LASER-CUT SMT STENCILS
Laser-Cut PCB Stencils (SMT Stencils): Framed, Frameless, Step and Nano-Coated
A PCB stencil (SMT stencil, solder paste stencil) is a thin stainless steel foil with laser-cut apertures that sets how much solder paste lands on each pad. APTPCB cuts framed and frameless stencils from your paste layer, with step-down areas and nano-coating where the board needs them. Foil thickness and aperture size decide paste volume, so they are checked against your smallest pitch before cutting.
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What is a PCB stencil and what does it control?
What stencil thickness should you use? Foil thickness by smallest pitch
| Board condition | Foil thickness | Stencil solution | Why |
|---|---|---|---|
| Standard 0805/1206 and mixed SMT | 127–150 µm | SUS304 laser-cut stencil | Stable general-purpose printing |
| Fine-pitch ICs, 0.5 mm pitch | 100–127 µm | Laser-cut + optimized apertures | Improves paste release on narrow apertures |
| 0.4 mm pitch and below | 80–100 µm | Laser-cut, electropolished, tight process control | Small apertures need smooth walls to release |
| QFN with exposed pad | Set by the finest pitch on the board | Window-pane aperture on the thermal pad | Controls voiding and float |
| Large connectors + fine BGA | Step stencil | Step-up or step-down areas | Two paste volumes on one board |
| High-volume production | Set by pitch | Nano-coated stencil | Longer intervals between under-stencil cleaning |
| Prototype builds | Set by pitch | Frameless stencil | Lower tooling cost |
Thickness is set by the finest-pitch part on the board, then other apertures are adjusted. Detailed aperture rules are in the SMT stencil design tutorial.
Stencil aperture design rules: area ratio and aspect ratio
| Rule | Formula | Target | What fails if it is missed |
|---|---|---|---|
| Area ratio | Aperture opening area ÷ aperture wall area | ≥ 0.66 | Paste stays in the aperture; open or starved joints |
| Aspect ratio | Aperture width ÷ foil thickness | ≥ 1.5 | Poor aperture filling on narrow rectangles |
| QFN thermal pad | Split into window-pane openings | Web ≈ 0.2 mm or more | Excess paste floats the part and traps voids |
| Fiducials | Global and local marks on paste layer and PCB | Present and matched | Print offset, especially below 0.5 mm pitch |
If area ratio falls below target, reduce foil thickness, enlarge the aperture within the pad, or move to a step or electropolished stencil.
Which type of PCB stencil fits your build?
| Type | How it is made | Choose it when | Tradeoff |
|---|---|---|---|
| Framed laser-cut stencil | Stainless foil laser-cut and glued into an aluminum frame under tension | Production runs on an automatic printer | Frame cost and storage space |
| Frameless laser-cut stencil | Stainless foil used with a reusable tensioning frame | Prototypes, NPI and frequent revisions | Needs a compatible tensioning system |
| Step stencil | Foil thinned or thickened locally | Large and fine-pitch parts on one board | Keep-out around the step; costs more |
| Electropolished stencil | Laser-cut, then aperture walls smoothed | Small apertures and difficult release | Added process step |
| Nano-coated stencil | Laser-cut, then coated to repel paste | High volume where cleaning frequency limits throughput | Coating cost |
| Electroformed stencil | Nickel built up by plating | Very fine apertures where laser-cut walls are not smooth enough | Longer lead time and higher cost |
What files do you need to order a PCB stencil?
- Paste layer: Gerber or ODB++ paste layer for each side, with revision.
- Board outline and fiducials: outline and fiducial positions so the print can be aligned.
- Smallest pitch: the finest-pitch part (BGA, QFN, 0201 or 01005) so foil thickness can be set.
- Foil and surface: target thickness, standard or electropolished, nano-coating if wanted.
- Frame: framed (frame size) or frameless, and the printer it will run on.
- Step areas: which parts need more or less paste, if any.
- Quantity and side: top, bottom or both, and number of stencils.
What affects PCB stencil price and lead time?
- Frame: framed stencils cost more than frameless foils and take more storage.
- Step areas and coatings: step-down, step-up, electropolish and nano-coating each add a process step.
- Foil size and thickness: larger boards and non-standard foils cost more.
- Electroformed: slower and more expensive than laser-cut; used only when laser-cut walls are not enough.
How should a PCB stencil be cleaned, stored and checked?
- Clean: remove paste from apertures and the underside at the interval the line needs; nano-coated stencils extend it.
- Store: keep framed stencils flat in racks, away from impact on the foil.
- Check incoming: measure apertures and tension, and check frame flatness before first use.
- Replace: retire a stencil when apertures are damaged or tension drops, or when the paste layer revision changes.
PCB stencil FAQ
What is a PCB stencil?
A thin stainless steel foil with laser-cut openings that match the PCB pads. A squeegee pushes solder paste through the openings onto the pads before parts are placed.
What thickness should an SMT stencil be?
127–150 µm for standard 0805/1206 boards, 100–127 µm for 0.5 mm pitch parts, and 80–100 µm for 0.4 mm pitch and below. The finest-pitch part on the board sets the thickness.
What is the area ratio rule for stencil apertures?
Area ratio is the aperture opening area divided by its wall area. Keep it at 0.66 or more so paste releases cleanly; below that, paste sticks in the aperture.
When do I need a step stencil?
When one board has parts that need very different paste volumes, such as large connectors or shields next to fine-pitch BGAs. The foil is thinned or thickened locally.
Framed or frameless stencil: which should I order?
Framed stencils suit production on an automatic printer. Frameless foils suit prototypes and frequent revisions, as long as the line has a compatible tensioning frame.
What is the lead time for a PCB stencil?
Laser-cut stencils are often turned in 24–48 hours. Electroformed and specialized stencils take longer.
Request a laser-cut PCB stencil quote
Send the paste layer, smallest pitch and frame type. Foil thickness and apertures are checked before the stencil is cut.