Component Substitution in PCBA: Approve the Change Before the Build

A component substitution should be treated as a controlled product change unless the exact alternative is already permitted by an approved BOM or purchasing rule. Similar descriptions, matching footprints and distributor cross-references can help identify a candidate, but they do not establish that it meets the product's electrical, mechanical, firmware, manufacturing and reliability requirements.

The practical sequence is to identify the affected build, compare the candidate against the relevant requirements, decide the validation needed and obtain approval from the designated authority before purchasing or assembly. Keep the approval linked to the actual part and build configuration.

Classify what is changing

Begin with the complete manufacturer and orderable part number. Identify the current approved item and the proposed item, including package and grade where applicable. A shortened family name can hide differences in rating, package, temperature range or options.

Separate these situations:

Situation	Initial question	Control needed
Existing approved alternative	Is this exact item approved for this revision and variant?	Confirm the approval boundary and purchasing records
Orderable-code or packaging difference	Does the change affect the device, grade, handling or assembly process?	Verify the manufacturer's definition and the applicable purchasing rule
New manufacturer or device	Which product requirements could change?	Technical comparison and a defined approval decision
Manufacturer product change notice	Does the notified change affect an item already in use?	Review the notice and decide whether requalification or other action is needed
Independent-source purchase	Can identity, source and required records be established?	Apply the approved sourcing and authenticity controls; this is separate from technical equivalence

A change in purchasing source and a change in component specification can occur together. Review both. A technically suitable candidate does not resolve source authenticity, and a reliable source does not make a different device equivalent.

Use a substitution request with a clear scope

The request should include the product identifier, board and assembly revisions, affected variant, reference designators, approved part, proposed part, reason for change, source, availability assumptions and affected quantity or lot. Identify any material already purchased or units already assembled.

State whether approval is requested for one build, a defined time period or the permanent approved parts list. An urgent one-order deviation should not quietly become a permanent BOM change. Assign a design authority and any additional customer, quality or regulatory approval roles required by the product.

Compare requirements, not just headline specifications

Build a comparison against the application's actual requirements:

• Electrical behavior: relevant ratings, tolerances, timing, protection behavior, accuracy and operating conditions.
• Mechanical fit: package outline, height, pin mapping, orientation and footprint compatibility.
• Thermal behavior: dissipation, mounting needs and the operating environment relevant to the product.
• Firmware and interfaces: registers, initialization, communication behavior and programming needs where applicable.
• Assembly and handling: soldering guidance, moisture handling where relevant, finish and packaging.
• Reliability and product obligations: qualification evidence, required declarations, lifecycle and customer-specific restrictions.
• Verification: which measurements or product tests demonstrate the requirements affected by the change.

Not every category applies to every part. The reviewing engineer should select the relevant differences and explain the disposition. A statement that the parts have the same nominal value is usually too narrow to close the review.

As an illustrative procurement situation, two capacitors may share a nominal capacitance and package while differing in voltage rating or behavior under operating conditions. That example is not a KeepBest project result; it shows why the comparison must follow the actual application.

Define the validation before authorizing use

Identify which differences can be resolved from controlled manufacturer data and which need testing or a design change. Specify the validation configuration, procedure, acceptance limits, required records and approval owner. Do not invent a universal test duration or sample size: those choices depend on product risk and the change.

If the candidate changes a footprint, thermal arrangement, firmware or test behavior, evaluate the related manufacturing and release documents. Passing a simple bench check may not demonstrate performance across the required operating conditions or production process.

Approval can be conditional, but the conditions should be explicit. For example, a limited pilot may be authorized while routine production remains on hold. Identify which activities are allowed, what is still prohibited and what evidence closes the condition.

Handle manufacturer notices as review inputs

TI's public PCN process describes information about affected products, the reason for a change and supporting qualification or implementation information. A manufacturer notice can therefore inform the review of a part already in use. It does not automatically approve a different manufacturer's part or close the customer's validation requirements. TI: Product change notification.

Assign responsibility for receiving relevant notices, assessing affected products and communicating approved actions to purchasing and production. The presence of the same ordering code should not be used as the only test for whether a notified change needs review.

Preserve source and build traceability

Record the source, required purchasing documents and material identification for the approved item. TI recommends direct or authorized channels for its products; check the corresponding guidance for the manufacturers in the actual BOM. Do not treat an attractive price or a claimed cross-reference as evidence of authenticity. TI: Anti-counterfeit guidance.

Link the decision to the revised BOM or deviation, purchase records, issued material and affected build. Where unit or lot traceability is required, record which configuration was assembled and tested. Reconcile remaining original and alternative stock so that later orders do not use an obsolete decision.

Do not let urgency remove the approval boundary

When a shortage threatens delivery, report the available options with their technical and schedule implications: wait for the approved part, use an already approved alternative, review a new candidate or revise the delivery plan. Purchasing or assembly should remain within the authorized decision.

This workflow does not declare any pair of parts equivalent. Product-specific requirements, customer restrictions and the designated design authority determine what may be used. It also does not establish a supplier's available stock or sourcing channels.

Discuss the sourcing and approval process

Review the component purchasing page and DFMA service page when defining the required review boundary. Contact KeepBest with the affected BOM lines, approved alternatives and the decisions you need resolved. Confirm sourcing, technical review and approval responsibilities before a change is released.