Abstract:
A laser machining process is described for laser machining glass or glass-like materials. This process machines articles or features in articles with chamfered edges in one manufacturing operation. Chamfered edges are desirable in glass and glass-like materials because they resist fracturing or chipping and eliminate sharp edges. Producing articles or features in articles in one manufacturing operation is desirable because it can save time and expense by eliminating the need to transfer the article to a separate machine for chamfering after laser machining. Alternatively, it can permit use of less expensive equipment because the same laser used for machining can be used to form the chamfer instead of having a separate process perform the chamfering. Producing chamfers with laser machining results in high quality chamfers without the need for a separate polishing or finishing step.

Description:
FIELD OF THE DISCLOSURE 
       [0001]    The field of the technical subject matter relates to laser machining glass or glass-like articles. In particular it relates to laser machining an article with a chamfer on an edge that adjoins the top or bottom surface of the article or on a feature laser machined into the article. In more particular it relates to laser machining glass or glass-like article with a chamfer in a single manufacturing operation 
       BACKGROUND OF THE INVENTION 
       [0002]    Laser machining chamfered features in glass or glass-like articles such as sapphire, ceramic or glass ceramics is desirable because adding a chamfer to an edge makes the edge safer, in the sense that it is less likely to cause cuts or scratches when handled, makes it less likely to chip or crack and in general, makes the edge stronger. While chamfered edges are desirable, no methods exist for creating an article with a chamfered edge in one manufacturing operation. Prior art methods of producing chamfered edges involve creating a feature such as a through cut or trench in one operation and then producing a chamfer in one or more additional steps. 
         [0003]    A chamfer is a bevel created on an edge formed by two adjoining surfaces. These surfaces typically are at approximately right angles at the edge where they adjoin, although other angles are possible.  FIG. 1  shows a schematic cross-section of an article  10  produced without a chamfer. In this case the sides  24 ,  26  have been formed by machining the article from the top surface  20  to the bottom surface  22 . Note the edges  12 ,  14 ,  16  and  18  where the top surface  20  and the bottom surface  22  adjoin the sides  24 ,  26 .  FIG. 2  shows the same article  10  except with chamfers  32 ,  34  applied to the edges where the top surface  20  adjoins the sides  24 ,  26 . Note that chamfers could also be applied to the edges  18 ,  16  where the bottom surface  22  adjoins the sides  24 ,  26  in the place of or in addition to the top surface chamfers  32 ,  34 . In addition to straight beveled chamfers as shown in  FIG. 2 , rounded chamfers are sometimes desirable.  FIG. 3  shows the same article  10  with rounded chamfers  52 ,  54  where the top surface  20  adjoins the sides  24 ,  26 . 
         [0004]    Glass cutting has been traditionally realized by a mechanical saw approach, which scribes the glass and follows this step with a mechanical breaking process step. In recent years, laser technology has been adopted for glass cutting, which typically employs a laser as a localized heating source, sometimes accompanied by a cooling nozzle, to generate stress and microcracks along the trajectories described by the passage of the laser beam to cut the glass. Such resultant stress and microcracks may either be sufficient to cause the glass to fracture and separate along the designed trajectories or may require a follow-up breaking step to separate the glass. Existing technologies utilizing a laser only without the match of a cooling source include MLBA (Multiple Laser Beam Absorption) cutting technology as described in US patent applications 2007/0039932 Device for Separative Machining of Components made Form Brittle Material With Stress-Free Component Mounting and 2007/0170162 Method and Device for Cutting Through Semiconductor Materials, which use a near infrared (IR) laser source in combination with a pair of reflective mirrors to maximize the volume absorption of photon energy in the glass along the path to be separated so that there will be sufficient thermal stress generated so as to break the parts without needing to apply additional force. This technology, however, does require an initial mechanical notch to function as a pre-crack. The laser generated stress will make the initial crack propagate to form the separation. Another method of cutting glass or other brittle material is described in U.S. Pat. No. 5,609,284 Method of Splitting Non-Metallic Materials, which uses a CO2 source to heat the glass following with a cooling nozzle to generate stress so as to initiate microcracks along the cutting path, and then applying a mechanical breaking step to separate the glass. None of these methods address forming a chamfer on the resulting edges. 
