Investigation of the Mechanical and Electrical Properties of Elastic Textile/Polymer Composites for Stretchable Electronics at Quasi-Static or Cyclic Mechanical Loads

In the last decade, interest in stretchable electronic systems that can be bent or shaped three-dimensionally has increased. The application of these systems is that they differentiate between two states and derive there from the requirements for the materials used: once formed, but static or permanently flexible. For this purpose, new materials that exceed the limited mechanical properties of thin metal layers as the typical printed circuit board conductor materials have recently gained the interest of research. In this work, novel electrically conductive textiles were used as conductor materials for stretchable circuit boards. Three different fabrics (woven, knitted and nonwoven) made of silver-plated polyamide fibers were investigated for their mechanical and electrical behavior under quasi-static and cyclic mechanical loads with simultaneous monitoring of the electrical resistance. Thereto, the electrically conductive textiles were embedded into a thermoplastic polyurethane dielectric matrix and structured by laser cutting into stretchable conductors. Based on the characterization of the mechanical and electrical material behavior, a life expectancy was derived. The results are compared with previously investigated stretchable circuit boards based on thermoplastic elastomer and meander-shaped conductor tracks made of copper foils. The microstructural changes in the material caused by the applied mechanical loads were analyzed and are discussed in detail to provide a deep understanding of failure mechanisms.EC/H2020/825647/EU/Re-Thinking of Fashion in Research and Artist collaborating development for Urban Manufacturing/REFREA

Washability of e-textiles: current testing practices and the need for standardization

Washability is seen as one of the main obstacles that stands in the way of a wider market success of e-textile products. So far, there are no standardized methods for wash testing of e-textiles and no protocols to comparably assess the washability of tested products. Thus, different e-textiles that are deemed equally washable by their developers might present with very different ranges of reliability after repeated washing. This paper presents research into current test practices in the absence of e-textile-specific standards. Different testing methods are compared and evaluated and the need for standardized testing, giving e-textile developers the tools to comparably communicate and evaluate their products’ washability, is emphasized

The Realization of Redistribution Layers for FOWLP by Inkjet Printing

The implementation of additive manufacturing technology (e.g., digital printing) to the electronic packaging segment has recently received increasing attention. In almost all types of Fan-out wafer level packaging (FOWLP), redistribution layers (RDLs) are formed by a combination of photolithography, sputtering and plating process. Alternatively, in this study, inkjet-printed RDLs were introduced for FOWLP. In contrast to a subtractive method (e.g., photolithography), additive manufacturing techniques allow depositing the material only where it is desired. In the current study, RDL structures for different embedded modules were realized by inkjet printing and further characterized by electrical examinations. It was proposed that a digital printing process can be a more efficient and lower-cost solution especially for rapid prototyping of RDLs, since several production steps will be skipped, less material will be wasted and the supply chain will be shortened.EC/H2020/737487/EU/(Ultra)Sound Interfaces and Low Energy iNtegrated SEnsors/SILENS

Recent Advances and Challenges of Nanomaterials-Based Hydrogen Sensors

Safety is a crucial issue in hydrogen energy applications due to the unique properties of hydrogen. Accordingly, a suitable hydrogen sensor for leakage detection must have at least high sensitivity and selectivity, rapid response/recovery, low power consumption and stable functionality, which requires further improvements on the available hydrogen sensors. In recent years, the mature development of nanomaterials engineering technologies, which facilitate the synthesis and modification of various materials, has opened up many possibilities for improving hydrogen sensing performance. Current research of hydrogen detection sensors based on both conservational and innovative materials are introduced in this review. This work mainly focuses on three material categories, i.e., transition metals, metal oxide semiconductors, and graphene and its derivatives. Different hydrogen sensing mechanisms, such as resistive, capacitive, optical and surface acoustic wave-based sensors, are also presented, and their sensing performances and influence based on different nanostructures and material combinations are compared and discussed, respectively. This review is concluded with a brief outlook and future development trends

Development and Characterization of a Novel Low-Cost Water-Level and Water Quality Monitoring Sensor by Using Enhanced Screen Printing Technology with PEDOT:PSS

A novel capacitive sensor for measuring the water-level and monitoring the water quality has been developed in this work by using an enhanced screen printing technology. A commonly used environment-friendly conductive polymer poly(3,4-ethylenedioxythiophene):poly (styrenesulfonate) (PEDOT:PSS) for conductive sensors has a limited conductivity due to its high sheet resistance. A physical treatment performed during the printing process has reduced the sheet resistance of printed PEDOT:PSS on polyethylenterephthalat (PET) substrate from 264.39 Ω/sq to 23.44 Ω/sq. The adhesion bonding force between printed PEDOT:PSS and the substrate PET is increased by using chemical treatment and tested using a newly designed adhesive peeling force test. Using the economical conductive ink PEDOT:PSS with this new physical treatment, our capacitive sensors are cost-efficient and have a sensitivity of up to 1.25 pF/mm

Washable, Low-Temperature Cured Joints for Textile-Based Electronics

Low-temperature die-attaching pastes for wearable electronics are the key components to realize any type of device where components are additively manufactured by pick and place techniques. In this paper, the authors describe a simple method to realize stretchable, bendable, die-attaching pastes based on silver flakes to directly mount resistors and LEDs onto textiles. This paste can be directly applied onto contact pads placed on textiles by means of screen and stencil printing and post-processed at low temperatures to achieve the desired electrical and mechanical properties below 60 °C without sintering. Low curing temperatures lead to lower power consumption, which makes this paste ecological friendly

On the Feasibility of Fan-Out Wafer-Level Packaging of Capacitive Micromachined Ultrasound Transducers (CMUT) by Using Inkjet-Printed Redistribution Layers

