Effect of substrate properties on isothermal fatigue of aerosol jet printed nano-Ag traces on flex
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Effect of substrate properties on isothermal fatigue of aerosol jet printed nano-Ag traces on flex Roshan Muralidharan1, Arun Raj1, Rajesh Sharma Sivasubramony1, Manu Yadav1, Mohammed Alhendi1, Matthew Nilsson1, Christopher Greene1, Mark D. Poliks1, Peter Borgesen1,a) 1
System Science and Industrial Engineering, Binghamton University, Binghamton, New York 13902, USA Address all correspondence to this author. e-mail: [email protected]
a)
Received: 20 March 2019; accepted: 20 June 2019
Sintered nanoparticle structures are macroscopically brittle but quite robust if deposited on a flexible substrate. The effects of a polymer substrate on the stretchability of both brittle and ductile coatings and traces are well established. Systematic effects of substrate properties on the fatigue resistance of aerosol printed nano-Ag are slightly more complex. The present work is focused on the early stages of fatigue, where the resistance increases significantly but cracks are not yet visible. Overall, the fatigue behavior is seen to vary with the combination of substrate modulus and viscoelastic deformation properties. Comparing two common polyimides, the rate of damage was seen to increase faster with increasing amplitude on the less compliant one. Consistently with this increasing the minimum strain in the cycle led to a significantly stronger reduction in damage rates. However, the damage rate remained lower on the less compliant substrate at all amplitudes and strain ranges of practical concern.
Introduction Inkjet, screen printing, and aerosol jet printing (AJP) offer widely advertised benefits for applications to flexible hybrid electronics. Each of these technologies and the individual materials involved lead to very different advantages and limitations [1, 2] but both the effective resistivity and its increase under a moderate strain are invariably higher than for, say, electroplated Cu. Depending very much on the flexible electronics application, the associated reliability concerns are often very different from those that we are used to for conventional electronics, but one concern common to a wide variety of products is fatigue of the conductors [3, 4]. As for other materials, the response to repeated loading is much more complex than the effects of a monotonically increasing load [3, 4, 5, 6, 7]. A comprehensive ongoing study of the combined and often interactive effects of design, process, and materials parameters, ambient exposure, long-term aging, and thermomechanical history aims to identify and characterize the degradation and damage mechanisms with the goal of allowing for optimization and perhaps even prediction of actual reliability under realistic use conditions. The present work is
ª Materials Research Society 2019
focused on a small part of this, interactions between AJP nanoAg traces and two common flex substrates. Initial sintering of the printed traces leads to the formation of a highly porous network of fused Ag nanoparticles [Fig. 1(a)]. This is very different from many inkjet or screenprinted trace
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