Zulki’s PCB Nuggets: DOEs on Call for New Wearable Medical Devices


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Medical electronics continue to make even greater technological advances with recent R&D developments and promise to take on new forms. Biosensors for human-machine interfaces (HMIs) and new, flexible electrodes are leading the way. They are among the most recent developments and promise more sophisticated medical wearable devices for health monitoring.

Here, biosensing refers to devices that touch the human body. The idea is to collect a great deal of information from our bodies so that medical personnel can get a better understanding of our health conditions and wellbeing. According to researchers, human saliva and sweat are excellent candidates for biosensors to capture a wealth of human health data. Medical personnel can check out certain characteristics of a human’s sweat to gauge that person’s chemical excess or deficiency.

Keep in mind that medical wearable devices are already small and thin. But this next round is designed with wearable skin-like electrodes, which are so thin that they are measured in microns and nanometers rather than in mils and inches. Moreover, these new electrodes are not rigid and gold-coated like traditional ones. Those are difficult to insert inside the body. Instead, they’re flexible, smaller in size, and nimble so that they can easily go into different parts of the body.

Medical wearable devices are getting smaller and thinner, but on the other hand, they have considerable intelligence thanks to the embedded biosensors in certain innovative formats. With the onset of these technological advancements, our industry is showing signs of a rapid transformation in the healthcare sector.

For example, some of that transformation stems from hydrogel-associated electronics research by MIT engineers. There are others beyond that serving as the foundation for flexible wearable products. One such device in that category is the piezoelectric sensor. It’s more commonly known as a piezo sensor and uses the piezoelectric effect to measure changes in pressure, acceleration, temperature, strain, or force by converting them to an electrical charge.

The flexible and stretchable circuit devices we’re talking about here are based on newly created materials that have some of the similar functionalities that human skin has. These devices can be worn for a lengthy time period for continuous and persistent HMI. Some have a conformal coating on the sensor that touches the human body most of the time to measure the biopotential at all times.

The use of gold-coated electrode metals and probes or a type of conductive gel or epoxy is the traditional way to check out different signals. But there are issues with that; specifically, the conductive gel dries out in a given period of time. This causes not only signal degradation over time, but the signal-to-noise ratio (SNR) also deteriorates.

These issues can result in small change in any human condition without giving the intended results. Sometimes, as these gels dry out and electrodes are left with inaccurate signals, the result is an inaccurate reading of human body signals and conditions; thereby, doctors cannot correctly diagnose these conditions.

DOEs Pick Up the Ball

Medical electronics advances and issues like these introduce perplexing, head-scratching, and difficult PCB assembly and manufacturing issues because they pose a great number of questions. At this stage, the role of design for experiments (DOEs) steps into the spotlight to pick up the ball.

A DOE is defined as a design of information-gathering experiment where variation is its main characteristic. It can be performed as a fully or partially controlled set of experiments. Controlled experiments involve changing one variable and keeping everything the same. DOEs are in the domain of the EMS provider or contract manufacturer (CM).

They have, or should have, the necessary experience to work hand in hand with medical equipment OEMs. Working together means investigating and deciding on a logical roadmap for assembling and manufacturing these advanced medical wearable devices based on biosensors and flexible, stretchable electrodes.

The objective of a DOE is to collect as much information as possible in terms of doing the same experiment in different ways to achieve the medical electronics OEM’s objective. Experimental designs can be used at the point of greatest leverage to reduce manufacturing complexity and introduce new technology.

When the prototype is being designed and manufactured, there is some uncertainty about how the design would work. Therefore, speeding up the process can reduce time to verify product functionality and time to market. This reduces the design chain cycle, product material, and labor complexity.

How to Effectively Conduct DOEs

In short, you need to know what you are doing and talking about when it comes to a DOE. Here’s what the OEM expects from the EMS provider or contract manufacturing when a DOE is handed over:

  • Nature of existing problems stated
  • Availability of common solutions
  • Brainstorming for out of the ordinary solutions
  • Ongoing controlled experiments, changing one variable at a time
  • Repeating these controlled experiments using other variables
  • Arriving at a desirable or semi-desirable result

To comply with those OEM requirements, the EMS provider must have extensive and detailed experience in PCB design/layout, fabrication, and assembly/manufacturing, including microelectronics.

Beyond those requirements, the management must be innovative and forward-thinking. In some cases, DOEs demand improvising, and in most instances, the success in improvising comes about due to experience. Factors involved, with either controlled or uncontrolled variables, come from personnel experience. Successful DOEs also take into account the willingness of an EMS provider to invest in experiments of its own at their own expense and time to figure out an OEM solution to a particular and troubling issue.

Zulki Khan is the president and founder of NexLogic Technologies Inc.

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