Patent Application
20160311717
The disclosure generally relates to 3D (3-dimensions) forming of glass sheets or and more particularly to forming or bending glass sheets by using laser induced perforations. A 3D shape is a non-flat shape where at least one area on the surface of the glass shape is not a plane, such as a bent shape or wavy shape for example.
New products are being announced and released on a regular basis with some form of three dimensional (3D) glass part incorporated in them. Some examples include curved LCD TV screens, curved smart-phones and wearable gadgets (e.g., wrist phones, watches) that are either flexible or have a curved shape. Other elements of design in these types of devices are the back covers that have gone from the traditional flat glass cover plates to three dimensional curved surfaces of different styles. These innovations bring new challenges to the manufacturing processes of these 3D parts that are made of glass, which invariably need to be scratch- and impact-resistant.
The 3D (i.e., not flat) glass sheets or articles having radii of curvature greater than 10 mm can be produced, but the process used is relatively slow. It is even more challenging to form 3D dish-shaped glass sheets or articles that have parts with small radii of curvature, for example around 2 mm. In order to do this today the glass is heated to very high temperatures and then bent, but in order to achieve good small bend radii, for example a 2 mm corner radii, the temperatures are too high and introduce surface defects. The surface defects may contribute to crack propagation in the glass, with crack propagation initiating at surface defects sites. The glass part that molded, for example, using conventional thermoforming, may have distortions in the glass material. Such a part is inadequate for many mobile device uses. This also lowers the yield of the molding process as many molded glass parts are unusable.
No admission is made that any reference cited herein constitutes prior art. Applicant expressly reserves the right to challenge the accuracy and pertinency of any cited documents.
At least one embodiment of the disclosure relates a method of making a glass article having a non-flat portion, said method comprising the steps of:
One embodiment of the disclosure relates a method of making a glass article having a non-flat portion, said method comprising the steps of:
(i) perforating a glass blank along a contour with a laser and forming multiple perforations in a glass blank, said perforations being less than 5 μm in diameter and have a length at least 20 times longer than said diameter;
(ii) bending the glass bank along the areas containing perforations to form a three dimensional shape, such that the glass is curved.
According to some exemplary embodiments the step of bending comprises heating the glass blank with the perforations and/or applying vacuum to at least perforated areas of the blank.
According to some exemplary embodiments the perforations are less than 2 μm, and in some embodiments less than 1.5 μm in diameter, and have a length at least 50 times longer than said diameter. For example, the perforation length may be at least 200 μm long (e.g., 200 μm to 1.2 mm).
According to some exemplary embodiments areas that are perforated contain at least 10 or perforations per mm2, for example at least 20, at least 30, at least 40, at least 50 or at least 100 perforations per mm2
According to some exemplary embodiments the perforating step is performed with laser line focus and the glass is 0.1 mm to 5 mm thick.
According to some exemplary embodiments the bending comprises bending the glass blank to a radius of curvature of 5 mm or less (e.g., 2 mm or less).
One exemplary method of making a glass sheet comprises the steps of:
(i) perforating a glass sheet with the laser line focus to create at least one perforated separation contour for creation of at least one glass blank;
One embodiment of the disclosure relates a method of making at least one glass article having non-flat portions, said method comprising the steps of :
One embodiment of the disclosure relates a method of making glass articles having non-flat portions, said method comprising the steps of:
(i) perforating a glass sheet with the laser line focus to create at a plurality of perforated separation contours for creation of a plurality of glass blanks;
(ii) perforating the glass sheet along other contour with the laser line focus to form a plurality of bend area perforations;
(iii) separating said glass blanks from the glass sheet and each other along perforated separation contour, thereby creating a plurality of singulated glass blanks, each containing bend area perforations ;
(iv) placing the singulated blanks and bending the glass banks along the areas containing bend area perforations such that the glass is curved.
According to some embodiments, a glass article comprising a curved surface or at least one non-flat surface, and has a plurality of defect lines or perforations extending at least 200 microns within said curved surface or said least one non-flat surface, the defect lines or perforations each having a diameter less than or equal to about 5 microns. According to some embodiments, the distance between the adjacent defect lines or perforations is between 7 micron and 50 microns. According to some embodiments, the glass article has subsurface damage up to a depth less than or equal to about 100 microns. According to some embodiments, the glass article has a thickness between about 10 microns and about 5 mm (e.g., 200 microns to 2mm).
Additional features and advantages will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from the description or recognized by practicing the embodiments as described in the written description and claims hereof, as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary, and are intended to provide an overview or framework to understand the nature and character of the claims.
The accompanying drawings are included to provide a further understanding, and are incorporated in and constitute a part of this specification. The drawings illustrate one or more embodiment(s), and together with the description serve to explain principles and operation of the various embodiments.
The foregoing will be apparent from the following more particular description of example embodiments, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon the illustrated embodiments.
A description of example embodiments follows.
Cover glasses with 3D surfaces are being developed for handheld products such as cell phones, for example. However, forming a 3D part from thin LCD glass, for example, becomes more difficult where curvature radii are smaller. A radius of curvature of 10 mm is relatively easy to achieve with thin LCD glass, for example. However, 3D dish-shaped parts with smaller bend radii of below 10 mm, such as 5 mm or 1 or 2 mm, for example, are more difficult to produce with existing methods, because the glass is typically so hot in existing methods that to achieve good small (e.g. 2 mm) corner radii, surface defects occur. Vacuum and pressure can even be required to force the glass into such tight features of molds. Further, to scale up production sizes and volumes, large formed sheets of thin glass are typically used for cost effectiveness, and creating tight corner radii over an array of parts can be even more challenging. Embodiment methods disclosed herein can facilitate production of glass parts with 3D surfaces having small radii of curvature, as further described in conjunction with
The present application provides processes for precision forming of arbitrary shapes of molded 3D thin transparent brittle substrates, with particular interest in strengthened or non-strengthened glasses. In one embodiment, the glass is Gorilla® glass (all codes, available from Corning, Inc.). Embodiment methods also allow cutting and extracting one or more 3D parts, or parts with a 3D surface, to their final size with no required post-process finishing steps. The method can be applied to 3D parts that are strengthened (for example, chemically ion-exchanged) or unstrengthened (raw glass).
