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. These large-area electronic (LAE) systems invariably require active electronic devices, either conventional silicon chips or flexible ICs. Fast and cost-effective methods are therefore needed for attaching active devices to low-temperature plastic electronic substrates. Currently the favoured approach is to use isotropic conductive adhesive (ICA) packaging, whereby a conductive adhesive 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 ITAPPE project investigated the use of Non Conductive Adhesive (NCA) packaging as an alternative route for integrating active devices on low‐temperature substrates. Electrical connections are mediated by conductive bumps on the active device. The role of the adhesive is purely to pull these bumps into contact with the pads on the substrate.
- Investigate the use of non-conductive adhesive (NCA) packaging as an alternative route for integrating active devices on low‐-temperature substrates.
- Explore the feasibility of using thermosonic (TS) bonding* to form metal‐-metal micro‐joints between the bumps and the substrate pads.
- Establish processes suitable for low-temperature polymer substrates with printed conductors, including appropriate methods for handling flexible ICs
*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
ITAPPE was initially established as a 6-month project, but was subsequently extended to 12 months following promising early results.
- Successfully demonstrated NCA processes for attaching both silicon chips and flexible ICs to PET substrates
- Successfully demonstrated TS attachment of flexible ICs to PET substrates
- NCA and TS combined into ‘Thermosonic-adhesive packaging’ process - advantages and findings:
- efficiency at the point of assembly - it does not require selective deposition of the adhesive
- improved reliability by providing underfill between device and substrate
- scalable to finer interconnect pitches which will become important in the future
- reliability improved by including the thermosonic bonding step
- Silicon-to-flex assemblies showed excellent performance in reliability tests
The success of the ITAPPE project led to the development of a new flagship project, SiPEM, which will continue to optimise this novel bonding technique, and develop a system integration technology for LAE based on laminated multilayer structures with embedded active and passive components.
“The ITAPPE Pathfinder project has been an invaluable way to explore a potentially game-changing packaging technology for flexible electronics. Early results are very encouraging and PragmatIC is excited to continue this collaboration with Prof. Holmes.”
Dr Richard Price, CTO