Functionalized polymers for nano- and microcomposites: towards improvement of the electrochemical reliability and humidity robustness of PCB assemblies

Functionalized polymer ligands are polymer chains equipped with functional groups that interact with surfaces, molecules or a polymer matrix. Their versatility, ease of processing and tuneable molecular weight make them suitable for modern applications. By interacting with nano- or microparticles, composite materials are created which are becoming increasingly important in miniaturized technologies such as optoelectronics, sensors, microelectronics and automotive engineering. Precise material selection and a thorough understanding of the interactions between the individual components of the composites are essential. Nanocomposites exhibit their optical properties through absorption and scattering at specific resonance wavelengths, provided size and shape remain stable. Microcomposites, which are intended to improve the corrosion resistance and lifetime of electronic components, require strong adhesion to polymer matrices, fillers or interfaces in order to increase homogeneous dispersion, moisture resistance and electrochemical reliability. This thesis focuses on how functionalized polymer ligands can address these challenges at both the nano- and microscale. Investigations of gold nanoparticles show that by varying the polymer molecular weight of multidentate amino-terminated polymer ligands, the interparticle distances and thus, the nanoparticle optical properties can be precisely controlled. It is demonstrated herein for the first time that the amino functionality and a moderate binding significantly enhance the shape stability of anisotropic particles by preferentially binding to their lateral surfaces. Furthermore, a polymer-assisted synthesis of gold nanoparticles with defined spacings is presented. Main focus of this work is on the functionalization of micrometer-sized fumed silica for polymer coatings in printed circuit board assemblies. Short-chain conventional organosilanes are found to exhibit migration effects that can lead to interactions with flux residues in solder pastes, resulting in corrosion. Inspired by the success of polymer ligands previously used for nanocomposites, short-chain organosilanes are replaced with glycidyl ether-terminated polymer ligands. Their higher molecular weight shows reduced migration, resulting in improved adhesion. Tests on printed circuit board assemblies confirm their high electrochemical reliability. As a future perspective, neutron imaging is proposed as an innovative method to detect critical defects in polymer coatings, offering a promising approach to evaluate future insulating materials.