Asymmetric chemical strengthening

Abstract

The disclosure relates to asymmetric chemical strengthening. More specifically, the present invention discloses an asymmetrically strengthened glass article, a method for producing the same, and the use of the article in a portable electronic device. Asymmetric chemical strengthening is optimized for the utility of the glass article using a budgeted amount of compressive and tensile stress. In some aspects, the strengthened glass article may be designed to reduce damage or damage propagation when dropped.

Description

[0001] This application is a divisional application of Chinese patent application No. 201780014676.8, whose application date is May 19, 2017 and whose invention name is “Asymmetric Chemical Strengthening”; the divisional directly targeted by this application is Chinese patent application No. 202210490594.3.

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This Patent Cooperation Treaty patent application claims priority to U.S. Provisional Patent Application No. 62 / 339,062, filed on May 19, 2016, entitled “Asymmetric Chemical Strengthening,” U.S. Provisional Patent Application No. 62 / 362,578, filed on July 14, 2016, entitled “Asymmetric Chemical Strengthening,” U.S. Provisional Patent Application No. 62 / 368,787, filed on July 29, 2016, entitled “Asymmetric Chemical Strengthening,” and U.S. Provisional Patent Application No. 62 / 368,792, filed on July 29, 2016, entitled “Asymmetric Chemical Strengthening,” the contents of which are incorporated herein by reference in their entirety. Technical Field

[0004] The described embodiments generally relate to asymmetric chemical strengthening of glass articles. More specifically, the present embodiments relate to calibrating the strength and safety of cover glass for use in portable electronic devices. Background Art

[0005] Cover windows and displays for small form factor devices are typically made of glass. While glass is transparent and scratch resistant, it is fragile and susceptible to failure due to impact. Providing a reasonable level of strength in these glass components is critical to reducing the likelihood of glass component failure and, therefore, device failure.

[0006] Chemical strengthening has been used to increase the strength of glass components. Typical chemical strengthening relies on a uniform and symmetrical increase in compressive stress across the surface of the glass component. Such strengthening processes have proven effective in reducing failures in glass components to some extent. However, there continues to be significant pressure to form thinner glass for use in small form factor devices where symmetrical chemical strengthening is insufficient to prevent impact failures in a reliable manner.

[0007] Thus, while chemical strengthening is known to be effective, there is a continuing need to provide improved and alternative means of strengthening glass, particularly thin glass. Summary of the invention

[0008] Various embodiments described herein encompass asymmetric strengthened glass articles. Asymmetric strengthened glass articles have enhanced reliability and safety as compared to symmetric strengthened glass articles. An asymmetric strengthened glass article has: a first region containing a first stress pattern; and a second region containing a second stress pattern. The first stress pattern and the second stress pattern are different from each other. The difference between the first stress pattern and the second stress pattern results in an overall stress imbalance in the asymmetric strengthened glass article. The overall stress imbalance can cause the glass article to exhibit warpage.

[0009] In additional embodiments, materials may be operatively attached to the glass article to counteract stress imbalance and warping of the glass article, or alternatively, additional regions may be formed in the glass, such additional regions having stress patterns useful for counteracting stress imbalances in the first and second regions. It is also contemplated that the first and second regions may be patterned to counteract each other and limit or avoid stress imbalances in the glass article.

[0010] In some aspects, the first region has a first stress profile and a first density that is greater than a second density found in the second region, the second density having a second stress profile. In other aspects, ion diffusion barriers and ion-inclusion coatings can be applied to the first region and / or the second region to permit the formation of such stress profiles. One ion diffusion barrier is composed of silicon nitride. Another ion diffusion barrier is composed of silicon dioxide.

[0011] Various embodiments described herein also encompass an asymmetric strengthened cover glass for use with an electronic device, wherein the cover glass is designed to reduce or limit damage caused by an impact (e.g., a drop). The cover glass includes three different stress patterns caused by asymmetric strengthening, the first stress pattern corresponding to the corner area of ​​the cover glass, the second stress pattern corresponding to the straight edge (or edges) or straight peripheral area of ​​the cover glass, and the third stress pattern corresponding to the remaining or center area of ​​the cover glass. The first area is strengthened the most; the second area is strengthened to a lesser extent than the first area; and the third area is strengthened the least compared to the first area and the second area. In order to maintain a stress budget corresponding to a cover glass that is practical for an electronic device, all of the stress budget is generally spent on the first area and the second area, allowing for little or no strengthening of the third area. This asymmetric strengthening pattern causes such corners (where most impacts occur) to be maximally strengthened and impact resistant, the second area has sufficient strengthening for impact protection, and the third area remains substantially flat.

[0012] Embodiments also include: portable electronic devices including glass articles according to the present disclosure; and methods of making the same. In some aspects, the glass articles can be monitored and tested to identify compliant asymmetric strengthened glass articles for use in electronic devices.

[0013] In method embodiments, the glass article is asymmetrically strengthened to calibrate the glass for use in a portable electronic device. The glass article can be calibrated to have a target geometry or to provide one or more flat surfaces.

[0014] Some methods of asymmetric strengthening include immersing a sodium-infused glass article in a potassium ion bath while preferentially delivering potassium ions at a predetermined surface of the glass article. In some aspects, immersing the sodium-infused glass article in the potassium ion bath is accompanied by subjecting the same predetermined surface of the glass article to microwave radiation.

[0015] In additional method embodiments, stress relationships are identified and implemented using chemical strengthening. In some aspects, glass forming is combined with asymmetric chemical strengthening to provide a glass article having a suitable geometry. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The present disclosure may be more easily understood through the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals refer to like structural components, and wherein:

[0017] Figure 1 Diagram showing a glass article according to embodiments herein.

[0018] Figure 2 is a flow chart of a glass strengthening process according to embodiments herein.

[0019] Figure 3 A glass strengthening system according to embodiments herein is presented.

[0020] Figure 4A is a cross-sectional view of a glass cover that has been symmetrically chemically treated according to embodiments of the present invention.

[0021] Figure 4B is a cross-sectional view of a glass cover that has been symmetrically chemically treated, as shown to include a chemically treated portion into which potassium ions have been implanted according to embodiments herein.

[0022] Figure 5A is a diagram of the lattice structure used for glass.

[0023] Figure 5B is a diagram of the lattice structure for the corresponding densified glass.

[0024] Figure 6 is an illustration of a partial cross-section of a glass cover showing two zones of densified glass.

[0025] Fig. 7A is an illustration of a partial cross-sectional view of a glass cover showing tension / compression stress distribution according to embodiments herein.

[0026] Figure 7B is an illustration of a partial cross-sectional view of a glass cover showing a reduced tension / compression stress distribution according to embodiments herein.

[0027] Figure 7C is an illustration of a partial cross-sectional view of a glass cover according to embodiments herein, showing an asymmetric tension / compression stress distribution.

[0028] Figure 8 is a flow chart of asymmetric glass strengthening according to embodiments herein.

[0029] Fig. 9 is a cross-sectional view of a glass cover that has undergone an asymmetric chemical treatment.

[0030] Fig.10 is a cover glass having a SiN coating applied to the center portion, while the edge and corner portions remain uncoated.

[0031] Fig.11A is a cross-sectional view of a glass cover having a combination of coatings applied to the top and bottom surfaces.

[0032] Fig. 11B is a cross-sectional view of the glass cover, which shows Fig.11AThe coating embodiment described in .

[0033] Fig. 12A and Fig. 12B The use of a high ion concentration paste on both the front and back surfaces of the cover glass is shown.

[0034] Fig.13

[00136] An alternative glass strengthening system according to embodiments herein is presented.

[0035] FIG. 14A to FIG. 14E A process for chemically strengthening pre-bent glass according to embodiments herein is shown.

[0036] Fig.15 A glass strengthening system for clad laminated glazing according to embodiments herein is presented.

[0037] Fig.16 is a flow chart of glass product production using asymmetric glass processing.

[0038] Fig.17A and Fig. 17B Chemical strengthening at potential crack spots is shown to minimize crack propagation.

[0039] Fig.18 is a crack pattern stress curve diagram according to an embodiment of the present invention.

[0040] Fig.19 is a flow chart for the production of a glass article, wherein the glass article has at least three zones of different chemical strengthening.

[0041] Fig. 20 is a flow chart for cover glass production wherein the glass article has a maximum amount of chemical strengthening at its corners, a lesser amount of chemical strengthening along its peripheral side edges, and a minimum amount of chemical strengthening in the remainder of the glass.

[0042] Fig.21 A diagram of a cover glass according to embodiments herein is shown.

[0043] Fig. 22 Shown in Fig.19 Cross-sectional view of the corner in FIG. 1 to illustrate asymmetric chemical strengthening.

[0044] Fig.23 is a flow chart for compensating for asymmetric chemical strengthening using glass forming techniques according to an embodiment of the present invention.

[0045] Fig.24 is a graphical representation of compressive stress versus depth of compression for three illustrative glass articles according to embodiments herein.

[0046] Fig.25 Shown are glass articles formed into predetermined geometric shapes according to embodiments herein.

[0047] Fig.26 Glass articles according to embodiments herein are shown subjected to CNC and polishing after being formed.

[0048] Fig. 27 Glass articles according to embodiments herein are shown partially coated with a diffusion barrier (SiN) after forming and CNC.

[0049] Fig.28A and Fig.28B Asymmetric chemical strengthening of the glass article of FIG. 12 is shown according to embodiments herein.

[0050] Fig.28C It is based on Fig.28A Stress distribution of the glass product shown in .

[0051] Fig.29A and Fig.29B The oxidation of a SiN layer to SiO2 on a glass article according to embodiments herein is shown.

[0052] Fig. 30A and Fig. 30B Asymmetric chemical strengthening of a formed glass article according to embodiments herein is shown.

[0053] Fig. 30C It is based on Fig. 30A Stress distribution of the glass product shown in .

[0054] Cross-hatching or shading used in the drawings is generally provided to clarify boundaries between adjacent components and also to aid in identification of the drawings in the specification. Therefore, the presence or absence of cross-hatching or shading does not express or indicate a preference or requirement for a particular material, material property, component ratio, component size, commonality of similarly illustrated components, or any other characteristic, attribute, or property of any component shown in the drawings.

