PATENT DOCUMENT

Publication Number: US-11571766-B2
Application Number: US-201916439547-A
Country: US
Kind Code: B2

Title: Laser marking of an electronic device through a cover

Abstract:
Markings for electronic devices are disclosed. Markings are formed through a laser-based process which transforms a colorant in a multilayer structure disposed along an interior surface of a cover. The transformed colorant defines a marking visible along an external surface of the electronic device.

Claims:
What is claimed is: 
     
       1. An electronic device comprising:
 an enclosure component; 
 a display positioned at least partially within the enclosure component; 
 a transparent cover attached to the enclosure component and having an interior surface and an exterior surface, the exterior surface defining a portion of an exterior surface of the electronic device; and 
 a multilayer structure disposed along at least a portion of the interior surface and comprising:
 an optically dense layer; and 
 a set of color layers positioned between the optically dense layer and the interior surface, the set of color layers comprising:
 a first color layer along the interior surface and comprising:
 a first form of a first colorant having first optical properties; and 
 a second form of the first colorant defining a marking visible along the exterior surface of the electronic device, the second form transformed from the first form using a laser-based process to have second optical properties different than the first optical properties, the second optical properties including a characteristic hue; and 
 
 a second color layer comprising a second colorant different from the first colorant, at least a portion of the second color layer positioned between the first color layer and the optically dense layer. 
 
 
 
     
     
       2. The electronic device of  claim 1 , wherein:
 the first color layer extends along a first portion of the interior surface of the transparent cover; 
 the portion of the second color layer positioned between the first color layer and the optically dense layer is a first portion of the second color layer; and 
 a second portion of the second color layer extends along a second portion of the interior surface. 
 
     
     
       3. The electronic device of  claim 1 , wherein the second color layer further comprises a third colorant other than the second colorant. 
     
     
       4. The electronic device of  claim 1 , wherein:
 the characteristic hue of the second form of the first colorant is a second characteristic hue; and 
 the first form of the first colorant has a first characteristic hue different than the second characteristic hue. 
 
     
     
       5. The electronic device of  claim 1 , wherein the first form of the first colorant appears colorless. 
     
     
       6. The electronic device of  claim 1 , wherein:
 the optically dense layer has an achromatic characteristic color; and 
 the optically dense layer is free of artifacts from the laser-based process. 
 
     
     
       7. The electronic device of  claim 1 , wherein:
 the transparent cover comprises a transparent glass sheet having a thickness of less than 1 mm; and 
 the transparent glass sheet is chemically strengthened. 
 
     
     
       8. An electronic device comprising:
 a display; and 
 an enclosure at least partially surrounding the display, the enclosure comprising:
 an enclosure component defining at least a portion of a side exterior surface of the electronic device; 
 a transparent cover attached to the enclosure component and defining at least a portion of a rear exterior surface of the electronic device; and 
 a multilayer structure disposed along at least a portion of an interior surface of the transparent cover and comprising:
 an optically clear layer disposed along the at least the portion of the interior surface; 
 an optically dense layer; 
 a metal layer positioned between the optically clear layer and the optically dense layer, the metal layer configured to at least partially transmit visible light and having a thickness less than 10 nm; 
 a first color layer positioned between the metal layer and the optically dense layer, the first color layer comprising a first colorant; 
 a second color layer positioned between the first color layer and the optically dense layer, the second color layer comprising a second colorant; 
 a first form of a laser-reactive colorant dispersed within at least one of the first or second color layers; and 
 a second form of the laser-reactive colorant dispersed within the at least one of the first or second color layers and defining a marking visible along the rear exterior surface. 
 
 
 
     
     
       9. The electronic device of  claim 8 , wherein the laser-reactive colorant transforms from the first form to the second form upon exposure to a laser beam comprising near infrared light. 
     
     
       10. The electronic device of  claim 8 , wherein the laser-reactive colorant comprises an irreversible thermochromic material. 
     
     
       11. The electronic device of  claim 8 , wherein:
 the laser-reactive colorant comprises a dye or a pigment; and 
 the marking has a minimum feature width of 50 microns. 
 
     
     
       12. The electronic device of  claim 8 , wherein the first color layer and the second color layer each has a thickness from 2 microns to 10 microns. 
     
     
       13. The electronic device of  claim 8 , wherein the optically clear layer has a thickness from 1 micron to 5 microns. 
     
     
       14. The electronic device of  claim 8 , wherein the metal layer comprises aluminum. 
     
     
       15. The electronic device of  claim 8 , wherein the optically dense layer has an optical density of 1 or more. 
     
     
       16. An enclosure for an electronic device, the enclosure comprising:
 an enclosure component at least partially defining an interior volume for receiving electronic components; 
 a transparent cover attached to the enclosure component and having an interior surface and an exterior surface, the exterior surface defining a portion of an exterior surface of the electronic device; and 
 a multilayer structure disposed along at least a portion of the interior surface and comprising:
 an optically dense layer; and 
 a set of layers positioned between the optically dense layer and the interior surface and comprising a first color layer between the interior surface and a second color layer, at least one of the first color layer or the second color layer having:
 a first region comprising a first form of a color-changing colorant; and 
 a second region defining a marking visible along the exterior surface and comprising a second form of the color-changing colorant, the second form of the color-changing colorant having a characteristic hue. 
 
 
 
     
     
       17. The enclosure of  claim 16 , wherein each of the first region and the second region further comprises a colorant other than the color-changing colorant. 
     
     
       18. The enclosure of  claim 16 , wherein:
 the second region is formed in the first color layer and the second color layer. 
 
     
     
       19. The enclosure of  claim 16 , wherein
 the set of layers further includes: 
 an optically clear layer positioned along the interior surface; and 
 a metal layer positioned between the optically clear layer and the first color layer. 
 
     
     
       20. The enclosure of  claim 19 , wherein the optically clear layer is a polymeric layer.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a non-provisional patent application of and claims the benefit of U.S. Provisional Patent Application 62/777,685, filed Dec. 10, 2018 and titled “Laser Marking of an Electronic Device Through a Cover,” the disclosure of which is hereby incorporated herein by reference in its entirety. 
    
    
     FIELD 
     The described embodiments relate generally to laser marking of electronic devices. More particularly, the present embodiments relate to markings formed, at least in part, using a transformable colorant 
     BACKGROUND 
     Electronic devices generally include a housing or other exterior component that may be marked or printed. For example, an exterior of a housing may be marked to provide identifying information such as the manufacturer and the model. In addition, an exterior of a housing may be marked to show that it conforms to regulations of a particular country or region. 
     Some traditional markings for metal housings are engraved into the metal. However, traditional markings may be subject to wear when applied to the exterior of a housing. 
     SUMMARY 
     The following disclosure is generally related to marking of electronic devices. In aspects of the disclosure, a multilayer structure inside the electronic device is marked using a laser-based process. The multilayer structure may be disposed along at least a portion of an interior surface of a transparent cover, allowing the marking to be visible along an exterior surface of the electronic device. 
     In embodiments, the multilayer structure includes a colorant which is transformable from a first form to a second form using a laser-based process. The marking is defined, at least in part, by the colorant in the second form. The first form and the second form have different optical properties giving the marking a distinct visual appearance. In embodiments, the transformable colorant is a color-changing colorant, such as an irreversible thermochromic colorant. 
     In embodiments, the colorant in the second form also defines a marking region formed within a set of layers of the multilayer structure. By the way of example, the set of layers comprises a set of color layers, with the marking region formed in at least one of the color layers. As another example, the set of layers comprises an optically clear layer and at least one color layer, with the marking region being formed in the optically clear layer or in at least one of the color layers. The marking may be defined, at least in part, by the colorant(s) in the marking region. The multilayer structure may further comprise additional layers as described herein, such as an optically dense layer or a metal layer. 
     In embodiments, an electronic device comprises an enclosure component, a display positioned at least partially within the enclosure component, a transparent cover attached to the enclosure component and having an interior surface and an exterior surface, the exterior surface defining a portion of an exterior surface of the electronic device, and a multilayer structure disposed along at least a portion of the interior surface. The multilayer structure comprises an optically dense layer and a set of color layers positioned between the optically dense layer and the interior surface. The set of color layers comprises a first colorant, a first form of a second colorant different than the first colorant and having first optical properties, and a second form of the second colorant defining a marking visible along the exterior surface of the electronic device, the second form transformed from the first form using a laser-based process to have second optical properties different than the first optical properties. 
     In additional embodiments, an electronic device comprises a display and an enclosure at least partially surrounding the display. The enclosure comprises an enclosure component defining at least a portion of a side exterior surface of the electronic device, a transparent cover attached to the enclosure component and defining at least a portion of a rear exterior surface of the electronic device, and a multilayer structure disposed along at least a portion of an interior surface of the transparent cover. The multilayer structure comprises an optically clear layer disposed along the portion of the interior surface, an optically dense layer, a metal layer positioned between the optically clear layer and the optically dense layer, the metal layer configured to at least partially transmit visible light, a first color layer positioned between the metal layer and the optically dense layer, the first color layer comprising a first colorant, and a second color layer positioned between the first color layer and the optically dense layer, the second color layer comprising a second colorant, a first form of a laser-reactive colorant dispersed within at least one of the first or second color layers, and a second form of the laser-reactive colorant dispersed within at least one of the first or second color layers and defining a marking visible along the rear exterior surface. 
     In additional embodiments, an enclosure for an electronic device comprises an enclosure component at least partially defining an interior volume for receiving electronic components, a transparent cover attached to the enclosure component and having an interior surface and an exterior surface, the exterior surface defining a portion of an exterior surface of the electronic device, and a multilayer structure disposed along at least a portion of the interior surface. The multilayer structure comprises an optically dense layer and a set of layers positioned between the optically dense layer and the interior surface and having a first region comprising a first form of a color-changing colorant and a second region defining a marking visible along the exterior surface and comprising a second form of the color-changing colorant. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like elements. 
         FIG.  1 A  depicts a front view of a simplified example of an electronic device. 
         FIG.  1 B  depicts a rear view of the electronic device of  FIG.  1 A . 
         FIG.  1 C  depicts a cross-sectional view of the electronic device of  FIGS.  1 A and  1 B . 
         FIG.  2    depicts a cover and a multilayer structure of an electronic device. 
         FIG.  3    schematically depicts an enlarged top view of a marking for an electronic device. 
         FIG.  4    depicts a cross-sectional view of a marking region formed in a color layer of a multilayer structure. 
         FIG.  5    depicts a cross-sectional view of a marking region formed in a localized color layer of a multilayer structure. 
         FIG.  6    depicts a cross-sectional view of a marking region formed in multiple color layers of a multilayer structure. 
         FIG.  7    depicts a cross-sectional view of a marking region formed in an optically clear layer of a multilayer structure. 
         FIG.  8    depicts a cross-sectional view of a marking region formed in a color layer of a multilayer structure and behind a metal layer. 
         FIG.  9    depicts a cross-sectional view of a marking region formed in an optically clear layer of a multilayer structure and in front of a metal layer. 
         FIG.  10    depicts a cross-sectional view of marking regions formed in two color layers of a multilayer structure and behind a metal layer. 
         FIG.  11    schematically depicts an enlarged top view of another marking for an electronic device. 
         FIG.  12    depicts a cross-sectional view of a marking region formed in a color layer of a multilayer structure. 
         FIG.  13    depicts a cross-sectional view of a marking region formed in a localized color layer of a multilayer structure. 
         FIG.  14    depicts a cross-sectional view of a marking region formed in a color layer of a multilayer structure and behind a metal layer. 
         FIG.  15    depicts a cross-sectional view of a marking region formed in an optically clear layer of a multilayer structure and in front of a metal layer. 
         FIG.  16    depicts a block diagram of example components of an example electronic device. 
     
