In Case You Missed It

Nanoscale Printing

“Curvilinear Soft Electronics by Micromolding of Metal Nanowires in Capillaries”
Authors: Yuxuan Liu, et al.
Abstract: Soft electronics using metal nanowires have attracted notable attention attributed to their high electrical conductivity and mechanical flexibility. High-resolution complex patterning of metal nanowires on curvilinear substrates remains a challenge, however. Here, a micromolding-based method is reported for scalable printing of metal nanowires, which enables complex and highly conductive patterns on soft curvilinear and uneven substrates with high resolution and uniformity. Printing resolution of 20μm and conductivity of the printed patterns of ~6.3 × 106S/m are achieved. Printing of grid structures with uniform thickness for transparent conductive electrodes (TCEs) and direct printing of pressure sensors on curved surfaces such as glove and contact lens are also realized. The printed hybrid soft TCEs and smart contact lens show promising applications in optoelectronic devices and personal health monitoring, respectively. This printing method can be extended to other nanomaterials for large-scale printing of high-performance soft electronics. (Science Advances, Nov. 18, 2022; https://doi.org/10.1126/sciadv.add6996)

Solder Reliability

“Intermediate Low-Melting-Temperature Solder Thermal Cycling Enhancement Using Bismuth and Indium Microalloying”
Authors: Young-Woo Lee, Tae-Kyu Lee and Jae-Pil Jung
Abstract: In general, SnAgCu solder is widely used for interconnections in semiconductor device packaging. Recently, however, several factors have been considered to implement low-melting-temperature solder (LTS), which has a lower assembly temperature than conventional SnAgCu solder material. Implementation of LTS solder though has a different driving force per each industry sector. Consumer electronics seek lower energy consumption, toward a carbon net-zero strategy, compared to the high-performance chip industry sector, which has a different reason based on larger component size-induced challenges, like dynamic warpage. Printed circuit board (PCB) and package components show deformation during reflow due to elevated temperatures. The behavior of dynamic component changes the package size, material characteristics and temperature range. Although most LTS are based on the low-melting-temperature range of 130°-140°C, a separate category of intermediate LTS is formed at around 180°-190°C to target an assembly peak temperature of 200°-210°C. The study presented here targets an LTS at an intermediate temperature assembly to avoid the most active dynamic warpage temperature region. LTS has significant benefits with less warpage and thermal damage toward the component and assembled board, due to the low reflow peak temperature. To improve thermal cycling performance by maintaining a low melting temperature, a small amount of indium is used as a microalloy element, with 12mm × 12mm ball grid array components on 62-mil-thick boards thermal cycled from -40° to 125°C with Sn-based LTS including In and Bi. The microstructure changes during thermal cycling are observed and electron-backscattered diffraction used to find a correlation between crack propagation and localized recrystallization. It was found that the added indium enhanced thermal cycling performance compared to conventional SnAgCu-based solders. To compare the paste-induced composition change which dilutes the indium-containing solder ball, a flux-only assembly has been compared. (Journal of Electronic Materials, Dec. 25, 2022; https://doi.org/10.1007/s11664-022-10121-y)

Sustainability

“A New Approach to Designing Easily Recyclable Printed Circuit Boards”
Authors: Dmitriy Khrustalev, et al.
Abstract: Due to the ever-increasing amount of electronic waste (e-waste) worldwide, the problem of the effective disposal of printed circuit board waste (WPCB), which are environmentally hazardous, difficult to recycle and economically valuable products, has become a major environmental challenge. Conventional WPCB recycling techniques have low efficiency and require tough processing, such as heat treatment and high pressure. This paper presents a new composite material for the manufacture of printed circuit boards (PCB) that can be easily recycled into their original components and reused. In addition, the most valuable PCB components (electronic components containing precious metals) can be easily separated from the printed circuit board and reused. This study demonstrates the benefit of using biodegradable polymers as binders for PCBs in terms of environmentally friendly and efficient recycling. (Scientific Reports, Dec. 23, 2022; https://doi.org/10.1038/s41598-022-26677-y)

Wireless Electronics

“Wirelessly Powered Large-area Electronics for the Internet Of Things”
Authors: Luis Portilla, et al.
Abstract: Powering the increasing number of sensor nodes used in the Internet of Things creates a technological challenge. The economic and sustainability issues of battery-powered devices mean that wirelessly powered operation – combined with environmentally friendly circuit technologies – will be needed. Large-area electronics – which can be based on organic semiconductors, amorphous metal oxide semiconductors, semiconducting carbon nanotubes and two-dimensional semiconductors – could provide a solution. Here the authors examine the potential of large-area electronics technology in the development of sustainable, wirelessly powered IoT sensor nodes. They provide a system-level analysis of wirelessly powered sensor nodes, identifying the constraints faced by such devices and highlighting promising architectures and design approaches. They then explore the use of large-area electronics technology in wirelessly powered IoT sensor nodes, with a focus on low-power transistor circuits for digital processing and signal amplification, as well as high-speed diodes and printed antennas for data communication and radiofrequency energy harvesting. (Nature Electronics, Dec. 28, 2022; https://doi.org/10.1038/s41928-022-00898-5)