Flip Chip Assembly of UHF-ID Electronics on Flexible Substrates

This paper describes the assembly of integrated circuits on flexible substrates in an industrial flip chip process allowing reel-to-reel production. Die bonding concepts to meet future demands for high-throughput solutions at low cost are introduced. Since the range of process parameters such as temperatures and bonding forces is closely linked to the properties of the substrates, an overview of different materials that can be used as flexible substrates is given. Material properties are compared and different processes for metallisation and structuring are described. Furthermore, the multi-stage tag production process is illustrated. Introducing straps, in order to decouple the pre-bonding and final bonding process steps, permits improvement of the achievable throughput and usage of very simple equipment for final assembly-Using these methods, a new type of UHF-ID tag based on thin polymer foil was produced. A unique antenna design matches different impedances and allows the tags to be mounted on different materials with little influence on their read range. Their tenuousness and flexibility allows to hide these tags, for example in cardboard packaging. Possible applications with focus on detecting plagiarism are discussed.