    
    
     The use of cross-hatching or shading in the accompanying figures is generally provided to clarify the boundaries between adjacent elements and also to facilitate legibility of the figures. Accordingly, neither the presence nor the absence of cross-hatching or shading conveys or indicates any preference or requirement for particular materials, material properties, element proportions, element dimensions, commonalities of similarly illustrated elements, or any other characteristic, attribute, or property for any element illustrated in the accompanying figures. 
     Additionally, it should be understood that the proportions and dimensions (either relative or absolute) of the various features and elements (and collections and groupings thereof) and the boundaries, separations, and positional relationships presented therebetween, are provided in the accompanying figures merely to facilitate an understanding of the various embodiments described herein and, accordingly, may not necessarily be presented or illustrated to scale, and are not intended to indicate any preference or requirement for an illustrated embodiment to the exclusion of embodiments described with reference thereto. 
     DETAILED DESCRIPTION 
     Reference will now be made in detail to representative embodiments illustrated in the accompanying drawings. It should be understood that the following descriptions are not intended to limit the embodiments to one preferred implementation. To the contrary, the described embodiments are intended to cover alternatives, modifications, and equivalents as can be included within the spirit and scope of the disclosure and as defined by the appended claims. 
     The following disclosure is generally related to laser marking of electronic devices. In aspects of the disclosure, a marking is defined, at least in part, by a marking region formed in a multilayer structure internal to the electronic device. For example, the multilayer structure may be disposed along an interior surface of a cover. The cover may be a transparent or translucent cover member that is formed from a glass sheet, polymer sheet, multiple sheets, or other similar materials. The marking region is protected by the transparent or translucent member and the marking is visible along the exterior surface of the electronic device. 
     Embodiments described herein are directed to marking techniques and markings that may have advantages as compared to some traditional techniques and markings. For example, the laser marking methods described herein can produce marking elements and/or marking regions in the multilayer structure without producing visible changes (e.g., artifacts) in the rest of the multilayer structure. Therefore, the laser marking methods described herein may be used to create custom markings on assembled electronic devices, enabling region-specific markings or device-specific markings. In addition, the markings described herein may have enhanced durability because the marking elements or regions defining them are protected by the (transparent) cover. 
     In aspects of the disclosure, the marking may be in the form of text, a glyph, a symbol, a pattern, an image, or some other type of graphical element. In embodiments, the marking may have a marking feature with a line width or minimum feature width that ranges between 10 microns and 500 microns. In some cases, the marking feature has a line width or minimum feature width that ranges between 25 microns and 100 microns. For example, the minimum feature width may be the smallest width of the marking features. In further embodiments, a dimension of the marking is less than 5 cm, less than 1 cm, less than 5 mm, or less than 1 mm. In additional embodiments, the marking may extend across a layer of the multilayer structure. For example, the marking may produce a color change across an entire region or substantially all of an exterior surface of the electronic device. In one example, the marking extends across substantially all of a rear surface of an electronic device. 
     The multilayer structure includes a transformable colorant that may be transformed from a first form to a second form by exposure to light from a laser beam. A laser-based process may be used to transform the colorant, thereby producing a marking region in the multilayer structure. As used herein, the transformable colorant may also be referred to as a laser-reactive colorant. When viewed through the cover, the marking region has a visual appearance different from that of the multilayer structure adjacent the marking. 
     In embodiments, the marking may be defined by a laser-formed marking region that includes one or more regions of colorant that have been transformed by a laser. The laser-formed marking regions may be positioned along one or more layers of a multilayer structure formed along an inner surface of the cover. As discussed in more detail below, the laser-formed marking regions may be defined by multiple marking elements, each of which may correspond to a laser-treated spot created by an exposure to a laser beam or pulse. Adjacent marking elements may overlap or may not overlap. In embodiments, lines and/or shapes of the marking may appear to be continuous rather than formed of discrete marking elements when viewed from a typical viewing distance. In other words, individual marking elements may not be separately visually distinguishable from a particular viewing distance, such as a distance greater than about 5 cm, 10 cm, or 25 cm. 
     In aspects described herein, at least one layer of the multilayer structure includes a colorant that is transformable from a first form to a second form (the colorant may also be referred to herein as a transformable colorant or a laser-reactive colorant). In some embodiments, the first form and the second form of the colorant have different optical properties (e.g., visual appearances). In embodiments, the colorant transforms from the first form to the second form upon exposure of the multilayer structure to light from a laser. By the way of example, the colorant may be a color-changing or a laser-reactive colorant. As an additional example, the second form of the colorant may be formed as a result of at least a portion of a pigment or dye being vaporized, diffused, and/or ablated from the marking region. To impart permanence to the marking, the transformation of the colorant from the first form to the second form may be irreversible. In some embodiments, the laser-based process transforms the colorant in one or more layers of the multilayer structure without producing artifacts, (e.g., visible changes) in other layers of the multilayer structure. 
     In embodiments, the optical properties of the transformed colorant determine, at least in part, the visual appearance of the marking. In additional embodiments, the visual appearance of the marking as observed through the cover is also determined by any additional colorants present in the layer including the transformable colorant, by optical properties of other layers of the multilayer structure, and combinations thereof. Similarly, the visual appearance of the multilayer structure as observed through the cover may be determined by the optical properties of multiple layers of the multilayer structure. 
     In embodiments, the visual appearance of the marking and/or the multilayer structure may be described by its color(s) and other optical properties as observed through the cover. In addition, elements of the multilayer structure such as color layers, optically dense layers, and colorants may be described in terms of a characteristic color (e.g., the color of the element by itself). The color(s) of the marking, the multilayer structure, and various layers of the multilayer structure may be characterized using a color model. For example, in the hue-saturation-value (HSV) color model, the hue relates to the wavelength(s) of visible light observed when the color feature is viewed (e.g., blue or magenta) and the value relates to the lightness or darkness of a color. The saturation relates to the perceived colorfulness as judged in proportion to its brightness. As another example, coordinates in CIEL*a*b* (CIELAB) color space may be used to characterize the color, wherein L* represents brightness, a* the position between red/magenta and green, and b* the position between yellow and blue. A broadband or semi-broadband illuminant may be used to determine the color of the color feature. For example, a CIE illuminant or other reference illuminant may be used. 
     Further, color(s) may be characterized in terms of perceived wavelengths of visible light (e.g., from about 380 nm to about 750 nm). Chromatic colors have a hue (such as predominantly red, blue, yellow or green). A spectral color is present in the visible spectrum and is associated with a relatively narrow band of wavelengths. Non-spectral colors may include achromatic colors (such as white, gray or black), colors that are mixtures of spectral colors (such as violet-red colors), colors that are mixtures of spectral colors with achromatic colors, and metallic colors. For example, a violet color may be associated with light having a wavelength from about 380 nm to about 450 nm, a blue color may be associated with light having a wavelength between about 450 nm to about 495 nm, a cyan color may be associated with light having a wavelength from about 490 nm to about 520 nm, a green color may be associated with light having a wavelength between 495 nm and 570 nm, a yellow color may be associated with light having a wavelength from about 570 nm to about 590 nm, an orange color may be associated with light having a wavelength from about 590 nm to 620 nm, and a red color may be associated with light having a wavelength from about 620 nm to about 750 nm. In addition, a magenta color may be associated with light having predominantly red wavelengths and blue/violet wavelengths. 
     In embodiments, the spectral reflectance curve of the marking and/or the multilayer structure may be used to describe its optical properties. The spectral reflectance curve may be obtained over the visible spectrum or over a broader range, such as from about 400 nm to about 1500 nm. In addition, the extent of specular reflection or directionality of the reflectance may be measured. A metallic color may have a spectral reflectance curve similar to that of a metal, with a relatively high reflectance (e.g., at least 80%) over a relatively large portion of the visible spectrum. A metallic color may be produced, in part, by including a thin layer of a metal in front of the layer including a colorant. 
     These and other embodiments are discussed below with reference to  FIGS.  1 A- 16   . However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these figures is for explanatory purposes only and should not be construed as limiting. 
       FIG.  1 A  depicts a front view of a simplified example of an electronic device. As shown in  FIG.  1 A , the electronic device  100  includes a housing  110 , which includes an enclosure component  120  and a cover  130 . The cover  130  has an exterior surface  132 . In embodiments, exterior surface  132  defines at least a portion of the front exterior surface of the electronic device  100 . 
     In this example, the front cover  130  is positioned over a display  192  (edges of display shown with broken lines) that is positioned at least partially within the enclosure component  120  of the housing  110 . Display  192  comprises a display element. The cover  130  may define a window or other transparent region for viewing the display. The cover  130  may also be integrated with or coupled to a touch sensor configured to detect or estimate a location of a touch along exterior surface  132 . In further embodiments, the display  192  is integrated with or coupled to a touch sensor. 
       FIG.  1 B  depicts a rear view of the electronic device  100 . In this example, the housing  110  further includes a cover  140 . The cover  140  has an exterior surface  142 . In embodiments, the exterior surface  142  defines at least a portion of the rear exterior surface of the electronic device. The cover  140  may define a window or other transparent region for viewing markings  152 ,  154 , and  156 , which are interior to the cover  140 . The enclosure component  120  may define a side exterior surface  122 ; the side exterior surface  122  may define at least a portion of a side exterior surface of the electronic device  100 . 
     The electronic device  100  comprises markings  152 ,  154 , and  156 , which are inward from the cover  140 . At least one of markings  152 ,  154 , and  156  may be formed by a metal layer disposed on an interior surface of the cover  140 . For example, the metal of the layer may be selected from aluminum, copper, nickel, silver, gold, platinum, and alloys thereof. 
     The housing  110  may be formed from one or more different materials. In some embodiments, the housing  110  includes one or more glass components, metal or metallic components, ceramic components, glass ceramic components, composite components, or a combination thereof. For example, the enclosure component  120  may comprise a metal or a metallic material. 
     In embodiments, the covers  130  and  140  may comprise a glass, a glass ceramic, sapphire, a polymer, or a combination thereof. For example, each of the covers  130  and  140  may comprise a sheet of glass. The cover or one or more sheets of the cover may be generally flat or may be formed to a curved shape. In embodiments, the covers  130  and  140  may be transparent to visible light or may define a transparent window. By the way of example, at least one of covers  130  and  140  may comprise a transparent glass sheet. Further, the cover  130  and/or the cover  140  may include a surface coating, such as a hydrophobic or oleophobic coating, along a surface of the glass, glass ceramic, polymer, or sapphire. The thickness of the cover  130  and/or the cover  140  may be less than 3 mm, less than 1 mm, from 50 microns to 1 mm, or from 100 microns to 500 microns. 
     In additional embodiments, covers as described herein may be included in an all glass or a multi-faceted glass enclosure. In such embodiments, a cover may define one or more surfaces of the enclosure, such as a front surface and a side surface, or a front surface, a side surface and a rear surface. 
     In embodiments, the cover comprises a glass component such as a glass sheet and at least one surface of the glass component is chemically strengthened through an ion exchange process. For example, a glass surface may be chemically strengthened by exchanging alkali metal ions in the glass with larger alkali metal ions at a temperature above the strain point of the glass. The ion exchange process may introduce a compressive stress region along one or more surfaces of the glass component. 
       FIG.  1 C  depicts a partial cross-sectional view of the electronic device  100  of  FIGS.  1 A and  1 B  (along line A-A). The enclosure component  120  of housing  110  at least partially defines an interior volume for receiving electronic components. As depicted in  FIG.  1 C , the electronic device  100  includes a display  192  that is at least partially positioned within the interior volume of the housing  120 . In this example, the display  192  is coupled to the cover  130 . The display  192  may include a liquid-crystal display (LCD), light-emitting diode, organic light-emitting diode (OLED) display, an active layer organic light emitting diode (AMOLED) display, organic electroluminescent (EL) display, electrophoretic ink display, or the like (as discussed further with respect to  FIG.  16   ). In some embodiments, the electronic device  100  may further include a touch sensor, which may be positioned between the cover  130  and the display  192 . Touch sensors are discussed in further detail below with respect to  FIG.  16    and that discussion is generally applicable herein. 
