Enabling paper-based flexible circuits with aluminium and copper conductors

Abstract

Implementing electronics systems on paper is an important area of flexible circuit technologies. One of the approaches is to print conductive inks onto paper substrates, on which silicon-based surface mount device components are mounted. However, one of the problems is that the printed conductors have unneglectable resistivity. In this paper, we present paper-based flexible circuits, using copper and aluminium conductors that are laminated onto paper substrates using a high-speed roll-to-roll method. Edge roughness inspections and repeated two-point bending tests are carried out to evaluate the manufactured flexible circuits. Three surface mount techniques are used to assemble standard surface mount device components onto the flexible circuits, including an isotropic conductive adhesive, an anisotropic conductive adhesive, and a low-temperature solder paste. Several characterizations are performed to the surface mount techniques, including contact resistance measurements, component bonding strength tests, assembled circuit bending tests, and scanning electron microscopy. The results of the characterizations suggest that flexible circuits made from Cu with paper substrate achieve satisfactory results for mechanical reliability, all surface mount techniques, and have the potential to be used on automatic component assembly lines. In order to test whether such flexible circuits and surface mount techniques can be used in implementing electronics systems, passive NFC tags with relative humidity sensing functionality are made, which are interrogated by an NFC equipped mobile phone.