Workpieces, parts or articles can include, for example, a glass cover for a phone that has a curved surface or automotive glass. The developed laser methods are well suited for materials that are substantially transparent (i.e., absorption less than about 50%, and less than 10%, for example less than about 1% per mm of material depth) to a selected laser wavelength.
The primary principle is to perforate holes in glass, using a laser focal line to create defects, for example via a process and by using a system which is described in a co-pending patent application No. 61/917127 filed Dec. 17, 2013 entitled “PROCESSING 3D SHAPED TRANSPARENT BRITTLE SUBSTRATE”, incorporated by reference herein. The laser creates a focal line, for creation of holes or elongated damage areas (defect lines) in thin glass sheets, thus forming perforated areas. The glass is weakened in those perforated areas, advantageously enabling formation of complex shapes, and/or curved areas under hot forming conditions. Since normal forming processes use the existing glass thickness as a given operating parameter, perforation of the glass sheets as described herein creates a 3D surface that is well suitable for easier shaping or forming. Forming in conjunction with use of perforated areas advantageously results in improvement of the hot forming product details like tight bend radii and other required feature details. This approach also enables forming of large array sheets of thin glass to achieve very fine forming details with a vacuum forming technology. Forming glass sheets or blanks with perforated areas can also be achieved by other methods as well. For example, at temperatures between about 500° C. and about 650° C. the viscosity of glass creates a plastic phase, that allows sag-bending to the desired shape. The specific temperature depends on the glass composition. The perforated glass is heated to the plastic phase and allowed to sag to the heated mold surface under its own weight to the required shape, and then is gradually allowed to cool (for example, to about 150 ° C. or 200° C.), at which point it can be moved out of the heated area, and allowed to cool to a room temperature.
According to some embodiments, a large, preformed cut glass sheet 1000 is perforated in step 1000A to form to create perforations 1200A or 1400A. More specifically, the glass is placed under the laser beam, and defect lines as described herein are created on the glass by tracing the laser (moving the laser focal line) along the desired line or contour). The perforated glass sheet 1000 is then bent along the perforation areas or lines (e,g, aras with perforations 1400A) to the desired shape, for example by heat molding or vacuum forming, forming a 3D shape. The bent radii can be relatively large, or can be small, for example 1 mm to 20 mm, and in some embodiments 1 mm to 10 mm, or not greater than 5 mm, for example 1 mm to 5 mm, or 2 mm or less. According to some embodiments, the glass is less than 3 mm thick, for example 2 mm (e.g., 1 mm or less). According to some embodiments the bend glass comprises a curvature (also referred herein as a bow or a bend) in it that has a greater than the thickness of the glass sheet itself. According to some embodiments the bend glass has a thickness of less than 3 mm, for example less than 2 mm or less than 1 mm. In some embodiments, the exemplary pitch (separation) between the perforations situated in the areas that will be bend (or that are bend) is between 5-50 μm, or between 7 and 50 μm (i.e., something wider than cutting pitch to prevent separation and just to act as weak points to help bendability without forming significant surface defects). According to the exemplary embodiments described herein these perforations are 2 μm or less in diameter and have a length at least 20 times longer than said diameter, with at least some regions of the glass having at least 10 perforations per mm2.
According to some embodiments the perforations are less than 2 μm in diameter (e.g., less 1.5 μm in diameter) and have a length at least 50 times longer than said diameter. For example, the perforations 1400A have a length at least 200 μm long. According to some embodiments least some of the areas that are perforated contain at least 25 perforations per mm2. According to some embodiments least some of the areas that are perforated contain at least 50 perforations per mm2. According to some embodiments the perforations are formed with a laser beam forming a laser line focus. According to some embodiments the perforations are formed by a Bessel beam. According to some embodiments the laser is pulsed laser has laser power of 10 W-10 W (e.g., 25 W-60 W), the laser produces burst pulses at least 2-25 pulses per burst, and the distance between the perforations (defect lines) is 7-100 microns (e.g., 10-50 microns, or 15-50 microns).
According to some embodiment a method of forming a 3D glass article includes the steps of:
(i) Forming a glass sheet 1000;
(ii) Perforating the glass sheet 10 along lines or perforated contours 1200 with the laser focal line to create perforations 1200A for creation of glass blanks 2000A (see
(iii) Perforating the glass sheet 1000 along a contour 1400 with the laser line focus (see
(iv) Singulating (or separating) the glass parts—i.e., separating glass blanks 20A from each other and/or from other area(s) of the glass sheet 1000. This can be done by applying stress along the perforated separation contours 1200. This stress may be, for example, thermal stress or mechanical stress (and be created, for example, by pressure or vacuum pull). Thermal stress may be created, for example, by heating the glass sheet 10 with a light from the CO2 laser, along perforated separation contours 1200;
(v) Placing the singulated blanks(s) 2000A over a mold 1300 such that the perforations 14A are situated over the areas where the glass blank 2000A will be bend or curved (see
(vi) Forming a 3D (curved) contour in the glass blanks(s) 2000A, or forming the originally flat glass blank 2000A into a 3D form, for example by heating the glass, and/or by conventional vacuum forming technology. The glass perforations 1400A allow relatively easy, precise 3D forming, without creating significant surface defects, advantageously resulting in a shape that has better resistance to crack formation in the bent areas than conventionally made 3D glass articles.
According to at least some embodiments, a glass article formed by the method(s) described herein comprises a curved surface or at least one non-flat surface, the article having a plurality of defect lines or perforations extending at least 200 microns (e.g. 250 microns or more) within said curved surface or said at least one non-flat surface, the defect lines each having a diameter less than or equal to about 5 microns. According to some embodiments the spacing of adjacent defect lines is between 7 micron and 50 microns. According to some embodiments the glass around said defect lines has subsurface damage up to a depth less than or equal to about 100 microns. According to some embodiments the glass Article has a thickness between about 10 microns and about 5 mm.
