PATENT DOCUMENT

Publication Number: US-9839974-B2
Application Number: US-201414261060-A
Country: US
Kind Code: B2

Title: Forming white metal oxide films by oxide structure modification or subsurface cracking

Abstract:
The embodiments described herein relate to forming white appearing metal oxide films by forming cracks within the metal oxide films. In some embodiments, the methods involve directing a laser beam at a metal oxide film causing portions of the metal oxide film to melt, cool, contract, and crack. The cracks have irregular surfaces that can diffusely reflect visible light incident a top surface of the metal oxide film, thereby imparting a white appearance to the metal oxide film. In some embodiments, the cracks are formed beneath a top surface of a metal oxide film, thereby leaving a continuous and uninterrupted metal oxide film top surface.

Claims:
What is claimed is: 
     
       1. A method of forming an anodic film on a part, the method comprising:
 forming a mirror finish on a substrate surface of a metal substrate; 
 forming the anodic film on the metal substrate, the anodic film having a first surface adjacent the substrate surface and a second surface opposite the first surface, wherein the mirror finish of the substrate surface is visible through the anodic film; and 
 forming clusters of cracks, wherein the clusters of cracks are equidistantly spaced apart and embedded within the anodic film between the first and second surfaces, and wherein visible light incident at the second surface of the anodic film diffusely reflects off the cracks within the clusters, thereby imparting a white appearance to the anodic film. 
 
     
     
       2. The method of  claim 1 , wherein forming the clusters of cracks comprises:
 directing a laser beam at the second surface of the anodic film such that a depth of focus of the laser beam is positioned entirely beneath the second surface of the anodic film. 
 
     
     
       3. The method of  claim 2 , wherein forming the clusters of cracks further comprises:
 directing the laser beam at the second surface such that the depth of focus of the laser beam is positioned below the substrate surface, thereby causing the laser beam to reflect off the substrate surface and focus within the anodic film. 
 
     
     
       4. The method of  claim 1 , wherein forming the clusters of cracks includes melting metal oxide material present within the clusters of cracks. 
     
     
       5. The method of  claim 1 , wherein a pitch between the clusters of cracks is between about 1 micrometer to about 10 micrometers. 
     
     
       6. The method of  claim 1 , wherein a pitch between the clusters of cracks is about twice a diameter of each cluster of the clusters of cracks. 
     
     
       7. The method of  claim 1 , wherein each of the clusters of cracks are positioned at different depths beneath the second surface. 
     
     
       8. The method of  claim 1 , wherein each of the clusters of cracks have a diameter that is between about 1 micrometer and about 5 micrometers. 
     
     
       9. A part comprising:
 a metal substrate having a substrate surface with a mirror finish; and 
 an anodic film disposed on the metal substrate, the anodic film having a first surface adjacent the substrate surface and a second surface opposite the first surface, wherein the mirror finish of the substrate surface is visible through the anodic film; and 
 clusters of cracks embedded within the anodic film and between the first and second surfaces, the clusters of cracks being equidistantly spaced apart, wherein visible light incident at the second surface diffusely reflects off the cracks within the clusters, thereby imparting a white appearance to the anodic film. 
 
     
     
       10. The part of  claim 9 , wherein the clusters of cracks include crystalline metal oxide material. 
     
     
       11. The part of  claim 9 , wherein a pitch between the clusters of cracks is between about 1 micrometer to about 10 micrometers. 
     
     
       12. The part of  claim 9 , wherein a pitch between the clusters of cracks is about twice a diameter of each cluster of the clusters of cracks. 
     
     
       13. The part of  claim 9 , wherein at least some of the clusters of cracks are embedded at different depths within the anodic film. 
     
     
       14. The part of  claim 9 , wherein each of the clusters of cracks have irregular surfaces that diffusely reflect the visible light. 
     