         [0005]    Laser machining of glass and glass-like articles can be performed for the purpose of machining shapes into the surface, for instance machining depressions to hold liquids, or machining thru holes for applying controls such as push buttons to the article or to provide a via to pass electrical signals, fluid or light through the article. U.S. Pat. No. 6,143,382 Glass Substrate Having Fine Holes describes a method of drilling fine holes in glass but this method requires doping the glass with silver atoms to promote absorption of the laser energy. Another U.S. Pat. No. 6,756,563 System and Method for Forming Holes in Substrates Containing Glass, describes a method of forming holes in glass substrates. Neither of these approaches discusses forming a chamfer on the finished hole. US patent application 2006/0127640 Glass Substrate With Fine Holes And Method For Producing The Same discusses drilling holes in a glass substrate with a laser and subsequently using a wet etch with strong acid to form rounded edges on the holes, but this involves adding one or more operations which add additional operations and equipment to the manufacturing process. This prior art illustrates the difficulty in creating chamfers on features internal to the article, such as holes or other openings machined into the article. Chamfering these edges often requires specialized equipment and fixturing in addition to requiring additional manufacturing steps. 
         [0006]    U.S. Pat. No. 6,521,862 Apparatus and Method for Improving Chamfer Quality of Disk Edge Surfaces With Laser Treatment describes a method for producing smooth chamfers on a glass disk by mechanically grinding the chamfers and then melting them slightly with a laser. This produces smooth chamfers but requires at least two extra manufacturing operations and at least two separate machines to achieve a chamfer of acceptable quality. 
         [0007]    What is needed then is a method and apparatus for forming features in glass or glass-like articles which can form high quality beveled or curved chamfers on both external and internal laser cut edges in one manufacturing operation. 
       SUMMARY OF THE INVENTION 
       [0008]    The instant invention is a method for forming chamfered features in glass or glass-like materials in one manufacturing operation. By one manufacturing operation we mean the article being processed is fixtured on a laser processing machine, the desired feature is laser machined into the article and one or more of the resultant feature edges are chamfered using the same laser processing equipment that formed the feature prior to the article being removed from the machine. While adding the chamfer in this fashion necessarily adds a step to the manufacturing operation, the additional time required is minimized because the chamfer is added while the article is still fixtured on the laser processing machine, thereby eliminating the need to remove the article from the machine, fixture the part on a different machine and then produce the chamfer. Producing a feature and chamfer in one operation eliminates the need to refixture the article and eliminate the need for an additional machine to perform the operation, thereby reducing the time and expense required to produce an article with chamfered edges. In the instant invention, the laser parameters can be varied to produce chamfers of different sizes and shapes without changing the equipment or fixturing. In addition, by varying the laser parameters appropriately, a desired level of surface smoothness and finish can be achieved without additional manufacturing operations or equipment. 
         [0009]    An embodiment of the instant invention is shown in  FIG. 4 , a top-down view of an article  60  being laser machined from a blank  62  of glass or glass-like material. The dotted lines  64 ,  66 ,  68  are three representative paths to be followed by a laser beam. The laser beam would trace up to N paths, where N can vary between 1 and typically less than 100, around the article  60  to be machined between lines  64  and  68 , varying the laser parameters to vary the depth of cut and thereby create a chamfer. The actual number of paths would depend on the desired size and finish of the chamfer. For some applications, along one or more of the paths the laser parameters would be adjusted to enable the laser to cut completely through the blank  62  to achieve complete separation of the article  60  from the blank  62 . This would typically require more than one pass along the same path, varying the depth of focus to remove material from the bottom of the cut with each pass. In other applications, the laser paths and parameters could be adjusted to machine a chamfered feature such as a hole, a blind hole or other shape in the article, where the laser may or may not penetrate completely through the article  60 .  FIG. 5  shows a cross sectional view of the article  60  being laser machined from a blank  62 , showing a cross section taken along line  70  from  FIG. 4 .  FIG. 5  shows multiple laser beams  72 ,  74 ,  76  representing three of N possible paths impinging the blank  62  perpendicular to the top surface  78 . 
         [0010]      FIGS. 6   a , b, c and d show the progression of cuts made by the laser beams in the blank  62 .  FIG. 6   a  shows the beginning chamfer  90  in the blank  62  after the first one or more laser cuts by the laser following paths as shown in  FIGS. 4 and 5 .  FIG. 6   b  shows the chamfer  92  after more laser cuts along paths.  FIG. 6   c  shows the completed chamfer  94 . In  FIG. 6   d  the laser beam has cut through the blank  62  to form the article  60  with appropriate chamfers on the edges. Note that the chamfer in this case is asymmetric, with the bevel towards the article  60 . By varying the laser parameters and the paths, the chamfer can be made symmetric, or made smaller or larger or curved as desired. This method works with materials that are transparent or opaque to the wavelength of laser radiation used to machine the materials. 
