What is a BOM (Bill of Materials)?
A BOM is the master document for any electronics assembly. It's your roadmap, detailing every component needed to build a printed circuit board (PCB) or full system. BOMs are used by engineers, buyers, planners, and contract manufacturers to:
- Procure correct materials
- Quote assemblies accurately
- Plan for manufacturing
- Track product revisions
1. Common BOM Columns Explained
Reference Designator (RefDes): Identifies the specific location of each component on the PCB (e.g., R1, C2, U3). Helps assemblers and test engineers place and verify parts.
Quantity Per Assembly: The number of units of a given part used on one assembly.
Manufacturer Part Number (MPN): The exact part identifier used by the original component manufacturer. This is the most critical field for sourcing and quoting.
Description: Basic info about the part: value, size, package, voltage, tolerance, etc.
Manufacturer Name: Tells you who makes the part which is important for traceability and quality assurance.
Internal Part Number: Your contract manufacturer may assign internal part numbers for cross-referencing and quoting.
Approved Vendor(s): Indicates authorized suppliers who can provide the part.
Approved Alternate(s): Customer-approved substitutes for parts in short supply or allocation.
2. BOM Hierarchy: Types of BOMs You May Encounter
- Flat BOM: A simple list of components for one assembly.
- Indented BOM: Shows parent-child relationships between subassemblies and components.
3. BOM Best Practices for OEMs
- Always provide MPNs and manufacturer names
- Avoid distributor SKUs unless approved
- Mark consigned, CSP, or non-standard parts clearly
- Update AML with every design revision
- Include alternate parts if pre-approved
4. Common BOM Red Flags (and How to Fix Them)
- Missing MPNs: can't source or quote without them.
- Inconsistent Descriptions: Leads to confusion during inspection or purchasing.
- Duplicate RefDes: Causes placement errors or confusion on the floor.
- Deprecated/NRND/Obsolete Parts: Should be flagged and updated.
5. Tools That Help
- BOM Scrubbers: Automatically clean and validate BOMs
- EDA Tools: Altium, OrCAD, KiCAD exports
- Cross-referencing software: Helps match alternates and standardized parts
Final Tip: Communicate Early
The best BOMs are living documents. If something's unclear, out of date, or in shortage, talk to your contract manufacturer early. A 10-minute call today can save weeks of delays.
