.
• Battery contacts: Leaf springs for coin-cell and rechargeable battery holders.
• Connector springs: Contact fingers for board-to-board and FPC connectors.
• Switch springs: Flat snap and return springs for tactile switches.
• Grounding springs: EMI grounding fingers for shielding and chassis contact.

Design Notes & Process Considerations

1. Beam versus force: Set beam width, length and thickness to reach the target force; small changes here shift deflection force sharply.
2. Fatigue margin: Keep maximum stress below the endurance limit and specify a stress-relief anneal where arms are long.
3. Plating callout: Name the plating and thickness on the contact face to hold contact resistance stable over life.
4. Bend allowance: State whether the spring is used flat or formed; etching suits flat profiles, with forming added downstream.
5. Edge condition: Require burr-free, crack-free edges, since edge defects are where fatigue failures begin.
6. Handling: Provide tab or carrier features so fine arms are not bent during plating and assembly.