     
       15. An enclosure for an electronic device, comprising:
 a metal substrate having a substrate surface with a mirror finish; and 
 an anodic film disposed on the metal substrate, the anodic film having a bottom surface adjacent to the substrate surface, and a top surface opposite from the bottom surface, wherein the mirror finish of the substrate surface is visible through the anodic film; and 
 clusters of cracks embedded within the anodic film, wherein the clusters of cracks are equidistantly spaced apart from each other, and wherein visible light incident at the top surface diffusely reflects off the clusters of cracks, thereby imparting a white appearance to the anodic film. 
 
     
     
       16. The enclosure of  claim 15 , wherein a pitch between the clusters of cracks is about twice a diameter of each cluster of the clusters of cracks. 
     
     
       17. The enclosure of  claim 15 , wherein a pitch between the clusters of cracks is between about 1 micrometer to about 10 micrometers. 
     
     
       18. The enclosure of  claim 15 , wherein each of the clusters of cracks have a diameter that is between about 1 micrometer and about 5 micrometers. 
     
     
       19. The enclosure of  claim 15 , wherein at least some of the clusters of cracks are embedded at different depths within the anodic film. 
     
     
       20. The enclosure of  claim 15 , wherein the clusters of cracks include crystalline metal oxide material.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims the benefit of priority under 35 U.S.C §119(e) to U.S. Provisional Application No. 61/903,890, filed on Nov. 13, 2013, the disclosure of which is incorporated herein by reference in its entirety. 
    
    
     FIELD 
     This disclosure relates generally to metal oxide films. More specifically, methods for producing white appearing metal oxide films using subsurface cracking techniques are disclosed. 
     BACKGROUND 
     Metal surfaces of many consumer products are often protected with a thin film of metal oxide. The metal oxide is generally harder than the underlying metal and thus provides a protective coating for the metal. Often, the metal oxide film is formed using an anodizing process. Anodizing is an electrolytic process that increases the thickness of a natural oxide layer on the surface of metal parts. The metal part to be treated forms an anode of an electrical circuit such that the surface of the metal part is converted to a metal oxide film, also referred to as an anodic film. The anodic film can also be used for a number of cosmetic effects. For example, techniques for colorizing anodic films have been developed that can provide an anodic film with a perceived color based. A particular color can be perceived when a light of a particular range of frequencies is reflected off the surface of the anodic film. 
     In some cases, it can be desirable to form an anodic film having a white color. However, conventional attempts to provide white appearing anodic films have resulted in anodized films that appear to be off-white, muted grey, and yellowish white instead of a crisp appearing white that many people find appealing. 
     SUMMARY 
     In one aspect, a method of modifying an appearance of an oxide film disposed on a substrate surface is described. The oxide film may be made of metal oxide material. The method may include forming at least one melted portion by heating the metal oxide material within a portion of the oxide film to a melting temperature of the metal oxide material. The method may further include creating several cracks within the oxide film by allowing the melted portion to cool and contract. Each of the several cracks is positioned substantially entirely beneath a top surface of the oxide film. The several cracks within the oxide film cause visible light incident a top surface of the oxide film to scatter imparting a white appearance to the oxide film. 
     In another aspect, a part is described. The part may include a metal substrate and a metal oxide layer. The metal substrate may include a substrate surface, the substrate surface having a mirror finish that specularly reflects substantially all visible light incident the substrate surface. The metal oxide layer disposed on the metal substrate, the metal oxide layer having a bottom surface adjacent the substrate surface and a top surface opposite the bottom surface. The metal oxide layer may include a first portion that is substantially translucent to visible light incident the top surface of the oxide layer such that at least a portion of visible light incident the top surface travels through the first portion and specularly reflects off the substrate surface. The metal oxide layer may also include a second portion having several cracks positioned beneath the top surface. Visible light incident the top surface of the oxide film diffusely reflects off the several cracks imparting a white quality to the second portion. 
     In another aspect, an enclosure for an electronic device is described. The enclosure may include a substrate and an oxide layer. The substrate may have several protrusions forming a first roughness. The oxide layer may be formed over the several protrusions. The oxide layer may include a first portion having several crystalline portions. A first light right ray reflected by the several crystalline structures forms a first appearance, and a second light ray absorbed by the several protrusions of a first roughness forms a second appearance. The second appearance may be different from the first appearance. 
     Other systems, methods, features and advantages of the embodiments will be, or will become, apparent to one of ordinary skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description and this summary, be within the scope of the embodiments, and be protected by the following claims. 
    
