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Fast sintering is of importance in additive metallization processes and especially on sensitive substrates. This work explores the mechanisms which set limits to the laser sintering rate of metal nano-particle inks. A comparison of sintering behavior of three different ink compositions with laser exposure times from micro-seconds to seconds reveals the dominant factor to be the organic content (OC) in the ink. With a low OC silver ink, of 2% only, sintering time falls below 100 μs with resistivity <×4 bulk silver. Still shorter exposure times result in line delamination and deformation with a similar outcome when the OC is increased.

3D printing has seen much progress in recent decades with the introduction of new materials and printing techniques. This article describes the combination of a novel, stereolithography (SLA) based method for structural material buildup with laser induced forward transfer (LIFT) printing of conductive and resistive elements and placement of commercial active and passive components for the additive manufacturing of 3D functional electronic devices. The structural material is composed of dry film photoresists that are exposed and laminated to form a stack which is later developed to remove unexposed area and reveal the desired free form shape. Interconnection using pillar penetration between the structural layers is described in detail. Several examples of functional objects (lamp, microphone) demonstrate the practicality of this novel, multi material printing method.

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A method is described where 3D electronic devices are fabricated using a hybrid printing approach which combines several steps: Top illumination stereolithography (SLA); Laser induced forward transfer (LIFT) printing of conductive materials; Placement of active and passive components and their electrical interconnection by a non-contact, metal LIFT process. By applying this approach, free-form 3D functional electronic structures could be manufactured by a single hybrid tool. The adhesion of LIFT printed metal droplets onto various organic substrates of interest for device fabrication was investigated. The results suggest two possible approaches for improved adhesion by either printing at elevated surface temperature or surface roughening by laser pre-treatment. The resulting track resistivities were found to be in the range of x5-10 higher than bulk copper resistivity. We present several exemplary printed devices with different complexities and functionalities as demonstrators of the proposed hybrid technology. &#xD;