Overview

Leadframe chemical etching is a process-parameter discipline as much as a patterning one. The same artwork will produce different lead widths, different half-etch depths and different coplanarity if bath concentration, temperature, spray pressure or line speed drifts between runs. In practice the window is held by three loops working together: chemistry (copper concentration, specific gravity and oxidation potential in a cupric chloride bath, or peroxide and sulphuric acid in the alternative), transport (line speed and nozzle pressure on a conveyorised spray etcher), and undercut (the single-side etch allowance expressed as a ratio to strip thickness).

Strips are usually copper alloy C194 or C7025, or iron-nickel alloy 42, between 0.10 mm and 0.50 mm thick, supplied on reels for downstream stamping, plating and moulding. Etching removes metal without a die, so a new frame layout is a new film rather than a new tool, and the same line holds 0.05 mm line and space at 0.15 mm stock. The chemistry also leaves a matte surface that gives mould compound a mechanical key, which is why leadframe chemical etching is often chosen for packages where delamination is the yield limiter.

Parameter Window

• Available Materials: copper alloy C194/C7025, iron-nickel alloy 42, 316L stainless steel for special frames
• Material Thickness Range: 0.10–0.50 mm strip
• Tolerance: ±0.025 mm on pattern profile, ±0.05 mm on strip edge, ±0.01 mm on half-etch depth
• Minimum Feature: 0.05 mm line and space at 0.15 mm stock; 0.30 mm minimum bond pad
• Surface Options: matte etch finish Ra 0.3–0.6 µm, selective silver, nickel, black oxide
• Compliance: ISO 9001 process control, RoHS/REACH material traceability

Manufacturing Process / Workflow (8 Steps)

1. Pattern Compensation Review — Set undercut allowance against strip thickness and write the single-side growth into the film before imaging.
2. Dewind and Clean — Unwind the reel under controlled tension, degrease and micro-etch so resist bonds evenly across the full strip width.
3. Dry Film Lamination — Apply 25–38 µm resist at 105–115 °C roll temperature, keeping pressure uniform to avoid edge voids.
4. Double-Sided Exposure — Expose both faces at 60–90 mJ/cm² against shared targets, holding front-to-back registration within ±0.01 mm.
5. Development — Develop in 1% sodium carbonate at 30 °C to a clear breakpoint, then confirm the finest space has opened fully.
6. Bath Etching — Hold cupric chloride at 1.28–1.32 specific gravity and 48–52 °C, run 2.5–4.5 m/min at 0.15–0.25 MPa spray, and log undercut.
7. Stripping and Plating — Remove resist in 3–5% caustic, neutralise, then apply selective silver or nickel only where wire bonding requires it.
8. Inspection and Cutting — Measure lead width, pitch, half-etch depth and coplanarity, then slit to reel or cut to strip length.

Core Advantages

1. No die, no tooling lead time: A frame revision is a film change, so first articles arrive without a stamping tool build or die trial.
2. Burr-free edges: Chemical removal leaves no roll-over, so leads seat flat in the mould and co-planarity stays inside package tolerance.
3. Half-etch in one pass: Down-set pads and die flags are produced by timed depth control rather than a separate coining step.
4. Matte surface for mould lock: The etched finish gives compound a mechanical key and reduces delamination at the lead exit.
5. Stable fine pitch: With bath and line speed held, 0.05 mm spaces repeat across the strip and from reel to reel.
6. Reel-to-reel handling: Frames stay on the carrier through etch, strip and plate, which suits automated assembly and avoids manual handling damage.

Typical Applications

• QFN and DFN frames: Fine-pitch lead arrays with half-etched stand-off pads on 0.20 mm copper strip.
• Leadless power packages: Thick die paddles and short leads for thermal paths in motor drivers and converters.
• Sensor and MEMS frames: Small outline frames with tight positional tolerance for moulded sensor bodies.
• Optical module frames: Alloy 42 frames matched to glass and ceramic for low expansion in laser housings.
• Discrete device strips: Diode and transistor frames etched in long reels for high-speed assembly.
• Prototype and low-volume frames: New package outlines proved on film before any hard tool is committed.

Design Notes & Process Considerations

1. Undercut allowance: Expect 0.8–1.2 × thickness of single-side growth; dimension finished lead width and state whether compensation is included.
2. Half-etch depth: Call depth as a percentage of stock with a tolerance — 50% ±0.01 mm is typical — and avoid depths beyond 70%, where the floor thins.
3. Lead width versus thickness: Keep the narrowest lead at 0.05 mm or 0.4 × thickness, whichever is larger, or the etch will taper the sidewall.
4. Bath control: Specify copper concentration, specific gravity and temperature limits in the control plan; drifting chemistry is the main cause of pitch loss.
5. Tie-bar and carrier design: Leave enough carrier rail for reel transport and keep tie-bars outside the moulding zone so they can be trimmed after assembly.
6. Surface for bonding: State the bonded area and finish, since selective silver must be defined before etching so the mask can protect it.