[0055] Furthermore, it should be understood that the proportions and sizes (relative or absolute) of the various features and components (and collections and groups thereof) provided in the accompanying drawings, as well as the boundaries, distances, and positioning relationships presented therebetween, are merely intended to facilitate understanding of the various embodiments described herein, and therefore, are not necessarily presented or illustrated to scale, and are not intended to indicate a preference or requirement for the illustrated embodiments to exclude embodiments described with reference thereto. DETAILED DESCRIPTION

[0056] Reference will now be made in detail to the representative embodiments shown in the accompanying drawings. It should be understood that the following description is not intended to limit the embodiments to the preferred embodiments. On the contrary, it is intended to cover various alternatives, modifications and equivalents that may be included within the spirit and scope of the described embodiments as defined by the appended claims.

[0057] The following disclosure relates to glass articles, methods of producing glass articles, and to the utility of such glass articles in electronic devices. Embodiments also relate to asymmetric increases in glass strength, and more particularly to asymmetric strengthening of glass articles to further calibrate the reliability and safety of the glass articles in electronic devices. In some embodiments, the electronic device may include: a housing; a display positioned at least partially within the housing; and a glass article, such as a cover glass according to embodiments herein.

[0058] In one example, the glass article may be an outer surface of an electronic device. The glass article may correspond to a glass article that helps form a component of a display area, or in some examples, relates to a component that forms the housing. Embodiments herein are particularly directed to use in portable electronic devices and small form factor electronic devices, such as laptop computers, mobile phones, media players, remote control units, and the like. Typical glass articles herein are thin, and generally less than 5 mm thick, and in most cases, between about 0.3 mm and 3 mm thick, and between 0.3 mm and 2.5 mm thick.

[0059] Figure 1 1 is a perspective view of a glass article according to an embodiment. The glass article 100 is a thin glass sheet having a length and width consistent with the present application. Figure 1 In the application shown in , the glass article is a cover glass for a housing of an electronic device 103. The glass article 100 may have a front surface 102, a rear surface (not shown), a top surface 104, a bottom surface 106, and side surfaces 108. The various surfaces and sides may be composed of zones and / or portions. For example, one zone of the glass article may be the entire front surface, while the rear surface would be considered a different zone. Another zone of the glass article may be a region corresponding to one or more corners of the glass. The zones do not have to be continuous, for example, all four corners of the glass article may be represented on a single zone. The strength requirements of surfaces and zones may vary depending on the application, for example, the front surface 102 exposed to the external environment may require different strength than the rear surface that is enclosed and isolated from the environment. As discussed in more detail below, the edge 110 of the glass article 100 may have a predetermined geometry.

[0060] References below Figures 2 to 30 discusses these and other implementations. However, those skilled in the art will appreciate that the detailed description given herein with respect to these figures is for illustrative purposes only and should not be construed as limiting.

[0061] Chemical strengthening

[0062] Embodiments herein may utilize a glass strengthening process in which a glass article is first strengthened by immersion in a first ionic solution (eg, sodium), and then strengthened by immersion in a second ionic solution (eg, potassium).

[0063] Figure 2 is a flow chart of a glass strengthening process 200 according to one embodiment. The glass strengthening process 200 includes: obtaining a piece of glass 202; strengthening the glass article 204 by chemical treatment; and strengthening the glass article 206 by further chemical treatment.

[0064] Figure 3 An embodiment 300 for strengthening a glass article according to embodiments herein is shown. A glass article 302 in need of glass strengthening is immersed in a first bath 304 containing a sodium solution 306. Next, the enhanced strength glass article is removed from the first bath 304 and immersed in a second bath 308 containing a potassium solution 310. At this stage, the glass article 302 is symmetrically strengthened, meaning that all exposed surfaces of the glass article have been equally strengthened and strengthened by immersion in a sodium solution and then in a potassium solution. In some embodiments, the strengthened glass article may be quenched to exclude further ion exchange from the treated glass article.

[0065] The degree of glass strengthening is generally controlled by: the type of glass (the glass may be, for example, alumina silicate glass or soda lime glass, and the like); the sodium concentration of the bath (sodium or sodium nitrate, typically 30 to 100 mol %); the time the glass spends in the bath (typically 4 to 8 hours); and the bath temperature (350 to 450°C).

[0066] The strengthening of the glass article in the second bath is controlled by the type of glass, the potassium ion concentration, the time the glass spends in the solution, and the solution temperature. Here, potassium or potassium nitride is in the range of 30 to 100 mol%, but the glass article will be maintained in the bath at a solution temperature between about 300 to 500°C for about 6 to 20 hours.

[0067] The chemical strengthening process relies on ion exchange. In each solution bath, the ions therein are heated to promote ion exchange with the glass article. During a typical ion exchange, diffusion exchange occurs between the glass article and the ion bath. For example, during the strengthening process, sodium ions diffuse to the surface of the exposed glass, allowing sodium ions to accumulate in the surface of the glass by replacing other ions found in silicate or soda-lime glass. Once the strengthened glass article is immersed in a potassium bath, the sodium ions in the surface area are replaced by potassium ions to a greater extent than the sodium ions found more toward the interior or middle of the glass. Therefore, the potassium ions that replace the sodium ions form a compressive layer near the surface of the glass article (basically, the larger potassium ions take up more space than the smaller sodium ions that are exchanged). The sodium ions that have been displaced from the surface of the glass article become part of the potassium bath ion solution. Depending on the factors discussed above, a compressive layer as deep as about 10 to 100 microns (and more generally 10 to 75 microns) may be formed in the glass article.

[0068] Figure 4A 4 is a cross-sectional view of a glass article 400 according to embodiments described herein that has been chemically treated such that a symmetrical chemically strengthened layer 402 is established. The glass article 400 includes the chemically strengthened layer 402 and a non-chemically strengthened inner portion 404. Although discussed in greater detail throughout, the effect of chemically strengthening the glass article is that the inner portion 404 is subjected to tension while the chemically strengthened layer 402 is in compression. The chemically strengthened layer has a thickness (Y) that can vary depending on the requirements of a particular application.

[0069] Figure 4B is a graphical representation of the chemical strengthening process. Note that some amount of sodium 405 diffuses from the strengthened glass article into the ion bath, while potassium (K) ions 406 diffuse into the surface of the glass article, forming a chemically strengthened layer 402. However, alkali metal ions (such as potassium) are generally too large to diffuse into the central portion of the glass, thereby causing the inner portion 404 to be subjected only to tension and not in compression. By controlling the duration of the treatment, the temperature of the treatment, and the concentration of the various ions involved in the treatment, the thickness (Y) of the strengthened compressive layer 402, as well as the ion concentration in the compressive layer, can be controlled. Note that the ion concentration involved in the chemical strengthening process can be controlled by maintaining a substantially constant amount of ions in each of the two baths during the treatment of the glass article (e.g., as potassium ions diffuse into the glass, the controller will add more potassium ions to the ion bath, thereby encouraging potassium to continue to diffuse into the glass). The relationship between the chemically strengthened compressive level (both at the surface ion concentration and at depth) and the inner tensile portion forms the stress profile of the chemically treated glass article.

[0070] Additional ion bath immersions may be added to the basic glass chemical strengthening process. For example, a third bath comprising sodium or sodium nitrate may be used to immerse the strengthened glass, exchanging potassium ions from the compressive layer with the sodium ions in the third bath. This is called a back-exchange or toughening process. The toughening process is used to further control the depth and strength of the compressive layer, and specifically to remove some of the compressive stress from near the top surface region while allowing the underlying potassium ions to remain in the lower regions of the compressive layer. In addition, the toughening process reduces the central tension of the glass article (see below).

[0071] Although sodium enhancement and potassium strengthening are described herein, other ion combinations are within the scope of the present disclosure, for example, using lithium instead of sodium, or using cesium instead of potassium, for example, sodium-potassium, sodium-cesium, lithium-potassium, lithium-cesium treatment combinations. Any ion combination that provides an increase in compression and compression depth at the surface of the glass article can be used herein.

[0072] Chemical strengthening is applied to the glass surface and relies on the glass surface being exposed to the chemical strengthening process. In the case of immersing a glass article so that all aspects of the article are equally exposed to the ion bath, the glass article surface will be symmetrically strengthened, allowing the glass article to have a uniform thickness and structured compressive layer (Y). As will be shown in the embodiments herein, in the case of a glass article surface that is not equally exposed to chemical strengthening, the surface is asymmetrically strengthened, allowing the glass article to have a non-uniform compressive layer. As above, the asymmetrically strengthened glass article has a stress pattern, however, the stress pattern is modified based on the asymmetry of the chemical treatment.

[0073] Preheating to increase glass density before chemical strengthening

[0074] Chemical strengthening can be enhanced or promoted by various thermal techniques performed prior to the chemical strengthening process. Chemical strengthening is limited by the saturation limit of the glass for the amount or volume of ions. The size, depth, and concentration of ions within the glass article are directly related to the property strengthening of the glass, which can be modified and calibrated as described herein to optimize the glass for a specific application.

[0075] In the saturated case, no additional compressive layer or depth modification is achieved (via diffusion). However, modifying the heat input to the glass article prior to chemical strengthening may allow for an enhancement of the glass surface density, which will directly contribute to the concentration and depth of the strengthened compressive layer.

[0076] In the case where a significant amount of thermal energy is added to the glass article prior to chemical strengthening, the glass density of the article can be increased. The glass density in these embodiments results in the glass lattice being heated to a densification point.

[0077] like Figure 5A and Figure 5B As shown in the figure, compared with the untreated glass 502 ( Figure 5A ) compared to the denser glass 500 ( Figure 5B ) provide a more limited lattice structure (more confined and less flexible) and are less able to withstand ion diffusion to deeper levels.

[0078] exist Figure 5A and Figure 5B In the embodiment of the present invention, the glass has a starting glass lattice structure 502, which, when heated to the densification temperature, is densified and provides a volume 506 for ions to move through that is less than the volume 508 of the non-densified glass 502. The confinement of the glass lattice allows fewer ions to diffuse inwardly, while the ion concentration in the chemical strengthening bath remains high (as compared to the ion bath for non-densified glass). In addition, although the glass lattice has been densified, the embodiments herein do not result in heat input to the lattice collapse point (not shown in the figure), but rather heat is applied to the lattice confinement point, and some ions are able to diffuse into the glass. The ions that do diffuse into the glass are tightly packed at the surface of the densified glass and thus provide a shallow depth of preferred surface compression layer.

