1.5 Printer Setup & Cleaning
Alignment, squeegee angle/pressure/speed, and dry/wet/vacuum understencil cycles—so prints look the same at 8:00 and 18:00.
Printer setup is the part of SMT where a few quiet, deliberate minutes can decide whether the whole shift runs smoothly or spends the day chasing defects. It starts with solid board support and a stencil gasket that seals evenly to the copper, then locks alignment with well-chosen fiducials. Squeegee angle, pressure, and speed are tuned to balance aperture fill and clean wipe, while separation settings and dwell prevent bridging as the stencil lifts. Understencil cleaning—dry, wet, or vacuum—is set to a predictable interval and adjusted with SPI feedback, just as bead size and pause handling keep paste in its best condition. By capturing the winning setup in the job recipe, along with photos of “good” prints, every changeover or shift handoff becomes repeatable. When this discipline holds, the printer fades into the background—quietly delivering identical, high-quality prints from the first board to the last.
1.5.1 The setup flow (five calm minutes that save an hour)
- Board support first. Use support pins/vacuum tooling so the PCB is flat under every paste region (especially center of large panels). No bow = no “squeegee trampoline.”
- Gasket check. Lightly lower the stencil onto copper, jog the stage, and look: you want tight, even contact at pads—no daylight, no rocking.
- Fiducials & offsets. Teach three global fiducials (or rail marks on panels) and verify X/Y/θ; save the offset trend so operators can spot drift.
- Bead & wipe. Lay a small bead (narrow ribbon ahead of the stroke), do one conditioning swipe, and print the First Article panel for SPI.
- Lock the recipe. Record angle/pressure/speed, separation speed, and cleaning interval in the job file before volume.
1.5.2 Alignment that survives real panels
- Teach globals, correct locally. Use three well-spaced fiducials for global alignment; if panels stretch, enable local correction (board or quadrant).
- Don’t chase bad rails. If rail fiducials are scuffed, switch vision to on-board fiducials you reserved in panelization.
- Watch the trend. If offsets “walk” during the shift, check board support and clamp force before you blame vision.
1.5.3 Squeegee basics (angle, pressure, speed)
Think of these as three sliders that control fill (paste pushed into apertures) and wipe (clean top surface):
Two quick tells: a faint gray film behind the blade = pressure too high; ragged aperture edges on the print = angle too steep or speed too high.
1.5.4 Separation & snap-off (where bridging begins or ends)
- Contact mode: keep snap-off = 0 unless your machine or board demands a gap.
- Separation speed: slow, steady peel so paste releases cleanly; larger QFN/BGA fields often like a brief dwell (hundreds of ms) before peel.
- Tall/crowded areas: if you see “stringers” between fine-pitch pads, slow the peel first; only then shrink apertures (7.4).
1.5.5 Understencil cleaning (dry / wet / vacuum)
Clogged walls print badly. Set a default interval, then let SPI tell you when to tighten/relax.
- Dry wipe: first line of defense for nano-coated or clean-running pastes. Fast, gentle on coatings.
- Wet + vac: use solvent wipe followed by vacuum when you see bridging/volume drift; don’t over-wet (solvent pools = smear).
- Decision rule (simple): start dry every X prints (e.g., 5–10), escalate to wet+vac if SPI transfer efficiency drops or bridging appears; reset to dry when stable. Log changes in the job file so the next crew inherits the lesson.
Special cases
- Water-soluble flux: needs more frequent wet/vac; always follow with a dry pass.
- Step stencils: clean after runs that cross steps; ramps collect paste.
- Nano-coating: longer intervals, gentler solvents; avoid scrubbing.
1.5.6 Bead management (little and often)
- Keep a narrow bead ahead of the blade (≈10–15 mm wide). Big pancakes over-shear and overheat paste.
- For pauses >15–20 min: scoop the bead, cap it, run an understencil clean, and restart with a fresh bead.
- Never return stencil-exposed paste to the original jar (7.2 has the hygiene rules).
1.5.7 SPI-driven tuning (close the loop)
Use SPI as your speedometer:
- Volume low on fine features → ease pressure, slow speed, check bead and cleaning.
- Bridging hotspots → slow separation, add a cleaning cycle; if persistent, apply the anti-bridging aperture tweaks (7.4.6).
- Lot-to-lot drift → confirm stencil wear, gasket, and support pins; then revisit paste age/handling (7.2).
Save the winning settings into the job recipe and enable closed-loop corrections if your SPI/printer combo supports them (7.6).
1.5.8 First Article & changeovers (make success repeatable)
- FA print: one pass, SPI review, tweak one knob at a time, reprint, then lock.
- Record everything: angle/pressure/speed, separation, cleaning cadence, bead policy, support map, and any local quirks (e.g., “add dwell at U17 QFN”).
- Golden photo set: top-side print close-ups of the tightest features so night shift knows what “good” looks like.
1.5.9 Pocket checklists
Start of run
- Support pins/tooling placed under large paste fields
- Stencil gaskets clean; fiducials taught; offsets saved
- Bead laid; First Article printed; SPI green
During run
- Angle/pressure/speed unchanged (unless noted)
- Cleaning on schedule (dry→wet+vac if SPI drifts)
- Bead small; pauses handled (scoop + clean)
Changeover / end
- Final clean; stencil stored per coating type
- Recipe updated with final winning settings
- SPI charts archived to the lot record
Bottom line: flat boards, tight gasket, sane blade settings, disciplined cleaning, and SPI-led tweaks. Do those five things and your printer stops being the hero of your day—because it just quietly does the same good thing, over and over.