A. Bar¹, K. Jaju¹, E. Keaney¹, S. Kenig², H. Dodiuk², J. Mead,* B. Budhlall¹, C. Stoessel³, A. Kumar⁴, S. Gonya^5
1University of Massachusetts Lowell, MA,; ²Shenkar College of Engineering, Israel; ³Eastman Chemicals Co.; ⁴Acellent Technologies Inc.; ⁵Lockheed Martin
Flexible Hybrid Electronics (FHE) offer benefits for a wide range of applications, such as healthcare wearables, smart layer-based integrated sensor networks, soft robotics, and digital microcontroller circuits. It is critical to developing flexible and stretchable encapsulants for FHE devices to protect them from environmental conditions. Encapsulants for advanced FHE devices require innovative materials and processes to ensure the microchips' physical/chemical protection without compromising the stretch or flex characteristics. Consequently, this work is focused on developing a superhydrophobic (SH) coating that can be spray-coated on FHE device for encapsulation. The SH coating is based on commercial conformal acrylic resin with alkyl treated SiO₂ nanoparticles that provide both the roughness and hydrophobic chemistry to be applied to alumina and treated polyimide. The resulted coatings possess low surface energy due to the formation of a micro/nano tailored hierarchical structure and hydrophobic moieties. The study investigates the durability of the superhydrophobic coatings using the Peel Test, Flexibility Test, Scratch Test, and Hardness Test on the two substrates. Experimental results indicated that the mechanical durability was improved when applying two coating layers with a mixing time of 1 hour first and then ½ hour withstanding more than 8 peels. Furthermore, the aluminum and polyimide substrates' Scratching indicates that the coating peels off completely with ˜0.5 [N] and˜4 [N], respectively. The Pencil hardness test results suggest that the polyimide substrate starts to fail at '5H' hardness, and the Alumina coating starts to fail at ‘H’ hardness. The final coatings show good durability overall and long shelf-life stability.