In Case You Missed It

Additive Manufacturing

“Creating 3-D Objects with Integrated Electronics via Multiphoton Fabrication In Vitro and In Vivo”

Authors: Sara J. Baldock, et. al.

Abstract: 3-D objects with integrated electronics are produced using an additive manufacturing approach relying on multiphoton fabrication (direct laser writing). Conducting polymer-based structures (with micrometer-millimeter scale features) are printed within exemplar matrices, including an elastomer (polydimethylsiloxane, or PDMS) have been widely investigated for biomedical applications. Printing process fidelity in PDMS is assessed by optical coherence tomography, and the conducting polymer structures are demonstrated to be capable of stimulating mouse brain tissue in vitro. Furthermore, the applicability of the approach to printing structures in vivo is demonstrated in live nematodes (Caenorhabditis elegans). These results highlight the potential for such additive manufacturing approaches to produce next-generation advanced material technologies, notably integrated electronics for technical and medical applications (e.g., human-computer interfaces). (Advanced Materials Technologies, March 2023, https://doi.org/10.1002/admt.202201274)

Flexible Electronics

“Colloidal Approaches to Zinc Oxide Nanocrystals”

Authors: Joel van Embden, et. al.

Abstract: Zinc oxide is an extensively studied semiconductor with a wide band gap in the near-UV. Its many interesting properties have found use in optics, electronics, catalysis, sensing, as well as biomedicine and microbiology. In the nanoscale regime the functional properties of ZnO can be precisely tuned by manipulating its size, shape, chemical composition (doping), and surface states. In this review, the authors focus on the colloidal synthesis of ZnO nanocrystals (NCs) and provide a critical analysis of the synthetic methods currently available for preparing ZnO colloids. First, the authors outline key thermodynamic considerations for the nucleation and growth of colloidal nanoparticles, including an analysis of different reaction methodologies and of the role of dopant ions on nanoparticle formation. They then comprehensively review and discuss the literature on ZnO NC systems, including reactions in polar solvents that traditionally occur at low temperatures upon addition of a base, and high temperature reactions in organic, nonpolar solvents. A specific section is dedicated to doped NCs, highlighting both synthetic aspects and structure–property relationships. The versatility of these methods to achieve morphological and compositional control in ZnO is explicated. The authors then showcase some of the key applications of ZnO NCs, both as suspended colloids and as deposited coatings on supporting substrates. Finally, a critical analysis of the current state of the art for ZnO colloidal NCs is presented along with existing challenges and future directions for the field. (Chemical Reviews, December 2022, https://doi.org/10.1021/acs.chemrev.2c00456)

Printed Electronics

“All-Carbon Thin-Film Transistors Using Water-Only Printing”

Authors: Shiheng Lu, et. al.

Abstract: Printing thin-film transistors (TFTs) using nanomaterials is a promising approach for future electronics. Yet, most inks rely on environmentally harmful solvents for solubilizing and postprint processing the nanomaterials. In this work, the authors demonstrate water-only TFTs printed from all-carbon inks of semiconducting carbon nanotubes (CNTs), conducting graphene, and insulating crystalline nanocellulose (CNC). While suspending these nanomaterials into aqueous inks is readily achieved, printing the inks into thin films of sufficient surface coverage and in multilayer stacks to form TFTs has proven elusive without high temperatures, hazardous chemicals, and/or lengthy postprocessing. Using aerosol jet printing, the approach involves a maximum temperature of 70°C and no hazardous chemicals – all inks are aqueous and only water is used for processing. An intermittent rinsing technique was used to address the surface adhesion challenges that limit film density of printed aqueous CNTs. These findings provide promising steps toward an environmentally friendly realization of thin-film electronics. (Nano Letters, February 2023, https://doi.org/10.1021/acs.nanolett.2c04196)

Solder Materials

“Characterizing Solder Materials from Random Vibration Response of Their Interconnects in BGA Packaging”

Authors: Joshua A. Depiver, Sabuj Mallik and Emeka H. Amalu

Abstract: Solder interconnection in electronic packaging is the weakest link, thus driving the reliability of electronic modules and systems. Improving interconnection integrity in safety-critical applications is vital in enhancing application reliability. This investigation qualifies the random vibration response of five essential solder compositions in ball grid array (BGA) solder joints used in safety-critical applications. The solder compositions are eutectic Sn63Pb37 and SnAgCu (SAC) 305, 387, 396, and 405. Computer-aided engineering (CAE) employing Ansys finite element analysis and SolidWorks software is implemented in this investigation. The Sn63Pb37 solder deformed least at 0.43µm, followed by SAC 396 at 0.58µm, while SAC 405 deformed highest at 0.88µm. Further analysis demonstrates that the possession of a higher elastic modulus and mass density culminates in lower solder joint deformation. Stress is concentrated at the periphery of the solder joints in contact with a printed circuit board (PCB). The SAC 396 solder accumulates the lowest stress of 14.1MPa, followed by SAC 405 at 17.9MPa, while eutectic SnPb accrues the highest at 34.6MPa. Similarly, strain concentration is found at the interface between the solder joint and copper pad on a PCB. SAC 405 acquires the lowest elastic strain magnitude of 0.0011mm/mm, while SAC 305 records the highest strain of 0.002mm/mm. These results demonstrate that SAC 405 solder has maximum and SAC 387 solder has minimum fatigue lives. (Journal of Electronic Materials, March 2023, https://doi.org/10.1007/s11664-023-10394-x)