Prof. C.P. Wong, Advisor, MSE
Prof. Meilin Liu, MSE
Prof. Zhiqun Lin, MSE
Prof. Seung Soon Jang, MSE
Prof. Vanessa Smet, ME
Transition Metal Complexes as Latent Catalyst and Adhesion Promoter in Epoxy Resin
Epoxy 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. Epoxy curing control towards designed temperature response and thermal profile are desired 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 include pre-treatment of substrate with physical/chemical etching and applying coupling agents. However, the covalent bond or hydrogen bond formation assisted by coupling agents are susceptible to hydrolysis degradation under moisture aging. Coordination bonds between copper and ligands with O or N doners on the other hand are more stable against moisture. Targeting at these issues, novel in-formulation metal complex based latent catalyst and adhesion promoter are proposed in this work.
s thesis demonstrates the effects of introducing transition metal chelates on the curing kinetics and moisture-stressed copper-adhesion performances of epoxy resin. First row transition metals (Co(II), Ni(II), Cu(II), Zn(II)) chelate-based modifiers bearing -diketonate and phthalocyanine ligands were investigated. The first part of the thesis is on effects of metal complexes on the curing kinetics of epoxy resin. A unique interaction between the metal -diketonates with Lewis base phosphine catalyst resulted in a controlled curing latency. It was found that other than the metal type, the inductive effects of original ligands played a crucial role in determining the metal-phosphine interaction and thus the latency pattern. In depth studies on the Co(II) based metal complexes on such curing control helped reveal the chemical equilibrium nature of the coordination reaction, and the underlying ligand mediated metal-base interaction through chemical characterizations and calculations. The second part of the thesis presents the effects of the metal complexes on the adhesion strength of epoxy-copper joints when subjected to moisture aging. The parametric studies on transition metal complexes with different metal and ligand types provided trend plots of the adhesion promoters. The mechanisms of the adhesion improvements are to be examined on each component of the joint: copper substrate, epoxy resin and the interfacial bonding zone. Extensive characterizations of the thermo-mechanical, chemical, electrical and physical properties will provide knowledge on the nature of adhesion and moisture resistance enhancement."