A factory tour is the only supplier evaluation that cannot be prepared for completely. Documents, quality certificates and audit questionnaires are all produced by the supplier, for the supplier. A two-hour walk through the plant with the right checklist tells you more about whether your boards will arrive conforming than a year of email correspondence — but only if you know what to look at, and in what order.
Most first-time buyers fly to Shenzhen with no plan beyond "see the lines". They are walked past the newest SMT line, shown a wall of certificates, photographed with the general manager, and leave with the same information they had before. This guide is the alternative: a structured, hour-by-hour inspection plan that produces evidence rather than impressions. At Huaxing PCBA, roughly 1 in 4 incoming customer audits surfaces at least one specification conflict that had gone unmentioned in email — almost always because the buyer asked to see the process rather than the showroom.
Before You Book the Flight: What the Visit Can and Cannot Prove
Be clear about the scope. A site visit verifies process and capability. It does not verify capacity allocation (how much of that line is actually reserved for you) and it does not verify long-run consistency, which only production data can show. Treat the visit as one input among three: the visit, the paper audit, and the trial order. Skipping any one of the three leaves a specific blind spot.
Set your objective before you arrive. A useful frame is to pick the two or three claims from the supplier's website, quote or quality manual that matter most to your program — say, "8 SMT lines", "IATF 16949" and "100% AOI" — and make the visit about converting each claim into something you personally observed. Claims you cannot convert get downgraded to unverified, not failed.
Key Takeaway: Book the visit for a production day, not a Friday afternoon or a holiday week. A plant running live orders shows you the real process; an idle plant shows you the equipment. If the supplier reschedules twice, that is itself a data point — ask directly what production was running and why it could not be shown.
The 12-Point Walkthrough Checklist
Run the tour in process order — raw material to shipping — rather than following whatever route the sales host prefers. Process order forces the gaps to reveal themselves: a missing inspection stage is obvious when you walk the line in sequence, and invisible when you are shown stations in isolation. For each item below, the point is not to hear an answer but to see the evidence supporting it.
Incoming Material Store — Ask for a Real Certificate of Conformance
Start where the board starts. Ask to see the laminate store and pick one panel at random. The supplier should be able to produce the laminate supplier's certificate of conformance for that lot, with a traceable lot number, and show you how it is filed against the job. TG value, thickness tolerance and copper weight on the certificate should match what was quoted to you. A store with unlabelled or loosely stacked laminate is a store where material substitution happens. Ask also how laminate is stored — humidity-controlled storage with a log is standard; a rack in the open with no record is not.
Drill and Imaging — Verify the Equipment Matches the Claimed Capability
Ask what the minimum mechanical drill diameter is on the machines that are actually running, not on the newest machine in the brochure. Look at the LDI (laser direct imaging) units and ask how many layers they can align. If the supplier quotes you 0.15 mm vias and 4 mil line width, the imaging and drill equipment on the floor should be consistent with that — ask the operator to show the current job's parameters on screen. Our guide to via technology and its manufacturing limits explains which capabilities genuinely require specific equipment.
Plating and Surface Finish — Check Bath Control Records, Not Just the Line
This is the single most informative stop on the tour. Ask two questions: how often are plating bath chemistries analysed, and where is that written down? A controlled process has analysis records at defined intervals with corrective actions noted when results drift. For ENIG, ask about the gold and nickel thickness targets and how they are verified — thickness testing should be routine, not on request. If your design uses a finish other than ENIG, the comparison in our surface finish selection guide sets the acceptance criteria you should be checking against.
Solder Mask and Silkscreen — Ask About Cure Verification
Mask cure affects adhesion, ionic cleanliness and long-term reliability, but it is rarely checked by buyers because the equipment looks the same everywhere. Ask how cure is verified — a documented cure schedule with periodic adhesion or solvent-resistance testing is the answer you want. Ask what happens when a board fails mask adhesion testing. The response should describe a containment and rework or scrap decision, not a reassurance.
Electrical Test — Confirm Fixture Ownership and Test Coverage
Ask to see the flying probe and bed-of-nails areas side by side. For flying probe, ask how net coverage is reported on a typical job — a percentage is a real answer, "full coverage" is not. For fixture test, ask who owns the fixture and whether you will own it at end of program. Test coverage decisions affect your escape rate more than any other process step; the trade-offs between the two methods are covered in our inspection methods comparison.
SMT Line — Watch a Real Changeover or Setup, Not a Demo
The SMT area is where most plants look competent and where the differences hide. Do not watch a demo. Ask to watch whatever is currently in setup or changeover, and time it. Changeover time is a direct proxy for how well the plant handles small and mixed-volume work — a plant that takes four hours to change over cannot economically serve a high-mix program regardless of what the quote says. The mechanics of setup reduction are covered in our SMT changeover and SMED guide.
SPI and AOI — Ask When the Programmes Were Last Validated
Having SPI and AOI installed proves nothing; a badly tuned AOI programme is worse than none because it generates false calls that mask real defects and depress reported yield. Ask two specific questions: when was the AOI programme on the current job last validated against a known-defect sample, and what is the current false-call rate? A plant with real process control tracks both numbers. Our guide to diagnosing first pass yield explains why the false-call rate changes the meaning of every yield figure the supplier reports.
X-Ray and Reflow — Look at the Defect Escape, Not the Machine Brand
Ask the X-ray operator to show you the most recent head-in-pillow or voiding reject on a real board, and how it was dispositioned. Process control is visible in how quickly the operator can produce a recent real example. At the reflow ovens, ask how profiles are validated and how often thermocouples are re-attached and the profile re-run — a profile run once at NPI and never revisited explains a large share of intermittent defects. See our reflow profile optimisation guide for the validation cadence that should be standard.