[0079] Thus, increasing the density of the glass at the beginning of the chemical strengthening process limits the diffusion of ions into the glass surface, allowing the glass to exchange a larger amount of ions at the surface of the glass, but only to a shallow depth. Glass articles treated by initial heat input prior to chemical strengthening generally exhibit higher chemical stresses at the surface, but to a shallow depth. These glass articles are most useful for articles with high compressive stresses but to a shallow depth, for example, where polishing or other similar processes may be required on the chemically strengthened glass, or where the glass would be exposed to increased risk of scratching rather than abrasion and cracking (impact).

[0080] One such thermal technique is to anneal the glass article prior to chemical strengthening. Annealing involves subjecting the glass article to a relatively high temperature in an annealing environment for a predetermined amount of time, and then subjecting the glass article to controlled cooling for a second predetermined amount of time. Once annealed and chemically strengthened, the glass article will have modified compressive stresses as compared to a similar glass article that was not annealed prior to chemical strengthening. As described above, annealing is particularly important in situations where a glass article requires high surface compressive stresses (but to a shallower depth).

[0081] The annealing process requires that the glass article be heated to a temperature between the strain point temperature and the softening temperature of the glass, also referred to as the glass annealing temperature (for aluminosilicate glass, the annealing temperature is between about 540 and 550°C). The time required to anneal the glass article varies, but is generally between 1 and 4 hours, and the cooling time is generally about ½°C / min for up to about 5 hours.

[0082] Generally, the annealed glass article can be taken directly from controlled cooling and immersed in an enhanced ion bath (sodium), or alternatively, the article can be further gas cooled and then immersed in a first ion bath. Once annealed, the glass will resist deeper ion diffusion, but allow some diffusion at the surface. Diffusion into the surface allows high compressive stresses (at shallow depths).

[0083] A second thermal technique for increasing the density of a glass article prior to chemical strengthening is hot isostatic pressing or HIP. HIP involves subjecting the glass article to both heat and pressure in an inert gas for a predetermined amount of time. The glass article is allowed to remain in the HIP pressure vessel until the glass article is denser, wherein the internal voids in the glass are confined. As with annealing, increasing the density of the glass by HIP prior to chemical strengthening allows for higher compressive stresses to be generated at the surface of the glass article, but to a shallower depth than would be expected for a glass article that has not been subjected to HIP.

[0084] HIP parameters will vary, but an illustrative process would involve placing the glass article to be chemically strengthened in a HIP pressure vessel, evacuating the vessel to a vacuum, and applying heat to the glass article in the vessel. The vessel may be heated to 600 to 1,450° C. under pressure, depending on the type and thickness of the glass. Heat and pressure are generally maintained for about 10 to 20 minutes, after which the treated glass is allowed to cool. In some embodiments, a suitable inert gas may be introduced into the vessel to facilitate the heating of the glass article. HIP is another tool for modifying or enhancing the chemical strengthening process.

[0085] like Figure 6 , preheating of the glass article 600 can be localized (rather than across the entire surface of the glass article) so that a target or predetermined area 602 of the glass article is densified. In this embodiment, local heating (as shown by arrow 604) is performed before chemical strengthening and is heated to a point between the strain point temperature and the softening temperature of the glass. Laser or induction coil heating can be used to preheat the location and thereby provide a glass article that includes both a densified glass surface 608 and a non-densified glass surface 610. Figure 6 A simplified cross-sectional view of a glass cover 600 is shown where the sides have been locally preheated to form densified glass 608 , while the center of the glass article exhibits non-densified glass 610 .

[0086] Embodiments herein include pre-treating glass articles by heating techniques to form densified glass over the entire surface, or to form densified glass in predetermined regions or locales, leaving regions of different glass density. When a glass article so treated is chemically strengthened 612, the article will be asymmetrically strengthened and have an asymmetrical stress profile, wherein the densified glass exhibits a higher surface compressive stress, but to a shallower depth, than the corresponding non-densified glass. It is contemplated that the timing and placement of pre-heating can be used to optimize the glass surface compressive stress and the depth of the compressive stress.

[0087] Although not explicitly noted in all embodiments herein, the glass articles of all embodiments herein may include the use of glass articles that have been preheated to densify the glass prior to chemical strengthening.

[0088] Chemical strengthening of preferred edge geometries

[0089] Certain glass article edge geometries may also be used in combination with chemical strengthening to strengthen a glass article for a specific purpose. For example, embodiments herein provide predetermined geometries useful for strengthening of glass covers. Edge manipulation may be achieved, for example, by machining, grinding, cutting, etching, molding, or polishing.

[0090] An illustrative rounded edge geometry for a glass cover that can be used in an electronic device includes adjusting the edge radius of the edge to 10% of the thickness of the cover glass, for example, a 0.1 mm edge radius for a 1.0 mm thick cover glass. In other embodiments, the adjustment of the edge may include an edge radius of 20% to 50% of the thickness of the cover glass, for example, a 0.2 mm edge radius for a 1.0 mm thick cover glass, a 0.3 mm edge radius for a 1.0 mm edge radius, etc.

[0091] Generally speaking, some embodiments herein demonstrate that rounding of the edge of a glass cover increases the strength of the glass cover. For example, rounding an otherwise sharp edge on a glass cover improves the strength of the edge, which thereby strengthens the glass cover itself. Generally speaking, the larger the edge radius, the more uniform the strengthening can be across the surface of the glass cover.

[0092] Thus, in some embodiments herein, a practical edge geometry can be combined with chemical strengthening to produce a more reliable and durable glass cover. For example, chemical strengthening for increasing the depth of the compressive stress layer along the perimeter of the glass cover is combined with four edges of the glass cover having an edge radius of 30%.

[0093] Although not explicitly noted in all embodiments herein, the chemically strengthened glass articles of all embodiments herein may include 1, 2, 3 or 4 edges thereof machined into a practical geometry. For cover glass designs, the rounding may be from 10% to 50% of the thickness of the cover glass.

[0094] Stress distribution

[0095] Chemically treating glass articles according to embodiments herein effectively strengthens the exposed or treated surface of the glass. Through such strengthening, stronger and tougher glass articles can be produced, allowing thinner glass to be used in portable electronic devices.

[0096] Fig. 7A FIG is a description figure of a cross-sectional view of a portion of a glass article (e.g., a glass cover). The figure shows an initial tension / compression stress distribution according to an embodiment. The initial tension / compression stress distribution can be obtained from an initial exchange process for the surface area of ​​symmetrically strengthened glass. A negative σ legend indicates a distribution area of ​​tension, while a positive σ legend indicates a distribution area of ​​compression. The vertical line (σ is zero) marks the crossover between compression and tension.

[0097] exist Fig. 7A , the thickness (T) of the cover glass is shown. The compressive surface stress (CS) of the initial tension / compression stress distribution at the surface of the cover glass is shown. The compressive stress of the cover glass has a depth of compressive stress layer (DoL) extending from the surface of the cover glass toward the central region. The initial central tension (CT) of the initial tension / compression stress distribution is at the central region of the cover glass.

[0098] As in Fig. 7A , the initial compressive stress has a distribution with a peak at the surface 700 of the glass cover 702. That is, the peak of the initial compressive stress 704 is at the surface of the glass cover. The initial compressive stress distribution shows that the compressive stress decreases as the depth of the compressive stress layer extends from the surface of the glass cover toward the central area of ​​the glass cover. The initial compressive stress continues to decrease inward until a crossover 706 between compression and tension occurs. Fig. 7A In FIG. 5 , right-to-left diagonal hatching is used to emphasize the region of reduced distribution of the initial compressive stress.

[0099] The peak at the surface of the glass cover indicates the bending stress that the glass article can absorb before failure, while the depth of the compressive layer provides protection against impact.

[0100] After the crossover between compression and tension, a distribution of initial central tension 708 extends to the central region shown in the cross-sectional view of the glass cover. Fig. 7A In the accompanying drawings of the specification, hatching is used to emphasize the area of ​​reduced distribution of the initial central tension (CT) extending into the central area.

[0101] Generally speaking, the combination of stresses on a glass product is budgeted to avoid failure and maintain safety, i.e., if too much stress is placed in a glass product, the energy will eventually cause the product to break or crack. Therefore, each glass product has a stress budget that provides the amount of compression versus tensile strength for a safe and reliable glass product.

[0102] Figure 7B is a description drawing of a cross-sectional view of a portion of a glass cover according to one embodiment, showing a reduced tension / compression stress distribution. The reduced tension / compression stress distribution can be obtained from a double exchange process. Figure 7B The reduced compressive surface stress (CS') of the reduced tension / compression stress distribution is shown in FIG. The depth of the compressive stress layer (D) now corresponds to the reduced compressive stress. In addition, a reduced central tension (CS') is shown in the central region.

[0103] Given that Figure 7B , it will be appreciated that the reduced compressive surface stress (CS') exhibits a profile that increases as the depth of the compressive surface layer extends from the surface of the glass cover and toward a submerged profile peak. Such an increased compressive stress profile can be beneficial in preventing cracks. Within the depth of the submerged peak (DoL), as a crack attempts to propagate from the surface deeper into the cover glass, the crack encounters increased compressive stress (up to DP), which can provide a crack-preventing action. Furthermore, extending further inward from the submerged profile peak toward the central region, the reduced compressive stress turns to provide a reduced profile until a crossover between compression and tension occurs.

[0104] Fig. 7A and Figure 7B Symmetrical stress distribution is shown, with equal compressive stress, compressive stress layer depth, and central tension on both sides of the cover glass.

[0105] Figure 7C An asymmetric stress distribution of glass article 714 is shown, where the top surface 716 exhibits a more significant compressive stress CS and compressive stress layer depth (DoL) than the bottom surface 718. Note that in this case, the top surface 716 will be more durable and more impact resistant than the bottom surface. Also note the stress budget, the additional compressive stress contained on the surface can be compensated by the very shallow compression depth on the bottom surface. In the uncompensated case, the tensile force 720 will extend to the left and ultimately result in a highly unsafe glass cover (the tensile strength will overcome the compressive strength).

