PCB Assembly in China: Buyer's Guide

Chinese PCBA factories can produce high-quality boards at 30–50% lower cost than equivalent European or North American shops — but only if you give them a clean package and know how to qualify the factory. The difference between a smooth run and a costly disaster is almost always in the preparation, not the factory itself.

This guide covers what a buyer needs to know before placing a PCBA order in China: how to read a quote, how to qualify a factory, what IPC class actually means for your product, and where inspection fits in.

PCB fabrication vs. PCB assembly — they are not the same thing

This confusion wastes weeks. PCB fabrication (often just called "PCB fab") is the process of producing the bare board: the laminated substrate, etched copper traces, drilled holes, solder mask, and silkscreen. PCB assembly (PCBA) is what happens next: components are placed and soldered onto the fabricated board.

Many factories in China do both under one roof. Many others do only one. When you search for "PCB manufacturer China," you may be talking to a bare-board fab, a pure assembly house, or a turnkey operation that does both. Clarify this immediately. A fab-only shop cannot populate your components; an assembly-only shop needs you to supply bare boards or will source them from a fab they work with.

Turnkey vs. consignment: Turnkey means the factory sources both boards and components. Consignment means you supply all components (sometimes called "supply your own parts" or SYOP). Most small and medium buyers should default to turnkey — sourcing 200 component line items yourself takes more time than you expect. The exception is when you have specific BOM requirements (exact part numbers, approved vendors) that the factory cannot meet through their distributors.

PCB types you will encounter

Not all boards are equal. The type of board affects cost, lead time, and which factories can handle it.

Single-layer boards have copper traces on one side only. Simple power supplies, LED drivers, basic sensors. Cheapest to make.

Double-layer boards (two copper layers) cover the majority of consumer electronics — Bluetooth accessories, basic IoT nodes, simple motor controllers. Standard spec for most projects.

Multi-layer (4, 6, 8+ layers) is required when you need controlled impedance for RF traces, dense component placement, or fine-pitch BGAs. A 4-layer board costs roughly 3–4× a 2-layer of the same size; 6-layer doubles that again. Lead time increases too: 2-layer boards can be fabbed in 5–7 days, 4-layer typically 7–10 days, 6+ layer 10–15 days.

FPC (Flexible PCB) uses polyimide substrates instead of rigid FR4. Used in wearables, cameras, compact consumer electronics — anywhere the board needs to bend or where space is extremely tight. FPC manufacturing is more specialized, requires different handling during assembly (fixtures, support jigs), and assembly yields are typically lower. Not every PCBA factory handles FPC well.

Aluminum substrate (metal core PCB) is used for high-power LEDs and power electronics where you need the board to dissipate heat directly. Assembly process is similar to standard FR4 but material handling differs.

What a Gerber package includes and why it matters

When you hand a board design to a factory, you don't send your native EDA files (KiCad, Altium, Eagle). You send a Gerber package — a set of standardized files that completely describe the board for manufacturing.

A complete Gerber files package includes:

• Copper layers — One file per layer (GTL = top copper, GBL = bottom copper, G2L/G3L = inner layers)
• Solder mask layers — GTS (top mask), GBS (bottom mask) — the green stuff that keeps solder off exposed copper
• Silkscreen layers — GTO (top overlay), GBO (bottom overlay) — component reference designators and outlines
• Drill files — NC drill file specifying hole positions and sizes (Excellon format)
• Board outline — GKO or GM1 — the mechanical boundary of the board
• BOM — Bill of Materials, listing every component with manufacturer part number and quantity
• Centroid/Pick-and-Place file — X/Y coordinates and rotation for every component, used by the SMT machine

Missing files or mismatched layer stackups are the most common cause of fab delays. Before sending a Gerber package, run a DRC (design rule check) in your EDA tool and review the generated files in a Gerber viewer. Misaligned drill hits, missing copper pours, or a board outline that doesn't close are invisible in the EDA tool but obvious in the Gerber viewer.