Rework and Repair Station — The Most Revealing Bench in the Building
An unusually large or heavily staffed rework station is a signal that yield losses are being absorbed downstream rather than fixed upstream. Ask how many boards per shift go through rework, and what the top three rework causes are this month. Ask whether reworked boards are counted as failures in the reported yield — if the answer is no, the yield figure you have been quoted measures inspection effectiveness, not process control. Also confirm the rework station follows a documented procedure under an accepted standard rather than operator judgement.
ESD Control — Test It Yourself With a Wrist Strap Meter
ESD is the area with the widest gap between policy and practice, and it takes thirty seconds to check. Bring a wrist strap tester, or ask to use theirs, and test three random operators on the line — not the three the host selects. Check that heel straps and smocks are in use, that EPA boundaries are marked with signs and that the floor is the correct dissipative type. A plant that fails an unannounced ESD spot check has an ESD problem regardless of the certificate on the wall.
Calibration and Test Equipment — Check Dates and Traceability
Walk to the metrology area and pick two or three instruments — a profilometer, an X-ray thickness gauge, a multimeter at test. Each should carry a calibration sticker with an in-date period and a traceable calibration certificate on file. Ask what happens when an instrument is found out of calibration: is there a documented recall of affected product? That specific question separates a functioning calibration system from a folder of certificates. Our IPC-6012 qualification guide covers how these records feed into the qualification package you should be collecting.
Shipping and Documentation — Ask to See a Complete Data Package
End at packing. Ask to see a finished order ready to ship: how is it packed, what desiccant and humidity indicator is used, and what documents travel with it? The correct answer includes a certificate of conformance, the test report, the first-article or cross-section report where applicable, and traceability records. Ask how long those records are retained and in what form — you will need them if a field failure occurs two years from now. Our test report and documentation guide lists the complete data package to request, and it is worth bringing a copy with you as your evidence sheet.
Questions That Reveal the Real Organisation Behind the Tour
The walkthrough tells you what the plant looks like on the day you visit. A short set of questions, asked across different people rather than only your host, tells you whether that state is stable. The technique is to ask the same question of the engineer, the line supervisor and the quality manager, and compare answers.
| Question | What a Controlled Answer Sounds Like | Warning Sign |
|---|---|---|
| Who signs off a process change? | A named role, with a documented change record and customer notification where the change affects form/fit/function | "The engineer decides" — no record, no notification path |
| What was your largest yield loss last month? | A specific defect type, a specific line, and a corrective action already closed | A vague or defensive answer; no Pareto available |
| Which customer do you consider your most demanding? | A named programme and a specific reason tied to requirements | Reluctance to name anyone; no differentiation between customers |
| What happens if you find out-of-calibration equipment? | A documented recall of affected product and re-verification | "We recalibrate and continue" — no product impact assessment |
| How do you handle a customer spec conflict? | A query process that stops work and returns a documented question | "We would just make it work" — silent deviation |
| Can I see the corrective action log? | Presented with customer names redacted, showing closures over months | "That is internal" — no visibility into improvement |
Two further questions are worth asking in person because they are almost never answered candidly in writing. First: what percentage of your capacity is currently committed, and to which regions? This tells you where you sit in the queue and how much leverage you have if a delivery slips. Second: what was the last order you declined, and why? A supplier that has never declined an order is not selective, which usually means it accepts work it cannot run well.
Procurement tip: Photograph nothing without permission, but do write down what you saw within an hour of leaving — equipment models, operator names and roles, the numbers quoted for rework volume and false-call rate. Six weeks later, when the first production lot is late, those notes are the difference between a productive conversation and a dispute. Our supplier quality scorecard guide shows how to convert visit findings into ongoing, measurable criteria.
Turning the Visit Into Contractual Commitments
A visit produces observations; a purchase order needs obligations. Within a week of returning, convert the three or four things you verified into written requirements in the quality agreement or on the PO itself. This is the step most buyers skip, and it is the reason visit findings rarely change outcomes.
Practical examples of the conversion: if you saw that rework is not counted as a yield failure, add a line requiring reworked and retested units to be counted as first-pass failures. If you saw a documented plating bath analysis schedule, require the analysis records for your lots to be available in the data package. If you tested ESD and it passed, require ESD spot-check records to be retained. If the changeover time you timed was four hours, get a commitment on the changeover time applicable to your order size. Each clause should name a record — something the supplier can produce on request.
This is also the moment to decide whether the visit changed your sourcing decision. If you found one or two correctable gaps in an otherwise controlled plant, proceed with a trial order and hold the clause list. If you found that the process records do not exist at all, the problem is not the plant but the management system, and no amount of follow-up email will fix it — move to the next candidate. Our guide to auditing a PCB supplier covers the paper-based evaluation that should happen in parallel with the visit, and the supplier transition guide covers how to move production without losing a quarter.
Summary / Next Steps
A Shenzhen factory visit is worth the trip only when it produces evidence. Walk the line in process order, ask for the record behind every claim, test ESD yourself, and time a real changeover. Then convert what you saw into written clauses before the first PO is issued. Doing this once properly is cheaper than learning the supplier's weaknesses across three failed production lots.
At Huaxing PCBA, customer audits are welcomed as standard practice, including unannounced ESD spot checks and live process review. Our facility runs 8 SMT lines, 4 DIP lines and full AOI, X-ray, SPI, ICT and functional test coverage under an IATF 16949 and ISO 9001 quality system, and we will produce the process records behind any claim you want to verify — plating bath analyses, AOI validation records, calibration certificates and the complete shipping data package. Our guide to remote factory auditing covers what can be verified without travelling, or contact our engineering team to arrange a visit or a live video walkthrough of the line.
