CAMBRIDGE, UK – Flexible hybrid electronics promises to combine the extensive processing capability of ICs with a flexible form factor, and with printed rather than etched conductive interconnects. This combination of attributes opens application possibilities and could be a $3 billion market by 2030, according to IDTechEx.

FHE provides a compelling technological approach toward the vision of ubiquitous electronics, says the firm. The combination of flexibility, processing/communication capability and compatibility with low-cost, high-volume continuous manufacturing methods is unique to FHE, but applicable to many different sectors.

Perhaps the most compelling opportunity for FHE is ubiquitous, low-cost wirelessly-enabled RFID sensors, says IDTechEx. These could be employed in industrial and environmental monitoring and in smart packaging. Such capability is a prerequisite for connected devices and the Internet of Things.

At present, passive RFID tags are produced by the billion. The firm estimates some 18 billion RFID tags will be produced in 2020. Passive RFID tags are only capable of communicating with a reader when specifically addressed. Furthermore, their only functionality is identification. FHE would enable RFID sensors that can monitor other attributes such as temperature, humidity, stress and strain at specified intervals, and then transmit that information either to a reader or via wireless networks.

RFID sensors will need to be manufactured in large volumes with a low cost per unit, requiring roll-to-roll manufacturing, which is currently employed for passive RFID tags. Adapting this method to FHE introduces some considerable challenges, since FHE circuits require a thinned die, and likely other passive components, to be mounted onto a flexible substrate, says IDTechEx.

Relative to basic RFID ICs that have limited functionality, thinned FHE ICs have much higher aspect ratios and more I/O pads, increasing both fragility and registration requirements during placement. Differential thermal expansion coefficients between polymeric substrates and silicon ICs pose additional challenges for robust attachment, particularly if the circuit is going to be exposed to a wide range of temperatures, such as in automotive applications.

Given this challenge, the production, handling and attachment of thinned dies are an innovation area. The research firm forecasts RFID sensors will start becoming widely adopted in 2025, with over 5 billion units sold per year by 2030.

The widespread adoption of RFID sensors requires them to be as cheap as possible, says the firm. This precludes the use of expensive PI (polyimide) substrates, which will likely be replaced with PET (and even paper for smart packaging applications).

This transition in substrate materials imposes challenges in that conventional lead-free solder can no longer be used. The development of component attachment methods that are compatible with thermally fragile substrates is an area of innovation, including both low-temperature solder, novel anisotropic conductive adhesives, and photo-sintered solder.

Conductive ink, required for the printed interconnects in an FHE circuit, provides another opportunity for cost reductions. Currently, most conductive ink is silver-based, but is intrinsically expensive due to the price of silver metal (around 400 $/kg). Copper-based inks are potentially much cheaper but have long suffered from unwanted oxidation that reduces conductivity. Developing stable copper inks with at least equivalent conductivity to silver inks, while reducing the curing times and temperatures to facilitate rapid manufacturing with thermally fragile substrates, is thus a substantial area of innovation.

FHE is a new approach to electronic circuits that bridges the gap between printed and conventional electronics, by combining flexibility with processing capability, along with the potential for both agile and continuous manufacturing methods. This combination of attributes is ideally suited to applications including smart packaging, wearable devices and industrial/environmental monitoring. Challenges, and hence innovation areas, are transitioning to cheaper thermally fragile substrates and low-temperature attachment methods, lowering the conductive ink, and making FHE circuit production compatible with R2R manufacturing.

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