     The multilayer structure  160  is coupled to the cover  140 .  FIGS.  4 - 10  and  12 - 15    show examples of cross-sectional views of multilayer structures and the description provided with respect to the multilayer structures of  FIGS.  4 - 10  and  12 - 15    is generally applicable herein. 
     As schematically depicted in  FIG.  1 C , an electronic component  194  is positioned at least partially within the interior volume. In this example, the electronic component  194  is coupled to the multilayer structure  160 . In further embodiments, additional electronic components may be positioned within the housing  110 . For example, the electronic device  100  may include one or more of a display, an input device, a sensor, memory, a processor, control circuitry, and a battery. Examples of electronic device components are described further with respect to  FIG.  16   . 
     The covers  130  and  140  may be attached to the enclosure component  120 . By the way of example, the covers  130  and  140  may be attached to the enclosure component  120  with an adhesive, a fastener, or a combination thereof. Fasteners include, but are not limited to clips or similar mechanical fastening elements. 
     In embodiments, the electronic device  100  may be a mobile telephone, a notebook computing device (e.g., a notebook), a tablet computing device (e.g., a tablet), a portable media player, a wearable device, or another type of portable device. The electronic device may also be a desktop computer system, a computer component, an input device, or virtually any other type of electronic product or device component. 
       FIG.  2    depicts a cover  240  and a multilayer structure  260  of a cover assembly  214  of an electronic device. For example, the cover assembly  214  may be included in an electronic device similar to electronic device  100  of  FIGS.  1 A- 1 C . The multilayer structure  260  is disposed along an interior surface  244  of the cover  240 . The multilayer structure  260  may be in contact with the interior surface  244 . Markings  252 ,  254 , and  256  are visible along the rear exterior surface  242  of the cover  240 . 
     When the cover assembly  214  is included in an electronic device, the markings  252 ,  254 , and  256  may be visible along the rear exterior surface of the electronic device. More generally, markings similar to the markings  252 ,  254 , and  256  may be located on the front, rear, and/or side exterior surfaces of the electronic device. The cover  240  and the multilayer structure  260  may be an example of the cover  140  and the multilayer structure  160  of  FIG.  1 C . 
     In the example of  FIG.  2   , the marking  252  is defined by a transformed colorant within the multilayer structure  260 , as is described further with respect to  FIGS.  3 - 15   . The markings  254  and  256  are formed by a metal layer disposed on the interior surface  244  of the cover  240 . In some embodiments, the metal layer forming the markings  254  and/or  256  is not included in the multilayer structure  260  and a portion of the multilayer structure  260  is disposed along the metallic marking. Each of the markings  254  and  256  may have a thickness configured to substantially prevent transmission of visible light through the marking. In additional embodiments, the metal layer forming the markings  254  and/or  256  is included in the multilayer structure  260  and the markings  254  and/or  256  are at least partially light transmissive. In some cases, the markings  254  and  256  are configured to produce a specular reflection and may have a mirror finish. The metal of the layer may be selected from aluminum, copper, nickel, silver, gold, platinum, and alloys thereof. 
       FIG.  3    depicts an enlarged view of a portion of a marking  352 . The marking  352  may be an example of the marking  252  of  FIG.  2    (Detail  1 - 1 ). The portion of the marking  352  illustrated in  FIG.  3    defines two curves  352   a  and  352   b . The curves  352   a  and  352   b  are visible through the cover  340 . Each of the curves  352   a  and  352   b  is defined by multiple marking elements  372  formed in the multilayer structure  360 . As previously described, lines and/or shapes in the marking  352  may appear to be continuous rather than formed of discrete marking elements  372  when viewed from a typical viewing distance. However, for the purposes of illustration,  FIG.  3    depicts discrete marking elements  372  which overlap one another. In additional embodiments, the marking elements  372  may abut one another or may be spaced apart from one another, as illustrated schematically in  FIG.  11   . 
     In embodiments, the marking elements  372  are formed by transforming a colorant in at least one layer of the multilayer structure  360  (e.g., a color layer). For example, the marking element  372  may be defined by a spot of colorant that has been exposed to a pulse from a laser, which transforms at least some of the colorant from a first form to a second form in a localized region of the layer. In additional embodiments, transformation of the colorant in the localized region produces a difference in optical properties between the localized region and an adjacent region of the layer. The marking elements  372  may cooperate to form a marking region in the layer of the multilayer structure. Examples of such marking regions are illustrated in the cross-sectional views of  FIGS.  4 - 10   . 
       FIG.  4    depicts a cross-sectional view of a marking region  452   a  formed in a color layer  464  of a multilayer structure  460 . The marking region  452   a  may at least partially define a marking  450  (typically viewed through a cover  440 ). The marking  450  may be an example of a portion of the marking  252  of  FIG.  2    (with the cross-section taken along line B-B in  FIG.  2   ) or of all or part of any other markings described herein. 
     As shown in  FIG.  4   , the multilayer structure  460  further comprises an optically dense layer  468 . As previously described, the multilayer structure  460  is disposed along an interior surface  444  of the cover  440 . As depicted in  FIG.  4   , the color layer  464  is disposed along the cover  440  and the optically dense layer  468  is disposed along the color layer  464 . The exterior surface  442  of the cover  440  is generally opposite the interior surface  444  as depicted in  FIG.  4   . The thickness of the cover  440  is indicated by T 0 , the thickness of the color layer  464  is indicated by T 1  and the thickness of the optically dense layer  468  is indicated by T 2 . The multilayer structure  460  depicted in  FIG.  4    is a simplified representation and may include additional layers or components, depending on the implementation. 
     In embodiments, the marking region  452   a  defines at least the shape and the position of the marking  450  visible along the exterior surface of the electronic device. As shown in  FIG.  4   , the marking region  452  is formed in the color layer  464 . The marking region  452   a  corresponds to an at least partially transformed region of the color layer  464  and therefore includes a second form of the transformable colorant. A region of the color layer  464  adjacent the marking region  452   a  is not transformed, providing a difference in optical properties between the marking region  452   a  and the adjacent region of the color layer  464 . Thus, the marking region  452   a  may be visually distinct from the adjacent region. In embodiments, this difference in optical properties contributes to a difference in color between the marking  450  and the adjacent multilayer structure  460  as observed through the cover. The color of the marking visible along the exterior surface of the electronic device typically also depends on other components of the multilayer structure  460 , as explained below. 
     Generally, the marking region  452   a  comprises multiple marking elements, as is depicted in  FIG.  3   . For simplicity, the details of the marking elements which make up marking region  452   a  are not shown in  FIG.  4   . Although the marking region  452   a  is hatched uniformly for convenience, it is not required that the transformation of the colorant in the marking region be uniform. In particular, variations in intensity across the laser beam and variations in the amount of overlap between marking elements may produce variations in the amount of transformation of the colorant in the marking region. Further, it is not required that all the colorant in the marking region be transformed to the second form in order to produce a marking. In embodiments, only enough colorant in the marking region is transformed to produce a marking  450  visibly different from that of the adjacent multilayer structure. In additional embodiments (e.g., as shown in  FIG.  6   ), the marking region extends across the entirety of one or more color layers. 
     The description of the marking region  452   a , the color layer  464 , the optically dense layer  468 , and optional additional layers may be generally applicable to multilayer structures as described herein. In addition, the description herein with respect to  FIG.  4    may apply more generally to the multilayer structures described herein and marking regions formed in such multilayer structures. 
     The color layer  464  comprises a colorant that is transformable from a first form to a second form upon exposure of the multilayer structure to light from a laser. This colorant may also be referred to herein as a transformable colorant or a laser-reactive colorant. Typically, at least one of the first form and the second form of the transformable colorant has a characteristic chromatic or achromatic color. Since the size of the colorants in the marking region  452   a  and the untransformed region of the color layer  464  is typically small, differences in colorants between the marking region  452   a  and the untransformed region is schematically indicated by hatching differences. 
     Generally the laser produces a beam, such as a pulsed beam, which is directed towards the multilayer structure  460  through the cover  440 . In embodiments, the laser is focused through the cover  440  onto the layer(s) comprising the colorant to be transformed. Exposing the colorant to the focused laser beam transforms the colorant from a first form to a second form. In embodiments, the transformation of the colorant does not produce artifacts (e.g., visible changes) in the rest of the multilayer structure. 
     In embodiments, the first form and the second form of the transformable colorant differ in optical properties, particularly over the visible range. For example, the first form may have a first absorption spectrum and the second form may have a second absorption spectrum different from the first absorption spectrum. As an additional example, the second form may have a first reflectance spectrum and the second form may have a second reflectance spectrum different from the first reflectance spectrum. 
     In additional embodiments, the color layer  464  includes multiple colorants mixed together. For example, the color layer  464  may comprise a first colorant and a second colorant, with the second colorant being a transformable colorant. In embodiments, the optical properties of the transformable colorant and the other colorant(s) in the color layer  464  together affect the optical properties of the color layer and the marking. When the marking region  452   a  includes both the transformable colorant in the second form and an additional colorant, color mixing (e.g., subtractive color mixing) may affect the color of the marking. In addition, if the marking region  452   a  also includes the first form of the transformable colorant and/or the marking region  452   a  does not extend through a thickness of the color layer  464 , color mixing due to the presence of the first form of the transformable colorant, the second form of the transformable colorant, and any additional colorants may also occur. 
     The transformable colorant may comprise an organic material, an inorganic material, an organometallic material, or a hybrid material. In embodiments, the transformable colorant comprises a dye or a pigment. In additional embodiments, the transformable colorant may comprise a dye or pigment in combination with at least one other component such as a developer and a solvent. 
     In embodiments, the transformable colorant comprises a color-changing material. The transformation of a color-changing material from the first form to the second form may contribute to the color of the marking and to a color difference between the marking  450  and the adjacent multilayer structure  460  as observed through the cover  440 . By the way of example, the first form of the color-changing material may have a first characteristic hue and the second form may have a second characteristic hue different than the first characteristic hue. As additional examples, the first form may appear colorless and the second form may have a characteristic chromatic or achromatic color (a positive transformation) or the first form may have a characteristic chromatic or achromatic color and the second form may appear colorless (a negative transformation). Further, the first form may have a first achromatic color (e.g., black) and the second form may have a second achromatic color. (e.g., white). 
     In aspects of the disclosure, the optical properties of color-changing material may change in response to stimuli including, but not limited to, light exposure, a temperature change (e.g., heating), exposure to a chemical agent, and combinations thereof. In embodiments, the color-changing material is an irreversible photochromic material or an irreversible thermochromic material. Irreversible thermochromic materials include, but are not limited to, leuco dye pigments, conjugated polymers, and complexes or compounds including a metal or a metal oxide. The optical properties of the color-changing material may change due to factors including, but not limited to, a change of phase (e.g., evaporation or phase change of an assembly of molecules), phase separation, a change in composition (e.g., due to a chemical reaction such as decomposition or oxidation), complex formation, a change in ligand geometry or coordination; and a change in structure such as molecular structure, crystalline structure, or electronic structure (including spin state). 
     In embodiments, the transformable colorant is sensitive to the wavelength(s) of light produced by the laser. In additional embodiments, the color layer further comprises another component (e.g., a photo sensitizer or an absorber) which is sensitive to the wavelength(s) of light produced by the laser and activates the transformable colorant. When one or more additional colorants are present in the layer, these additional colorants may or may not be sensitive to the wavelength(s) of light produced by the laser or the optional photosensitizer or absorber. 
     The one or more additional colorants may comprise a dye, a pigment, or a combination thereof. Further, the one or more additional colorants may comprise an organic material, an inorganic material, an organometallic material, or a hybrid material. Example of inorganic pigments include, but are not limited to carbon-based pigments (e.g., carbon black) and metal based pigments such as oxides (e.g., titanium dioxide, chromium oxide, iron oxides), sulfides, phosphates, and silicates (e.g., ultramarine). Examples of organic pigments include, but are not limited to azo pigments and phtalocyanine pigments. Examples of organic dyes include, but are not limited to, azo dyes, anthraquinone dyes, and phtalocyanine dyes. 