One specific mistake: many engineers forget to include the stencil layer in their Gerber package. The stencil (also called a paste layer — GTP/GBP) defines the apertures in the stainless steel stencil used to apply solder paste. Without it, the factory has to create one from your courtyard layers, which introduces errors.

How to read a factory quote

A PCBA quote will itemize several cost categories. Understanding each one helps you compare quotes fairly and spot inflated line items.

PCB fabrication cost — Cost to make the bare boards, usually priced per panel or per unit. Varies by layer count, board size, surface finish (HASL vs. ENIG), minimum trace/space, and hole count.

Stencil cost — One-time cost for the laser-cut stainless steel stencil used for paste printing. Typically $80–200 for a standard-size stencil. Amortizes quickly over volume but hits hard on prototypes.

NRE (Non-Recurring Engineering) — A catch-all term for one-time setup costs: programming SMT feeders, creating test programs, building ICT/FCT fixtures. NRE can range from zero (for simple boards at friendly factories) to several thousand dollars (for boards requiring custom test fixtures). Always ask what NRE covers — some factories hide fixture costs here.

Component cost — The BOM cost. For turnkey orders, this is the factory's cost to source your components plus their margin (typically 10–20% markup). If prices seem high, ask for a BOM breakdown with individual component costs. For commodities like passives (resistors, capacitors), this margin is often where factories make their money.

Assembly cost — Labour and machine time to place and solder. Priced per board or per placement. Typical range: $0.02–0.08 per SMT placement, plus wave or hand solder charges for through-hole. This is where high-volume orders get cheap.

Test cost — Functional test (FCT) charge per board, if applicable. Some factories include basic power-on test; full functional testing against your test spec is usually extra.

Packaging and labeling — Often overlooked. If you need boards individually bagged, labeled with barcodes, or packaged in trays, add this to your RFQ explicitly.

When comparing quotes from multiple factories, normalize to a common volume (say, 1,000 units) and separate recurring from non-recurring costs. A factory with high NRE but low unit cost may be better for production runs; a factory with zero NRE but high per-unit cost is better for prototypes.

How to qualify a Chinese PCBA factory

Not all factories that claim PCBA capability are equal. Here is what to evaluate specifically for assembly work — beyond the general checks covered in the factory audit checklist.

SMT line age and brand — Modern pick-and-place machines from Fuji, Panasonic, JUKI, Yamaha, or ASM can place down to 0201 metric (imperial 008004) components accurately at high speed. Older generic Chinese machines struggle with anything below 0402 imperial. Ask specifically: "What is your pick-and-place machine brand and year of purchase?" Equipment older than 10 years is acceptable; older than 15 years raises questions; older than 20 years means they're running outdated tolerances.

Solder paste printer — The paste printing step has the highest impact on defect rates. Fully automated printers with vision alignment (Heller, DEK, MPM) produce consistent deposits. Manual or semi-automated printing is fine for prototypes but not for production volumes above ~500 units/month.

SMT process flow — Confirm they use a proper reflow profile verified with thermocouple measurements, not just "we run our standard profile." Lead-free (SAC305) reflow has a narrow process window; a factory that cannot show you a reflow profile trace for your board type is not ready for quality production.

Reflow oven zones — A good reflow oven has at least 8 heating zones for stable temperature profiling. Fewer zones make it difficult to achieve the correct ramp rate, soak, and peak temperature for lead-free solder without damaging sensitive components.

AOI (Automated Optical Inspection) — Ask if they have in-line AOI (runs after reflow on the production line) or offline AOI (boards pulled for batch inspection). In-line is better for catching defects early. If they have AOI, ask to see the defect library and recent defect rate reports.

X-ray inspection — Required if your board has BGA, QFN, or other bottom-terminated components where solder joints are not visible. Ask: "Do you have X-ray in-house?" Some smaller factories outsource X-ray; that adds days and a break in custody.

ESD protection — Walk the floor. Are operators wearing wrist straps connected to grounded mats? Is ESD-sensitive material stored in anti-static bags or trays? Is the assembly area labeled as an EPA (ESD-Protected Area)? ESD damage is invisible and shows up as latent failures weeks after shipment.

