Abdelhafid Zehri, Microtechnology and Nanoscience - MC2

​Title: Characterization of Multifunctional Nanomaterialsfor Electronics Thermal Management and Sintering Applications
Abdelhafid is a PhD student at the Electronics Materials and Systems Laboratory
Faculty opponent: Professor Changqing Liu, Loughborough University, UK
Main supervisor and examiner: Prof. Johan Liu

The defence will be held in Kollektorn and online: https://chalmers.zoom.us/j/66048897642
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The science of manipulating materials at their nanoscale level is nowadays allowing endless possibilities to disrupt the current limitations on the conventional production processes and products. In electronics, the need for more capable thermal management strategies led to the exploration of advanced approaches and focus on new materials and allowed to push further the thermal dissipation capabilities of each generation of products. In this thesis, we investigate different thermal management concepts and propose new solutions based on carbon and metallic nanomaterials, while we explore the possibility to combine the size effect with the composition effect of the nanoscale materials. 

Due to their high surface to volume ratio, nanoscale particles show different thermodynamics properties that led to their potential implementation in electronics fabrication processes. More specifically, silver nanoparticles (Ag NPs) have been under focus in recent years for applications to replace lead-free solder and contribute to energy saving. Due to a poor trade-off between the process parameters, the production costs, and the reliability of the silver related application, different strategies are being suggested to optimize its applications. In this present study, we investigate multiple sintering parameters of Ag NPs and use the nanoscale effect in a hybrid approach for the sintering of microscopic powder. The results of the sintering parameters are correlated to the density of the samples and their properties in terms of thermal and electrical conductivity. While the sintering of Ag NPs occurs at low temperatures and allows to obtain relatively high densities, the thermal and electrical properties are still limited and the increase in the temperature and fraction of the NPs higher than 400 degrees and 2wt.% has a much-pronounced effect to improve the physical properties of the samples. 

The sintering of Ag NPs was also explored in this thesis to propose a novel approach to use graphene foam as a heat sink. While graphene is known for its outstanding physical, chemical, and mechanical properties, its integration as a practical solution in electronics is still missing. The use of Ag NPs in this work allowed to successfully attach the 3D graphene foam on its substrate and further improve both its mechanical and thermal properties by coating the graphene with Ag NPs. Also, the integration of Ag NPs as a die-attach for the 3D porous structure allowed its further use as a container for Phase Change Materials (PCM). Different amounts of PCM were introduced in the lightweight foam and the junction temperature of the hot spot was correlated to the power and the presence of the PCM. We found that graphene foam presents a real advantage for its use in thermal dissipation strategies. 

2D graphene material is developed herein as a coating for micro-and nanoscale particles. Using Chemical Vapor Deposition (CVD) and Arc Discharge (AD) methods, we introduce the possibility to produce graphene coating on copper particles for application in thermal management. In addition, we explore the possibility to introduce a doping effect on the coated NPs to further study its effect on the thermal performances of NPs. The morphology and the composition of the coating were investigated and correlated with the bottom-up production process of CVD and AD. The thermal conductivity and chemical stability of the produced particles were studied for their use as fillers in thermally conductive pastes and additives water-based nanofluids. The thermal properties of the different systems were linked to the fraction of the additives and nanofillers. The graphene-coated particles were found to have a multifunctional effect. In both micro-and nanoscale particles, the graphene coating was found to act as a corrosion resistance that stabilizes the metallic core of the particles. The graphene coating also was found to act as a carbon source to reduce the microparticles in a bimodal powder at high temperatures. Finally, the encapsulation of the nanoscale powder allowed to observe a melting point depression related to the composition of the core of the nanoparticles and their nanoscale size. 

In an effort to combine the size effect of the nanoparticles and their compositions, different alloyed nanoparticles were produced using AC. The morphology, the composition, and their sintering properties were compared to highlight their composition effect. The produced nanopowders were also used as a sintering aid in the spark plasma sintering approach (SPS) and the results show a positive contribution of the nanopowders in the reduction of the sintering temperature and the densification of the samples. An additional effect is also reported and arises from the possibility to use those particles to fine-tune the chemical composition of the bimodal particles.

Keywords: Low Temperature Sintering, Graphene Foam, Thermal Management, Nanofluids, Graphene Coated Nanoparticles, Thermally Conductive Adhesive, Spark Plasma Sintering, Alloy Based Nanoparticles, Arc Discharge.

Kategori Disputation
Plats: Kollektorn, lecture room, Kemivägen 9, MC2-huset
Tid: 2021-11-29 10:00
Sluttid: 2021-11-29 13:00

Sidansvarig Publicerad: ti 23 nov 2021.