Fracture Behavior and Intrinsic Strength of FPD Substrates Technical Information Paper TIP 203 Issued: November 2004 Supercedes: February 2003 R. A. Allaire and P. L. Bocko Technology Group, Corning Incorporated, Corning, NY 14831 Paper presented at SID 1996 – San Diego, CA Abstract The ultimate practical strength of an FPD depends largely upon the fracture behavior of its substrate. Commercial FPD substrates differ substantially in their response to localized stresses occurring in panel score and break processes, edge finishing and packaging. The scoring process, used as a reliable and inexpensive technique for the sizing of glass sheets, in particular, can have a substantial effect upon the strength of the final display. This paper will review the effect of glass composition on score behavior and its impact on AMLCD glass substrates. Introduction The choice of the substrate for flat panel displays directly impacts the strength of the final display. As FPD technology extends into new applications, the issue of display strength is becoming increasingly a priority. This paper will discuss intrinsic glass mechanical properties and behaviors in the display fabrication process that control display reliability. In a previous paper by the authors1 , a broad discussion was presented on intrinsic glass properties that can influence AMLCD robustness. The properties discussed included thermal expansion coefficient (its effect upon thermal shock resistance) mechanical properties that influence the functional strength of glass, and glass thermal properties that enabled the use of advanced display component technologies. It was asserted that low expansion, high strain point glasses with favorable deformation and fracture properties would optimize the mechanical reliability of AMLCDs. Functional Strength of Glass Failure of glass under load usually initiates at a preexisting surface flaw; therefore, extrinsic factors such as the quantity and characteristics of surface flaws determine the functional strength of glass as much as intrinsic material properties. Fracture toughness is the material property that is most commonly used to quantify the intrinsic strength of a material. When compared to the range of fracture toughness values for crystalline materials, glasses have

a much more narrow range of fracture toughness values even across a broad very disparate compositional types than there is in crystalline materials. Almost all glasses have fracture toughness in the range of 0.6 to 0.8 Mpa.m1/2 . In actual experience, significant variation is seen in the mechanical robustness between glasses composition types even when differences in the extrinsic factors are removed. For example, differences between substrate glasses microscopic behavior in the score and break process are indeed determined strongly by composition factors and can make substantial impact on the...

An unwanted secondary fracture morphology that occurs during the scribe process is the lateral crack. Lateral cracks occur in a direction approximately perpendicular to that of median ("good") crack. This was also measured for Code 1737 and glass A in the same score load regime. As seen in figure 2, substantially higher lateral crack growth occurs in glass A at lower score load than that in Code 1737. Impact Upon Panel Strength Supporting microscopic analysis was done that graphically illustrates the fundamental qualitative difference in how the two glasses fractured under the score load. The...

Structural Interpretation of Substrate Behaviors Differences between the response of different types of glass compositions under local load has been well documented in the literature3,4. At this early stage in the analysis of fracture behavior of AMLCD glass compositions, a detailed structural interpretation is premature. However, inspection of the glasses compositions suggests a qualitative explanation. Code 1737 and glass A have similar compositions at first glance. They are both non-alkali boroaluminosilicates containing a mixture of alkaline earths (RO: MgO, CaO, SrO and BaO). In glass chemistry...

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