Abstract:
A method for producing glass plates of any desired contour from sheet glass, comprising the following steps: scribing scribe lines into a least one face of the sheet glass along the contour down to a depth, using a cutting device, and positioning the glass plate on a support. The method is further characterized in that a defined force F is applied to the sheet glass so that it breaks along the scribe lines, said break extending through the entire thickness of the sheet glass. The flat glass may be sandwiched between two flexible plates prior to being placed on a base pad and being subjected to the breaking force.

Description:
BACKGROUND OF THE INVENTION 
   The invention relates to a method for manufacturing glass plates of any contour from flat glasses, a separation line being driven, in a first stage, along a contour up to a predetermined depth in at least one side of a glass plate by means of a cutting device. Then, the glass plate is positioned and severed from the flat glass along the contour. The method is more specifically intended for manufacture of glass substrates for electronic storage media. 
   In addition to the method, the invention also provides a device for breaking glass plates of any contour out of flat glass. The device as well is more specifically directed to be used for manufacturing glass substrates for electronic storage media with an outside diameter and an inside diameter from a glass plate, such a device being comprised of a base pad and of a pressing facility. 
   Glass substrates for magnetic storage media, more specifically hard disks, are currently mainly made use of in laptop applications. The advantage of glass substrates over the currently widely used aluminium substrates lies in the increased rigidity, hardness, E-module and, as a result thereof, in the better resistance from impacts and the reduced fluttering. 
   Heretobefore, the applicability of glass substrates for magnetic storage media, more specifically hard disks, was made difficult because glasses with suited surface properties could only be provided with very high expense of technique. 
   This more specifically applies to the manufacturing of glass substrates by pressing and floating but also to glass ribbons manufactured by way of a drawing method as disclosed for example in U.S. Pat. No. 5,725,625. 
   With the drawn glass ribbons according to U.S. Pat. No. 5,725,625, the surface of the drawn glass must be subjected to two lapping steps and to two additional polishing steps. 
   A novel method as it is explained in the application Ser. No. 09/477,712, filed in the U.S. Patent Office on Jan. 5, 2000, the disclosure of which is fully incorporated herein, permits to achieve a drawn glass substrate that has a flatness ≦25 μm, more specifically ≦10 μm, a waviness &lt;100 Å, more specifically &lt;40 Å, a thickness variation of ±20 μm, more specifically +15 μm, and a surface roughness &lt;10 Angström, more specifically &lt;5 Å. 
   The surface properties, flatness, waviness and surface roughness are determined according to the known method like for example standard measurement methods for display substrates as described in SEMI D15-1296 of SEMI (1996). The term flatness is to be construed as the departure from an ideal flat surface measured over the entire surface, the term waviness as the mean wavelength part of the departure from an ideal surface related to a medium sized reference distance and the term surface roughness as the departure in the short wavelength range related to a short distance of measurement for evaluation. Such good surfaces need no longer be finished as this is for example the case with the surfaces according to U.S. Pat. No. 5,725,625. For glass substrates, it is therefore desirable to indicate methods for manufacturing electronic storage media with which the surface finishing process may be dispensed with altogether or be considerably reduced. 
   Current state of the art methods are not suited for further processing the drawn or floated glass ribbons with a flatness ≦25 μm, a waviness &lt;100 Å, a thickness variation of ±20 μm, and a surface roughness &lt;10 Å that must be cut so as to obtain smooth edges, with any predetermined contour of the cuts being possible and the surfaces being largely prevented from being damaged during processing. 
   One approach to avoid both slivers, recesses and microcracks is to separate glass on the basis of thermally generated mechanical stresses. The beam of a heat source directed onto the glass is thereby moved relative to the glass at a constant speed, a high thermomechanical stress which causes the glass to crack being generated in the process. This thermomechanical stress is further increased by a cooling spot that follows the heat beam. Infrared radiators, special gas burners and more specifically lasers meet the property requirement placed on the heat source which consists in being capable of locally positioning the thermal energy, i.e., of positioning it with an accuracy better than one millimeter, more preferably better than 100 micrometers, which corresponds to the typical cutting accuracies. Lasers have proved efficient and have gained acceptance because of their good focusability, the good controllability of performance and the possibility to form the beam and to thus distribute the intensity on glass. The glass is pre-scribed by the laser beam prior to being mechanically broken. This method is known as the scribe and break process. 
   Methods of laser cutting that induce a thermomechanical stress reaching beyond the resistance to breaking of the material by locally heating it through the focussed laser beam in connection with a cooling step from the outside have been proposed in EP 0 872 303 A2, DE 693 04 194 T2 and DE 43 05 107 C2 as well as in U.S. Pat. No. 5,120,926. 
