Mechanical durability of RFID chip joints assembled on flexible substrates (2012)

Purpose The purpose of this paper is to investigate the durability of radio‐frequency identification (RFID) chips assembled on flexible substrates (paper and foil), with materials evaluated with regard to mechanical stresses and dependence on the applied substrate, antenna materials, chip pad printing and chip encapsulation. Design/methodology/approach RFID chips were assembled to antennas screen printed on flexible substrates. Shear and bending tests were conducted in order to evaluate the mechanical durability of the chip joints depending on the materials used for mounting the RFID chip structures. X‐ray inspection and cross sectioning were performed to verify the quality of the assembly process. The microstructure and the resistance of the materials used for chip pads were investigated with the aim of determining the conductivity mechanism in the printed layers. Findings Addition of carbon nanotubes to the conductive adhesive (CA) provided a higher shear force for the assembled RFID chips, compared to the unmodified conductive adhesive or a polymer paste with silver flakes. However, this additive resulted in an increase in the material's resistance. It was found that the RFID substrate material had a significant influence on the shear force of mounted chips, contrary to the materials used for printing antennas. The lower shear force for chips assembled on antennas printed on paper rather than on foil was probably connected with its higher absorption of solvent from the pastes. Increasing the curing temperature and time resulted in an additional increase in the shear force for chips assembled to antennas printed on foil. A reverse dependence was observed for chips mounted on the antennas made on paper. An improvement in the durability of the RFID chip structures was achieved by chip encapsulation. Bending tests showed that a low‐melting adhesive was the best candidate for encapsulation, as it provided flexibility of the assembled structure. Research limitations/implications Further studies are necessary to investigate the mechanical durability of RFID chips assembled with a conductive adhesive, with different addition levels and types of carbon nanotubes. Practical implications The results revealed that the best candidate for providing the highest RFID chip durability related to mechanical stresses was the low‐melting adhesive. It can be recommended for practical use, as it simplified the assembly process and reduced the curing step in the encapsulation of the RFID devices. From the results of shear testing, conductive adhesives with carbon nanotubes can be used in RFID chip assembly because of their ability to increase the shear force of joints created between the antenna and the chip. Originality/value In this paper, the influence of the materials used for antenna, chip pads, encapsulation and the curing conditions on the mechanical durability (shear and bending) of RFID chips was analyzed. Commercial and elaborated materials were compared. Some new materials containing a conductive adhesive and carbon nanotubes were proposed and tested in RFID chip assembly to antennas printed on flexible substrates (paper and foil).