     As shown in  FIG.  4   , the color layer  464  may extend across a lateral dimension of the multilayer structure  460 . In additional embodiments, the color layer  464  is more localized and forms a localized layer over the interior surface  444  of the cover  440  (as described further with respect to  FIG.  5   ). 
     Generally, the color layer  464  further comprises a polymer, with the transformable colorant and any additional colorants being dispersed in the polymer. The polymer may act as a binder for the colorants. For example, the polymer may be polyester-based, epoxy-based, or urethane-based, or another suitable polymer. In embodiments, the polymer does not significantly absorb the wavelength(s) of light produced by the laser. The color layer  464  includes an effective amount of the colorant. In embodiments, the weight percentage of the colorant is from about 5 wt % to about 40 wt %. In embodiments, the color layer  464  is a polymeric layer, with the polymeric layer including the polymer, the colorant(s), and optional additives. Optional additives include, but are not limited to, one or more extenders, diluents, polymerization initiators, and/or stabilizers. The thickness of color layer  464  may be from about 2 microns to about 10 microns. Alternately, a color layer  464  may be referred to herein as an ink layer. 
     The color layer  464  may be transparent, translucent, or opaque. A translucent color layer  464  may include a colorant that scatters visible light, but does not completely prevent transmission of visible light through the color layer. A transparent color layer  464  may include a colorant which primarily absorbs, rather than scatters, light. 
     The layer  468  is an optically dense layer. For example, the optical density of the optically dense layer  468  may be described by OD=log 10  (initial intensity/transmitted intensity) may be greater than or equal to 1, greater than or equal to 2, or greater than or equal to 3. Generally, the optically dense layer  468  comprises a polymer. For example, the polymer may be polyester-based, epoxy-based, or urethane-based, or another suitable polymer. In embodiments, the optically dense layer  468  is a polymeric layer. The optically dense layer  468  may further comprise one or more pigments, dyes, or a combination thereof. As an example, the optically dense layer  468  has substantially wavelength independent (neutral) reflectance and/or absorption spectrum over the visible range. In addition, the optically dense layer  468  may have an achromatic characteristic color. The thickness of the optically dense layer  468  may be from about 2 microns to about 10 microns. 
     In embodiments, the optical properties of the optically dense layer  468  also contribute to the color of the marking  450  and the adjacent multilayer structure  460  as observed through the cover  440 . In further embodiments, the optical properties of the optically dense layer  468  may be configured to adjust the lightness and/or the chroma of the marking. In addition, the optically dense layer  468  may be configured so that it does not substantially affect the hue of the marking. As referred to herein, the chroma relates to the perceived colorfulness of an area and may be judged as a proportion of the brightness of a similarly illuminated area that appears white or highly transmitting. For example, an optically dense layer  468  having a characteristic white or light gray color may produce a lighter marking than an optically dense layer having a characteristic dark gray or black color. 
     In embodiments, the optically dense layer  468  is substantially free of artifacts from the laser-based process. For example, the optical properties of the optically dense layer  468  may be substantially the same in a region corresponding to the marking region and in an adjacent region. 
     In additional embodiments, the multilayer structure  460  may comprise additional layers. If the additional layers are located in front of the optically dense layer  468  (i.e., towards the cover), the optical properties of these additional layers may also affect the color of the marking  450  and the multilayer structure  460  as observed through the cover  440 . For example, the multilayer structure  460  may comprise multiple color layers, with at least one of the color layers comprising a transformable colorant. Other layers of the multilayer structure  460  may comprise colorants which are not sensitive to the wavelength(s) of light produced by the laser. Examples of multilayer structures including multiple color layers are shown in  FIGS.  5 - 10  and  12 - 15   . 
     The multilayer structure  460  may further comprise a metal layer. In embodiments, the metal layer may have a thickness configured to allow transmission of visible light. For example, the metal layer may transmit at least 40% of light in the visible spectrum. In embodiments, the metal layer may have a thickness greater than about 0.5 nm and less than 10 nm, less than 5 nm, less than 3 nm, less than 2 nm, or less than 1 nm. Thin metal layers may be formed by a deposition process such as a physical vapor deposition process. The metal of the metal layer may be selected from aluminum, copper, nickel, silver, gold, platinum, and alloys thereof. Such a metal layer may give a metallic or mirror effect to the marking and multilayer structure as seen through the cover. Typically the metal layer is in front of the color layer(s), but in additional embodiments the metal layer may be positioned behind the color layer(s). Examples of multilayer structures including a metal layer are depicted in  FIGS.  8 - 9  and  14 - 15   . 
     Further, an optically clear layer may be included in the multilayer structure  460  in front of the color layer(s) or in front of a metal layer and the color layer(s) as depicted in  FIGS.  7 - 10  and  14 - 15   . In some embodiments, an optically clear layer may include a stabilizer to limit UV degradation of color layers behind the optically clear layer. In embodiments, the optically clear layer is a polymeric layer. In embodiments, the thickness of the optically clear layer is from about 1 micron to about 5 microns. The optically clear layer may be transparent to visible light and may appear essentially colorless. 
     In addition, the multilayer structure  460  may comprise additional polymeric layers behind and disposed along the optically dense layer  468  (as depicted in  FIG.  10   ). If components of the electronic device are glued to the multilayer structure, these additional layers may include a protective layer which protects the color layers of the multilayer structure from damage due to the glue. The additional layers may further include a layer inwards of the protective layer which facilitates adhesion of the multilayer structure to the glue. These additional polymeric layers may be polyester-based, epoxy-based, urethane-based, acrylic-based, or may comprise any other suitable polymer. The thickness of these additional layers may be from about 2 microns to about 20 microns or from about 5 microns to about 15 microns. 
     The total thickness of the multilayer structure  460  may be from about 30 microns to about 70 microns. In embodiments, the layers of the multilayer structure adhere or bond to each other due to intermolecular forces. In additional embodiments, the multilayer structure  460  adheres or bonds to the cover. 
       FIG.  5    depicts a cross-sectional view of marking region  552   a  formed within a set of color layers  564  and  566 . The marking region  552   a  may at least partially define a marking  550  (typically viewed through a cover  540 ). The marking  550  may be an example of a portion of the marking  252  of  FIG.  2    (with the cross-section taken along line B-B in  FIG.  2   ) or of all or part of any other markings described herein. 
     As depicted in  FIG.  5   , the marking region  552   a  is formed in the color layer  564 . The color layer  564  has a lateral dimension less than that of the color layer  566  and therefore may be referred to as a localized layer. The color layer  566  conforms to the shape of the color layer  564 . The multilayer structure  560  further comprises an optically dense layer  568  in addition to the set of color layers  564  and  566 . The details of the marking elements comprising the marking region  552   a  are not shown in  FIG.  5   . 
     The color layer  564  comprises a transformable colorant as previously described. The marking region  552   a  corresponds to an at least partially transformed region of the color layer  564  and defines the marking  550  visible along the exterior surface of the electronic device. A region of the color layer  564  adjacent the marking region  552   a  is not transformed, providing a difference in optical properties between the marking region  552   a  and the adjacent region of the color layer  564 . Further, a similar difference in optical properties may be present between the marking region  552   a  and a nearby region of the color layer  566 . In embodiments, the difference(s) in optical properties contributes to a difference in color between the marking  550  and the adjacent multilayer structure  560  observed through the cover  540 . As previously described with respect to  FIG.  4   , the color layer  564  may include one or more colorants in addition to the transformable colorants(s). 
     The color layer  566  also includes one or more colorants. In embodiments, the colorant(s) in the color layer  566  produce a similar visual effect to the colorant(s) in the color layer  564  prior to laser marking. In other words, the color layer  564  may be color matched to the color layer  566  (and vice versa). In some embodiments, the colorant in the color layer  566  is not sensitive to the wavelength(s) of light produced by the laser. By the way of example, the color layer  564  may include a first colorant and a second colorant which is a transformable colorant and the color layer  566  may also include the first colorant. 
     As previously described, the multilayer structure  560  is disposed along the interior surface  544  of the cover  540 . As depicted in  FIG.  5   , the color layer  564  and a portion of the color layer  566  are disposed along the cover  540 , another portion of the color layer  566  is disposed along the color layer  564 , and the optically dense layer  568  is disposed along the color layer  566 . The exterior surface  542  of the cover  540  is generally opposite the interior surface  544  as depicted in  FIG.  5   . 
     In aspects described herein, the optical properties of the marking region  552   a , the color layer  566 , and the optically dense layer  568  contribute to the visual appearance of the marking  550  as observed through the cover  540 . If the marking region  552   a  does not extend through the thickness of the color layer  564 , the optical properties of the color layer  564  may also contribute to the visual appearance of the marking  550 . In additional aspects described herein, the optical properties of the color layers  564  and  566  and the optically dense layer  568  contribute to the visual appearance of the multilayer structure  560  adjacent the marking  550  as observed through the cover  540 . 
       FIG.  6    depicts a cross-sectional view of a marking region  652   a  formed in a set of color layers,  664  and  666 . The marking region  652   a  may at least partially define a marking  650  (typically viewed through a cover  640 ). The marking  650  may be an example of a portion of the marking  252  of  FIG.  2    (with the cross-section taken along line B-B in  FIG.  2   ) or of all or part of any other markings described herein. 
     As depicted in  FIG.  6   , each of the color layers  664  and  666  comprise a transformable colorant and the marking region  652   a  is formed in the color layer  664  and a portion of the color layer  666 . The multilayer structure  660  further comprises an optically dense layer  668  in addition to the set of color layers  664  and  666 . 
     As previously described, the multilayer structure  660  is disposed along the interior surface  644  of the cover  640 . As depicted in  FIG.  6   , the color layer  664  is disposed along the cover  640 , the color layer  666  is disposed along the color layer  664 , and the optically dense layer  668  is disposed along the color layer  664 . The exterior surface  642  of the cover  640  is generally opposite the interior surface  644  as depicted in  FIG.  6   . 
     Each of the color layers  664  and  666  comprise a transformable colorant as previously described. The marking region  652   a  corresponds to an at least partially transformed region of the color layers  664  and  666  and defines the marking  650  visible along the exterior surface of the electronic device. The regions of the color layers  664  and  666  adjacent the marking region  652   a  are not transformed, providing a difference in optical properties between the marking region  652   a  and the adjacent regions of the color layers  664  and  666 . In embodiments, these differences in optical properties contribute to a difference in color between the marking  650  and the adjacent multilayer structure  660  as observed through the cover  640 . In additional aspects of the disclosure, each of the color layers  664  and  666  may include one or more colorants in addition to the transformable colorants(s). 
     By the way of example, the color layer  664  may include a first colorant and a second colorant which is a transformable colorant. The color layer  666  may include a third colorant and a fourth colorant which is a transformable colorant. The first and the third colorant may be the same or may be different. The second colorant and the fourth colorant may be the same or may be different. 
     In aspects described herein, the optical properties of the marking region  652   a  and the optically dense layer  668  contribute to the visual appearance of the marking region  652   a  as observed through the cover. The optical properties of the color layer  666  may also contribute to the visual appearance of the marking  650 . In additional aspects described herein, the optical properties of the color layers  664  and  666  and the optically dense layer  668  contribute to the visual appearance of the multilayer structure  660  adjacent the marking  650  as observed through the cover  640 . 
       FIG.  7    depicts a cross-sectional view of marking region  752   a  within a set of layers comprising an optically clear layer  762  and two color layers,  764  and  766 . The marking region  752   a  may at least partially define a marking  750  (typically viewed through a cover  740 ). The marking  750  may be an example of a portion of the marking  252  of  FIG.  2    (with the cross-section taken along line B-B in  FIG.  2   ) or of all or part of any other markings described herein. 
     As depicted in  FIG.  7   , the optically clear layer  762  comprises a transformable colorant and the marking region  752   a  is formed in the optically clear layer  762 . The multilayer structure  760  further comprises an optically dense layer  768  in addition to the optically clear layer  762  and the color layers  764  and  766 . 
