# PCBA sourcing China buyer's guide: from Gerbers to tested boards
A printed circuit board assembly, the PCB with all components soldered and tested, is the heart of every electronic product. It is also the part buyers understand least. The board looks like a commodity: green, flat, covered in tiny parts. In reality, PCBA quality is determined by dozens of decisions you never see, from solder paste profiles to component sourcing to the test jig at the end of the line. This PCBA sourcing China buyer's guide walks through those decisions in the order you will face them.
China assembles more PCBs than the rest of the world combined, at every quality level from disposable toys to medical devices. That range is the opportunity and the trap. The same city block can hold a world-class SMT operation and a shop that will substitute your components without telling you. The difference between the two is rarely visible in a quote. It shows up in the handoff package you send, the questions the assembler asks, and the testing you require. This guide covers each of those, so the boards you receive match the boards you designed. Treat this PCBA sourcing China buyer's guide as a checklist to work through in order, not as background reading.
The handoff package: Gerbers, BOM, and assembly drawings
Everything starts with what you send. A complete handoff package lets any competent assembler quote accurately and build correctly. An incomplete one forces the assembler to guess, and guesses become defects.
The Gerber files define the PCB itself: copper layers, solder mask, silkscreen, and drill data. Send the full set, generated from your ECAD tool, plus the drill files and a readme naming the stackup. Include the PCB fabrication drawing with material, copper weight, surface finish, and impedance requirements if the design has controlled-impedance traces. The assembler either fabricates the bare board in-house or subcontracts it; either way, they need the full specification to quote it.
The BOM, bill of materials, lists every component with manufacturer part numbers, not just values. "10k resistor" is not a line item. "Yageo RC0603FR-0710KL" is. Include alternates where you have approved them, and mark which parts are critical: no substitution without written approval. The BOM is also where counterfeit defenses begin, because specified part numbers from authorized distributors are far harder to fake than vague descriptions. BOM precision is a recurring theme in this PCBA sourcing China buyer's guide because it underpins quoting, sourcing, and inspection alike.
Assembly drawings show component placement, polarity marks for diodes and electrolytics, and any special instructions: conformal coating areas, staking, or press-fit connectors. Include the centroid (pick-and-place) file so the assembler's machines can be programmed without manual data entry. Manual entry is where wrong rotations and mirrored placements come from.
A professional assembler reviews this package and comes back with questions: DFM feedback on pad sizes, component availability issues, or process concerns. An assembler who quotes a complex board from Gerbers alone, with no questions about the BOM or assembly, is not reviewing your design. They are pricing a guess. In this PCBA sourcing China buyer's guide, the handoff package gets this much attention because every downstream problem is cheaper to prevent here than to fix later. The questions an assembler asks are the first quality signal you will get.
Turnkey versus consigned: who buys the parts
The biggest structural decision in PCBA sourcing is who procures the components. In the turnkey model, the assembler buys everything. In the consigned (or kitted) model, you supply some or all of the parts and the assembler provides labor, the PCB, and usually the commodity components. Each has a place, and the choice shapes cost, risk, and control.
Turnkey is simpler. One purchase order, one party responsible, no logistics of shipping reels across the world. It suits standard designs with available parts and assemblers you trust. The risk is substitution: the assembler chooses the suppliers, and under cost pressure the temptation to buy cheaper or broker-sourced parts is real. Mitigate it with the contract terms below: specified part numbers, authorized-distributor requirements for critical parts, and incoming inspection rights. The turnkey decision is one of the highest-leverage choices in this PCBA sourcing China buyer's guide, so make it deliberately rather than by default.
Consigned gives you control of the critical supply chain. You buy the expensive, scarce, or counterfeit-prone parts through your own authorized distributors and ship them to the assembler. This removes the substitution incentive for the parts that matter most and guarantees traceability. The cost is logistics and effort: you manage procurement, shipping, customs, and the inevitable shortages. Many buyers use a hybrid: consign the critical parts, let the assembler buy the passives and standard components turnkey.
Make the decision per part, not per project. Microcontrollers, specialized ICs, and anything with counterfeit history get consigned or strictly controlled. Resistors, capacitors, and connectors from the assembler's regular stock go turnkey. This hybrid approach is standard among experienced buyers, and it is the model this PCBA sourcing China buyer's guide recommends as the default: control what matters, delegate the rest. Revisit the split whenever the BOM changes, because new parts bring new risks.
