COVER GLASS FOR ELECTRONIC DEVICES
A cover glass element can extend to the edges of an electronic device while maintaining the optical flatness and thickness needed for the cover glass. A first glass sheet with the desired thickness and flatness can be thermally bonded to a second glass sheet machined to include an opening to be received by the edges of the electronic device. The resulting three-dimensional cover element forms a uni-body frame that is significantly stiffer than a single sheet of glass, and the larger surface area of the edge provides for enhances pressure distribution, particularly after chemical strengthening, thus enhancing the durability of the electronic device. Further, the thermal bonding process uses lower temperatures than processes such as slumping or pressing, which could potentially affect the flatness and optical clarity of the original sheet glass.
This application is a divisional of U.S. application Ser. No. 13/414,549 filed Mar. 7, 2012, entitled “Cover Glass for Electronic Devices,” which claims the benefit of U.S. Provisional Application No. 61/535,724 (Attorney Docket No. 20346.0171.PZUS00), filed Sep. 16, 2011, and entitled “Cover Glass for Electronic Devices,” the full disclosure of which are hereby incorporated in their entirety by reference.
BACKGROUNDPeople are increasingly utilizing portable computing devices, such as smart phones and tablet computers, for a variety of tasks. In many instances, these devices include at least one display screen including a display element, such as a liquid crystal display (LCD) element, at least one touch sensitive component, and an overlying transparent layer. This overlying layer typically comprises a sheet of cover glass, which generally has a uniform thickness to ensure proper connection with various components of the display screen, as well as to prevent unintended optical artifacts. As the size of the display screens increase, and as the thickness of the devices decrease, the transparent cover layers are increasingly subject to damage due to actions such as dropping a device or applying an unexpected point pressure. The edges of the cover layer can be particularly susceptible to damage, which is increasing problematic as the edges of the screen approach the edges of the various computing devices.
Various embodiments in accordance with the present disclosure will be described with reference to the drawings, in which:
Systems and methods in accordance with various embodiments of the present disclosure may overcome one or more of the aforementioned and other deficiencies experienced in conventional cover layers utilized with various electronic devices. In particular, various embodiments utilize a glass fusion process to bond at least two glass layers in order to form a cover glass element that provides a smooth, consistent cover glass surface with a robust edge. The cover glass element can have a thin glass cross-section corresponding to a central area of an electronic device to receive the cover glass element and to accommodate device components while providing the ability to have variable cross-section dimensions at other areas. An example cover glass element provides enhanced strength at the edges with respect to conventional cover glass layers, but maintains the uniformity needed for the primary optical display portion of the cover glass element. Such an approach can be used to manufacture multiple cover glass elements concurrently, in order to provide an economical approach to the formation of such elements.
Due at least in part to the increased strength of the cover glass elements with respect to conventional cover layers, a glass element can be designed to extend to and/or over one or more edges of an electronic device. The ability to wrap the cover glass around the edge(s) can provide for a smooth, polished edge that is also durable to dropping or other impact actions. Further, such a design can be aesthetically pleasing, and can enable other functionality, such as display or touch inputs, to be extended to the sides or edges of a device as well. An additional benefit of such a design is that the radio frequency (RF) transparent regions of the device as enlarged, providing for improved performance and increased flexibility in antennae placement.
Various other applications, processes, implementations, and uses are presented below with respect to the various embodiments.
It is not straightforward, however, to form such a shaped glass element for these types of devices. Certain approaches to forming three-dimensional glass elements utilize processes such as glass slumping, wherein a sheet of glass is heated beyond the transition temperature while placed on a one-sided mold (or in a two-sided mold). Gravity (or other applied force) causes the glass to slowly flow into the mold. These processes are not ideal for computing device displays, however, as they typically have problems with uniformity and optical flatness. Further, for devices with touch-sensitive displays there typically must be a proper connection between the touch sensors and the cover layer in order to ensure proper touch sensitivity. Since the cover glass is part of the display screen it also can be desirable to ensure as few optical defects or artifacts as possible. Certain approaches attempt to flatten or smooth the glass using a grinding or polishing process, but such an approach is of limited use for three-dimensional shapes with corners and other difficult-to-polish features.
