KEMI Docs · PCB Practice
Top 7 PCB Ordering Mistakes
Last updated: 2026-08-30
Once a PCB order is placed there is no undo — one mistake means a respin and one to two weeks lost. These seven are the mistakes KEMI sees most often in real pre-order reviews, roughly in order of frequency.
1
Layer-count mismatch
The most common and most expensive. The order says 4 layers, the ZIP holds two copper files — the inner layers were dropped at export. Prevention is simple: count the copper Gerbers yourself right before ordering and compare with the ordered count.
2
Missing or open outline
Without a closed outline the fab does not know where to cut. Good fabs reject the order; others guess. Slots and internal cutouts must be on the outline layer too. A frequent cause: the outline was drawn on a mechanical layer that was excluded from export.
3
Drill unit and format errors
Excellon headers declare units and decimal format; a mismatch shows holes 10x off. Check a few known holes (e.g. an M3 clearance at 3.2mm) in a viewer, and make sure both PTH and NPTH files made it into the ZIP.
4
Solder mask not opened
A pad without a mask opening arrives covered in ink — unsolderable. Usually a home-made footprint missing its mask layer. View the mask layer alone and scan for openings on every pad.
5
Silk over pads
Silk crossing a pad gets clipped in production, leaving half-cut designators; if printed, it hurts solderability. Any CAD's DRC catches this — run it before ordering.
6
Thickness and copper weight unspecified
Board thickness (typically 1.6mm) and copper weight (1oz outer default) are order parameters, not Gerber data. Defaults are wrong answers when card-edge fit or high-current traces are involved. Controlled-impedance boards additionally need the stack-up stated on the order.
7
Violating fab minimums
Trace/space below the process minimum (about 0.15/0.15mm on budget processes), drills under 0.3mm, or thin via annular rings cost yield or surcharges. Load the target fab's limits into your DRC rules at the start of the design.
Review the exported files, not the CAD screen
All seven share one prevention: load the actual exported Gerber/drill files into a viewer. Export mistakes never show on the CAD screen. KEMI's online Gerber viewer classifies layers and checks copper count, outline and drill automatically.
FAQ
Won't the fab catch these?
Obvious defects (no outline, no drill) are often rejected, but anything that could be intentional — layer mismatch, closed mask — gets built as sent. Responsibility sits with whoever supplied the data.
Anything extra for panelized orders?
Check V-cut lines against the outline, mouse-bite spacing, that the panel fits the fab's maximum working size, and the panel-count arithmetic (boards needed ÷ boards per panel).
Where do special requirements go?
Anything not in the Gerbers — thickness, copper, surface finish, via treatment, impedance — goes on the order form or a readme. Comments inside the files are effectively never read.
Can pre-order checks be automated?
Basic completeness is checked free by KEMI's Gerber viewer; the PCB Design Inspector produces a full report covering power trace width, clearance and bypass placement.
See also
This article summarises the working rules KEMI uses in real design and fabrication work. For production, part datasheets and fab specifications take precedence.