In accordance with some embodiments described below, a laser can be used to create highly controlled full or partial perforations through the material (for example, in a single pass,), with extremely little (<75 μm, often <50 μm) subsurface damage and debris generation. Sub-surface damage may be limited to the order of 100 μm in depth or less, or 75 μm in depth or less, or 60 μm in depth or less, or 50 μm in depth or less, and the cuts may produce only low debris. This method can be can be used for material perforation (e.g., glass perforation) in contrast to the typical use of spot-focused laser to ablate material, where multiple passes are often necessary to completely perforate the glass thickness, large amounts of debris are formed from the ablation process, and more extensive sub-surface damage (>100 μm) and edge chipping occur.
Thus, with the methods described herein, it is possible to create microscopic (i.e., <2 μm and >100 nm in diameter, and in some embodiments <0.5 μm and >100 nm in diameter) elongated defect lines (also referred to herein as perforations, holes, or damage tracks) in transparent materials using one or more high energy pulses or one or more bursts of high energy pulses. The defect lines, or perforations, or fault lines, represent regions of the substrate material modified by the laser. The laser-induced modifications disrupt the structure of the substrate material and constitute sites of mechanical weakness. Structural disruptions include compaction, melting, dislodging of material, rearrangements, and bond scission. The perforations extend into the interior of the substrate material and have a cross-sectional shape consistent with the cross-sectional shape of the laser (generally circular). The average diameter of the perforations may be in the range from 0.1 μm to 50 μm, or in the range from 1 μm to 20 μm, or in the range from 2 μm to 10 μm, or in the range from 0.1 μm to 5 μm. In some embodiments, the perforation is a “through hole”, which is a hole or an open channel that extends from the top to the bottom of the substrate material. In some embodiments, the perforation may not be a continuously open channel and may include sections of solid material dislodged from the substrate material by the laser. The dislodged material blocks or partially blocks the space defined by the perforation. One or more open channels (unblocked regions) may be dispersed between sections of dislodged material. The diameter of the open channels is may be <1000 nm, or <500 nm, or <400 nm, or <300 nm or in the range from 10 nm to 750 nm, or in the range from 100 nm to 500 nm. The disrupted or modified area (e.g., compacted, melted, or otherwise changed) of the material surrounding the holes in the embodiments disclosed herein, preferably has diameter of <50 μm (e.g., <10 μm).
The individual perforations can be created at rates of several hundred kilohertz (several hundred thousand perforations per second, for example). Thus, with relative motion between the laser source and the material these perforations can be placed adjacent to one another with spatial separations varying from sub-micron to several or even tens of microns as desired. Distance between adjacent defect lines along the direction of the fault lines can, for example, be in range from 0.25 μm to 50 μm, or in the range from 0.50 μm to about 20 μm, or in the range from 0.50 μm to about 15 μm, or in the range from 0.50 μm to 10 μm, or in the range from 0.50 μm to 3.0 μm or in the range from 3.0 μm to 10 μm. The spatial separation is selected in order to facilitate weakening of the glass along the perforated contours, or cutting.
In addition to transparency of the substrate material in the linear intensity regime, selection of the laser source is further predicated on the ability to induce multi-photon absorption (MPA) in the transparent material. MPA is the simultaneous absorption of multiple photons of identical or different frequencies in order to excite a material from a lower energy state (usually the ground state) to a higher energy state (excited state). The excited state may be an excited electronic state or an ionized state. The energy difference between the higher and lower energy states of the material is equal to the sum of the energies of the two or more photons. MPA is a nonlinear process that is generally several orders of magnitude weaker than linear absorption. It differs from linear absorption in that the strength of MPA depends on the square or higher power of the light intensity, thus making it a nonlinear optical process. At ordinary light intensities, MPA is negligible. If the light intensity (energy density) is extremely high, such as in the region of focus of a laser source (particularly a pulsed laser source), MPA becomes appreciable and leads to measurable effects in the material within the region where the energy density of the light source is sufficiently high. Within the focal region, the energy density may be sufficiently high to result in ionization.
At the atomic level, the ionization of individual atoms has discrete energy requirements. Several elements commonly used in glass (e.g., Si, Na, K) have relatively low ionization energies (˜5 eV). Without the phenomenon of MPA, a wavelength of about 248 nm would be required to create linear ionization at ˜5 eV. With MPA, ionization or excitation between states separated in energy by ˜5 eV can be accomplished with wavelengths longer than 248 nm. For example, photons with a wavelength of 532 nm have an energy of ˜2.33 eV, so two photons with wavelength 532 nm can induce a transition between states separated in energy by ˜4.66 eV in two-photon absorption (TPA), for example. Thus, atoms and bonds can be selectively excited or ionized in the regions of a material where the energy density of the laser beam is sufficiently high to induce nonlinear TPA of a laser wavelength having half the required excitation energy, for example.
MPA can result in a local reconfiguration and separation of the excited atoms or bonds from adjacent atoms or bonds. The resulting modification in the bonding or configuration can result in non-thermal ablation and removal of matter from the region of the material in which MPA occurs. This removal of matter creates a structural defect (the defect line, damage line, or perforation referred to hereinabove) that mechanically weakens the material and renders it more susceptible to cracking or fracturing upon application of mechanical or thermal stress. By controlling the placement of perforations, a contour or path along which cracking occurs can be precisely defined and precise micromachining of the material can be accomplished. The contour defined by a series of perforations may be regarded as a fault line and corresponds to a region of structural weakness in the material. The fault line defines the preferred contour for bending, or for separation of a part from the material and controls the shape of the separated part. In one embodiment, micromachining includes separation of a part from the material processed by the laser, where the part has a precisely defined shape or perimeter determined by a fault line defining a closed contour of perforations formed through MPA effects induced by the laser. In one embodiment, the glass perforated parts processed by the laser is bent to a tight radius (e.g., 1 mm to 5 mm), where the part has a precisely defined shape or perimeter determined by a fault line defining a closed contour of perforations formed through MPA effects induced by the laser. As used herein, the term closed contour refers to a perforation path formed by the laser line, where the path intersects with itself at some location. An internal contour is a path formed where the resulting shape is entirely surrounded by an outer portion of material.
