Overview

Custom wafer bumping stencil etching produces the thin stainless plates used to print solder or copper-pillar bumps onto wafers for flip-chip and wafer-level packaging. The stencil is a full-field sheet in which every aperture is etched through, sized and positioned to match the bump map of a specific die. Because the artwork is generated from the customer's bump layout, a custom stencil matches the exact pitch, aperture diameter and die stepping of the wafer — no standard tool applies.

The key requirements are aperture uniformity and a flat, evenly tensioned foil. Etching delivers apertures with smooth, tapered sidewalls and consistent diameter across the full field, which keeps the deposited bump volume and height uniform. Stencils are typically 304 stainless steel from 0.03 mm to 0.15 mm thick, with aperture diameters scaled to the target bump size and pitch down to fine levels. Custom wafer bumping stencil etching therefore suits fine-pitch flip-chip, wafer bumping and chip-scale packaging, where stencil thickness, aperture size and field flatness directly control bump coplanarity.

Parameter Window

• Available Materials: 304 stainless steel (full-hard), optional nickel electroformed foil
• Material Thickness Range: 0.03–0.15 mm
• Tolerance: aperture diameter ±0.005 mm, aperture position ±0.01 mm across the field
• Minimum Feature: aperture down to 0.05 mm at fine pitch
• Surface Options: electropolished sidewalls, nano-coated for paste release, framed or frameless
• Compliance: ISO 9001 process control, RoHS/REACH material traceability

Manufacturing Process / Workflow (8 Steps)

1. Bump Map Import — Read the die bump layout and merge aperture size, pitch and stepping into a full-wafer pattern.
2. DFM & Aperture Sizing — Adjust aperture diameter and shape against stencil thickness so bump volume and release both land on target.
3. Material Selection — Choose full-hard 304 stainless at the specified thickness, matched to the required paste or bump height.
4. Cleaning & Lamination — Degrease the foil and laminate dry film resist on both sides for double-side etching.
5. Double-Side Exposure — Expose with front-to-back registration so apertures etch straight with smooth, tapered sidewalls.
6. Etching — Etch with matched chemistry, controlling time and temperature to reach diameter while keeping sidewall angle consistent.
7. Stripping & Finishing — Strip resist, neutralize, electropolish the sidewalls, then mount and tension the foil in the frame if required.
8. Inspection & Packaging — Measure aperture diameter, position and thickness optically, verify flatness and tension, then pack protected.

Core Advantages

1. Full-field aperture uniformity: Every aperture etches at the same rate, so bump volume and height stay consistent across the wafer.
2. Smooth tapered sidewalls: Etched sidewalls release paste cleanly, reducing bridging and improving transfer repeatability.
3. Tight dimensional control: Aperture diameter and position hold to ±0.005 mm and ±0.01 mm, matching fine-pitch bump maps.
4. No tooling: A custom stencil is a new film, so revised layouts and new die steps cost nothing to re-tool.
5. Flat, evenly tensioned foil: Double-side etching leaves the foil flat, so frame tension distributes evenly without wrinkles.
6. Fast iteration: Design changes to aperture size or pitch are implemented as artwork updates, not new dies.

Typical Applications

• Flip-chip bumping: Solder bump deposition stencils for die with fine pitch and high bump count.
• Wafer-level packaging: Full-wafer stencils for redistribution and ball placement.
• Copper pillar printing: Apertures sized for pillar height and diameter control.
• Ball grid array stencils: Fine apertures for BGA and CSP bump printing.
• MEMS wafer stencils: Small, precise apertures for micro-scale paste or solder transfer.
• Prototype bump stencils: Single-wafer and engineering stencils for process development.

Design Notes & Process Considerations

1. Aperture-to-thickness ratio: Size the aperture relative to stencil thickness; below a minimum ratio, paste release degrades.
2. Sidewall taper: Specify the sidewall angle, since a slight taper improves release for small apertures.
3. Field flatness: Call out flatness across the stencil field, as bow disturbs the print gap and bump coplanarity.
4. Tension and frame: State framed or frameless delivery and the target mesh tension so the stencil stays taught in service.
5. Coating: Name a nano or release coating for small apertures to improve paste transfer and reduce cleaning.
6. Pitch accuracy: Confirm die stepping and pitch from the actual wafer map, since stencil errors scale to every die.