What the "no stencil needed" pitch leaves out
A question that keeps showing up in enquiries: if digital jet dispensing skips the stencil and the tooling wait, why build a stencil at all?
Fair question, but the marketing usually covers only the tooling side. The goal of paste deposition was never "get paste onto the board". It is a controlled volume on every pad, in the right position, repeatable from batch to batch. Stencils and jetting reach that goal through two different physical mechanisms, and the costs are different too.
The conclusion first: the decision sits in your board, not in the sales copy. Pitch, area ratio, the spread of paste-volume demand across mixed components, board flatness, volume and changeover count. Run those numbers and the route is largely settled.
The physical difference in one paragraph each
Stencil contact printing. A squeegee pushes paste into the stencil apertures while the foil sits against the board; on separation the paste releases onto the pads. The volume on each pad is fixed by aperture geometry (aperture area × foil thickness), and every pad on the board is completed in the same stroke.
Non-contact jetting. A head shoots a metered dot onto each pad, without touching the board and without any stencil. Volume per dot comes from machine parameters, and whole-board deposition is the sum of individual shots.
Everything downstream follows from that. A stencil solves volume consistency at the moment the apertures are cut: once the holes are right, the distribution is locked, and the thousandth board sees the same geometry as the first. Jetting hands that problem to machine state and to each individual shot, in exchange for needing no tooling at all.
Start with area ratio, not with equipment
The first gate on the stencil route is area ratio — aperture area divided by aperture wall area. The industry works to the IPC rule of thumb of keeping it at 0.66 or above. Below that, friction against the aperture walls beats adhesion to the pad, paste stays in the aperture, and you get insufficient deposits or open joints.
So the engineering order is:
- Take the smallest pad on the board, usually the finest-pitch BGA or QFN.
- Compute area ratio against a candidate foil thickness. Available: 0.08, 0.10, 0.12, 0.15, 0.20 mm.
- Ratio ≥ 0.66 → the stencil route holds; fix the foil thickness.
- Ratio short → thin the foil and recompute; only then look further.
There is a side effect between steps 3 and 4 that gets missed: thinning the foil serves the smallest pad, but it reduces volume on every pad at once. If the board also carries large pads, shield frames or power devices that need a full deposit, a thin foil starves them. That is the core tension on mixed boards, and section five deals with it.
On the assembly side our registered limits are 0.2 mm minimum pitch for BGA and 0.3 mm for QFN/QFP, with 01005 as the smallest placed component. Aperture design has to land inside that envelope.
Four cases where the stencil is still the answer
One: uniform paste demand across the board. Similar component types, no location needing an unusually thick or thin deposit. One stroke, whole board, and nothing competes on throughput or consistency.
Two: mid to high volume, and repeat builds. A stencil is reusable tooling. Once the apertures are cut and verified, every subsequent batch inherits the same geometry rather than drifting with machine state. Jetting cycle time grows linearly with pad count, so the more complex the board, the longer each one takes.
Three: closed-loop SPI on the whole board. SPI measures deposited volume pad by pad after printing. On the stencil route a deviation usually traces back to a specific aperture or to the squeegee stroke — the object to adjust is identifiable, so the loop converges.
Four: mixed demand that a step stencil can absorb. See section five.
Where jetting genuinely wins, and what it costs
The industry adopts jetting for reasons that are easy to state:
- No tooling wait. Frequent revisions, one-offs and small pilot runs do not justify cutting a new stencil for every change.
- Local touch-up and rework. A handful of pads is not worth printing the whole board for.
- Irregular or recessed areas. Uneven surfaces, pads blocked by already-placed parts, cavity interiors — anywhere a foil cannot seal against the board.
- Different volumes on the same board. Metering per dot makes this native.
The costs are equally concrete. Cycle time scales with dot count, so a board with a thousand pads is not in the same league as a stencil stroke. And dot-to-dot consistency depends on machine state — paste condition, nozzle condition, temperature. Stability comes from maintenance and process monitoring rather than from geometry locked into a piece of tooling.
To be explicit: we supply stencil fabrication and stencil-printed assembly, not jetting or dispensing services. The jetting content here is a process comparison to help you decide which route your board belongs on. If the answer is jetting, that sits with your own line or with a supplier holding that equipment.
The third route for mixed boards: step stencils and split stencils
Back to the tension from section three: a 0.3 mm pitch QFN wants a thin deposit while a power pad wants a thick one, and a single foil thickness cannot serve both ends. The stencil route has two answers, neither of which abandons contact printing.
Step stencil. Different thickness zones on one foil: thinned where the fine pitch sits, full thickness where the large pads sit. The cost is squeegee sealing across the step, which requires clearance around it — so fine-pitch and large-pad regions cannot sit too close together. That is a manufacturability constraint worth honouring at layout time.
