Overview

Copper wafer stencil chemical etching produces the thin apertured masks used to print solder paste or bump flux onto wafers before reflow. From C1100 copper foil between 0.05 and 0.20 mm, photochemical machining opens aperture arrays down to 0.08 mm with a positional tolerance near ±0.005 mm, and the same film repeats the layout across the whole panel. Because the metal is dissolved rather than melted, aperture walls stay smooth and free of recast layer or heat-affected edge, which is what governs paste release. The finished foil is then bonded under tension to an aluminium frame so it stays flat through thousands of print strokes.

Two numbers dominate this part: aperture geometry and mesh tension. Area ratio, aperture opening divided by wall area, must stay above 0.66 for reliable paste transfer, so foil thickness and aperture size are chosen together, and walls are given a slight taper by controlling etch time and spray pressure. This route also allows stepped or nano-coated foils where mixed bump sizes print in one pass. Mounting tension of 35–45 N/cm and a squared frame keep registration stable; without it, even a perfectly etched foil smears fine-pitch bumps on a 300 mm wafer. That is why copper wafer stencil chemical etching is judged as much by the mount as by the aperture.

Parameter Window

• Available Materials: C1100 oxygen-free copper foil, C194 copper alloy, nickel-plated copper on request
• Material Thickness Range: 0.05–0.20 mm, selected against aperture area ratio
• Tolerance: aperture ±0.005 mm, position ±0.010 mm over 300 mm, thickness ±0.005 mm
• Minimum Feature: 0.08 mm aperture, 0.10 mm web, 0.15 mm pitch at 0.05 mm foil
• Surface Options: bare, nano-coating, electropolished walls, framed at 35–45 N/cm, adhesive gasket
• Compliance: ISO 9001 process control, RoHS/REACH material traceability

Manufacturing Process / Workflow (8 Steps)

1. Data & Panelisation — Import the wafer bump map, verify aperture area ratio and step the layout across a production panel.
2. Foil Selection — Choose gauge from the smallest aperture, then confirm thickness uniformity and flatness of the copper roll.
3. Cleaning & Lamination — Degrease the foil and laminate dry film on both faces so apertures etch symmetrically from two sides.
4. Dual-Side Exposure — Expose registered front and back artwork, holding web width to the bump pitch datum.
5. Development — Develop both faces and inspect every aperture field for scumming before the foil enters etchant.
6. Controlled Etching — Spray cupric chloride at fixed Baume and temperature to open apertures and set a slight wall taper.
7. Stripping & Coating — Strip resist, electropolish the walls, then apply optional nano-coating for paste release.
8. Tensioning & Framing — Bond the foil to the frame at 35–45 N/cm, verify tension, aperture size and registration, then pack flat.

Core Advantages

1. Smooth aperture walls: Chemical dissolution leaves no recast layer or dross, so solder paste releases cleanly from fine-pitch openings.
2. Two-sided symmetry: Dual-face etching gives a near-vertical, slightly tapered wall that improves transfer efficiency on small bumps.
3. Tight aperture control: ±0.005 mm aperture tolerance holds bump volume consistent across a 300 mm wafer and from stencil to stencil.
4. No thermal distortion: Foil is never heated locally, so it stays flat and free of the edge curl that laser cutting can introduce.
5. Fast revision: A new bump map is a new film, so prototype and engineering changes need no new mandrel or hard tooling.
6. Mounting included: A verified copper wafer stencil chemical etching line delivers the foil already tensioned on its frame, ready for the printer.

Typical Applications

• Wafer bumping stencils: Flux or solder-paste printing for flip-chip bump arrays on 200 mm and 300 mm wafers.
• Fine-pitch paste masks: Printing for 0.15 mm pitch micro-bumps in advanced packaging lines.
• Underfill dams: Step-etched apertures that define dam regions around low-k die areas.
• MEMS solder transfer: Small-volume deposit masks for sensor and actuator assembly.
• LED flip-chip printing: Aperture arrays for phosphor and die-attach material deposition.
• Rework and prototype masks: Short-run framed stencils for process development and bump-metallurgy trials.

Design Notes & Process Considerations

1. Area ratio: Keep opening area divided by wall area above 0.66, or thin foils will not release paste reliably at fine pitch.
2. Gauge versus aperture: Fix foil thickness from the smallest aperture first; a thinner foil prints smaller bumps but wrinkles more easily on the frame.
3. Wall taper: Specify the taper direction and angle, since a 1–2 degree wall helps release without widening the printed deposit.
4. Positional datum: Tie the aperture field to the wafer flat or notch datum and state tolerance over the full 300 mm span.
5. Fiducials: Add alignment marks outside the print field, half-etched or through-cut, for printer camera registration.
6. Tension callout: State mesh tension and frame flatness, and require a tension map, because a loose mount ruins otherwise good apertures.