This is a positioning method that wasn't obvious to me until I'd tried a few other approaches. Sharing it in case it saves someone time.
The basic idea: use needles and fiducial holes to fix the stencil and PCB to a silicone mat. It's far more accurate and practical than building a makeshift frame with tape.
Use case
- Hobby use — assembling a few boards occasionally
- Open source projects where reproducibility matters (many people will build it)
What's out there
- SMT stencil printers (full-size) — large, require dedicated space. Fine for production runs, overkill at home. Also needs a larger stencil, which drives up cost and shipping.
- Compact stencil printers — appeared only recently. Much better suited for hobby use. Still somewhat large — might make sense for a dozen boards, but overkill for 1–2.
- Fiducial hole positioning — has its nuances, but nearly ideal for hobby use. Unbeatable on price.
Hobby boards typically don't exceed 100×100 mm. In that case a steel stencil runs about $3. The question "solder by hand or use paste?" pretty much answers itself.
Worth noting: in "proper" stencil use the stencil doesn't touch the board — it snaps off during squeegee travel. With fiducial positioning the stencil lies directly on the board. In theory that's worse, but the results are good enough not to worry about.
How to do it
"Use needles and fiducial holes" sounds simple. In practice there are subtleties — needles come in different diameters, and repeatability matters.
For a long time I used AWG 22 steel wire with 0.7 mm holes:
- Total offset no more than 0.1 mm
- Sufficient for 0.5 mm pitch components
Downsides:
- Still need to source the wire
- Wire deforms when clipped, so zero clearance is impossible
On recent boards I tried something different. It turns out there are "location pins" at 1 mm diameter and smaller. At one well-known three-letter Chinese fab you can order them for pennies along with the boards. As shown in the photo, each location area has 4 holes — 0.6, 0.65, 1.0, and 1.05 mm — for 0.6 and 1.0 mm pins.
I went with 1.0 mm pins. Very happy with the results:
- Pins drop straight into the board — no pushing into the mat
- Zero play
- Prints are even more precise. Multiple squeegee passes don't smear anything
- Result does not depend on user experience
It's too early to call it 100% reproducible, but I've ordered boards this way three times with no issues. For extra safety you could add 1.05 mm holes next to the 1.0 mm ones, but I've never needed them.
If you know other convenient methods — share them.