    
     
       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 structural elements, and in which: 
         FIGS. 1A-1D  illustrate various reflection mechanisms for providing a perceived color or quality of an object; 
         FIG. 2A  shows a cross section of a portion of part that includes an oxide layer with crystalline metal oxide portions that diffusely reflect incident light and give the oxide layer a white appearance; 
         FIG. 2B  shows a cross section of a portion of part that includes an oxide layer with cracks that diffusely reflect incident light and give the oxide layer a white appearance; 
         FIGS. 3A-3C  show cross section views of a portion of part that includes an oxide layer undergoing a laser melting procedure in accordance with described embodiments; 
         FIGS. 4A and 4B  show cross section views of different parts undergoing different types of laser melting procedures in accordance with described embodiments; 
         FIGS. 5A-5C  show cross section and top views of different parts having oxide layers with different patterns of spots of crystalline metal oxide or cracks; 
         FIGS. 6A-6C  show cross section and top views of different parts having oxide layers with different patterns of lines of crystalline metal oxide or cracks; 
         FIGS. 7A-7C  show cross section views of different parts having oxide layers with spots of crystalline metal oxide or cracks positioned at different depths within the oxide layers; 
         FIG. 8  shows a flowchart indicating a method for forming a white oxide layer using a melting process in accordance with described embodiments; 
         FIG. 9A  shows a cross section view of a part with a first portion that diffusely reflects incident light and a second portion that specularly reflects light; 
         FIG. 9B  shows a flowchart indicating a method for tuning a melting process for producing a white oxide film having a target amount of diffuse and specular reflectance; 
         FIG. 10  shows a cross section view of a portion of a part with an oxide layer having light diffusing spots positioned over a substrate having a roughed surface; 
         FIG. 11  shows a top view of a part with an oxide layer having light diffusing spots and having different colored portions and in accordance with described embodiments; 
         FIG. 12  shows a top view of a part with an oxide layer having light diffusing spots and having different dyed portions and in accordance with described embodiments; and 
         FIG. 13  shows a flowchart indicating a method for forming an oxide layer on a part having a particular optical quality using the described melting methods. 
     
    
    
