Preparation of selective conductive copper patterns by pen-on-paper writing combined with electroless plating

Abstract

Conductive Cu patterns were constructed on flexible paper via selectively electroless plating method, which including multistep procedures, namely, 3-aminopropyltrimethoxysilane (APTMS)-modification, selective Cu⁰-seeding and Cu-lines deposition. Herein, the Cu⁰ activation process could be divided into two stages: the Cu²⁺-absorption in cupric citrate solution and subsequently the Cu²⁺-reduction using a roller pen filled with sodium borohydride ink. The interaction of APTMS onto paper was confirmed by FT-IR measurement and the results indicated that the –NH₂ groups originating from APTMS were grafted on the paper. The elemental analysis of the samples in each step was conducted using XPS measurement. Paper-based conductive patterns were investigated by SEM, XRD and Scotch^®-tape test. SEM images illustrated that the Cu lines on the APTMS modified paper substrate was compact and composed of ball-shaped copper nuclei. Moreover, the Cu lines could be selectively plated on the required area of the paper substrate. XRD analysis showed that the obtained Cu patterns had a structure with Cu (1 1 1) preferred orientation, revealing an excellent electromigration resistivity. The resultant Cu patterns exhibited an admired adhesion to modified paper, while the Cu patterns obtained in absence of APTMS modification suffered a failure in the adhesive Scotch^®-tape test. The resistivity of copper patterns characterized by the digital four-point probe was 10.3 µΩ cm, which was 6.3 times of the bulk Cu. Meanwhile, paper-based Cu pattern remained excellent conductivity after multifolding. Those results indicated that the method proposed in the present work offered a robust and efficient alternative to manufacture flexible electronics.