The most common line in a stencil data review is "we ran the area ratio, apertures are fine." Running the area ratio does settle half the problem — it answers how much paste fits in the aperture. It does not answer whether that paste comes back out.
The second half lives on the aperture wall. Wall condition governs both release on a single print and whether transfer after several hundred prints still matches the first one. Those are two different problems with two different options attached, and picking the wrong one means paying for a change that does not touch the fault you have.
This article covers only the three surface treatments and the order in which to judge them. Aperture geometry itself is in stencil aperture area ratio and paste release; foil thickness and frame tension are in stencil material and frame tension selection.
1. An aperture has two independent variables: geometry and wall
Whether an aperture prints repeatably depends on two sets of variables that cannot substitute for each other.
Geometry — aperture size, foil thickness, and the area ratio derived from both. The definition on our SMT stencil service page is: area ratio = aperture area ÷ aperture wall area, and the IPC rule of thumb keeps it at 0.66 or above. Below that, paste tends to stay in the aperture and you get insufficient deposits or open joints. Geometry decides whether release is possible at all.
Wall condition — the surface state of the aperture sidewall and the foil face. It decides whether release actually happens once geometry allows it, and at which print it starts to degrade.
The two are in series, not in parallel: if geometry fails, no wall treatment will print it; once geometry passes, wall condition starts to matter. Every judgement below rests on that order.
2. Grinding polish: the standard step, a floor rather than an option
The polishing row on the service page is explicit: grinding polish is standard; electrolytic polish is an option.
Read that distinction correctly. Grinding polish is not a "base tier you can upgrade from." After laser cutting, the foil face and aperture wall inevitably carry the basic topography left by cutting, and grinding polish addresses that layer. Every stencil goes through it, which is exactly why it is not a field you have to decide in your data package.
There is only one engineering judgement to make here: when the symptom points at the wall, do not treat "grinding polish is included" as "wall condition is already optimised." Grinding polish delivers a consistent baseline, not a treatment targeted at fine pitch or long service life. The other two options are the targeted ones.
3. Electrolytic polish: improves release, serves the single print
The service page gives electrolytic polish one line, and that line bounds its job precisely: electrolytic polish (option, improves paste release).
"Improves paste release" means it acts at the scale of one print. So the cases where it is worth specifying are the cases where single-print release is already tight:
- Area ratio close to the 0.66 floor. Geometry passes, but with no margin, so any improvement in release conditions shows up directly in deposit volume.
- Fine pitch and micro components. The service page lists fine-pitch / micro components as their own scenario and notes that available material, apertures and thickness are confirmed from customer data. Fine-pitch apertures are small, wall share is high, and release is more sensitive to wall condition.
- High aperture aspect ratio. The same aperture size on a thicker foil — the service page offers 0.08 / 0.10 / 0.12 / 0.15 / 0.20 mm — gives a relatively deeper wall and a longer release path.
There is one case where specifying electrolytic polish is wasted spend: area ratio below 0.66. That is a geometry failure, the earlier link in the series relationship from section 1. The correct action is to change aperture design or foil thickness, and where needed move to a step stencil that zones paste volume — not to optimise the wall of an aperture that cannot release in the first place.
4. Nano-coating: fewer wipes and longer life, serves continuous stability
The coating line on the service page is equally short: optional nano-coating to cut wipe frequency and extend service life.
Note what it does not say: it does not say "raises transfer efficiency." Its two targets are wipe frequency and service life, both on the time axis. The coating reduces paste residue in the apertures, so wipe intervals stretch and transfer efficiency holds steadier across a run. The matching scenario in the selection table reads long runs with less wiping.
So the fault description nano-coating answers looks like this: the first board prints well, deposit volume drifts after a few dozen boards, and one wipe restores it. That is a continuity problem.
This description is not one to solve with coating: the very first board fails to print, or one class of fine-pitch pads is short of paste from beginning to end. That is geometry or single-print release, covered in sections 2 and 3.
5. Judgement order: geometry, then release, then continuity
Put the three on one flow and the order is fixed:
| Order | Question | What to check | Action |
|---|---|---|---|
| 1 | Is release possible at all | Is area ratio ≥0.66 (IPC rule of thumb on the service page) | Change aperture design / foil thickness / move to step stencil |
| 2 | Does a single print actually release | Area ratio margin, pitch class, aperture aspect ratio | Consider electrolytic polish (option) |
| 3 | Is continuous printing stable | Wipe interval, deposit drift across print count | Consider nano-coating (option) |
Work the table top down, without skipping. The two classic skip errors:
- Using a level-3 remedy (coating) on a level-1 problem (insufficient area ratio) — money spent, deposits still short.