         [0011]      FIGS. 12   a  and  b  show an embodiment of the current invention being used to form chamfers in materials transparent to laser radiation of the wavelength used. In this method, the laser beam  142  is focused so as to concentrate laser energy sufficient to ablate material initially at the surface  143  of the bulk material  146  at a constant angle α (alpha). The laser beam is angled with respect to the surface but kept perpendicular to the path  140 . As the chamfer is machined into the bulk material  146  the focal point is set to be a constant distance from the bottom of the kerf as it progresses through the material being machined, rather than at the machining surface. Since the material is transparent to laser radiation, only the material at the focal point is ablated. By changing the focal point to a greater depth in the material as the path is changed, an angled cut can be made in the material.  FIG. 7   a  shows the beginning chamfer  100  made by focusing the laser beam at the surface of the transparent material  108 .  FIG. 7   b  shows the chamfer  102  being cut more deeply into the material by focusing the laser beam below the surface of the material and moving along a path as in  FIGS. 4 and 5 . In  FIG. 7   c  the chamfer  104  is complete. In  FIG. 7   d  the laser is moved along a path directly one or more times over the cut  107  beginning at the end of chamfer  104 . The laser is focused more deeply with each pass over the cut  107  until the article  109  is separated from the bulk material  108 . Note that in the case of materials transparent to the wavelength of laser radiation used, the chamfer could be machined into the bottom surface of the article. This is accomplished by adjusting the laser beam focal spot to be within the material being machined. By adjusting the laser parameters so that the fluence of the laser beam is lower than the ablation threshold of the material except at the focal spot, where the fluence of the beam in J/cm 2  is greater than the ablation threshold. 
         [0012]    A further embodiment of the instant invention is shown in  FIGS. 8   a  and  b . In this embodiment the laser beam is moved along paths as shown in  FIG. 4 , however, the angle at which the laser impinges the material is varied with the location of the path on or in the material.  FIG. 8   a  shows three representative laser beams and angles, with laser beam  110  at angle α 1 , laser beam  112  at angle α 2  and laser beam  114  at angle αN, where N is an integer and angle αN&gt;α 2 &gt;α 1 .  FIG. 8   b  shows a top-down view with one representative path  116  shown on the bulk material  118 . The arrows, one of which is indicated  119 , on the path indicate that the angle that the laser beam impinges the material  118  is always perpendicular to the path  116  as the article  117  is machined from the bulk material  118 . The advantage of this approach is that it permits better control over the quality of the finish of the chamfer with fewer passes, but requires an apparatus that is able to control the angle of the laser beam with respect to the workpiece. 
         [0013]      FIG. 9  shows a further embodiment of the instant invention.  FIG. 9  is a side view showing laser beams  120 ,  122 , and  124  impinging on bulk material  128 . In this embodiment, the mechanism (not shown) moving the laser beam along a path with respect to the material does not change its path, rather the angle at which the laser beam is directed to the material is altered. The laser beam is pivoted about point  126  as it travels around a path on the bulk material  128 , but only in a plane perpendicular to the path. This allows more control over the shape and size of the chamfer, but at the cost of slightly more complex mechanism.  FIG. 10  shows a chamfer  130  machined into bulk material  128  using this method.  FIG. 11  shows an article  129  separated from bulk material  128  by machining cuts  132  which extend from the bottom of the chamfer to the bottom of the material  128  by machining the material with a laser beam  121  which is perpendicular to the surface. 
         [0014]      FIG. 12   a  shows another embodiment of the instant invention. This embodiment works with materials that are transparent to the wavelengths of light used to machine the material. As shown in  FIG. 12   a , the laser beam (not shown) is moved along a path  140  on the bulk material  146 . The arrows indicate that the angle the laser beam has with respect to the material is always perpendicular to the path.  FIG. 12   b  shows the laser beam  142  at an angle α with respect to the material.  FIGS. 7   a - d  show a chamfer  100 ,  102 , and  104  laser machined into the material by focusing the laser more and more deeply with each pass along the path, thereby ablating material and machining the chamfer. The chamfer could be machined into either the top surface  143  or the bottom surface  144 . The advantage of this approach is that in the case of transparent materials, the angle of the laser with respect to the workpiece would not have to be altered while machining, making the apparatus required to implement this method simpler and less expensive to build. Also, less material is remove with this approach, thereby speeding the process. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  (Prior Art) shows an article following laser machining 
           [0016]      FIG. 2  (Prior Art) shows an article following laser machining and chamfering. 
           [0017]      FIG. 3  (Prior Art) shows an article following laser machining and chamfering with a rounded chamfer. 
           [0018]      FIG. 4  shows exemplary paths for laser machining chamfers in one manufacturing step. 
           [0019]      FIG. 5  shows laser beams impinging perpendicularly on material to be laser machined. 
