Technical Abstracts
In Case You Missed It
Adhesives
“Weak Bonds in a Biomimetic Adhesive Enhance Toughness and Performance”

Authors: Michael G. Mazzotta, Amelia A. Putnam, Michael A. North, and Jonathan J. Wilker.

Abstract: Developing high-performance adhesives is predicated upon achieving properties including strength and ductility. However, designing tough materials that are simultaneously strong and soft is usually contradictory in nature. Biological materials including shells and wood achieve impressive toughness by using weak bonds to connect larger structures at several length scales. Here, the authors show that this toughness design approach can be applied to synthetic adhesives. A biomimetic adhesive polymer, poly(catechol-acrylic acid), was examined in conjunction with several compounds containing two organic functional groups. In a typical example, the diol ethylene glycol decreased the overall system modulus. Performance was seen to increase significantly. Spectroscopic and physical methods indicated these bifunctional additives created an interpolymeric network of weak hydrogen bonds. Material toughness was enhanced when breakable bonds were available to dissipate mechanical stresses, while leaving the surrounding matrix intact. These discoveries illustrate how a biological materials strategy of interplay between strength and ductility can be achieved with sacrificial bonds in an adhesive. Such an approach may be a general principle applicable to designing higher performance electronics, transportation, and aerospace systems. (Journal of the American Chemical Society, February 2020; https://pubs.acs.org/doi/10.1021/jacs.9b13356)

Final Finishes
“Comparing the Reliability Performance of Electroless Palladium and Autocatalytic Gold in Production Environment”

Authors: Tom Scimeca, et al; tomscimeca@floridacirtech.com.

Abstract: The development of nanoscale surface finishes over copper pads such as electroless palladium and autocatalytic gold (EPAG) has been evolving in recent years due to increasing demands in terms of reliability, component miniaturization, and signal transmission. The authors conducted a full investigation of the production reliability of EPAG. As soldering and bonding are both possible with EPAG and of special interest in the microelectronics industry, the solder joint reliability and bonding results were evaluated. Increasing I/O counts have led to decreasing cross-sectional contact areas or, by default, an increase in solder performance expectations. The evaluation of this high solder joint reliability demand was satisfied by cold ball pull testing and high-speed shear testing. To examine EPAG’s bonding abilities, the as-received (ASR) mode and aged condition at 150°C for 4 hr. were applied. Also, general storage reliability of the EPAG finish was simulated via aging for 100 to 1,000 hr. after bonding, assessing ENEPIG finish. In addition to soldering and bonding, the reliability of a final finish is also reflected in its wetting behavior and adhesion; therefore, solder indicator, dewetting and solder spread testing were performed. Reliability against external harsh conditions was tested via salt spray testing and compared to other common final finishes. (IPC Apex Expo, February 2020)

Materials
“Skin-Inspired Electronics”

Authors: Zhenan Bao, Ph.D.; http://baogroup.stanford.edu.

Abstract: New organic-based electronic materials permit an electronic system of fully integrated multifunctional components operating on the surface of or inside the body to enable smart healthcare for disease prevention and treatment and to enhance the functional capabilities of natural skin, and also serve as a module to connect our human body to the Internet, thereby allowing human integration with IoT. (Flex/MEMS & Sensors Technical Congress [MSTS], February 2020)

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.