How to Read a BOM Like a Pro

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  If something's unclear, out of date, or in shortage, talk to your contract manufacturer early.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.