IQC (Incoming Quality Control) — Do they verify component authenticity and spec compliance when components arrive? Counterfeit passives and ICs are real in the China supply chain. A factory without IQC is passing that risk to you.

Run a factory audit before your first production order, not after. The checklist above is useful for remote evaluation; the audit confirms it in person.

IPC-A-610 Class 2 vs. Class 3 — what it means in practice

IPC-A-610 is the global standard for acceptability of electronic assemblies. Every factory claims to work to it. Most do not enforce it consistently. Here is what the classes mean:

Class 1 — General electronic products where appearance is less important than function. Not relevant for most commercial products.

Class 2 — Dedicated service electronic products. This covers the vast majority of consumer electronics, IoT devices, industrial equipment, and commercial products. Solder joints must wet properly but minor cosmetic variations are acceptable. This is the right spec for most hardware startup products. The full acceptance criteria are defined in IPC-A-610, the globally recognized standard for electronic assembly quality.

Class 3 — High-performance electronic products where continued performance is critical and equipment downtime is unacceptable. Medical devices, avionics, military equipment. Much stricter — tighter tolerances, more inspectors, higher cost, slower throughput.

In practice, asking for Class 2 means the factory uses IPC-A-610 as their acceptance criterion during inspection. Asking for Class 3 means you will pay 15–30% more for assembly and significantly more for inspection, and you should only ask for it if you genuinely need it.

When placing an order, specify your class requirement in writing. If you don't, the factory defaults to whatever class they feel like — usually Class 1.

PCB materials: when FR4 isn't enough

FR4 (Flame Retardant 4, a woven fiberglass/epoxy laminate) is the standard PCB substrate for most applications. It's cheap, widely available, easy to process, and adequate for frequencies up to roughly 1 GHz in most designs.

When FR4 is not enough:

RF and microwave designs above ~1 GHz — FR4's dielectric constant (Dk ≈ 4.4) varies with frequency and temperature, causing impedance drift. For WiFi 6E (6 GHz), 5G mmWave, or any precision RF design, you need low-loss laminates: Rogers RO4003C, Rogers RO4350B, Taconic TLX, or similar. These cost 5–10× more than FR4. Not every Chinese PCB fab handles them; check explicitly.

High-temperature applications — Standard FR4 glass transition temperature (Tg) is 130–140°C. High-Tg FR4 (Tg 170°C) handles lead-free reflow better and is more stable in hot environments. Specify high-Tg FR4 for boards near heat sources or in automotive/industrial environments.

Controlled impedance traces — Even in FR4, if your design has differential pairs, RF traces, or high-speed digital signals (DDR, USB 3.x, PCIe), you need controlled impedance. This requires the fab to adjust trace width to hit the target impedance (typically 50Ω single-ended, 100Ω differential). They need to know your stack-up before quoting. IPC-6012 (Qualification and Performance Specification for Rigid Printed Boards) is the standard that defines bare board acceptance criteria including controlled impedance requirements.

If your design has RF content, always specify your substrate, stack-up, and controlled impedance requirements in the Gerber package. A factory that quotes without asking about this is guessing.

DFM review before you order

Design for Manufacturability (DFM) is the process of checking your design against the factory's process capabilities before you commit. It prevents the most expensive kind of problem: finding out after fabrication that something can't be assembled.

Common DFM issues that kill prototype runs:

• Trace/space violations — Your design calls for 3-mil traces but the factory's minimum is 4 mil. Now the board either cannot be made or the factory has to modify your Gerbers without telling you.
• Soldermask bridge problems — Pads too close together with no soldermask dam between them, causing solder bridges during reflow.
• Via-in-pad without plugging — Via holes under SMT pads wick solder away during reflow. Either fill/plug vias in the design or specify via-in-pad filling in your fab notes.
• Component clearance violations — Pick-and-place nozzles and reflow fixtures need clearance around components. Tall components (connectors, electrolytic caps) need buffer distance from other SMT components.
• Pad-to-board-edge distance — Components too close to the board edge interfere with depaneling (v-score or routing).
• Paste aperture size for small components — For 0201 or smaller passives, the stencil aperture must be sized correctly relative to the pad to get the right paste volume. Most factories will do this automatically if you send the stencil layer; if you don't send it, check what they generate.