     Those skilled in the art will appreciate and understand that, according to common practice, various features of the drawings discussed below are not necessarily drawn to scale, and that dimensions of various features and elements of the drawings may be expanded or reduced to more clearly illustrate the embodiments of the present invention described herein. 
     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 embodiment. To the contrary, it is intended to cover alternatives, modifications, and equivalents as can be included within the spirit and scope of the described embodiments as defined by the appended claims. 
     This application relates to various methods and apparatuses used for treating a metal oxide film such that the metal oxide film appears white. In some embodiments, methods involve modifying at least a portion of the metal oxide film to a crystalline form metal oxide. In some embodiments, methods involve creating cracks or small gaps within the metal oxide film and beneath a top surface of the metal oxide film. In some embodiments, methods involve creating crystalline portions combined with creating cracks. The crystalline metal oxide or cracks within the metal oxide can interact with visible light incident the top surface of the film to give the metal oxide film a white appearance. The white appearing metal oxide films are well suited for providing protective and attractive surfaces to visible portions of consumer products. For example, methods described herein can be used for providing protective and cosmetically appealing exterior portions of metal enclosures and casings for electronic devices, such as those manufactured by Apple Inc., based in Cupertino, Calif. 
     As used herein, the terms oxide film, oxide layer, metal oxide film, and metal oxide layer may be used interchangeably and can refer to any appropriate metal oxide material. In some embodiments, the oxide film is formed using an anodizing process and can be referred to as an anodic film or anodic layer. The metal oxide films are formed on metal surfaces of a metal substrate. The metal substrate can include any of a number of suitable metals. In some embodiments, the metal substrate includes pure aluminum or aluminum alloy. In some embodiments, suitable aluminum alloys include 1000, 2000, 5000, 6000, and 7000 series aluminum alloys. 
     In general, white is the color of objects that diffusely reflect nearly all visible wavelengths of light. Thus, a metal oxide film can be perceived as white when nearly all visible wavelengths of light incident a top surface of the metal oxide film are diffusely reflected. FIG.  1 A, shows how incident light can be diffusely reflected off a surface and scattered in many directions. Diffuse reflection can be caused by incident light reflecting off multi-faceted surfaces at a top surface or within an object. For example, facets of ice crystals that form a snowflake diffusely reflect incident light, rendering the snowflake white in appearance. This is in contrast to specular reflection ( FIG. 1B ) where light is reflected in one direction, colored objects ( FIG. 1C ) where some wavelengths of light are absorbed and only certain wavelengths of light are diffusely reflected, and black objects ( FIG. 1D ) where substantially all the wavelengths of light are absorbed and no light is reflected. 
     The amount of perceived whiteness of a metal oxide film can be measured using any of a number of color analysis techniques. For example a color opponent process scheme, such as an L,a,b (Lab) color space based in CIE color perception schemes, can be used to determine the perceived whiteness of different oxide film samples. The Lab color scheme can predict which spectral power distributions (power per unit area per wavelength) will be perceived as the same color. In a Lab color space model, L indicates the amount of lightness, and a and b indicate color-opponent dimensions. In some embodiments described herein, the white metal oxide films have L values ranging from about 85 to 100 and a,b values of nearly zero. Therefore, these metal oxide films are bright and color-neutral. 
     Some embodiments described herein involve forming crystalline portions of metal oxide within an oxide film such that incident light diffusely reflects off interfaces created by the crystalline portions, thereby imparting a white appearance to the oxide film. To illustrate,  FIG. 2A  shows a cross section of a portion of part  200 , which includes substrate  202  and oxide layer (or oxide film)  204 . Oxide layer  204  can be a glass-like amorphous metal oxide material  205  that is substantially translucent or transparent to visible light. Oxide layer  204  includes crystalline portion  220 , which has a different structure than surrounding amorphous metal oxide material  205 . Crystalline portion  220  includes multiple metal oxide crystals, each having light reflective facets. Incoming visible light can reflect off the crystalline facets at different angles, causing the light to scatter and diffusely reflect. For example, light ray  210  can enter oxide layer  204 , reflect off of a first crystalline facet of crystalline portion  220  oriented at a first angle relative to top surface  208 , and exit oxide layer  204 . Light ray  212  can enter oxide layer  204 , reflect off of a second crystalline facet of crystalline portion  220  oriented at a second angle different from the first angle relative to top surface  208 , and exit oxide layer  204 . In this way, multiple light rays entering oxide layer  204  can reflect off of crystalline portion  220  at multiple different angles, causing light to be diffusely reflected off of crystalline portion  220 , thereby imparting a white appearance to oxide layer  204 . In addition, the crystalline form of metal oxide within crystalline portion  220  will have a different refractive index compared to surrounding amorphous metal oxide material  205 , which can cause further diffraction of light incident top surface  208  and contribute to the white appearance of oxide layer  204 . Note that in some embodiments, substantially the entire oxide layer  204  is transformed to a crystalline form. 
     As shown in  FIG. 2B , in some embodiments, crystalline portion  220  has cracks  206  formed therein such that incident light diffusely reflects off of interfaces of the cracks, thereby contributing a white appearance to the oxide film. In some embodiments, cracks  206  are formed without formation of crystalline portion  220 . Cracks  206  are breaks in the metal oxide material of oxide layer  204 . Cracks  206  have surfaces that are irregularly oriented within oxide layer  204 . Incoming visible light can reflect off the irregularly oriented surfaces at different angles, causing the light to diffusely reflect off of cracks  206 . For example, light ray  211  can enter oxide layer  204 , reflect off of a first surface of cracks  206  oriented at a first angle relative to top surface  208 , and exit oxide layer  204 . Light ray  213  can enter oxide layer  204 , reflect off of a second surface of cracks  206  oriented at a second angle different from the first angle relative to top surface  208 , and exit oxide layer  204 . In this way, multiple light rays entering oxide layer  204  can reflect off of cracks  206  at multiple different angles, causing light to be diffusely reflected off of cracks  206 , thereby imparting a white appearance to oxide layer  204 . 
     Crystalline portion  220  and cracks  206  can have any suitable shape and size. As described above, crystalline portion  220  can include a portion or make up substantially the entire metal oxide material of oxide layer  204 . If substantially the entire metal oxide material of oxide layer  204  is in a crystalline form, cracks  206  can be formed throughout oxide layer  204 . Note that the size of cracks  206  are generally smaller than as depicted in  FIG. 2B  with respect to an overall thickness of oxide layer  204 . In some embodiments, individual features of cracks  206  are substantially non-visible to an observer, but rather give at least a portion of oxide layer  204  a generally white appearance. In some embodiments, the lengths of cracks  206  are on the scale of micrometers (microns) or longer. In some embodiments, cracks  206  are on the scale of between about 0.5 and 30 microns in length. In some embodiments, cracks  206  form air-filled voids within oxide layer  204 . The air within the voids has a different refractive index than the surrounding metal oxide material, which can cause further diffraction of light. Note that cracks  206  can have any suitable shape. In some embodiments, cracks  206  are elongated, as shown in  FIG. 2B . In some embodiments, the cracks are circular, elliptical (spherical or ellipsoidal) or pore-like in shape. Crystalline portion  220  or cracks  206  can be in any suitable location within oxide layer  204 . In some embodiments, substantially the entirety of crystalline portion  220  or cracks  206  is positioned beneath top surface  208  of oxide film  204 . Forming cracks  206  subsurface of top surface may be used in applications wherein it is undesirable for top surface  208  to have cracks. For instance, in some applications it may be desirable to have a continuous and uninterrupted top surface  208 . In some embodiments, top surface  208  is smooth, shiny and specularly reflective. 
     Crystalline portion  220  or cracks  206  can be formed using any suitable procedure. In some embodiments, crystalline portion  220  or cracks  206  are formed using a laser procedure. In some embodiments, crystalline portion  220  and cracks  206  are formed using other heating processes such as a plasma process. In some embodiments, the laser is tuned to form crystalline portion  220  or cracks  206  within oxide layer  204  between the top surface  214  of substrate  202  and top surface  208  of oxide layer  204 . This can be accomplished by directing a laser beam at oxide layer  204  such that energy from the laser beam is focused on local areas within oxide layer  204 . The energy causes the metal oxide material in the local areas to melt. As the melted oxide material cools, it can re-solidify in a crystalline form. In some embodiments, the cooling process can form cracks  206 . To illustrate,  FIGS. 3A-3C  show cross section views of a portion of part  300 , which includes oxide layer  304  integrally formed on substrate  302 , undergoing a laser procedure in accordance with described embodiments. 
