Sustained Percolation in Stretched Silver Nanowire Networks for Stretchable Inter-Connection Applications
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Sustained Percolation in Stretched Silver Nanowire Networks for Stretchable InterConnection Applications Jae Sung Park1, and Woo Soo Kim1 1 School of Mechatronic Systems Engineering, Simon Fraser University, Surrey, B.C. Canada V3T 0A3
ABSTRACT Here we introduce a highly stretchable Printed Circuit Board (PCB) inter-connection technology achieved through the combination of flexibility allowed by the silver nanowire (AgNW)-based electrode and stretchability provided by the meander-shaped substrate. Horseshoe-shaped elastic material, polydimethylsiloxane, is used as a substrate of the AgNW conductors for relaxed stress concentration. Continuously maintained 2-D percolation of stretchable AgNW networks overcomes the usage restrictions with ordinary rigid Printed Circuit Board (PCB). The horseshoe-shaped inter-connection is physically reliable with repeated stretching/releasing processes and maintains its conductivity under tensile strains up to 20 %, allowing the durable and stretchable PCB inter-connecting applications.
INTRODUCTION Nowadays, the printed circuit boards (PCBs) are broadly used on electronic devices in various shapes, sizes, and materials. As the next-generation flexible electronic devices are emerging [1], the flexible PCBs have been studied and developed in diverse ways [2–3]. But these approaches require cost-ineffective electron beam evaporation and sputtering process. Here, we present a cost-effective stretchable inter-connection that can be readily used for ordinary PCBs fabricated by normal manufacturing process. The polydimethylsiloxane (PDMS) was chosen as a substrate of the stretchable interconnection thanks to its well-known mechanical durability proved by its usages in various electrical applications [4–5]. The other key element in the stretchable inter-connection is the stretchable electrode. The AgNWs are employed as the electrode in this study to gain benefits of its great conductivity, mechanical flexibility and low-cost simple applications [6-9]. Based on the recent researches [10-11], the polydopamine was used to enhance hydrophilicity therefore, increasing adhesion strength between AgNWs and PDMS. One other important factor for superior mechanical durability of the electrode depends on its physical design. Optimized horseshoe-shaped electrode was designed and adopted here to minimize stress concentration [12]. In this study, we introduce a stretchable PCB inter-connection as in Figure 1, which is allowed by highly flexible AgNWs electrode spray-deposited on polydopaminetreated PDMS substrate.
Figure 1. Digital photographic image of the stretchable PCB inter-connection made by AgNWs spraydeposition on the horseshoe-patterned PDMS substrate.
EXPERIMENTAL DETAILS The PDMS substrate which has shape of 1500 µm-thick horseshoe structure standing on top of 500 µm-thick plane film was obtained through the casting method of 3g PDMS liquid (Sylgard 184 elastomer kit, w/w = 1:10) with 7 cm × 3.6 cm-sized acrylic mold designed and laser cut respectively by graphical software (CorelDraw X6) a
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