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ItemHigh Thermal Conductivity Epoxy Composites In The Application Of 3D Semiconductor Packaging(Georgia Institute of Technology, 2022-11-11) Sun, ZhijianWith the ultra-fast development of high-performance semiconductor devices through the increase of power and on-chip integration density, heterogeneous integration heat dissipation is becoming more crucial to maintain desired operating temperatures for chips. Excellent thermal management in 3D electronic encapsulation is very important because it can ensure the performance and reliability of the electronic device. Epoxy-based composites are one of the most common thermal management materials in electronic packaging due to their excellent adhesion strength, low cost, light weight, good processibility, etc. However, epoxy itself only has a thermal conductivity of around 0.2 W/mK, so it needs to combine with thermally conductive fillers, such as aluminum oxide, aluminum nitride, and metal particles to improve its thermal conductivity. However, traditional thermal management materials struggle to dissipate large amounts of heat efficiently to meet the requirements of next generation microelectronic devices. Therefore, new epoxy composites, especially those with novel nanofillers, need to be explored to maximize heat transfer efficiency. In this dissertation, graphene nanosheets are chosen as one of fillers to combine with epoxy for achieving a high thermal conductivity because of its ultrahigh thermal conductivity of 3500–5300 W/mK and large surface area of 2630 m2/g. However, graphene nanosheets easily aggerate, similar to particulate graphite platelets with low surface area, due to strong van der Waals attraction. Additionally, their surface is too smooth, resulting in poor interfacial connections with the polymer matrix. This ultimately causes phonon scattering that lowers the thermal conductivity of composites. Thus, modifying graphene nanosheets, including surface modification and morphology change, are discussed to solve these issues. In addition to the thermal conductivity of graphene-based epoxy composites, other properties like viscosity, CTE, storage modulus, and so on are also discussed for meeting the requirements of electronic packaging materials. Another filler is boron nitride nanosheets (BNNS), also known as white graphene, and it has attracted much attention due to its high thermal conductivity (200–600 W/mK), low density, and a large band gap (nearly 5.9 eV), excellent thermal stability, and superior anti-oxidation ability. These properties make it suitable for applications, requiring electrical insulation, in thermal management materials in semiconductor packaging. The modification of BNNS and pre-formed network of BNNS will also be explored. These two nanofillers can be used to create epoxy composites whose resulting properties could support the idea that these composites have potential to be applied in the next generation of semiconductor packaging materials for high-power and high-density ICs.
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ItemTransition Metal Complexes As Latent Catalyst And Adhesion Promoter In Epoxy Resin(Georgia Institute of Technology, 2022-11-09) Li, JiaxiongEpoxy based materials are widely used in electronic packaging, serving as key enablers for many structures and in various aspects determining the process efficiency and package reliability. As a thermosetting polymer, epoxy curing control towards designed temperature response and thermal profile are desirable to fulfill the needs of specific applications such as no-flow underfill in advanced flip-chip packages. As such, controllable latent catalysts have been pursued for decades. Epoxy-copper interfaces are commonly found at encapsulant, substrate and printed circuit board applications where the contacts of epoxy composites are made with lead frame, mentalizations and bond wires. The delamination and crack of epoxy-copper interfaces is one of the major failure mechanisms of a package. Traditional approaches for improving the epoxy/copper adhesion include pre-treatment of substrate with physical/chemical etching and applying coupling agents. Adhesion promoter additives in the epoxy resin would be further appreciated for saving cost and process time, as well as for accessing numerous novel structures. In addition, the covalent bond or hydrogen bond formation assisted by coupling agents are susceptible to hydrolysis degradation under moisture aging. Coordination bonds between transition metal species and organic ligands with O or N doners on the other hand are more stable against moisture, in the meantime benefitting the crosslinks at interface without being consumed by the bulk. Targeting at these issues, this dissertation explores in-formulation metal complex based chemistry for latent catalyst and adhesion promoter in epoxy resins. This dissertation systematically studies the effects of introducing a series of transition metal chelates on the curing kinetics and copper-adhesion performances of epoxy/anhydride resin systems. First row transition metal (Co(II), Ni(II), Cu(II), Zn(II)) chelate-based modifiers bearing different β-diketone ligands were used as model compounds to differentiate metal and ligand effects. The first part of the dissertation introduces the controllable curing kinetics of epoxy resin using metal chelate additives. The interaction between metal β-diketonate with Lewis base phosphine catalyst manifested distinguished and useful thermal latent cure characteristics. It was found that other than the species of metal cation, inductive effects of the diketone ligands played a crucial role in determining the metal-phosphine interaction and thus the catalytic response of the resin. In-depth feed ratio studies on the Co(II) based metal complexes in curing control helped reveal a chemical equilibrium nature of these coordination reactions. The temperature induced coordination paradigm shift in especially the hexafluoroacetylacetonate (6Facac2) chelates were examined in the second part, and the underlying ligand mediated metal-base interaction strength upon heat treatment was analyzed in detail through structural characterizations and calculations. The third part of the dissertation presents the effects of the metal complexes on the adhesion strength of epoxy-copper joints and the resistance to moisture aging. The parametric studies on transition metal complexes with different metal and ligand types provided trend plots revealing metal and ligand dependence in the resin adhesion enhancement. The mechanisms of such adhesion improvements were investigated through extensive chemical characterizations of the fractured surfaces, along with associated understandings of both copper and epoxy behaviors when incorporating transition metal chelate species. Both the favorable interfacial chemical reactions, which is related to the cure kinetics regulation discussed in the first section, and the metal-polymer coordination effects were determined to be responsible for adhesion enhancement in the metal complex doped resin systems.