Overview

A custom copper test spring is a fine elastic contact used in probe cards, test sockets and board-level fixtures, etched from beryllium copper or phosphor bronze foil. Photochemical machining forms the spring beam, contact tip and mounting frame without mechanical load, so the part keeps a uniform cross-section, burr-free edges and a repeatable spring rate. Copper alloys combine high conductivity with good fatigue life, which keeps contact resistance low over hundreds of thousands of test cycles. Stock is typically 0.05–0.30 mm with feature tolerance held to ±0.01 mm.

Test engineers specify a custom copper test spring when a probe must deliver stable force and low resistance in a very small pitch. Because the geometry comes from a phototool rather than a die, beam length, tip shape and preload can be tuned to hit a target force-deflection curve without a tooling programme. A custom copper test spring also leaves the line flat and stress-free, so an array of springs seats evenly against a wafer or a device under test.

Parameter Window

• Available Materials: beryllium copper C17200, phosphor bronze, copper C11000, nickel silver
• Material Thickness Range: 0.05–0.30 mm (common 0.08, 0.10, 0.15, 0.20 mm)
• Tolerance: ±0.01 mm on feature, ±0.02 mm on profile, ±10% on half-etched spring relief
• Minimum Feature: 0.08 mm beam, 0.10 mm slot, 0.20 mm pitch
• Surface Options: degreased, passivated, Ni/Au plating, hardened and set, carrier strip or loose piece
• Compliance: ISO 9001 process control, RoHS/REACH material traceability

Manufacturing Process / Workflow (8 Steps)

1. Artwork Review — Confirm beam length, tip geometry, target force and array pitch against the test fixture drawing.
2. Material Selection — Choose BeCu C17200 or phosphor bronze by conductivity and fatigue needs, and check coil flatness.
3. Cleaning & Lamination — Degrease and laminate dry film on both faces, keeping the resist thin over narrow beams.
4. UV Exposure — Expose through registered high-resolution film with tips referenced to the carrier edge.
5. Development — Wash out unexposed resist and inspect narrow beams and tips for complete opening.
6. Etching — Spray-etch with alloy-matched chemistry, controlling time and speed for straight, burr-free beam edges.
7. Stripping & Finishing — Strip resist, neutralize, then plate Ni/Au and heat-set the alloy to lock in spring force.
8. Inspection & Packaging — Measure beam width and force, verify flatness and resistance, then pack on carrier or in trays.

Core Advantages

1. Repeatable spring force: A uniform etched section gives consistent force from spring to spring across a dense array.
2. Low contact resistance: BeCu or plated copper keeps resistance stable over long test runs and many touchdowns.
3. Burr-free tips: Smooth contact tips do not scratch a wafer pad or a device ball, protecting the surface under test.
4. Fine-pitch arrays: 0.08 mm beams on 0.20 mm pitch fit high-density probe cards and fine-pitch sockets.
5. Tool-free force tuning: Changing beam length or preload is a film change, so force can be tuned without die charges.
6. Material flexibility: A custom copper test spring can run in BeCu, phosphor bronze or nickel silver and be plated for wear life.

Typical Applications

• Wafer probe cards: Spring contacts that touch die pads during wafer-level electrical test.
• IC test sockets: Elastic beams that hold a packaged device with steady force through burn-in.
• Burn-in boards: Contact arrays that survive long high-temperature test cycles.
• Board-level test fixtures: Springs that reach test points on assembled PCBs without soldering.
• RF and high-speed test: Low-resistance, short-path contacts for signal integrity at high frequency.
• Fine-pitch device interfaces: Probe tips for small-pitch BGAs and wafer-level packages.

Design Notes & Process Considerations

1. Beam width versus thickness: Keep the beam at 0.08 mm or 1.2 × thickness, whichever is larger, to avoid uneven etching.
2. Force-deflection callout: State force at a defined deflection, since beam length, width and thickness set the spring rate together.
3. Plating and life: Name the plating metal and thickness, and relate it to the target touchdown count.
4. Heat setting: Confirm the ageing or setting cycle that locks spring force, especially for BeCu parts.
5. Flatness and carrier: Specify carrier flatness and whether parts ship on strip or loose for automated assembly.
6. Inspection criteria: Agree beam width, force and sampling plan; documenting these on the drawing cuts review cycles.