Optoelectronics manufacturers are under continuous pressure for miniaturisation of optoelectronic modules. One route to further miniaturisation is to reduce the spacing between the optical and optoelectronic components in the optical path adhesively mounted to ceramic carriers. Flow control of the adhesives over the ceramic surface is then imperative. Uncontrolled wetting can lead to an excessive adhesive footprint which interferes in the application of other adhesives for subsequent components. However, insufficient wetting can lead to low strength bonds vulnerable to thermal fatigue and shear failure. The goal of the work was to minimise the potential for uncontrolled wetting while maintaining unmodified bond properties. In addition positional stability of adhered parts on cure and in-service must not be detrimentally affected.
Epoxy bleed and fillet size issues were experienced in the assembly processes of Oclaro plc. They approached Loughborough University and proposed a project be created to tackle these issues. This project was proposed by Oclaro plc and was funded by Oclaro and the EPSRC.
The first step in the practical investigation was to characterise the surface properties of alumina and aluminium nitride ceramic plates variously processed by commercial suppliers. The surface conditions included lapped, polished, etched and as-fired. Initial characterisation was performed by XPS, contact angle, SEM and surface texture analysis, amongst others. Commercially available conductive and thermally conductive adhesives were applied to the ceramics and their wetting behaviour linked to the surface properties observed.
Once the primary factors which affect wetting were identified the investigation focussed upon modification of these parameters to optimise wetting and adhesion. Chemical and physical modifications were studied, including adventitious carbon adsorption, laser micromachining and self assembled monolayer application. Each showed promising results but the use of self assembled monolayers stood out as a good candidate for a solution to the problem, which could be incorporated into the assembly line of Oclaro's operations.
This thesis is confidential until 31st December 2016. A Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough University.