     At  3 A, laser beam  310  is directed at top surface  308  of oxide layer  304 . Laser beam  310  is tuned to generate enough heat to melt localized portions of the metal oxide material of oxide layer  304 . In some embodiments, laser beam  310  is scanned over substantially the entire top surface  308  of oxide layer  304  to melt substantially all of oxide layer  304 . Laser beam  310  parameters such as wavelength, spatial energy distribution (e.g., spot size and beam shape), and temporal energy distribution (e.g., pulse duration and pulse separation) can be adjusted to cause a sufficient amount of energy to heat and melt the metal oxide but not so high an energy to negatively impact the structural integrity of oxide layer  304  too much. In some embodiments, the metal oxide material within oxide layer  304  is heated to a temperature of about 600 degrees C. or greater. In some embodiments, the metal oxide material within oxide layer  304  is heated to a temperature ranging between about 600 and 1200 degrees C. In some embodiments, the wavelength of laser beam  310  ranges within the infrared spectrum of light. In some embodiments, a CO2 laser is used, which produces infrared laser light having principle wavelength bands centering around 9.4 and 10.6 micrometers. 
     Laser beam  310  is tuned such that depth of focus (DOF)  318  is positioned within oxide layer  304  between top surface  308  of oxide layer  304  and top surface  314  of substrate  302 . In some embodiments, spot size of laser beam  310  is small enough to melt localized portions within oxide layer  304  without substantially affecting surrounding portions of metal oxide material. In general, a smaller spot size corresponds to a smaller beam waist  317 , a larger beam width  316 , a smaller DOF  318 , and a higher energy density (e.g., Joules/cm2). In some embodiments, the spot size and DOF  318  are each less than about 10 micrometers. In some embodiments, the spot size and DOF  318  each range from about one micrometer and about 10 micrometers. It should be noted that the spot size and DOF  318  used in the applications described herein for melting localized portions within a metal oxide film are generally small compared to traditional laser ablating and marking procedures. For example, typical laser marking applications use a spot size in the range of about 20 micrometers and 100 micrometers and a DOF  318  in the range of about 100 micrometers to about 200 micrometers. In addition, the beam width  316  used in the applications described herein are generally large compared to traditional laser ablating and marking procedures. In some embodiments, the shape of laser beam  310  is adjusted to optimize the effect of laser beam  310  on oxide layer  304 . For example, a Gaussian beam shape (as shown in  FIG. 3A ) can have a different effect on the metal oxide material within oxide layer  304  compared to a flat top beam shape. 
       FIG. 3B  shows spot  320 , which corresponds to the area within oxide layer  304  that is melted by an impinging laser beam. The diameter of spot  320  can vary depending on laser parameters, such as those described above, as well as the nature of the metal oxide material of oxide layer  304 . In some embodiments, spot  320  has a diameter ranging from about 1 micrometer and about 5 micrometers. In some embodiments, spot  320  has a diameter ranging from about 2 micrometers and about 5 micrometers. The depth  322  of spot  320  relative to top surface  308  of oxide layer  304  can be adjusted using a number of methods. In some embodiments, an additional laser system is used to measure thickness  323  of oxide layer  304  prior to the laser cracking procedure. The measurement of thickness  323  can then be used to adjust laser parameters of the laser used to perform the laser procedure such that spot  320  is positioned within a depth  322  that is predetermined within oxide layer  304 . In some embodiments, top surface  308  is substantially planar such that depth  322  is substantially constant throughout the area of top surface  308 . As the laser beam is directed at oxide layer  304 , the energy of the laser beam generates localized heat within spot  320  of oxide layer  304  sufficient to at least reach the glass transition temperature of the metal oxide material within spot  320 . Accordingly, at least a portion of the metal oxide material within spot  320  melts. In some embodiments, as heat generated by the laser beam dissipates and the metal oxide material within spot  320  cools, the metal oxide material transitions to a crystalline form. In some embodiments, the amorphous form of metal oxide material is a hydroxide or hydrated form of aluminum oxide, such as boehmite. The heat from the laser beam can drive off water from the hydroxide or hydrated form of the aluminum oxide, leaving a crystalline form of aluminum oxide (i.e., alumina). As described above, light incident top surface  308  of oxide layer  304  can diffusely reflect off of the crystalline facets within spot  320  and give oxide layer  304  a white appearance. 