     As previously described, the multilayer structure  760  is disposed along the interior surface  744  of the cover  740 . As depicted in  FIG.  7   , the optically clear layer  762  is disposed along the cover  740 , the color layer  764  is disposed along the optically clear layer  762 , the color layer  766  is disposed along the color layer  764 , and the optically dense layer  768  is disposed along the color layer  766 . The exterior surface  742  of the cover  740  is generally opposite the interior surface  744  as depicted in  FIG.  7   . 
     The optically clear layer  762  comprises a transformable colorant. In the embodiment shown in  FIG.  7   , the first form of the transformable colorant appears colorless. For example, the optically clear layer  762  prior to laser marking has a relatively high transmittance (e.g., at least 80%, or at least 85%) and does not appear to selectively absorb some wavelengths of visible light. If an optional additive is included in this layer, it also appears colorless. The second form of the transformable colorant does not appear to be colorless. For example, the second form of the transformable colorant may selectively absorb some wavelengths of visible light. Therefore, the marking region  752   a  has reduced optical clarity as compared to an adjacent region of the optically clear layer  762 . 
     The marking region  752   a  corresponds to an at least partially transformed region of the optically clear layer  762  and defines the marking  750  visible along the exterior surface of the electronic device. A region of the optically clear layer  762  adjacent the marking region  752   a  is not transformed, providing a difference in optical properties between the marking region  752   a  and the adjacent region of optically clear layer  762 . In embodiments, this difference in optical properties contributes to a difference in color between the marking region  752   a  and the adjacent multilayer structure  760  as observed through the cover. As referred to herein, an optically clear layer  762  may include one or more optically clear regions as well as one or more marking regions  752   a  which are not optically clear. 
     The color layers  764  and  766  also include one or more colorants. The colorant(s) in the color layers  764  and  766  may be the same or may differ from one another. In some embodiments, the colorant(s) in the color layers  764  and  766  are not sensitive to the wavelength(s) of light produced by the laser. 
     By the way of example, the optically clear layer  762  may comprise a first colorant which is a transformable colorant. The color layer  764  may comprise a second colorant and the color layer  766  may comprise a third colorant. The second and the third colorants may be the same or may be different. 
     In aspects described herein, the optical properties of the marking region  752   a , the color layers  764  and  766 , and the optically dense layer  768  contribute to the visual appearance of the marking  750  as observed through the cover  740 . In additional aspects described herein, the optical properties of the color layers  764  and  766  and the optically dense layer  768  contribute to the visual appearance of the multilayer structure  760  adjacent the marking  750  as observed through the cover  740 . 
       FIG.  8    depicts a cross-sectional view of marking region  852   a  within a set of layers comprising an optically clear layer  862  and two color layers,  864  and  866 . The marking region  852   a  may at least partially define a marking  850  (typically viewed through a cover  840 ). The marking  850  may be an example of a portion of the marking  252  of  FIG.  2    (with the cross-section taken along line B-B in  FIG.  2   ) or of all or part of any other markings described herein. 
     In particular, the color layer  864  comprises a transformable colorant and the marking region  852   a  is formed in the color layer  864 . The multilayer structure  860  further comprises a metal layer  863  and an optically dense layer  868 . 
     As previously described, the multilayer structure  860  is disposed along the interior surface  844  of the cover  840 . As depicted in  FIG.  8   , the optically clear layer  862  is disposed along the cover  840 , the metal layer  863  is disposed along the optically clear layer  862 , the color layer  864  is disposed along the metal layer  863 , the color layer  866  is disposed along the color layer  864 , and the optically dense layer  868  is disposed along the color layer  866 . The exterior surface  842  of the cover  840  is generally opposite the interior surface  844  as depicted in  FIG.  8   . 
     The color layer  864  comprises a transformable colorant as previously described. The marking region  852   a  corresponds to an at least partially transformed region of the color layer  864  and defines the marking  850  visible along the exterior surface of the electronic device. A region of the color layer  864  adjacent the marking region  852   a  is not transformed, providing a difference in optical properties between the marking region  852   a  and the adjacent region of color layer  864 . In embodiments, the difference in optical properties contributes to a difference in color between the marking  850  and the adjacent multilayer structure  860  observed through the cover  840 . In additional aspects of the disclosure, the color layer  864  may include one or more colorants in addition to the transformable colorant. 
     The color layer  866  also includes one or more colorants. In embodiments, the colorant(s) in the color layer  866  produce a similar visual effect to the colorant(s) in the color layer  864  prior to laser marking. In other words, the color layer  864  may be color matched to the color layer  866  (and vice versa). In some embodiments, the colorant in the color layer  866  is not sensitive to the wavelength(s) of light produced by the laser. 
     By the way of example, the color layer  864  may include a first colorant and a second colorant which is a transformable colorant. The color layer  866  may include a third colorant. The first and the third colorants may be the same or may be different. 
     The metal layer  863  has a thickness configured to allow transmission of visible light. Such a metal layer may give a metallic effect to the multilayer structure as seen through the cover. The metal layer  863  may be as previously described with respect to  FIG.  4   . 
     When the metal layer  863  is present, the optically clear layer  862  may be included between the transparent cover  840  and the metal layer  863 . If a crack is introduced into the metal layer  863 , the optically clear layer  862  may limit or prevent propagation of the crack into the cover  840 . The optically clear layer  862  may be as previously described with respect to  FIG.  4   . 
     In aspects described herein, the optical properties of the marking region  852   a , the color layer  866 , and the optically dense layer  868  contribute to the visual appearance of the marking  850  as observed through the cover  840 . If the marking region  852   a  does not extend through the thickness of the color layer  864 , the optical properties of the color layer  864  may also contribute to the visual appearance of the marking  850 . In additional aspects described herein, the optical properties of the color layers  864  and  866  and the optically dense layer  868  contribute to the visual appearance of the multilayer structure  860  adjacent the marking  850  as observed through the cover  840 . 
       FIG.  9    depicts a cross-sectional view of a marking region  952   a  within a set of layers comprising an optically clear layer  962  and two color layers,  964  and  966 . The marking region  952   a  may at least partially define a marking  950  (typically viewed through a cover  940 ). The marking  950  may be an example of a portion of the marking  252  of  FIG.  2    (with the cross-section taken along line B-B in  FIG.  2   ) or of all or part of any other markings described herein. 
     As depicted in  FIG.  9   , the optically clear layer  962  comprises a transformable colorant and the marking region  952   a  is formed in the optically clear layer  962 . The multilayer structure  960  further comprises a metal layer  963  and an optically dense layer  968 . 
     As depicted in  FIG.  9   , the optically clear layer  962  is disposed along the cover  940 , the metal layer  963  is disposed along the optically clear layer  962 , the color layer  964  is disposed along the metal layer  963 , the color layer  966  is disposed along the color layer  964 , and the optically dense layer  968  is disposed along the color layer  966 . The exterior surface  942  of the cover  940  is generally opposite the interior surface  944  as depicted in  FIG.  9   . 
     The optically clear layer  962  comprises a transformable colorant. In the embodiment shown in  FIG.  9   , the first form of the transformable colorant appears colorless. For example, the optically clear layer  962  prior to laser marking has a relatively high transmittance (e.g., at least 80%, or at least 85%) and does not appear to selectively absorb some wavelengths of visible light. The second form of the transformable colorant does not appear to be colorless. For example, the second form of the transformable colorant may selectively absorb some wavelengths of visible light. Therefore, the marking region  952   a  has reduced optical clarity as compared to an adjacent region of the optically clear layer  962 . 
     The marking region  952   a  corresponds to an at least partially transformed region of the optically clear layer  962  and defines the marking  950  visible along the exterior surface of the electronic device. A region of the optically clear layer  962  adjacent the marking region  952   a  is not transformed, providing a difference in optical properties between the marking region  952   a  and the adjacent region of the optically clear layer  962 . In embodiments, this difference in optical properties contributes to a difference in color between the marking  950  and the adjacent multilayer structure  960  as observed through the transparent cover  940 . 
     The color layers  964  and  966  also include one or more colorants. In embodiments, the colorant(s) in the color layer  966  produce a similar visual effect to the colorant(s) in the color layer  964  prior to laser marking. In other words, the color layer  964  may be color matched to the color layer  966  (and vice versa). In some embodiments, the colorant in the color layers  964  and  966  is not sensitive to the wavelength(s) of light produced by the laser. 
     By the way of example, the optically clear layer  962  may comprise a first colorant which is a transformable colorant. The color layer  964  may comprise a second colorant and the color layer  966  may comprise a third colorant. The second and the third colorants may be the same or may be different. 
     The metal layer  963  has a thickness configured to allow transmission of visible light. Such a metal layer may give a metallic effect to the multilayer structure as seen through the cover. When the metal layer  963  is present, an optically clear layer  962  may be included between the transparent cover  940  and the metal layer  963 . If a crack is introduced into the metal layer  963 , the optically clear layer  962  may limit or prevent propagation of the crack into the transparent cover  940 . The metal layer  963  and the optically clear layer  962  may be as previously described with respect to  FIG.  4   . 
     In aspects described herein, the optical properties of the marking region  952   a , the metal layer  963 , the color layers  964  and  966 , and the optically dense layer  968  contribute to the visual appearance of the marking  950  as observed through the cover  940 . In additional aspects described herein, the optical properties of the metal layer  963 , the color layers  964  and  966 , and the optically dense layer  968  contribute to the visual appearance of the multilayer structure adjacent the marking  950  as observed through the cover  940 . 
       FIG.  10    depicts a cross-sectional view of marking regions  1052   a  and  1052   b  with a set of layers comprising an optically clear layer  1062  and two color layers,  1064  and  1066 . The marking regions  1052   a  and  1052   b  may at least partially define a marking  1050  (typically viewed through a cover  1040 ). The marking  1050  may be an example of a portion of the marking  252  of  FIG.  2    (with the cross-section taken along line B-B in  FIG.  2   ) or of all or part of any other markings described herein. 
     As depicted in  FIG.  10   , the marking region  1052   a  is formed in the color layer  1066  and the marking region  1052   b  is formed in the color layer  1064 . The multilayer structure  1060  further comprises the metal layer  1063 , the optically dense layer  1068 , and the protective layer  1069 . 
     As previously described, the multilayer structure  1060  is disposed along the interior surface  1044  of the cover  1040 . As depicted in  FIG.  10   , the optically clear layer  1062  is disposed along the cover  1040 , the metal layer  1063  is disposed along the optically clear layer  1062 , the color layer  1064  is disposed along the metal layer  1063 , the color layer  1066  is disposed along the color layer  1064 , and the optically dense layer  1068  is disposed along the color layer  1064 . The exterior surface  1042  of the cover  1040  is generally opposite the interior surface  1044  as depicted in  FIG.  10   . 
     The color layer  1064  comprises a transformable colorant as previously described. The marking region  1052   b  corresponds to an at least partially transformed region of the color layer  1064  and partially defines the marking  1050  visible along the exterior surface of the electronic device. A region of the color layer  1064  adjacent the marking region  1052   b  is not transformed, providing a difference in optical properties between the marking region  1052   b  and the adjacent region of the color layer  1064 . In embodiments, the difference(s) in optical properties contributes to a difference in color between the marking region  1052   b  and the adjacent multilayer structure  1060  observed through the transparent cover  1040 . In additional aspects of the disclosure, the color layer  1064  may include one or more colorants in addition to the transformable colorants(s). 
     The color layer  1066  also comprises a transformable colorant. The transformable colorant of the color layer  1066  may be the same as that of the color layer  1064  or may be different. The marking region  1052   a  corresponds to an at least partially transformed region of the color layer  1066  and partially defines the marking  1050  visible along the exterior surface of the electronic device. A region of the color layer  1066  adjacent the marking region  1052   a  is not transformed, providing a difference in optical properties between the marking region  1052   a  and the adjacent region of the color layer  1066 . In embodiments, the difference(s) in optical properties contributes to a difference in color between the marking region  1052   a  and the adjacent multilayer structure  1060  observed through the transparent cover  1040 . 
     By the way of example, the color layer  1064  may include a first colorant and a second colorant which is a transformable colorant. The color layer  1066  may include a third colorant and a fourth colorant which is a transformable colorant. The first and the third colorants may be the same or may be different. The second colorant and the fourth colorant may be the same or may be different. 
