Technical Abstracts
In Case You Missed It
Soldering
“Influence of Ultrasounds on Interfacial Microstructures of Cu-Sn Solder Joints”

Authors: Xu Han, et al.

Abstract: This study aims to investigate the interfacial microstructures of ultrasonic-assisted solder joints at different soldering times. Solder joints with different microstructures are obtained by ultrasonic-assisted soldering. To analyze the effect of ultrasounds on Cu6Sn5 growth during the solid-liquid reaction stage, the interconnection heights of solder joints are increased from 30 to 50µm. Scallop-like Cu6Sn5 nucleate and grow along the Cu6Sn5/Cu3Sn interface under the traditional soldering process. By comparison, the authors observed some Cu6Sn5 are formed at Cu6Sn5/Cu3Sn interface, and some Cu6Sn5 are randomly distributed in Sn when ultrasonic-assisted soldering process is used. The reason for the formation of non-interfacial Cu6Sn5 has to do with the shock waves and micro-jets produced by ultrasonic treatment, which leads to separation of some Cu6Sn5 from the interfacial Cu6Sn5 to form non-interfacial Cu6Sn5. The local high pressure generated by the ultrasounds promotes the heterogeneous nucleation and growth of Cu6Sn5. Also, some branch-like Cu3Sn formed at the Cu6Sn5/Cu3Sn interface render the interfacial Cu3Sn in ultrasonic-assisted solder joints present a different morphology from the wave-like or planar-like Cu3Sn in conventional soldering joints. Meanwhile, some non-interfacial Cu3Sn are present in non-interfacial Cu6Sn5 due to reaction of Cu atoms in liquid Sn with non-interfacial Cu6Sn5 to form non-interfacial Cu3Sn. Overall, full Cu3Sn solder joints are obtained at ultrasonic times of 60 sec. (Soldering and Surface Mount Technology, July 2021, www.emerald.com/insight/content/doi/10.1108/SSMT-06-2020-0026/full/html)

Sustainable Electronics
“Recycling of Nanowire Percolation Network for Sustainable Soft Electronics”

Authors: Yuxuan Liu, et al.

Abstract: Researchers at North Carolina State University have demonstrated a low-cost technique for retrieving nanowires from electronic devices that have reached the end of their utility, and then using those nanowires in new devices. The researchers demonstrated an approach that allows them to recycle nanowires, and think it could be extended to other nanomaterials – including nanomaterials containing noble and rare-earth elements. “Our recycling technique differs from conventional recycling,” says Yong Zhu, corresponding author and professor of mechanical and aerospace engineering at NC State. “When you think about recycling a glass bottle, it is completely melted down before being used to create another glass object. In our approach, a silver nanowire network is separated from the rest of the materials in a device. That network is then disassembled into a collection of separate silver nanowires in solution. Those nanowires can then be used to create a new network and incorporated into a new sensor or other devices.” (Advanced Electronic Materials, July 2021; https://onlinelibrary.wiley.com/doi/abs/10.1002/aelm.202100588)

Transfer Printing
“Instant, Multiscale Dry Transfer Printing by Atomic Diffusion Control at Heterogeneous Interfaces”

Authors: Seungkyoung Heo, et al.

Abstract: Transfer printing is a technique that integrates heterogeneous materials by readily retrieving functional elements from a grown substrate and subsequently printing them onto a specific target site. These strategies are broadly exploited to construct heterogeneously integrated electronic devices. A typical wet transfer printing method exhibits limitations related to unwanted displacement and shape distortion of the device due to uncontrollable fluid movement and slow chemical diffusion. In this study, a dry transfer printing technique that permits reliable and instant release of devices by exploiting the thermal expansion mismatch between adjacent materials is demonstrated, and computational studies are conducted to investigate the fundamental mechanisms of the dry transfer printing process. Extensive exemplary demonstrations of multiscale, sequential wet-dry, circuit-level, and biological topography-based transfer printing demonstrate the potential of this technique for many other emerging applications in modern electronics that have not been achieved through conventional wet transfer printing over the past few decades. (Science Advances, July 2021; https://www.science.org/doi/10.1126/sciadv.abh0040)

Others of Note
Discovery of new types of defects in 2-D materials may give insight into how to create materials without such imperfections, leading to better ultra-compact electronic devices, according to a group of Penn State researchers. (https://phys.org/news/2021-08-2d-material-defects-enable-electronics.html)

Recently, there has been renewed interest in mature thin film silicon technologies for display backplanes and sensing applications. However, the presence of kink effect remains a challenge for TFT design. (https://onlinelibrary.wiley.com/doi/10.1002/aelm.202100533)

This column provides abstracts from recent industry conferences and company white papers. Our goal is to provide an added opportunity for readers to keep abreast of technology and business trends.