Overview

A copper wafer bumping stencil etching process cuts an array of fine apertures through thin C1100 copper sheet so that solder paste, solder balls or plating current reach only the designated pads on a wafer. Aperture diameter, not outline accuracy, is the figure that governs deposited bump volume, so the process is tuned around hole size, wall taper and positional accuracy rather than around the outer profile. Typical stencils run 0.05–0.30 mm thick, with apertures from 0.05 mm to 0.30 mm held to ±0.005 mm and registered to the wafer map within ±0.01 mm over a 300 mm span.

Photochemical machining suits this part because a single film can carry tens of thousands of apertures at once, all etched at the same rate, with no punch wear and no burr to trap paste. A copper wafer bumping stencil etching supplier can also build a slight trapezoidal wall by etching from both faces, which improves paste release at fine pitch. Electropolishing and optional nano-coating on the aperture walls further cut transfer loss. Because there is no hard tooling, a new bump map is simply a new film, keeping prototype and revision lead times short.

Parameter Window

• Available Materials: C1100 (Cu-ETP) and oxygen-free C1020 copper; nickel-iron and stainless alternatives on request
• Material Thickness Range: 0.05–0.30 mm (stencil gauge selected to match target bump height and solder volume)
• Tolerance: aperture diameter ±0.005 mm, positional accuracy ±0.01 mm over 300 mm, thickness ±0.008 mm
• Minimum Feature: 0.05 mm aperture diameter, 0.08 mm web, 0.10 mm pitch on fine-pitch arrays
• Surface Options: electropolished walls, nano-coat / polymer release layer, anti-tarnish, framed or frameless, protective liner
• Compliance: ISO 9001 process control, RoHS/REACH material traceability

Manufacturing Process / Workflow (8 Steps)

1. Wafer Map Review — Import the bump layout, check aperture-to-pad alignment, pitch and area ratio against the stencil gauge.
2. Material Selection — Certify C1100 copper gauge and flatness, then cut blanks with stress relieved before lamination.
3. Cleaning & Lamination — Degrease and laminate dry film on both faces so no particle sits inside a sub-0.1 mm aperture.
4. Dual-Side Exposure — Expose top and bottom artwork to shared fiducials, biasing aperture size to offset lateral undercut.
5. Development & AOI — Develop both sides and run automated optical inspection on every aperture before etching.
6. Two-Side Etching — Etch from both faces in controlled chemistry to form straight or slightly tapered release walls.
7. Electropolish & Coat — Strip resist, electropolish the aperture walls, then apply nano-coating and mount into a frame if required.
8. Metrology & Pack — Measure aperture diameter, positional error and wall finish against the approved article, then vacuum-pack.

Core Advantages

1. Aperture accuracy sets bump volume: Tight control of hole diameter and taper gives consistent solder deposit, so bump height spread stays narrow.
2. Tooling-free wafer maps: A copper wafer bumping stencil etching program issues a new film for each device revision, with no die cost.
3. Tens of thousands of holes at once: All apertures on a panel etch simultaneously, so transfer behaviour is uniform across the whole array.
4. Clean burr-free walls: Electropolished, burr-free apertures release paste cleanly and resist clogging at fine pitch.
5. Tunable wall taper: Dual-side etching builds a controlled trapezoid that improves release without laser recast or mechanical stress.
6. Fast prototype turnaround: Without hard tooling, a new bump layout moves from file to sample in days rather than weeks.

Typical Applications

• WLCSP wafer bumping: Solder-paste or ball-drop stencils for wafer-level chip-scale packaging.
• Flip-chip solder printing: Fine-pitch stencils that deposit paste on die pads before reflow.
• Micro-ball attach masks: Aperture arrays that place solder balls or copper pillars on interposers.
• MEMS and sensor packaging: Small-volume, high-accuracy paste deposits on delicate device wafers.
• LED and power device bumping: Stencils for larger apertures where volume uniformity controls thermal joints.
• 2.5D interposer and RDL printing: Registered aperture grids for redistribution-layer and via filling.

Design Notes & Process Considerations

1. Area and aspect ratio: Keep aperture area ratio above 0.66 and aspect ratio above 1.5, or paste release becomes erratic at fine pitch.
2. Side-etch compensation: Bias the artwork aperture smaller by roughly twice the lateral undercut so the etched opening lands on nominal diameter.
3. Wall taper for release: Specify the taper direction and angle, typically 1–2 degrees wider on the squeegee side, to aid paste transfer.
4. Positional registration: Provide wafer-map fiducials and state allowable cumulative error over the full 300 mm span.
5. Flatness and gasket seal: Call out flatness and frame tension, since a bowed stencil leaks paste at the wafer contact line.
6. Handling and cleanliness: A copper wafer bumping stencil etching drawing should require electropolished walls, nano-coating and cleanroom packing.