The preferred laser is an ultrashort pulsed laser (pulse durations on the order of 100 picoseconds or shorter) and can be operated in pulse mode or burst mode. In pulse mode, a series of nominally identical single pulses is emitted from the laser and directed to the workpiece. In pulse mode, the repetition rate of the laser is determined by the spacing in time between the pulses. In burst mode, bursts of pulses are emitted from the laser, where each burst includes two or more pulses (of equal or different amplitude). In burst mode, pulses within a burst are separated by a first time interval (which defines a pulse repetition rate for the burst) and the bursts are separated by a second time interval (which defines a burst repetition rate), where the second time interval is typically much longer than the first time interval. As used herein (whether in the context of pulse mode or burst mode), time interval refers to the time difference between corresponding parts of a pulse or burst (e.g. leading edge-to-leading edge, peak-to-peak, or trailing edge-to-trailing edge). Pulse and burst repetition rates are controlled by the design of the laser and can typically be adjusted, within limits, by adjusting operating conditions of the laser. Typical pulse and burst repetition rates are in the kHz to MHz range.
The laser pulse duration (in pulse mode or for pulses within a burst in burst mode) may be 10−10 s or less, or 10−11 s or less, or 10−12 s or less, or 10−13 s or less. In the exemplary embodiments described herein, the laser pulse duration is greater than 10−15.
One feature of embodiment processes is the high aspect ratio of defect lines created by an ultra-short pulsed laser. The high aspect ratio allows creation of a defect line that extends from the top surface to the bottom surface of the substrate material. The present methods also permit formation of defect lines that extend to a controlled depth within the substrate material. The defect line can be created by a single pulse or single burst of pulses, and, if desired, additional pulses or bursts can be used to increase the extension of the affected area (e.g., depth and width).
The generation of a line focus may be performed by sending a Gaussian laser beam into an axicon lens, in which case a beam profile known as a Gauss-Bessel beam is created. Such a beam diffracts much more slowly (e.g. may maintain single micron spot sizes for ranges of hundreds of microns or millimeters as opposed to few tens of microns or less) than a Gaussian beam. Hence the depth of focus or length of intense interaction with the material may be much larger than when using a Gaussian beam only. Other forms or slowly diffracting or non-diffracting beams may also be used, such as Airy beams.
As illustrated in
The created fault lines in a glass sheets may be different from one another—for example, the defect lines 120 (or holes) may be spaced closer in the contours along which one wants the glass to separate, and further apart in the areas when glass will be bent, but where one wants to avoid spontaneous separation. The exact pitch or separation between defect lines or perforations will be determined by the glass composition, but will typically be within the ranges described herein, for example from about 1 μm to about 25 μm.
According to some exemplary embodiments the areas that will be bend or curved have 10 or more holes (perforations) or defect lines per mm2, for example 10-100 holes, defect lines, or perforations 1400A per mm2. According to some exemplary embodiments the areas that will be bend have at least 10 and preferably 20 or more holes or defect lines in area(s) that will be curved or bent, for example 25 or more holes, defect lines, or perforations 1400A per area (e.g., 25-500 holes, fault lines, or perforations, or 50-100, or 50-200 holes, fault lines, or perforations). The large number of holes facilitates bending. For example, a small corner of the glass piece that needs to be bent may contain 20-50, or more holes or perforations. The number of holes or perforations will depend on the size of the glass area that will be bend or curved. In some exemplary embodiments the perforations or wholes are separated by 7 to 100 microns (i.e., the pitch may be 7-100 microns, for example 15 to 100 micron, 25 to 100 micron, or 25 to 50 micron), and the holes, fault lines, or perforations 1400A are less than 5 microns in diameter, and in some embodiments 3 microns or less in diameter, in some exemplary embodiments 2 micron or less) in diameter (e.g., 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 1 μm, 1.2 μm, 1.5 μm, or therebetween). In some exemplary embodiments the number of perforations in these areas may be, for example 10 to 50 or 10 to 30 per mm2 area. Preferable the fault lines or perforations are formed by a laser beam, produced by a pulse burst laser, where the laser powers 10 W to 100 w (e.g., 25 W to 60 W) and the bursts contain at least 2 pulses, (e.g., 2-25 pulses)
In some cases, the created fault line is not enough to separate the part from the substrate material spontaneously, and a secondary step may be necessary for the separation of the glass (i.e., for singulation of parts from a larger sheet). For example, if desired, a second laser can be used to create thermal stress to separate glass parts from each other. For example, in the case of 0.55 mm thick Gorilla® 2319 glass produced by Corning Incorporated of Corning N.Y., glass separation can be achieved after the creation of a defect line, for example, by application of mechanical force or by using a thermal source (e.g., an infrared laser, for example a CO2 laser) to create thermal stress and force separation of the part from the substrate material along the fault line. Another option is to use an infrared laser to initiate the separation, and then finish the glass part separation manually. The optional infrared laser separation can be achieved with a focused continuous wave (cw) laser emitting at 10.6 microns and with power adjusted by controlling its duty cycle. Focus change (i.e., extent of defocusing up to and including focused spot size) is used to vary the induced thermal stress by varying the spot size. Defocused laser beams include those laser beams that produce a spot size larger than a minimum, diffraction-limited spot size on the order of the size of the laser wavelength. For example, defocused spot sizes (1/c2 diameter) of 2 mm to 20 mm, or 2 mm to 12 mm, or about 7 mm, or about 2 mm and or about 20 mm can be used for CO2 lasers, for example, whose diffraction-limited spot size is much smaller given the emission wavelength of 10.6 microns.
