Wearable PCB Isolation Layout for Moisture-Resistant Glucose Sensing
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Solution Overview
Problem
Wearable devices, such as continuous glucose monitors, face challenges in maintaining moisture resistance and electrical isolation while maintaining a low profile to ensure comfort and accuracy of glucose level readings.
Innovation Solution
A multi-layer printed circuit board design with specific electrical trace routing, guard rings, and selective application of potting compound to protect against moisture and electrical interference, ensuring the sensor wire is electrically isolated and the device maintains a low profile.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the device uses a multi-layer PCB with guard rings and encapsulant to improve moisture resistance and electrical isolation, then reliability is improved, but device complexity increases
Solution Approach 1:
The device is divided into multiple functional layers within the PCB structure, with each layer serving specific purposes (sensor trace layer, guard ring layer, ground plane layer, encapsulant layer). This segmentation allows moisture resistance and electrical isolation to be achieved through distributed protective structures rather than a single complex barrier.
Solution Approach 2:
Guard rings are introduced as intermediary conductive structures between the sensor trace and ground plane, acting as electrostatic shields that intercept leakage currents before they reach sensitive sensor circuits. The encapsulant serves as an intermediary protective layer that seals the PCB from moisture exposure.
2Measurement precision
If the device uses a multi-layer PCB with guard rings and encapsulant to improve electrical isolation, then measurement precision is improved, but device complexity increases
Solution Approach 1:
Guard rings serve as intermediary electrostatic shields positioned between the sensor trace and ground plane, intercepting leakage currents that would otherwise corrupt sensor measurements. This intermediary structure preserves measurement precision by electrically isolating the sensitive sensor circuit from noisy ground references.
Solution Approach 2:
The guard ring structure provides localized electrical isolation precisely where needed around the sensor trace, rather than requiring uniform isolation throughout the entire PCB. This localized approach maintains measurement precision while minimizing overall device complexity.
3Ease of operation
If the device uses a low-profile design to improve comfort and wearability, then ease of operation is improved, but moisture resistance becomes more difficult to achieve
Solution Approach 1:
The PCB structure utilizes vertical layering (z-dimension) to achieve moisture protection through multi-layer construction and encapsulant sealing, rather than relying on horizontal thickness. This allows a low-profile device to maintain robust moisture resistance by protecting sensitive areas through layered barriers rather than increasing overall device thickness.
Solution Approach 2:
The encapsulant is applied as a thin conformal coating that seals the PCB and component interfaces without adding significant thickness. This thin-film protective layer maintains the low-profile design while providing effective moisture barrier protection.
Data Source
AI summary
An example continuous glucose monitor includes a printed circuit board (“PCB”) having first and second outer layers and an inner layer; a semiconductor package having a plurality of pins coupled to the first outer layer of the PCB; an electrical contact formed on the second outer layer of the PCB; a trace having a first portion disposed on the first outer layer, a second portion disposed on the inner layer, and a third portion disposed on the second outer layer, the trace having a first end coupled to a first pin of the plurality of pins and a second end coupled to the electrical contact; and an encapsulant disposed around a perimeter of the semiconductor package, the encapsulant covering the plurality of pins, the first portion of the sensor trace, the third portion of the sensor trace, wherein an upper surface of the semiconductor package remains exposed.