Short answer: judge a PCB assembly manufacturer on four things that predict outcomes — equipment you can verify, inspection coverage at every stage, prototype-friendliness, and communication speed — then confirm with certifications, references and a small first order. Price differences of 10–20% are noise next to one scrapped batch or a four-week delay.
The fastest test: send every shortlisted supplier the same RFQ (Gerbers + BOM) and compare response time, question quality, and whether the quote is itemized. How a supplier handles your first email predicts how they'll handle your first production crisis.
The 12-point checklist
1. Equipment you can verify, not equipment on a slide
Ask for the actual line configuration: machine brands and models, number of lines, and placement capacity. Specifics matter — "6 YAMAHA YRM20 high-speed placement lines" tells you something; "advanced SMT equipment" tells you nothing. Published equipment lists with model numbers are a good sign; refusal to name machines is not.
2. Fine-pitch and special-process capability
If your roadmap includes BGA, 0402/0201 passives, or flex boards, confirm the factory runs them routinely — not "can discuss". For FPC specifically, the factory should ask you for board thickness and stiffener requirements during quoting, because that's where feasibility is decided.
3. Inspection coverage at every stage
Inspection is where quality is actually made visible. The minimum set for a serious SMT house: SPI (solder-paste inspection, before placement), AOI (post-reflow optical inspection), and X-RAY for BGA. Then ask what wraps the process: first-article inspection (FAI), in-process IPQC patrols, and outgoing OQC. A three-point pre-shipment-only check is a different quality world than stage-by-stage coverage.
4. Certifications — ask for the number
ISO 9001 and a lead-free RoHS process are the baseline for international buyers. For regulated products, match the standard to your industry (ISO 13485 medical, IATF 16949 automotive, AS9100 aerospace). Ask for the certificate number and issuing body; a supplier that can't produce it doesn't have it.
5. Prototype MOQ and attitude
A prototype-friendly assembler accepts 1–10 pcs with no hard MOQ — prototyping is how customers qualify the factory, and a factory confident in its yield doesn't fear small batches. Suppliers that push big minimums before your design is validated are asking you to carry their risk.
6. Lead-time honesty
Compare quoted schedules line by line. Trustworthy quotes separate production, customs and shipping — e.g. 5–7 days factory + 2 days customs + 3–5 days express for a simple consigned prototype. A single vague "2 weeks" number hides the schedule risk you'll inherit. See our full lead-time breakdown.
7. Component sourcing discipline
For turnkey work, ask: where do parts come from (franchised distributors vs gray market), what happens on a shortage, and who approves substitutions. The correct answer is: BOM reviewed at quote stage, shortage notified immediately with drop-in suggestions, production starts only after your confirmation.
8. Engineering support before the order
The best signal is a free, substantive DFM review — real comments on your layout or BOM, not a form letter. An assembler that finds your problems before production is showing you what they'll do when it matters.
9. Communication speed and clarity
Timezone-tolerant support (email + chat), replies in hours not days, and answers that address the question asked. Test it: the RFQ round is the audition. 24 working hours is a fair standard for a DFM-checked quote.
10. IP protection
Sign an NDA before sending Gerbers. Prefer one contract manufacturer for fabrication + assembly to reduce file hand-offs, and version-control every file you send. Hesitation around an NDA is itself a data point.
11. Traceability and problem response
Ask in advance: when a defect is reported, what happens? The mature answer includes root-cause analysis, a clear split of responsibility (process vs PCB vs components), and a written report with corrective actions. "We will check" without a process is a red flag in slow motion.
12. Transparent, itemized pricing
Insist on quotes itemized into PCB fab, components, assembly, NRE and test/shipping. Itemization is how you compare apples to apples — and how you spot margin games. More on that in our PCBA cost breakdown.
Red flags — walk away if you see these
- Won't name equipment models or share line count.
- Certificate logos without certificate numbers.
- Quote arrives in minutes with no questions asked (nothing was reviewed).
- All-in, un-itemized pricing only.
- Pushes large MOQs on a first-time prototype.
- Reacts to a shortage by silently substituting parts.
- Reluctant to sign an NDA.
The 8 questions to send any shortlisted supplier
- What SMT lines and placement machines do you run, and how many?
- Do you run SPI, AOI and X-RAY inline? Is FAI standard on new products?
- What is your prototype MOQ and typical production lead time, itemized?
- Can you share your ISO 9001 certificate number and date of issue?
- Where do you source components, and what is your shortage procedure?
- Do you provide a DFM review before production, and is it free?
- What is your defect-report and root-cause process after shipment?
- Will you sign an NDA before receiving our files?
A supplier that answers all eight crisply — with specifics — is worth a first order. Send us the same questions; we answer them before you ask.
Run a paid pilot before committing volume
Whatever the checklist says, the strongest evidence is a small real order: one prototype run of 5–10 boards, judged on quote speed, DFM quality, communication during build, and the condition of what arrives. Then scale. This is why prototype-friendliness (point 5) is on the list — it's not charity, it's the factory letting you audit it cheaply.
Key takeaways
- Verify equipment and inspection (SPI/AOI/X-RAY + FAI/IPQC/OQC) — don't accept adjectives.
- Prototype MOQ of 1–10 pcs signals a factory confident in its yield.
- Itemized quotes and honest lead-time breakdowns separate professionals from resellers.
- Use the RFQ round as the audition: response time and question quality predict everything.
- De-risk with a small paid pilot before volume commitment.