Electrical and mechanical properties of RFID chip joints assembled on flexible substrates

Abstract

Purpose – The purpose of this paper is to examine electrical and mechanical properties of radio frequency identification (RFID) chip joints assembled on a flexible substrate and made from isotropic conductive adhesives (ICAs) reinforced with graphene nanoplatelets (GPNs) or graphite nanofibers (GFNs). Design/methodology/approach – The ICAs reinforced with GPNs or GFNs were prepared and screen printed on a test pattern to investigate resistance and thickness of these adhesive layers. Differential Scanning Calorimetry (DSC) was performed to assess a curing behaviour of the prepared ICAs. Then, RFID chips were mounted with the prepared ICAs to the pattern of silver tracks prepared on foil. Shear test was carried out to evaluate mechanical durability of the created chip joints, and resistance measurements were carried out to evaluate electrical properties of the tested ICAs. Findings – The 0.5 per cent (by weight) addition of GFNs or GPNs to the ICA improved shear force values of the assembled RFID chip joints, whereas resistance of these modified adhesives increased. The DSC analysis showed that a processing temperature of the tested adhesives may range from 80 to 170°C with different curing times. It revealed a crucial influence of curing time and temperature on electrical and mechanical properties of the tested chip joints. When the chip pads were cured for too long (i.e. 60 minutes), it resulted in a resistance increase and shear force decrease of the chip joints. In turn, the increase of curing temperature from 80 to 120°C entailed improvement of electrical and mechanical properties of the assembled chips. It was also found that a failure location changed from the chip – adhesive interface towards the adhesive – substrate one when the curing temperature and time were increased. Research limitations/implications – Further investigations are required to examine changes thoroughly in the adhesive reinforced with GFNs after a growth of curing time. It could also be worth studying electrical and mechanical properties of the conductive adhesive with a different amount of GFNs or GPNs. Practical implications – The tested conductive adhesive reinforced with GFNs or GPNs can be applied in the production of RFID tags because it may enhance the mechanical properties of tags fabricated on flexible substrates. Originality/value – Influence of GFNs and GPNs on the electrical and mechanical properties of commercial ICAs was investigated. These properties were also examined depending on a curing time and temperature. New conductive materials were proposed and tested for a chip assembly process in fabrication of RFID tags on flexible substrates.