Medical Design Technology - November/December 2015

Flexible 3D Circuits
Power Medical Devices

By Greg Kuchuris, Marketing Manager, Printed Circuit Products, Molex Incorporated

As demand for healthcare continues to grow, medical practitioners are turning to mobile-monitoring, therapeutic, and diagnostic devices that can improve the quality and efficacy of medical care.

As a result, medical devices have been downsized, from bulky to portable to handheld to wearable. Device manufacturers are selling their products to increasingly tech-savvy clinicians and patients who are accustomed to using myriad portable and handheld electronic devices. Having experienced the high functionality of smart phones, for example, consumers expect the same from medical devices with small form factors.

In some cases, these medical devices
and related communications devices have
become part of remote medical treat-
ment systems. For example, the practice
of “telehealth” uses digital information
and communication technologies, such
as computers and mobile devices, to
manage patients’ health and well-being.
Early detection of symptoms or changes
in physiology allows for preventative
measures and earlier treatment before a
patient’s health deteriorates or becomes a
medical crisis.

Wearable technologies and other small medical devices that provide continuous real-time feedback help make telehealth possible. Telehealth practitioners make use of online health information and remote patient communication facilitated by remote monitoring of health indicators, such as blood glucose, blood pressure, heart rhythm, pulse, and other vital signs, read via sensors attached to or worn by a patient. These miniaturized real-time medical monitoring devices can benefit patients with chronic and potentially life-threat-ening conditions — and their healthcare providers, who face mounting pressures to improve outcomes, while reducing costs and hospital readmission rates.

Lightweight Circuitry

Compact medical devices are made possible by lightweight circuitry that fits within tight spaces. Anyone who has packed a suitcase knows firsthand that the contents must bend or flex in order to maximize space and efficiency.

Among a number of proven technol-
ogies that have migrated from consumer
electronics into medical devices, flexible
circuits and flexible printed electronic
solutions help designers optimize space
in tightly packaged medical devices.

Products such as insulin pumps, wearable patient monitoring devices, portable defibrillators, and CPAP machines (used to treat sleep and breathing disorders) typically employ flex circuits.

Unlike conventional 2D circuits, flexible printed circuits and printed electronics occupy three dimensions and can be bent around packaging, and even folded over to fit in miniaturized device enclosures. There are several other advantages. Flexible substrates with single-, double-sided, and multi-layer circuitry are ideal for high performance signal and power connections at an economical applied cost. Flex products can also be mounted in through-hole, surface mount, and press-fit configurations.

Flex circuits allow designers to make electronic interconnection simpler and more reliable. Unlike hard board materials containing woven glass fibers that tend to result in signal loss, the materials used in flex circuits, such as polyimide, help maintain signal and power integrity. Polyimide dissipates heat quicker, so the flex circuit requires less cooling. Additionally, flex materials closely match thermal expansion rates, which make them more reliable in hot and cold temperature extremes and temperature fluctuations found in mobile healthcare applications.

Medical device miniaturization requires producers to adapt flex circuits for 3D packaging, tighter copper flex spacing, and trace widths. As the device package size shrinks, the flex circuit must also shrink. Incorporating features like blind and buried vias can help retain flexibility as the device package continues to decrease in size.