Robust packaging of printed flexible electronics with functional SiOx coatings via cold atmospheric plasma assisted deposition

Abstract

The ubiquity of printed flexible electronics (PFEs) spans diverse sectors, from healthcare to automotive, aerospace, agriculture, and consumer electronics, owing to their low cost, lightweight, flexibility, and conformability. However, addressing the critical challenge of ensuring robust packaging to enhance the durability and reliability of PFEs remains imperative. The limitation lies in the functionality of traditional polymer-based dielectric encapsulants, resulting in weak bonding between electrical components on the circuit and the encapsulant. As a consequence, when PFEs are exposed to harsh environmental conditions, water condensation occurs at the interface, leading to device failure. While hybrid multi-layer inorganic and organic encapsulation methods have demonstrated promise in providing robust packaging for electronic devices, the required deposition of inorganic coatings involves complex, time-consuming, and costly processes, rendering them unsuitable for scalable manufacturing of PFE devices. To address this challenge, a novel approach is investigated using cold atmospheric plasma (CAP) technology for the deposition of SiOx coatings as an intermediate layer between the printed circuit and the dielectric encapsulant coating. This effective intermediate layer promotes adhesion and enhances barrier properties of commonly used polymeric coatings in PFE devices. The CAP method enables selective deposition of high-quality and consistent SiOx thin films onto desired substrates under atmospheric conditions. Through a systematic study of CAP deposition conditions, the optimum thickness (∼820 nm) of the SiOx coating was determined, providing the required functionality to enhance barrier properties for corrosion protection of printed circuits while maintaining high mechanical flexibility. A remarkable 105-fold improvement in corrosion protection properties was observed through accelerated corrosion protection tests in saline water with the developed hybrid inorganic–organic coating process, compared to traditional encapsulation without the SiOx intermediate layer. As a proof-of-concept, the improved packaging of printed antennas, typically used in automobile rooftop shark fin applications, is showcased, highlighting the utility of the developed process in creating fully functional PFEs capable of reliable operation in harsh environmental conditions. This research represents a significant advancement towards scalable and cost-effective manufacturing of high-performance and reliable PFEs, introducing new possibilities for a broad range of applications.