Healthcare is moving out of the hospital and onto — and into — the body. Wearable and portable medical devices represent the fastest-growing segment of the medical device industry, driven by the convergence of sensor miniaturization, ultra-low-power electronics, wireless connectivity, and a healthcare system increasingly focused on prevention, remote monitoring, and patient empowerment. Continuous glucose monitors (CGMs) the size of a coin, smartwatches capable of detecting atrial fibrillation, hearing aids smaller than a fingertip, and portable oxygen concentrators that restore mobility to COPD patients — all of these devices depend on printed circuit boards that push the boundaries of miniaturization, power efficiency, and human-body interfacing. This article explores PCB design and manufacturing for wearable and portable medical devices.

1. The Wearable Medical Device PCB Landscape

Wearable medical devices span a spectrum from disposable patches worn for days to implantable-adjacent devices intended for years of continuous use. Despite this diversity, they share common PCB design imperatives: minimize size and weight, maximize battery life, ensure reliable skin or body contact, and maintain medical-grade measurement accuracy in the face of motion artifacts, environmental variation, and user behavior.

1.1 Continuous Glucose Monitor (CGM) PCB Design

Continuous glucose monitors measure interstitial glucose levels every 1–5 minutes using a subcutaneously inserted enzyme-based electrochemical sensor. The CGM transmitter — the reusable electronics module that snaps onto the disposable sensor — contains a PCB approximately 20–30 mm in diameter that performs sensor biasing, current measurement, signal processing, and Bluetooth Low Energy (BLE) communication.

The CGM sensor measurement circuit must resolve glucose-dependent currents in the 1–50 nA range with 12–14 bit effective resolution. This demands a transimpedance amplifier front-end with these characteristics:

• Input bias current: < 100 pA to avoid loading the electrochemical sensor, which has an output impedance in the hundreds of megohms

• Low-frequency noise: < 1 µV p-p in the 0.1–10 Hz bandwidth, as glucose concentration changes slowly and low-frequency noise translates directly to measurement error

• Potentiostat control: The sensor's working electrode must be held at a precise bias voltage (typically +0.4V to +0.7V relative to a reference electrode) with microvolt-level stability to prevent bias drift from corrupting the glucose measurement

• Ultra-low power: The entire analog front-end — potentiostat, TIA, and ADC — must draw < 100 µA from a 3V supply to achieve the 7–14 day battery life typical of disposable CGM transmitters from a small coin cell (CR2032, ~225 mAh)

The CGM PCB layout must be exceptionally clean. The nA-level measurement currents are vulnerable to contamination-induced leakage — a salt bridge formed by sweat or humidity across the PCB surface between the sensor input and adjacent circuit nodes can introduce errors of tens of nanoamps. Conformal coating, guard rings around the sensor input, and a solder mask with high surface resistivity are essential.

1.2 Wearable ECG / Cardiac Monitor PCB Design

Wearable cardiac monitors — from single-lead patches (Zio, BioTelemetry) to multi-lead smart garments — record ECG continuously for days to weeks to detect arrhythmias that would be missed by a standard 10-second clinical ECG. The PCB in these devices must extract microvolt-level cardiac signals from dry or semi-dry electrodes in the presence of motion artifacts that can be orders of magnitude larger than the ECG signal itself.

Motion artifact rejection is the central challenge of wearable ECG PCB design. When the patient moves, the electrode-skin interface impedance changes due to relative motion and deformation of the stratum corneum, modulating the DC electrode offset potential (typically 100–300 mV for dry electrodes) and producing low-frequency artifacts that overlap the ECG frequency band (0.05–150 Hz). The PCB employs several strategies to combat this:

• High input impedance: The ECG amplifier input impedance should exceed 10⁹ ohms to minimize the voltage divider effect when the electrode-skin impedance varies. This drives the use of CMOS instrumentation amplifiers with input bias currents in the low picoamp range

• Driven right leg (DRL) or driven ground: Active common-mode cancellation reduces the effective common-mode impedance, suppressing the motion artifact that appears as a common-mode signal