     The metal layer  1063  has a thickness configured to allow transmission of visible light. Such a metal layer may give a metallic effect to the multilayer structure as seen through the cover. When the metal layer  1063  is present, an optically clear layer  1062  may be included between the transparent cover  1040  and the metal layer  1063 . If a crack is introduced into the metal layer  1063 , the optically clear layer  1062  may limit or prevent propagation of the crack into the transparent cover  1040 . The metal layer  1063  and the optically clear layer  1062  may be as previously described with respect to  FIG.  4   . 
     In aspects described herein, the optical properties of the marking region  1052   a , the metal layer  1063 , the color layer  1064 , and the optically dense layer  1068  contribute to the visual appearance of the marking  1050  as observed through the cover  1040 . In addition, the optical properties of the marking region  1052   b , the metal layer  1063 , the color layer  1066 , and the optically dense layer  1068  contribute to the visual appearance of the marking  1050  as observed through the cover  1040 . If the marking region  1052   a  and/or  1052   b  does not extend through the thickness of the color layer  1064  and/or  1066 , the optical properties of the color layer  1064  and/or  1066  may also contribute to the visual appearance of the marking  1050 . In additional aspects described herein, the optical properties of the metal layer  1063 , the color layers  1064  and  1066 , and the optically dense layer  1068  contribute to the visual appearance of the multilayer structure  1060  adjacent the marking  1050  as observed through the cover  1040 . 
       FIG.  11    depicts an additional embodiment of an enlarged view of a portion of marking  252  of  FIG.  2    (Detail  1 - 1 ). The portion of marking  1152  illustrated in  FIG.  11    defines two curves  1152   a  and  1152   b . The curves  1152   a  and  1152   b  are visible through the cover  1140 . Each of the curves  1152   a  and  1152   b  are defined by multiple marking elements  1172  formed in a multilayer structure  1160 . As previously described, lines and/or shapes in the marking may appear to be continuous rather than formed of discrete marking elements when viewed from a typical viewing distance. However, for the purposes of illustration,  FIG.  11    depicts discrete marking elements  1172 , some of which are separated from one another and others of which abut one another. 
       FIG.  12    schematically depicts a cross-sectional view of discrete marking elements  1272   a ,  1272   b , and  1272   c  within a set of two color layers,  1264  and  1266 . The discrete marking elements  1272   a ,  1272   b , and  1272   c  may at least partially define a marking  1250  (typically viewed through a cover  1240 ). The marking  1250  may be an example of a portion of the marking  252  of  FIG.  2    (with the cross-section taken along line B-B in  FIG.  2   ) or of all or part of any other markings described herein. 
     As depicted in  FIG.  12   , color layer  1264  comprises a transformable colorant and the markings  1272   a ,  1272   b , and  1272   c  are formed in color layer  1264 . Multilayer structure  1260  further comprises an optically dense layer  1268  in addition to the set of color layers. 
     As previously described, the multilayer structure  1260  is disposed along the interior surface  1244  of the cover  1240 . As depicted in  FIG.  12   , the color layer  1264  is disposed along the cover  1240 , the color layer  1266  is disposed along the color layer  1264 , and the optically dense layer  1268  is disposed along the color layer  1264 . The exterior surface  1242  of the cover  1240  is generally opposite the interior surface  1244  as depicted in  FIG.  12   . 
     The marking elements  1272   a ,  1272   b , and  1272   c  each correspond to an at least partially transformed region of the color layer  1264  and define the marking(s) (e.g.,  1250 ) visible along the exterior surface of the electronic device. A region of the color layer  1264  adjacent the marking elements  1272   a ,  1272   b , and  1272   c  is not transformed, providing a difference in optical properties between the marking elements  1272   a ,  1272   b , and  1272   c  (and marking  1250 ) and the adjacent region of the color layer  1264 . In embodiments, the difference(s) in optical properties contribute to a difference in color between the marking elements  1272   a ,  1272   b , and  1272   c  and the adjacent multilayer structure  1260  observed through the cover  1240 . In additional aspects of the disclosure, the color layer  1264  may include one or more colorants in addition to the transformable colorants(s). 
     In aspects described herein, the optical properties of the marking elements  1272   a ,  1272   b , and  1272   c , the color layer  1266 , and the optically dense layer  1268  contribute to the visual appearance of the marking elements  1272   a ,  1272   b , and  1272   c  as observed through the cover  1240 . If the marking elements  1272   a ,  1272   b , and  1272   c  do not extend through the thickness of the color layer  1264 , the optical properties of the color layer  1264  may also contribute to the visual appearance of the marking  1250 . In additional aspects described herein, the optical properties of the color layers  1264  and  1266  and the optically dense layer  1268  contribute to the visual appearance of the multilayer structure  1260  adjacent the marking  1250  as observed through the cover  1240 . 
     The color layer  1266  also includes one or more colorants. In embodiments, the colorant(s) in the color layer  1266  produce a similar visual effect to the colorant(s) in the color layer  1264  prior to laser marking. In other words, the color layer  1264  may be color matched to the color layer  1266  (and vice versa). In some embodiments, the colorant in the color layer  1266  is not sensitive to the wavelength(s) of light produced by the laser. 
     By the way of example, the color layer  1264  may include a first colorant and a second colorant which is a transformable colorant. The color layer  1266  may include a third colorant. The first and the third colorants may be the same or may be different. 
       FIG.  13    schematically depicts a cross-sectional view of marking elements  1372   a ,  1372   b , and  1372   c  within a set of color layers  1362 ,  1364 , and  1366 . The marking elements  1372   a ,  1372   b , and  1372   c  may at least partially define a marking  1350  (typically viewed through a cover  1340 ). The marking  1350  may be an example of a portion of the marking  252  of  FIG.  2    (with the cross-section taken along line B-B in  FIG.  2   ) or of all or part of any other markings described herein. 
     As depicted in  FIG.  13   , the marking elements  1372   a ,  1372   b , and  1372   c  are formed in the color layer  1362 . The multilayer structure  1360  further comprises an optically dense layer  1368  in addition to the set of color layers  1362 ,  1364 , and  1366 . The color layer  1362  has a lateral dimension less than that of the color layers  1364  and  1366  and therefore may be referred to as a localized layer. The color layer  1364  conforms to the shape of the color layer  1362 . 
     As previously described, the multilayer structure  1360  is disposed along the interior surface  1344  of the cover  1340 . As depicted in  FIG.  13   , the color layer  1362  and a portion of the color layer  1364  are disposed along the cover  1340 , another portion of the color layer  1364  is disposed along the color layer  1362 , the color layer  1366  is disposed along the color layer  1364 , and the optically dense layer  1368  is disposed along the color layer  1366 . The exterior surface  1342  of the cover  1340  is generally opposite the interior surface  1344  as depicted in  FIG.  13   . 
     The marking elements  1372   a ,  1372   b , and  1372   c  each correspond to an at least partially transformed region of the color layer  1362  and define the marking(s) (e.g.,  1350 ) visible along the exterior surface of the electronic device. A region of the color layer  1362  adjacent the marking elements  1372   a ,  1372   b , and  1372   c  is not transformed, providing a difference in optical properties between the marking elements and the adjacent region of the color layer  1362 . Further, a similar difference in optical properties may be present between the marking elements and a nearby region of the color layer  1364 . In embodiments, the difference(s) in optical properties contributes to a difference in color between the marking  1350  and the adjacent multilayer structure  1360  observed through the cover  1340 . In additional aspects of the disclosure, the color layer  1362  may include one or more colorants in addition to the transformable colorants(s). 
     The color layers  1364  and  1366  also include one or more colorants. In embodiments, the colorant(s) in the color layer  1364  produce a similar visual effect to the colorant(s) in the color layer  1362  prior to laser marking. In other words, the color layer  1364  and/or the color layer  1366  may be color matched to the color layer  1362  (and vice versa). In some embodiments, the colorant in the color layer  1364  is not sensitive to the wavelength(s) of light produced by the laser. 
     By the way of example, the color layer  1362  may include a first colorant and a second colorant which is a transformable colorant. The color layer  1364  may include a third colorant and the color layer  1366  may include a fourth colorant. The first, the third, and the fourth colorants may all be different or all or some of them may be the same. 
     In aspects described herein, the optical properties of the marking elements  1372   a ,  1372   b , and  1372   c , the color layers  1364  and  1366 , and the optically dense layer  1368  contribute to the visual appearance of the marking  1350  as observed through the cover  1340 . If the marking elements  1372   a ,  1372   b , and  1372   c  do not extend through the thickness of the color layer  1362 , the optical properties of the color layer  1362  may also contribute to the visual appearance of the marking  1350 . In additional aspects described herein, the optical properties of the color layers  1362 ,  1364 , and  1366  and the optically dense layer  1368  contribute to the visual appearance of the multilayer structure  1360  adjacent the marking  1350  as observed through the cover  1340 . 
       FIG.  14    schematically depicts a cross-sectional view of marking elements  1472   a ,  1472   b , and  1472   c  within a set of layers comprising an optically clear layer  1462  and two color layers,  1464  and  1466 . The marking elements  1472   a ,  1472   b , and  1472   c  may at least partially define a marking  1450  (typically viewed through a cover  1440 ). The marking  1450  may be an example of a portion of the marking  252  of  FIG.  2    (with the cross-section taken along line B-B in  FIG.  2   ) or of all or part of any other markings described herein. 
     As depicted in  FIG.  14   , the color layer  1464  comprises a transformable colorant and the marking elements  1472   a ,  1472   b , and  1472   c  are formed in the color layer  1464 . The multilayer structure  1460  further comprises a metal layer  1463  and an optically dense layer  1468 . As previously described, the multilayer structure  1460  is disposed along the interior surface  1444  of the cover  1440 . As depicted in  FIG.  14   , the optically clear layer  1462  is directly disposed along the cover  1440 , the metal layer  1463  is disposed along the optically clear layer  1462 , the color layer  1464  is disposed along the metal layer  1463 , the color layer  1466  is disposed along the color layer  1464 , and the optically dense layer  1468  is disposed along the color layer  1466 . The exterior surface  1442  of the cover  1440  is generally opposite the interior surface  1444  as depicted in  FIG.  14   . 
     The marking elements  1472   a ,  1472   b , and  1472   c  each correspond to an at least partially transformed region of the color layer  1464  and define the marking(s) visible along the exterior surface of the electronic device. A region of the color layer  1464  adjacent the marking elements  1472   a ,  1472   b , and  1472   c  is not transformed, providing a difference in optical properties between the marking elements  1472   a ,  1472   b , and  1472   c  and the adjacent region of the color layer  1464 . In embodiments, the difference(s) in optical properties contributes to a difference in color between the marking  1450  and the adjacent multilayer structure  1460  observed through the cover  1440 . In additional aspects of the disclosure, the color layer  1464  may include one or more colorants in addition to the transformable colorants(s). 
     The color layers  1464  and  1466  also include one or more colorants. In embodiments, the colorant(s) in the color layer  1466  produce a similar visual effect to the colorant(s) in the color layer  1464  prior to laser marking. In other words, the color layer  1466  may be color matched to the color layer  1464  (and vice versa). In some embodiments, the colorant in the color layer  1464  is not sensitive to the wavelength(s) of light produced by the laser. 
     By the way of example, the color layer  1464  may include a first colorant and a second colorant which is a transformable colorant. The color layer  1466  may include a third colorant. The first and the third colorants may be the same or may be different. 
     The metal layer  1463  has a thickness configured to allow transmission of visible light. Such a metal layer may give a metallic effect to the multilayer structure as seen through the cover. When the metal layer  1463  is present, an optically clear layer  1462  may be included between the cover  1440  and the metal layer  1463 . If a crack is introduced into metal layer  1463 , the optically clear layer may limit or prevent propagation of the crack into the cover  1440 . The metal layer  1463  and the optically clear layer  1462  may be as previously described with respect to  FIG.  4   . 
     In aspects described herein, the optical properties of the marking elements  1472   a ,  1472   b , and  1472   c , the metal layer  1463 , the color layer  1466 , and the optically dense layer  1468  contribute to the visual appearance of the marking  1450  as observed through the cover  1440 . If the marking elements  1472   a ,  1472   b , and  1472   c  do not extend through the thickness of the color layer  1464 , the optical properties of the color layer  1464  may also contribute to the visual appearance of the marking  1450 . In additional aspects described herein, the optical properties of the metal layer  1463 , the color layers  1464  and  1466 , and the optically dense layer  1468  contribute to the visual appearance of the multilayer structure  1460  adjacent the marking  1450  as observed through the cover  1440 . 
       FIG.  15    depicts a cross-sectional view of marking elements  1572   a ,  1572   b , and  1572   c  within a set of layers comprising an optically clear layer  1562  and two color layers  1564  and  1546 . The marking elements  1572   a ,  1572   b , and  1572   c  may at least partially define a marking  1550  (typically viewed through a cover  1540 ). The marking  1550  may be an example of a portion of the marking  252  of  FIG.  2    (with the cross-section taken along line B-B in  FIG.  2   ) or of all or part of any other markings described herein. 
     As depicted in  FIG.  15   , marking elements  1572   a ,  1572   b , and  1572   c  are formed in an optically clear layer  1562 . The multilayer structure  1560  further comprises a metal layer  1563  and an optically dense layer  1568 . 
