---
title: How to Read a BOM Like a Pro
description: This BOM guide breaks down every column, part type, and critical nuance so you can review BOMs like an expert and avoid costly mistakes.
---

[SMT Blog ](https://www.teamsmt.com/blog)

# [How to Read a BOM Like a Pro](https://www.teamsmt.com/blog/how-to-read-a-bom-like-a-pro)

 Written by [Brian Lamers](https://www.teamsmt.com/blog/author/brian-lamers) | June 23, 2025

 

#### 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.

 

 

[View full post](https://www.teamsmt.com/blog/how-to-read-a-bom-like-a-pro)

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