A novel process utilizing specialized continuous inkjet (CIJ) printing technology and innovative conductive inks to fabricate three-dimensional electronic products is introduced in the current investigation. The major advantage of the CIJ process is that it not only provides a fast and cost-effective method for applying electronic components, but it also allows the printing of conductive traces in three-dimensional space. The greatest challenge for inkjet printing of electrical circuits is the formulation of the conductive inks, which define not only the convenience of the materials being deposited, but also the final comprehensive properties and the major expense. Several conductive inks were investigated and compared mainly based on their electric conductance and mechanical adherence to a substrate. Two different particle-free solution conductive inks were specifically researched for low cost, deposition convenience and improved properties. A novel aqueous solution of silver nitrate with a corresponding adhesion promoter is introduced for the first time. It has been found that the traces produced by the process have excellent adherence and have an electrical resistivity of only 2.9 times that of bulk silver. Low temperature curing plus further annealing of a specified metallo-organic decomposition (MOD) ink produces close-packed silver crystal substructures. The electrical conductance of the final conductive trace was close to that of bulk silver, and wearability was significantly improved from ductile deformation. These two particle-free solution inks are expected to find a number of applications in various industries.Fundamental concepts in formulating and post-processing of inkjet printing are fully discussed. The two primary problems faced by inkjet printed components are low deposited thickness and porosity. An interlayer oxide film was found to be necessary to bond the precious metal layer with the glass substrate. Porosity can be significantly reduced through high temperature annealing, which not only increases electrical conductance, but also mechanical strength. Special curing methods are proposed to consolidate the printed conductors and avoid overheating of temperature sensitive substrates.
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