IllustrationA bill of materials for electronics lists every part needed to build a device. Each line gives reference designators, quantity, the manufacturer part number, the manufacturer, approved alternates, lifecycle status and lead time. Keep an engineering BOM for the design and a manufacturing BOM for the build, and review end-of-life and single-source risk at every gate.
The BOM is the file a buyer, an assembler and a test lab all read. If a row is vague, someone guesses, and the guess shows up later as a wrong part, a missed shipment or a redesign. This guide covers the fields an electronics BOM needs, EBOM vs MBOM, alternates, lifecycle status and the BOM checks for each development gate.
What goes in a bill of materials for electronics?
A BOM for a connected device covers board parts, mechanical parts and the items needed to finish and pack the product. Each row is one part number in one assembly. The table lists the fields we treat as the minimum for a device headed for certification and small-batch builds.
| Field | What it holds | Why it matters |
|---|---|---|
| Reference designators | The board labels the line covers, such as R1, R2 and C14. | The assembler places parts by these labels. The count of designators must equal the quantity. |
| Quantity and unit | How many of the part one board or device uses, with a unit of measure. | Board parts are counted in pieces. Items such as adhesive, foam or wire need a stated unit. |
| Manufacturer part number (MPN) | The full orderable number, including package, temperature grade and packaging suffix. | A short MPN without its suffix can buy the wrong package or grade. |
| Manufacturer | The company that makes the part. | Two makers can use similar numbers for different parts. |
| Description and key values | Value, tolerance, voltage rating, package and temperature range. | A buyer can judge a substitute without the schematic. |
| Approved alternates | Other MPNs your engineers have checked for this exact line. | An empty cell means the line is single source. Say so on purpose. |
| Lifecycle status | The maker status, such as active or not recommended for new designs, and the date you checked it. | Status changes over the life of the product, so a status with no date is stale. |
| Lead time and date quoted | The lead time a distributor or maker gave, and when. | Lead times move. The date tells the reader how much to trust the figure. |
| Compliance data | RoHS and any other material declarations your markets need, per part. | You collect these from suppliers, part by part. |
| Fit or do not place | Whether the part is fitted in this build variant. | Debug parts and options stay off production boards. |
| Internal number and BOM revision | Your own part number and the revision of the BOM the row belongs to. | Links each row to its change records. |
Two of these fields are easy to get wrong. The MPN must be complete, because the package and grade often live in the suffix. The designators must match the quantity, because the assembler programs the machine from them. A quick script that counts designators per row and compares the count with the quantity finds mismatches before a quote goes out.
Compliance data belongs on the BOM too. The EU RoHS Directive, 2011/65/EU, restricts ten substances in electrical and electronic equipment, including lead, cadmium and mercury, as of November 2026 (European Commission RoHS page). For EU sales, keep each supplier's declaration with its row. This article does not quote the concentration limits.
What is the difference between an EBOM and an MBOM?
The engineering BOM (EBOM) describes what the design needs. The manufacturing BOM (MBOM) describes how the product is built on a specific line. They share most part numbers, and they are organized for different readers.
| Topic | Engineering BOM (EBOM) | Manufacturing BOM (MBOM) |
|---|---|---|
| Question it answers | What does the design need? | How is the product built on this line? |
| Owner | Electrical and mechanical engineering. | Manufacturing, working with the assembler and buyers. |
| Built from | Schematic, PCB layout and mechanical CAD. | The EBOM plus the build process. |
| Structure | Grouped by design assembly: main board, flex, enclosure. | Grouped by build step: board assembly, sub-assembly, final assembly, pack-out. |
| Extra items | Few beyond the parts in the design. | Labels, packaging, process materials, programming and test steps. |
| Changes when | The design changes. | The line, the assembler or the process changes, or the EBOM changes. |
| Used by | Design review, test, certification planning. | Purchasing, kitting, incoming inspection, quality control. |
Keep one rule: every MBOM revision names the EBOM revision it builds. When the two drift apart, a factory can build an old design with new labels. For a small pilot, one spreadsheet with an EBOM tab and an MBOM tab can be enough, as long as both carry a revision and a date.