[0106] As will be discussed in more detail below, by using the asymmetric chemical strengthening process described herein, a Figure 7CDesign and production of glass cover articles with modified stress profiles for calibrated utility. By asymmetrically strengthening a glass article, calibrated and highly practical glass articles can be produced. In such examples, the stress budget of any glass sheet can be used to provide a stress profile and, therefore, a glass article having an optimized surface for its utility.

[0107] Asymmetric chemical strengthening

[0108] Embodiments herein result in the production of asymmetric strengthened glass articles. Asymmetric strengthened glass articles (eg, cover glass) can be designed to be more reliable, more damage resistant, and safer than corresponding symmetric strengthened glass articles.

[0109] Figure 8 An illustrative flow chart 800 for asymmetrically strengthening a glass article is shown. A glass article is identified for desired utility based on its dimensions, its thickness, and its inherent composition 802. A budget for how much stress the glass can withstand is determined based on the utility of the identified glass 804, and a budget is determined for optimal reliability and safety of the glass, i.e., stresses in the glass are balanced to provide both strength and safety 806. The glass article is then calibrated to exhibit a practical stress pattern to maximize stress budget and utility 808 by using asymmetrical chemical strengthening.

[0110] For example, a thin sheet of cover glass used on a portable electronic device optimally requires different properties on its surface. Asymmetric chemical strengthening may be required on the front side versus the back side of the glass article, on the periphery versus the center of the glass article, around features in the glass article, or in areas of the glass article that are difficult to polish. However, as discussed above, each glass article has a stress profile in which compressive and tensile stresses must be roughly balanced to avoid failure. Thus, asymmetric chemical strengthening is used for specific applications to optimize the properties of the glass article within the stress budget of the specific glass article.

[0111] Generally speaking, asymmetric chemical strengthening can be used to provide a higher (or lower) surface compression layer or a deeper (or shallower) stress layer for specific areas, while maintaining the safety of the glass by not overstressing the tensile stress within the glass article. In cases where the surface of the glass requires additional strength, the compression of the layer can be increased, in cases where the glass requires wear and break protection, the depth of the compression layer can be modified, and so on. The ability to maximize the stress within the glass article for areas or portions of the glass article allows for the design of reliable and safe glass parts. Generally speaking, the relationship of the compressive stress (amount and depth) on the top and bottom surfaces of the glass article in relation to the resulting tensile stress gives the stress profile of the glass article. The stress profile can be along the X, Y, or Z axis of the glass article.

[0112] In embodiments herein, asymmetric chemical strengthening of glass articles is provided to: increase the reliability of the glass article for use in a particular application; increase the safety of the glass article for use in a particular application; promote a target shape or form (flat or substantially flat) of the glass article for use in a particular application; be used in combination with other techniques to promote a target shape or form of the glass article; and other similar utilities.

[0113] Fig. 9 Demonstrating asymmetric chemical strengthening is dependent upon differential incorporation of ions into the surface of the glass article. As described above, based on the density of the glass article and the overall ion saturation point (i.e., there is only so much volume in the glass that can involve exchanging larger sized ions to increase article compression (see 901 vs. 903)), the glass article 900 can exchange and incorporate ions to a particular depth and concentration along any surface region 902. The change in ion concentration along the surface and to a particular depth modifies the glass internal stress relationship, which extends across the glass thickness 904, as well as throughout the glass interior portion (how the internal tension / compression stress changes across the middle of the glass article) 906. As such, and as discussed previously, the stress pattern can be across the thickness of the glass article (vertically - top to bottom surface) 904 and across or throughout the glass article (horizontally - side to side) 906.

[0114] Embodiments herein exploit these stress relationships for calibration purposes to provide modified glass articles for use in portable electronic devices and small form factor devices.

[0115] Asymmetric strengthening via masking or coating

[0116] Embodiments herein include applying a shield or ion diffusion barrier to portions of a glass article prior to immersion in an ion-containing bath. For example, during a chemical strengthening process, a portion of a glass surface may be physically shielded from ions by sealing the area where diffusion is not desired with a diffusion impermeable material such as a metal or ceramic. This type of physical shielding completely limits ion diffusion into the surface and provides asymmetric strengthening, i.e., the shielded surface will not receive ion exchange as compared to other exposed surfaces of the glass article. Once chemically treated, the physical barrier will generally be removed from the glass article. At this point there will be a treated surface and an untreated surface.

[0117] In another embodiment, Fig.10 In the example shown in FIG. 1 , a coating or film composed of silicon nitride (SiN) or other similar materials is used instead of physical masking. Fig.10 In the embodiment, coating 1000 is applied to the central portion of glass cover 1002, while edges and corners 1004 remain uncoated. This coating will limit or exclude ion diffusion at the central region or portion of the cover glass, while allowing chemical strengthening of the non-coated regions (edges and corners).

[0118] A coating is applied to the glass article prior to the strengthening treatment to substantially block all ion diffusion through the coated portion of the glass article. The coating may have a thickness of about 5 to 500 nm, although other thicknesses may be used where appropriate. In this interpretation, upon completion of the chemical strengthening process, the coated surface of the glass article will not include a compressive layer, while the remainder of the glass article will exhibit a compressive layer. Upon completion of the chemical strengthening process, the coating may be removed from the glass article via polishing, providing a surface with asymmetric strengthening, or the coating may remain on the glass surface as part of the finished glass article. In this aspect, the coating will be adjusted to a suitable thickness and composition to remain part of the glass article.

[0119] In other embodiments, after the chemical strengthening process is complete, the SiN coating can be oxidized to provide a more ion permeable barrier. The same glass article can now be re-immersed and treated with chemical strengthening so that some ion diffusion occurs through the silicon dioxide barrier and thus some compressive layer is formed at that location (while the rest of the glass article has been treated twice).

[0120] As just described, coatings composed of alternative materials (e.g., silicon dioxide) may also be used to limit (rather than exclude) ion diffusion to the surface of the glass article. For example, a coating composed of silicon dioxide will only limit ion diffusion to the surface of the glass article, allowing some degree of compression layer formation in the coated area, rather than the full strengthening expected by ion exchange baths. As above, the coating will be removed after the chemical strengthening process is completed, or left in place as part of the finished article. In either case, the glass article will have an asymmetrically strengthened surface.

[0121] FIG. 11 shows the combinations of coating types (1100, 1102, 1104, ...) and thicknesses that can be used when designing an asymmetric strengthened glass surface. Fig.11A In FIG. 1 , a series of coatings ( 1100 , 1102 , 1104 ) are applied to both the top and bottom surfaces ( 1106 and 1108 , respectively) of a glass cover 1110 . Each combination of coating materials is intended to control ion diffusion to the target glass surface and thereby modify the chemical strengthening of the surface 1112 .

[0122] Based on ion diffusion through coatings 1100, 1102, and 1104, the glass article can exchange and incorporate ions to a specific depth and concentration. As described above, the change in ion concentration along the surface and to a specific depth modifies the stress relationship within the glass. Fig. 11BThe stress pattern shown in shows that the edge 1114 (no coating) of the top surface 1106 receives the strongest ion concentration along the surface and to the greatest depth. The rest of the top surface 1106 shows some reduced ion incorporation, but to a lesser extent than the edge 1116. The bottom surface 1108, which is the interior, has multiple regions defining three ion incorporation areas 1116, 1118, 1120, for example, based on the build-up coating. The center region 1120 of the bottom surface has little or no ion incorporation due to the coatings 1100, 1102, and 1104. The combined coatings exclude almost all ion diffusion into the center region. Other regions show some ion diffusion from either a single coating or a combination of coatings. Thus, a stress relationship is achieved where multiple coatings (ion barriers) have been applied to prepare an asymmetric strengthened glass article.

[0123] It is further contemplated that multiple layers of coatings may also be used to control the ion diffusion process into the target glass surface. For example, a thin coating that limits 25% of the diffusion of sodium and potassium ions from the chemical strengthening process may be laminated across a first thicker coating that limits 50% of the diffusion of sodium and potassium ions. The glass surface area will potentially have areas that limit 0% (uncoated), 25% (first coating), 50% (second coating), and 75% (laminated coating) ion diffusion; other embodiments may have different percentages for each coating. As above, the finished glass article surface may include each of such coatings, or may be treated to remove such coatings, leaving only the underlying asymmetric strengthened surface. It is also contemplated that such ion diffusion barrier coatings may be combined with ion barrier shielding to further allow for calibrated glass article surface strength, for example, physically shielding the bottom surface of the glass cover and coating a pattern or location with a 25% ion diffusion barrier on the top surface of the cover.

[0124] Heat-Assisted Asymmetric Chemical Strengthening

[0125] Embodiments herein include asymmetric glass strengthening by targeted application of heat during a chemical strengthening process. Preferential heating of a glass surface location can be used to promote stress relaxation at that location and thereby allow increased ion diffusion at that location during the chemical strengthening process. Note that the heat is less than the amount required for densifying the glass as discussed above. Increased ion diffusion allows for the exchange of additional ions into the glass, thereby altering the stress profile of the heated surface (compared to the non-heated surface). For example, a localized area of ​​a glass article can be heated by using a heating coil, laser, microwave radiation, and the like while the glass article is immersed in a chemical strengthening ion bath.

[0126] As described above, the increase in heat at the targeted location allows for increased ion diffusion in the glass surface at the heated location. Enhanced heating at the targeted location on the glass surface provides asymmetric chemical strengthening at the heated location (compared to the non-heated surface). Asymmetric chemical strengthening using modified heat profiles is particularly valuable where a laser or microwave beam can be directed to modify the chemical strengthening for portions with known failure points. For example, cover glass requires additional chemical strengthening at corners to limit damage due to impact.

[0127] Heating temperatures are suitable where the heat is sufficient to relax the glass lattice, but does not cause densification of the glass or cause the ions in the ion bath to boil.

