The challenge
A European industrial automation customer needed 12,000 wireless sensors for factory floor deployment. The use case was harsh: deployed near welding stations, exposed to oil mist, temperature swings (-10°C to 60°C), and continuous vibration. Required IP65 sealing against water jets and complete dust ingress.
Specs:
- LoRaWAN connectivity (868 MHz EU band)
- Industrial temp sensor + accelerometer
- 3-year battery life on 2x AA
- IP65 enclosure (water jet + dust tight)
- Conformal coating on PCBA for humidity resistance
- -10°C to 60°C operating range
- EN 61000-6-2 industrial EMC compliance
Why conformal coating was the make-or-break
The customer had a working prototype that passed IP65 in lab testing. But after 3 months of field deployment, they started seeing 4% failure rate — sensor readings drifting due to moisture ingress through the IP65 gasket, which then corroded the BLE antenna matching network.
The fix: add a urethane-acrylic conformal coating to the PCBA before final assembly. This seals the PCB against humidity, even if the gasket fails.
The challenge: conformal coating can be over-applied, masking connectors and rework points. SkyTech's selective coating process uses a programmable 3-axis robot that sprays only the components we want protected, leaving BGA balls, test points, and programming headers clean.
Process sequence
- SMT assembly on Yamaha YSM20 line, 01005 passives, BGA-8 LoRa module
- AOI + X-ray inspection (BGA verification critical for LoRa antenna)
- In-circuit test (ICT) via flying probe — validates every component value and connection
- Conformal coating (acrylic-urethane, 25-75 μm thickness, 3-axis robot)
- Curing (30 min @ 75°C)
- Functional test (LoRaWAN join, sensor calibration, battery test)
- Enclosure assembly with silicone gasket, IP65 verification per unit
- Burn-in (4 hours @ 50°C)
- Final QC + packaging
What we caught that the customer's first supplier missed
The customer had previously tried a Shenzhen EMS for an initial 500-unit pilot run. The Shenzhen supplier:
- Used spray-can manual conformal coating (inconsistent coverage, 15-150 μm variation)
- Skipped the burn-in step (saved $0.40/unit but caused 4% field failures)
- Used generic IP65 gaskets that didn't pass EN 60529 testing at the temperature extremes
By the time they came to us, they had 6 weeks of customer escalation on their hands. We rebuilt the process from scratch, ran a 100-unit validation run, and committed to the 12,000-unit run with 99.7% yield target.
"Our Shenzhen pilot looked fine in the lab but failed in the field. SkyTech rebuilt the process and delivered 12,000 units with zero field returns in year one. The 0.3% RMA is from connector issues, not the board." — VP Operations, European industrial automation customer
Numbers that mattered
| Metric | Shenzhen pilot | SkyTech production |
|---|---|---|
| Conformal coating thickness variation | 15-150 μm | 25-75 μm |
| IP65 pass rate (post-assembly) | 92% | 99.4% |
| Field failure rate (year 1) | 4% | 0.3% |
| Burn-in | None | 4 hours @ 50°C |
| EMC compliance | Failed retest | Passed first run |
Building industrial-grade hardware?
IP-rated enclosures, conformal coating, burn-in, industrial EMC compliance — all in-house. Send us your environmental spec and we'll quote.
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