Accordingly, systems and methods in accordance with various embodiments utilize a process such as thermal bonding to enable multiple glass sheets to be formed into a single glass element. The ability to utilize multiple sheets or layers of material enables portions of the resulting element to be of a controlled thickness and flatness at various portions, by utilizing a first sheet having those characteristics, and portions to be of a controlled and polished shape, by utilizing a second sheet that is able to be machined to a desired level of quality without worrying about affecting the quality of the first sheet or polishing complex three-dimensional features.
For example,
A second sheet 304, herein referred to as an edge sheet, can be made of a similar material to that of the cover sheet, but in at least some embodiments need not have critical flatness or thickness control requirements as those of the cover sheet. The edge sheet can be formed of an appropriate thickness (e.g., 1.6 mm thick) determined for reasons such as a desired amount of rigidity and/or the amount of distance which the cover glass element is to wrap around the edges of a computing device. As illustrated in
Once the cover and edge sheets are formed and machined to an appropriate size and shape, the sheets can be cleaned to an appropriate level of cleanliness for the thermal bonding process. In one embodiment, the sheets are taken to a clean environment to prevent particulates from adhering to the glass, wherein the sheets can undergo appropriate cleaning processes such as ultrasonic cleaning and/or passage through a sodium bath. In some embodiments, the surfaces of the sheets that are to be bonded can undergo a fine micro-etch or similar process as well, which can substantially maintain the thickness and flatness of the sheets but provide a level of surface roughness that can assist with the thermal bonding process and improve adhesion between the sheets. In other embodiments, the sheets could undergo a polishing process before bonding in order to increase their relative attraction to each other by way of optical contacting.
Once the sheets are properly prepared, the cover sheet 302 and edge sheet 304 can be positioned in a desired orientation with respect to each other, in at least some embodiments involving a combination 400 of the edge sheet 304 on the cover sheet 302 as illustrated in
As mentioned, the cover sheet can be placed on the platen first in at least some embodiments to ensure that the flatness is not affected by the high temperatures. The temperatures used can depend at least in part upon the material(s) used, but for a material such as LAS80 with a glass transition temperature around 505 degrees Celsius, the temperature can be around or approaching 500 degrees Celsius. Since the softening point of that material is around 720 degrees Celsius, the sheets should substantially retain their respective shapes and avoid any decrease in flatness. Once the sheets are under an appropriate temperature for an appropriate amount of time, which can be on the order of minutes in some embodiments, the van der Waals forces will actually hold or bond the two sheets together such that the combined sheets effectively form a single glass element. Such an approach is advantageous at least for the reason that no adhesive is needed to bond the layers, which could impact the optical properties and/or appearance of the cover glass, and could adversely affect the chemical strengthening process.
It should be understood that various other bonding approaches can be used as well within the scope of the various embodiments. For example, a float approach can be used in place of a furnace platen in some embodiments. Further, some approaches can use bonding agents such as glass frit to assist with the bonding process, where those agents are not incompatible with the chemical strengthening process used in at least some embodiments. In embodiments where an etching process is used to increase the surface roughness of the sheets, the small peaks resulting from the etch can begin flowing shortly after the application of heat, such that those peaks can quickly being atomically fusing together.
After the sheets are bonded together in the furnace or other such machine, a relatively slow temperature ramp-down process can be used to relieve stress and/or prevent damage to the glass due to fast and/or uneven temperature decreases. The amount of time can vary depending on factors such as the materials, substrate mass, dimensions or thickness of the glass, and temperatures used, but can be on the order of at least tens of minutes. After the bonded sheets are sufficiently cooled, the sheets can go through a separation process whereby the individual glass elements are cut or otherwise separated into pieces of a specific size and shape, forming multiple elements from a single sheet. The separation process of cutting out shapes, particularly shapes with round edges, in glass is not straightforward.