[0128] In one embodiment, a glass article is chemically strengthened by immersion in a first ion bath and a second ion bath. While immersed in the first ion bath and / or the second ion bath, the heat profile of a predetermined portion of the glass article is increased by using directed heating (coil, laser, microwave, etc.). With the lattice relaxation and expansion of the glass, the targeted locations on the glass article undergo additional ion exchange. Once the heat input is deemed sufficient, the asymmetric strengthened locations, which now have additional ions accumulated into the surface, can be quenched to inhibit ion exchange back from the locations. Increasing the heat profile during chemical strengthening can be used to increase both the compressive stress at the glass surface and the depth of the compressive stress layer at the glass surface.

[0129] Local asymmetric strengthening via paste and heat

[0130] As discussed in more detail below, it is important to form a glass article in which the stresses in the glass article are matched to provide a particular shape (eg, to provide a flat surface).

[0131] In one embodiment, localized chemical strengthening techniques can be used to promote ion diffusion into specific areas or zones of the glass article. These high concentration chemically strengthened areas can be matched with targeted patterns or points on the glass article to instill higher surface ion concentrations and / or deeper compressive layers. Incorporating enhanced chemical strengthening can be used to provide slight curvature to the glass surface (if desired), or enhanced chemical strengthening can be used to resist each other on opposite sides of the glass surface (e.g., front and back surfaces).

[0132] For example, a paste including a high concentration of potassium may be used in combination with heat to enhance or promote ion diffusion directly from the paste into the localized surface of the glass article. This high concentration and direct ion diffusion is superior to ion diffusion achieved by immersion in an ion bath. In one embodiment, a glass article that needs to increase the amount of ion diffusion according to a predetermined pattern is coated with a high ion concentration paste according to the predetermined pattern. The paste may be, for example, 30 to 100 mol% sodium or potassium nitride, and more generally 75 to 100 mol%. The thickness of the paste layer is determined by how much ions need to diffuse into the surface of the glass article. The coated glass article is then placed in an oven and heated for a predetermined amount of time to increase the ion diffusion into the glass surface according to the predetermined pattern. The oven may be an electric oven or a gas oven (or other similar ones) and may reach a temperature of from about 250 to 500°C. In some embodiments, the oven may be under pressure, allowing higher temperatures to be used during the heating step (and thereby avoiding evaporation or boiling of the paste).

[0133] Fig. 12A and Fig. 12B The front surface of the cover glass 1206 is shown ( Fig. 12A ) and rear surface ( Fig. 12B A high concentration ion paste 1200 is used on the back cover (1202 and 1204, respectively). The paste application pattern can be used to promote the distribution of asymmetric reinforcement and to counteract the stress applied to the front cover with the stress applied to the back cover. Fig. 12A and Fig. 12B , illustrative front and back surface patterns are presented.

[0134] In other embodiments, the strengthened coated glass article is coated with the high ion concentration paste (e.g., potassium) and then placed in a potassium ion bath. The coated glass article and ion bath are then placed in an oven for heating so that the paste deposits potassium directly onto the glass surface while the potassium ion bath allows ions to diffuse to non-coated or exposed surfaces of the glass article.

[0135] Varying the ion concentration in the paste, the application of the paste pattern on the glass surface, the heating parameters of the paste, and the coating thickness of the paste provide various design options for creating an asymmetric strengthened glass article.

[0136] It is contemplated that pastes containing high ion concentrations may also be combined with masking, ion barrier coatings, and glass density to further optimize the necessary chemical strengthening of the target glass article. It is also contemplated that pastes containing multiple ions may be used, and that a glass article surface may be coated with one or more, two or more, three or more, etc. different pastes, each having a different concentration of one or more ions.

[0137] Electric field assisted asymmetric chemical strengthening

[0138] As shown above, embodiments herein include asymmetric glass strengthening during a chemical strengthening process. In this embodiment, ion transport in an ion bath is preferentially increased toward a target surface of a glass article, thereby increasing ion diffusion at the target surface. The increased ion concentration at the surface allows for an increased amount of ions incorporated into the glass surface, up to the ion saturation point of the glass article, compared to the remainder of the article surface that is not in-line with the increased ion concentration.

[0139] Aspects of this embodiment are maximized by utilizing ion concentrations in the ion bath that provide chemical strengthening but are below the ion saturation point of the glass article. In this aspect, the electric field will significantly increase the ion concentration at the surface in-line with preferential ion transport across the electric field.

[0140] In an illustrative embodiment, an electric field is established in a suitable ion bath to cause ions to preferentially diffuse across the target surface of the immersed glass article. Fig.13 , a glass article 1304 that requires asymmetric chemical strengthening is positioned in an ion bath 1300 between a positive electrode 1306 and a negative electrode 1308. Electron flow through an external circuit 1310 allows ions (e.g., potassium) of the bath to flow toward the negative electrode and thereby into the front surface 1302 of the positioned glass article (as shown by arrows 1312). Increasing the ion concentration at the front surface of the glass article provides asymmetric strengthening of the front surface because the front surface 1302 will have increased ion diffusion (compared to the back surface 1314 of the glass).

[0141] Alternative embodiments for the electric field gradient include performing preferential ion diffusion in combination with coil, laser, radiation, or other thermal heating (as shown by arrow 1316). In this embodiment, the glass article 1304 is exposed to localized microwave radiation 1316 (e.g., where additional chemical strengthening is desired). The microwave radiation promotes stress relaxation at the target surface 1302. The surface of the glass article that receives preferential ion diffusion due to the established electric field in the ion bath may have additional ions diffused into the surface, where the microwave radiation promotes stress relationships (providing more space for ions to enter the glass surface). It is conceivable that the glass article 1304 treated in this way may have multiple different asymmetric strengthened regions: a region 1318 that is heated and corresponds to ions in the electric field; a region 1320 that is not heated but corresponds to ions in the electric field; a region that is heated but not in line with ions in the electric field (not shown); and a region (1322) that is not heated and not yet in line with ions in the electric field.

[0142] Asymmetric strengthening by introducing pre-bend

[0143] Asymmetric strengthening can be introduced into the surface of the glass by prestressing the glass article before and during the strengthening and strengthening process. In one embodiment, the glass article is formed (molded, drawn, etc.) to have a pre-required curvature. The formed glass article is placed under the correct force to maintain the form, and then the formed glass article is chemically strengthened using the embodiments described above. For example, the formed glass article is placed in an ion exchange bath in the prestressed or formed shape. Since the glass bends when the glass is chemically strengthened, it is strengthened in a strengthening manner. Therefore, for curved or bent glass articles, the outer curved surface will be chemically strengthened primarily (ions diffuse more easily into the stretched glass lattice), while the compressed inner surface is subjected to limited chemical strengthening. Different portions of the outer surface of the glass article can be selectively chemically strengthened, or chemically strengthened differently, and / or the glass article can be selectively or differently bent to offset the asymmetric chemical strengthening of such different portions. After the prestressed glass article is released from its pre-bend, the outer surface will have a greater amount of strengthening (compared to the inside), thereby exhibiting an asymmetric strengthening distribution.

[0144] FIG. 14A to FIG. 14E A chemically strengthened glass article is shown according to one embodiment. Fig.14A , the glass article 1400 is shown to have a thickness T. The thickness T can be substantially as described throughout this disclosure (0.3 to 5 mm). The glass article 1400 has an outer surface 1402 and an inner surface 1404.

[0145] exist Fig. 14B , an ion exchange coating (as discussed above) 1406 is coated on the interior surface 1404 of the glass article 1400. In this manner, the ion barrier limits the diffusion of ions into the interior surface of the glass article.

[0146] exist Fig. 14C , the glass article has been bent such that the bent glass article 1400' curves inwardly toward the inner surface 1404. The bending of the glass article produces a glass article having a curvature C. The curvature in the glass article 1400' can be of varying degrees and can be imparted by force (clamping) or by including a heated environment (slumped over).

[0147] exist Fig.14D In, from Fig. 14CA curved glass article 1400" is subjected to chemical strengthening to produce a glass article 1400" having a strengthened region 1406. The chemically strengthened region 1406 is provided adjacent to the outer surface 1402 and not adjacent to the inner surface 1404. The chemically strengthened region extends inwardly from the outer surface to a depth of layer (DoL) deeper into the glass than the depth of layer (DoL) at the inner surface (which is minimal or non-existent). Because the outer surface is substantially more chemically strengthened than the inner surface, the chemically strengthened glass article 1400" may be referred to as asymmetric chemical strengthening.

[0148] Fig.14E A chemically strengthened glass article 1400''' is shown after the chemical strengthening process is complete. Following completion of the process, the glass article 1400''' is depicted as being planar, or at least substantially planar. The completed glass article 1400''' has an outer surface 1402 of increased compression and an inner surface 1404, the inner surface 1404 being simultaneously curved inwardly and coated with an ion exchange coating to limit or preclude chemical strengthening. In this distribution design, the chemically strengthened glass article 1400''' tends to wrap inwardly from the outer surface: meaning that the outer surface compresses and expands. In such cases, the warping due to chemical strengthening of the outer surface (rather than the inner surface) causes the curvature C to be offset. As a result, the chemically strengthened glass article 1400''' no longer has a curvature as it had before chemical strengthening began.

[0149] Asymmetric reinforcement of different coating layers

[0150] Fig.15 Another embodiment of the present invention is shown, which includes forming an asymmetric strengthened glass article 1500 by immersing a glass article coating 1502 in a chemical strengthening bath 1504, wherein each glass article in the coating has a different starting ion concentration and composition. The coating having the first glass article and the second glass article is then strengthened using the chemical strengthening process described herein to provide two asymmetric strengthened glass articles.

[0151] In one aspect, because the starting compositions of the two glass articles are different, the exposed surfaces and edges of each glass article will incorporate available ions differently. The end result of the chemical treatment step will be two glass articles containing protected surfaces (to the interior of the coating) and chemically modified exposed surfaces and edges. Modification of the exposed surfaces may be performed by masking or coating, or by other embodiments herein, as described above. Any number of articles may be strengthened in this manner, for example, in Fig.15 , strengthen three glass items at the same time.