           [0020]      FIG. 6   a  shows the beginning of a laser machined chamfer. 
           [0021]      FIG. 6   b  shows further laser machining of a chamfer. 
           [0022]      FIG. 6   c  shows a complete laser machined chamfer. 
           [0023]      FIG. 6   d  shows a laser machined chamfer with final separating cuts. 
           [0024]      FIG. 7   a  shows the beginning of a chamfer laser machined into transparent material. 
           [0025]      FIG. 7   b  shows further laser machining of a chamfer in transparent material. 
           [0026]      FIG. 7   c  shows completed laser machining of a chamfer in transparent material. 
           [0027]      FIG. 7   d  shows a laser machined chamfer in transparent material with final separating cuts. 
           [0028]      FIG. 8   a  shows a further embodiment of the instant invention using angled laser beams. 
           [0029]      FIG. 8   b  shows how angled laser beams are arranged with respect to the laser beam paths. 
           [0030]      FIG. 9  shows another embodiment of the instant invention using angled laser beams that share a single path. 
           [0031]      FIG. 10  shows laser machined chamfers. 
           [0032]      FIG. 11  shows laser machined chamfers with a final cut. 
           [0033]      FIG. 12   a  shows another embodiment using an angled laser beam along a single path to machine chamfers. 
           [0034]      FIG. 12   b  shows an example angle used in the embodiment from  FIG. 12   a.    
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0035]    One of the goals of the instant invention is to permit laser machining of chamfered features in glass or glass-like materials in one manufacturing operation. An exemplary machine that can produce a and control a laser beam capable of ablating glass and glass-like materials, fixture the materials and move the laser beam(s) with respect to the material is the MM5800 laser micromachining system produced by Electro Scientific Industries, Inc., Portland, Oreg., the assignee of the instant invention. 
         [0036]    The laser beam can be either continuous wave (CW) or pulsed. Laser parameters which are controlled to provide the desired ablation rate include wavelength, average power, spatial distribution, spot size and speed of travel. In the case of pulsed lasers, pulse width, pulse energy, pulse temporal distribution and repetition rate can be controlled to provide the desired ablation. Laser wavelengths can range from infrared (IR), such as 10.6 micron wavelengths emitted by CO2 lasers down to frequency tripled or quadrupled solid state laser which operate in the ultraviolet (UV) range below 355 nm. Average power can range up to tens of Watts. Spatial distribution can either be Gaussian, modified or clipped Gaussian or shaped distributions such as “top hat” or annular. See for example U.S. Pat. No. 6,791,060 Beam Shaping and Projection Imaging with Solid State UV Gaussian Beam to Form Vias, assigned to the assignee of the instant invention. Spot sizes can typically range from a few microns to more than 100 microns. Exemplary rates of travel for the laser beam with respect to the material surface being ablated can range from a few mm/s to 500 mm/s depending upon the amount of material to be removed. For pulsed lasers, pulse width can range from femtosecond pulses up to tens of nanoseconds. Pulse energy can range from a few microJoules per pulse to hundreds of milliJoules, depending upon the pulse width. Pulses can have Gaussian temporal distribution or be shaped or sliced to have faster rise and/or fall time. Pulses can also be produced with more complex tailored temporal distribution. For an example of this type of pulse see U.S. Pat. No. 7,348,516 Methods of and Laser Systems for Link Processing using Laser Pulses With Specially Tailored Power Profiles, assigned to the assignee of the instant invention. The repetition rate of pulsed lasers used for this purpose can range from a few kHz to over 1 MHz. 
         [0037]    In one embodiment of the instant invention, referring to  FIGS. 4 and 5 , an article  60  is to be machined from a blank  62  of glass or glass-like material. The assumption is that this material is opaque to the wavelength of laser light used. A laser beam  72  is directed perpendicular to the top surface  78  of a blank  62  and focused so that the laser power exceeds the ablation threshold of the material to be machined at the point where the laser beam impinges the material. Once the laser parameters are selected to provide the desired ablation rate, the laser beam is then directed to begin ablating material along a path  64  parallel to the final through-cut which will separate the article  60  from the blank  62 . The laser beam is directed to follow this path one or more times until the desired amount of material is ablated. The result of this is shown in  FIG. 6   a  as beginning chamfers  90 . The laser beam is the directed to follow a path adjacent to the one previously followed, for example path  66 , to ablate more material. In order to form a chamfer, the laser parameters are adjusted to ablate more material with each adjacent pass. For example, the laser power could be increased, the pulse width could be increased, or the number of passes around the path could be increased or some combination of these or other parameter changes could be controlled to form the chamfer. This is shown in  FIG. 6   b  as intermediate chamfer  92 . This is repeated until a path such as path  68  is reached, yielding the result shown in  FIG. 6   c  as completed chamfer  94 . At this point the laser is directed to complete separating the article  60  from the blank  62  by laser ablating a cut  98  through the material to complete the separation. 
