8,000 Smart Home Hubs Shipped to 4 Markets with Zero EMC Failures
A Seoul IoT company needed a triple-radio gateway board — WiFi 6, Zigbee, and BLE 5.3 on a single PCB — that passes FCC, CE, and KC certification without redesign between markets.
A Series B IoT Platform Company, Seoul, South Korea
This 30-person company builds a smart home ecosystem — hub gateway, door sensors, smart plugs, and a cloud platform — sold through telecom operator partnerships in South Korea, Japan, Germany, and the US. Their second-generation hub consolidates three wireless protocols onto a single board to reduce BOM cost and simplify manufacturing while supporting Matter/Thread interoperability.
Product Type
Smart home gateway hub with WiFi 6 (2.4/5GHz), Zigbee 3.0, BLE 5.3, Ethernet, and USB-C power — supporting up to 200 paired devices per hub
Technical Complexity
Single 6-layer PCBA with 3 radio subsystems, each requiring isolated antenna paths, dedicated shielding cans, and independent 50Ω RF feed lines — plus a quad-core application processor with DDR4 memory
Production Volume
Scaling from 500 operator evaluation units to 8,000 units across 4 markets — with regional certification requirements (FCC, CE RED, KC, TELEC) that must all pass on the same board revision
What They Needed
A PCBA partner that understands multi-radio EMC design, shield can soldering, controlled impedance RF traces, and production-level RF testing — with documentation supporting 4-market certification filing
What Went Wrong with Their Previous Supplier
The first-generation hub used separate boards for each radio. Consolidating to a single board was a cost optimization — but it turned into an EMC nightmare when the assembler didn't understand multi-radio coexistence.
Failed FCC Radiated Emissions on First Submission
The consolidated board failed FCC Part 15 radiated emissions testing at 2.4GHz — the WiFi 6 transmitter was coupling into the Zigbee antenna path through an unshielded ground plane gap. The previous assembler had placed the Zigbee shield can 0.3mm off-pad, creating a gap in the ground fence. A 0.3mm placement error on a shield can doesn't show up in AOI — it shows up as a 6dB spike in the EMC chamber. Re-testing cost $12,000 and delayed the US launch by 10 weeks.
Zigbee Range Dropped 50% After Assembly
The Zigbee radio achieved 45-meter indoor range on the prototype (hand-assembled by the RF engineer). Production boards from the assembler measured only 20–25 meters. Root cause: solder paste overflow from an adjacent pad contaminated the Zigbee antenna feed trace, changing its impedance from 50Ω to 38Ω. The assembler's stencil design didn't account for the tight spacing between the RF trace and the shield can ground pads.
Shield Cans Detached During Thermal Cycling
The three EMC shielding cans are soldered to perimeter ground pads on the PCB. The previous assembler used their standard reflow profile, but the shield cans act as large thermal mass objects that require extended time-above-liquidus to wet properly. After thermal cycling testing (-10°C to +55°C, 200 cycles), shield cans on 18% of boards showed cracked joints or partial detachment — enough to break the EMC containment they were supposed to provide.
Different Certification Requirements, Same Board — No Documentation Support
Selling in Korea, Japan, Europe, and the US means passing KC, TELEC, CE RED, and FCC certification — all on the same board revision. Each certification body requires different documentation formats, test configurations, and technical file structures. The previous assembler provided a single generic test report and told the team to "figure out the rest." The regulatory consultant spent three months reformatting assembly documentation for four different submissions.
WiFi 6 Throughput Degraded When Zigbee Was Active
In coexistence testing, WiFi 6 throughput dropped by 40% whenever the Zigbee radio was actively transmitting. The root cause was insufficient ground isolation between the two radio sections — the assembler's panelization had placed a tooling hole that interrupted the ground plane partition between WiFi and Zigbee zones. The hole wasn't in the original design; it was added by the assembler for manufacturing convenience.
"Our first-gen hub used three separate boards — one per radio — and it worked fine. We consolidated to save $4.20 per unit on a BOM of 8,000 units. But the assembly mistakes on the consolidated board cost us $180,000 in failed EMC tests, re-engineering, and delayed market launches. The savings evaporated before we shipped a single unit."
Why They Chose Queen EMS
After the FCC failure, the team needed an assembler who understood that multi-radio boards aren't just denser versions of single-radio designs — they're RF coexistence problems disguised as PCBAs.
Multi-Radio RF-Aware Assembly
Our DFM review includes antenna isolation analysis, shield can pad geometry verification, and controlled impedance trace audit for every RF feed line. Panelization tooling holes, fiducials, and breakaway tabs are positioned to never interrupt ground plane partitions between radio zones.
Shield Can Soldering with Dedicated Profile
EMC shield cans get a dedicated reflow consideration — extended time-above-liquidus for proper wetting on large perimeter ground pads. Shield can placement verified to ±0.1mm using vision-assisted pick-and-place. Post-reflow X-ray confirms continuous solder fillets around the entire can perimeter.
Multi-Market Certification Documentation
Production test records, material declarations, and assembly documentation structured for FCC, CE RED, KC, and TELEC filing requirements. One production run generates documentation for four markets — no reformatting, no consultant markup, no three-month delay.
