Adhesive Bonding Technology for the Assembly of Wearable Devices

There is an ever growing demand from consumers to companies to produce electronic wearable devices. AZoM talks to Venkat Nandivada about the role adhesives play in electronic wearable devices.

What types of adhesive formulations has Master Bond developed for manufacturing electronic wearable devices?

Master Bond offers one and two component epoxies, one and two component silicones, two component epoxy-polyurethane hybrids, cyanoacrylates, and UV curing compounds. These products provide solutions for challenging application needs, in the field of wearable devices.

What is the intended use of these different chemical compositions?

Technologically advanced Master Bond compounds are employed for structural bonding, underfills, encapsulation, conformal coating, electrical connection, and heat dissipation. For opto-electronic components, compounds with superior light transmission characteristics are available. UV/visible light curing systems facilitate ultra-fast alignment of optical components. Our compositions have enabled electronic wearable device manufacturing companies to assemble thinner, lighter weight, flexible, and more comfortable products.

What are some fundamental considerations in choosing the right adhesive for the assembly of electronic wearable devices?

Miniaturization of devices and the need to meet critical performance specifications with multiple substrates requires an analysis of which chemical composition is most suitable to satisfy the required parameters. These preliminary decisions are often predicated on the tradeoffs between different adhesive chemistries. They often vary widely and in many cases are essential in achieving the needed goals in adhering parts/surfaces properly.

The shape of the device, the flexing/bending requirements, joining similar/dissimilar substrates, how long it will be worn, and where it will be worn are factors that are a prerequisite in deciding the type of adhesive. The types of stresses the device will be exposed to and the environmental conditions are also consequential. Viscosity, cure speed, and gel time/working life/pot life are significant from a processing standpoint.

Why are adhesives gaining popularity for wearable electronic devices?

Many adhesives provide structural integrity, good drop, shock, impact performance, thermal stability, and resistance to moisture, fluids such as sunscreen oil, soda, water immersion, sweat, as well as normal wear and tear. Specific grades feature good electrical/thermal conductivity, bond well to dissimilar substrates, minimize stress, have high elongation/flexibility and can be applied in ultra small areas for miniaturized designs. Special, dual curing products have a UV tacking capability combined with a secondary heat cure mechanism for fast cures. User friendly solvent/lead free compositions have low halogen content, excellent thermal cycling capability and adhere well to metals, composites, many plastics, fabrics.

Are there any case studies referencing the use of Master Bond products in wearable electronic devices?

Yes, in fact, Master Bond EP37-3FLF¹ epoxy adhesive was singled out for its outstanding ability to withstand shear and bending forces in a flexible electronic packaging structure, as part of an e-textile development effort. The combination of a silicon die, a 0.048-0.052-mm thick Kapton substrate, and a 0.05mm-thick layer of EP37-3FLF adhesive exhibited the best performance of all the materials and dimensions tested.

The study demonstrated that bonds made with EP37-3FLF were capable of withstanding substantial shear and bending loads, making EP37-3FLF well suited for e-textile applications that involve movement, bending, and washing. Also, considering that EP37-3FLF is optically clear, its use may be extended to flexible displays, optoelectronics, and other applications that require both flexibility and optical transmission. Thus, Master Bond EP37-3FLF can help maximize reliability while keeping electronic packaging as thin and flexible as possible, which is a major benefit for wearable devices.

How is easy it to automate the application of an epoxy for high volume electronic assemblies?

Precise, repeatable dispensing of microvolumes is of prime importance to ensure reliable & high quality bonding, and dependable performance for electronic wearable device manufacturing. Adjustments in flow rates can improve throughput/yields even on complex configurations. Digitally controlled dispensers are successfully employed to decrease rejects, lower wastage, prevent operator fatigue, upgrade safety, and lower labor expenses. Appropriate microvolume dispensers have been incorporated for challenging high volume production to fulfill lean manufacturing needs that have enabled the production of highly competitive devices at affordable prices.

Master Bond also has available for purchase two component epoxy systems in premixed and frozen syringes. They are shipped in specially insulated cartons packaged in dry ice (stored at -40°C/-40°F). The adhesive is simply removed from the freezer prior to use and thawed before applying.

How are these adhesives being improved?

To keep pace with the technological advances in this area, Master Bond research and development is busy designing products that feature improved handling, processing, curing, and environmental resistance. Recent improvements include one part products that will not flow when heated (during curing), nanosilica filled compounds for enhanced abrasion resistance, exceptionally high thermal/electrical conductive characteristics, and products featuring exceptionally fast cures/fixturing speeds.

References and Further Reading

1. Li, Menglong, et. al., Stress Analysis and Optimization of a Flip Chip on Flex Electronic Packaging Method for Functional Electronic Textiles, IEEE Transactions on Components, Packaging and Manufacturing Technology, Vol. 8, No. 2, February 2018, pp. 186-194.

About Venkat Nandivada

Venkat Nandivada has been the Manager of Technical Support at Master Bond Inc since 2010. He has a Masters in Chemical Engineering from Carnegie Mellon University.  He analyzes application oriented issues and provides product solutions for companies in the aerospace, electronics, medical, optical, OEM and oil/chemical industries.