To make a PCB stencil, export the correct top or bottom solder-paste Gerber, review every aperture against the component land-pattern guidance, choose a foil and cutting process that can release the smallest deposits, then inspect both the stencil and a trial print. Cutting holes is only the middle of the job. The deliverable is a repeatable paste deposit on the pad—not a sheet that merely looks correct against a light.
This guide follows the handoff from CAD to the first accepted print. If the board includes fine-pitch packages, a mixed component population, a large thermal pad, or a panel, send the Paste Gerber, PCB Gerbers, assembly drawing, BOM and package notes to QFPCB for an assembly review. The review should resolve paste volume and alignment risks before the stencil is cut.
What Is a PCB Stencil, and What Must It Control?
A PCB stencil is a thin foil with openings that transfer solder paste to surface-mount pads. Its three practical controls are deposit location, deposit area and deposit height. Aperture geometry controls the first two; foil thickness strongly influences the third.
This is why “copy every copper pad exactly” is not a reliable design rule. Some packages need a manufacturer-recommended paste pattern, divided thermal-pad windows, or a local change in paste volume. The component datasheet, land-pattern recommendation and intended printing process take precedence over a blanket reduction percentage.
Which Files Should You Start With?
Start with the solder-paste layers generated by the PCB CAD system—not the solder-mask layers. The top paste layer drives a top-side stencil; the bottom paste layer drives a separate bottom-side stencil. Open the exported Gerber in an independent viewer and compare it with the copper, mask, outline and assembly layers.
| Input | What to verify | Failure if wrong |
|---|---|---|
| Top/Bottom Paste Gerber | Correct side, 1:1 scale, apertures only where paste is required | Missing deposits, unwanted paste, or a mirrored stencil |
| PCB Gerbers and outline | Pad registration, board edge, rails and usable foil margin | Stencil cannot align or fit the fixture |
| Assembly drawing | Population side, component orientation and do-not-populate parts | Apertures remain for uninstalled parts |
| BOM and package data | Fine-pitch, bottom-terminated and special package requirements | Generic apertures create too much or too little paste |
| Panel drawing | Step-and-repeat, tooling holes, fiducials and rail geometry | Registration error accumulates across the panel |
Before release, check one known dimension in the viewer. A 10 mm board feature must still measure 10 mm after any SVG, DXF, PDF or cutter-software conversion. This catches silent scaling changes before material is wasted.
How Should PCB Stencil Apertures Be Designed?
Apertures should be designed from the required solder joint backward. Begin with the CAD paste layer, then review exceptions by component family and printing capability. Do not reduce every opening by the same percentage without evidence.
Use the package recommendation before a generic rule
For BGAs, QFNs, LGAs, wafer-level packages and fine-pitch connectors, check the component manufacturer’s stencil guidance. These documents may specify aperture shape, segmentation or a relationship between the aperture and pad. If the recommendation conflicts with other components on the board, ask whether a stepped stencil, a second print or a process change is required.
Check release capability, not just opening width
Paste must fill an aperture and release onto the pad when the foil separates. Very small openings in a thick foil have more wall area relative to the open area, so paste can remain in the aperture. Area-ratio and aspect-ratio checks are useful engineering screens, but their acceptance limits depend on foil process, wall quality, paste and supplier capability.
Divide large thermal-pad openings
A single full-size opening over a QFN or DFN exposed pad can deposit excessive paste, float the package or promote voiding. A window-pane pattern divides the deposit while leaving paths for flux volatiles. The total paste area and window pattern should follow the package and assembly recommendation rather than an arbitrary pattern.
Which Stencil Material and Cutting Method Should You Choose?
Choose the method by feature size, print count and repeatability. A cut polymer film can be useful for a coarse, low-volume prototype; a laser-cut stainless-steel stencil is the normal starting point when fine features or repeat production matter.
| Route | Best fit | Main limitation | Release decision |
|---|---|---|---|
| Hand-cut or blade-cut film | Large pads, one-off learning fixtures | Ragged corners, stretching and limited minimum feature | Use only when every critical opening can be inspected |
| Laser-cut polymer film | Fast prototype with compatible material and controlled equipment | Heat distortion, debris and lower durability | Run scale and material tests; reject melted or tapered openings |
| Laser-cut stainless steel | Fine pitch, repeated prints and production handoff | Requires a capable stencil supplier and complete release data | Confirm foil, thickness, wall finish, frame and fiducials |
| Stepped metal stencil | One board needs materially different deposit heights | More design and manufacturing constraints | Use only after the assembly process confirms the need |
Do not copy laser power, speed or pass counts from another machine. Wavelength, optics, focus, material chemistry and exhaust change the result. Use only materials approved by the equipment manufacturer, operate an enclosed/interlocked machine with suitable extraction, and follow its manual and the material safety data.
How Do You Make a PCB Stencil Step by Step?
1. Freeze the assembly inputs
Confirm the PCB revision, assembly revision, populated side and panel format. A stencil made from an older paste layer can look internally consistent and still be unusable on the released board.
2. Export and independently view the Paste Gerber
Plot the top or bottom paste layer at native scale. Overlay it with copper, mask and outline data. Check orientation text or asymmetric features so a conversion does not mirror the artwork.
3. Review aperture exceptions
Flag fine-pitch leads, bottom-terminated packages, thermal pads, tiny passives, connectors and unusually large terminals. Compare each exception with the package guidance and the planned printing process. Record deliberate changes so they are not “corrected” back to pad size later.
4. Select foil thickness, material and format
Balance the paste height needed by the largest joints against release from the smallest openings. Decide whether the stencil is frameless, framed or used in a dedicated tensioning system, and reserve enough margin for safe handling and printer clamping.