     As previously described, a multilayer structure  1560  is disposed along an interior surface  1544  of cover  1540 . As depicted in  FIG.  15   , the optically clear layer  1562  is directly disposed along the cover  1540 , the metal layer  1563  is disposed along the optically clear layer  1562 , the color layer  1564  is disposed along the metal layer  1563 , the color layer  1566  is disposed along the color layer  1564 , and the optically dense layer  1568  is disposed along the color layer  1566 . The exterior surface  1542  of the cover  1540  is generally opposite the interior surface  1544  as depicted in  FIG.  15   . 
     The optically clear layer  1562  comprises a transformable colorant. In the embodiment shown in  FIG.  15   , the first form of the transformable colorant appears colorless. For example, the optically clear layer  1562  prior to laser marking has a relatively high transmittance (e.g., at least 80%, or at least 85%) and does not appear to selectively absorb some wavelengths of visible light. The second form of the transformable colorant does not appear to be colorless. For example, the second form of the transformable colorant may selectively absorb some wavelengths of visible light. Therefore, the marking elements  1572   a ,  1572   b , and  1572   c  have reduced optical clarity as compared to an adjacent region of the optically clear layer  1562 . 
     Marking elements  1572   a ,  1572   b , and  1572   c  each correspond to an at least partially transformed region of the optically clear layer  1562  and define the marking(s) (e.g.,  1550 ) visible along the exterior surface of the electronic device. A region of the optically clear layer  1562  adjacent the marking elements  1572   a ,  1572   b , and  1572   c  is not transformed, providing a difference in optical properties between the marking elements  1572   a ,  1572   b , and  1572   c  and the adjacent region of the optically clear layer  1562 . In embodiments, this difference in optical properties contributes to a difference in color between the marking  1550  and the adjacent multilayer structure  1560  as observed through the cover. 
     The color layers  1564  and  1566  also include one or more colorants. In embodiments, the colorant(s) in the color layer  1566  produce a similar visual effect to the colorant(s) in the color layer  1564  prior to laser marking. In other words, the color layer  1564  may be color matched to the color layer  1566  (and vice versa). In some embodiments, the colorant in the color layers  1564  and  1566  is not sensitive to the wavelength(s) of light produced by the laser. 
     By the way of example, the optically clear layer  1562  may comprise a first colorant which is a transformable colorant. The color layer  1564  may comprise a second colorant and the color layer  1566  may comprise a third colorant. The second and the third colorants may be the same or may be different. 
     The metal layer  1563  has a thickness configured to allow transmission of visible light. Such a metal layer may give a metallic effect to the multilayer structure as seen through the cover. When the metal layer  1563  is present, an optically clear layer  1562  may be included between the cover  1540  and the metal layer  1563 . If a crack is introduced into the metal layer  1563 , an optically clear layer may limit or prevent propagation of the crack into the cover  1540 . The metal layer  1563  and the optically clear layer  1562  may be as previously described with respect to  FIG.  4   . 
     In aspects described herein, the optical properties of the marking elements  1572   a ,  1572   b , and  1572   c , the metal layer  1563 , the color layers  1564  and  1566 , and the optically dense layer  1568  contribute to the visual appearance of the marking  1550  as observed through the cover. In additional aspects described herein, the optical properties of the metal layer  1563 , the color layers  1564  and  1566 , and the optically dense layer  1568  contribute to the visual appearance of the multilayer structure  1560  adjacent the marking  1550  as observed through the cover  1540 . 
     Additional aspects of the disclosure relate to laser-based processes for marking electronic devices. In embodiments, the electronic device comprises a multilayer structure disposed along an interior surface of a cover. In further embodiments, at least one layer of the multilayer structure comprises a colorant which transforms upon exposure to light from a laser, thereby producing a marking region in the layer. In embodiments, the colorant is not substantially transformable upon exposure to ambient light over a typical lifetime of the electronic device. The marking region defines the marking visible along the exterior surface of the electronic device. 
     In embodiments, the laser produces a pulsed laser beam which is directed towards the multilayer structure through the cover. In embodiments, the laser is focused through the cover onto the layer comprising the colorant to be transformed. Exposing the colorant to a pulse of the focused laser beam transforms the colorant from a first form to a second form in a localized region of the layer, thereby forming a marking element in the localized region. In embodiments, any effect of the pulse of the focused laser beam outside this localized region is not visually observable through the cover. The amount of transformation from the first form to the second form of the colorant in the localized region of the layer depends, in part, on the extent of the exposure of the colorant to pulse(s) of the laser beam. 
     In embodiments, exposure of the layer to a single pulse of the laser beam produces a marking element in the layer in which at least some of the colorant has transformed to the second form in a localized region of the layer. In embodiments, the laser is operated so that adjacent marking elements overlap or overlay one another. For example, the adjacent marking elements may overlap so that individual marking elements are not distinguishable. In additional embodiments, the laser is operated so that adjacent marking elements are separated from one another or abut, but do not substantially overlap, one another (as schematically illustrated in  FIG.  11   ). Further, a given marking region may include different amounts of overlap between marking elements. 
     The spot size of the laser may substantially determine the width and/or shape of the marking elements. The marking elements may have shapes that are generally circular, elliptical, rectangular, square, or combinations thereof. Further the marking elements may have shapes formed by overlapping of circles, ellipses, rectangles, squares, or combinations thereof. 
     In embodiments, the laser may be operated in raster mode, in vector mode, or a combination thereof. In embodiments, the laser may produce a wavelength in the near infrared range (e.g., from about 700 nm to about 1500 nm). The average laser power may be from about 1 W to about 20 W. The spot size may be from about 10 μm to about 50 μm. In some embodiments, the laser may be operated in burst mode, with each burst including multiple pulses. In some embodiments, the laser is a femtosecond laser producing pulses having an effective pulse duration in the femtosecond range. 
     By the way of example, a process of forming a marking in a multilayer structure may include focusing a laser beam within a layer of the multilayer structure comprising a colorant in a first form. The process may further include moving the laser beam to transform at least some of the colorant to a second form within a marking region. As viewed through the cover, the multilayer structure in the marking region may have a first color prior to the marking process and a second color different than and visually distinct from the first color after the marking process. The multilayer structure adjacent the marking may retain the first color. In additional embodiments, the multilayer structure is not substantially ablated by the laser marking process. In embodiments, marking regions may be sequentially formed in different layers of the multilayer structure by forming a first marking region in a first layer, adjusting the focus of the laser beam, and then forming a second marking region in a second layer different from the first layer. 
       FIG.  16    is a block diagram of example components of an example electronic device. The schematic representation depicted in  FIG.  16    may correspond to components of the devices depicted in  FIGS.  1 A- 15   , described above. However,  FIG.  16    may also more generally represent other types of electronic devices including a laser marking. 
     The electronic device  1600  also includes a processor  1604  operably connected with a computer-readable memory  1602 . The processor  1604  may be operatively connected to the memory  1602  component via an electronic bus or bridge. The processor  1604  may be implemented as one or more computer processors or microcontrollers configured to perform operations in response to computer-readable instructions. The processor  1604  may include a central processing unit (CPU) of the device  1600 . Additionally and/or alternatively, the processor  1604  may include other electronic circuitry within the device  1600  including application specific integrated chips (ASIC) and other microcontroller devices. The processor  1604  may be configured to perform functionality described in the examples above. 
     The memory  1602  may include a variety of types of non-transitory computer-readable storage media, including, for example, read access memory (RAM), read-only memory (ROM), erasable programmable memory (e.g., EPROM and EEPROM), or flash memory. The memory  1602  is configured to store computer-readable instructions, sensor values, and other persistent software elements. 
     The electronic device  1600  may include control circuitry  1606 . The control circuitry  1606  may be implemented in a single control unit and not necessarily as distinct electrical circuit elements. As used herein, “control unit” will be used synonymously with “control circuitry.” The control circuitry  1606  may receive signals from the processor  1604  or from other elements of the electronic device  1600 . 
     As shown in  FIG.  16   , the electronic device  1600  includes a battery  1608  that is configured to provide electrical power to the components of the electronic device  1600 . The battery  1608  may include one or more power storage cells that are linked together to provide an internal supply of electrical power. The battery  1608  may be operatively coupled to power management circuitry that is configured to provide appropriate voltage and power levels for individual components or groups of components within the electronic device  1600 . The battery  1608 , via power management circuitry, may be configured to receive power from an external source, such as an alternating current power outlet. The battery  1608  may store received power so that the electronic device  1600  may operate without connection to an external power source for an extended period of time, which may range from several hours to several days. 
     In some embodiments, the electronic device  1600  includes one or more input devices  1610 . The input device  1610  is a device that is configured to receive input from a user or the environment. The input device  1610  may include, for example, a push button, a touch-activated button, a touch screen (e.g., a touch-sensitive display or a force-sensitive display), capacitive touch button, dial, crown, or the like. In some embodiments, the input device  1610  may provide a dedicated or primary function, including, for example, a power button, volume buttons, home buttons, scroll wheels, and camera buttons. 
     In embodiments, an electronic device  1600  may include one or more sensors  1620 . For example, the sensors  1620  may be a force sensor, a capacitive sensor, an accelerometer, a barometer, a gyroscope, a magnetometer, a proximity sensor, a light sensor, or the like. The sensors  1620  may be operably coupled to processing circuitry. In some embodiments, the sensors  1620  may detect deformation and/or changes in configuration of the electronic device and be operably coupled to processing circuitry which controls the display based on the sensor signals. In addition, the sensors  1620  may include a microphone, acoustic sensor, light sensor, optical facial recognition sensor, or other types of sensing device. 
     In some embodiments, the electronic device  1600  includes one or more output devices  1612  configured to provide output to a user. The output device  1612  may include a display  1614  that renders visual information generated by the processor  1604 . The output device  1612  may also include one or more speakers to provide audio output. 
     The display  1614  may include a liquid-crystal display (LCD), light-emitting diode (LED) display, organic light-emitting diode (OLED) display, an active layer organic light emitting diode (AMOLED) display, organic electroluminescent (EL) display, electrophoretic ink display, or the like. If the display  1614  is a liquid-crystal display or an electrophoretic ink display, the display may also include a backlight component that can be controlled to provide variable levels of display brightness. If the display  1614  is an organic light-emitting diode or organic electroluminescent type display, the brightness of the display  1614  may be controlled by modifying the electrical signals that are provided to display elements. In addition, information regarding configuration and/or orientation of the electronic device  1600  may be used to control the output of the display  1614  as described with respect to input devices  1610 . 
     The electronic device  1600  may also include a communication port  1616  that is configured to transmit and/or receive signals or electrical communication from an external or separate device. The communication port  1616  may be configured to couple to an external device via a cable, adaptor, or other type of electrical connector. In some embodiments, the communication port  1616  may be used to couple the electronic device  1600  to a host computer. 
     The electronic device  1600  may also include at least one accessory  1618 , such as a camera, a flash for the camera, or other such device. The camera may be connected to other parts of the electronic device  1600  such as the control circuitry. 
     The following discussion applies to the electronic devices described herein to the extent that these devices may be used to obtain personally identifiable information data. It is well understood that the use of personally identifiable information should follow privacy policies and practices that are generally recognized as meeting or exceeding industry or governmental requirements for maintaining the privacy of users. In particular, personally identifiable information data should be managed and handled so as to minimize risks of unintentional or unauthorized access or use, and the nature of authorized use should be clearly indicated to users. 
     The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the described embodiments. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the described embodiments. Thus, the foregoing descriptions of the specific embodiments described herein are presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the embodiments to the precise forms disclosed. It will be apparent to one of ordinary skill in the art that many modifications and variations are possible in view of the above teachings.

