Why process control is the whole game
Yield is not luck; it is the sum of small controls applied every step. A board that passes at 99% per step still fails about 1 in 5 times after ten steps. Good assembly is a chain of inspections, each one catching the defect before it propagates. That is what separates a line you can trust from one that ships surprises.
Key takeaways
- A board that passes AOI but not FCT can still fail in the field — functional test is where real defects surface.
- X-Ray is non-negotiable for any BGA or BTC part; 20–30% voiding in a ball is a latent field failure.
- Good QC means the same test plan on lot 1 and lot 10,000, with full lot traceability — not a visual glance.
- IPC Class 2/3 acceptance plus ICT + FCT is the baseline for automotive, medical and industrial.
| Check | Tool | What it catches |
|---|---|---|
| Solder defects | AOI | Bridges, insufficient solder, missing/shifted parts, polarity |
| Hidden joints | X-Ray | Voids, head-in-pillow, open BGA/BTC balls |
| Continuity / shorts | ICT / flying probe | Open/short, wrong component values |
| Real-world function | FCT | Boot, I/O, power rails, end-use behaviour |
| Authenticity | Visual/X-Ray + docs | Counterfeit, reflow damage |
AOI: the first net
Automated Optical Inspection scans every board for solder bridges, tombstones, missing or misaligned parts and insufficient paste. It is fast and catches the majority of visual defects. Insist on 100% AOI, not sampling — the cost is trivial next to a field return.
X-Ray: seeing the hidden joint
BGA and QFN joints sit under the package where AOI cannot look. X-Ray verifies voiding, opens and alignment in those hidden joints. For any board with BGAs, X-Ray is not optional — it is the only window you have into the most failure-prone connections.
ICT and FCT: does it actually work?
In-Circuit Test checks individual nets and components; Functional Circuit Test exercises the board as a product. Together they confirm not just 'soldered' but 'correct and working'. A per-batch test report should travel with your order.
What to demand from your CM
- 100% AOI on every board, not lot sampling.
- X-Ray on any BGA/QFN placement.
- ICT/FCT with a retained test report per batch.
- Traceable first-article inspection before volume runs.
Our standard
We run IQC, IPQC and FQC with AOI, X-Ray and functional testing on every batch, plus a 5-year warranty. See the full process on our PCBA assembly page, then request a quote and ask for the test report with your first order.
