Flexible Circuitry for Medical Wearables

If you were to crack open any random electronic gadget from the past 40 years, chances are you would find a rigid circuit board substrate made of one of two materials. The first is phenolic paper, referred to as FR-2, which tends to be brown in color and used for single-sided boards. (Phenolic refers to the family of resins used in the boards’ manufacturing.) The other is the more common fiberglass-woven resin referred to as FR-4.

The Future Is Flexible

The future, however, is much more flexible, in terms of the substrate and circuit trace materials and, ultimately, design possibilities. Leading this change is the growing demand for advanced wearable medical devices across a vast array of use cases, including therapeutic, diagnostic and monitoring applications.

Today it is not uncommon to find fitness trackers or even smartwatches with heart-health-monitoring technology. But the medical wearables of tomorrow promise much greater capability. They also promise to be very cost-effective, to the point of having advanced biosensors that are disposable after a single use.

Flexible printed circuits (FPCs or flex) and associated cables and connectors offer medical device designers significant advantages over other circuit interconnect technologies. FPC-based products can be smaller, lighter and more flexible, which are crucial design criteria for medical wearable devices. Such devices need to be comfortable and unobtrusive, so the patient can focus on rehabilitation and not get distracted by the technology enabling their medical care.

Molex offers both Copper Flex and Silver Flex Circuit options. For high-power applications in which thermal management is crucial or for applications where signal integrity is valued for speeds up to 10 Gbps, either Copper flex circuits or circuits made with both flex and PCB materials (rigid-flex) are effective. Up to eight conductive layers are possible with trace widths measured in the 10s of micrometers. Copper flex typically uses a substrate with a Copper film that is chemically etched away to create the traces and pads.

For other applications that don’t need such performance and where there is significant cost sensitivity, designers might consider the environmentally friendly Silver flex circuit options. Unlike Copper flex, Silver flex uses an additive manufacturing process where Silver ink is used to print or screen the traces onto a polyester substrate (other potential substrates include paper, fabric and LDPE thermoplastic), creating the equivalent of thin, flexible, 4-to-6-layer PCBs. Molex can print traces as thin as 0.127mm (.005”). Microcontrollers, sensors and other components are bonded to the flex substrate using unique techniques designed by Molex engineers that deliver both reliability and uncompromised flexibility. In the future, we will also be able to attach BGA packages and bare dies to Silver flex circuits.

Better Technology, Better Healthcare

The manufacturing techniques used in flex circuits offer exciting design possibilities for makers of medical wearables. Flex circuits allow a designer to design circuits in three dimensions. As a result, the surface area of a medical wearable can be reduced, leading to more comfortable experiences for patients. Furthermore, antennas printed onto the substrate of a flexible circuit in a medical wearable device can transmit patient vital signs or biometrics (think telemetry-like data of autonomous vehicles but for the human body). Future developments include printed batteries integrated with the flex itself, further reducing the bulkiness and complexity of medical wearables.

The future of medicine is about tailoring care to every patient’s unique physiology. That requires understanding exactly what is happening in every individual’s body rather than making an assumption based on how the average body performs or reacts to medicines or other treatments. A variety of biofluids (e.g., blood, saliva, sweat) and other biomarkers can be sampled to gather this insight. Flexible circuits enable this data gathering in a noninvasive, continuous and inexpensive manner — all of which would be a significant boon for improving healthcare for those suffering from chronic conditions ranging from cancer and heart conditions to Lyme disease and depression.

The benefit of flex circuits isn’t limited to diagnostics. Devices that can comfortably and reliably conform to a patient’s body to allow for targeted drug delivery in a safe and controlled manner without a healthcare provider needing to be present.

The Molex Advantage

Quality and safety are paramount when designing medical-grade wearable devices. Molex engineers have the experience and knowledge to help our clients achieve their product realization and production goals. We have U.S. design and manufacturing locations to ensure compliance with regulations such as ISO 13485: Quality Management for Medical Devices. Our proven track record of success in medical applications is grounded in our commitment to reliability, repeatability, robustness and uncompromising design. Let Molex combine our FPC technologies with your ideas to build the next generation of medical wearables for the benefit of patients around the globe.