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Best practices for hybridization and injection moulding of rigid control units on in-mould flexible devices

This document presents a study for the construction of an in-mould smart tag as a robust flexible and battery-free label with a radiofrequency energy harvesting sub-system and enhanced geolocation features. Conventional tags based on Printed Circuit Board (PCB) with a protective casing limit the type of objects to be tracked according to their shape and surface material. The proposed tag is intended to be attached to objects such as tools, vehicles, and parts in assembly lines compatible with curved surfaces for their geolocation.

The key innovation of the tag is that it is obtained by In-mould electronics (IME) which combines the functional printing of electronics and the hybridisation of electronic components with traditional plastic transformation processes, such as injection. In the case under study, IME processing is applied over printed antennas with a directly hybridized rigid control module and both elements protected by an over-moulded flexible superstrate.

IME is prompted as a high-speed and competitive manufacturing methodology to ensure robustness and conformability of the tag. IME combines two dissimilar manufacturing processes, which are printed electronics and plastic processing, an already established high-volume production technology based on plastic injection and thermoforming. Polymer embedded antennas have been proven advantageous due to the enhanced protection towards harsh environments, temperatures, wetness and the low-permittivity of polymers which make them a suitable option for higher-frequency applications. Other advanced materials such as nanocellulose-based substrates and highly conductive inks based on silver nanoparticles (Ag NP) are used.

The geotracking tag will consist in a flexible foil based on nanocellulose with a combination of printed antennas (Ultra High Frequency and Ultra Wide Band), a small rigid multipoint control unit part (MCU). Both parts will be fully integrated into a flexible plastic piece through an overmoulding process. Therefore, TPU or related flexible thermoplastic will be the preferred choice.