Overview

A stainless steel lead frame etching process produces the stamped-and-etched lead frames used to carry semiconductor dies, by dissolving the lead pattern and tie bars from thin metal instead of blanking them with a progressive die. Grades 304/316L, iron-nickel 42 alloy and Invar, 0.10–0.50 mm thick, are laminated on both faces, exposed and developed, then etched in matched ferric-chloride chemistry that cuts clean, burr-free leads and half-etched pad recesses in one pass. Because the metal is removed chemically, no shear stress is introduced and the lead tips stay flat.

For a lead frame the property that governs wire bonding and solder joint yield is coplanarity, and stainless steel lead frame etching protects it by etching both faces symmetrically and avoiding the bending a die imparts. Side etch is compensated at roughly 0.6–0.8 × thickness per side so a 0.15 mm lead holds ±0.02 mm, while a timed half-etch forms the die-pad recess and locking features without a separate operation. The whole strip shares one film, so lead pitch and flatness repeat identically from the first sample to high-volume reels.

Parameter Window

• Available Materials: stainless steel 304/316L, iron-nickel 42 alloy (Kovar-type), Invar, copper-clad stainless
• Material Thickness Range: 0.10–0.50 mm (0.15–0.25 mm typical)
• Tolerance: lead width ±0.02 mm, pitch ±0.02 mm, coplanarity ≤ 0.03 mm over 50 mm
• Minimum Feature: 0.12 mm lead width, 0.15 mm gap, half-etch depth 30–60% of thickness
• Surface Options: selective Ni/Ag/Au plating, matte or bright finish, spot plating on bond areas, reel/strip format
• Compliance: ISO 9001 process control, RoHS/REACH material traceability

Manufacturing Process / Workflow (8 Steps)

1. Artwork & Coplanarity Design — Draw the lead pattern with balanced dual-side lands and compensate side etch at 0.6–0.8 × thickness per side.
2. Material Selection — Choose 42 alloy for matched thermal expansion or 316L for corrosion resistance, and verify temper and flatness.
3. Cleaning & Lamination — Laminate dry-film resist on both faces so fine leads, tie bars and half-etch pads are fully protected.
4. Dual-Side UV Exposure — Expose top and bottom artwork in tight registration so both etch fronts meet at the sheet mid-plane.
5. Development — Wash out unexposed resist to open the lead outlines and recess lands, inspecting the narrow gaps for scumming.
6. Etching — Spray ferric chloride to cut the leads through while a controlled dwell forms the half-etched pad recess.
7. Stripping & Plating — Strip resist, neutralize, then apply selective Ni/Ag/Au plating on bond and lead areas.
8. Inspection & Packaging — Verify lead width, pitch and coplanarity, check burr-free tips, then reel or tray the strips.

Core Advantages

1. Coplanar lead tips: Symmetric dual-side etching keeps all leads in one plane, so solder joints form evenly.
2. Burr-free bonding: Chemical removal leaves no shear burr on bond pads, protecting fine wire bonds.
3. Half-etch features in one pass: Die-pad recesses and locking dimples are etched with the outline, removing a coining step.
4. No die-induced stress: Without blanking force, the strip stays flat and lead pitch does not spring back.
5. Fine pitch at thin stock: 0.12 mm leads with 0.15 mm gaps hold on 0.15 mm foil where a die would smear.
6. Reel-ready from one film: stainless steel lead frame etching produces strip or reel format from a single artwork, so prototype and volume runs use the same geometry.

Typical Applications

• IC and discrete packages: 42-alloy lead frames for diodes, transistors and small-outline packages.
• LED and opto devices: 304 frames with selective silver plating for reflective lead areas.
• Sensor and MEMS packages: 316L frames with half-etched die recesses for cavity packages.
• Power modules: Thicker frames with robust tie bars for high-current devices.
• RF and microwave packages: Low-stress frames with tight coplanarity for wire-bonded die.
• Prototype and low-volume assembly: Etched frames that avoid a hard-tooling charge for new packages.

Design Notes & Process Considerations

1. Coplanarity callout: State the allowable coplanarity over a defined span, since it drives solder joint yield.
2. Half-etch depth: Give the residual thickness at the die pad, typically 40–60% of stock, and confirm on a cross-section.
3. Thermal expansion match: Choose 42 alloy or Invar when the die and frame must expand together during reflow.
4. Plating definition: Specify which areas get Ni/Ag/Au and the thickness, so bond and solder regions are protected.
5. Tie-bar design: Keep tie bars wide enough to hold the strip through etching and plating, then define the trim line.
6. Flatness and format: stainless steel lead frame etching strips should ship flat in reel or tray, with flatness per 100 mm called out.