Photonic Curing of Low-Cost Aqueous Silver Flake Inks for Printed Conductors with Increased Yield

Cronin, Harry, Stoeva, Z, Brown, M, Shkunov, Maxim and Silva, Ravi (2018) Photonic Curing of Low-Cost Aqueous Silver Flake Inks for Printed Conductors with Increased Yield ACS Applied Materials & Interfaces Manuscript, 10 (25). pp. 21398-21410.

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Abstract

Printing of highly conductive tracks at low cost is of primary importance for the emerging field of flexible, plastic and large area electronics. Commonly, this is achieved by printing of metallic conductive inks, often based on Ag or Cu nanoparticles dispersed in organic solvents. The solvents must be safely removed and have particular storage and handling requirements, increasing process costs. By using water-based inks containing micron-sized silver flakes both material and process costs can be reduced, making these inks attractive for industrial applications. However, the sintering of flake inks requires higher temperatures than nano-sized inks owing to the particles’ smaller surface area-to-volume ratio, meaning that when cured thermally the conductivity of many flake inks is lower than nano-particle alternatives. This problem can be addressed by the application of visible light photonic curing; however, the substrate must be protected and so process parameters must be defined for each material / substrate combination. Here we report results of a large scale trial of photonic curing of aqueous flake silver inks on PET substrates in an industrial setting. The resistivity of printed patterns after an optimised photo-curing regime matched those reported for typical nano-particle inks; on the order of 100 μΩ.cm depending on substrate and geometry. Scanning electron microscopy (SEM) revealed evidence for structural changes within the printed films consistent with localised melting and necking between adjacent particles, leading to an improved percolation network. Furthermore, in the large-scale industrial trial employing screen printed silver lines, the manufacturing yield of conductive lines was increased from 44% untreated to 80% after photo-curing, and reached 100% when photo-curing was combined with thermal curing. We believe this to be the first reported observation of an increase in the yield of printed electronic structures following photo-curing. We propose a crack-healing mechanism to explain these increases in yield and conductivity. We further report on the effects of the photonic curing on the mechanical bending stability of the printed conductors, and discuss their suitability for wearable applications.

Item Type:	Article
Divisions :	Faculty of Engineering and Physical Sciences > Electronic Engineering
Authors :	Name Email ORCID Cronin, Harry h.cronin@surrey.ac.uk Stoeva, Z Brown, M Shkunov, Maxim M.Shkunov@surrey.ac.uk Silva, Ravi S.Silva@surrey.ac.uk
Date :	4 June 2018
Funders :	EPSRC
DOI :	10.1021/acsami.8b04157
Copyright Disclaimer :	Copyright 2018 American Chemical Society
Depositing User :	Melanie Hughes
Date Deposited :	27 Jun 2018 08:07
Last Modified :	06 Jul 2019 05:25
URI:	http://epubs.surrey.ac.uk/id/eprint/848600

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