The biaxial strength of ultrathin AMLCD glass substrates with thickness ranging from 0.25mm to 0.70mm was measured in the concentric ring fixture. The data, based on a large sample size of 25mm x 25mm square specimens, show that the strength is independent of glass thickness and approaches 630 MPa. The choice of 25mm x 25mm specimens for measuring the biaxial strength was dictated by minimizing large deflections and associated membrane tension in the test region. The effect of surface area under test was taken into account by using Weibull distribution which demonstrated constancy of surface strength irrespective of substrate thickness. Thus, thin and ultrathin AMLCD susbtrates have similar biaxial strength as measured in the concentric ring fixture..

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The biaxial strength using ring-on-ring (ROR) test and uniaxial strength using 4-point bend test (4PB) were measured for 13.3" panels with substrate thicknesses ranging from 0.25 mm to 0.5 mm. The effect of thinning process was quantified by these data along with identifying break sources using fractography. Strain gages were used to convert failure load to strength.

The cylindrical bend test offers the unique advantage of stressing both the #1 and #4 surfaces along with their corresponding edges in a uniform manner thereby proofing all of the exposed surfaces to a prescribed stress value dictated by the radius of cylindrical bend fixture. Several LCD panels, comprised of Eagle 2000 and Code 1737 glasses with substrate thicknesses of 1.1 and 0.7 mm and with diagonal dimensions ranging from 5″ to 23″, were tested in the cylindrical bend fixture to stresses ranging from 34 MPa to 83 MPa. Failure modes, fracture origins and strain values on #4 surface and the edges were recorded. The stresses based on cylindrical bend theory were found to be in good agreement with those computed from measured strain components and/or mirror radius. The failure origins were observed both on #4 surface as well as on the edges depending on handling damage and the quality of edge finish. In general, edges appear to be weaker due to their i) inadequate finish and ii) greater vulnerability to handling damage during panel manufacturing.

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