# Gerber File Preparation Checklist Before Ordering
In PCB prototyping and volume production, more than half of all delivery delays come not from factory capacity but from incomplete or ambiguous Gerber files. Ten extra minutes of self-checking before you order often saves three to five days of back-and-forth. Sunking PCB (HQ in Shenzhen, factory in Huizhou, founded in 2009 with 15+ years of manufacturing experience) has distilled a pre-order Gerber checklist to help your design pass engineering review (EQ) on the first attempt.
RS-274X vs ODB++: Pick the Right Format First
Gerber is the industry-standard format that describes the graphics of each PCB layer. Two families dominate:
- RS-274X (Extended Gerber): The most common format. Each layer is exported as a separate file with aperture (pad) definitions embedded, offering excellent compatibility. Nearly every fabricator can read it.
- ODB++: An intelligent package that bundles layers, drills, stackup, netlist, and component data into a single database directory. It carries more complete information with fewer ambiguities and suits complex, high-layer-count, and HDI boards.
For a standard multilayer board, RS-274X is enough. For high-density, tightly impedance-controlled, or rigid-flex designs, exporting ODB++ reduces repeated factory clarifications. Either way, include a PDF plot for human verification.
Required Layers: Leave None Out
A complete Gerber set should contain at least the following layers. Missing any one of them can trigger an EQ:
- Copper layers: Top, bottom, and all inner-layer traces. Multilayer boards should be named in order (L1, L2, and so on).
- Solder mask: Top/bottom mask openings. Note that openings are usually 2–4 mil larger per side than the pad.
- Silkscreen: Top/bottom legend. Keep line width at least 5 mil and character height at least 25 mil, and avoid silkscreen over pads.
- Paste mask (stencil): Used for SMT stencil apertures. Needed only when surface-mount components are present.
Drill Files: NC Drill Is Critical
Drill data is usually exported separately as an NC Drill (Excellon format) file and must clearly specify:
- Plated through holes (PTH) and non-plated holes (NPTH) separated or clearly labeled.
- A drill table that maps one-to-one with actual holes, including hole tolerances.
- Buried and blind vias (HDI) provided as distinct drill pairs (for example L1-L2, L1-L4) and documented in the stackup.
Sunking's process supports a minimum hole size of 0.075mm, but small holes drive up drill wear and cost, so avoid shrinking holes unnecessarily.
Fabrication Drawing and Notes
The fab drawing is the "instruction manual" for your Gerber set, conveying requirements that graphics alone cannot:
- Board thickness, layer count, and layer stackup.
- Copper weight (Sunking can build heavy copper over 12oz).
- Material type (FR-4, high-frequency, metal core, etc.) and Tg value.
- Surface finish (HASL, lead-free HASL, ENIG, OSP, and more).
- Impedance-control requirements, special tolerances, and outline/V-cut/mouse-bite notes.
- Outline dimensions (Sunking supports boards up to 1250Ă—570mm).
Common Mistakes: The Biggest Delay Triggers
| Common Issue | Consequence | Recommended Practice |
|---|---|---|
| Missing or confusingly named layers | Stackup cannot be determined | Use standard naming with a layer list |
| No drill file provided | Cannot be manufactured | Export NC Drill and verify the drill table |
| Trace/space below process limit | Immediate re-spin | Sunking min trace/space is 2mil/2mil; keep margin |
| Solder mask opening too small or over trace | Short/bridging risk | Leave 2–4 mil per side |
| Silkscreen over pads | Soldering issues | Clear silkscreen off pads |
| No board outline layer | Cannot be routed to shape | Provide a dedicated mechanical/outline layer |
| Mixed units (imperial/metric) | Dimension errors | Standardize units and label them |
Pre-Order Self-Check List
- [ ] Copper, solder mask, silkscreen, and paste layers complete
- [ ] NC Drill file exported with PTH/NPTH clearly separated
- [ ] Board outline layer provided
- [ ] Fab drawing states thickness, layers, copper weight, material, finish
- [ ] Impedance control / special tolerances documented
- [ ] Trace width, spacing, and hole sizes within process capability
- [ ] Units unified, with a PDF plot for verification
Confirm each item on this list before packaging and uploading, and you will minimize EQ rounds and speed up both prototyping and production.
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If you would like a professional engineering team to pre-review your Gerber files for free before ordering, or have questions about stackup, impedance, or process capability, contact Sunking PCB for a quote and advice. Certified to ISO9001, ISO14001, ISO13485, IATF16949, UL, RoHS, and REACH, we are glad to help you get the files right the first time.