NextFlex

The present generation of additive printable inks used for the realization of conductive circuits are nano-particles in volatile solvents such as isopropyl alcohol, xylene, methyl-ethylketone, formic acid, ethyl alcohol, polyvinyl pyrrolidone (PVP), and sodium borohydride. Environmental, social, and geographic factors have become increasingly important for electronics manufacturing owing to increased attention to sustainability. The use of lower temperature substrates requires a lower thermal ceiling for the processing of additively printed circuits and interconnection of components in comparison with traditional processes, which regularly use SnAgCu solders and a processing range of <tex>$200-300 \mathrm{C}$</tex>. Furthermore, the realized assemblies' reliability compared to traditional electronics is not well understood. The current paper addresses this void in the state of art. This study explores direct write, aerosol-jet, and screenprinting methods to fabricate circuits with water-based inks, biodegradable substrates, and low-temperature interconnects, comparing them to designs using VOC-based inks. The circuits have been subjected to sustained high temperatures of 85C to quantify the stability, reliability, and long-term performance of the circuits. Substrates examined include biodegradable PET (bPET) and seed paper. Circuits have been fabricated with aqueous and non-aqueous silver conductible ink, including amplifiers, oscillators, differentiators, integrators, and filter circuits for signal processing. Component attachment for the circuits has been performed using electrically conductive adhesive (ECA) and low-temperature solder (LTS). The circuits have been subjected to long-term accelerated life cycling to study the effect on trace resistance and output response provided by circuits printed with both inks. Furthermore, the printed circuits were subjected to a repairability study wherein the attached components were manually removed; the component pads then underwent site redressal using relevant conductible material, followed by curing and subsequent testing to compare the repaired performance with that of the pristine circuit.

Abstract The application of room-temperature curable adhesive and water-based ink offers an economical and sustainable method in the field of electronics production. On the other hand, little is known about how encapsulation and thermal cycling affect the functionality of circuits fabricated using these materials. The purpose of this study is to look into how thermal cycling circumstances and encapsulation techniques affect the reliability and performance of circuits made with room-temperature curable adhesive and water-based ink. Understandings from this research will fill this knowledge gap and improve the processes involved in the design and production of environmentally friendly electronic circuits, leading to the development of sustainable electronics technology. Even with the progress made in electronics production, not much is known about how encapsulation will affect the thermal cycling reliability of a circuit made with water-based ink and room-temperature curable adhesive. Comprehensive studies addressing the performance and reliability test of circuits made using this environmentally friendly method are lacking in the current literature. This lack of systematic studies that examine these circuits’ behavior in different environmental settings — like thermal cycling with encapsulation procedures — is the limitation. As a result, the lack of knowledge makes it difficult to optimize manufacturing procedures and compromises the production of robust, reliable electronics made of eco-friendly materials. It is crucial to address this shortcoming to further sustainable electronics technology and encourage the electronics industry to embrace environmentally friendly manufacturing practices. This paper investigates the effect of encapsulation in flexible printed circuits fabricated with water-based inks and room-temperature curable adhesives, undergoing thermal cycling processes. A comparison will be made between the encapsulated and non-encapsulated circuits manufactured with room-temperature processable interconnects, coupled with water-based inks, for both test designs: individual components test and functional circuit test. The study includes the realization of a differentiator circuit through aerosol jet printing, employing room temperature interconnects for component attachment, and comparing the performance of encapsulated circuits with that of the non-encapsulated circuit, under Thermal Cycling.

Abstract Rapid progress in technology necessitates an in-depth understanding of the enduring reliability of flexible printed circuitry constructed using different connecting materials. The adaptability of flexible printed circuits and their potential applications in a wide range of electronic devices, from automotive systems to wearable electronics, has garnered substantial interest in recent years. Thermal aging is an important factor that might potentially compromise the structural integrity and performance of electronic assemblies used in real-world applications. The reliability of flexible printed circuit assembly, particularly the bonding materials employed, is critical to the effective integration of flexible printed circuits into various applications. To gain a better understanding of the adhesive’s reliability under thermal aging, this study intends to carefully examine the effects of thermal aging on flexible printed circuitry. The objective of this study is to fill a gap in the literature by thoroughly investigating how thermal aging affects flexible printed circuit assemblies that are fabricated with room-temperature curable adhesives and high-temperature curable adhesives. This paper investigates processes aimed at achieving interconnects suitable for room-temperature processes, along with the use of water-based inks in printed electronics. The research delves into the examination of electrical performance and reliability tests within functional electronic circuitry. A comparison is made between the performance of low-temperature processable interconnects, coupled with water-based inks, and high-temperature processable interconnects for both test designs: individual components test and functional circuit test. The study includes the realization of a differentiator circuit through aerosol jet printing, employing low-temperature interconnects for component attachment. The circuit’s response is then compared with the simulated output. Finally, both the fabricated circuits are subjected to a thermal aging test for 1000 hours at a temperature of +85°C.