   GB-A-1433563 shows a method in which a separation line is driven in a glass substrate using a laser, the glass being then broken along said separation line by means of a cutting device which is harder than glass. Examples of such type cutting devices are diamond or aluminium cutting devices. 
   An alternative scribe and break process is disclosed by U.S. Pat. No. 2,372,215. According to this method, a separation line of a depth T is scribed in a glass surface using a cutting tool, such as a small diamond wheel for example, and the glass is then broken by mechanical action along said separation line for example. 
   In a preferred embodiment, the glass is broken along the separation line T by introducing on purpose temperature stresses in the glass. 
   With the prior art scribe and break techniques, glass substrates, more specifically for electronic storage media, cannot be manufactured so as to meet the required quality more specifically because of their thickness. 
   SUMMARY OF THE INVENTION 
   It is the object of the invention to indicate a method for manufacturing glass plates of any contour from flat glass, more specifically glass substrates for storage media, that involves as few steps as possible and that enables the manufacturing of individual glass substrates for electronic storage media largely without damaging the surfaces obtained during the glass drawing process. These methods are more specifically intended not to substantially degrade the surface properties obtained during the glass drawing or floating process which are: a flatness ≦25 μm, a waviness &lt;100 Å, a thickness variation of ±20 μm, and a surface roughness &lt;10 Å. 
   In accordance with the invention, the solution to this object is that, after having positioned the glass plate and scribing a contour, a defined force is applied onto the glass plate using a pressing facility so that the glass plate breaks along the separation line and said break is driven through the entire substrate. In an advantageous embodiment of the invention, there is provided that the glass plate is turned upside down prior to being broken on the base pad so that the side into which the separation or scribe line has been scribed is now lying on the base pad. 
   In a first embodiment of the invention, the base pad used has a large surface with a defined hardness. If the base pad is rotatable, the center of the inner or outer circle defined by the for instance annular separation line may be brought to coincide with the rotation center of the base pad or of the work table while the base pad is placed onto the glass plate. A pressure is exerted with a defined force onto the glass substrate, using a pressing tool such as a small wheel or a ball. The thus obtained break is driven completely through the glass plate by rotating the table. 
   In an alternative embodiment, the glass is disposed between two flexible plates. The thus obtained stack is placed onto a ring base for example, the diameter of which is greater than the diameter defined by the one contour of the separation line. Then, pressure is exerted from the opposite side using a punch, the diameter of the punch being smaller than that of the aperture. The force exerted by the punch causes the flexible plates and the glass to bend. Tensile stresses develop in the scribed line and the scribed line is driven through the material so that an external region of a flat glass can be completely severed from an internal region thereof. 
   The advantage of this method more specifically is that the flexible material reliably prevents the border from breaking off under transverse stresses, thus preventing the surface of the glass substrate from breaking off and forming recesses. 
   In a third method in accordance with the invention, the flat glass out of which the glass plate is to be broken is placed onto a board provided with a pocket. A vacuum is preferably applied to the pocket so that an annular surface load is created on the plate. Tensile stresses then develop in the scribed line and cause said scribed line to be driven through the material so that an external region can be completely severed from an internal region. Due to the for example annular shape of the pocket, the tensile stresses are greatest at the scribed line. Instead of applying a vacuum on the underside of the glass, compressed air or fluid pressure may also be utilized on the opposite side. 
   All of the methods according to the invention are suited for breaking or cutting both an internal hole out of the glass plate and the very glass plate from the flat glass. The terms breaking and cutting are to be construed herein in such a way that the separation line is completely driven through the glass substrate without the internal region and the external region having to be physically separated from one another. 
   In an additional stage of the process, the internal region may be separated, or the external region isolated, along the separation lines driven through the flat glass by the step of breaking or cutting. For this purpose, temperature differences are built between internal and external region and/or between external region and the surrounding flat glass. For this purpose, the internal region may be cooled selectively with liquid nitrogen for example. To isolate the external region, the surrounding flat glass may for example be heated by hot air with a temperature of 200° C. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be described in closer detail herein after with reference to the drawing in which 
       FIG. 1A  is a view of a separation line scribed in a flat glass substrate using a mechanical cutting device 
       FIG. 1B  shows how the flat glass is broken along the separation line 
       FIGS. 2A and 2B  show how a separation line is driven to a depth T in a flat glass using a laser device 
       FIG. 3  shows the breaking of a glass plate on a base pad with a predetermined hardness 
       FIG. 4  shows the breaking of a glass plate with a punch in combination with a ring 
       FIG. 5  shows the breaking of a glass plate using vacuum. 
   

