Fracture Properties of Glass-Ceramics: II, Failure Prevention by Compressive Surface Stresses

A mechanism is demonstrated for preventing mechanical failure of cordierite glass-ceramic substrates that does not degrade the electrical performance or manufacturability. The mechanism relies on the introduction of a surface compressive stress into the substrate by a small compositional modification of the multilayer substrates outer layers. Controlled-flaw identation techniques are used to determine the effects of the surface stress and the general indentation fracture mechanics analysis is developed for the behavior of cracks in multilayer structures. In the test cased examined here significant enhancements in mechanical properties were achieved: Suppression of crack initiation threshold by a factor of 10. Decrease in contact crack length by a factor of 2. Increase in toughness by a factor of 4. Increase in strength by a factor of 3. Decrease in strength variability by a factor of 2. Increase in safe 10-year lifetime stress by a factor of 5.