High‐Conductivity Crack‐Free 3D Electrical Interconnects Directly Printed on Soft PDMS Substrates. Issue 12 (22nd June 2022)

• Record Type: Journal Article
• Authors: Brenneman, Jacob; Tansel, Derya Z.; Fedder, Gary K.; Panat, Rahul
• Is Part Of: Advanced materials technologies. Volume 7:Issue 12(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-06-22
• Subjects: 3D printing -- aerosol jet printing -- nanoparticle ink -- reliable interconnects -- stretchable electronics; Materials science -- Periodicals; Technological innovations -- Periodicals; Materials science; Technological innovations; Periodicals; 620.1105
• DOI: 10.1002/admt.202200396
• Languages: English
• ISSNs: 2365-709X

Abstract

Abstract: Nanoparticle 3D printing and sintering is a promising method to achieve freeform interconnects on compliant substrates for applications such as soft robotics and wearable healthcare devices. However, previous strategies to sinter metallic nanoparticles while preserving the soft polymer substrate are rife with problems such as cracking and low conductivity of the metallic features. In this paper, the mechanisms of cracking in nanoparticle‐based 3D printed and sintered stretchable interconnects are identified and architecture and processing strategies are demonstrated to achieve crack‐free interconnects fully embedded in thin (<100 μm in thickness) stretchable polydimethylsiloxane (PDMS) with external connectivity. Capillary forces between nanoparticles developed through rapid solvent evaporation in the colloidal ink is hypothesized to initiate cracking during drying. Additionally, the presence of oxygen promotes the removal of organic surfactants and binders in the nanoparticle ink which increases nanoparticle agglomeration, grain growth, and subsequently conductivity. An experimental step‐wise variation of the thermal/atmospheric process conditions supports this hypothesis and shows that the presence of air during a low temperature drying step reduces the capillary stress to produce crack‐free interconnects with high conductivities (up to 56% of bulk metal) while having an excellent compatibility with the underlying polymer materials. Finally, stretchable interconnects fully‐encapsulated in PDMS polymer, with 3D pillar architectures for external connectivity are demonstrated, thus also solving an important "last‐mile" problem in the packaging of stretchable electronics. Abstract : A hybrid air and vacuum thermal process is developed to sinter printed 3D electrical interconnects directly on a soft stretchable substrate utilizing a low temperature drying step in air followed by a higher temperature sintering step under vacuum to preserve the material properties of the soft polymer, while achieving a highly conductive crack‐free stretchable electrical interconnect.