How to Prepare Gerber and BOM Files for PCB Assembly (2026 Guide)

When you request a PCB assembly quote, the quality of your Gerber and BOM files directly affects how fast you get an accurate quotation — and how smoothly your project moves into production.

This guide covers exactly what files PCB assembly manufacturers need, what each file should contain, and the most common mistakes that delay quoting.

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What Files Do You Need to Send?

For a complete turnkey PCB assembly quote, you should typically send:

If you only have Gerber and BOM, that's still enough to get started — your manufacturer can request the rest later.

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Part 1: Preparing Gerber Files

Gerber files describe each copper layer, solder mask, silkscreen, and board outline of your PCB. Most modern EDA tools export them automatically.

Required Gerber Layers

A standard 2-layer PCB needs at minimum:

• Top Copper (.GTL or F.Cu)
• Bottom Copper (.GBL or B.Cu)
• Top Solder Mask (.GTS or F.Mask)
• Bottom Solder Mask (.GBS or B.Mask)
• Top Silkscreen (.GTO or F.SilkS)
• Bottom Silkscreen (.GBO or B.SilkS)
• Board Outline (.GKO or Edge.Cuts)
• Drill File (.DRL or .TXT)

For 4-layer or multilayer boards, add inner layer files.

Best Practices

1. Use RS-274X format — Not the older RS-274D. Most modern tools default to RS-274X.
2. Include drill files — Many engineers forget this. Without drill data, your board can't be manufactured.
3. Check board outline — The outline should be a closed shape on the Edge.Cuts layer.
4. Pack everything in a ZIP — Don't send individual files. Compress all Gerber layers into a single .zip.

Common Gerber Mistakes

• Sending only the .pcb or .brd source file (CAD format) — Manufacturers need exported Gerbers
• Missing drill files
• Solder mask openings wrong size
• Silkscreen text overlapping pads
• Component reference designators missing from silkscreen

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Part 2: Preparing the BOM

The Bill of Materials (BOM) tells your manufacturer exactly which components to source and place. A clean BOM saves days of back-and-forth.

What a Good BOM Looks Like

Your BOM should be an Excel or CSV file with these columns:

Why Manufacturer Part Number (MPN) Matters Most

The MPN is the single most important field. Without it, your manufacturer has to guess which exact component you want, which delays sourcing and can lead to wrong parts being installed.

Bad: 10k resistor 0603

Good: RC0603FR-0710KL (Yageo, 10k 1% 0603)

BOM Tips That Save You Time

1. Group identical components — Instead of one row per component, group them.
2. Mark DNP parts clearly — Use a "Do Not Populate" column or a separate sheet.
3. List alternates if you're flexible — Save your manufacturer hours of sourcing time.
4. Include polarity-sensitive notes — For LEDs, diodes, electrolytic caps.
5. Avoid generic part numbers — LM358 could be from 10 manufacturers. Use full MPN.

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Part 3: Pick-and-Place File (Centroid File)

The pick-and-place file (also called centroid or CPL) tells the SMT machine where each component goes and at what rotation.

Required Columns

• Designator (R1, C5, U2…)
• X coordinate (mm)
• Y coordinate (mm)
• Rotation (0, 90, 180, 270)
• Layer (Top / Bottom)

Most EDA tools export this automatically as a CSV. Just make sure your origin point is set correctly — usually the bottom-left corner of the PCB.

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Part 4: What to Send for Faster Quotation

Here's a checklist for the fastest possible turnaround:

• Gerber + drill files in one ZIP
• BOM with MPNs in Excel
• Pick-and-place CSV
• Quantity needed
• Lead time preference
• Testing requirements (AOI / X-Ray / Functional)
• Surface finish preference (HASL / ENIG / OSP)
• Special requirements (impedance control, conformal coating, etc.)

The more clarity you give upfront, the faster your engineering review and quotation.

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Common Questions

What if my BOM is only 70% complete?

Send what you have. A good manufacturer can review the BOM, identify missing parts, and suggest sourcing alternatives. Engineering review before quotation should catch incomplete BOMs and help you finish them.

Can I send my CAD source files instead of Gerbers?

It's better to export Gerber files. CAD source files (Altium .PcbDoc, KiCad .kicad_pcb, Eagle .brd) require your manufacturer to re-export, which can introduce errors. If you must send the source, include both formats.

Do I need a schematic?

Not always. Schematics help with functional testing planning and DFM review, but they're not required for assembly itself. If your project has any signal integrity or impedance requirements, send the schematic.

What's a reasonable file size?

A typical Gerber ZIP is 1-5 MB. BOM files are usually under 100 KB. If your files exceed 25 MB total, contact your manufacturer to confirm upload limits.

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Ready to Get a Quote?

Once your Gerber and BOM files are ready, you can upload them directly for engineering review and quotation. Our team will check files before quoting — no automated black-box pricing.

If you're missing files or unsure if your design is ready, send what you have. We'll review and let you know what's needed.

Next steps:

• Get a PCB Assembly Quote
• Learn about turnkey PCB assembly
• See our PCB assembly capabilities