Epoxy Resin-Assisted Cu Catalytic Printing for Flexible Cu Conductors on Smooth and Rough Substrates

Abstract

Flexible copper conductors have been extensively utilized in flexible and wearable electronics. They can be fabricated by using a variety of patterning techniques such as vacuum deposition, photolithography, and various printing techniques. However, vacuum deposition and photolithography are costly and result in material wastage. Moreover, traditional printing inks require posttreatment, which can damage flexible substrates, or grafting polymers, which involve complex processes to adhere to flexible substrates. Therefore, this study proposes a facile method of fabricating flexible metal patterns with high electrical conductivities and remarkable bonding forces on a diverse range of flexible substrates. Catalytic ink was prepared by using a mixture of epoxy resin, copper nanopowder, and nanosilica. The ink was applied to a variety of flexible substrates, including a poly­(ethylene terephthalate) (PET) film, polyimide film, and filter paper, using screen printing to establish a bridge layer for subsequent electroless deposition (ELD). The catalytic efficiency was significantly improved by treating the cured ink patterns with air plasma. The fabricated flexible metals exhibited excellent adhesion and desirable electrical conductivity. The sheet resistance of the copper layer on the PET substrate decreased to 9.2 mΩ/□ after 150 min of ELD. The resistance of the flexible metal on the PET substrate increased by only 3.125% after 5000 bending cycles. The flexible metals prepared in this study demonstrated good foldability, and the samples with filter paper and PET substrates failed after 40 and 70 folds, respectively. A pressure sensor with a bottom electrode consisting of a copper interdigital electrode on a PET substrate displayed favorable sensing performance.

Enhancing the Delamination Efficiency of Polyimide–Copper Bilayers with UV/Heat-Activated Foamable Adhesive: Insights and Applications

“…Some flexible films possess a degree of stretch or deformation that surpasses the flexibility of epoxy. While epoxy typically demonstrates brittleness, flexibility is crucial for certain types of electronic devices. , In its rigid state, epoxy is unsuitable for flexible substrate or bending applications . Likewise, when applied to a PI film, neat epoxy adhesive lacks flexibility and displays low adhesion, resulting in adhesion failure.…”

Recent Progress in Wearable Near-Sensor and In-Sensor Intelligent Perception Systems

“…Reducing the thickness of rigid functional materials such as ITO, mica and metal conductors is a method used to obtain stretching and bending properties. For example, metal oxide epitaxial thin films grown on flexible substrates also exhibit good flexibility [52][53][54]. In order to alleviate the concentration of stress, the thickness of rigid materials can be thinned, which can significantly reduce defects.…”