BOM (Bill of Materials)

Notes

BOM cost reduction programmes are the standing reason customers requalify second sources after launch.

Overview

A BOM (bill of materials) is the structured list of every component, with its part number and quantity, needed to build one unit of a product. For a circuit board it lists chips, passive components, connectors and the board itself; for a chip package it lists the die, substrate or lead frame, wire, moulding compound and other materials. The BOM is where a supplier's design win is recorded and where component costs are compared line by line.

How it works

Engineering teams create the BOM as the design takes shape, usually from the schematic and the product data management system. Each line gives a part number, description, quantity, reference designators and often approved manufacturers and alternative parts. Purchasing uses it to buy components, manufacturing uses it to build, and finance totals it to give the material cost of the product.

For chip suppliers, getting a part onto a customer's BOM is the design win: once a board is qualified with that part, changing it costs the customer time and money, so the part may ship for the product's whole life. Customers often list a second source for important parts, and approved vendor lists control which suppliers may be used. A part's lifecycle status matters too: an end-of-life notice for one line of a BOM can force a redesign.

Chip packages have their own BOM, controlled by the supplier and its assembly house. Changing any item, such as the wire metal, moulding compound or substrate supplier, is a product change that may need new qualification and, under industry practice set out in JEDEC J-STD-046, customer notification. Analysts also estimate the BOM cost of finished products such as phones by taking them apart, to see what each component is worth.

Examples

• A smartphone BOM listing the processor, memory, power management, radio chips and hundreds of passive components.
• A design win confirmed when a supplier's sensor is added to a customer's board BOM.
• A package BOM listing die, substrate, solder balls, underfill and moulding compound.
• An end-of-life notice for one capacitor forcing a customer to qualify an alternative part.
• A teardown analysis estimating the BOM cost of a new consumer device.

Why it matters

The BOM connects engineering, purchasing, manufacturing and finance, and for chip companies it is where sales are won or lost. BOM management specialists, component engineers, supply chain planners and sales teams all work from it, and quality teams control changes to package BOMs.

Related terms

• Socket
• Content per system
• Orderable part number
• Gross margin

Where it appears on the Hub

Used on 64 pages of the Hub. In each group, the pages that mention it most come first.