         [0038]      FIGS. 12   a  and  b  illustrate another embodiment of the instant invention. This embodiment requires that the glass or glass-like material be transparent to the wavelength of laser radiation used to ablate the material  146 . In this embodiment the laser follows a single path  140  around the article  147  to be chamfered. The laser beam  142  is angled to match the angle α of the desired chamfer with respect to the surface  143  of the bulk material  146 . The arrows, one of which is indicated  145 , on the path  140  indicate that the laser beam is held to be perpendicular to the path  140  while being angled with respect to a surface  143  of the bulk material  146 . Machining a chamfer may require several passes around the path by the laser beam  142 . This embodiment requires that the laser beam parameters be adjusted so as to make the laser beam fluence, measured in J/cm 2 , greater than the ablation threshold of the material only at the focal spot and not elsewhere within the beam. With each pass the laser focal point is adjusted to be deeper in the material as the material is removed so as to ablate material at the bottom of the kerf.  FIGS. 7   a - d  illustrate this process. In  FIG. 7   a  the first pass has begun machining the chamfer  100 . In  FIG. 7   b  the focal point of the laser beam  142  is adjusted to move the ablation point deeper into the material as more passes around the path  140  are taken to machine more material from the bottom of the kerf  102  that will form the chamfer. In  FIG. 7   c , after additional passes around the path  140 , the kerf  104  forming the chamfer is complete. In  FIG. 7   d , the laser beam focal spot (not shown) is adjusted to move perpendicular to the surface  143  of the material  109  to form the cut  107  which separates the article  109  from the bulk material  108  as the laser beam is focused deeper into the material  109  with each pass. Note that in the case of material that is transparent to the wavelength of laser radiation used, the cuts may form a chamfer (not shown) on the bottom surface  144  of the article  109 . 
         [0039]    In yet another embodiment of the instant invention a laser beam makes multiple passes along multiple adjacent paths to form a chamfer, changing the angle at which the laser beam impinges the material as the path changes. As shown in  FIG. 8   a , laser beams  110 ,  112  and  114  show how the angle with which the laser beam impinges the bulk material  118  changes with respect to the top surface  115 . As shown in  FIG. 8   a , as the path moves from the beginning of the chamfer to the outside edge, the angle at which the laser beam impinges the surface changes from angle α 1  for laser beam  110  through angle α  2  for laser beam  112  to angle α N for laser beam  114 , where N is an integer and N equals the number of paths followed around the top surface  115 , where αN&gt;α 2 &gt;α 1 .  FIG. 8   b  shows a top view of this embodiment, showing a sample path  116  separating the bulk material  118  from the article to be machined  117 , with the arrows indicating that the laser beam is at an angle to the top surface  115  but perpendicular to the path  116 . This embodiment can make it easier to form curved or multiple beveled chamfers but requires additional equipment to vary the angle of the laser beam with respect to the workpiece in a controlled fashion. 
         [0040]    In yet another embodiment of the instant invention, the laser beam angle is varied with respect to the workpiece. In this embodiment, the equipment that changes the angle of the laser beam with respect to the workpiece is designed to change the angle of the laser beam in a plane about a point at a fixed distance from the workpiece. In addition, the equipment that changes the angle will rotate to keep the plane within which the laser beam changes angle perpendicular to the path that the laser beam follows on the workpiece. This arrangement will be made clearer by referring to  FIG. 9 . In  FIG. 9 , the laser beam  120 ,  122 ,  124  changes angle about a point  126 . The point  126  is moved with respect to the bulk material  128  along a path (not shown), maintaining a fixed relationship between the point  126  and the surface of the material  125  so that the point  126  is directly above the path. Several passes are then made, with the laser beam  120 ,  122 ,  124  changing angle as the chamfer is machined. The laser beam focal point is changed as material is removed to maintain the focal point at the surface of the bulk material  128 .  FIGS. 10 and 11  show a chamfer  130  machined with this embodiment. The cut that separates the article  129  from the bulk material  128  is made by holding the laser beam  121  perpendicular to the surface of the material  125  and making passes around the path until the article  129  is separated from the bulk material  128  by a cut  132 . 
         [0041]    It will be obvious to those having skill in the art that many changes may be made in the details of the above described embodiments of the instant invention without departing from the underlying principles thereof. The scope of the instant invention should, therefore, be determined only by the following claims.