Pulsed Photonic Curing of Conformal Printed Electronics

As next-generation electronic products emerge, there is a need to create more electronic functionality in compact spaces. One of the techniques to achieve this is by integrating electronic circuitry on mechanical stress bearing parts of electro-mechanical products. Direct-write printing processes like inkjet printing and aerosol jet printing can be used to print conductive inks on conformal surfaces of mechanical components. Advanced curing/sintering processes such as pulsed photonic curing can be used to cure/sinter printed inks to produce conductive traces. However, the use of photonic curing on conformal surfaces introduces two sources of variability into the process, which are the distance and slope between the flash lamps and the conformal substrate. This research studies the effects that distance and slope between the flash lamps and substrate have on the characteristics of the photonically cured material. Screen printed samples of copper nanoparticle ink on paper substrates were photonically cured at various distances and slope settings in a Novacentrix Pusleforge 3300 machine. Analysis of the experimental data reveals that there is significant decrease in the conductivity of the cured copper ink with increase in both the distance and slope between the flash lamps and the substrate. The lowering of conductivity of the coupons with increase in distance was correlated to the reduction in the intensity of pulsed light with distance from the source. Similarly, the lowering of conductivity of the coupons with increase in slope was correlated to the reduction in the intensity of pulsed light with increase in angle between the incident light and the surface normal. A spectrophotometer was used to correlate the lowering of the conductivity of the printed coupon to the reduction in the amount of light absorbed by the coupon surface with increase in the slope from the flash lamps. This research highlights that distance and slope variations are important considerations to achieve uniform electrical properties in conformal printed electronics undergoing photonic curing

Additive manufacturing of copper vertical interconnect accesses by laser processing

This paper introduces a new manufacturing process for vertical interconnect accesses (VIA). In contrast to industrially established VIA metallization technologies, the presented approach takes place without any chemical plating by combining copper ink and epoxy insulator coating with CO2 laser processing for VIA drilling and copper ink sintering. The minimum VIA resistances are less than 50 mΩ, fitting the theoretically calculated value. A laboratory application scenario testing a 10 × 10 contact pad array with a pitch of 800 µm successfully demonstrates routing across five printed metallization layers, including 128 blind and 112 buried VIA. © 2021 The Author

Integration of Ultrasonic Consolidation and Direct-Write to Fabricate an Embedded Electrical System Within a Metallic Enclosure

A research project was undertaken to integrate Ultrasonic Consolitation (UC) and Direct-Write (DW) technologies into a single apparatus to fabricate embedded electrical systems within an ultrasonically consolidated metallic enclosure. Process and design guidelines were developed after performing fundamental research on the operational capabilities of the implemented system. In order to develop such guidelines, numerous tests were performed on both UC and DW. The results from those tests, as well as the design and process guidelines for the fabrication of an embedded touch switch, can be used as a base for future research and experimentation on the UC-DW apparatus. The successful fabrication of an embedded touch switch proves the validity of the described design and process parameters and demonstrates the usefulness of this integration

Comparative Study of Inkjet-Printed Silver Conductive Traces With Thermal and Electrical Sintering

Thermal sintering has traditionally been the most popular sintering method to enhance conductivity after the printing process in the manufacturing of printed electronics. Nevertheless, in recent years, there has been a growing interest in electrical sintering as an alternative method to overcome some of the limitations of thermal curing. This paper makes a comparative study of both sintering methods in terms of surface morphology, electrical dc conductance, and radiofrequency performance for different applied voltage waveforms. To this end, microstrip transmission lines have been inkjet-printed using nanoparticle-based silver ink on flexible polyimide substrate. The traces have been tested under different sintering conditions, achieving electrical sintering resistivity values only 2.3 times higher than that of bulk silver. This implies a 62% reduction in comparison with the best resistivity value achieved using thermal sintering in our samples. The main novelty of this contribution lies in the analysis of RF behavior as a function of electrical sintering conditions. Lower resistivities have been achieved with slower voltage ramps or allowing higher density current during sintering. It has also been proved that electrically sintered lines have similar RF performance than high-temperature thermally sintered lines in terms of insertion losses, regardless of their very different surface topology. Therefore, we can take advantage of the benefits that electrical sintering offers over thermal sintering regarding significant shorter sintering times maintaining suitable RF performance.This work was supported in part by the Spanish Ministry of Economics and Competitiveness under Grant CTQ2016-78754-C2-1-R

