Electric heating – Metal heating – By arc
Reexamination Certificate
2002-08-27
2004-09-07
Heinrich, Samuel M. (Department: 1725)
Electric heating
Metal heating
By arc
C219S121690
Reexamination Certificate
active
06787732
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for cutting or shaping sheets of brittle materials into desired configurations or geometries utilizing a laser-scribing technique. The present invention has particular applicability in laser-scribing brittle non-magnetic sheets along curvilinear paths to produce substrates for use in the manufacture of magnetic recording media.
BACKGROUND OF THE INVENTION
Two techniques are conventionally employed for cutting or shaping a sheet of brittle material, such as a glass, amorphous glass, glass-ceramic or ceramic material, to form a sheet or substrate with a desired configuration or geometry. A first such conventional method involves mechanical scribing of the sheet employing a hard device, such as a diamond tip, to score the surface of the brittle material, which is then broken along the score line or pattern. The second of such conventional techniques involves laser-scribing. Currently employed laser-scribing differs from traditional high power (i.e., >1 KW) laser-drilling/cutting and utilizes a lower power (i.e., <500 W) for achieving scribing with less material removal and better edge quality subsequent to breaking/separation. Such laser-scribing typically utilizes a continuous wave (“CW”) laser, such as a CO
2
laser, to heat a localized zone of a brittle material, such as an amorphous-glass sheet (similar to float glass), up to a temperature below the softening point of the material, and then immediately quenching the heated zone by applying a coolant, e.g., a gas such as air or a liquid such as water.
In a typical process for laser-scribing an amorphous glass sheet, the output beam of a CW CO
2
laser, or a high frequency pulse repetition rate CO
2
laser, is re-shaped into a beam with an elongated spot shape, which beam is utilized in an unfocussed manner for locally heating the glass. The locally heated zone is then chilled by spraying cool air or an air/liquid (e.g., air/water) mixture. When the localized heating/cooling process starts from a small surface defect or micro-crack made in the glass, e.g., by a means of a mechanical scriber or indenter, or by application of suitable laser pulses, the defect or micro-crack propagates to form a scribing line due to the combination of localized heating-quenching which initiates tiny surface cracks arising from compression-tension stress effects. The sheet of material is then separated, i.e., broken, along the scribing line by applying an external thermal or mechanical stress.
A conventional laser-scribing technique utilizing a low power CO
2
laser is disclosed by Kondratenko in U.S. Pat. No. 5,609,284, wherein an elliptical target area is impinged with a beam of coherent radiation along the intended direction of the crack, while a stream of fluid coolant is directed at a point on the heated surface on the intended line of the crack. U.S. Pat. No. 6,259,058 B1 to Hoekstra discloses a modification of U. S. Pat. No. 5,609,284 wherein dual laser beams are utilized after cooling in order to assist separation along the laser-scribing line. Allaire et al. in U.S. Pat. No. 5,776,220 disclose a laser-scribing technique for brittle materials wherein the laser spot has an extremely elongated elliptical shape such that its major axis is greater than 20 mm to enable rapid scribing.
Conventional substrates for use in manufacturing magnetic recording media include various brittle materials, such as glasses, ceramics and glass-ceramics. In order to form annular disk-shaped substrates suitable for use in magnetic and/or magneto-optical (MO) recording media, two circular scribings must be performed with high precision, one defining the outer diameter (e.g., ranging from about 65 to about 95 mm, such as 84 mm) and one defining the inner diameter (e.g., ranging from about 20 to about 25 mm). However, applicability of current linear laser-scribing techniques, such as utilized with flat panels, to circular scribing for producing annularly-shaped substrates suitable for manufacture of disk-shaped magnetic and/or magneto-optical recording media, is limited, for at least the following reason: laser-scribing is very sensitive to variations of the glass material, including optical reflectivity of the surface, glass composition, surface and thickness uniformity, etc., resulting in that the CO
2
laser-based scribing process requires very precise control of defect initialization, laser power distribution, and cooling stream. As a consequence, current laser-scribing technology of amorphous glass substrates is generally restricted to linear scribing.
Another drawback/disadvantage of conventional laser-scribing technology is associated with the methodology for separating/breaking the brittle substrate (e.g., of amorphous glass) subsequent to laser-scribing. Specifically, because of the nature of the localized heating/cooling of the laser-scribing process, and due to the formation of a compression layer on the surface of the amorphous glass sheet, the propagation of micro-cracks during the laser-scribing process occurs in the layer nearest the glass surface. As a consequence, the scribe line provided by a single laser beam at the surface of a glass surface is insufficiently deep, and application of additional mechanical force to the glass sheet is typically required during the laser-scribing process or subsequent thereto, disadvantageously resulting in edge defects, residual stresses, increased risk of cracking resulting in product loss (i.e., low yield), reduced product throughput, and poor cost-effectiveness arising from a requirement for complicated, thus expensive, processing.
In view of the above-described disadvantages, drawbacks, and difficulties associated with utilization of laser-scribing technology for forming curvilinear-shaped brittle sheets, conventional practices for cutting/shaping brittle glass substrates for use in magnetic recording media involve the use of diamond tips to induce mechanical stresses. However, the required high tolerances are not fully satisfied by mechanical scribing. Moreover, it is necessary to perform extensive polishing and lapping after the mechanical scribing, thereby significantly increasing manufacturing costs.
Thus, there exists a need for a method and apparatus for laser-scribing a brittle substrate along a curvilinear path, particularly a substantially circular path. There exists a particular need for an apparatus and methodology for laser-scribing brittle materials, such as glasses, ceramics and glass-ceramics, along substantially circular paths to form annular disk-shaped substrates for use in manufacturing magnetic and MO recording media.
The present invention, therefore, addresses and solves the above-described drawbacks, disadvantages, difficulties, and shortcomings of the conventional methodologies and instrumentalities for performing laser-scribing of brittle glass substrates, particularly when utilized for performing curvilinear laser-scribing of amorphous glass substrates suitable for use in the manufacture of disk-shaped magnetic and MO media. According to the invention, a UV-based laser-scribing process and apparatus is provided which is especially well-adapted for shaping glass sheets into annular-shaped disks with inner and outer diameters, which methodology and apparatus provide a simple, readily controllable manufacturing process with increased product throughput and cost-effectiveness.
DISCLOSURE OF THE INVENTION
An advantage of the present invention is an improved method of shaping a sheet of brittle material.
Another advantage of the present invention is an improved method of separating a sheet of a brittle material into portions by means of laser-scribing.
Yet another advantage of the present invention is an improved method of shaping a sheet of brittle material along concentric inner and outer circular paths to form an annular disk.
A further advantage of the present invention is an improved apparatus for shaping a sheet of brittle material.
A still further advantage of the present invention is an improved apparatus for separ
Nguyen Thanh Duc
Shih Chung-Yuang
Xuan Jialuo Jack
Heinrich Samuel M.
McDermott Will & Emery LLP
Seagate Technology LLC
LandOfFree
Method for laser-scribing brittle substrates and apparatus... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for laser-scribing brittle substrates and apparatus..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for laser-scribing brittle substrates and apparatus... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3239535