How do you set up alternates and an approved vendor list?
An approved vendor list (AVL) records which makers and exact MPNs are allowed for each line. Alternates give purchasing room when a part is short. They also add risk, because a part that matches on paper can behave differently on the board. The type of part sets how much checking it needs.
| Type of change | Example | What to check | Who signs off |
|---|---|---|---|
| Passive with the same value and package | Resistor or capacitor from a second maker. | Tolerance, voltage rating, dielectric type and temperature range match the line. | Electrical engineer. |
| Same-function chip from another maker | A regulator or load switch with the same footprint. | Pinout, footprint, thermal data and startup behavior. Run a bench test on a real board before you list it. | Electrical engineer, after a bench test. |
| Part in the radio path | Crystal for the radio, RF switch, matching parts, antenna, power amplifier. | Whether the change touches items 47 CFR 2.1043 names, such as frequency-determining circuitry or maximum power ratings. | Compliance owner and test lab, before the change ships. |
| Radio module | A different module in the same slot. | Treat it as a new design review and ask your test lab what it means for your equipment authorization. | Compliance owner, test lab and firmware lead. |
| Memory or flash | Flash from a second maker. | Firmware support, boot timing and update behavior. Re-run firmware tests. | Firmware lead. |
| Battery cell | A cell from a different maker. | Ask whether your existing safety and shipping test records still apply to the new cell. | Compliance owner. |
Why radio-path parts need extra care
A wearable, tracker or voice device has a radio, and its certification covers the design as tested. Under 47 CFR 2.1043, changes to the basic frequency-determining and stabilizing circuitry (including clock or data rates), frequency multiplication stages, the basic modulator circuit, or the maximum power or field strength ratings need a new grant of certification, apart from one narrow exception the rule lists. A Class I permissive change does not degrade the characteristics reported to the FCC and needs no filing. A Class II permissive change degrades them while still meeting the rules. The grantee must file test results for the affected characteristics, and the changed product cannot be marketed under the existing grant until the change is acknowledged as acceptable. That is the rule as of November 2026 (47 CFR 2.1043, Cornell LII).
Mark every radio-path line in the BOM and require a compliance review before anyone adds an alternate to one. This is an engineering summary and not legal advice. Ask your test lab how a given change is classed.
How do you read lifecycle status and longevity data?
Every maker publishes a status for each part, and the words differ by maker. TI's definitions are a clear example. The definitions below follow TI's product life cycle page closely, as of November 2026 (TI). The last column is our suggestion for the BOM.
| TI status | TI definition | What to do on your BOM |
|---|---|---|
| Preview | Not in production, although prototype or experimental parts are available for purchase. | Fine for a prototype. Flag it in the risk register and track the production release date before you lock the BOM. |
| Active | Released to the market and available for purchase. | Normal choice. Record the date you checked. |
| Not Recommended for New Designs (NRND) | Available for existing designs. For new designs, TI recommends considering an alternate. | Avoid on a new design unless you have a written reason. Read each maker's own definition. |
| Last Time Buy | In the process of being discontinued. New designs should consider an alternate. | Do not design it in. On a shipping product, decide on a final purchase quantity or start a redesign. |
| Obsolete | No longer in production. New designs should consider an alternate. | Replace it. Any stock offered on the open market needs extra inspection. |
TI also says its product life cycles are typically 10 to 15 years and often extend longer, as of November 2026. Some makers publish a longevity commitment per product. Espressif lists a minimum of 12 years from January 1, 2021 for the ESP32-S3 and ESP32-C3, and 15 years from January 1, 2016 for the original ESP32, as of November 2026 (Espressif longevity commitment). Espressif says it reserves the right to update this information at any time, so record the date you read it.