• Adaptive filtering: The ECG signal is digitized with sufficient dynamic range (16–18 bits) to accommodate the motion artifact without saturation, then processed with adaptive filters (LMS or RLS algorithms) that use an accelerometer signal as the artifact reference

• Electrode impedance monitoring: A low-level AC signal (typically 1–10 nA at a frequency outside the ECG band, such as 1–2 kHz) is injected into each electrode, and the resulting voltage is measured to continuously monitor electrode-skin impedance. When impedance exceeds a threshold, the device can alert the user to re-attach the electrode

2. Hearing Aid and Audiology Device PCB Design

Modern hearing aids represent the pinnacle of medical device miniaturization. A completely-in-canal (CIC) hearing aid PCB may measure just 4 × 8 mm, yet must integrate two or more MEMS microphones, a digital signal processor (DSP) implementing multi-band compression and noise reduction algorithms, a Class D audio amplifier driving a balanced-armature receiver (speaker), a wireless radio (BLE or proprietary near-field magnetic induction), and a rechargeable battery management system.

Hearing aid PCB manufacturing pushes the limits of miniaturization technology:

• Layers and feature size: 6–10 layer HDI constructions with laser-drilled microvias (50–75 µm), line/space of 35/35 µm or finer, and component placement on both sides of the board

• Component packaging: 0201 (0.6 × 0.3 mm) and 01005 (0.4 × 0.2 mm) passive components, wafer-level chip-scale packages (WLCSP) for active ICs, and custom ASICs integrating the DSP, RF, and power management into as few as 1–2 die

• Flex and rigid-flex: The PCB is often a rigid-flex construction with a rigid section hosting the components and flexible arms connecting to the battery, microphones, and receiver — eliminating connectors and wiring that would consume precious volume

• Acoustic considerations: The PCB layout must avoid placing noisy digital signals near the microphone inputs, as even microvolt-level crosstalk can be amplified through the hearing aid's 40–60 dB gain and become audible to the user as a buzz or whine

3. Insulin Pump and Drug Delivery Device PCB Design

Insulin pumps — both traditional tethered pumps (tubed) and patch pumps (tubeless, adhered directly to the skin) — deliver precise basal and bolus insulin doses through a subcutaneous cannula. The pump PCB must control a micro-stepping motor or shape-memory alloy actuator with dose accuracy of ±5% (per IEC 60601-2-24), track remaining insulin, monitor occlusion pressure, and communicate with a handheld controller or smartphone via BLE.

The safety-critical nature of insulin delivery — where an unintended 1-unit bolus (0.01 mL) can cause severe hypoglycemia — demands a PCB design with multiple independent safety mechanisms:

• Redundant dose verification: The motor drive circuit includes an encoder that counts motor steps, while a separate sensor (pressure transducer or optical interrupter) independently verifies that fluid was actually delivered

• Watchdog with independent clock: A hardware watchdog timer with its own RC oscillator continuously monitors the main processor; if the processor fails to service the watchdog within a timeout period (typically 100–500 ms), the motor drive is disabled and an alarm sounds

• Occlusion detection: A pressure sensor in the fluid path detects downstream occlusions (kinked cannula, blocked infusion set) that would prevent insulin delivery. The pressure transducer signal must be amplified with high common-mode rejection to extract the small pressure changes (typically 0–5 psi full scale) from the ambient pressure baseline

4. Portable Oxygen Concentrator PCB Design

Portable oxygen concentrators (POCs) extract oxygen from ambient air using Pressure Swing Adsorption (PSA) technology, delivering 1–5 LPM (liters per minute) of 87–96% oxygen to patients with chronic respiratory conditions. Unlike the ultra-miniaturized wearable devices discussed above, POC PCBs are power electronics designs managing the compressor motor, solenoid valves for the sieve beds, oxygen concentration sensors, and battery management for a 50–150 Wh Li-ion battery pack.