   DETAILED DESCRIPTION 
   In the  FIGS. 1A and 1B , a flat glass T is severed by scribing and breaking which is known as the scribe and break process. In a scribe and break process, the flat glass  1  is scribed up to a predetermined depth T glass substrate  along a separation line  26  using a cutting device that is placed onto the surface of the glass  24 . 
   After the glass is scribed along a separation line using the cutting tool  22 , it is broken along the separation line as illustrated in  FIG. 2B . The cutting tool  22  may for example be a mechanical cutting device such as a small cutting wheel. 
   It is particularly advantageous when the surface  24  of the glass plate is scribed along the separation line using a laser device. A particularly preferred method of laser cutting is described in the  FIGS. 2A through 2B . 
   When scribing and breaking is performed using a laser cutting device, the surface of the glass is but slightly damaged. Therefore, a protective coating may be completely dispensed with. 
     FIG. 2A  shows the fundamental principle of scribing for cutting a ring-shaped glass substrate for electronic storage media, in the present case a hard disk  100 , out of a flat glass  1  by means of a laser beam. The flat glass serving as a starting product typically has a thickness d ranging from 0.3 to 5 mm. 
   In the example according to  FIG. 2A , the laser beam profile is configured to form a V-shaped focal spot  102  on the flat glass  1 , said spot being curved according to the circular contour to be severed. It is followed by a cooling spot  104  that increases the thermomechanical stress generated by the laser beam beyond the resistance to breaking of the glass. Said cooling spot may for example be realized by blowing a cooling gas, preferably cold air or a water-air mixture, thereon. The V-shaped focal spot may preferably be realized as described in EP 0 873 303 A2 for example. 
   Other focal spot geometries may be used instead of the V- or U-shaped focal spot  102  illustrated herein. 
   The flat glass  1  is severed in two stages. 
   In the first stage according to  FIG. 2A , the parameters with regard to laser performance, laser beam profile, focus deposition, chart speed, meaning the speed of the relative motion between focal spot  102 , flat glass  1  and cooling  104  are defined in such a manner that a thermomechanical stress is built in the glass which scribes said glass to a predetermined depth T. Typically, the depth T of the scribed line ranges from 0.08 to 0.3 mm. 
   Both the external contour  106  for the glass substrate and the internal contour  107  for the inner hole of the glass substrate may be scribed with the thus defined parameters, a mechanically scribed line  108  serving in both cases as a pre-scribed line being formed by means of the known methods, a cutting wheel for example. A particular advantage is obtained when the pre-scribed line  108  is continued by a laser scribed line  110  so that it tangentially runs into the circular curve of the external and internal contour. This superficial scribing assists in achieving a separation without offset of the closed contours  106  and  107 . 
   According to the invention, the glass is broken along the separation line as described hereinafter. 
     FIG. 3  shows a first possibility that permits to drive scribed lines formed in the way described herein above by means of a laser for example and constituting the inside and the outside diameter of a hard disk  100  deep through the thickness thereof. There is provided, in accordance with the invention, that, after the separation lines for the inside and the outside diameter are laser scribed, the flat glass  1  to be processed is turned upside down and positioned onto a base pad  200  of a defined hardness. It is particularly advantageous when the base pad  200  is placed on a rotatable work table  202 . When using a rotatable work table, it is advantageous to dispose the glass plate from which the circular glass substrate, the future hard disk for example, is cut out in such a manner that it enables as exact a superposition of the center of the hard disk and of the rotation center of the work table  202  as possible. A pressure is exerted onto the glass substrate  1  by means of a pressing facility in the form of a small wheel  204  or of a ball for example, a defined force F being applied over the separation line for the outside diameter or over the separation line for the inside diameter. The break line  206  obtained is driven further by rotating the work table  202 . The distance from the wheel or the ball may vary depending on the position of the break  206  in the glass substrate. This influence is compensated for by an adjustable force. 
   The hardness of the base pad  200  correlates to the breaking force to be applied. Generally speaking, the following applies: the lower the hardness of the base pad  200 , the lower the breaking force needed. The process is more difficult to control with soft bases, though. 
   Furthermore, it has been found out that the positioning accuracy of the wheel  204  on the scribed line  110  influences the angularity of the work piece&#39;s edge. With wide wheels, the positioning is non-critical. However, wide wheels are but conditionally usable for the small inside diameters on account of the high deflection. For breaking the inside diameter, the use of a ball is therefore advisable. 
     FIG. 4  discloses a method for breaking glass plates out of flat glass  1  that represents an alternative to that illustrated in  FIG. 3 . The flat glass  1 , from which a glass plate of any contour is to be severed, is placed between two flexible plates  300 . 1  and  300 . 2  made of plexiglass. The flat glass  1  is sandwiched between plates  300 . 1  and  300 . 2  thus forming a kind of stack  302 . The stack consisting of the flat glass  1  and the flexible plates  300 . 1  and  300 . 2  rests on a base pad  200  with an aperture  304 . The diameter do of the aperture is always greater than the diameter of the separation line d KT  which is shaped like an arc of a circle. 
