Recently, as research on developing electronic devices for simultaneous implementation of flexibility and conductivity has been continuously conducted, ensuring stable and high reliability of devices in preparation for various mechanical deformation is becoming important. When a physical force such as bending, twisting, or folding is applied, the bonding area between two substrates should ensure stability due to high stress generation. Epoxy resin materials used as standard adhesive agents have brittleness due to the nature of the material, and are weak in terms of flexibility due to increased bonding thickness due to high temperature hardening. In addition, it is difficult to apply as a bonding material in consideration of thermal deformation of the polymer substrate exposed to high temperatures during the process. To improve both flexibility and durability against fatigue deformation, Flexible bonding process is required without adhesive such as epoxy resin with poor brittleness. Surface activation bonding technologies by ion beams and vacuum ultraviolet rays have been developed in previous studies, bonding between plastic substrates by activating thin metal films surface of adhesive layer with ion beam or improving adhesive force by direct-UV radiation on the surface of the polymer substrate. In this study, a flexible bonding process between polymer substrates was developed by heating carbon nanotubes (CNTs) through microwave irradiation. High microwave absorption properties of CNT lead to heat dissipation behavior and light emission characteristics. Heat transfer mechanism of CNT applied to CNT-polymer composites, CNT electrodes fields and has been microwave assisted purification. By utilizing the microwave heating effect, we selected CNT materials for flexible substrates. Multi-walled carbon nanotubes (MWNTs) were coated on a bonded PET polymer substrate and then local heating was performed by microwaves to induce mechanical entanglement between the CNTs and the PET. In the bonding process, the output power of the microwave was adjusted to 600,800 and 1000 Watt, and the bonding strength was evaluated by quantifying the bonding strength was evaluated. For the analysis of the bonding mechanism in the area where mechanical entanglement took place, the CNT-PET bonding interface was analyzed through electron scanning microscope (SEM) measurement, and further analysis was performed for each process condition. In addition, a fracture mechanism analysis that occurred at the junction was performed after the overlapping shear strength test.

Acknowledgments This work was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2020M3H4A3106413, Development of Evaluation Method for Mechanical Deformation of Micro-joints in Micro-LED Module)