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Bill of Materials Management: Process, Versions, and the Mistakes That Cost Builds
Bill of materials management for hardware teams: part numbers, revisions, change orders, alternates, lifecycle checks and the mistakes that cost builds.
by the HardwareMap editors4 min read
Contents
Bill of materials management is the process that keeps one correct BOM per product revision and controls every change to it. It decides part numbers, revision rules, who approves changes, how alternates are qualified and how the released BOM reaches purchasing and the factory. This note gives a process a small team can run. For the BOM itself, start with the bill of materials example.
The bill of materials management process
Five rules carry most of the weight.
- One owner, one source of truth. A named engineer owns the BOM. There is one master, in a spreadsheet or a tool, and every other copy is an export with a revision on it.
- Part numbers that never get reused. Assign internal part numbers from a register. A retired number stays retired. Keep the number meaningless or lightly coded (a class prefix such as 100 for PCBAs, 200 for molded parts); smart numbers that encode material or color break the first time a part changes.
- Released means frozen. Once a revision is released to a factory, it changes only through a change order. Work in progress lives in a draft revision.
- Every line has a source. Manufacturer, manufacturer part number and at least one supplier for bought parts. Drawing number and revision for made parts.
- The BOM travels with its revision. Purchase orders, build tickets and test records name the BOM revision they were built against.
A typical flow, from design to build:
The engineering BOM and the factory's manufacturing bill of materials are different documents. Keep them linked by revision, and do not let the factory's version become the master by accident.
Revisions, part numbers and change orders
The rule that settles most arguments is form, fit and function. If a changed part still swaps one-for-one with the old part in every assembly, bump its revision. If it does not, it needs a new part number. A worked example for a sensor product:
Every one of those goes through a change order: what changes, why, which documents, what happens to stock on the shelf and boards on the line (use, rework or scrap), and from which serial number or date it applies. Approval comes before the BOM edit, not after.
Bill of materials management in the supply chain
A BOM is also a purchasing plan. Three columns keep it honest:
- Lifecycle status. Active, not recommended for new designs, last-time buy, obsolete. Check it before every build and when a supplier sends a product change notice.
- Alternates. An approved vendor list (AVL) for each critical part, with alternates qualified on real boards, not just matched on a datasheet. Single-source parts get flagged.
- Lead time and stock. Long-lead parts set your build date. Track them separately and order them first.
Compliance data lives here too. If you sell into the EU, the RoHS directive restricts specific hazardous substances in electrical equipment, and REACH adds reporting duties for substances of very high concern. Store each supplier's declaration against the part, not in someone's inbox. Certification paths are covered in hardware certifications.
BOM mistakes that cost builds
The fix for nearly all of them is the same: a controlled release and a change order. Frank Watts's Engineering Documentation Control Handbook is the long-form reference on that discipline. Terms like AVL, ECO and EOL are defined in the hardware startup glossary.
Spreadsheet or software
A spreadsheet works for one product, one engineer and one factory, if the five rules above hold. Move to a tool when several people edit the BOM, when you run more than one revision in production, or when change orders need approval trails. Our bill of materials software roundup compares options. Some teams now use AI tools to draft and clean BOMs; the AI bill of materials note covers what to check in their output.
Frequently asked questions
What is bill of materials management?
It is the process that keeps one correct, current BOM for each product revision and controls how it changes. It covers part numbering, revision rules, who may approve a change, how alternates are qualified, how lifecycle and compliance data stay current, and how a released BOM reaches purchasing and the factory. The goal is that every build uses the BOM you meant it to use.
When should a change get a new part number instead of a new revision?
Use the form, fit and function rule. If the changed part is still interchangeable with the old one in every assembly that uses it, bump the revision. If it is not, because a hole moved, a pinout changed or a material no longer meets the spec, issue a new part number. Mixing the two is how old and new parts end up in the same bin.
What is an ECO in hardware?
An engineering change order is the controlled record of a change to a released design. It names the parts and documents affected, the old and new revisions, the reason, the disposition of existing stock and work in progress, and the effective date or serial number. It is approved before anyone updates the BOM. Small teams can run it as a numbered form, not a heavy system.
How often should I check my BOM for obsolete parts?
Check lifecycle status before every build and whenever a supplier sends a product change or end-of-life notice. Distributor and part-search tools show active, not recommended for new designs, last-time-buy and obsolete states. A single-source part going end of life with no qualified alternate can stop a build, so the alternates column matters as much as the status check.
HardwareMap catalogues hardware startups like parts on a datasheet. Building one? Submit it and get a part number.
Building one?
Submit it to the index and get a part number. Every entry is reviewed by hand.