Begin with failure mechanisms
List the faults that matter: missing or incorrect components, connection defects, shorts, wrong firmware, calibration errors and performance outside limits. Identify which method can detect each fault, at what stage and with what limitations. Document untested functions rather than implying full coverage.
Match the method to access
Some techniques need probe access, boundary-scan support, a powered interface or a dedicated fixture. Test access has to be considered during design, not improvised at the end of assembly. Ask how board geometry, sensitive nodes and connectors affect both coverage and fixture cost.
Write objective acceptance criteria
A test instruction needs inputs, operating conditions, expected outputs, limits and an unambiguous decision rule. “Powers on” is rarely enough. Define firmware versions, calibration data, load conditions, reference equipment and the record required for each serial number or batch.
Plan failure handling
A test plan should state what happens when a unit fails. Separate repair, retest, authorized deviation and scrap. Retain enough information to connect recurring failures to material lots or process changes. Decide who approves rework and whether repair changes the product’s qualification status.
At a glance
| METHOD | USEFUL FOR | LIMITATION TO DISCUSS |
|---|---|---|
| AOI | Visible placement and solder features | Hidden joints and electrical function |
| X-ray | Selected concealed joints and structures | Coverage and interpretation depend on setup |
| ICT / flying probe | Electrical networks and selected components | Access, fixture and coverage constraints |
| Functional test | Specified behavior in defined conditions | Untested modes remain outside coverage |
A practical checklist
- Map important faults to detection methods.
- Define the test conditions and pass/fail limits.
- Identify fixture and programming ownership.
- Agree the retained record format.
- Record firmware and hardware revisions.
- Define repair and retest authorization.
Assign an owner to each open item and keep the decision with the project revision. A checked box should point to a document, approval or piece of evidence; it should not simply indicate that a topic was discussed.
A common mistake to avoid
Treating inspection as proof of complete product function. A visually acceptable assembly can still contain the wrong firmware or fail in an operating mode that the inspection process never exercises.
Put the guidance to work
Start with the RFQ preparation checklist, keep component information in the BOM template, and compare evidence using the supplier scorecard. Confirm project-specific requirements with your design team and manufacturing partner.
Explore the related manufacturing scope or return to the Testing & Inspection guide hub.