Use these statements to compare candidates early. A maker policy can change, so keep watching for change and discontinuance notices once you ship.
How should BOM management work at each development gate?
BOM management is a set of checks that repeat as the design matures. The table maps them to our gates. The middle column is the BOM deliverable each gate lists in our gated prototype development process. The last column is the risk review we suggest at that point.
| Gate | BOM deliverable | Risk review |
|---|---|---|
| Gate 0: Feasibility | BOM draft and risk register | Check lifecycle status and published longevity for the main chips and modules. List every part with only one maker. Record the dates you checked. |
| Gate 1: Works-like prototype | No separate BOM deliverable | Mark which module lines are placeholders and which stay on the custom board. |
| Gate 2: EVT · first custom PCB | BOM with alternates | Every line has an MPN, maker, designators and quantity. Alternates are listed, or the line is marked single source with a reason. |
| Gate 3: DVT / PVT · small batch | Locked BOM with second sources | The BOM is frozen. Any change goes through a written change review, and radio, battery and sealing changes are checked against the certification and test records. |
| Gate 4: Mass production | End-of-life and lead-time alerts | Watch maker change and discontinuance notices. Decide on final purchases or redesigns before stock runs out. |
Two risks deserve a check at every gate: end-of-life parts and single-source parts. Review both and write the result into the risk register with a date. A part that was active at Gate 0 can carry a different status by the time you order a small batch. For what each gate hands you beyond the BOM, see EVT, DVT and PVT explained.
What a lead-time field should and should not tell you
Record the lead time with its source and date. An old figure tells you little about today. Before you commit to a build date, refresh the lead time on every single-source and long-lead line, then decide which parts to buy early.
What should you ask your hardware team about the BOM?
Bring this list to any gate review.
- Which file is the current BOM, and what is its revision?
- Does the designator count match the quantity on every board line?
- Which lines are single source, and why did we accept each one?
- When was lifecycle status last checked, and by whom?
- Which main chips have a published longevity statement, and from what start date?
- Who approves an alternate, and what test does each type of alternate need?
- Which lines sit in the radio path, and what happens to certification if one changes?
- Do we have RoHS data for every part, or only for the main chips?
- Who watches for change and discontinuance notices once we ship?
Questions about electronics BOMs
What is the difference between a BOM and an SBOM?
A hardware BOM lists the physical parts in a device. A software bill of materials (SBOM) lists the software components in the firmware and apps. A connected device needs both. Our SBOM and source-file handover checklist covers the software side.
What does NRND mean on an electronics BOM?
It stands for not recommended for new designs. TI defines it as a part that is available for existing designs, with an alternate recommended for new ones (TI product life cycle, as of November 2026). Espressif says NRND status does not affect its longevity commitment (Espressif, as of November 2026). Always read the maker's own definition.
Can I swap a part after FCC certification?
Some changes are permissive and some need a new grant. Under 47 CFR 2.1043, changes to frequency-determining circuitry, the basic modulator circuit or maximum power ratings need a new grant (47 CFR 2.1043, as of November 2026). This is an engineering summary and not legal advice. Ask your test lab before you ship the change.
How can Duobay help with my bill of materials?
A Gate 0 Feasibility study includes a BOM draft and a risk register. Later gates deliver a BOM with alternates, then a locked BOM with second sources. We do not publish prices. Tell us about your device and we will explain how the BOM work fits your project.
If you want your BOM reviewed for lifecycle and single-source risk before a build, tell us about your device.
Sources. All pages accessed November 5, 2026. Maker policies and rules change, so confirm current versions before you decide.
- Texas Instruments, Product life cycle (link)
- Espressif, Product Longevity Commitment (link)
- European Commission, RoHS Directive (link)
- 47 CFR 2.1043, Changes in certificated equipment, Cornell Legal Information Institute (link). eCFR could not be fetched, so the Cornell LII copy is cited.
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