Epoxy adhesive behaviour on ceramic surfaces in commercial optoelectronic assemblies

Chemical and physical variability in the as-received state of aluminium oxide and aluminium nitride ceramic substrate materials used in optoelectronic modules currently leads to a process yield less than 100% when adhesives are used for assembly and interconnection. The phenomenon of epoxy bleed is a contributing factor to this yield and steps are not yet taken in the industry to control or inhibit the undesirable wetting. Standard surface texture measurement techniques, XPS and contact angle measurements were implemented to characterise and compare commercial as-received samples. The quality controls currently in place are assessed and additional analysis methods in the QC stage are suggested for increasing yield. Commercially available conductive and thermally conductive adhesives, also used in optoelectronic module manufacture, were studied along with the surfaces. In this work the surface property measurements, wetting observations and shear failure modes are compared and discussed. It was found that varying as-received surface properties did not affect adhesion strength between the adhesives and ceramics enough to induce an undesirable failure mode, although epoxy bleed distance varies dramatically with varying surface conditions.