Metadata:
Filing Date: 20190612
Publication Date: 20230207
Grant Date: 20230207
Priority Date: 20181210
Inventors: ROGERS, MATTHEW S.
MITTAL, MANISH
GIACHINO, MARTA M.
NASHNER, MICHAEL S.
Assignee: APPLE INC
CPC Classifications: [{"code": "B32B2451/00", "inventive": false, "first": false, "tree": "[]"}, {"code": "B32B2307/404", "inventive": false, "first": false, "tree": "[]"}, {"code": "B23K26/354", "inventive": true, "first": false, "tree": "[]"}, {"code": "B23K26/53", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04M1/0283", "inventive": true, "first": false, "tree": "[]"}, {"code": "B23K2103/166", "inventive": false, "first": false, "tree": "[]"}, {"code": "B41M5/26", "inventive": true, "first": false, "tree": "[]"}, {"code": "B32B2457/20", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K5/0252", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04M1/0283", "inventive": true, "first": true, "tree": "[]"}, {"code": "H05K5/0243", "inventive": true, "first": false, "tree": "[]"}, {"code": "B44C1/005", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K5/0252", "inventive": true, "first": false, "tree": "[]"}, {"code": "B23K26/18", "inventive": true, "first": true, "tree": "[]"}, {"code": "B32B2255/28", "inventive": false, "first": false, "tree": "[]"}, {"code": "B32B17/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "B32B2307/404", "inventive": false, "first": false, "tree": "[]"}, {"code": "B32B2457/20", "inventive": false, "first": false, "tree": "[]"}, {"code": "B41M5/26", "inventive": true, "first": false, "tree": "[]"}, {"code": "B23K26/354", "inventive": true, "first": false, "tree": "[]"}, {"code": "B23K2103/166", "inventive": false, "first": false, "tree": "[]"}, {"code": "B32B2451/00", "inventive": false, "first": false, "tree": "[]"}, {"code": "B32B2255/28", "inventive": false, "first": false, "tree": "[]"}, {"code": "B23K26/18", "inventive": true, "first": true, "tree": "[]"}, {"code": "B44C1/005", "inventive": true, "first": false, "tree": "[]"}, {"code": "B23K26/53", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K5/0252", "inventive": true, "first": false, "tree": "[]"}, {"code": "B32B17/10", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 70972220