A PCB component substitute is ready for use only when the exact manufacturer and full manufacturer part number (MPN) have been evaluated against the design requirements and explicitly authorized for a defined project and production scope. A matching description, nominal value or package code is not approval.
During a shortage, keep the proposed alternate separate from the released BOM while engineering checks its form, fit, function and manufacturing compatibility. Then obtain the required design-owner and customer permissions, record the effectivity, and control the actual lots used. If a check or permission is missing, the substitute remains pending—not generically equivalent.
This process goes beyond BOM error checking and component procurement, which focuses on BOM data quality. For the basic role and structure of a BOM, see What Is a BOM?.
Identify what is changing
Not every supply change is a substitute request, but each can require review:
- Proposed alternate: An identified manufacturer and exact MPN offered in place of the released part. It has not yet received all required technical and commercial approvals.
- Approved substitute: An exact alternate authorized by the responsible parties for a documented scope. Approval may be limited by board revision, product, order, date, quantity or lot.
- Manufacturer product-change notice (PCN): A notice from the component manufacturer describing a change to its product or supply. A PCN is not, by itself, approval to change the customer’s BOM or evidence that the customer has accepted the change. Review the notice against contractual and design requirements.
- Same MPN, different manufacturer: A different manufacturer offering the same printed or listed part number. Treat the manufacturer-and-MPN pair as a distinct identity. Do not assume the products are interchangeable because their part-number text matches.
Texas Instruments’ product-change-notification guidance describes a PCN as a manufacturer notification. Whether a particular change needs customer approval is a separate project and contractual question.
A part can also retain its MPN while its manufacturer changes a production site, material or internal revision. Preserve the relevant notice and lot information, and assess the change where the design or customer requirements call for it.
Start with a scoped part record
For both the primary part and every candidate, record:
- Manufacturer’s legal or recognizable name and full orderable MPN, including suffixes.
- Component description, package and ordering options, such as tape-and-reel or temperature grade.
- Applicable data-sheet revision, product revision if identified, and relevant PCNs or manufacturer notices.
- BOM line, reference designators, assembly part number and board revision.
- Source, quoted quantity, availability, price basis and traceability information.
- Proposed use: project, customer, build, location, dates, quantity and lots, as applicable.
- Status of each technical check and each required permission.
Inventory scope matters. A candidate may be suitable for one board revision but unsuitable for another with a different footprint, operating temperature or firmware. Existing stock, open purchase orders, work in process and finished assemblies may also need separate treatment.
Do not turn a distributor’s abbreviated description or internal stock code into the approved part identity. Resolve it to the manufacturer and full orderable MPN before release.
Decision table: primary versus proposed alternate
The following record illustrates how to separate a technical result from permission to use a part. A and B are hypothetical 10 µF X7R MLCCs; they are not real MPNs or supplier data.
| Record or check | Primary A | Proposed alternate B |
|---|---|---|
| Manufacturer and full MPN | Pending entry and verification | Pending entry and verification |
| Specified-condition capacitance check | Pass: assumed 8 µF against a 6 µF minimum | Fail: assumed 5 µF against a 6 µF minimum |
| Other electrical and operating conditions | Pending | Pending |
| Package, land pattern, reflow and materials | Pending | Pending |
| Lifecycle, source and lot traceability | Pending | Pending |
| Permission and scope | Pending verification of the released BOM and its project, revision, time and lot scope | Not authorized; failure must be resolved before any approval decision |
A pass in one row is not an overall pass. In particular, B’s failure cannot be erased by an attractive price or availability. B fails the stated requirement and is not authorized on that basis. The designated design or disposition authority must decide whether to reject it or pursue a separately controlled design or requirement change with the necessary validation and approvals.
Check form, fit and function
Mechanical fit and assembly
Compare manufacturer package drawings, not just package nicknames. Check body dimensions and tolerances, height, terminal dimensions, seating, orientation and clearance to neighboring parts or enclosures. Compare the proposed package with the actual PCB land pattern, solder mask and stencil approach.
Verify pin numbering and function against the schematic and footprint. For polarized parts, check polarity markings and the physical orientation on the assembly. Similar-looking packages can have different pinouts, exposed pads or thermal requirements.
Then review the assembly process:
- Reflow temperature profile and the part’s permitted thermal exposure.
- Moisture sensitivity level (MSL), packing, storage and floor-life controls.
- Terminal finish, solder compatibility and any applicable material restrictions.
- Whether inspection access, repair or cleaning constraints change.
IPC/JEDEC J-STD-020, Moisture/Reflow Sensitivity Classification for Nonhermetic Surface Mount Devices, addresses moisture/reflow sensitivity classification. Use the component manufacturer’s actual classification and handling information for the selected part; do not infer it from another MPN.
Electrical performance across the operating envelope
Compare the parameters that matter in the circuit, including tolerances and limits rather than headline values alone. Depending on the device, this can include voltage and current ratings, leakage, ESR, switching behavior, frequency response, noise, power dissipation, thermal performance and startup behavior.
Evaluate the conditions in which the assembly will operate: supply range, load, transient events, temperature and required lifetime. Check worst-case margins and interactions with neighboring circuitry. A higher voltage rating, for example, does not by itself establish full equivalence for an MLCC.
For programmable or intelligent devices, also check interface timing, logic levels, memory configuration, firmware support, device identification and programming requirements. A package-compatible IC may still need a firmware change or different production programming procedure.
The failure mechanisms worth investigating depend on the component and application. The overview of electronic component failure modes can help frame the review, but it does not replace a part-specific analysis.
