An Interdisciplinary Study of Sustainable Electronics in Reliability, Recycling, and Stem Education

Congying Wang, Purdue University

Abstract

Our next-generation engineers must be able to design technologies and create partnerships for broad applications that sustain the environment and protect human health. This dissertation reports on technologies and partnerships that support sustainable electronics by (1) improving the reliability of Sn-alloys in electronics by understanding the formation of whiskers in Sn thin films under thermomechanical stresses, (2) assessing the social, political, and economic determinants of a town's transition to cleaner recycling of e-waste, and (3) establishing a framework highlighting the contextualization and shared value to integrate sustainability in STEM education.Tin whiskers grow spontaneously from shallow surface grains with oblique grain boundaries (GBs) to relax the stresses in Sn films via GB-sliding-limited creep due to local compressive stress gradients. Understanding how shallow grains nucleate relative to local stress states and microstructure is a prerequisite for suppressing Sn whiskers and improving system reliability because the nucleation of shallow grains determines the distribution of Sn whiskers in films. In polycrystalline films, Sn whiskers were observed to nucleate and grow during thermal cycling below temperature, indicating that whisker formation is highly sensitive to local stress states. To simplify the identification of heterogeneous stress localization resulting from β-Sn's anisotropic elasticity and thermal expansion, large-grained Sn films were prepared and employed to quantify the evolution of stress relaxation responses observed near GBs on free surfaces during thermal cycling. The observed responses include (1) nucleation of new grains accompanied by local yielding as evidenced from slip bands and grain misorientation changes, (2) GB sliding and diffusion with local surface uplift, (3) localized GB migration, and (4) whisker formation. Different combinations of processes occurred at different GBs, with GB sliding and near-GB rotation occurring at fewer thermal cycles than other phenomena. The significantly different nucleation, whisker growth, and GB sliding phenomena observed are discussed in light of surface and sub-surface changes in orientation and morphology and the occurrence of slip traces along the GBs displaying GB sliding. These results suggest that local yielding and surface rotation are essential in determining whether whisker growth or GB sliding occurs along a given grain boundary. Secondly, incremental characterization of local microstructure and orientation as a function of the increased number of thermal cycles together with crystal plasticity simulations suggest that the local crystallographic and morphological changes are due to subgrain formation near some GBs, leading to recrystallization and whisker formation. Furthermore, slip bands were commonly observed, demonstrating that dislocations are active in Sn under these conditions, even at low strains. Lastly, we have shown the interplay between mechanisms that simultaneously affect whisker nucleation, such as slip, GB sliding, rotation, diffusion, and GB migration. For these contributions, the results of this work have important implications for understanding whisker nucleation and growth phenomena resulting from multiple stress relaxation mechanisms.For the end-of-life treatment of e-waste, recent studies have examined the formal and informal sectors and suggested that the two sectors might merge. However, few studies provide any quantitative analysis of the components of the informal sector and the implications of the reformation of e-waste recycling. This study fills this gap by investigating the political, technological, and economic solutions that reformulated the local recycling industry in Guiyu China.

Degree

Ph.D.

Advisors

Blendell, Purdue University.

Subject Area

Energy|Design|Sustainability|Science education|Condensed matter physics|Education|Educational technology|Electrical engineering|Industrial engineering|Materials science|Mechanics|Physics

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