[0152] Chemically strengthened glass products

[0153] In other aspects, asymmetric strengthened glass articles having substantially the same stress profile can be stacked together for common processing to relieve or modify stresses in the stacked glass. Here, the glass articles can be stacked into multiple sheets with one another and processed together to maximize efficiency. The glass articles can be stacked into non-planar parts, processed and then joined to exhibit the joining stress or can be pre-bent and then joined to exhibit the joining stress.

[0154] Asymmetric strengthening of glass products with concentration gradients

[0155] In another embodiment, two glass articles of different compositions may be fused together prior to the chemical strengthening process. Here, the fused glass article will have a top surface (top glass) that is chemically strengthened based on its starting glass ion concentration and composition, and a bottom surface (bottom glass) that is chemically strengthened based on its starting glass ion concentration and composition.

[0156] Furthermore, using the same premise, a glass sheet having a concentration gradient (composition or ion) can also be chemically strengthened to provide an asymmetrically strengthened glass. As above, the glass article has different ions to be exchanged in an ion bath at different locations of the glass article so that the resulting surface will be asymmetrically strengthened.

[0157] Therefore, the design of the starting glass, including its starting ion concentration and location, can be used to calibrate the ion-diffused and asymmetrically strengthened glass.

[0158] Mechanical and / or chemical modification to tune stress distribution

[0159] Embodiments herein include the use of post chemical strengthening, mechanical and / or chemical processes to fine tune the stress of a glass article. In the case where a glass article has been prepared according to any of the embodiments described herein, it may be desirable to, for example, fine tune the compressive stress layer in the glass or adjust the relationship between tensile and compressive forces. Mechanical (grinding, polishing, cutting, etc.) or chemical (application of HF or other similar acids) removal of material may be used to locally modify the stress profile of the glass article.

[0160] For example, in cases where the extent of the compressive surface stress layer is determined to be too large or too deep, removing some amount of the layer will relieve the stress and recalibrate the stress distribution of the glass article. These post-chemical strengthening embodiments are particularly useful in cases where only a small amount of stress modification is desired (e.g., removing 10 μm from a limited area of ​​the cover glass).

[0161] Asymmetric chemical strengthening during glass production

[0162] Embodiments herein include gradually modifying the stress profile of a glass article based on the use of one or more of the chemical strengthening embodiments described herein. For example, in situations where the production of a glass article results in non-compliant or unsatisfactory results, the asymmetric chemical strengthening embodiments described herein can be used to reform the stresses to bring the glass article into compliance. This may require localized asymmetric chemical strengthening, or conversely, removal of material, with the goal of adding or removing stress where necessary to correct any defects in the glass article.

[0163] Fig.16 A flow chart 1600 is shown that includes a process for asymmetric chemical strengthening during glass article production. A glass article having been assigned a specific calibration stress profile 1602 is properly processed 1604 using any of the embodiments described herein. The reliability and safety of the glass is tested 1606 by determining whether the glass cover exhibits the correct strengthening parameters. In the case where the glass article meets the asymmetric chemical strengthening, the glass article is submitted for use 1608. In the case where the glass article fails to exhibit its appropriate chemical strengthening, the glass article is reapplied with appropriate chemical strengthening and tested 1610 through the processes and embodiments described herein. This process can be repeated as many times as necessary to obtain a glass article that meets the standards for its use.

[0164] Thus, embodiments herein include monitoring and correcting a glass article to predetermine a stress profile. Correction may include multiple iterations of stress modification until a desired stress profile of the glass article is achieved.

[0165] Asymmetric chemical strengthening to manage crack patterns

[0166] Embodiments herein include asymmetrically strengthened glass articles to exhibit or manage predetermined crack patterns. Fig.17A and Fig. 17B Show applied to cover sheet 1704 to minimize crack propagation ( Fig.17A ) or minimize corner damage 1710 ( Fig. 17B ) of the Interpretive Chemical Strengthening 1706 / 1708.

[0167] Fig.18 A surface stress (CS) versus distance graph is shown illustrating that tension points 1800 may develop along the surface of the glass article where cracks are more likely to occur than at high surface stress points 1802 .

[0168] Using any of the embodiments described herein, an optimal crack pattern for a particular glass article application can be developed. Embodiments include locating the amount of surface compressive stress, compressive stress depth, top surface to bottom surface tensile versus compressive stress, and planar tensile versus compressive stress with an optimized pattern. The glass article can be calibrated to control the crack pattern after damage or excessive wear and cracking by identifying and then incorporating the necessary compressive surface stress, stress, and depth of tensile stress to promote a crack in some areas compared to other areas (if it occurs). In this way, cracks along the periphery can be promoted, for example, compared to the center of the cover glass. In one example, a more significant tensile stress is located at a desired crack location 1706 or 1710 compared to a less preferred location. Crack development and propagation can be managed, for example, by irregular use and locating stress 1706.

[0169] Design cover glass to reduce damage or damage propagation caused by impact

[0170] Embodiments herein result in the production of asymmetric strengthened cover glasses for portable electronic devices. As discussed previously, the combination of stresses on the glass article is budgeted to avoid failure and maintain safety, i.e., with a limited volume of glass, there is only so much ionic material that can be added to that volume before the glass will crack or fail simply because the tensile stresses become excessive and exert enough pressure to break the glass.

[0171] In embodiments herein, the asymmetric strengthened cover glass has a stress budget that is optimized to resist damage caused by impacts from dropping the device, being dropped from the hand, being hit, and the like (e.g., a mobile phone being dropped from the user's hand and falling to the floor). In view of this, most portable devices tend to be impacted first at the corners of the device, or to a lesser extent, at the peripheral straight edges of the device when impacted. Thus, the impact is directed to the corners of the cover glass, and to a lesser extent, the perimeter or edges of the cover glass. It is less likely and less common that the front or back side of the dropped device will be impacted first, i.e., its front or back side will land flat on the ground. As such, embodiments herein are optimized to design the cover glass by anticipating that the impact will occur at the corners of the cover glass, or at least at the peripheral straight edges of the cover glass, to limit or reduce damage (or propagation of damage) in the cover glass.

[0172] As discussed above, asymmetric chemical strengthening can be used to provide modified surface compression within the cover glass. Asymmetric strengthening must comply with a stress budget for the specific parameters of the glass. Embodiments herein include cover glass designs in which a stress budget is utilized to provide maximum impact resistance at the cover glass corners, followed by impact resistance along the straight peripheral edges, and a lesser degree of impact resistance of the substantially flat front and rear surfaces of the glass. Thus, budgeted stresses are substantially utilized at the corners of the cover glass and to some extent along the periphery. Almost no or no stress budget is allocated to the center or remaining areas of the cover glass. The strengthening imparted is sufficient to enhance impact resistance to prevent damage. In addition, since little stress budget is used in the center or remaining areas of the cover glass, the area is in a state of little to no imbalance and can be maintained substantially flat.

[0173] Fig.19 An illustrative flow chart 1900 is shown for asymmetrically strengthening a glass article having multiple zones, each zone having a different stress distribution. At operation 1902, a glass article is obtained for a desired utility based on the size of the glass article, its thickness, and its inherent composition. At operation 1904, a budget for how much stress the glass can withstand is determined based on the utility of the identified glass and a budget determined for enhanced resistance to impact damage caused by, for example, a drop. As described throughout, the budget must fit within the limited volume of the glass because incorporating too much stress in the glass would cause tensile stresses to cause cracking or damage under normal use limits.

[0174] At operation 1906, the glass article is then segmented into a plurality of zones. For example, a first zone in the glass may have the highest amount of chemical strengthening, followed by a second zone, followed by a third zone having the least amount of chemical strengthening. At operation 1908, the glass article has a stress profile based on the three different zones, for example, a first stress profile having the greatest strength with respect to impact, a second stress profile having an amount less than the strength of the first zone, and a third stress profile having the lowest strength level. In some embodiments, the third zone has little or no chemical strengthening.

[0175] Fig. 20An illustrative flow chart 2000 for asymmetrically strengthening a glass article for a portable electronic device having three or more zones, each zone having a different stress profile. At operation 2002, a cover glass is obtained having dimensions, thickness, and composition generally required for use in the portable electronic device of interest. At operation 2004, a budget for how much stress the cover glass can withstand is determined, wherein the budgeted stress maintains a substantially flat cover glass having enhanced resistance to damage under impact events (e.g., drops). The cover glass can be segmented into three zones, a first zone corresponding to a corner portion or region of the cover glass; a second zone corresponding to a straight peripheral portion (also referred to as a peripheral edge region) of the cover glass; and a third zone corresponding to the remainder or center region of the cover glass. In some embodiments, the three zones refer to the top surface of the cover glass, or to the stress profile extending from the top surface to the bottom surface. The first zone and the second zone may include up to 50% of the cover glass area (leaving 50% of the cover glass area for the third zone), up to 40% of the cover glass area (leaving 60% of the cover glass area for the third zone), up to 30% of the cover glass area (leaving 70% of the cover glass area for the third zone), up to 20% of the cover glass area (leaving 80% of the cover glass area for the third zone), up to 15% of the cover glass area (leaving 85% of the cover glass area for the third zone), up to 10% of the cover glass area (leaving 90% of the cover glass area for the third zone), up to 5% of the cover glass area (leaving 95% of the cover glass area for the third zone), up to 2.5% of the cover glass area (leaving 97.5% of the cover glass area for the third zone), and up to 1% of the cover glass area (leaving 99% of the cover glass area for the third zone).

[0176] In general embodiments herein, at operation 2006, the glass article may be segmented into: a first zone including a first stress pattern applicable to a corner portion of the cover glass; a second zone including a second stress pattern applicable to a straight perimeter portion or edge portion of the cover glass; and a third zone having a stress pattern applicable to the remainder of the cover glass. At operation 2008, the budgeted stress is distributed among the three zones, wherein the first zone is more strengthened than the second zone, and the second zone is more strengthened than the third zone. In some embodiments, the third zone undergoes little or no chemical strengthening, and the entire stress budget is used on the first zone and the second zone. Using the entire stress budget on the first zone and the second zone results in a glass article in normal use being in tensile stress, but with improved ability to prevent or reduce damage caused by impact to the article. Note also that the first zone and the second zone may form a continuous perimeter around the third zone.

