Conductive traces printed onto compatible flexible substrates to interconnect conventional silicon-based components and printed components are key building blocks and technologically unique to flexible hybrid electronics (FHE). This form of innovative integration offers durability, flexibility, conformity, and low-temperature processing of particular relevance to applications in fields such as wearable medical devices, IoT, solar cells, communications, aerospace, and defense. [1-7] Moreover, it enables new use of materials and a wide range of applications and functionalities. This facilitate in producing low power-consumption devices allowing for rapid and large volume production at low cost. [8,9] Printed traces are fabricated using techniques such as screen printing, inkjet printing, precision dispensing, and aerosol jet printing (AJP), depending on key ink properties including the ink viscosity. [10] Among these, AJP is probably the most attractive method for fabrication of printed electronics. Fine features down to 10 μm trace width and spacing, large stand-off distances, a large ink matrix, and design flexibility are the key advantages of AJP technique. [11] AJP process starts by atomization of an ink either pneumatically (used in this study) or ultrasonically, depending on the ink viscosity and solid content size and percentage (Table 1). In the pneumatic atomizer, an inert gas (nitrogen) is applied into the ink container to form mists/aerosols of the ink (around 1-5 μm diameter). Then the aerosol flow is carried out using a carrier gas to the deposition head passing by the virtual impactor where the aerosols are filtered based on their inertia. In the deposition head, a surrounding sheath gas flow (nitrogen) is used to collimate and direct the aerosols flow stream into the substrate. Figure 1 summarizes the working principle of the pneumatic atomization. The AJP print quality is governed by many factors including ink and substrate properties and their interaction,

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Sintered copper nano particles are being considered as alternatives to solder and/or sintered silver in different applications. Like for the alternatives, interpretation of accelerated fatigue test results does however require modeling, typically involving prediction of stresses and strains vs. time and temperature based on constitutive relations. This poses a challenge as the inelastic deformation properties depend strongly on both the initial particles and details of the processing, i.e. unlike for solder general constitutive relations are not possible. The present work provides a mechanistic description of the early transient creep of relevance in cycling, including effects of sintering parameters and subsequent oxidation. Inelastic deformation is dominated by diffusion, rather than dislocation motion. Generalized constitutive relations are provided to the extent that quantitative modeling of a specific structure only requires the measurement of a single creep curve for that.

The inelastic deformation properties of sintered metal nanoparticle joints are complicated by the inherent nanocrystalline and nanoporous structures as well as by dislocation networks formed in sintering or under cyclic loading. Creep rates of sintered nanocopper structures were found to be dominated by the diffusion of individual atoms or vacancies, while dislocation motion remained negligible up to stresses far above those of practical interest. Rapid sintering of one material led to unstable structures the creep of which could be strongly reduced by subsequent annealing or aging. Longer sintering of another material led to more stable structures, but creep rates could still be strongly enhanced by subsequent work hardening in mild cycling.