Emerging from 2D printed electronics, 3D printed electronics promise a breakthrough in additive manufacturing and prototyping of electronics. However, transferring the know-how from 2D flexible electronics to 3D parts with complex structures (e.g. internal vias and external interconnects) might not be a straightforward approach. As an example, the variation of light intensity with respect to the distance and angle of incidence casts doubt on the efficiency of the intense pulsed laser (IPL) as a robust sintering method for metallic traces in 3D printed bulk structures, whereas IPL is currently by far the most prevailing sintering technique for 2D printed flexible electronics. Sintering of metallic traces in 3D printed parts can be executed either as a sequential layer-by-layer printing and processing step (LP) or as a bulk post-processing step (BP). In the current study, a survey on the most common sintering strategies for inkjet printed silver nanoparticles was conducted, while the compatibility to 3D printed structures was brought into the focal point. To discover the capabilities and limitations of six sintering methods (i. e. IPL, ohmic curing, thermal heating, laser, atmospheric plasma and microwave sintering) for 3D printed electronics, a comparative study utilizing the same materials and diagnostic methods was pursued. The results revealed that for 3D functional parts, some of the sintering techniques can be considered as complementary methods for each other, whereas a few showed readily the potential to be adapted in 3D printed electronics production.

Resistive temperature sensors on two different commercially available uncoated paper substrates have been manufactured using inkjet printing of silver nanoparticles. Their dedication is to be integrated in lightweight materials made from natural fibre-reinforced biopolymers for condition monitoring during the manufacturing process and beyond. The printed sensors have nominal resistances of a few hundred Ohms and kOhms, depending on the roughness and porosity of the respective paper substrate. Compared to previous research in this field, the manufactured sensors were fully characterised and extensively tested as part of this work. Furthermore, the influence of the individual paper characteristics on the electrical properties was studied using white-light interferometry and SEM imaging. All sensors show a good linear temperature dependence, minimal hysteresis and low baseline drift in the temperature range of interest (20 °C–80 °C). In an extended temperature range (−25 °C to 150 °C) and exposed to humidity (0%rH–80%rH) the accuracy and overall quality of the sensors decrease expectedly, still the temperature sensing principle can be exploited depending on the individual application and precision requirements.

To date, additions of different oxide nanoparticles is one of the most widespread procedures to improve the mechanical properties of metals and metal alloys. This research deals with the effect of minor ceramic nanoparticle additions (SiO₂, TiO₂ and ZrO₂) on the microstructure and mechanical properties of Cu/solder/Cu joints. The reinforced Sn3.0Ag0.5Cu (SAC305) solder alloy with 0.5 wt.% and 1.0 wt.% of ceramic nanoparticles was prepared through mechanically stirring. The microstructure of as-solidified Cu/solder/Cu joints was studied using scanning electron microscopy. The additions of ceramic nanoparticles suppressed the growth of the intermetallic compound layer Cu₆Sn₅ at the interface solder/Cu and improved the microstructure of the joints. Furthermore, measurements of mechanical properties showed improved shear strength of Cu/composite solder/Cu joints compared to joints with unreinforced solder. This fact related to all investigated ceramic nanoinclusions and should be attributed to the adsorption of nanoparticles on the grain surface during solidification. However, this effect is less pronounced on increasing the nanoinclusion content from 0.5 wt.% to 1.0 wt.% due to agglomeration of nanoparticles. Moreover, a comparison analysis showed that the most beneficial influence was obtained by minor additions of SiO₂ nanoparticles into the SAC305 solder alloy.

The effect of nanosized Co admixtures on the microstructure and physical properties of Sn–3.8Ag–0.7Cu solder and corresponding solder joints was investigated. The composite Sn–3.8Ag–0.7Cu ribbons with minor additions of Co nanoparticles (up to 1.0 wt%) were fabricated using the conventional planar flow casting method. The structure of nanostructured alloys was studied by X-ray diffraction and transmission electron microscopy. The electrical resistivity of Sn–3.8Ag–0.7Cu ribbons doped with nanoCo was measured by the standard four-point method. The microstructure and mechanical properties of corresponding solder joints (with Cu as substrate) were studied. It was shown that nanoCo additions led to minor changes in the electrical resistivity of Sn–3.8Ag–0.7Cu solder ribbons, while the nanoCo doped Sn–3.8Ag–0.7Cu solder joints (up to 0.5 wt% Co) revealed the reinforced microstructure accompanied by enhanced mechanical properties.