Fan-out wafer-level packaging (FOWLP) is an interesting platform for Microelectromechanical systems (MEMS) sensor packaging. Employing FOWLP for MEMS sensor packaging has some unique challenges, while some originate merely from the fabrication of redistribution layers (RDL). For instance, it is crucial to protect the delicate structures and fragile membranes during RDL formation. Thus, additive manufacturing (AM) for RDL formation seems to be an auspicious approach, as those challenges are conquered by principle. In this study, by exploiting the benefits of AM, RDLs for fan-out packaging of capacitive micromachined ultrasound transducers (CMUT) were realized via drop-on-demand inkjet printing technology. The long-term reliability of the printed tracks was assessed via temperature cycling tests. The effects of multilayering and implementation of an insulating ramp on the reliability of the conductive tracks were identified. Packaging-induced stresses on CMUT dies were further investigated via laser-Doppler vibrometry (LDV) measurements and the corresponding resonance frequency shift. Conclusively, the bottlenecks of the inkjet-printed RDLs for FOWLP were discussed in detail.EC/H2020/737487/EU/(Ultra)Sound Interfaces and Low Energy iNtegrated SEnsors/SILENS

Bondfolie, elektronisches Bauelement und Verfahren zur Herstellung eines elektronischen Bauelements

Die vorliegende Anmeldung betrifft eine Bondfolie (301), ein elektronisches Bauelement (1) und ein Verfahren zur Herstellung eines elektronischen Bauelements (1). Die vorgeschlagene Bondfolie (301) ist geeignet zum Aufbringen auf einen Halbleiterchip (104) und eine Leiterplatte (201) und ist weiterhin geeignet zum Verbinden von zumindest einer Kontaktfläche (105) des Halbleiterchips (104) mit zumindest einer Kontaktfläche (204) der Leiterplatte (201). Die Bondfolie (301) weist eine erste elektrisch isolierende Folie (403), eine auf der ersten elektrisch isolierenden Folie (403) angeordnete Leiterzugschicht (404) und eine auf der Leiterzugschicht (404) angeordnete zweite elektrisch isolierende Folie (405) auf. Außerdem weist die Bondfolie (301) eine auf der zweiten elektrisch isolierenden Folie (405) angeordnete obere elektrisch leitende Abschirmungsschicht (406) und/oder eine untere elektrisch leitende Abschirmungsschicht (402) auf, wobei die erste elektrisch isolierende Folie (403) auf der unteren elektrisch leitenden Abschirmungsschicht (402) angeordnet ist. Die erste elektrisch isolierende Folie (403) weist zumindest ein erstes Durchgangsloch (303) zum Anordnen über der Kontaktfläche (105) des Halbleiterchips (104) auf. Außerdem weist die erste elektrisch isolierende Folie (403) zumindest ein zweites Durchgangsloch (302) zum Anordnen über der Kontaktfläche (204) der Leiterplatte (201) auf. Darüber hinaus weist die Leiterzugschicht (404) einen zwischen dem ersten Durchgangsloch (303) und dem zweiten Durchgangsloch (302) verlaufenden und mit dem ersten und dem zweiten Durchgangsloch (303, 302) überlappenden Leiterzug (409) auf. Weiterhin überlappen elektrisch leitende Bereiche der oberen elektrisch leitenden Abschirmungsschicht (406) beziehungsweise der unteren elektrisch leitenden Abschirmungsschicht (402) mit dem Leiterzug (409) zumindest bereichsweise

Entwicklung eines neuartigen, quantitativen Adhäsionsmessverfahren für Dünnfilmlagen in der Mikroelektronik

New packaging technologies like Fan-Out lead to a higher integration density causing the layer interfaces to experience a higher stress due to the more dense packaging of materials with different properties e.g. a different coefficient of thermal expansion. This work presents a novel test method (Stripe Lift-off Test - SLT) for the adherence characterization of thin film layers used in microelectronics like the interdielectric polymer layers. The method is based on a modified edge lift-off test (mELT). The value for the adherence of the polymer layer on different material surfaces, like silicon, silicon dioxide and metals, can be measured. Based on the results of the test, the critical energy release rate (J/m²) can be estimated, which allows the quantification of the interface’s fracture toughness. The energy release rate sets the basics for fracture simulation of microelectronic devices and could be used for packaging reliability predictions. Due to the usage of intrinsic forces, no clamping or gluing of the layer is necessary for the adhesion measurement. The measurement can be done at room temperature – in contrast to a mELT, which is running at negative temperatures. Exemplary adhesion measurements are presented for polymer films

Development and status of Cu ball/wedge bonding in 2012

Starting in the 1980s and continuing right into the last decade, a great deal of research has been published on Cu ball/wedge (Cu B/W) wire bonding. Despite this, the technology has not been established in industrial manufacturing to any meaningful extent. Only spikes in the price of Au, improvements in equipment and techniques, and better understanding of the Cu wire-bonding process have seen Cu B/W bonding become more widespread-initially primarily for consumer goods manufacturing. Cu wire bonding is now expected to soon be used for at least 20% of all ball/wedge-bonded components, and its utilization in more sophisticated applications is around the corner. In light of this progress, the present paper comprehensively reviews the existing literature on this topic and discusses wire-bonding materials, equipment, and tools in the ongoing development of Cu B/W bonding technology. Key bonding techniques, such as flame-off, how to prevent damage to the chip (cratering), and bond formation on various common chip and substrate finishes are also described. Furthermore, apart from discussing quality assessment of Cu wire bonds in the initial state, the paper also provides an overview of Cu bonding reliability, in particular regarding Cu balls on Al metalization at high temperatures and in humidity (including under the influence of halide ions)