How to Laser-Cut Your Own SMD Stencils: Mylar and Kapton Sheet Stencils from Gerber Files

Our surface mount soldering guide covers stencils only as something you buy — send Gerbers to JLCPCB or OSHStencils and a laser-cut stainless sheet shows up in the mail a week later. For a one-off prototype board or a quick revision, that turnaround is often the bottleneck. A diode laser like the Ray5 20W can cut a usable solder paste stencil from polyester (Mylar) or polyimide (Kapton) sheet in the time it takes to run the job, using the exact same Gerber-derived paste layer you'd send out for a professional stencil. This guide covers the material choice, file prep from KiCad or any Gerber-producing EDA tool, and the cutting settings that keep tiny SMD apertures clean instead of melted shut.

Why Not Just Use a Stainless Stencil for Everything?

Stainless steel stencils are more durable and give crisper apertures for fine-pitch parts (0.5mm pitch QFN, 0201 passives), and they're worth ordering for any board you'll assemble more than a few times. A laser-cut polymer stencil is the right tool when you need paste down today, you're prototyping a board that will change again next week anyway, or your smallest pitch is 0.65mm or coarser (TSSOP, SOIC, 0603/0805 passives) — well within what a diode laser can cut cleanly.

Material Choice

MaterialThicknessCuts Cleanly WithNotes Polyester (Mylar) sheet4-7 mil (0.1-0.175mm)Diode or CO2 laserCheapest option, widely available as laminating pouches or dedicated stencil film; slightly less dimensionally stable than polyimide Polyimide (Kapton) sheet2-5 mil (0.05-0.125mm)Diode or CO2 laserBetter edge quality, more heat-resistant, costs more; the same material used for heat-set bed tape PVC / vinyl sheetAnyDo not cutReleases chlorine gas when laser cut — never use for this or any laser project

Preparing the File

1. Export the paste layer from your EDA tool as a Gerber (in KiCad: File → Fabrication Outputs → Gerbers, select only the F.Paste or B.Paste layer for the side you're stenciling).
2. Convert the Gerber to a vector file your laser software can read. gerbv or a free online Gerber-to-SVG converter works; alternatively, KiCad can export the paste layer directly to SVG via Plot → SVG with only the paste layer enabled.
3. Import the SVG into LightBurn. Each pad aperture becomes a closed vector shape — verify aperture count matches your BOM's pad count before cutting; a missed or merged aperture here means a missed or bridged paste deposit later.
4. Add 2-4 registration holes or a full board outline in a separate cut layer, positioned using two or three known-good board features (mounting holes, board corners) so the stencil aligns to the bare PCB by eye or with a jig, the same way a purchased stencil would.
5. For fine-pitch apertures (0.65mm QFP/TSSOP pitch), consider shrinking the aperture by 10-15% in your CAD tool before export — this is standard "stencil reduction" practice used by every commercial stencil house to account for paste release and kerf, and it applies just as much here.

Cutting Settings

Start from your acrylic-cutting baseline and scale down aggressively — polyester and polyimide film are thin and cut at much lower power than 3mm acrylic. These are starting points; always run a test grid on scrap film first, since kerf width directly determines paste deposit accuracy.

MaterialPower (Ray5 20W)SpeedPasses 5 mil Kapton15-20%250-350 mm/min1 5 mil Mylar20-25%200-300 mm/min1 7 mil Mylar25-30%150-250 mm/min1-2

• Use a fine spot size and keep focal height dead-on — this is not a project where being slightly out of focus is forgiving. A soft focus rounds off aperture corners and can weld QFN thermal-pad apertures shut.
• Air assist on, but keep it gentle — full-power air assist can flutter thin film mid-cut and shift the material, ruining registration on tightly packed apertures.
• Tape the film flat to a sacrificial backing (cardboard or scrap acrylic) at all four corners; film left loose on the honeycomb bed will curl from heat and drift out of focus mid-job.
• Cut smallest/tightest apertures first while the material is coolest and flattest, then larger board-outline cuts last.

Applying Paste with a DIY Stencil

Registration is the whole game. Use a simple jig: a piece of stiff cardboard or acrylic with the board outline cut out, taped down so the bare PCB drops into the cutout and sits flush. Lay the stencil over it using your registration marks, hold it down firmly (painter's tape at the corners works), and drag paste across with a squeegee or old credit card in one smooth pass. Lift straight up — don't peel at an angle, which smears fine-pitch deposits.

Safety Notes

Only cut polyester or polyimide film — never PVC, vinyl, or any chlorine-bearing plastic, which off-gases hydrochloric acid and other toxic byproducts when laser cut. Run your fume extraction the same as any laser job; thin polymer film produces less smoke than wood or acrylic but still releases fine particulate. Keep a fire extinguisher within reach as with any laser cutting, and never leave the machine unattended during the cut, especially with tape holding material in place near the cut path.

Wrapping Up

A laser-cut polymer stencil won't outlast or out-precision a real stainless stencil for production runs, but for same-day prototype assembly of boards with 0.65mm pitch or coarser, it turns a week-long stencil order into a five-minute laser job using files you already have from your PCB fab output. Keep a roll of 5 mil Kapton on hand next to your acrylic and plywood stock and it becomes a routine part of the prototyping workflow rather than a special case.