The compressor motor drive is the dominant PCB design challenge: a brushless DC motor consuming 30–100 watts at 12–24V must be driven with field-oriented control (FOC) to maximize efficiency and minimize acoustic noise — a critical consideration for a device worn by the patient in public settings. The motor drive MOSFETs on the PCB dissipate 3–10 watts of heat and require thermal management through copper pours, thermal vias, and often a small heatsink. The PCB must also survive the vibration environment of the compressor, with mechanical mounting points sufficient to prevent flexure-induced solder joint fatigue over the device's 5-year expected lifetime.

5. Flexible and Stretchable PCB Technologies for Wearables

The transition from rigid to flexible and stretchable PCB substrates is enabling a new generation of body-conformal medical wearables. Flexible PCBs using polyimide substrates (typically 25–100 µm thick) can bend to conform to body contours, while emerging stretchable technologies embed serpentine copper traces in elastomeric substrates (silicone, TPU) that can elongate 10–30% without trace fracture.

Flexible PCB manufacturing for medical wearables requires attention to several factors:

• Bend radius: The minimum bend radius for a flexible PCB is approximately 6–10× the total thickness for single-layer, and 10–20× for multi-layer. Traces on the outer radius of a bend experience tensile stress — the neutral bend axis should be positioned at the copper layer for dynamic flexing applications and at the center of the construction for static "bend-to-install" applications

• Component placement: Components should be placed away from bend zones, with rigid stiffeners applied under large or heavy components (connectors, batteries) to prevent flexing at the solder joints

• Trace design: Traces crossing bend zones should be perpendicular to the bend axis (not parallel), with curved rather than sharp angle transitions, and should use tear-drop or filleted pad connections to prevent stress concentration at pad-trace junctions

• Coverlay vs. solder mask: Flexible PCBs use a polyimide coverlay film (adhesive-bonded) rather than liquid photoimageable solder mask, as solder mask cracks under flexing. The coverlay adhesive must be selected for medical compatibility and low outgassing

6. Wireless Connectivity and Security for Wearable Medical PCBs

Wearable medical devices universally include wireless connectivity — predominantly BLE (Bluetooth Low Energy) for short-range communication to a smartphone hub, with emerging adoption of Wi-Fi, NFC, and UWB for specific use cases. The wireless section of the PCB must coexist with sensitive analog measurement circuits on the same board, often without the benefit of metallic shielding due to size constraints.

The BLE antenna on a wearable device PCB is typically a chip antenna (ceramic multilayer) or a PCB trace antenna (meandered monopole or inverted-F). The antenna placement is critical: it should be at the edge of the PCB with a keep-out zone free of copper on all layers (minimum 5–10 mm clearance), oriented away from the body (the human body is highly absorptive at 2.4 GHz), and isolated from noisy digital traces that could desensitize the receiver.

Medical device cybersecurity is increasingly a regulatory requirement (FDA premarket guidance, EU MDR Annex I). The wearable PCB must support hardware-based security features including secure boot (cryptographic verification of firmware at startup), encrypted storage for patient data, and authenticated wireless pairing that prevents unauthorized access to the device. These features are typically implemented in a secure element IC or within a TrustZone-enabled microcontroller, with the PCB providing isolated communication paths for the security functions.

7. Manufacturing Wearable and Portable Medical PCBs

Superb Tech's capabilities for wearable and portable medical device PCBs include:

• HDI microvia: 6–12 layer constructions with 50–75 µm laser-drilled microvias, 35/35 µm minimum line/space

• Flex and rigid-flex: Polyimide flexible circuits, 2–8 layer rigid-flex constructions, with stiffeners and PSA attachment options

• Miniaturization: 0201 and 01005 component placement, WLCSP and fine-pitch BGA assembly

• Ultra-low-leakage: Clean manufacturing environment, high-resistivity solder mask, ionic contamination control < 1.56 µg/cm² NaCl equivalent

• Conformal coating: Parylene, acrylic, silicone, or polyurethane coating for moisture and contamination protection

• Medical quality: ISO 13485 quality management system, full traceability, and device history records for every PCB lot