In Case You Missed It
“An All-in-One Nanoprinting Approach for the Synthesis of a Nanofilm Library for Unclonable Anti-Counterfeiting Applications”
Authors: Junfang Zhang, et. al.
Abstract: Current materials for anti-counterfeiting labeling typically contain toxic inorganic quantum dots and the techniques to produce unclonable patterns require tedious fabrication or complex readout methods. Here the authors present a nanoprinting-assisted flash synthesis approach that generates fluorescent nanofilms with physical unclonable function micropatterns in milliseconds. This all-in-one approach yields quenching-resistant carbon dots in solid films, directly from simple monosaccharides. Moreover, the authors establish a nanofilm library comprising 1,920 experiments, offering conditions for various optical properties and microstructures. The authors produce 100 individual physical unclonable function patterns exhibiting near-ideal bit uniformity (0.492±0.018), high uniqueness (0.498±0.021) and excellent reliability (>93%). These unclonable patterns can be quickly and independently read out by fluorescence and topography scanning, greatly improving their security. An open-source deep-learning model guarantees precise authentication, even if patterns are challenged with different resolutions or devices. (Nature Nanotechnology, June 2023, https://doi.org/10.1038/s41565-023-01405-3)
Solder Joint Reliability
“Mechanical Characterization of SAC305 and SnPb36Ag2 BGA Assemblies Under Static Flexural Loading”
Authors: Jean Baptiste Libot, Olivier Dalverny, Joël Alexis and Jeremy Bosq
Abstract: Static bending-induced solder joints damage is a main reliability concern for aerospace and military industries whose printed circuit board assemblies (PCBAs) are required to remain functional under flexural loading. To dissipate heat in equipment, it is common to install thermal gap pads on electronic packages. When compressing thermal gap pads during the fixture process, the PCBA can bend and solder joints can therefore crack if the deflection is too much. This paper reports the durability of 96.5Sn-3.0Ag-0.5Cu (SAC 305) and 62Sn-36Pb-2Ag (SnPb36Ag2) ball grid array (BGA) assemblies under static flexural loading at -55°C, 20°C and 125°C. As electronics equipment can be stored at high temperature for prolonged durations, some SAC 305 test vehicles were also aged at 125°C for 192hr. For each test configuration, the bending tests were conducted at a ramp-rate of 2mm/min and the central displacement-to-failure was measured. Finite element modeling (FEM) analysis was conducted considering a global-local approach, and the transfer function between the central displacement-to-failure and the local PCB strain near the critical solder joints were determined for each test configuration. The results give the necessary data for designers to assess whether a specific PCBA design subjected to static bending is at risk. (Journal of Surface Mount Technology, vol. 36, no. 1, March 2023; https://journal.smta.org/index.php/smt/article/view/34)
“Enhanced Thermal Conductivity of Nanodiamond Nanosheets/Polymer Nanofiber Composite Films by Uniaxial and Coaxial Electrospinning: Implications for Thermal Management of Nanodevices”
Authors: Zhouqiao Wei, et al.
Abstract: Smaller and smarter electronics have revolutionized many aspects of life, from communication to medicine. But shrinking sizes mean these devices concentrate heat in smaller areas, which can cause lagging computing speeds and even force devices to completely shut down unexpectedly to prevent damage. To dissipate this heat, researchers are turning to nanocomposite materials that contain a flexible polymer and thermally conductive filler. A simple way to make nanocomposites is by electrospinning, in which a solution of polymer and filler is jetted out of a syringe through an electrically charged nozzle, forming fibers that build up into a thin film. While simple, electrospinning from a single solution, or uniaxial electrospinning, makes it difficult to control the material’s properties. The authors used a two-solution technique, called coaxial electrospinning, to better control the fiber design and improve heat dissipation of a new nanocomposite. The researchers chose polyvinyl alcohol and a separate solution with the thermally conductive filler, a nanodiamond material, to produce the new nanocomposite. By fitting a syringe of each solution onto a nozzle that combined the two, the researchers made fibers with a polyvinyl alcohol core and nanodiamond coating, rather than a random distribution of the two components. The researchers say the coated fibers act as a “highway” to direct heat, like traffic, along and across the fibers throughout the film. In tests, the new materials dissipated heat better than those made with the traditional nozzle and were four times as thermally conductive as previously reported nanocomposites. (ACS Applied Nano Materials, May 17, 2023; https://pubs.acs.org/doi/10.1021/acsanm.3c00591)