Overview

Terminal chemical etching is a photochemical machining route for connector contacts, lead-frame-like terminal strips and fine contact fingers where a clean edge and stable conductivity matter more than raw cutting speed. A dry-film resist image defines the finger outline, the exposed copper or copper-alloy is dissolved in a controlled etchant, and the result is a burr-free part whose electrical properties are unchanged: no heat-affected zone, no work hardening, no smeared metal to bridge adjacent fingers. Strip materials are typically C1100 copper, phosphor bronze C5191/C5210, brass, beryllium copper C17200 and Alloy 42, from 0.05 mm to 0.8 mm, with finger pitches down to 0.3 mm and widths to 0.1 mm held at ±0.01 mm.

For a connector designer, terminal chemical etching is as much about protecting conductivity as about shaping metal. The etchant must remove metal without attacking the resist wall or leaving residues that raise contact resistance, and the fine fingers must survive development, etching and stripping without bending or shorting. Lateral undercut narrows each finger as it cuts, so artwork is oversized by the etch factor and bath dwell is logged against CuCl2 or FeCl3 concentration, temperature, ORP and conveyor speed. Selective Ni/Au or Sn plating is then applied to the contact zone for solderability and corrosion resistance, while half-etch bend lines and carrier tabs are built into the same mask. The sections below set out the parameter window, the eight-step flow and the design rules that keep fine-pitch terminals repeatable.

Parameter Window

• Available Materials: C1100 copper, phosphor bronze C5191/C5210, brass, beryllium copper C17200, nickel silver, Alloy 42
• Material Thickness Range: 0.05–0.8 mm strip, with 0.1–0.3 mm typical for fine-pitch terminals
• Tolerance: ±0.01 mm on finger width and pitch, ±0.005 mm on 0.1 mm stock
• Minimum Feature: 0.1 mm finger width, 0.15 mm gap, 0.3 mm pitch, 0.1 mm bend-line half-etch
• Surface Options: selective Ni/Au, bright or matte Sn, Ni underplate, anti-tarnish, reflow-ready finish
• Compliance: ISO 9001 process control, RoHS/REACH material traceability

Manufacturing Process / Workflow (8 Steps)

1. Artwork & Etch Compensation — Oversize fine fingers in the mask by the expected undercut so the finished width lands on target after lateral attack.
2. Strip Selection — Choose alloy temper for spring properties and conductivity, then slit and level the strip for uniform resist contact.
3. Cleaning & Lamination — Degrease and hot-roll dry-film resist on both faces; bubbles over a finger root would open a hidden weak point.
4. UV Exposure — Expose the finger and carrier pattern through registered tooling, keeping the contact zone and bend lines in one image.
5. Development — Open the unwanted metal areas and inspect fine gaps for scumming that could electrically bridge two adjacent fingers.
6. Controlled Etching — Spray CuCl2 or FeCl3 matched to the alloy, holding Baumé, temperature, ORP and conveyor speed to protect wall straightness and conductivity.
7. Stripping & Plating — Strip resist, neutralize and clean, then selectively plate Ni/Au or Sn on the contact zone and apply anti-tarnish.
8. Inspection & Reeling — Verify finger width, pitch, flatness and continuity, then reel or tray-pack with interleaf to protect fine fingers.

Core Advantages

1. Fine, burr-free fingers: Chemical removal leaves no rolled edge or sliver, so adjacent contacts cannot short and insertion force stays predictable.
2. Conductivity preserved: No heat or cold work means bulk resistivity and spring temper of copper or phosphor bronze are retained as supplied.
3. No stamping die: New terminal geometries are new films, so fine-pitch prototypes and frequent revisions carry no tooling cost.
4. Half-etch features in one pass: Bend lines, carrier tabs and stepped thicknesses are imaged with the outline, removing secondary forming steps.
5. Flat, stress-free strips: Etched terminals stay flat for automated reel-to-reel assembly and reflow without distortion from punching.
6. Plating ready: Clean, oxide-free edges accept selective Ni/Au or Sn uniformly, giving stable contact resistance and solderability.

Typical Applications

• Board-to-board connectors: Fine-pitch contact fingers in phosphor bronze or beryllium copper with selective gold on the mating zone.
• FPC/FFC terminals: Thin etched tails and reinforcement tabs for flexible printed circuit connectors.
• Battery and cell contacts: C1100 copper tab arrays with burr-free edges for welded or soldered cell interconnects.
• Lead-frame-style strips: Etched terminal arrays on a carrier for overmolding and singulation.
• Spring contacts: Beryllium copper or phosphor bronze fingers that need both conductivity and controlled spring force.
• Shielding and grounding clips: Flat etched contacts with half-etch fold lines for EMI grounding in housings.

Design Notes & Process Considerations

1. Etch factor on fingers: Give foil thickness and expected undercut ratio; fingers are oversized in artwork or they finish narrow and resistance rises.
2. Gap-to-thickness ratio: Keep the gap between fingers at or above material thickness, or lateral attack can merge two contacts into a short.
3. Grain and spring direction: Orient fine fingers across the rolling direction when spring force matters, and state temper on the drawing.
4. Plating mask: Define the selective-plating boundary; allow for plating thickness on finger width so the finished contact stays within tolerance.
5. Carrier and handling: Retain a carrier frame and break-off tabs so fine fingers survive etching, plating and reel transport without bending.
6. Chemistry and residue: Log Baumé, temperature, ORP and conveyor speed, and require a clean rinse; trapped etchant residue raises contact resistance, a known risk in terminal chemical etching.