Some component batches require additional testing beyond visual inspection. The following signs can help inform a risk-based inspection plan.
Paperwork that does not match
Inconsistent date codes, lot numbers or labels between packaging and parts are a reason to look closer.
Marking and surface anomalies
Uneven marking, sanding marks or blacktopping can indicate remarked parts.
Lead and terminal condition
Signs of previous soldering, oxidation or re-tinning suggest refurbished stock.
Unusual sources or pricing
Parts offered far below market from an unfamiliar source call for X-ray and electrical testing.
Safety-critical applications
For safety-critical builds, a deeper test plan is justified whatever the visual result.