Nanomechanical characterization of conductive printed ink with silver nanoparticles

Silver nanoparticles are used in printed electronics for improving conductivity of deposited conductive paths. The nanoparticles can be sintered at lower temperatures which allows their deposition also on polymers. This application report shows how to measure the effects of sintering on mechanical properties of conductive ink with silver nanoparticles.

Printed electronics (PE) includes methods that are used to print thin electronic devices on various substrates. It has attracted great attention because the printing process is well mastered and it is relatively cheap. PE enables manufacturing of large area flexible electronics components or even create 3D electronic structures. All these features have opened many new areas of applications. These include wearable electronics such as oxygen and blood pressure sensors, RFID patches, flexible screens, intelligent labels, antennas, etc.
Many methods in printed electronics use deposition of conductive inks. The ink is generally not conductive until printed on the substrate and sintered. The new types of conductive ink contain polymeric binder with silver (Ag) nanoparticles. Silver has excellent electric conductivity and being a noble metal, it has excellent resistance to oxidation. It is also easy to control the final nanomorphology of Ag particles which can take form of nanospheres, nanotubes or nanowires. One of the biggest advantages of inks with Ag nanoparticles is that they do not require high sintering temperature. Sintering is a thermal process done at elevated temperature after the ink deposition and it transforms the non-conductive layer to conductive layer.
While electric properties of inks are crucial for printed electronic devices, their mechanical properties and namely adhesion is of also of great interest: inks are often deposited on flexible substrates and they must have excellent adhesion to avoid premature delamination. There are various deposition (printing) and sintering methods in which the printing and namely sintering parameters can vary. It is therefore important to understand how the process parameters affect the mechanical properties and adhesion of the ink. Scratch test and nanoindentation are excellent tools for such investigation and they bring new insights on the influence of sintering on the mechanical properties of the printed ink layer.
This application report shows how different sintering temperatures affect mechanical properties of very thin printed ink layers containing Ag nanoparticles. The adhesion of the layers was measured using nano scratch test and their hardness and elastic modulus by low load nanoindentation.

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