What is a BOM (Bill of Materials)? Required fields, common mistakes, format tips and how to create the perfect parts list for your PCBA request.
What is a BOM?
The BOM (Bill of Materials) is the parts list – the central document for PCB assembly. It contains all electronic components to be mounted on the board. A precise, complete BOM speeds up quoting and prevents ordering errors.
Required Fields
Every BOM needs: reference designator, quantity, description, manufacturer, manufacturer part number (MPN), package/footprint, and DNP marking. The MPN is the most important field.
Common BOM Mistakes
Top mistakes: missing MPN, obsolete components (EOL), imperial/metric package confusion (0402 imperial ≠ 0402 metric), unmarked DNP positions, grouped references without individual rows.
BOM Format and Delivery
Use Excel (.xlsx) or CSV for BOM delivery. Never use PDF as the primary format. Export directly from your EDA tool (KiCad, Altium, Eagle) to minimize errors.
BOM Export from EDA Tools
How to export the BOM from common EDA programs:
- KiCad: Schematic Editor → Tools → Generate Bill of Materials → Select CSV plugin
- Altium Designer: Reports → Bill of Materials → Excel format
- Eagle: ULP → bom.ulp → CSV or Excel export
- OrCAD: Tools → Bill of Materials → Standard Template
Make sure all fields (especially MPN and footprint) are included in the export. A clean BOM saves time and avoids unnecessary queries with your EMS provider.
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