Flexible hybrid electronics (FHE) have gained popularity due to their speed and soft tooling, and their applications in various sectors like consumer electronics, automotive, healthcare, and transportation. Historically, printed circuits used volatile organic solvent-based inks, which have been criticized for their environmental impact. However, water-based inks have emerged as a promising alternative, offering a significantly reduced environmental footprint. This study aims to explore the application of biodegradable PET substrates in the aerosol jet printing process, which is known for fabricating 3D and 2D surfaces on micron scales. Key components were attached to the circuits using electrically conductive adhesives. The evaluation included a detailed analysis of component performance, mechanical stability, and electrical performance. The study also examined the electrical properties of the circuits, focusing on resistance values across varying sintering temperatures and durations. Preliminary findings suggest that modifying these parameters can enhance electrical properties, with optical methods used to characterize printed trace outcomes. This paper presents a pioneering foray into the utilization of biodegradable PET substrates in sustainable electronics manufacturing, offering insights into potential enhancements in environmental sustainability without compromising on functional efficacy.

Earlier generations of flexible electronic devices were often fabricated using high-temperature processable interconnect materials. These high-temperature processable interconnects provided distinct benefits, such as low resistivity and higher mechanical strength, but also exhibited drawbacks, including higher energy consumption and the need for high-temperature capable substrate materials. In addition, the earlier generation of printed electronics was realized using volatile organic solvent carrier inks. In this paper, processes for the realization of room-temperature processable interconnects along with water-based inks in printed electronics have been examined. This research focuses on the study of electrical performance and reliability within functional electronic circuitry. The performance of low-temperature processable interconnects in conjunction with water-based inks has been compared with high-temperature processable interconnects for both single components and functional circuits. A differentiator circuit has been realized using aerosol jet printing with both high- and low-temperature interconnects for component attachment. The magnitude and phase response of the circuit has been compared with the theoretically expected output. Fabricated circuits have been studied for consistency of performance and reliability under thermal cycling in the range of -40°C to +85°C required of automotive grade3 components.

The emergence of additively manufactured electronics has made it possible to integrate safety features into automotive touch surfaces for the assessment of driver alertness and state of stress. Current touch surfaces in vehicles are mainly for aesthetics, but integrating human-machine interfaces through additively printed in-mold electronics is a potential advancement. The processes for printing sensors and integrating surface mount electronics for signal processing in additively printed conformal electronics are still unknown. In-mold electronics provide additional opportunities for the elimination of wire harnesses and lightweighting of the vehicle to meet stricter CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> emission standards and reduce carbon footprint. This paper investigates direct ink write, and gravure offset print processes for thermoformed in-mold electronics on diverse substrates. Surface mount component attachment is explored using conductive adhesive and creating signal processing and electrodermal sensors for measuring galvanic skin response, useful in assessing driver emotions and health. The study aims to establish fabrication guidelines for in-mold electronic circuits, including ink print parameters, curing times for ink and adhesive, and thermoforming parameters for optimal electrical performance and mold conformity.

Abstract The earlier generation of additive printable inks was based on volatile organic solvent carrier fluids. Increased awareness of the environmental impact of electronic waste has resulted in the emergence of environmentally friendly water-based inks with low-impact waste. The repairability of additively printed circuits can be used to reduce electronic waste and enable life extensions of deployed electronics through repair and replacement. However, the repairability potential, processes, and impact on reliability are relatively unexplored for new sustainable materials. This study consists of a thorough study of component attachment and the reparability of the components on performance and reliability. Repair procedures have been pursued on circuits printed with sustainable conductive ink on an aerosol jet printer (AJP). Adhesives are printed on the pads at the location where the component is to be attached using a direct-write technique that can print highly viscous materials such as ECA. This procedure entails attaching a component to a flexible printed circuit, measuring the output response, removing the attached component from the circuit, replacing it with a new component of the same rated value, measuring the output again, and comparing it to the prior output and the simulated output. Furthermore, the mechanical strength of the attached components is characterized in terms of shear load to failure. The force required to remove the attached component using a metal tip before and after the repair is compared for each of the passive components. Finally, a functional differentiator circuit is used to validate the findings.