Worked example: nominal capacitance is not effective capacitance
Assume two hypothetical capacitors, A and B, each marked 10 µF, X7R. At the same specified DC bias and temperature, independently assume their effective capacitances are:
- A: 8 µF
- B: 5 µF
- Hypothetical design minimum at that condition: 6 µF
The arithmetic is:
- A: 8 µF − 6 µF = 2 µF above the minimum.
- B: 5 µF − 6 µF = 1 µF below the minimum.
Under these assumptions, A passes that one specified-condition comparison and B fails it. The values are illustrative assumptions, not measurements from a supplier or evidence that either device is approved.
Murata Manufacturing Co., Ltd.’s MLCC FAQ on DC-bias characteristics explains qualitatively that applied DC bias can reduce the effective capacitance of high-dielectric-constant ceramic capacitors and that the result depends on conditions. Obtain the relevant manufacturer data and evaluate the actual circuit conditions.
Even for A, a complete review may need to address tolerance, temperature range, aging, AC conditions and the rest of the application’s electrical and manufacturing requirements. The example does not establish a universal derating rule.
Qualify the candidate before authorizing it
The design owner should define the evidence needed for the risk and application. Depending on the part and contract, that might involve document comparison, calculations, fit review, prototype builds, electrical measurements, functional testing or reliability assessment. Define acceptance criteria and who is responsible for each activity before relying on its result.
Record:
- Requirement and acceptance limit.
- Evidence source, revision and applicable conditions.
- Reviewer and date.
- Pass, fail or pending status.
- Open issues, restrictions and required follow-up.
A supplier or assembly provider can supply data and identify manufacturing concerns within the agreed scope. The party with design authority decides whether the part meets design requirements; the customer provides approval where required. Neither a procurement recommendation nor an assembly-provider suggestion should silently become design approval.
If the candidate fails, document the disposition. Possible paths include rejecting it, seeking another MPN, or initiating a controlled change to the design or requirement. A waiver, if permitted, must identify the risk, authorizer and scope; it should not be represented as an unrestricted equivalence approval.
Release permission with controlled effectivity
Technical acceptance and permission to use the part are related but distinct. An approval record should name the exact manufacturer and MPN and state where and when use is permitted.
Include, as applicable:
- Customer and project; assembly part number and board revision.
- Primary manufacturer and MPN, plus approved alternate manufacturer and MPN.
- Affected BOM lines and reference designators.
- Released BOM revision and change-order or deviation identifier.
- Effective date or build, purchase orders, production location and quantity.
- Permitted component lots or lot-approval requirements.
- Qualification evidence, restrictions and expiration or review trigger.
- Design-owner approval and any required customer approval.
A lot-specific approval is not permission for a different lot. A temporary shortage deviation is not automatically a permanent alternate. If a customer approval covers only a particular order or date range, the production and procurement records must retain that limit.
Control stock physically or in the inventory system so unapproved candidates cannot be picked as released material. At receipt and build, verify the manufacturer, full MPN, source documentation and lot against the authorization. Record which lots were used in the affected assemblies to the traceability level agreed for the project.
If the approval expires, the lot changes outside its scope, or new manufacturer information affects the assessment, stop and route the issue for review. Do not extend the permission merely because an earlier build used the part.
What to include in the RFQ
A useful substitution RFQ gives procurement enough information to investigate supply without giving it authority to change the design. Include:
- Build identity: customer/project, assembly part number, PCB revision, BOM revision and expected quantities.
- Shortage line: reference designators, quantity per assembly, primary manufacturer and full MPN.
- Candidate details: proposed manufacturer and full MPN, data-sheet revision and any known PCN or revision information.
- Technical constraints: critical electrical limits, operating conditions, footprint, height, reflow, MSL, finish and applicable material requirements.
- Qualification plan: required evidence or tests, acceptance criteria, responsible party and required approvals.
- Supply details: offered source, available quantity and lot information, packaging, quoted price basis and relevant delivery terms.
- Authorization limits: whether a deviation is being requested and its proposed project, revision, order, date, quantity and lot scope.
- Traceability and disposition: records required at receipt and build, and instructions for unapproved, excess or unused material.
Ask suppliers to mark unknown information as pending, rather than filling gaps with assumed equivalence. Compare offers on the same quantity, packaging and commercial basis; price and availability do not substitute for technical approval.
The PCB assembly quote guide provides related context for preparing build information. For a project involving procurement and assembly, discuss the intended responsibilities through turnkey assembly, and agree in advance who supplies evidence, performs any qualification and authorizes changes. Submit the defined requirement through Quote or contact HILPCB to discuss an unresolved substitution question.
FAQ
Can procurement approve an alternate based on a matching description?
No. A matching description is a starting point. The exact manufacturer and MPN need the required technical review and authorization from the responsible parties.
Does a PCN mean the customer has approved the change?
No. A PCN is a manufacturer notice. Product-specific customer review or approval may still be required by the contract or project process.
Is the same MPN from a different manufacturer automatically equivalent?
No. Treat the manufacturer-and-MPN pair as a distinct part identity and compare the relevant specifications, manufacturing constraints and traceability.
Can an approved substitute be used on every board revision?
Only if the approval explicitly covers those revisions and other applicable limits. Check the released BOM and the approval’s project, time, quantity and lot scope.
What if a candidate passes one test but fails another?
It is not fully qualified against the stated requirements. Record the failure and reject it or pursue a separately controlled change or waiver with the necessary authority.