Printed electronic circuits on low‐temperature plastic substrates have enormous potential across a range of consumer markets, including automotive windows, wearable devices, healthcare devices and smart labels. Many of these applications require a combination of both printed electronics, which offers large area and flexibility at low cost, and conventional silicon electronics which allows much greater functionality. Currently, the main technique used for integrating silicon devices with plastic electronics is Isotropic Conductive Adhesive (ICA) packaging. With this approach, a conductive adhesive (typically a silver‐loaded paste) is printed onto the substrate at sites where electrical connection is required. The silicon device is then placed in position, and the adhesive is cured. The same approach is also being used to mount flexible plastic electronic chips on plastic substrates.
Interconnection Technologies for integration of Active devices with Printed Plastic Electronics (ITAPPE) project we will investigate the use of Non Conductive Adhesive (NCA) packaging as an alternative route for integrating active devices on low‐temperature substrates. With the NCA approach, electrical connections are mediated by conductive bumps on the active device and the role of the adhesive is purely to pull these bumps into contact with the pads on the substrate. NCA packaging offers several advantages over ICA. Firstly, it is more efficient at the point of assembly because it does not require selective deposition of the adhesive; instead, the NCA is dispensed (or applied in film form) over the entire device area. Secondly, it inherently provides an underfill between device and substrate which improves reliability. Thirdly, it is scalable to finer interconnect pitches which will become important in the future. In addition to working on pure NCA packaging, we will also explore the feasibility of using thermosonic (TS) bonding to form metal‐metal micro‐joints between the bumps and the substrate pads. TS bonding uses a combination of heat, pressure and ultrasonic energy to facilitate the formation of direct metal‐metal bonds at lower temperatures and pressures than would be required for thermo‐compression bonding. If a working process can be established for plastic electronics then it will provide more reliable interconnections than any purely adhesive‐based approach.