Quality Control Guide
Inspection checklists and AQL sampling.
1. Why it matters
Quality control is how you make order five look like the approved sample from order one. It runs across three gates — incoming material, in-process, and pre-shipment — and rests on a written specification plus an agreed AQL sampling plan, so "acceptable" is a number both sides signed, not an opinion.
2. The three inspection gates
| Gate | When | Checks |
|---|---|---|
| IQC (incoming) | Before assembly | LED bins, drivers, housings vs BOM |
| IPQC (in-process) | During production | Solder, torque, ageing, first-article |
| FQC / pre-shipment | At ~80% packed | Function, photometric spot, packaging, marks |
3. AQL sampling in plain terms
AQL (Acceptable Quality Limit, ISO 2859-1) tells the inspector how many units to pull from a lot and how many defects allow the lot to pass. A common commercial setting is AQL 2.5 for major defects and 4.0 for minor; use tighter levels (e.g. 1.0/1.5) for safety-critical items. Agree the levels and the defect classification before the run.
- Critical defect: safety hazard — usually zero allowed.
- Major defect: affects function or saleability.
- Minor defect: cosmetic, within tolerance.
4. Make defects unarguable
Attach photos of accept/reject boundaries to the spec (a "limit sample" set). Require the pre-shipment report with photos, measured values and the AQL result before you release the balance payment — inspection after payment has no leverage.
5. Checklist
- Freeze a written spec + limit-sample photos before production
- Agree AQL levels and defect classes in the contract
- Require first-article approval before mass production
- Book a pre-shipment inspection at ~80% packed
- Release balance payment only after the passed report