Conductive adhesives enable electrical interconnections on disposable medical devices, offering flexibility and reliability. Isotropic and anisotropic options direct current flow and simplify manufacturing.
In today's world, reliability is critical when it comes to electronic devices. Technology companies continue to redefine the possibilities with their ability to shrink components and develop cutting-edge technologies within these devices. Electrically conductive adhesives (ECAs) are becoming essential in the assembly and ruggedisation of electronic devices, especially in the medical field. In an interview with Dr Mark Currie, Senior Scientific Principal at Henkel, we explore more on this topic of ECAs and their role in the production of electronics.
Electrically conductive adhesives have been available for several decades and provide an alternative to solder as an interconnect solution delivering electrical, mechanical and thermal performance. Solder is very rigid and less malleable and does not share the same flexible attributes as an ECA, which is an interconnect hybrid solution of silver dispersed in a malleable polymer matrix. Furthermore, the application temperatures of ECA interconnects lies between 25⁰C and 200⁰C only (chemistry-dependent) and can withstand continuous operating temperatures up to 175⁰C.
We asked the question, "why are ECAs becoming the solution for more applications?" An important single question, with four answers to provide context: process, reliability, sustainability and macro technological breakthroughs.
Process: high-density integration has allowed miniaturised solutions to become the norm. When considering a circuit board that is flexible, or contains components that are sensitive to temperature, the interconnect solution must accommodate these challenges. If process temperatures are too high for the board/component combination, CTE mismatches can yield warpage at the board or component levels, resulting in poor interconnect yields. If we consider ECAs as the counter solution, we provide a low-temperature interconnect option with potentially fast cure times.
Reliability: CTE mismatch can lead to early false/true failures that may not be anticipated further down the road. Using a technology solution that can embrace both low-temperature process attachment and high operating temperatures can only be beneficial to field applications.
Sustainability: all solutions must consider this impact. Two aspects of ECAs that assist are the low-temperature and potential fast-curing chemistry options that reduce energy consumption.
Macro Technological Breakthrough: the macro drivers of today are causing the medical market to consider how we treat patients. The miniaturisation aspect, coupled with both 5G and IoT (Internet of Things) are solution enhancers in the medical market that were not in scope a decade ago, and have the biggest impact on the solutions being provided.
Let's combine those answers and apply them to the medical industry. The past 18 months have provided everyone with context for patient monitoring, but as we look to the future, with smart technology embracing connectivity with 5G, we find remote patient monitoring in the medical (or bioscience) market and the application subject of sensors.
Sensors can be considered solutions that provide signals of a patient's well-being. Four sensor categories are often referred to: electrophysiological (EEG, ECoG); physical (body temperature, skin hydration); biomedical (blood glucose, sweat composition) and vitals (blood oxygen, blood pressure).
What are the consistent reliability metrics for all these sensor solutions? All applications are small electronic assemblies, but they must absorb a patient's chemical and physical body changes as they are all potentially "wearable". For the finished assembly to absorb a patient's movement, flexible circuit boards are commonly used. These boards can be temperature-sensitive when populated with components, and this particular property, combined with the mandatory interconnect flexibility, allows ECAs to be the current dynamic trend in medical remote patient monitoring capitalising on 5G and the Internet of Things (IoT).
Our first flexi-board "wearable" application example that embraces ECAs is the glucose monitoring disposable patch. This patch is about the size of a silver dollar and the width of your finger and comprises very small and sensitive components that benefit from the low application- and cure temperature of an ECA and its inherent flexibility.
Another medical device that requires flexibility and low-curing temperature during assembly is the ECG sensor adhesive bandage used for continuous cardiac activity monitoring. In this application, reliability is essential and the correct chemistry choice of the ECA carrier system is paramount to absorb all motion stress.
Next are hearing aids, which themselves are rigid and will not flex during use. However, they are made up of softer plastics and contain other temperature-sensitive components that could be damaged during the assembly process using traditional solutions.
Gait sensors can be placed in the shoe of a person to monitor their stride and diagnose a problem. These sensors need to bear the weight of the person and they need to be flexible to adjust to the shape of someone's foot.
"Bioscience applications are clearly going to develop as technology evolves," says Currie, "and closed-loop remote patient feedback monitoring is very much now and the future, and ECAs fit in as one key enabling technology solution".
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