Investigation of fabrication and encapsulation processes for a flexible tag microlab

The aim of this paper is to present an integrated process flow for a smart tag with integrated sensors and RFID communication, a flexible tag microlab (FTM). 

The heart of the designed container tracing system is an RFID system (Reader + Tag) with gas sensing capabilities on board. In the former prototypes, the chemical sensors were integrated on the reader, whereas the tags where addressed like conventional RFID-tags containing also physical (temperature, humidity and light) sensors. However, this paper will show how the gas sensing reader functionalities are being transferred to the tag, reaching a FTM, which represents a real innovation in the field of flexible labels. Key issues for the realisation of the FTM, such us flexible substrates and gas sensor integration technologies will be presented. The process flow employed for the two metal levels interconnect fabrication will be described in detail. The material used is the DuPont (TM) Pyralux (R) AP 8525R double-sided copper-clad laminate, formed by a Kapton foil with a copper layer on each side. The vias and windows openings are performed by femtosecond laser ablation. The copper interconnections are realized by photolithography and wet chemical etching. The MOX sensors hotplates specially developed to fulfil the FTM constrains in terms of low power consumption has been used to prove two integration technologies into the flexible substrates: chip on flex (COF) wire bonding and anisotropic conductive adhesive (ACA) flip chip bonding. Both technologies will be compared and benchmarked for future product developments.