- Using a level-2 remedy (electrolytic polish) on a level-3 problem (wiping too often) — release was never the fault, so the change does not show up in the symptom.
There is also a case where none of the three is the answer: pads on the same board needing very different paste volumes. The service page points this directly at multilayer / step stencils — different thickness zones on one stencil let large connector pads take more paste while fine-pitch areas take less. That is a structural fix at the geometry level, and no wall treatment substitutes for it.
6. Electroformed stencils: forming route first, treatment second
The material row on the service page lists three: stainless-steel foil (standard), nickel (electroformed), and Kapton / PET for hand printing.
Electroforming is a different forming route, and its aperture wall condition arises from the forming process itself rather than from laser cutting followed by grinding polish. The forming difference is covered separately in laser-cut versus electroformed stencil fabrication.
Only one judgement is needed here: forming route and surface treatment sit at different levels — fix the forming route first, then discuss the treatments available within it. Comparing "electrolytic polish or not" against "electroformed or not" inside one option box produces a meaningless answer: the first is an increment on the same stainless-steel stencil, the second is a different forming route.
7. Surface-treatment fields to declare with your data package
Step one of the service-page flow is paste-layer data review — extracting the paste layer from Gerber or ODB++, cross-checking it against pads and solder-mask openings, and flagging missing fiducials or outline edges. Step two is aperture design and area-ratio check, reviewed group by group against component pitch. Engineering review happens before any cutting, so aperture issues come back to you at that stage.
To keep those two steps from looping, write the following as explicit fields rather than mentioning them in the body of an email:
- Stencil type: framed (glue-in) or unframed foil. Framed needs a frame size; common framed sizes on the service page are 370×470, 420×520, 450×550, 550×650, 584×584 mm.
- Foil material: stainless steel (standard) / electroformed nickel / Kapton or PET for hand printing.
- Foil thickness: specify from 0.08 / 0.10 / 0.12 / 0.15 / 0.20 mm; if unspecified it must be confirmed during data review.
- Sides: top, bottom, or top+bottom on one stencil versus on separate stencils.
- Surface treatment: grinding polish is standard; electrolytic polish must be declared explicitly, with the reason pointing at fine pitch or thin area-ratio margin.
- Coating: nano-coating must be declared explicitly, with the reason pointing at long runs or reduced wiping.
- Input files: Gerber RS-274X (paste, solder-mask and outline layers), ODB++, or DXF. A missing outline layer or absent fiducials gets returned at step one.
One more line on the service page belongs with this list: order quantity and quotation are confirmed after review of Gerber data, quantity and process requirements. In other words, leaving these fields unwritten blocks the quotation step itself, not just process risk.
If the stencil is to be built alongside assembly, raise it at order time through our PCBA assembly service. Board-side minimum trace, hole size and outline tolerances are in manufacturing capabilities and tolerance standards. With data complete you can submit an RFQ. For checks after the stencil arrives, see stencil incoming inspection and handoff; for paste-layer to cut-file conversion, see the stencil data package.
FAQ
Q1: Are grinding polish and electrolytic polish an either/or choice?
No. Grinding polish is the standard step every stencil passes through; electrolytic polish is an optional increment on top of it, and the service page states its effect as improving paste release. The question is not which one, but whether the standard needs that addition.
Q2: Area ratio is only 0.55 — can electrolytic polish rescue it?
Do not treat it as the fix. An area ratio below 0.66 is a geometry failure against the IPC rule of thumb quoted on the service page. The correct action is to change aperture design, change foil thickness, or move to a step stencil with a thinner zone in that area. Wall treatment does not substitute for geometric margin.
Q3: Does nano-coating raise transfer efficiency?
The effect stated on the service page is cutting wipe frequency and extending service life, which points at stability across a continuous run rather than the absolute value of a single print. Judge by symptom: if the first board is already short of paste, the fault is outside what coating addresses.
Q4: Do electroformed stencils still need a polish option considered?
Settle the forming route first. Electroformed nickel and laser-cut stainless steel are different routes and their wall condition forms by different mechanisms. Comparing the two in the same option list is not meaningful — one is a route change, the other an increment within a route.
Q5: Should surface treatment go in the data package or be mentioned at order time?
Write it as an explicit field. Step one of the flow is paste-layer data review and step two is aperture design and area-ratio check, with quantity and quotation confirmed only after data and process requirements are reviewed. Surface treatment is a process requirement; spoken and unrecorded, it causes rework or leaves the quotation open.