There are several methods to create the defect line. The optical method of forming the focal line or line focus can take multiple forms, using donut shaped laser beams and spherical lenses, axicon lenses, diffractive elements, or other methods to form the linear region of high intensity. The type of laser (picosecond, femtosecond, etc.) and wavelength (IR, green, UV, etc.) can also be varied, as long as sufficient optical intensities are reached to create breakdown of the substrate or workpiece material in the region of focus to create breakdown of the substrate material through nonlinear optical effects (e.g., nonlinear absorption, multi-photon absorption).
In the present application, an ultra-short pulsed laser is used to create a high aspect ratio vertical defect line in a consistent, controllable and repeatable manner. The details of the optical setup that enables the creation of this vertical defect line are described below and in U.S. application Ser. No. 14/154,525 filed on Jan. 14, 2014, the entire contents of which are incorporated by reference as if fully set forth herein. The essence of this concept is to use an axicon lens element in an optical lens assembly to create a region of high aspect ratio taper-free microchannels using ultra-short (picoseconds or femtosecond duration) Bessel beams. In other words, the axicon condenses the laser beam into a high intensity region of cylindrical shape and high aspect ratio (long length and small diameter) in the substrate material. Due to the high intensity created with the condensed laser beam, nonlinear interaction of the electromagnetic field of the laser and the substrate material occurs and the laser energy is transferred to the substrate to effect formation of defects that become constituents of the fault line. However, it is important to realize that in the areas of the substrate where the laser energy intensity is not high (e.g., substrate surface, volume of substrate surrounding the central convergence line), the substrate is transparent to the laser and there is no mechanism for transferring energy from the laser to the substrate. As a result, nothing happens to the substrate when the laser intensity is below the nonlinear threshold.
Turning to
As
As
Representative optical assemblies 6, which can be applied to generate the focal line 2b, as well as a representative optical setup, in which these optical assemblies can be applied, are described below. All assemblies or setups are based on the description above so that identical references are used for identical components or features or those which are equal in their function. Therefore only the differences are described below.
To ensure high quality (regarding breaking strength, geometric precision, roughness and avoidance of re-machining requirements) of the surface of the separated part along which perforation or separation occurs, the individual focal lines positioned on the substrate surface along the line of perforation, separation or detachment (fault line) should be generated using the optical assembly described below (hereinafter, the optical assembly is alternatively also referred to as laser optics). In cases of separation, the roughness of the separated surface (or cut edge) is determined primarily from the spot size or the spot diameter of the focal line. Roughness of a cut (separated) surface can be characterized, for example, by an Ra surface roughness parameter defined by the ASME B46.1 standard. As described in ASME B46.1, Ra is the arithmetic average of the absolute values of the surface profile height deviations from the mean line, recorded within the evaluation length. In alternative terms, Ra is the average of a set of absolute height deviations of individual features (peaks and valleys) of the surface relative to the mean.
In order to achieve a small spot size of, for example, 0.5 microns to 2 microns for a given wavelength λ of the laser 3 that interacts with the material of substrate 1, certain requirements must usually be imposed on the numerical aperture of laser optics 6. These requirements are met by laser optics 6 described below. In order to achieve the required numerical aperture, the optics must, on the one hand, dispose of the required opening for a given focal length, according to the known Abbé formulae (N.A.=n sin (theta), n: refractive index of the material or workpiece to be processed, theta: half the aperture angle; and theta=arctan (DL/2f); DL: aperture diameter, f: focal length). On the other hand, the laser beam must illuminate the optics up to the required aperture, which is typically achieved by means of beam widening using widening telescopes between the laser and focusing optics.
The spot size should not vary too strongly for the purpose of a uniform interaction along the focal line. This can, for example, be ensured (see the embodiment below) by illuminating the focusing optics only in a small, circular area so that the beam opening and thus the percentage of the numerical aperture only vary slightly.
According to
As illustrated in
One potential disadvantage of the type of a focal line formed by lens 7 and the system shown in
In the case shown in
It is particularly advantageous to position the focal line 2b in such a way that at least one of surfaces 1a, 1b is covered by the focal line, so that the section of induced absorption 2c starts at least on one surface of the substrate. In this way it is possible to achieve virtually ideal cuts while avoiding ablation, feathering and particulation at the surface.
However, the depicted layout is subject to the following restrictions: Since the region of focal line 2b formed by axicon 9 begins within axicon 9, a significant part of the laser energy is not focused into the section of induced absorption 2c of focal line 2b, which is located within the material, in the situation where there is a separation between axicon 9 and the substrate material or workpiece. Furthermore, length 1 of focal line 2b is related to the beam diameter through the refractive indices and cone angles of axicon 9. This is why, in the case of relatively thin materials (several millimeters), the total focal line is much longer than the substrate thickness, having the effect that much of the laser energy is not focused into the material.
For this reason, it may be desirable to use an optical assembly 6 that includes both an axicon and a focusing lens.
It is therefore advantageous if the focal line is formed at a certain distance from the laser optics, and if the greater part of the laser radiation is focused up to a desired end of the focal line. As described, this can be achieved by illuminating a primarily focusing element 11 (lens) only circularly (annularly) over a particular outer radial region, which, on the one hand, serves to realize the required numerical aperture and thus the required spot size, and on the other hand, however, the circle of diffusion diminishes in intensity after the required focal line 2b over a very short distance in the center of the spot, as a basically circular spot is formed. In this way, the defect line formation is stopped within a short distance in the required substrate depth. A combination of axicon 10 and focusing lens 11 meets this requirement. The axicon acts in two different ways: due to the axicon 10, a usually round laser spot is sent to the focusing lens 11 in the form of a ring, and the asphericity of axicon 10 has the effect that a focal line is formed beyond the focal plane of the lens instead of a focal point in the focal plane. The length 1 of focal line 2b can be adjusted via the beam diameter on the axicon. The numerical aperture along the focal line, on the other hand, can be adjusted via the distance Z1 (axicon-lens separation) and via the cone angle of the axicon. In this way, the entire laser energy can be concentrated in the focal line.