Evaluating the assembler: lines, people, and process
Assessing a PCBA assembler means looking at the production floor with educated eyes. The equipment tells you what they can build. The people tell you whether they will build it right.
Look at the SMT lines: pick-and-place machines with the speed and accuracy your board needs, reflow ovens with proper profiling, solder paste printers, and AOI (automated optical inspection) after placement. For fine-pitch or BGA components, ask about X-ray inspection capability. A shop without AOI is doing visual inspection on boards the human eye cannot reliably check. That is a capability gap, not a cost saving.
Talk to the process engineers. Ask about their solder profiles, how they handle lead-free versus leaded processes, and what their first-article procedure looks like. Ask which components they consider risky on your BOM and why. Good engineers have opinions about your design. They will flag the QFN with the tricky thermal pad or the connector with tight tolerances. An assembler whose engineers say nothing about a complex board is either not reading it or not staffed to.
Check the testing area. There should be test jigs, programming stations, and burn-in racks appropriate to the products they build. Ask to see the jig for a current product and how it was developed. A shop that builds custom test fixtures for its customers runs a different operation than one that powers the board on and calls it tested. The testing area is where this PCBA sourcing China buyer's guide suggests spending the most time during a visit, because it reveals the assembler's real quality standard.
Verify the business basics too: business license scope covering manufacturing, certification paperwork in the right entity name where applicable, and references from buyers with similar products. The floor tells you the capability. The paperwork tells you the legitimacy. You need both, and the section of this PCBA sourcing China buyer's guide on verification exists because buyers keep skipping the second half.
First-article inspection and pilot runs
Never go from quote to full production in one jump. The first-article inspection (FAI) and the pilot run are the two gates between your design and a production commitment, and each catches different problems.
The first article is the first small batch built on the production process: usually a handful of boards assembled exactly as production will run them. Inspect them completely against the design: component placement and orientation, solder quality under magnification and X-ray for hidden joints, programming and firmware version, and full functional test. The FAI approves the process, not just the product. If the process cannot build five boards correctly, it cannot build five thousand.
The pilot run scales up: a few hundred boards through the full line, including the test jigs and packing. The pilot reveals what the first article cannot: whether the line holds pace, whether the test jig keeps up, whether component reels run out mid-shift and get replaced with the right parts, whether the packaging survives. Pilot-run discipline is what separates professional PCBA sourcing from gambling, and factories that resist pilots are telling you about their process. This gate is non-negotiable in any serious PCBA sourcing China buyer's guide.
Approve each gate in writing before the next begins. The FAI report, signed by both sides, becomes the reference for production. The pilot results set the expectations for yield and test coverage. Rushing these gates to save two weeks is the most expensive schedule saving in electronics: it moves the discovery of problems from cheap small batches to expensive full production. Gate discipline is a theme this PCBA sourcing China buyer's guide will not apologize for repeating.
Testing jigs, programming, and functional test
An untested board is a promise, not a product. The testing setup determines whether the PCBA you receive works, and the assembler's approach to testing tells you how seriously they take quality.
Bed-of-nails or flying-probe testing checks the bare assembly: shorts, opens, and component values. AOI catches placement and solder defects optically. X-ray inspects hidden joints on BGAs and QFNs. These are manufacturing tests, and a good assembler runs the appropriate combination as standard. Ask which ones apply to your board and see them running.
Functional testing goes further: the programmed board is powered and exercised through its actual functions using a custom test jig. The jig is built for your product, with pogo pins contacting test points, and it runs a defined sequence: power rails, microcontroller boot, peripheral checks, communication interfaces. Developing the jig takes engineering effort, which is why assemblers charge for it and why buyers should insist on it. A functional test jig is the single best investment in PCBA quality after the design itself, and this PCBA sourcing China buyer's guide treats it as mandatory for anything you plan to sell under your brand.
Programming and firmware control deserve explicit terms. Who provides the firmware image, which version is programmed, how version changes are controlled, and how the programmed version is verified on the line. Firmware mix-ups across production batches are a classic PCBA failure, and the fix is procedural: version control, verification at programming, and records tying firmware versions to production lots.
