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Published online by Cambridge University Press: 06 March 2019
X-ray residual stress analysis was used to investigate the role of various phases in the formation of residual stress in laser-scribed alumina microelectronic substrates. Previous work by our group shows that the stress induced in the vicinity of a laser-scribe line is 20 to 50 percent of the modulus of rupture of this multiphase material. Our concern with the resulting stress is fracture of the substrate during subsequent firing processes and in-service fracture of the finished microelectronic device.
The phases investigated, in addition to the alumina matrix, included a glassy phase (7% by volume), a spinel structure (3%), and porosity (4%) in 96% alumina. Electron probe microanalysis (EPMA), electron spectroscopy for chemical analysis (ESCA). scanning electron microscopy (SEM), and quantitative metallography were used to characterize the microstructure and composition of these phases. A Nd:YAG laser was used to scribe lines which raised the state of stress in the substrate.
X-ray residual stress analysis shows that a uniform residual stress exists across the laser-scribed substrate, contrary to expected results. X-ray composition analysis suggests that the spinel phase of the material is vitrified in the heat affected zone of the laser scribe. The formation of this brittle glass phase, mainly at triple points and grain boundaries, may act as a pathway for inter-granular fracture and lead to subsequent failure of the finished microelectronic device.