Industrial Wireless Sensor Node PCBA for UK Smart Factory Platform
Overcoming component shortages, antenna placement interference, and achieving IP67-ready conformal coating on a 2-layer flex board
Project Overview
A Manchester-based Industrial IoT company had developed a wireless vibration and temperature sensor node for predictive maintenance in manufacturing plants. The device used a 2-layer flexible PCB with a Nordic nRF52840 BLE/Thread SoC, a MEMS accelerometer, and a coin cell battery — all packaged in a 30mm diameter circular form factor. The customer needed 500 units for a pilot deployment across 3 automotive plants in Germany and needed conformal coating for IP67 protection.
The Challenge: Circular Flex PCB, Antenna Keep-Out, and Component Shortage
The circular flex PCB design had the nRF52840's integrated PCB antenna running along the board edge — a common layout error that causes 8-12 dB of antenna gain loss due to ground plane proximity. The customer had already built 50 prototype units with their previous supplier and was seeing inconsistent BLE range (3-8 meters instead of the specified 30 meters).
The MEMS accelerometer (STMicroelectronics LIS2DH12) was on a 12-week lead time due to the global semiconductor shortage. The customer's pilot deployment timeline could not accommodate a 12-week wait.
The conformal coating specification (Humiseal 1A33 acrylic, 50-75μm) had to be applied selectively — excluding the battery contacts, the programming header, and the pressure vent membrane. The customer's previous supplier had applied coating over the battery contacts, causing contact resistance issues.
The coin cell battery holder required a specific insertion force to ensure reliable contact in high-vibration environments (up to 20g RMS). The original BOM specified a standard through-hole holder that had shown contact intermittency in vibration testing.
Our Engineering Approach
Our RF engineer reviewed the antenna layout and confirmed the ground plane proximity issue. We recommended a 3mm keep-out zone extension on the antenna side and a modified ground plane cutout — a standard fix per Nordic's nRF52840 hardware design guide. We provided a corrected Gerber overlay and the customer's firmware team re-validated the RF performance, achieving consistent 35-meter BLE range in open-air testing.
For the LIS2DH12 shortage, our component sourcing team identified an authorized distributor with 8,000 units in stock at a 12% premium over standard pricing. We also qualified a pin-compatible alternative (Kionix KX022-1020) and provided the customer with a datasheet comparison and register map differences — allowing their firmware team to support both parts with a single firmware build.
We developed a custom conformal coating masking fixture for the circular board, using laser-cut silicone masks to protect the battery contacts, programming header, and pressure vent. Post-coating inspection used a UV lamp to verify coverage uniformity, and coating thickness was measured at 5 points per board using a Fischer Dualscope probe.
We substituted the through-hole battery holder with a Keystone 3034 SMT holder with a higher contact force spring, rated for 50g vibration. We validated the substitution with a 2-hour vibration test on 10 sample boards before approving it for production.
Measurable Results
""The antenna fix alone transformed our product. We went from a 3-meter range to 35 meters — that's the difference between a product that works and one that doesn't. Kingdta's engineering depth is what sets them apart from typical assembly houses."
— CTO, Industrial IoT Company (Manchester)
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