"Queen EMS reviewed our consolidated board layout and immediately identified the ground plane partition issue that our previous assembler caused. They also flagged two stencil apertures near the Zigbee antenna trace that would have caused the same impedance contamination problem. They found those issues from the Gerbers alone — before a single board was built."
How We Engineered the Build for Their Application
Three wireless radios on one board means three sets of RF rules that must coexist without interference. Here's how we addressed each challenge at the assembly level.
Controlled impedance + antenna keep-out enforcement
50Ω controlled impedance on 2.4GHz and 5GHz feed lines verified by TDR coupon on every production panel. WiFi antenna keep-out zone checked against Qualcomm reference design. Shield can placement isolates WiFi section from Zigbee and BLE zones with continuous ground fence.
Stencil design protecting RF trace from paste contamination
Custom stencil aperture reduction on all pads within 0.5mm of the Zigbee antenna feed trace — preventing paste overflow that changes trace impedance. SPI verification on every panel confirms paste volume on critical RF-adjacent pads stays within ±10% of target.
Isolated ground pour with via-stitched partition
BLE module's ground pour separated from WiFi and Zigbee grounds by via-stitched partition wall. DFM review verified via spacing at ≤λ/20 at 2.4GHz to maintain shielding effectiveness. No tooling features permitted within 3mm of any ground partition boundary.
Extended reflow profile with X-ray verified solder fillets
All three EMC cans placed with ±0.1mm accuracy using vision-referenced pick-and-place. Reflow profile provides 45 seconds above liquidus (vs. standard 30s) for full wetting on large-perimeter ground pads. X-ray inspection on every board confirms continuous solder fillets — any gap in the can's ground fence means the shielding doesn't work.
Per-radio transmit power and sensitivity verification
Automated RF test fixture tests each radio independently: WiFi 6 throughput at 2.4GHz and 5GHz, Zigbee transmit power and receiver sensitivity at 2.4GHz, and BLE RSSI at 1-meter reference distance. Coexistence test runs WiFi and Zigbee simultaneously to verify throughput degradation stays below 5%.
BGA with DDR4 impedance verification
Quad-core processor in 0.65mm BGA package with DDR4 memory routed on inner layers. 100% X-ray on BGA joints. DDR4 signal integrity verified by impedance coupon measurement at 90Ω differential. Memory stress test runs during functional testing to catch any marginal timing issues.
From Gerber Upload to Hubs on the Shelf
9-day turnkey delivery including component sourcing, multi-radio assembly, shield can soldering, RF testing, and certification-ready documentation.
DFM + RF Audit
Day 1–2
BOM Sourcing
Day 1–3
SMT + Shields
Day 4–6
X-Ray + AOI
Day 6–7
RF Test
Day 7–8
Ship DDP
Day 9
Measurable Impact After 11 Months
From the first EMC-clean production batch to 8,000 hubs shipped across South Korea, Japan, Germany, and the US.
| Metric | Previous Supplier | Queen EMS |
|---|---|---|
| 📋 First-Pass Yield | 82.4% (RF + shield can issues) | 99.6% |
| 📡 FCC/CE/KC Submissions | Failed FCC, delayed CE | All 4 certifications passed first try |
| 📶 Zigbee Range | 20–25m (degraded by paste contamination) | 42–48m (matching RF engineer's prototype) |
| 🛡️ Shield Can Integrity (thermal cycle) | 18% cracked joints at 200 cycles | 0% failures at 500 cycles |
| 📶 WiFi/Zigbee Coexistence Degradation | 40% WiFi throughput drop | <4% throughput drop |
| 📈 Market Coverage | Korea only (US/EU blocked by failures) | Korea, Japan, Germany, US — all active |
"During our second production run, Queen EMS noticed we'd specified a standard tin finish on the WiFi antenna pad. They recommended ENIG for that specific pad to improve impedance consistency across production batches. We tested both finishes — the ENIG version showed 1.2dB better return loss. A small suggestion that improved WiFi performance across 8,000 units."
Is This Approach Right for Your Project?
This engagement model works best for teams building smart home devices, IoT gateways, wireless routers, or any product with multiple radio subsystems that must coexist on a single board and pass multi-market certification.
✅ Good Fit If You…
- Build devices with 2+ wireless radios on a single PCB (WiFi, Zigbee, BLE, Thread, Z-Wave)
- Need EMC shield can assembly with verified solder integrity
- Require controlled impedance on multiple 50Ω RF feed lines
- Sell into multiple markets requiring FCC, CE, KC, or TELEC certification
- Need production-level RF testing for each radio protocol independently
- Want certification-ready documentation generated during production — not after
🔍 What You Should Ask Us
- How do you verify shield can solder integrity after reflow?
- What stencil design changes do you make to protect RF traces from paste contamination?
- Can you test each radio independently on a production line?
- How do you ensure panelization doesn't compromise ground plane partitions?
- What documentation do you provide for multi-market certification filing?
- What coexistence testing can you perform during production?
Ready to Build with Confidence?
Upload your smart home gateway Gerber files and BOM. Our engineering team will review your multi-radio layout for EMC compliance, antenna isolation, and shield can integrity — with a detailed quote within 24 hours.