Most reputable Chinese PCBA factories offer a free DFM review before you confirm the order. Always request it. If the factory doesn't offer DFM review and doesn't ask questions about your design, that's a warning sign.

Inspection at three stages

A single final inspection catches defects after all the damage is done. Three-stage inspection catches problems when they're cheapest to fix.

Incoming component inspection — Before components go into the SMT line, spot-check against the BOM: correct part numbers, correct values, authentic manufacturer markings. Fake passives are less common than fake ICs, but both exist. Check date codes on electrolytic capacitors; old stock can cause early life failures. This stage costs almost nothing relative to discovering a BOM error after 5,000 boards are assembled.

In-process inspection — After the reflow oven, before any conformal coating or enclosure assembly. This is when AOI and X-ray run. In-process defects include solder bridges, missing components, tombstoned components, insufficient solder. Catching them here means rework happens on bare boards, not finished products.

Pre-shipment inspection — A statistical sample of finished goods, inspected against your acceptance criteria. This is when you (or a third party) verify appearance, functionality, and packaging. The pre-shipment inspection should use an AQL sampling plan — AQL 2.5 is standard for most consumer products, meaning you accept a lot with up to 2.5% defects at a 95% confidence level.

The rule: never release the final payment before pre-shipment inspection results are confirmed. For a first run with a new factory, consider an in-process inspection as well — it's an investment that pays for itself if it catches a systematic defect at board 200 rather than board 5,000.

MOQ and typical lead times

PCB fabrication lead time: 5–7 working days for standard 2-layer FR4, 7–10 days for 4-layer, 10–15 days for 6+ layer. Expedited service (24–48 hour turnaround) is available from many fabs at 1.5–3× cost. MOQ for bare boards is typically 5 panels, which translates to 20–100 boards depending on your board size and panel layout.

PCB assembly lead time: add 5–15 working days to the bare board lead time for SMT assembly, depending on board complexity and factory loading. A turnkey order (fab + assembly, factory sources components) is typically 15–25 working days total from Gerber approval to finished boards.

Component sourcing is the wildcard. Standard passives and common ICs are in stock at major Chinese distributors (Lichuang Market, SZLCSC, Arrow China). Specialty components, long lead-time ICs, or anything supply-constrained can add 4–12 weeks. Always confirm component availability before committing to a delivery date.

Minimum order quantities for PCBA are more flexible than most buyers expect. Many Chinese factories will run 50–100 board prototype runs at prototype pricing. The economics only become favorable at 500+ units; at 1,000+ units you'll see significant per-unit cost reductions as NRE amortizes and SMT setup efficiency improves.

Cost breakdown for a typical project

To calibrate expectations, here is a rough breakdown for a moderately complex consumer electronics board — 4-layer, 100mm × 80mm, ~250 SMT components, 10K units:

At 10K units, the one-time NRE is negligible. The BOM cost dominates. This is why getting your BOM right — avoiding long-lead components, qualifying alternatives, locking in component pricing — matters more than negotiating the assembly charge down.

Where to go from here

If you're sourcing PCBA for the first time, the sequence is: clean Gerber package → DFM review → factory qualification → sample run → production with three-stage inspection.

The PCB assembly industry page covers what types of factories exist in China and which situations call for different approaches. To start the sourcing process, the sourcing service covers how we find and qualify PCBA factories specific to your board type and volume.

If you're evaluating a factory you've already identified, our factory audit process covers PCBA-specific checks in detail — SMT line verification, ESD audit, quality system review — before you commit to a production order. For a real-world example of how PCB assembly quality control plays out on a complete product, see how a 5,000-unit Bluetooth speaker run for an EU startup achieved a 0.4% defect rate using three-stage inspection on the PCBA and final assembly.