Define the test coverage and the failure handling in the QC plan. What percentage of boards gets functional test, what happens to failures, and whether failed boards are repaired or scrapped. For high-reliability products, 100% functional test is standard. For simpler boards, sampled test may be defensible. The number should be a decision, not an accident. Test coverage decisions are where this PCBA sourcing China buyer's guide asks you to spend real thought, because they determine what escapes to your customers.
PCBA sourcing China buyer's guide to pricing: reading the quote honestly
PCBA quotes have a structure, and reading it honestly protects you from the two classic traps: the too-cheap quote and the vague quote.
A proper quote breaks down PCB fabrication, component costs, SMT assembly (often priced per point or per board), testing, programming, and packaging. Compare the component section against authorized distributor pricing for your critical parts. The cheapest PCBA quote is suspect: components have market prices, and assembly has known costs. A total far below the others means substituted components, skipped testing, or a price that will change once you are committed.
Watch for the vague quote: a single number with no breakdown. It cannot be compared, it cannot be verified, and it hides whatever the assembler chose not to tell you. Always require the breakdown. An assembler that will not provide it is either disorganized or hiding something, and neither builds good boards. Quote transparency is a core principle of this PCBA sourcing China buyer's guide because the breakdown is what lets you compare honestly.
Price the testing and tooling separately in your own budget. Test jigs, programming fixtures, and any custom tooling are one-time costs amortized over the production volume. An assembler that folds them invisibly into the unit price is either eating the cost (unlikely) or skipping the work (likely). Ask for the line items.
Finally, remember that the cheapest board is rarely the cheapest product. A board that costs 10% less but yields 5% field failures is enormously more expensive than the alternative. Total cost includes rework, returns, and reputation. Buyers who internalize this stop shopping for the lowest quote and start shopping for the best process. That shift is the real lesson of this PCBA sourcing China buyer's guide: you are not buying boards, you are buying the system that produces them.
Conclusion
This PCBA sourcing China buyer's guide comes down to a sequence: prepare a complete handoff package with Gerbers, a specified BOM, and assembly drawings; decide turnkey versus consigned per part; evaluate the assembler's lines, engineers, and testing capability; gate production with first-article inspection and a pilot run; require real functional testing with custom jigs; and read quotes for honesty rather than just price. None of these steps is exotic. Together they form the difference between boards that work and boards that almost work. The assemblers worth building with are the ones who welcome every step of this PCBA sourcing China buyer's guide, because it is also the process that lets them do their best work.
Frequently asked questions
### What files does a PCBA assembler need to quote?
Gerber files with drill data, a PCB fabrication drawing, a BOM with manufacturer part numbers, assembly drawings, and the centroid file for pick-and-place programming. Incomplete packages produce guessed quotes and guessed builds.
### Should I choose turnkey or consigned component sourcing?
Use a hybrid as the default: consign or strictly control the critical, expensive, and counterfeit-prone parts through your own authorized distributors, and let the assembler buy standard components turnkey. Decide per part based on risk, not per project. This hybrid model is the recommendation this PCBA sourcing China buyer's guide returns to because it balances control and simplicity.
### What is first-article inspection?
A complete inspection of the first small batch built on the production process, covering placement, solder quality, programming, and functional test. It approves the process before full production begins. Never skip it on a new design or a new assembler. FAI is the gate this PCBA sourcing China buyer's guide considers the best money in the whole process.
### How much functional testing is enough?
For high-reliability or high-value products, 100% functional test with a custom jig is standard. Simpler products may use sampled testing. Define the percentage in the QC plan as a deliberate decision, and always test with the actual firmware version.
### Why is the cheapest PCBA quote usually a bad sign?
Because components and assembly have real market costs. A quote far below the others typically means substituted components, skipped testing, or a price designed to change later. Break quotes into components and compare against distributor pricing. Price discipline is one of the quieter lessons of this PCBA sourcing China buyer's guide: the quote tells you about the assembler before the boards tell you about the quote.
### What should the contract cover for PCBA?
Specified part numbers with no unapproved substitution, authorized-distributor sourcing for critical parts, incoming inspection rights including X-ray, firmware version control, defined test coverage, and payment tied to inspection results. Put the quality system in writing before production. A contract built on this PCBA sourcing China buyer's guide checklist gives you leverage when it matters instead of arguments after the fact.