[0177] Fig.21 A cover glass 2100 is shown having three zones, each zone having a stress pattern useful for reducing damage or damage propagation in the cover glass. As described above, there is a finite stress budget for the cover glass 2100. The stress budget is allocated to each of the three zones, wherein the first zone 2102 (which corresponds to the corner portion or region of the cover glass) receives the highest amount of chemical strengthening, the second zone 2104 (which corresponds to the straight peripheral side or peripheral edge region) receives the second highest amount of chemical strengthening, and the third zone 2106 (which corresponds to the center or remaining area of ​​the cover glass 2100) receives the least amount of chemical strengthening. In some embodiments, the third zone 1906 may undergo little or no chemical strengthening. The third zone 2106 may include an outer surface, a portion of which (but not the entire third zone) is generally substantially flat. The third zone 2106 is also surrounded by the higher strengthened first zone 2102 and the second zone 2104, which form a connected perimeter around the third zone. The connected first and second zones form a higher strength glass at the perimeter of the cover glass, which forms a protective barrier to resist impacts to the lower strengthened glass found in the third zone. In some embodiments, the first zone and the second zone each form an edge and such edges may contact each other to form an oblique angle. A stress budget is used to reduce damage or damage propagation caused by a possible impact event to the first zone 2102 (and to a lesser extent, the second zone 2104) while keeping the third zone substantially flat or unaffected by warping. At least, the impact is likely to be distributed to the first zone and the second zone of the cover glass 2100, which form a perimeter around and surround the centrally positioned third zone 2106. In addition, the first zone can be thermally heated to a temperature that allows increased chemical strengthening (compared to the same zone without thermal heating). The second zone can also be thermally heated during asymmetric strengthening to also enhance or increase the amount of stress induced in the zone. Heating is described throughout this specification, but can be performed by microwave or laser heating. In some embodiments, the temperature of the thermal heating is below the densification temperature of the glass, and in other embodiments, the temperature of the thermal heating is above the densification temperature of the glass.

[0178] Fig. 22 Display along Fig.21 21 '. As compared to the third region 2106, the first region 2102 exhibits an increase in the amount of ions 2200 to a particular depth and concentration. The change in ion concentration along the surface of the first region and to a particular depth modifies the stress relationship within the glass. Adding chemical strengthening to the first region provides additional compressive stress along that region or portion of the cover glass that is most likely to impact. Fig. 22, the first zone defines a curved edge which, in this embodiment, extends from the top surface of the cover glass to the bottom surface. Note that this is also the zone of the cover glass that is at greatest risk for impact, because it has limited area for distributing the force or energy imparted by the impact. Increasing the ion volume at the corners can thereby resist the force or energy imparted by the impact and reduce or prevent damage to the cover glass. Alternatively, the third zone 2106 has a larger area for distributing the forces associated with the impact and is less likely to be involved in the impact itself. In this way, some of the chemical strengthening that is not needed in the third zone can be budgeted for the first zone and the cover glass can still be maintained within its budgeted amount of stress. As in Fig. 22 As described in the specification, the third region defines a substantially flat outer surface.

[0179] Flattening asymmetric stress distribution

[0180] Embodiments herein include processes that use asymmetric chemical strengthening in combination with other compensating forces to provide useful glass articles (eg, articles having planar surfaces).

[0181] In one embodiment, a glass article that has been asymmetrically chemically strengthened exhibits a stress imbalance due to, for example, an overall excess compressive stress on the top surface (compared to the bottom surface). The stress imbalance in the glass article can be resisted by attaching to a very strong material, or a strong material with a geometry that resists the stresses imparted by the asymmetrically strengthened glass article. The best material will resist the imparted asymmetrical stresses of the glass article to maintain flatness (or maintain the desired geometry of the glass material). In general embodiments, the strong material will be attached along the surface of the glass article (generally, the bottom surface). In some cases, the strong material will be transparent. Only enough strong material will be needed to achieve the amount and coverage of resisting stress.

[0182] In another embodiment, the stress imbalance of a glass article that has been asymmetrically chemically strengthened is counteracted by adjusting the mechanical or chemical removal of material. In this embodiment, polishing or other mechanical techniques may be used to optimally remove stress from the glass article. Alternatively, aspects of the stress imbalance of the glass article may be removed by partially immersing the glass article in a chemical removal bath (e.g., an HF bath). In the chemical removal bath, non-problematic glass surfaces may be sealed from HF or only selective areas of the glass surface may be exposed to HF. Removal of material will be achieved to provide a glass article with the correct geometry or flatness (again, based on counteracting the overall stress in the strengthened glass article).

[0183] In yet another embodiment, the desired asymmetric compressive stresses (for damage control and reliability) are resisted by introducing additional, localized, chemical strengthening. For example, the use of a coating or paste (previously described) can be incorporated into an asymmetric strengthened glass article to resist warping introduced by the desired asymmetric chemical strengthening. In some aspects, the coating or paste can be patterned.

[0184] Embodiments herein also include not only arrangements to resist chemical strengthening, but also the amount and depth of compressive surface stress of chemical strengthening on the glass. Here, incorporating specific compressive surface stresses can act as a stiffening barrier to prevent or resist warping introduced by other asymmetric chemical strengthening. For example, using a short, peaked spike of potassium ions into the surface of a glass article can act to provide a very shallow but hard point. These hard (high compressive surface stress layers) can have Young's modulus as high as 60 to 80 and can be used to prevent warping, in a sense, acting as the stiffening material discussed above.

[0185] Compensation for asymmetric chemical strengthening including molding

[0186] Embodiments herein include combining the advantages of asymmetric strengthening of surfaces on a glass article with the design and production of glass-shaped glass articles.

[0187] As described throughout this disclosure, asymmetric chemical strengthening allows for targeted increases in either the compressive surface stress of a glass article and / or the depth of compression of the glass surface. In most cases, the glass article is calibrated to have the intended utility and maximize damage or scratch protection of the glass article. This generally requires some combination of the processes and embodiments described herein, for example, increasing the depth of compression along the perimeter of the cover glass with normal symmetrical chemical strengthening of the center of the cover glass.

[0188] However, incorporating asymmetric chemical strengthening introduces stress imbalance into the glass article (note the stress distribution discussed above). When sufficient stress imbalance is introduced into the glass article, the glass article will warp. Warping in a glass article is generally detrimental to the utility of the article and there is a limit to how much asymmetric stress can be introduced into a glass article.

[0189] As discussed previously, the introduced warpage can be compensated by introducing competing stress imbalances, for example, introducing asymmetric chemical strengthening in the glass article to provide both utility and to provide resistive stresses. However, the present embodiment utilizes the glass forming process to minimize the stress imbalance introduced by asymmetric chemical strengthening. Further, glass forming provides a stiffer glass article that can be formed to combine with the forces induced through asymmetric chemical strengthening to produce a glass article having a desired shape.

[0190] In one embodiment, a glass article is designed to resist the stress imbalance introduced by asymmetric chemical strengthening using glass forming. In one aspect, asymmetric chemical strengthening is resisted by forming the glass article with a suitable geometry. The appropriate glass article geometry for a particular stress distribution provides stiffness to resist the stress introduced by the asymmetric chemical strengthening process. In an alternative embodiment, asymmetric chemical strengthening is combined with glass forming to provide the desired geometry, for example, the strengthened warp is combined with the glass forming curvature to produce the desired shape.

[0191] In cases where the desired glass article shape requires a non-uniform cross-sectional shape or thickness, symmetric chemical strengthening will actually facilitate a more extensive possible warp. Asymmetric chemical strengthening allows both the desired compressive stress layer and depth to be incorporated and avoids significant warp. Glass forming is combined with the strengthening to provide an optimized glass article.

[0192] Fig.23 2300 is a flow chart showing that a glass article having suitable local stiffness can be identified and formed to resist the proposed asymmetric chemical strengthening. The formed glass 2302 can be subjected to CNS and polishing 2304. Next, the glass article is subjected to various steps required to introduce asymmetric chemical strengthening, including, for example, the use of barrier layers, pastes, heat, etc. (2306, 2308, 2310, 2312, 2314, and 2316). The formed glass article having enhanced stiffness can be processed multiple times to obtain a highly calibrated surface or surfaces.

[0193] Optimal glass product design based on stress distribution

[0194] Embodiments herein include processes for calibrating the strength of a glass article for a specific application using any one or more of the following: preheating the glass article to a higher glass density; modifying the edge geometry of the glass article to maximize geometric strengthening; modified chemical strengthening using shielding, ion barriers, or confining coatings; chemical strengthening using ion enhancement pastes and heat; thermally assisting the chemical strengthening; guided or preferential ion diffusion using electric fields and heat; introducing prestress into a target article; and adjusting for stresses found in asymmetrically prepared glass articles.

[0195] Calibration can also occur during the glass manufacturing process, for example, by differential strengthening of glass in cladding layers, by identifying practical ion gradients and concentrations in the starting glass, by fusing glass products together, and the like.

[0196] Aspects herein utilize each of the above-described embodiments to calibrate glass products with budgeted amounts of stress on the vertical and horizontal axes. Budgeted and irregular stresses allow for the placement of compressive stress layers of predetermined hardness and depth on the front, back, top side, and edges of the glass product to optimize the reliability of the glass product and to safely use the glass product for its intended use. Budgeted irregular stresses in the glass product can also be offset by other materials or by the geometry of the glass itself to resist stress input. This is particularly useful when the finished glass product is designed to be flat or otherwise targeted. In this way, for example, a glass cover can be evaluated for its intended use, i.e., how much surface compressive stress is required on the top surface, bottom surface, edge, etc. of the product; how deep the compressive stress needs to extend at each of these zones; how much tensile strength will be caused by these compressive stress requirements; how much tensile strength will be caused; whether chemical strengthening alone can balance the required stress; whether glass molding can be used; and the like. Then, the embodiments herein are utilized to perform calibration to provide a high-performance glass cover with a maximized or optimized value.

[0197] The following examples are for illustrative purposes only and are not intended to limit the scope of the present disclosure.

