I am developing a compact wearable health tracker (Nasal Smart Dilator) designed to monitor breathing and movement. The design uses the BMP388 for pressure sensing and BMI270 for activity tracking. The device is built on a 0.11mm 2-layer Flexible PCB (FPC) and will be fully encapsulated in medical-grade silicone.
To ensure 150% reliability for this student project, I would appreciate your feedback on these layout points:
1. BMP388 Mechanical Stress: Since the FPC will be curved around the nose, I’ve placed a Polyimide stiffener under the BMP388. Is this needed and does prevent MEMS offset shifts caused by mechanical strain, or do you recommend a rigid FR4 stiffener for better stability?
also do you recommend some other models for this very small kind of pcb?
2. Venting & Silicone: The BMP388 needs to sense breathing air. I have planned a 0.4mm vent hole through the silicone case. Do you have any guidelines do i need hole in the pcb also? Would a small air cavity around the sensor be recommended?
3. Thermal Isolation: The sensors are located approximately 10mm from an nRF52840 SoC. On such a thin FPC, should I take extra steps (like specific copper cutouts) to prevent thermal drift on the BMP388 pressure readings?
4. BMI270 Placement: For activity tracking on the nose, are there any specific orientation or mounting recommendations to ensure the highest accuracy for gesture/movement detection on a flexible substrate?