What is DFM and why it matters
Design for manufacture (DFM) is the engineering review where a contract manufacturer compares your Gerbers, drill files, and BOM against the actual capabilities of their fab and assembly line. The goal: catch problems before tooling — when fixes cost nothing — instead of after build, when each rework is €5-50 of labour.
At Energetika-VDS DFM is free on every quote and runs in 24-48 hours. We use it to flag issues we know will bite our DDM Novastar SPR-45 / LS60 / GF-120HT line: aperture ratios under 0.66, courtyards too tight for 0201 placement, BGA escape routes that violate our 100 µm trace/space minimum.
The 30-point checklist
Copper (1-6)
| # | Check | Pass threshold |
|---|---|---|
| 1 | Minimum trace width | ≥100 µm (4 mil) standard, ≥75 µm fine |
| 2 | Minimum trace spacing | ≥100 µm standard, ≥75 µm fine |
| 3 | Annular ring | ≥50 µm minimum |
| 4 | Copper-to-edge clearance | ≥250 µm |
| 5 | Plane-to-plane clearance (HV) | ≥0.4 mm per 100 V |
| 6 | Polygon pour fill | Solid or hatched, no slivers <100 µm |
Drill (7-11)
| # | Check | Pass threshold |
|---|---|---|
| 7 | Drill-to-copper | ≥150 µm |
| 8 | Drill-to-drill | ≥300 µm centre-to-centre |
| 9 | Aspect ratio | ≤10:1 (board thickness / hole diameter) |
| 10 | Minimum mech drill | 0.30 mm finished |
| 11 | Minimum laser via | 0.10 mm finished |
Silkscreen (12-15)
| # | Check | Pass threshold |
|---|---|---|
| 12 | Line width | ≥150 µm |
| 13 | Text height | ≥1.0 mm |
| 14 | Silk-on-pad | None allowed |
| 15 | Reference designator visible after assembly | Not hidden under component body |
Reference designators hidden under chip bodies is the #1 silkscreen mistake. Place them outside the courtyard so the operator can read them during rework.
Solder mask (16-19)
| # | Check | Pass threshold |
|---|---|---|
| 16 | Mask sliver | ≥75 µm between pads |
| 17 | Mask-to-pad expansion | 50-75 µm per side |
| 18 | Vias under BGA | Filled and capped (Type VII IPC-4761) |
| 19 | Mask over plane fill | Allowed (no copper exposed) |
Tented vs filled-and-capped vias under BGA is the #1 BGA failure cause we see — covered in our BGA assembly guide.
Paste / stencil (20-23)
| # | Check | Pass threshold |
|---|---|---|
| 20 | Aperture ratio | ≥0.66 (area/wall area) |
| 21 | Paste mask reduction (QFN) | -10% per side, windowpane |
| 22 | No paste on tooling/fiducial | Required |
| 23 | Stencil thickness | 100 µm (0.4 mm pitch), 125 µm (≥0.5 mm) |
Components / courtyard (24-28)
| # | Check | Pass threshold |
|---|---|---|
| 24 | Courtyard clearance | ≥200 µm between adjacent component bodies |
| 25 | Polarity marking on PCB | Pin 1 and cathode marked in copper or silk |
| 26 | Tall component near short | ≥1.5 mm clearance from chip caps |
| 27 | Heat-sensitive parts in shadow | Not next to large copper pours |
| 28 | Fine-pitch on outer rows | Avoid centre placement |
Panelisation and fiducials (29-30)
| # | Check | Pass threshold |
|---|---|---|
| 29 | Fiducials | ≥3 per panel, ≥1 mm copper dot in mask opening |
| 30 | Edge rail | ≥5 mm tooling rail, free of copper and parts |
Real numbers — what DFM catches
On a representative 4-layer, 100 × 80 mm board with 400 placements, our DFM review flags an average of 3-7 issues. Breakdown of issues found across 2024 RFQs:
| Category | % of issues |
|---|---|
| Courtyard / placement too tight | 28% |
| Silkscreen on pad or under component | 19% |
| Drill / annular ring marginal | 14% |
| BGA vias not capped | 11% |
| Paste aperture ratio | 9% |
| Trace/space below capability | 8% |
| Other | 11% |
A board with 5+ flagged issues usually needs one design revision before we tool. A board with 0-1 issues goes straight to stencil.
Common DFM errors we see most
- Tented vias under BGAs — vias should be filled and capped (IPC-4761 Type VII) or moved outside the BGA shadow. Otherwise paste wicks into the via, voiding climbs above 25%.
- 0402 courtyards <200 µm — placement head clearance is the limit. Sub-200 µm courtyards cause shadows that AOI flags.
- Reference designators under part bodies — invisible after assembly, killing rework. Move outside the courtyard.
- Polygon slivers <100 µm — break off during etching, fall onto adjacent traces, cause shorts. Use a polygon clearance filter.
- No fiducials, or only 2 — the LS60 needs three for accurate panel registration. Three is mandatory; we add them ourselves if missing.
See our SMT process step-by-step for what happens after DFM clears.
Who pays for DFM fixes
At Energetika-VDS, DFM review is free. Fixes are the customer's responsibility (their design). If the issue is small (silkscreen on pad, missing fiducial, polygon sliver), we offer a free Gerber patch on request. Major issues (re-routing BGAs, swapping packages) go back to the designer.
The economics: a DFM round is 1-4 engineer-hours, free. A rework cycle on 100 boards because of bad DFM is 2-8 hours of operator labour plus a 2-week schedule slip. Pay attention to the DFM report.
Submit your Gerbers and BOM — we return a DFM report and a binding quote within 48 hours. Try the quote estimator for a price band before sending files.
Frequently asked questions
What is DFM? Design for manufacture: a pre-production review where the EMS compares your design files against the fab and assembly line capabilities, then flags anything the line cannot build reliably. The output is a written DFM report.
Why DFM before assembly? A 1-2 hour DFM review prevents 80% of stop-line issues. Fixing a Gerber is free; reworking 500 boards is €2500-15 000. The math is obvious.
What are common DFM errors? Tented vias under BGAs, silkscreen on pads, reference designators under component bodies, courtyards under 200 µm on 0402, missing fiducials, polygon slivers, and trace/space below the fab capability minimum.
Who pays for DFM fixes? Design issues are the customer's responsibility. Most EU EMS partners — Energetika-VDS included — run DFM for free and offer free Gerber patches for small fixes (silkscreen, fiducials). Major redesigns go back to the original designer.