5. Prepare manufacturing data
Supply native Paste Gerber whenever possible. Add board outline, panel drawing, fiducials, tooling holes, foil thickness, frame specification, side identification, stencil quantity and any stepped regions. If a cutter needs SVG or DXF, keep the original Gerber as the comparison master.
6. Cut, clean and inspect the stencil
After cutting, inspect against backlight and under magnification. Look for incomplete cuts, merged apertures, burrs, slag, distortion and debris. Measure selected critical openings and a known overall dimension; appearance alone cannot confirm scale.
7. Build a repeatable alignment fixture
Support the PCB at the same height around its edges so the foil stays in contact with the pad surface. A taped hinge can work for a coarse prototype, but it must lift vertically and return without lateral movement. Production uses defined board support, fiducials and a controlled printer setup.
8. Run and judge a trial print
Print onto a clean sample board using the intended paste and process. Inspect before placement: deposits should be centered, separated and consistent, with no smear between fine-pitch pads. If available, solder paste inspection provides area, height and volume evidence; for prototypes, magnified inspection and a controlled reflow sample are the minimum feedback loop.
How Do You Know the First Print Is Acceptable?
Judge the deposit, not the stencil in isolation. A clean-looking aperture may still release poorly, and reflow self-alignment cannot reliably rescue grossly misplaced or bridged paste.
| Observed print | Likely causes to check first | Next action |
|---|---|---|
| Paste shifted from every pad | Artwork mirrored, fixture moved, wrong origin or panel registration | Stop and verify overlay/orientation before changing paste settings |
| Bridging across fine-pitch pads | Stencil lifted from board, smear during separation, excessive deposit or damaged opening | Restore board contact and vertical release; then review aperture and foil |
| Repeated missing or thin deposits | Poor aperture release, blocked opening, insufficient fill or foil too thick for feature | Clean and inspect the opening; review release geometry and paste condition |
| Excess paste on a thermal pad | Undivided/oversized opening or unsuitable local foil height | Review package guidance and window pattern |
| Good print near one panel edge but shifted at the other | Panel scale, stretch, step-and-repeat or fabrication registration mismatch | Compare measured panel coordinates and revise the datum/fiducial plan |
| Print starts well then degrades | Aperture contamination, paste condition, underside smear or loss of tension | Define cleaning frequency and inspect foil support/tension |
What Should Be on the Stencil Release Checklist?
- PCB, assembly, BOM and Paste Gerber revisions match.
- Correct top/bottom side, orientation, units and 1:1 scale are confirmed.
- Do-not-populate components do not receive paste unless intentionally required.
- Critical package datasheets and land-pattern recommendations were reviewed.
- Thermal-pad windows and other aperture exceptions are documented.
- Smallest openings are compatible with the chosen foil and supplier process.
- Panel fiducials, tooling holes, rails and support method are defined.
- Foil thickness, frame/frameless format and quantity are stated.
- Critical aperture measurements and cleanliness criteria are agreed.
- A first-print inspection and reflow verification plan exists.
When Should You Order a Professional Stencil Instead of Making One?
Order a professional stainless-steel stencil when aperture release, alignment or repeatability controls the assembly yield. Fine-pitch ICs, BGAs/QFNs, 0201-class passives, dense boards, panels and more than a few repeated prints quickly exceed what an improvised film and hinge can prove.
The right supplier question is not merely “Can you cut this Gerber?” Ask what data they review, how they evaluate small-aperture release, what wall-finish options exist, how foil and frame are identified, which measurements appear on the inspection record, and how an engineering change is controlled.
Frequently Asked Questions
Can I make a PCB stencil from the solder-mask Gerber?
No. Use the top or bottom Paste Gerber. Solder-mask openings serve a different purpose and may include clearances that would deposit paste where it is not wanted.
Should stencil apertures always be smaller than PCB pads?
No single reduction fits every component. Start with the land pattern and package recommendation, then account for foil thickness, paste, cut quality and process capability.
Do I need separate stencils for both sides?
Yes, when both sides contain SMT parts that are assembled by paste printing. The top and bottom paste patterns, orientations and often process conditions are different.
Can a hobby laser cut a PCB stencil?
It may cut compatible polymer film for coarse prototypes, but results depend on the machine and material. Never cut unidentified or prohibited material, and do not assume a film stencil represents production capability.
Why does solder paste smear under the stencil?
The foil may not be in full contact with the PCB, the board or stencil may move, or separation may drag sideways. Correct support, alignment and vertical lift before redesigning every aperture.
What causes too much solder paste?
Possible causes include excessive foil thickness, oversized apertures, stencil-to-board gaps, multiple uncontrolled print passes or an unsuitable thermal-pad pattern. Inspect the printed deposit and change one cause at a time.
How should a QFN thermal-pad aperture be made?
It is commonly divided into multiple windows rather than opened as one solid area. Use the component manufacturer’s guidance and the assembler’s process recommendation to set the pattern and total paste coverage.
What files should I send for a stencil quotation?
Send the Paste Gerber, PCB Gerbers, assembly drawing, BOM, panel drawing, stencil side, foil/frame preference, quantity and notes for special packages or stepped areas. State whether the stencil will be used manually or in a printer.
Turn the Paste Layer into a Controlled Assembly Input
A usable stencil connects CAD intent to measured paste deposits. For a DFM review and quotation, send your Paste Gerber, PCB data, assembly drawing, BOM, panel information and package notes through the QFPCB contact page. We can review the stencil together with PCB assembly requirements so aperture, alignment and first-print risks are resolved before production.
