PCB assembly (PCBA) is the process of soldering electronic components onto a bare printed circuit board to turn its copper wiring into a working device. It splits into surface-mount (SMT) and through-hole (THT) techniques, and is the core service an electronics manufacturing services (EMS) provider runs from your design files.
What does PCB assembly mean?
A printed circuit board (PCB) is the bare green or yellow board with copper traces — the wiring. PCB assembly (PCBA) is the next step: soldering components onto that board so the wiring becomes a working device. Without assembly the bare board does nothing.
The PCBA process is what an electronics manufacturing services (EMS) provider runs on your behalf. You send design files; they return finished, tested boards.
SMT vs through-hole: the two assembly families
| Family | What it is | When it dominates |
|---|---|---|
| Surface-Mount Technology (SMT) | Components sit on top of the board, soldered to pads. Pick-and-place machine + reflow oven. | Modern boards. ICs, passives, BGAs, QFNs. Typically 80-95% of a board's parts. |
| Through-Hole (THT) | Component leads pass through drilled holes and are soldered on the back side. | Connectors, large electrolytics, transformers, anything that takes mechanical stress. |
Most production boards run both: SMT first, then THT (selective wave or hand insertion).
What is AOI? Why does every credible EMS run it?
AOI = Automated Optical Inspection. A camera-based system photographs every board after reflow and compares it against a known-good reference. It catches missing components, misalignments, tombstoning, solder bridges, and pad voids — defects the human eye misses on dense boards.
When you read "AOI on every board", that is the difference between an EMS that inspects 100% of output and one that samples 1-in-20. For anything that matters in the field, AOI on every board is the only acceptable default.
What files do you need to send?
Three are mandatory:
- Gerbers — layer-by-layer mask of copper, silkscreen, soldermask, drill.
- BOM (Bill of Materials) — parts list with manufacturer name and manufacturer part number (MPN). See how to prepare your BOM.
- CPL (Component Placement List) — also called pick-and-place file.
Optional: schematic, assembly drawing, test procedure, firmware file.
How is PCB assembly cost built?
A common misconception: most of the cost is labour. It is not. The cost stack:
- Component sourcing — 60-80%. What the parts cost on the open market the week you order.
- Setup — fixed overhead per job. Stencil, feeder load, first-article inspection.
- Placement labour — €0.012 to €0.020 per component.
- AOI inspection — €0.25 to €0.55 per board.
- Shipping — €25 to €200 depending on volume.
For a live indicative range, try our quote estimator.
EU PCBA vs Asian PCBA: when does each win?
Asian PCBA (JLCPCB, PCBWay) wins on raw quote price, especially for prototypes and low-complexity boards under 500 units. They lose once you factor in:
- 4-6 week sea transit (or air freight that erodes the cost advantage)
- Customs duty and VAT pre-payment on EU entry
- IP and data-handling risk for industrial or regulated products
- Tolerance for spec drift on IPC-A-610 Class 3 or PPAP documentation
EU PCBA wins on:
- 1-2 week lead time door-to-door inside Europe
- GDPR-grade data handling
- IPC-A-610 Class 2/3 with proper documentation
- Per-unit traceability for recall scenarios
The crossover point is around 1 000 units of a mid-complexity board. Below that, EU usually wins on landed cost when you include time.
How to choose an EMS partner
- AOI: in-house or sampled? In-house every-board is the right answer.
- What IPC-A-610 class do you accept work under? Class 2 default, Class 3 for medical/aerospace/defense.
- What is your MOQ? Production EMS from 50 units; prototype shops from 1.
- Who sources the BOM? Turnkey, partial, or consigned.
- Do you do per-unit traceability? Non-negotiable for recallable products.
- Typical lead time for a 500-unit job? Credible EU shop: 2-4 weeks.
Frequently asked questions
What does PCB stand for? Printed Circuit Board.
What does PCBA stand for? Printed Circuit Board Assembly. PCB = bare board. PCBA = board with components soldered on.
What is the difference between EMS and OEM? OEM designs and sells the product. EMS builds it for them.
Is PCB assembly worth it? For anything past a handful of hand-soldered prototypes, yes. An EMS line places parts faster, inspects every board with AOI, and gives you per-unit traceability you cannot match by hand. The crossover is usually around 10-25 boards.
What is a PCB assembly service? A contract service where you send gerbers, BOM, and CPL files and the provider returns finished, inspected boards. It covers SMT and through-hole assembly, AOI, optional firmware loading, and sourced functional test. See our PCB assembly service.
How much does PCB assembly cost? Setup €150-250, then €0.015 average per SMT placement, plus AOI and shipping. A 100-unit run of a 200-component board lands around €1 800-2 400 in labour and inspection — before BOM cost. See PCB assembly cost in Europe.
Is JLCPCB a Chinese company? Yes. Based in Shenzhen, China. See our JLCPCB alternative guide.
What is the SMT process? Print solder paste, place components, reflow oven solidifies the joints, then AOI inspection. See the full SMT assembly process.