How to ruggedize medical electronics like wearables? Adhesives protect against shock, vibration, liquids while maintaining aesthetics. Soft gels, silicones and rigid epoxies bring reliability.
Many of the electronic devices used today serve a similar purpose as they did 10 years ago, and yet many have become smaller, faster, lighter and with the ability to be used virtually everywhere. For this to be possible, electronics need to be protected against shock, water, heat, and other elements encountered during their use. This forms the question, “how are these shrinking and lightweight electronic devices assembled to function reliably and stay protected long term?” To help answer this question, we connected with Jeff Bowin, TCS Principal Engineer at Henkel to learn more about this topic and the technologies that have been developed to help ruggedize electronic devices. Ruggedization involves a multi-protection solution from damaging environmental factors, such as extreme temperatures, fluids, corrosive elements, shock and vibration. It provides both mechanical reinforcement and electrical insulation.
In the medical field reliability within these devices is essential, and allows for continuous and advanced patient care. Ruggedization can be seen in all electronics but some require special protection to their environments. For example, a continuous glucose monitoring patch is placed onto the human body and it might not need to withstand extreme temperatures as the human body is not that hot but it needs to be protected against other factors like sweat and impacts. Some of the applications used in this patch might be underfills and structural staking.
Underfill is an application used to protect solder joints and solder balls that connect a chip to a printed circuit board (PCB). This creates a solid electronic piece with mechanical reinforcement preventing mechanical fatigue and increasing the lifespan of the electronic. “Simply using a device as intended or pushing buttons on the device causes stress and could result in fatigue throughout the device,” said Bowin. Dropping a portable electronic device that doesn’t include underfill could rattle the internal components and break solder joints or negatively affect the functionality and lifespan of the device.
Materials are available that deliver ultimate processability with fast flow speeds and the capability to effectively fill bottom-side component spaces with extremely low bump heights. These products are designed to reduce stress caused by mismatched expansion coefficients and provide reliability in thermal cycling, thermal shock, drop testing, and other demanding tests, as well as in use.
To enhance the reliability of many handheld devices, underfills quickly fill the space between the package and board, cure fast, and offer protection for solder joints against mechanical strains such as drop shock and vibration, and allow for reworkability. For applications where full underfill is not required, cornerbond and edgebond technologies provide a cost-effective solution, with strong perimeter reinforcement and self-centering capability combined with fast processing speed. View the application video below.
There are underfill formulations available in pre-applied formulations, that deliver high levels of reliability with wide processability and good gap filling of ultra-fine-pitch, low bump height devices.
Conformal coating, a form of circuit board protection has historically been used in industries such as aerospace, and other markets have increasingly integrated this application to protect PCBs from fluids and develop waterproof characteristics within the electronic. Conformal coating also protects against thermal shock, moisture, corrosive liquids, and other adverse environmental conditions. Medical consumer wearables such as smart watches, as well as the continuous glucose patch would benefit from protection against sweat that could penetrate the electronic assembly.
While potting and low pressure molding techniques generally encapsulate the entire assembly, conformal coating allows for selective protection of certain areas. This capability becomes important for assemblies that may require rework of specific components in order to preserve the integrity of the rest of the PCB, as in the case of high-value boards. Normally, when a PCB is conformally coated, there are areas of the board that need to be kept free of coating. These areas are often referred to as “keep out zones” and traditionally have been masked off with tapes, liquid masks or UV curable masks.
Each process has advantages and disadvantages. Uniting the advantages of conventional masking materials (good adhesion to multiple surfaces, low residues, compatibility with miniaturized dimensions and automated processes) and eliminating the downsides (time-consuming manual application, lengthy cure steps, residues and odor), Henkel has developed a solution for isolation of PCB keep out areas which has led to cost savings for manufacturers.
Compatible with automated dispensing systems, the material is quickly dispensed precisely where required with no risk of migration to non-designated areas, which is an important consideration for today’s highly miniaturized board and component dimensions. The hot melt adhesive remains firmly in place as it passes through the coating process, following which it peels off quickly and cleanly, leaving defined edges and zero residue.(1)
For more information on this simplied, sustainable solution read the technical article or view the video below.
To summarize, ruggedization is a key element involved with the production and assembly of medical electronic devices. As the use of medical wearables continues to increase in the future, ruggedization will protect these devices to provide people with reliable functions in their daily lives as well as consistent monitoring of their health.
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