The Shenzhen EMS Ecosystem
Electronics Manufacturing Services (EMS) in Shenzhen spans an enormous range — from tiny workshops doing hand-assembly for prototypes to sophisticated factories with automated SMT lines, X-ray inspection, flying probe test, and IATF 16949-certified processes for automotive clients. Understanding where your product sits on this spectrum is the starting point for factory selection.
For most hardware startups and mid-volume OEM buyers, the relevant tier is mid-size EMS factories with two to six SMT lines, in-house solder paste inspection (SPI), automated optical inspection (AOI), and the ability to handle both SMT and through-hole (THT) assembly on the same line. These factories typically handle volumes from a few hundred units per run to 50,000+ units per month and have English-language project management capability.
SMT vs THT: What Your Design Requires
Surface Mount Technology (SMT) dominates modern electronics. Components are mounted directly onto the surface of the PCB and soldered through a reflow oven. The process is highly automated, consistent, and suitable for high-density designs. Most modern designs are predominantly SMT.
Through-Hole Technology (THT) is used for components where mechanical strength is required — connectors, large capacitors, transformers — or for legacy components without SMT equivalents. THT requires either wave soldering or selective soldering equipment, and adds cost and complexity relative to pure SMT. Some smaller factories only have wave solder capability; higher-quality factories have selective solder machines that apply solder only where needed, reducing thermal stress on nearby SMT components.
Mixed-technology boards (SMT top and bottom sides, with THT components) are common. Make sure any factory you consider quotes on the complete assembly, not just the SMT portion.
DFM Review: Do Not Skip This Step
Design for Manufacturability (DFM) review is a formal analysis of your PCB design files (Gerbers, BOM, assembly drawings) by the factory's engineering team before production begins. The review identifies issues that would cause assembly defects, increase rework, or reduce yield — things like insufficient solder mask clearance, tombstoning risk on small passives, component spacing violations, or test point accessibility.
A competent EMS factory will provide a written DFM report within 2–5 working days of receiving your design package. The report should identify specific component references or board locations with concerns, not just generic observations. If a factory gives no DFM feedback at all, that is a warning sign — either they lack the engineering capacity to review properly, or they are planning to work around problems during production and charge you for rework.
DFM review is typically provided free as part of the NPI (New Product Introduction) process. Treat it as a meaningful technical exchange, not a formality.
IPC Standards: What Class Your Product Requires
IPC-A-610 is the global acceptability standard for electronic assemblies. It defines three classes of workmanship:
- Class 1 — general electronics where function is the primary requirement. Consumer products with short life cycles.
- Class 2 — dedicated service electronics where reliable performance is required and uninterrupted service is desired but not critical. Most commercial and industrial products.
- Class 3 — high-performance electronics where continued performance or performance on demand is critical. Military, aerospace, medical.
Specify your IPC class requirement in your RFQ. Most Shenzhen EMS factories work to Class 2 by default. Class 3 requires more rigorous inspection, tighter process controls, and is typically only available at factories with explicit quality system certifications for those markets.
What to Include in Your RFQ
A complete RFQ package to a PCBA factory should contain:
- Gerber files (RS-274X format) or ODB++ for the PCB design
- BOM with full MPNs, approved manufacturers, and quantity per board
- Assembly drawing (pick-and-place file and reference designator overlay)
- Stackup specification if you have controlled impedance requirements
- Test specification — what ICT, functional test, or flying probe requirements apply
- IPC class requirement and any specific workmanship standards
- Target volume: prototype quantity, pilot run quantity, monthly volume forecast
- Component supply model: consigned (you supply components), turnkey (factory sources all), or partial consignment
Factories that receive complete RFQ packages quote more accurately and faster. Incomplete packages lead to assumptions that inflate prices or — worse — create misaligned expectations that surface during production.
NPI Process: From Prototype to Volume
New Product Introduction at a professional EMS factory follows a staged process. Understanding each stage helps you set realistic timelines and identify where delays typically occur.
- Engineering review (1–3 days) — DFM, DFT (Design for Test), and BOM validation
- PCB procurement (5–10 days) — if not consigned; lead time depends on layer count and specifications
- Component procurement (7–21 days) — for turnkey orders; longest lead-time items drive the schedule
- First article build (1–2 days) — typically 1–5 boards to validate process before committing to full run
- First article inspection and approval (2–5 days) — your team or a third party inspects and signs off
- Production run (3–10 days depending on volume)
- Final test and QC (1–3 days)
Total NPI timeline for a moderately complex board: 4–8 weeks. Volume repeat orders with approved components in stock: 2–3 weeks.
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