How to use a solder paste stencil correctly
A solder stencil is a thin stainless steel foil with laser-cut apertures that deposits solder paste precisely onto the SMD pads before placement and reflow. Foil thickness and aperture size set the paste volume. Framed stencils suit series production, frameless foils suit prototypes. Alignment and squeegee technique decide the result.
View solderingHow does a solder stencil work?
A solder stencil is a thin stainless steel foil with openings (apertures) that sit exactly over the SMD pads. As you wipe solder paste across it with a squeegee, only those openings are filled. When the stencil lifts off, a precisely dosed paste deposit stays on each pad, ready for the parts to be placed and reflow soldered.
Apertures are usually laser-cut today, giving clean, slightly tapered walls and good paste release. The foil must sit flat on the board so paste does not smear underneath the stencil.
Framed stencil or foil - which fits?
For series production use a tensioned framed stencil that sits rigidly in the printer. For prototypes and small batches a frameless foil is enough - cheaper, used manually or in a tensioning frame. Foil thickness and use are driven by the finest components.
| Foil thickness | Typical components | Use |
|---|---|---|
| 100 µm | Fine pitch, small chips (0402), fine QFP | Fine pitch, low paste volume |
| 120-130 µm | Mixed 0603/0805, common QFP/SOIC | Universal standard for many assemblies |
| 150 µm | Larger passives, connectors, robust pads | More paste, coarser pitch |
Low cost for prototypes and small batches, used manually or in a tensioning frame.
ViewHow do I apply the paste step by step?
Align the stencil exactly to the pads, draw the paste across the apertures with the squeegee in one even stroke, lift the stencil straight up and check the print. Then place the parts and reflow solder. Keep the stencil clean so the apertures do not clog.
- Fix the board and align the stencil so it registers exactly with the pads.
- Apply a bead of solder paste at the edge of the print area.
- Wipe across the apertures with the squeegee in one even stroke at constant pressure (angle about 45‑60 degrees).
- Lift the stencil straight up so the paste deposits stay clean.
- Check the print: defined deposits, no bridges, no washed-out pads.
- Place the components and reflow the assembly to profile.
- Clean the stencil after printing and store it dry and flat.
The actual soldering step follows next: see the article Reflow soldering.
Frequently asked questions
Which foil thickness should I choose?
As a standard, 120‑130 µm suits many mixed assemblies. For fine pitch and small chips choose 100 µm; for larger passives and robust pads up to 150 µm. The finest components set the thickness.
Framed stencil or frameless foil?
Framed stencils are dimensionally stable and made for series work in the stencil printer. Frameless foils are cheaper and suit prototypes and small batches, used manually or in a tensioning frame.
Why laser-cut apertures?
Laser cutting produces clean, slightly tapered aperture walls. This improves paste release and gives a more even print at fine pitch than older etched processes.
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