Flat-plate solar array project. Volume 5: Process development

The goal of the Process Development Area, as part of the Flat-Plate Solar Array (FSA) Project, was to develop and demonstrate solar cell fabrication and module assembly process technologies required to meet the cost, lifetime, production capacity, and performance goals of the FSA Project. R&D efforts expended by Government, Industry, and Universities in developing processes capable of meeting the projects goals during volume production conditions are summarized. The cost goals allocated for processing were demonstrated by small volume quantities that were extrapolated by cost analysis to large volume production. To provide proper focus and coverage of the process development effort, four separate technology sections are discussed: surface preparation, junction formation, metallization, and module assembly

Flash processing of copper electrodes printed from copper oxide nanoparticle ink

Deposizione di inchiostro di nanoparticelle di rame ossido tramite tecnologie di stampa tradizionali e conversione e sinterizzazione delle nanoparticelle tramite tecnologia "intense pulsed light

Conductive inks and films via intense pulsed light.

This research focuses on the investigation of Earth abundant copper and carbon based nanomaterials that are subjected to Intense Pulsed Light Processing to create conductive films, as future flexible electronics and renewable energy solutions would benefit from the quick and scalable production of conductive films. Use of nanomaterials in their oxide/hydroxide forms leads to higher stability in aqueous inks for efficient large area solution deposition. IPL Processing utilized 2044 μs pulses ranging from 589 J - 2070 J over an area of 1.9 cm x 30.5 cm, with energy densities of 10.1, 12.8, 15.8, 19.2, 22.9, 26.8, 31.1 and 35.7 Jcm-2, of non-coherent white light in wavelengths ranging from UV to NIR (240 nm – 1,000 nm) through a xenon lamp. The rapid pulses induce localized temperature increases in the films, flexible plastic substrates can be used without degradation. Three different morphological systems and nanomaterials were studied: 1D (copper hydroxide nanowires), 2D (Graphene Oxide nanosheets), and 3D (cuprous oxide encapsulated by nickel oxide nanoparticles & also copper nitrate hydroxide nanoparticles). The nanomaterials were rapidly reduced into conductive films via Intense Pulsed Light Processing aided through the organic decomposition of additives, providing a reducing environment. Through inclusion of different materials and morphologies, nanoscale manipulations can lead to breakthroughs in advanced materials and additive manufacturing. Cu2O (20nm) nanoparticles encapsulated with a NiO layer were synthesized to explore protecting the Cu from oxidation and diffusion into Si based photovoltaic applications. The room temperature synthesis and IPL processes easily prevented formation of alloys at the copper-nickel interface. The encapsulation was shown to reduce Cu diffusion into Si. Copper nitrate hydroxide, Cu2(OH)3NO3, was synthesized under ambient conditions with copper nitrate and potassium hydroxide reagents and processed by IPL. Films were deposited by screen-printing and then subjected to IPL Processing. Since Cu2NO3(OH)3 isn’t a thermally stable material, initially transformed into CuO. However, when fructose or glucose were intentionally included as additives in the inks, IPL Processing provided direct conversion of the Cu2(OH)3NO3 into Cu. Between the two sugars, fructose was more advantageous as it led to faster reduction and lower sheet resistances, with the lowest sheet resistance being 0.224 Ω/□. Graphene oxide was reduced with Intense Pulsed Light Processing to explore potential towards scalable conductive films without the need for harsh/toxic reductants. The graphene oxide films on displayed a four magnitude decrease in sheet resistance from 55.1 MΩ/□. to 2280 Ω/□ after IPL. Plastic substrates required less energy to display reduction, with a four magnitude decrease in sheet resistance (62.5 MΩ/□. to 3.43 kΩ/□.) after IPL. When combined with Cu(OH)2 nanowires at weight percentages of 1.82%, 8.47%, and 32.65%, films exhibited decreased sheet resistances by 25%, 45%, and 66%, respectively

