Ensuring structural integrity stands as a paramount consideration across various applications where the utilization of specific materials is pivotal in attaining optimal performance levels. This critical aspect necessitates the meticulous research and development of novel materials, including but not limited to 2D materials, nanostructured materials, high entropy alloys, metallic glasses, and materials subjected to severe plastic deformation. This impetus towards innovation has gained momentum as it strives to cater to the escalating demands for enhanced performance capabilities under the extreme operating conditions foreseen in the future.
A few broad topics of immediate interest are listed below.
1. Microstructure and Mechanical Properties of Pb-free Solders
In the rapidly evolving consumer electronics landscape, the industry's trajectory has swiftly shifted toward Pb-free solders, driven by pressing environmental and health concerns associated with Pb. Simultaneously, the escalating performance demands of emerging microelectronic devices, spanning an expansive gamut of operating temperatures spanning from cryogenic lows to searing highs, have accelerated the exploration of Pb-based solders. These solders are critical in circuit board assembly and are indispensable interconnect solutions for processes like wafer bumping, substrate bumping, and die-attach.
While Pb-free alternatives like Sn-Ag-Cu (SAC alloys), with lower eutectic temperatures, offer a promising avenue, there are several reliability issues that hinder the use of these alloys in practical applications. Particularly within the realm of ball grid arrays, thermal fatigue, impact resistance, and time-dependent deformation, such as creep and creep-fatigue interaction, reduce their overall performance. A microscopic lens reveals that all quandaries trace their origins to the intricate process of Sn nucleation. This complexity impairs the precise engineering of reflowed solder joint microstructures, as reviewed by Reeve, Holaday, Choquette, and colleagues in their work [J. Phase Equilib. Diffus. 37, 369–386 (2016)]. The specter of whisker growth from Pb-free solders further compounds the reliability matrix, painting a comprehensive picture of challenges to be surmounted.
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2. Engineered thin films and coatings
Thin films and coatings play a pivotal role in advanced engineering applications, encompassing an expansive spectrum that spans semiconductors, microelectronic devices, solar cells, batteries, optical devices, thermal insulation, healthcare devices, and MEMS devices. However, it's imperative to recognize that fabricating thin films/coatings for specific applications is complex. Throughout their deposition and subsequent processing stages, the emergence of excessive stresses within their delicate structures cast a profound shadow on the very devices they serve. As a result, the thin film synthesis, coupled with a comprehensive grasp of their microstructure and thermomechanical behaviors, emerges as a linchpin in the success of these diverse applications.
The arsenal at our disposal encompasses a repertoire of distinct deposition techniques, each tailored to the specific demands of thin film fabrication. Augmenting this toolkit is a variety of in-situ diagnostic tools such as laser optics-based substrate curvature measurement system and Reflection High Energy Electron Diffraction (RHEED). These innovative tools empower us with the real-time ability to ascertain the average biaxial stresses embedded within thin films and multilayers and the crystallography of films. Such insight informs our understanding and stands as a lighthouse guiding the pursuit of optimal performance.
3. Severe Plastic Deformation for developing ultra-high strength materials
Utilizing Severe Plastic Deformation (SPD) techniques, we venture into a realm of transformation, where ordinary bulk materials undergo a metamorphosis into extraordinary entities characterized by ultra-fine crystalline structures. This intricate refinement on a microscopic scale is a key that unlocks the doors to unparalleled strength. This phenomenon finds its foundation in the well-established Hall-Petch relation, a cornerstone that underpins the relationship between grain size reduction and the resulting enhanced mechanical properties.
In this ever-evolving scientific exploration, the allure of SPD techniques beckons researchers from every corner of the globe. Their pursuit is singular yet multifaceted: to overcome the strength-ductility paradox encountered in various materials. Moreover, the significance of this work extends beyond mechanical attributes, delving into the functional properties such as electrical conductivity to magnetism, the mysteries of optics, and hydrogen storage performance.