Laser micromachining of polycrystalline alumina and aluminium nitride to enable compact optoelectronic interconnects

Polycrystalline aluminium oxide and aluminium nitride sleds were machined using a CO₂ laser to explore the capability of the method to produce passive alignment and assembly features for use in optoelectronic assemblies. The geometry of machined features and surface texture of machined surfaces were characterised and found to be limited by the ablation method. Consequently, a KrF excimer laser was utilised in the trials for bulk machining of the ceramics but was observed also to be restricted by its slow ablation rate. However, the combined CO₂ with KrF excimer laser were then employed to exploit the benefits offered by both, fast processing time of the CO₂ laser and enhanced geometry and texture control with the KrF excimer laser. In this study, the geometry and surface texture generated by the individual and the combined methods are characterised and compared to identify the processing limitations. The ability for the machining methods to produce patterns of sufficient accuracy to act as passive alignment features is therefore discussed. The suitability to produce the various artifacts to enable adhesive flow control was also examined, which can be applied for micro-scale precise assembly of high density packaging. By considering the production of such features with desirable geometry and textures, the effects of the processing parameters on the bulk material and the substrate surfaces where the energy of laser beam directly interacted was particularly investigated. This will ultimately assist to establish optimum settings of processing parameters in association with the type, properties and thickness of the substrates.