[0198] Example

[0199] Glass forming to compensate for asymmetric chemical strengthening

[0200] The depth of compression in ion exchange chemical strengthening is correlated with the ability of the glass article to resist damage-induced failure. Given this, maximizing the depth of compression is an important driver for producing more durable and reliable glass for use in portable electronic devices.

[0201] Once the ions have diffused through the thickness of the glass article, the compression depth in the glass is saturated. This demonstrates that asymmetric strengthening can be used to achieve a deeper compression depth and thereby improve the ability of the glass article to resist failure. Further, while asymmetric strengthening introduces warping via stress imbalance in the glass article, the warping can be compensated for using glass forming.

[0202] The use of glass forming includes using a more rigid cover glass design and forming a cover glass geometry to compensate for the introduced asymmetric warpage. For example, glass forming can be used to compensate for or exacerbate asymmetric chemical strengthening stresses to ensure that the combined process results in the desired final part shape.

[0203] Compression depth into the cover glass can be achieved by using one or more of the asymmetric chemical strengthening processes described herein. Fig.24As shown in , the cover glass must be generally designed to have a balanced stress budget. Thus, cover glass 2400 exhibits a high compressive stress (~750 MPa), but a fairly shallow compression depth (~40 µm), while cover glass 2402 has a two-step strengthening, where the compressive stress is still 750 MPa for a very limited depth, followed by a compression depth of ~100 µm. Cover glass 2404 exhibits a lower compressive stress (~450 MPa) and a much deeper compression depth than found in either cover glass 2400 or 2402 (~150 µm). The failure rates of cover glasses 2400, 2402, and 2404 indicate that when cover glasses fail due to impact, especially in the case of being dropped on an asphalt surface, compression depth provides a significant advantage over compression stress (cover glass 900 = 71.2% vs. cover glass 904 = 35%).

[0204] Because asymmetric chemical strengthening is beneficial in cover glass design, glass shaping is used to correct and maintain the stress imbalance that results from designing the material with asymmetric strengthening.

[0205] Figure 25 to Figure 3 0 shows one such asymmetric chemical strengthening and glass forming process.

[0206] exist Fig.25 In the process, a glass cover is obtained and the glass cover undergoes CNC to adapt its basic design needs. A cross-sectional view shows the initial cover glass geometry. Fig.25 It is shown that glass forming can be used to introduce a bend 2502 (via bending stress) at the end of the cover glass 2500. Note that symmetric chemical strengthening of this formed glass would result in a highly warped glass article and would be of little value.

[0207] exist Fig.26 In the embodiment, the cover glass 2600 may be subjected to further CNC and polishing to further prepare the cover glass. Fig. 27 2704). The bottom planar surface 2702 of the cover glass 2700 (up to the formed curvature) is coated with a layer of ion exchange diffusion barrier (SiN 2704). The SiN will significantly inhibit ion diffusion through the planar bottom surface of the cover glass. This will further ensure that the surface it covers remains substantially planar.

[0208] exist Fig.28A and Fig.28B In the embodiment of the present invention, the formed and partially masked cover glass is treated according to the chemical strengthening process described herein. Fig.28AAs can be seen, a cross section of glass 2800 indicates that the top surface 2802 of the cover glass has a depth of compressive layer DoL formed by diffusion of potassium 2803. The bottom surface 2804 coated with SiN has no or very little chemical strengthening as expected. Fig.28B A cross-sectional view showing a state of the formed cover glass 2800.

[0209] Fig.28C is a corresponding stress distribution in which the top surface 2802 of the glass cover 2800 exhibits high compressive stress and significant DoL, and in which the unreinforced bottom cover 2804 exhibits no compressive and only tensile stress (which results from balancing the stress at the top surface).

[0210] Fig.29A and Fig.29B The SiN layer shown on the bottom surface 2902 of the glass cover 2900 can be oxidized to SiO2 2903, which is no longer a complete barrier to chemical strengthening. A second round of chemical strengthening is performed on the formed glass to provide Fig.29A Note that the bottom surface 2502 now includes a shallow compression layer 2904, while the top surface 2906 has been further enhanced to have a higher surface compression ( Fig.29B ).

[0211] at last, Fig. 30A and Fig. 30B The final cover glass 3000 is shown, which includes a cover glass geometry to complement the asymmetric stress distribution from a series of chemical strengthening processes. The cover glass has excellent top cover surface compression 3002 and DoL, matched by geometry and high compressive stress with limited DoL at the bottom surface 3004 (see Fig. 30B ).

[0212] Fig. 30C 3008. The top surface 3006 of the cover glass 3000 exhibits a high surface compression 3008. The bottom surface 3010 exhibits a certain amount of surface compression 3012, which corresponds to the lower tolerance of chemical strengthening. The cover glass 3000 has a corresponding but budgeted amount of tensile stress 3014 to offset the top and bottom asymmetric surface compression.

[0213] For purposes of illustration, the foregoing description uses specific nomenclature to provide a thorough understanding of the described embodiments. However, it will be appreciated by those skilled in the art that the specific details are not necessary to practice the described embodiments. Therefore, the foregoing description of the specific embodiments described herein is presented for purposes of illustration and description, and is not intended to be exhaustive or to limit the embodiments to the precise form disclosed. It will be appreciated by those skilled in the art that many modifications and variations are possible in light of the foregoing teachings.

Claims

1. An electronic device, comprising: shell; a display located at least partially within the housing; as well as a cover glass coupled to the housing and defining a window over the display, the cover glass comprising: multiple chemically enhanced corner areas; as well as A contiguous region separates at least two of the plurality of chemically strengthened corner regions, each of the plurality of chemically strengthened corner regions being strengthened to a higher level than a contiguous region of the cover glass.

2. The electronic device of claim 1, wherein the abutment region has a compression depth from an outer surface of the cover glass that is less than a compression depth from an outer surface of each of the plurality of chemically strengthened corner regions.

3. The electronic device according to claim 2, wherein: at least one of the plurality of chemically strengthened corner regions defines a first stress profile that is asymmetric across a thickness of the at least one chemically strengthened corner region and has a first compressive depth from the outer surface of the cover glass and a second compressive depth from the inner surface of the cover glass; the abutting region defining a symmetrical second stress profile across a thickness of the abutting region, the second stress profile having a third compression depth from the outer surface of the cover glass; as well as The third compression depth of the second stress profile is less than the first compression depth of the first stress profile. 4 . The electronic device of claim 3 , wherein the first compressive depth of the first stress profile is greater than the second compressive depth of the first stress profile. 5 . The electronic device of claim 3 , wherein a surface compressive stress at the outer surface defined by the first stress pattern is greater than a surface compressive stress at the outer surface defined by the second stress pattern.

6. The electronic device according to claim 3, wherein: Each of the plurality of chemically strengthened corner regions extends to an edge of the cover glass; and The abutting region partially surrounds each of the plurality of chemically strengthened corner regions.

7. The electronic device according to claim 3, wherein: The cover glass defines four sides and four corners, the four sides defining two pairs of opposing sides; The cover glass includes four chemically strengthened corner regions; and The abutment region extends between each pair of opposing side edges.

8. A cover glass for an electronic device, comprising: a corner region having a first stress profile that is asymmetric across a thickness of the corner region; as well as A central region having a second stress profile across a thickness of the central region, the second stress profile being different from the first stress profile.

9. The cover glass according to claim 8, wherein: The first stress profile defines: a first compression depth from a first surface of the cover glass; as well as a second compression depth from a second surface opposite the first surface of the cover glass, the second compression depth being greater than zero and less than the first compression depth; as well as The second stress pattern is symmetric across the thickness of the central region.

10. The cover glass of claim 9, wherein the second stress profile defines a third compression depth that is less than the first compression depth of the first stress profile. 11 . The cover glass of claim 10 , wherein the third compressive depth of the second stress profile is greater than the second compressive depth of the first stress profile. 12 . The cover glass of claim 10 , wherein the cover glass further comprises a peripheral region having a third stress pattern different from the first stress pattern. 13 . The cover glass of claim 12 , wherein the third stress profile has a fourth compression depth from the first surface, the fourth compression depth being less than the first compression depth of the first stress profile.

14. The cover glass of claim 8, wherein the cover glass is formed of aluminosilicate glass.

15. An electronic device, comprising: monitor; a cover glass located over the display and comprising: a first compressive stress region extending from a surface of the first region of the cover glass, the cover glass having a first density within the first compressive stress region; as well as A second compressive stress region different from the first compressive stress region extends from a surface of a second region of the cover glass, the cover glass having a second density within the second compressive stress region that is less than the first density.

16. The cover glass according to claim 15, wherein: The first compressive stress region defines a first compression depth; and The second compressive stress region defines a second compression depth greater than the first compression depth.

17. The electronic device according to claim 16, wherein: The peripheral portion of the cover glass includes the first region; and The central portion of the cover glass includes a second region.

18. The electronic device according to claim 16, wherein: The first compressive stress region defines a first compressive stress at a surface of the first region; and The second compressive stress region defines a second compressive stress at a surface of the second region.

19. The electronic device according to claim 16, wherein: The first compressive stress region comprises a first silicate glass lattice structure defining the first density; and The second compressive stress region includes a second silicate glass lattice structure defining the second density.

20. A cover glass for an electronic device, the cover glass comprising: A first zone, the first zone comprising: a first compressive stress region extending from the first surface of the cover glass; and a first density within the first compressive stress region; and The second area, the second area comprises: a second compressive stress region extending from a second surface of the cover glass, the second compressive stress region being different from the first compressive stress region; and A second density within the second compressive stress region, the second density being less than the first density.

21. The cover glass according to claim 20, wherein: the first region includes a first glass lattice structure defining the first density; and The second region includes a second glass lattice structure defining the second density.

22. The cover glass according to claim 21, wherein: The first compressive stress region defines a first compression depth; and The second compressive stress region defines a second compression depth greater than the first compression depth.

23. The cover glass according to claim 22, wherein: The first compressive stress region defines a first surface compressive stress; and The second compressive stress region defines a second surface compressive stress that is less than the first surface compressive stress.

24. The cover glass of claim 22, wherein each of the first compressive stress region and the second compressive stress region comprises potassium ions introduced by ion exchange.

25. The cover glass of claim 22, wherein the first region at least partially defines a perimeter of the cover glass.

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