If the defect line formation is intended to continue to the back side of the substrate, the circular (annular) illumination still has the advantage that (1) the laser power is used optimally in the sense that most of the laser light remains concentrated in the required length of the focal line and (2) it is possible to achieve a uniform spot size along the focal line —and thus a uniform separation of part from substrate along the focal line—due to the circularly illuminated zone in conjunction with the desired aberration set by means of the other optical functions.
Instead of the plano-convex lens depicted in
In order to generate very short focal lines 2b using the combination of an axicon and a lens depicted in
As shown in
The optical assembly 6 depicted in
In the depicted example, it is possible to achieve a length of the focal line 1 of less than 0.5 mm using a typical laser beam diameter of 2 mm, a focusing lens 11 with a focal length f=25 mm, a collimating lens with a focal length f=150 mm, and choosing distances Z1a=Z1b=140 mm and Z2=15 mm.
Finally, in the case of an axicon, as shown in
For the purpose of cutting and extracting parts from a 3D molded Gorilla® glass part or other 3D workpiece in a representative demonstration, one embodiment of the uses a 1064 nm picosecond pulsed laser in combination with line-focus beam forming optics to create lines of damage (also referred to herein as defect lines, damage tracks, or fault lines) in a Gorilla® glass substrate.
As illustrated in
The required energy to modify the material can be described in terms of the burst energy—the energy contained within a burst (each burst 500 contains a series of pulses 500A), or in terms of the energy contained within a single laser pulse (many of which may comprise a burst). For these applications, the energy per burst (per millimeter of the material to be cut) can be from 10-2500 μJ, or from 20-1500 μJ, or from 25-750 μJ, or from 40-2500 μJ, or from 100-1500 μJ, or from 200-1250 μJ, or from 250-1500 μJ, or from 250-750 μJ. The energy of an individual pulse within the burst will be less, and the exact individual laser pulse energy will depend on the number of pulses 500A within the burst 500 and the rate of decay (e.g., exponential decay rate) of the laser pulses with time as shown in
The use of lasers capable of generating such pulse bursts is advantageous for cutting, perforating, or modifying transparent materials, for example glass (e.g., glass sheets 1000). In contrast with the use of single pulses spaced apart in time by the repetition rate of a single-pulsed laser, the use of a burst pulse sequence that spreads the laser energy over a rapid sequence of pulses within burst 500 allows access to larger timescales of high intensity interaction with the material than is possible with single-pulse lasers. While a single-pulse can be expanded in time, conservation of energy dictates that as this is done, the intensity within the pulse must drop as roughly one over the pulse width. Hence if a 10 psec single pulse is expanded to a 10 nsec pulse, the intensity drops by roughly three orders of magnitude. Such a reduction can reduce the optical intensity to the point where non-linear absorption is no longer significant and the light-material interaction is no longer strong enough to allow for cutting. In contrast, with a burst pulse laser, the intensity during each pulse or sub-pulse 500A within the burst 500 can remain very high—for example three pulses 500A with pulse duration Td 10 psec that are spaced apart in time by a separation Tp of approximately 10 nsec still allows the intensity within each pulse to be approximately three times higher than that of a single 10 psec pulse, while the laser is allowed to interact with the material over a timescale that is three orders of magnitude larger. This adjustment of multiple pulses 500A within a burst thus allows manipulation of timescale of the laser-material interaction in ways that can facilitate greater or lesser light interaction with a pre-existing plasma plume, greater or lesser light-material interaction with atoms and molecules that have been pre-excited by an initial or previous laser pulse, and greater or lesser heating effects within the material that can promote the controlled growth of defect lines (perforations). The amount of burst energy required to modify the material will depend on the substrate material composition and the length of the line focus used to interact with the substrate. The longer the interaction region, the more the energy is spread out, and the higher the burst energy that will be required.)
A defect line, a perforation, or a hole is formed in the material when a single burst of pulses strikes essentially the same location on the glass. That is, multiple laser pulses within a single burst can produce a single defect line, perforation, or a hole location in the glass. Of course, if the glass is translated (for example by a constantly moving stage) or the beam is moved relative to the glass, the individual pulses within the burst cannot be at exactly the same spatial location on the glass. However, they are well within 1 μm of one another—i.e., they strike the glass at essentially the same location. For example, they may strike the glass at a spacing sp where 0<sp≦500 nm from one another. For example, when a glass location is hit with a burst of 20 pulses the individual pulses within the burst strike the glass within 250 nm of each other. Thus, in some embodiments 1 nm<sp<250 nm. In some embodiments 1 nm<sp<100 nm.
In one embodiment, a Corning glass code 2319 Gorilla® glass substrate 1000 with 0.55 mm thickness was positioned so that it was within the region of the focal line produced by the optical system. With a focal line of about 1 mm in length, and a picosecond laser that produces output power of about 40 W or greater at a burst repetition rate or frequency of 200 kHz (about 200 microJoules/burst measured at the material), the optical intensities (energy densities) in the focal line region can easily be high enough to create non-linear absorption in the substrate material. A region of damaged, ablated, vaporized, or otherwise modified material within the substrate was created in the glass that approximately followed the linear region of high intensity.
These damage tracks generally take the form of holes or perforations with interior dimensions (e.g. diameters) in the range of about 0.2 microns to 2 microns, for example 0.5-1.5 microns Preferably the holes or perforations are very small (single microns or less) in dimension. The defect lines, holes or perforations may or may not perforate the entire thickness of the material, and may or may not be a continuous opening throughout the depth of the material.
The lateral spacing (pitch) between the defect lines is determined by the pulse rate of the laser as the substrate is translated underneath the focused laser beam. Only a single picosecond laser pulse or burst is usually necessary to form an entire hole, but multiple pulses or bursts may be used if desired. To form holes or perforations at different pitches or defect line separations, the laser can be triggered to fire at longer or shorter intervals.
For cutting operations, the laser triggering generally is synchronized with the stage driven motion of the substrate beneath the beam, so laser pulses are triggered at a fixed interval, for example, every 1 microns, every 3 microns, or every 5 microns. For cutting or separating, the exact spacing between adjacent defect lines is determined by the material properties that facilitate crack propagation from perforated hole to perforated hole, given the stress level in the substrate.
