3D Printed Interconnects for Heterogenous Integration on Flexible Substrates

Flexible hybrid electronics (FHE) that combines thin silicon (Si) chips and printed electronics has emerged as a practical solution to achieve high-performance with features such as flexible form factors and large area integrations. However, there are several manufacturing and integration challenges that need to be addressed for effective use of FHEs in emerging applications such as wearables, robotics etc. These include fabrication and integration of fragile ultrathin chips (UTCs), printed electronics with high-performance and uniform response over large area and forming high-resolution interconnects without damaging thin chips, suitable encapsulating etc. The high-resolution metal interconnects are particularly the major limiting factor when integration of UTCs is considered. This is because traditional bonding methods do not offer the desired solution due to thermal and mechanical mismatches. As a potential solution for this issue, we present in this paper the drop-on-demand jet printing-based approach for realizing the conductive tracks and 3D micropillars to access the contact pads on UTCs. The challenges experienced in forming robust and reliable high-resolution 3D printed interconnects are also discussed. The presented approach builds on our recent work on high aspect ratio (52) and high resolution (diameter ~4μm) out-of-plane printed conductive micropillars and offers a resource-efficient alternative for formation of interconnects in FHE systems as well as new opportunity for other applications such as measurement of 3D cellular activity in tissue generation.