PCBA DFM Checklist: 15 Things to Check Before Production
Corevia engineering · Aug 7, 2026 · 8 min read
Fifteen checks catch the majority of assembly-side DFM problems before they reach the line: trace/space, board-edge clearance, fiducials, panel rails, copper balance, pad symmetry, mask slivers, via-in-pad, fine-pitch pad strategy, polarity marks, test points, tab clearance, shadow zones, thermal balance, and mixed SMT/THT sequencing. Each one below has a single pass criterion. If your layout passes all fifteen, a DFM review should come back with comments, not delays.
Illustrative render — BGA escape routing, where via-in-pad and fine-pitch pad decisions get made.
Most DFM guides are written for the PCB fab. This one is for the assembly line — the fifteen things that actually decide whether your boards run cleanly through stencil printing, pick & place and reflow, in the order an engineer reads a new layout. The printable version is below the list.
The 15 checks
01Trace / space within capability
Pass: every net ≥ 4/4 mil (0.10 mm) — or confirmed with your assembler before layout freeze. Designing at the edge of a line's capability is a yield decision, not a layout decision.
02Board-edge clearance
Pass: no copper or components within 3 mm of any edge — 5 mm if the panel is V-scored. Conveyor rails and depanelization stress both live at the edge.
03Fiducials placed
Pass: 3 global fiducials (1 mm bare copper, mask-free, not on a silkscreen mark) plus local fiducials for any part under 0.5 mm pitch. No fiducials, no fine-pitch accuracy.
04Panel rails / tooling holes
Pass: boards under 50 mm wide are panelized with 5 mm rails and tooling holes. A bare 30 mm board cannot ride an SMT conveyor on its own.
05Copper balance
Pass: pour distribution is roughly symmetric across layers. Lopsided copper warps at 245 °C peak — and a warped panel misprints paste before the first part is placed.
06Symmetric pads on small passives
Pass: 0201/0402 pads have identical geometry and matched thermal relief on both ends. Asymmetric pads are the classic tombstoning recipe.
07Solder mask slivers
Pass: ≥ 3 mil (0.075 mm) mask web between pads. Thinner slivers lift during reflow and become solder bridges.
08Via-in-pad on BGA / QFN thermal pads
Pass: vias in pads are filled and capped, or tented — never open. An open via wicks solder off the joint and into the barrel, and the void shows up on X-ray.
09Fine-pitch pad strategy is deliberate
Pass: pads under 0.5 mm pitch follow a consistent NSMD (non-solder-mask-defined) strategy with mask expansion per the fab's spec — not a mix of SMD and NSMD on the same footprint.
10Polarity and pin-1 marking
Pass: pin-1 and polarity marks sit outside the pad area and stay visible after the part is placed. Marks under the component help nobody at AOI.
11Test points accessible
Pass: ≥ 1 mm diameter, ≥ 2.54 mm pitch, on one side if ICT is planned. Probe access decided after layout is a fixture redesign, not a tweak.
12Components clear of tabs and V-score lines
Pass: no parts within 3 mm of a V-score line or mouse-bite tab. Depanelization flex is enough to crack ceramic caps sitting on the break line.
13Tall parts out of shadow zones
Pass: tall components are not adjacent to fine-pitch or low-profile parts — they shadow them in reflow and occlude them in AOI.
14Large pads thermally balanced
Pass: connectors and large copper pours use thermal relief, so small pads sharing the net reflow at the same rate. One cold joint on a shared net is the usual symptom.
15Mixed SMT/THT sequencing noted
Pass: every THT part is marked with its intended process — wave, selective, or hand-solder — before quoting. Undecided THT is the most common cause of a stalled quote on mixed boards.
DFM checklist (printable PDF)All 15 checks with checkboxes and pass lines on one A4 page — print it and pin it next to your CAD seat.
Run the list twice. First at placement review, when moving a component still costs nothing — checks 02, 03, 06, 10, 12 and 13 are pure layout decisions. Then at release, before files go out — that's when 01, 04, 07, 08, 09, 11, 14 and 15 get locked. Ten minutes against a checklist is cheaper than one engineering question that stops a purchase order for two days.
Two honest caveats. First, every line has its own limits — the numbers here reflect our typical capability (2–8 layer FR-4, 4/4 mil), so confirm against your assembler's spec, not ours. Second, a checklist doesn't replace a review: it clears the mechanical issues so the human review can spend its time on the judgment calls — thermal strategy, test coverage, component lifecycle.
What a DFM review looks like on our side
Every new design that comes to us gets a first-article review before production: Gerbers and CPL cross-checked against the BOM, stencil apertures reviewed, panelization confirmed, and anything borderline flagged back to you with a specific question, not a generic warning. If your files pass this checklist, that review is a formality. If something fails, you'll hear exactly which check and why — before anything gets built, not after.
Want an engineer to run the review?
Send your Gerbers, BOM and CPL — the DFM pass is part of every quote, not an add-on. You'll hear back in 24–48 hours.