Once the individual cover sheet elements are separated, the elements can go through one or more machining processes to generate the final outer shape of the elements. For example, the dicing process discussed above might result in elements with a substantially rectangular outer shape with relatively sharp edges. In at least some embodiments, at least one machining process can be used to adjust the shape of the outer edge of the cover glass elements, such as to round corners to substantially match the outer edge of the electronic device intended to receive the cover glass. The inner edge from the edge layer can be used in at least some embodiments as a guide or reference for the outer edge machining process. In at least some embodiments, the same or a separate machining process can also be used to shape, radius, or spline the exposed edges or corners of the cover sheet, such that there are no sharp exposed edges or stress risers of the cover glass and the edges have a smooth, rounded feel. The radiusing of the outside edges also helps distribute pressure and load, which can help increase the strength of the cover glass element. A separate polishing process can be utilized as well where appropriate and/or desired. Once the individual cover glass elements have the desired final shape, at least for this portion of the process, the elements can undergo an appropriate chemical strengthening process in order to increase the strength and durability of the glass elements. For example, the glass elements can be submersed in a bath containing a potassium salt or potassium nitrate solution, whereby potassium ions replace sodium or other ions in the surface of the glass elements. Since the potassium ions are larger, the surface glass enters a state of compression which can cause the elements to be strengthened by several times the strength of untreated glass. After processing, a set 600 of cover glass elements 602 can result, as illustrated in
The cover glass elements can also go through one or more inspection processes to ensure quality of the formed elements. For example, the elements can undergo at least one optical inspection to search for gaps in bonding or dust between the layers, as might be evidenced by van der Walls rings or Newton rings visible in the elements. Various tests such as four point bending tests can also be used to verify the bonds, as well as fine measurement processes to detect thickness variations and the like.
Additional processes can be used in the various embodiments as well. For example, through holes or blind holes might be drilled or otherwise formed in the edges of the elements for purposes such as enabling screw access for assembly, passage for audio, lighting, or image content, etc. In some embodiments, additional sheets might be bonded to enable more complex three-dimensional shapes, while maintaining optical flatness where critical. In some embodiments, touch or display functionality might be utilized on a side or back of an electronic device, such that thickness and flatness might be more important on those areas in some embodiments. In some embodiments, a cover glass element can be used on the front at back of the device, as may be held together using a metal interface or other such approach.
Accordingly, systems and methods in accordance with various embodiments may utilize various automated and/or manual processes to form the cover glass element. A cover glass element in at least some embodiments can be designed utilizing a computer-aided design (CAD) program. Various machines, such as those known in the art used to cut/separate, heat, grind, polish, and/or clean the cover glass element along the various stages of production, can be automated utilizing a computer-aided manufacturing (CAM) program. These programs can produce a computer file that is interpreted to extract commands needed to operate their respective machine, which is then loaded into a computer numerical control (CNC) machine for production. Various computers and computer systems also can be used to control various aspects of components used to form a cover glass element. These computers and computer systems can execute various instructions, as may be embedded in a non-transitory computer-readable storage medium, for performing portions (or causing portions to be performed) of various processes discussed herein.
It should be understood that the specification and drawings are to be regarded in an illustrative rather than a restrictive sense. It will, however, be evident that various modifications and changes may be made thereunto without departing from the broader spirit and scope of the various embodiments as set forth in the claims.
Claims
1. A cover glass, comprising:
- a first glass component formed from a first glass sheet, the first glass sheet of a specified thickness and a specified flatness; and
- a second glass component formed from a second glass sheet, the second glass sheet including a plurality of through-holes, the second glass component including at least one through-hole of the plurality of through-holes, the first glass sheet and the second glass sheet being thermally bonded together,
- wherein the cover glass has at least one planar region of the specified thickness and the specified flatness and at least one edge formed, at least in part, by the second glass component.
Type: Application
Filed: Mar 16, 2015
Publication Date: Jul 9, 2015
Inventors: David N. Bibl (Santa Cruz, CA), Leo B. Baldwin (San Jose, CA)
Application Number: 14/659,392