Engineering Change Control with Thai Factories (2026)
Most quality disasters in offshore manufacturing are not bad workmanship — they are undocumented changes. A supplier swaps a resin grade, a plating vendor, or a screw length, and three months later your product fails in the field.
Change types and who may approve them
| Change | Risk | Approval |
|---|---|---|
| Cosmetic (print, colour) | Low | Buyer email |
| Dimensional / tolerance | Medium | Buyer engineering sign-off |
| Material or component substitution | High | Buyer + retest |
| Sub-supplier change | High | Buyer + re-audit |
| Process or plant move | High | Full requalification |
Write into your contract that no change in the bottom three rows may ship without written approval. Substitutions without notice should be a stated breach.
The ECR/ECN loop that works across time zones
- ECR raised — either side describes the change, reason, and affected drawings.
- Impact review (5 working days) — cost, tooling, lead time, certification, existing stock.
- ECN issued — new drawing revision, effective date, and cut-in rule.
- Cut-in — by PO number or serial, never "next production".
- Verification — first article from the new revision inspected before bulk release.
Cut-in and stock disposition
Every ECN needs a disposition line for material already in the chain: use-as-is, rework, scrap, or run-out. Agree who pays before the change is approved — this is the single most common dispute. Keep a revision log so a returned unit can be traced to a drawing revision; see recordkeeping requirements.
Certification impact
Material and component changes can invalidate CE, UL/ETL, FCC or food-contact test reports. Check before, not after — see UL/ETL/FCC certification. If the change affects tariff classification or origin, revisit your HTS code and origin marking.
FAQ
What is the difference between an ECR and an ECN?
An ECR requests a change and captures impact; an ECN authorises it with a revision number and effective date. Never let a factory act on an ECR alone.
How fast should a Thai factory respond to an ECR?
Ask for cost and lead-time impact within five working days. Anything slower usually means the sub-supplier has not been consulted.
Can a factory change a component without telling me?
Contractually, no — but it happens. Deter it with an approved-vendor list in the contract, periodic material certificates, and unannounced pre-shipment inspections.
Who pays for stock made obsolete by a change?
Whoever requested the change, unless the change corrects a defect the factory caused. Put this rule in the supply agreement.
Do I need a new first article after every change?
For anything dimensional or material, yes. Cosmetic-only changes can be verified with photos and a golden sample.