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Scoring of AMLCD Glass
Technical Information Paper
TIP 302
Issued: November 2004
Supercedes: November 2001
R. A. Allaire and J. C. Lapp
Technology Group, Corning Incorporated, Corning, NY 14831
Paper presented at Display Works 1996 – San Jose, CA
Abstract
The scoring process is often used for sizing of glass
sheets, the score wheel generates a small crack on the
glass surface, which is then propagated through the glass
for complete separation. This report will present a
description of the scoring process and an interpretation
of the marking found on the substrate edges from the
point of view of AMLCD fabrication.
open crack, forcing the crack open with a wedging
action. The scoring wheel penetrates into the glass
surface only to a depth of 2-5 µm, yet the median crack
typically reaches a depth of 50 - 120 µm. The individual
panels are then separated by the application of a bending
stress for driving the median crack through the glass
thickness.
Introduction
In addition to driving the median crack along the glass
surface, the scoring process results in other changes to
the glass surface. The contact stresses imposed by the
rolling wheel creates a damage zone 3-7 µm deep. The
glass responds to the creation of this region through a
combination of plastic flow and brittle failure1. The
former results in densification of the glass, while the
latter results in the formation of microcracks either on,
or slightly below, the glass surface. These microcracks
can, in turn, form the nuclei for larger cracks known as
lateral cracks. Recent work has shown that the presence
of these cracks have a significant impact on the edge
strength2. Extensive lateral cracks may also result in the
creation of glass chips. Figure 1 schematically illustrates
these principles.
The scoring process is often used as a reliable and
inexpensive method for sizing of glass sheets. Glass
substrate manufacturers use it for removing undesirable
portions of their formed sheet and for sizing of the glass
(mother sheet) to the customers specifications. AMLCD
manufacturers use the scoring process to do the final
separation of the individual display panels.
Fundamentals of Scoring
In the scoring process, a score wheel is used to generate
a median or vent crack in the glass surface. As the wheel
rolls on the glass, the median crack is pushed downward
and ahead of the wheel. The wheel rides on top of an
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