Evaluation of Bending Strength of Window Glass Substrate With Considerations of Uni- and Bi-Axial Loading and Free Edge Stresses

摘要

The window glass substrates are commonly used in optical semiconductor and micro-electrical-mechanical system packages. The determination of bending strength of such glass substrates is important for guaranteeing good yield rate and reliability of those packages. To evaluate the dicing effect on the bending strength of window glass substrate, a three-point bending (3PB) test with a uni-axial loading is adopted in this study. Since the failure initiation of the glass substrate specimen in the most of cases starts at its free edges caused by the dicing, the calculation of the free edge stress of the glass substrate specimen becomes essential and needs to be performed using a finite element analysis during the 3PB test. Furthermore, a point-load on elastic foundation (PoEF) test, which features bi-axial stresses and can avoid the edge chipping effect caused by the dicing, is also applied to evaluate the surface roughness effect on the bending strength of the glass substrate. The test results are presented in terms of both bending strengths for frontside and backside surface control cases, along with the corresponding failure modes. And precise edge-stress calculations for the 3PB test are discussed in detail through the finite element analyses with various models, including noncontact and contact models associated with both displacement and force boundary conditions.