Abstract Throughout the past decade, the field of printed electronics has gained increased research impetus and has started to make entryways into the consumer electronics product market. The applications of additive printed electronics are numerous and range from healthcare devices and smart packaging to energy harvesting systems and intelligent textiles. Another novel application area for printed electronics is in-mold electronics (IME) which is a process that involves the integration of printed electronic circuits into injection-molded parts. In this process, electronic circuits are printed onto a thin, flexible substrate, such as polyethylene terephthalate glycol (PETG) or polycarbonate (PC), which is then thermoformed using a mold. The thermoformed sample is then overmolded with another thermoplastic which results is a single, integrated part that combines the functionality of the electronic circuit with the mechanical properties of the plastic part. Using IMEs offers several benefits such as weight and bulk minimization along with maintaining ergonomic design, which are important concerns in automotive design. In this study, additively printed lines have been printed using gravure offset printing technique on different substrates such as PETG and PC have been subjected to vacuum thermoforming wherein the substrates are heated to their heat deflection temperature and vacuum formed on an aluminum mold. The change in resistance of the lines pre- and post-thermoforming, as well as the effect of degree of material stretching of the substrate with different thermoforming parameters such as thermoforming temperature and thermoforming time has been studied. Finally, a component attachment study has been conducted for thermoformed circuits with a functional thermoformed full wave rectifier circuit demonstrator.

Abstract Additively printed thermoformable circuitry for In-Mold Electronics (IME) is getting tremendous research focus because of its numerous advantages: design flexibility, cost-effectiveness, weight reduction, and potential for seamless integration into structural components. This study uses a direct write printing technique to produce conductive FWR circuits using stretchable silver ink. A stretchable ink capable of thermoforming was used for circuit fabrication. Once the conductive traces were printed, SMDs were joined to the circuit using ECA. An impedance analyzer was used to examine the performance of the additively printed FWR circuit. Thermo-forming capable High Impact Polystyrene sheet and Polycarbonate substrates have been used for this study. The cross-section of the printed lines has been measured using white-light interferometry. The effect of the process parameters on the printed line resistivity has been studied. Optimized parameters from the printing process and sintering analysis are used to print FWR circuitry. The OrCAD software is used to simulate the FWR circuit. The simulated performance of the circuit is compared to the actual output of the printed thermoformed circuit. This work highlights the possibility of an additively printed FWR circuit in IME using a direct write process with thermoformable silver conductive ink and ECA.

Abstract The process of in-mold electronics (IME) is an innovative technology that integrates printed electronics with film insert molding to produce plastic components that contain electronics. The process involves the combination of printing, thermoforming, and injection molding to create complex and customized electronic devices. This technology has found numerous applications in various industries, including automobile components, household appliances, and consumer electronics, where customized user interfaces are required to manage or monitor the system. A customized user interface is required for a variety of applications in automotive, industrial electronics, and consumer technology to manage or monitor the system. Knobs, pressure and toggle switches, analog instruments, and flat-screen technology with touch sensor capabilities are also options. The key advantage of IME technology is its ability to create flexible and stretchable electronic devices capable of functioning under strain when bent, stretched, and deformed. Despite its potential, the IME process faces several challenges. One of the critical factors affecting the performance of IME products is the electrical resistance of the printed circuit, which changes during thermoforming. This presents a significant design challenge, as over-deformation of printed circuits can lead to poor performance and reliability issues. In this study, we have developed new design strategies and methods to optimize the performance of the IME process. This includes the use of electrically conductive adhesives to attach components in their undeformed state and later subject to thermoforming. This approach helps to maintain the integrity of the printed circuit and improve the performance of the interconnects. To evaluate the performance of the IME process, we have employed the OrCAD software to build and simulate a digital circuit. The performance of the inverting circuit was compared and evaluated against the tolerance limits of the COTs.