   To cut the glass plate out of the flat glass along the separation line, a pressure is exerted, from the side  304  opposite the aperture, with a force F by means of a punch  306  for example. The punch  306  has a diameter d s  that is smaller than the diameter of aperture d o . The force F causes the flexible plates  300 . 1  and  300 . 2  and the flat glass  1  to bend. A tensile stress is thus generated in the scribed or separation line  110 . The force F drives the scribed line through material  1  so that the external region of flat glass  308 . 1  is completely severed from the internal region  308 . 2  which corresponds for example to the contour of the glass plate to be cut out and, as a result thereof, to the outside diameter. With the method according to the second embodiment of the invention it is particularly advantageous that the flexible material  300 . 1 ,  300 . 2  surrounding the flat glass  1  prevents it from breaking off at the border as a result of transverse stresses. Further, the surface of the flat glass is protected. 
     FIG. 5  shows a third method according to the invention. The flat glass  1  lies on a base pad  200  with an annular pocket  400 . The annular pocket has an inside diameter d i  that is smaller than the diameter d KT  of the circular separation line which corresponds either to the inside or to the outside diameter of the glass plate that is to be cut out of the flat glass. The outside diameter of the pocket d A  is greater than the diameter of the separation line d KT  that is shaped like an arc of a circle. If a vacuum is applied to the pocket via connections  402 , an annular surface load is exerted on flat glass  1 . The annular surface load creates a tensile stress in the scribed or separation line  110 . As a result thereof, the scribed line is driven through the material so that an external region  308 . 1  is completely separated from an internal region  308 . 2  like in the embodiment according to  FIG. 4 . 
   All of the methods described herein above are suited both for cutting or breaking the entire glass plate out of flat glass  1  and for cutting or breaking the internal hole when the glass plate is used to form a hard disk for example. 
   The annular pocket  400  causes the tensile stresses to be greatest at the scribed line. However, the method is also possible using a hole-shaped pocket, i.e., a pocket without a central part of a diameter D i . Then, it must only be ensured that the diameter D A  of such a hole-shaped pocket is greater than the diameter of the separation line D KT  that is shaped like an arc of a circle. 
   In an alternative embodiment, compressed air may be applied on the side opposite the pocket instead of applying, via a vacuum connection  402 , a vacuum on the underside of flat glass  1 . 
   A concrete exemplary embodiment of the invention will be given herein after: 
   A hard disk plate with an outside diameter of 65 mm and an inside diameter of 20 mm is cut out of a flat glass plate having the dimensions: 80×80×0.7 mm as follows: at first, the upper side is scribed using a laser cutting device in the following manner: first, the glass plate is scribed with a diamond that forms a pre-scribed line on the periphery of the circle. Then, the plate is heated with a laser expanded to form a V-shaped focal spot and is cooled by a jet of ethanol and air. After the separation lines are formed, the inside diameter and the outside diameter are broken out according to the punch/ring method until the following applies: for the inside diameter Ø d(punch)=20 mm, d(ring)=50 mm, h(plexiglass)=2 mm; for the outside diameter Ø d(punch)=65 mm, d(ring)=80 mm, h(plexiglass)=2 mm, the punch being supplied through a power-controlled linear axis. 
   The isolation or separation of the broken or separated parts is performed with hot air of approximately 200° C. for the outer part and with liquid nitrogen for the inner part. 
   The present method indicates novel scribe and break techniques by means of which glass substrates may be broken out of glass plates without damaging the surface thereof. 
   LIST OF IDENTIFICATION NUMERALS 
   
     
       
             
             
           
         
             
                 
             
           
           
             
               1 
               flat glass 
             
             
               22 
               cutting tool 
             
             
               24 
               glass surface 
             
             
               26 
               separation line 
             
             
               100 
               hard disk 
             
             
               102 
               focal spot of the laser 
             
             
               104 
               cooling spot 
             
             
               106 
               external contour 
             
             
               107 
               internal contour 
             
             
               108 
               scribed line 
             
             
               110 
               laser scribed line 
             
             
               200 
               base pad 
             
             
               202 
               rotatable work table 
             
             
               204 
               wheel 
             
             
               208 
               break 
             
             
               300.1 
             
             
               300.2 
               flexible plates 
             
             
               302 
               stack 
             
             
               304 
               aperture of the base pad 
             
             
               306 
               punch 
             
             
               308.1 
               internal region 
             
             
               308.2 
               external region 
             
             
               400 
               pocket 
             
             
               402 
               vacuum connection