Overview

Precision lead frame etching is the photochemical route to producing fine-pitch semiconductor leadframes, where lead fingers, die pads, tie bars and dam bars are dissolved out of a thin metal strip instead of being punched by a progressive die. A photoresist image is laminated, exposed and developed on both faces of the strip, and a matched etchant removes the unprotected metal from both sides at once, so the fingers keep a straight, burr-free sidewall and the strip stays flat. Stock is typically C1100 oxygen-free copper, C194 or C7025 copper alloys, Alloy 42 (Fe-Ni 42) and Kovar 4J29, in thicknesses from 0.08 mm to 0.30 mm.

Because precision lead frame etching is chemical rather than mechanical, it removes the die cost and the mechanical stress of stamping: a new leadframe design is simply a new photo-tool, and half-etched steps, dimples and locking features can be formed in the same pass as the through profile. Fine-pitch QFN, DFN, SOP and QFP strips down to 0.10 mm finger pitch hold ±0.01 mm on finger width and ±0.005 mm on pitch position, with coplanarity held across the strip for reliable wire bonding and mold registration. Selective plating, stress-relief annealing and tape-and-reel packing follow on the same line.

Parameter Window

• Available Materials: C1100 oxygen-free copper, C194/C7025 copper alloys, Alloy 42 (Fe-Ni 42), Kovar 4J29, stainless 304 carriers
• Material Thickness Range: 0.08–0.30 mm (0.15 / 0.20 / 0.25 mm standard)
• Tolerance: ±0.01 mm on finger width, ±0.005 mm on pitch position, ±0.01 mm on half-etched depth
• Minimum Feature: 0.08 mm finger width, 0.10 mm finger pitch, 0.03 mm half-etch step
• Surface Options: selective silver plating, Ni/Pd/Au (PPF), anti-tarnish, anneal flattening, tape-and-reel
• Compliance: ISO 9001 process control, RoHS/REACH material traceability

Manufacturing Process / Workflow (8 Steps)

1. Artwork & Panelization — Convert the leadframe drawing to vector artwork, set etch compensation per alloy and thickness, and lay the strips on a panel with shared fiducials.
2. Material Selection & Slitting — Choose C1100 copper, a copper alloy or Alloy 42, then slit and level the coil to the specified temper and flatness.
3. Cleaning & Double-Side Lamination — Degrease and micro-etch the strip, then laminate dry-film resist on both faces so top and bottom patterns register.
4. UV Exposure — Expose both sides through registered high-resolution film, aligning die pads and fingers to the strip datum.
5. Development — Wash out the unexposed resist to open through-cut and half-etch windows, then inspect fine fingers under magnification.
6. Etching — Spray ferric chloride or cupric chloride matched to the alloy, controlling time, temperature and conveyor speed for straight sidewalls and target half-etch depth.
7. Stripping & Plating — Remove resist, neutralize, stress-relieve anneal, then apply selective silver or Ni/Pd/Au plating to the bond areas.
8. Inspection & Packing — Measure finger width, pitch, coplanarity and plating thickness against the approved sample, then pack in tape-and-reel or trays.

Core Advantages

1. Fine pitch without a die: Fingers at 0.10 mm pitch and 0.08 mm width are formed by photo-tooling, so QFN and DFN designs need no progressive stamping die.
2. Burr-free flat strips: Chemical removal leaves no roll-over or shear burr, so coplanarity holds for wire bonding and the strip feeds smoothly through molding.
3. Half-etched features in one pass: Dimples, locking grooves, tie-bar thinning and die-pad steps are etched together with the outer profile.
4. No stamping stress: There is no work-hardened shear edge or residual stress at the leads, which improves plating adhesion and reduces package delamination.
5. Fast, low-cost revisions: A design change is a new film, not a new tool, so engineering lots and pin-out variants stay economical.
6. Copper and Alloy 42 on one line: Precision lead frame etching runs C1100, C194 and Alloy 42 with only a chemistry change, so prototypes and production share one tooling set.

Typical Applications

• QFN / DFN leadframes: Fine-pitch, pad-down packages for power management and RF ICs on 0.20 mm copper.
• SOP / QFP strips: Multi-row leadframes with tie bars and dam bars etched for logic and analog devices.
• Leadless carriers & pads: Etched die pads and land grids for MOSFET and LED packages.
• Opto and sensor frames: Reflective-cup and cavity features half-etched into silver-plated copper.
• Discrete component frames: Fine fingers for diodes, transistors and small-signal packages in tape-and-reel.
• Prototype / engineering lots: Short-run leadframes for package development and reliability testing before tooling.

Design Notes & Process Considerations

1. Etch factor and compensation: State the alloy and thickness so artwork compensation can be set; thin C1100 etches faster than Alloy 42 and needs a different allowance.
2. Half-etch depth callout: Specify step depth (commonly 0.03–0.08 mm) and remaining thickness, and mark which areas are through-cut versus half-etched.
3. Finger width versus thickness: Keep the minimum finger near 1.2 × material thickness, or fingers may undercut and lose width on fine-pitch rows.
4. Coplanarity requirement: Call out strip flatness and coplanarity (e.g. ≤ 0.05 mm) when the frame runs through automatic wire bonders.
5. Plating and bond area: Name the plating system and thickness on bond fingers; selective silver and Ni/Pd/Au need clear masking boundaries.
6. Panel datum and rail: Provide fiducials, rail holes and a strip datum so exposure, plating and tape-and-reel all register to the same reference.