Electric heating – Metal heating – By arc
Reexamination Certificate
1999-01-29
2001-04-03
Evans, Geoffrey S. (Department: 1725)
Electric heating
Metal heating
By arc
C219S121670, C219S121760, C225S002000, C225S093500
Reexamination Certificate
active
06211488
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention generally relates to the physical separation of a non-metallic substrate into a plurality of smaller substrate pieces. In particular, the invention relates to a method and apparatus for splitting a non-metallic substrate by the process of micro-cracking and controlled propagation.
BACKGROUND OF THE INVENTION
Many products made from a brittle non-metallic material, for example glass and semi-conductor wafer materials, are formed by separating a piece, sheet, wafer, or panel into a number of smaller pieces of the desired size or sizes. For example, many glass products are formed by a large sheet of glass separated into smaller pieces of the desired size. The most common method for cutting these sheets and other substrates includes the use of mechanical cutting tools. For example, glass sheets have been cut by scribing the glass with a diamond-tipped scribe or a carbide wheel to weaken the molecular structure. After the scribe has been made, physical pressure is applied to create a force at the scribe line to hopefully break the glass along the scribe line.
However, cutting with mechanical tools has significant disadvantages. One significant disadvantage is the inability to obtain smooth edges. his may be unacceptable for many products because of the required quality of the edge faces. Accordingly, as an attempt to rectify this drawback, secondary steps such as grinding, edge seaming, and polishing may be performed. However, such secondary steps slow down the manufacturing process and can be expensive. Another disadvantage is that edge defects on some of these rough edges may result in crack propagation during further processing or in the ultimate product. The edge strength of the substrate is also reduced by this process. Yet another disadvantage is the creation of glass particulates and “shards” during the cutting stage. These glass shards and particulate are undesirable because they can contaminate the substrate being separated, and require that additional clean-up steps be performed to minimize their impact on the manufacturing process. Mechanical tools also create wide scribe lines which are undesirable because the process reduces the useful area of the substrate from which the parts are cut. Further, mechanical tools are subject to wear, and worn tools result in inconsistent and unreliable cuts.
One alternative to mechanical division of pieces of non-metallic brittle substrates is using a laser to melt the substrate along a predetermined line. European Patent Application No. 82301675.3 discloses one such method. According to this method, a sheet of glass is mounted to a plate. A high-powered laser beam is applied to cause rapid localized heating of the glass in a small heat affected zone that extends through the entire thickness of the glass. This heats the glass above its annealing temperature so that part of the glass is vaporized and part of the glass becomes viscous. A pressurized air jet removes the molten glass from the heat affected zone to divide the glass substrate. However, this process also suffers from drawbacks.
A drawback of this process is that predictable and highly accurate cuts are unobtainable because the glass is subjected to extreme temperatures and is removed from the cutting line. This lack of precision is magnified with thicker pieces of glass. Additionally, secondary steps such as grinding, edge seaming, and polishing may also need to be performed to achieve desired edge face quality.
Another alternative to mechanical cutting of pieces of non-metallic brittle materials has been the process of creating a localized fracture through a substrate, and propagating the localized fracture to part the substrate. On such method is disclosed in U.S. Pat. No. 3,629,545 to Graham et al. According to this process, light from a laser is focused by a lens system upon the upper surface of the substrate at an extreme edge of the substrate. The lens system is adjusted so that the focal point of the laser beam image falls precisely at the upper surface of the substrate. The concentrated laser energy creates a localized fracture in the substrate. The substrate is moved relative to the beam. This relative movement propagates the initial localized fracture along a desired partition path. There have been many variations to this process.
The processes of creating a localized fracture and propagating the fracture have also suffered drawbacks. One drawback is that these processes include inefficiencies rendering them impractical and/or ineffective for many commercial applications. For example, some of these processes are limited by cutting speed. Further, some of these processes still require manual breakage of the substrate after the passage of the laser. Another drawback to these processes is the inherent limitations imparted due to the coefficient of thermal expansion of the substrate being cut.
Therefore, there exists a need for an improved method of dividing or parting substrates is of brittle non-metallic material that overcomes these and other problems.
SUMMARY OF THE INVENTION
It is an object of the present invention to overcome the drawbacks associated with current methods of microcrack initiation.
It is an object of the present invention to initiate a microcrack by using a laser in the process of separation by microcracking The present invention accomplishes this laser initiated scribe process by using a pulse laser to crack the substrate between its upper and lower surfaces. The pulsed laser can be tuned to form a desired mircocrack shape.
It is an object of the present invention to provide a method for separating a non-metallic substrate. The substrate has an upper surface and a lower surface. The method includes forming a crack in the substrate between the upper surface and the lower surface that does not extend vertically to reach either the upper surface or the lower surface. The crack is propagated for separation of the substrate.
It is another object of the present invention to provide a method for separating a non-metallic substrate. The substrate has an upper surface and a lower surface. The method includes directing a pulsed laser towards the substrate so that the focal point of the laser is between the upper and lower surface of the substrate. The laser is pulsed. An incident beam of coherent radiation is directed onto the substrate to impinge at a spot positioned at least behind the focal point of the pulsed laser. Additionally, a stream of coolant is directed onto the substrate at a location behind at least a portion of the spot caused by the incident beam.
In another object of the present invention, an apparatus is used for dividing a non-metallic substrate having an upper surface and a lower surface. The apparatus includes a pulsed laser to emit a pulsed first beam to be directed at the substrate. The apparatus also includes an incident second beam of coherent radiation positioned to impinge on the substrate at a location at least partially behind the pulsed first beam.
It is an object of the present invention to provide an apparatus for dividing a non-metallic substrate having an upper surface and a lower surface. The apparatus includes a pulsed laser, optics, a second laser, and a quenching device. The pulsed laser emits a pulsed beam. The optics direct the focal point of the emitted pulsed beam to lie between the upper and lower surfaces of the substrate at a first spot. The second laser emits an incident beam of coherent radiation positioned to impinge on the substrate at a second spot positioned at least partially behind the first spot. The quenching device projects a steam of coolant onto the substrate at a location behind the first spot and behind at least a portion of the second spot.
These and other objects and features of the invention will be apparent upon consideration of the following detailed description of preferred embodiments thereof, presented in connection with the following drawings in which like reference numerals identify like elements throughout.
REFERENCES:
patent: 3894208 (197
Efimov Oleg M.
Glebov Leonid B.
Hoekstra Brian L
Accudyne Display and Semiconductor Systems, Inc.
Banner & Witcoff , Ltd.
Evans Geoffrey S.
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