However, in contrast to cutting a substrate, it is also possible to use the same method to only perforate the material (e.g., for the areas of glass that need to be curved or bent). In this case, the holes (or damage tracks, or perforations) may be separated by larger spacings (e.g., a 7 micron pitch, 8 micron pitch, 10 micron pitch, 25 micron pitch, 30 pitch, 50 pitch or greater). Depending on the glass used (e.g., unstrengthened glass, the pitch for perforations may be smaller than 7 or even smaller than 5 microns.
The laser power and lens focal length (which determines the focal line length and hence power density) are particularly important parameters to ensure full penetration of the glass and low surface and sub-surface damage.
In general, the higher the available laser power, the faster the material can be perforated or cut with the above process. The process(s) disclosed herein can perforate or cut glass at a perforation or cutting speed of 0.25 m/sec, or faster. A perforation speed or cut speed (or cutting speed) is the rate the laser beam moves relative to the surface of the substrate material (e.g., glass) while creating multiple defect lines holes. High speeds, such as, for example 350 mm/sec, 400 mm/sec, 500 mm/sec, 750 mm/sec, 1 m/sec, 1.2 m/sec, 1.5 m/sec, or 2 m/sec, or even 3.4 m/sec to 4 m/sec are often desired in order to minimize capital investment for manufacturing, and to optimize equipment utilization rate. The laser power is equal to the burst energy multiplied by the burst repetition frequency (rate) of the laser. In general, to perforate or cut glass materials at high speeds, the defect lines are typically spaced apart by 1-25 μm, in some embodiments the spacing is preferably 3 μm or larger—for example 3-12 μm, or for example 5-10 μm.
For example, to achieve a linear perforation or cutting speed of 300 mm/sec, a 3 μm hole pitch corresponds to a pulse burst laser with at least 100 kHz burst repetition rate. For a 600 mm/sec perforation or cutting speed, a 3 μm pitch corresponds to a burst-pulsed laser with at least 200 kHz burst repetition rate. A pulse burst laser that produces at least 40 μJ/burst at 200 kHz, and perforates and/or cuts at a 600 mm/s cutting speed needs to have a laser power of at least 8 Watts. Higher perforation speed or higher cut speeds require accordingly higher laser powers.
For example, a 0.4 m/sec perforation or cut speed at 3 μm pitch and 40 μJ/burst would require at least a 5 W laser. Similarly, a 0.5 m/sec peroration or cut speed at 3 μm pitch and 40 μJ/burst would require at least a 6 W laser. Thus, preferably the laser power of the pulse burst picosecond laser is 6 W or higher, more preferably at least 8 W or higher, and even more preferably at least 10 W or higher. For example, in order to achieve a 0.4 m/sec perforation or cut speed with a 4 μm pitch (defect line spacing, or damage tracks spacing) and 100 μJ/burst, one would require at least a 10 W laser, and to achieve a 0.5 m/sec perforation/cut speed at 4 μm pitch and 100 μJ/burst, one would require at least a 12 W laser. For example, a to achieve a perforation/cut speed of 1 m/sec at 3 μm pitch and 40 μJ/burst, one would require at least a 13 W laser. Also, for example, 1 m/sec perforation/cut speed at 4 μm pitch and 400 μJ/burst would require at least a 100 W laser.
The optimal pitch between defect lines (damage tracks) and the exact burst energy is material dependent and can be determined empirically. However, in case of cauuting or glass separation, it should be noted that raising the laser pulse energy or making the damage tracks at a closer pitch are not conditions that always make the substrate material separate better or with improved edge quality. A pitch that is too small (for example <0.1 micron, or in some exemplary embodiments <1 μm, or in other embodiments <2 μm) between defect lines (damage tracks) can sometimes inhibit the formation of nearby subsequent defect lines (damage tracks), and often can inhibit the separation of the material around the perforated contour. An increase in unwanted micro cracking within the glass may also result if the pitch is too small. A pitch that is too long (e.g. >50 μm, and in some glasses >25 μm or even >20 μm) may result in “uncontrolled microcracking”—i.e., where instead of propagating from defect line to defect line along the intended contour, the microcracks propagate along a different path, and cause the glass to crack in a different (undesirable) direction away from the intended contour. This may ultimately lower the strength of the separated part since the residual microcracks constitute flaws that weaken the glass. A burst energy for forming defect lines that is too high (e.g., >2500 μJ/burst, and in some embodiments >500 μJ/burst) can cause “healing” or re-melting of previously formed defect lines, which may inhibit separation of the glass. Accordingly, it is preferred that the burst energy be <2500 μJ/burst, for example, <500 μJ/burst. Also, using a burst energy that is too high can cause formation of microcracks that are extremely large and create structural imperfections that can reduce the edge strength of the part after separation. A burst energy that is too low (e.g. <40 μJ/burst) may result in no appreciable formation of defect lines within the glass, and hence may necessitate especially high separation force or result in a complete inability to separate along the perforated contour.
Typical exemplary perforation speeds or cutting rates (speeds) enabled by this process are, for example, 0.25 m/sec and higher. In some embodiments, the perforation speeds or cutting rates are at least 300 mm/sec. In some embodiments, the cutting rates are at least 400 mm/sec, for example, 500 mm/sec to 2000 mm/sec, or higher. In some embodiments the picosecond (ps) laser utilizes pulse bursts to produce defect lines with periodicity between 0.5 μm and 13 μm, e.g. between 0.5 and 3 μm. In some embodiments, the pulsed laser has laser power of 10 W-100 W and the material (e.g. glass sheet 1000) and/or the laser beam are translated relative to one another at a rate of at least 0.25 m/sec; for example, at the rate of 0.25 m/sec to 0.35 m/sec, or 0.4 m/sec to 5 m/sec. Preferably, each pulse burst of the pulsed laser beam has an average laser energy measured at the workpiece (such as glass sheet 1000, for example) greater than 40 μJ per burst per mm thickness of workpiece. Preferably, each pulse burst of the pulsed laser beam has an average laser energy measured at the workpiece greater of less than 2500 μJ per burst per mm thickness of workpiece, and preferably lass than about 2000 μJ per burst per mm thickness of workpiece, and in some embodiments less than 1500 μJ per burst per mm thickness of workpiece; for example, not more than 500 μJ per burst per mm thickness of workpiece.