Split stencils. Top and bottom can share one stencil or be separated, and differing volume demands can be split across stencils printed in sequence. We produce top, bottom, or top+bottom on one stencil or on separate stencils. The cost is an extra print pass and an extra alignment.
Which one applies depends on how large the thickness gap is, how far apart the regions sit, and whether volume absorbs a second stencil. That call needs the Gerber data and belongs in engineering review.
Verification: is the evidence chain already there?
This is where the two routes differ most, and it is the part enquiries raise least.
On the stencil-print plus in-house assembly route, paste deposition quality has a ready-made evidence chain:
- SPI — per-pad deposited volume after printing, so problems are caught before placement.
- In-line 2D AOI — position and polarity after placement.
- Post-reflow 3D AOI — joint geometry after soldering.
- X-Ray — voiding and bridging under BGA/QFN where joints are not visible. Void rate target under nitrogen reflow is <10%.
- ICT / FCT — electrical and functional verification.
- Assembly acceptance to IPC-A-610 Class 3; bare boards additionally get 100% electrical test (flying probe or fixture).
The value is that this chain exists, produces reports and has defined criteria. Move to jetting and SPI, AOI and X-Ray all still apply — but you have to establish equivalent criteria and monitoring for the metered-dot process: what volume counts as a pass, what sampling rate, how often the machine is verified. All doable, none free, and typically not yet in place during early pilot runs.
Put differently: jetting saves stencil tooling time and cost, and asks you to supply process-capability evidence instead. That trade is often worth it at pilot stage and usually is not at volume.
Quoting: what the stencil route needs from you
- Files: Gerber RS-274X with paste, solder mask and outline layers, or ODB++ or DXF.
- Specs to fix up front: foil thickness (0.08–0.20 mm), framed or unframed, frame size (370×470, 420×520, 450×550, 550×650, 584×584 mm are the common sizes), and layers (top, bottom, or top+bottom on one stencil or separately).
- Options: polishing (grinding polish is standard, electrolytic polish is optional and helps paste release) and nano-coating to cut wipe frequency and extend service life.
- Material: stainless-steel foil as standard, nickel for electroformed, Kapton/PET for hand printing.
Quantity and price are confirmed after review of the Gerber data, quantity and process requirements. That step cannot be skipped, because area ratio, step requirements and any need to split stencils are only visible in the data. Custom frames, oversized foils and specialty coatings are reviewed case by case.
Full specifications and the ordering path are on SMT stencil manufacturing; assembly capability on PCB assembly; aperture design has to line up with the trace widths, hole sizes and outline tolerances the board itself supports — see manufacturing tolerances and manufacturing capabilities; inspection criteria on quality assurance.
FAQ
Is stencil-free jetting cheaper?
Stage-dependent. It removes stencil cost and the tooling wait, so it often wins for one-offs, small batches and frequent revisions. But jetting cycle time grows with pad count, so at volume the throughput cost overtakes the one-time tooling cost. The real comparison is not "stencil cost vs zero" — it is "stencil cost plus stable cycle time" against "no stencil cost plus per-dot cycle time plus process criteria you build yourself".
Which route for a 0.3 mm pitch QFN?
Compute area ratio first, using the smallest pad against a target foil thickness in the 0.08–0.20 mm range. At 0.66 or above, take the stencil. 0.3 mm pitch is inside our assembly envelope (0.3 mm for QFN/QFP, 0.2 mm for BGA) and normally works with a thinner foil. If the same board also has large pads needing a thick deposit, go step or split stencil rather than switching to jetting.
When is a step stencil worth it?
When paste demand splits into two clear tiers and those regions sit far enough apart on the board. The step needs clearance for squeegee sealing; if fine-pitch and large-pad areas crowd each other the step approach breaks down and split stencils are the safer answer. Feasibility is confirmed by engineering after reviewing the Gerber data.
Do you offer jetting?
No. We provide stencil fabrication and stencil-printed SMT assembly. The jetting material here is a process comparison to help you place your board on the right route; if that route is jetting, it has to run on your line or at a supplier holding the equipment.
What if the area ratio comes out short?
Order of moves: thin the foil, then look at aperture shape optimisation, then electrolytic polish to improve release, and only then revisit the pad design itself. If thinning the foil would starve large pads on the same board, move to a step or split stencil. These recommendations come back with the Gerber review.
Which files does a quote need?
Gerber RS-274X including paste, solder mask and outline layers, or ODB++ or DXF. Tell us your foil thickness preference, framed or unframed, frame size, layers and quantity. A missing outline layer means frame fit cannot be confirmed; a missing solder mask layer means aperture-to-pad correspondence cannot be checked. Those two are the most common causes of a confirmation round trip.