Design and Development of Non-Equilibrium Plasmas for the Medical Field

There is great interest in the plasma research community on the potential medical applications of non-equilibrium plasmas, called cold atmospheric plasma (CAP), yet currently no such plasma device is approved by the US Food and Drug Administration (FDA). This dissertation seeks to take a holistic look at five novel plasma systems with potential use in the medical field. These systems are all analyzed from an engineering point of view to characterize the plasma and basic biocompatibility from an electrical and thermal approach. The overall design life-cycle for these devices is also examined, with an emphasis on deciding an approval pathway through the Food and Drug Administration, where the intended use of the device is the driving factor. The first device considered is a nanosecond puling circuit devised for skin electroporation. An electrode is developed to help maximize the electric field applied to a substrate and ensure user safety. Voltage and current traces and optical emission spectroscopy are used to characterize the plasma generated for various substrates, showing the non-equilibrium behavior of the plasma for a wide operating range. The second device considered is an existing FDA-cleared electrosurgical device power supply and hand piece, which has been modified for use as a CAP source. By varying the tube length the plasma can be operated in a non-equilibrium state. The third device is a direct write system for depositing thin films in a controlled pattern. This system consists of a dielectric barrier discharge jet attached to a three-dimensional printer head for spatially controlling the plasma location. Various methods of depositing material are used, including directly onto biological substrates. The final two devices are for improving the strength of additively manufactured parts intended for use in custom printed prosthetics. The first is a nanosecond pulsed discharge onto a printed part, which shows 100% strength improvement from the plasma treatment. The second is a planar dielectric barrier discharge mounted onto the head of a three-dimensional printer, which is able to print parts with the same strength as injection molded parts

Printing conductive traces to enable high frequency wearable electronics applications

With the emergence of the Internet of Things (IoT), wireless body area networks (WBANs) are becoming increasingly pervasive in everyday life. Most WBANs are currently working at the IEEE 802.15.4 Zigbee standard. However there are growing interests to investigate the performance of BANs operating at higher frequencies (e.g. millimetre-wave band), due to the advantages offered compared to those operating at lower microwave frequencies. This thesis aims to realise printed conductive traces on flexible substrates, targeted for high frequency wearable electronics applications. Specifically, investigations were performed in the areas pertaining to the surface modification of substrates and the electrical performance of printed interconnects. Firstly, a novel methodology was proposed to characterise the dielectric properties of a non-woven fabric (Tyvek) up to 20 GHz. This approach utilised electromagnetic (EM) simulation to improve the analytical equations based on transmission line structures, in order to improve the accuracy of the conductor loss values in the gigahertz range. To reduce the substrate roughness, an UV-curable insulator was used to form a planarisation layer on a non-porous substrate via inkjet printing. The results obtained demonstrated the importance of matching the surface energy of the substrate to the ink to minimise the ink de-wetting phenomenon, which was possible within the parameters of heating the platen. Furthermore, the substrate surface roughness was observed to affect the printed line width significantly, and a surface roughness factor was introduced in the equation of Smith et al. to predict the printed line width on a substrate with non-negligible surface roughness (Ra ≤ 1 µm). Silver ink de-wetting was observed when overprinting silver onto the UV-cured insulator, and studies were performed to investigate the conditions for achieving electrically conductive traces using commercial ink formulations, where the curing equipment may be non-optimal. In particular, different techniques were used to characterise the samples at different stages in order to evaluate the surface properties and printability, and to ascertain if measurable resistances could be predicted. Following the results obtained, it was demonstrated that measurable resistance could be obtained for samples cured under an ambient atmosphere, which was verified on Tyvek samples. Lastly, a methodology was proposed to model for the non-ideal characteristics of printed transmission lines to predict the high frequency electrical performance of those structures. The methodology was validated on transmission line structures of different lengths up to 30 GHz, where a good correlation was obtained between simulation and measurement results. Furthermore, the results obtained demonstrate the significance of the paste levelling effect on the extracted DC conductivity values, and the need for accurate DC conductivity values in the modelling of printed interconnects