We discovered that much higher (5 to 10 times higher) volumetric pulse energy density (μJ/μm3) is required for perforating alkaline earth boroaluminosilicate glasses with low or no alkali content. This can be achieved, for example, by utilizing pulse burst lasers, preferably with at least 2 pulses per burst and providing volumetric energy densities within the alkaline earth boroaluminosilicate glasses (with low or no alkali) of about 0.05 μJ/μm3 or higher, e.g., at least 0.1 μJ/μm3, for example 0.1-0.5 μJ/μm3.
Accordingly, it is preferable that the laser produces pulse bursts with at least 2 pulses per burst. For example, in some embodiments the pulsed laser has a power of 10 W-150 W (e.g., 10 W-100 W) and produces pulse bursts with at least 2 pulses per burst (e.g., 2-25 pulses per burst). In some embodiments the pulsed laser has a power of 25 W-60 W, and produces pulse bursts with at least 2-25 pulses per burst, and periodicity or distance between the adjacent defect lines produced by the laser bursts is 2-10 μm. In some embodiments, the pulsed laser has a power of 10 W-100 W, produces pulse bursts with at least 2 pulses per burst, and the workpiece and the laser beam are translated relative to one another at a rate of at least 0.25 m/sec. In some embodiments the workpiece and/or the laser beam are translated relative to one another at a rate of at least 0.4 m/sec.
For example, for cutting 0.7 mm thick non-ion exchanged Corning code 2319 or code 2320 Gorilla® glass, it is observed that pitches of 3-7 μm can work well, with pulse burst energies of about 150-250 μJ/burst, and burst pulse numbers that range from 2-15, and preferably with pitches of 3-5 μm and burst pulse numbers (number of pulses per burst) of 2-5.
At 1 m/sec perforation speeds (or cut speeds), the perforation and/or cutting of Eagle XG® glass or 2320 Gorilla®, glass typically requires utilization of laser powers of 15-84 W, with 30-45 W often being sufficient. In general, across a variety of glass and other transparent materials, applicants discovered that laser powers between 10 W and 100 W are preferred to achieve perforation and/or cutting speeds from 0.2-1 m/sec, with laser powers of 25-60 W being sufficient (or optimum) for many glasses. For perforation and/or cutting speeds of 0.4 m/sec to 5 m/sec, laser powers should preferably be 10 W-150 W, with burst energy of 40-750 μJ/burst, 2-25 bursts per pulse (depending on the material that is cut), and defect line separation (pitch) of 3 to 15 μm, or 3-10 μm. The use of picosecond pulse burst lasers would be preferable for these cutting speeds because they generate high power and the required number of pulses per burst. Thus, according to some exemplary embodiments, the pulsed laser produces 10 W-100 W of power, for example 25 W to 60 W, and produces pulse bursts at least 2-25 pulses per burst and the distance between the defect lines is 2-15 μm; and the laser beam and/or workpiece are translated relative to one another at a rate of at least 0.25 m/sec, in some embodiments at least 0.4 m/sec, for example 0.5 m/sec to 5 m/sec, or faster.
The laser perforation, or defect (hole) formation according some embodiments described herein was performed on both strengthened and unstrengthened glass.
The laser conditions and material perforation speed used for the demonstrations described above are summarized below for reference. For example, in some embodiments, to separate the singulated parts from the glass matrix, forces were manually applied at the release lines. The forces caused breaks at the perforation lines (defect lines) and propagation of cracks along the fault line that eventually separated the shapes from the glass matrix.
As an alternative to the process just described, another embodiment utilizing a defocused CO2 laser to aid in releasing the parts (for part separation/singulation) has been demonstrated. The defocused CO2 laser follows the picosecond laser as it traces the desired contour (fault line) to effect separation of the part from the surrounding substrate matrix. The thermal stress induced by the defocused CO2 laser is enough to initiate and propagate cracks that lead to separation of the part along the desired contour defined by the fault line, thereby releasing the shaped part from the substrate panel. For this case, the best results were found for the following optics and laser parameters:
Picosecond laser
Input beam diameter to axicon lens˜2 mm
Axicon angle=10 degrees
Initial collimating lens focal length=125 mm
Final objective lens focal length=40 mm
Incident beam convergence angle=12.75 degrees
Focus set between zero and 10 mm, varying in steps of 200 microns each tracing.
Laser power at 75% of full power (˜30 Watts)
Pulse repetition rate of the laser=200 kHz.
3 pulses/burst
Pitch=6 microns
Multiple laser focal line pass of same trace Motion stage speed=12 m/min=200 mm/s
CO2 laser
Laser translation speed: 130 mm/s
Laser power=100%
Pulse duration 13 microseconds (95% duty cycle)
Laser modulation frequency 20 kHz
Laser beam defocus is 21 mm
Single pass
Unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not actually recite an order to be followed by its steps or it is not otherwise specifically stated in the claims or descriptions that the steps are to be limited to a specific order, it is no way intended that any particular order be inferred.
It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit or scope of the invention. Since modifications combinations, sub-combinations and variations of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and their equivalents.
This application claims the benefit of priority under 35 U.S.C. §365 of International Patent Application Serial No. PCT/US14/70724 filed on Dec. 17, 2014 which claims the benefit of priority to U.S. Provisional Patent Application Ser. No. 62/024,724 filed on Jul. 15, 2014, and provisional patent application no. 62/024,581 filed on Jul. 15, 2014, and U.S. application No. 61/917,127 filed Dec. 17, 2013, the contents of which are relied upon and incorporated herein by reference in their entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US14/70724 | 12/17/2014 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62024724 | Jul 2014 | US | |
| 62024581 | Jul 2014 | US | |
| 61917127 | Dec 2013 | US |
