No abstract

No abstract

Growing advances in printed flexible electronics enable novel design and manufacturing processes of electrical circuits and components in aircraft and automotive industries, [1][2][3] as well as in consumer electronics for fabrication of printed passive components, semiconductor devices, and sensing elements. [4][5][6][7][8][9][10][11][12][13][14][15] In the healthcare domain, the impact of printed electronics becomes more profound and offers a wide range of applications from printed RF coils for medical imaging, [16] biochemical sensing, [17,18] vital sign monitoring [19][20][21][22][23][24][25] to assistive wearable devices. [26,27] At the industrial level, its low cost and high-throughput manufacturing process are the key motivators for transition from conventional solutions to printed technologies. In wearable applications, its capability to realize soft wearable sensors, which can comply with the dynamic deformations of human skin, is attractive.Despite the promising opportunities of printed electronics in different domains, there are concerns regarding the reliability of printed materials (i.e., conductive inks, isolators, and adhesives) and their interconnections to electronic components for longterm use in real-life applications. Over the past decade, there has been an increasing number of studies on the reliability of printed conductors, interconnections, and chip-on-flex assembly. As a fundamental test, the cyclic bending endurance of printed conductors was investigated to analyze the characteristics of conductive tracks on a flexible substrate. [28][29][30] In more complicated test protocols, the influence of environmental parameters (e.g., temperature, humidity, etc.) was included in the test procedure. [31] More advanced test setups and protocols were developed to evaluate the reliability of complex hybrid integration of chip-on-flex, flexto-flex assemblies, and roll-to-roll (R2R) printed circuits. [32][33][34] This work presents a comprehensive study on the reliability of hybrid integration of thinned bare die chip on soft and stretchable substrate. More specifically, the findings of this study are expected to provide fundamental insights on the failure mechanisms, their corresponding contributors, and ways to minimize them. This study is divided into three phases as shown in Figure 1A. In the screening phase, the electromechanical performance of five different ink variants is evaluated and the most suitable ink variants are selected to be used in combination with three different types of conductive adhesive for fabrication and assembly of the test device. In the last phase of the study, the fabricated test devices are tested through a cyclic strain test and a comprehensive analysis of failure mechanisms is performed. The importance of the failure analysis is recognized in refining of the design steps, material selection, and processing parameters for improved reliability.

In the recent years, there has been a growing interest towards printed stretchable electronics used in diagnostics, health-monitoring, and wearable applications. Double-sided electronic circuits with through-substrate vias offer a solution where the amount of printed circuitry and assembled SMDs (surface-mount devices) in direct contact with the human skin can be minimized. This improves not only the wearability and cost-effectiveness of the printed electronic devices but also the product safety and comfort to wear. Another factor decreasing the unit costs in printed electronics is the use of high volume, high speed, and continuous roll-to-roll (R2R) manufacturing processes. In this current paper, a full R2R process for the manufacturing of through-substrate vias on stretchable thermoplastic polyurethane (TPU) substrate was developed and verified. The through-substrate via-holes were manufactured in R2R using either laser-cutting or die-cutting. Rotary screen printing was used to print conductive tracks onto both sides of the stretchable substrate and to fill the via-holes. Eventually, conductive and stretchable through-substrate vias with low sheet resistance and low resistance deviation were reliably achieved with the developed process.

No abstract