       FIG. 3C  shows spot  320  having cracks  306  formed therein. In some embodiments, during the cooling of metal oxide material within spot  320 , the metal oxide material contracts forming cracks  306 . The size of cracks  306  can vary depending upon a number of parameters including laser energy parameters, cooling time, and type of oxide layer  304 . In some embodiments, cracks  306  are on the scale of between about 0.5 and 30 microns in length. As described above, light incident top surface  308  of oxide layer  304  can diffusely reflect off of the irregular surfaces of cracks  306  and give oxide layer  304  a white appearance. 
     As described above, in some embodiments, oxide layer  304  can be formed using any suitable method. In some embodiments, methods such as plasma electrolytic oxidation are used to form oxide layer  304  that is in largely crystalline form. In some embodiments, an anodizing process is used to form oxide layer  304  that is in largely amorphous form. In some embodiments, the laser is tuned to reflect off of the top surface of an underlying substrate and back onto the oxide layer to cause melting within the oxide layer. To illustrate,  FIG. 4A  shows a cross section view of a portion of part  400 , which includes oxide layer  404  positioned on substrate  402 . Laser beam  410  is tuned such that the depth of focus  418  of laser beam  410  is positioned below oxide layer  404 , i.e., below top surface  414  of substrate  402 . Laser beam  410  then reflects off of top surface  414  of substrate  402  and becomes focused at spot  420  within oxide layer  404 , thereby causing spot  420  of crystalline metal oxide or cracks  406  to form. As with the embodiments described above with reference to  FIGS. 3A-3C , the crystalline metal oxide and/or cracks  406  within spot  420  can cause light incident top surface  408  to diffusely reflect off of the surfaces of the crystalline metal oxide or cracks  406  and give oxide layer  404  a white appearance. 
     In some embodiments, the laser beam is directed at an oxide layer at a non-normal angle relative to a top surface of the oxide layer.  FIG. 4B  shows a cross section view of a portion of part  450 , which includes oxide layer  454  positioned on substrate  452 . As shown, part  450  is skewed relative to beam path  456  of laser beam  460 . That is, top surface  458  of part  450  is positioned at a non-perpendicular angle  457  relative to beam path  456 . One advantage of using such a skewed configuration is that laser beam  460  can impinge upon a greater effective thickness  462  of oxide layer  454  compared to the actual thickness  464  of oxide layer  454 . In some embodiments, this allows for greater control over the depth of spot  466  within oxide layer  454 . 
     An amount of whiteness of an oxide film can be adjusted by choosing an amount of spots of crystalline metal oxide material or cracks within the oxide film, the spatial distances between the spots within the oxide film, and the depth of the spots within the oxide film. The spots can be formed in patterns within an oxide films. In some embodiments, the spots are formed in clusters within spots as described above with reference to  FIGS. 3 and 4 . In other embodiments, the cracks are formed in substantially continuous lines.  FIGS. 5-7  show cross section and top views of different parts having different amounts of spots, different patterns of spots, and spots that are positioned in different locations within oxide films. 
       FIG. 5A  shows a cross section view of part  500 , which includes oxide layer  504  disposed on substrate  502 . Oxide layer  504  includes spots  506 , which correspond to crystalline metal oxide portions or clusters of cracks created by a laser operation as described above. Spots  506  are positioned an average distance  509  from each other, sometimes referred to as pitch. Pitch  509  can be chosen such that the overall appearance of oxide layer  504  is white as viewed from top surface  508 . In some embodiments, the pitch is about twice the diameter  511  of spots  506 . In some embodiments, pitch  509  ranges from about 1 micrometer and about 10 micrometers. In some embodiments, spots  506  are spaced equidistantly from each other while in other embodiments spots  506  are spaced at substantially random distances from each other. The whiteness of oxide layer  504  can be chosen by adjusting pitch  509 , with smaller pitches corresponding with whiter appearing oxide layers. Spots  506  can be formed using a pulsed laser beam or a continuous laser beam. For example, each spot  506  can correspond to a pulse of a pulsed laser beam, which is scanned over top surface  508 . The laser beam can pulsed one or more time at each of spots  506 . If a continuous laser beam is used, the laser beam can be positioned over each of spots  506  for a predetermined time period and moved quickly over distances between each of spots  506 . Alternatively, mirrors can be used to position a continuous laser beam at locations corresponding to each spot  506 . 
       FIGS. 5B and 5C  show top views of different parts  510  and  520 , respectively, having different patterns of spots of crystalline metal oxide portions or clusters of cracks.  FIG. 5B  shows a top view of part  510  having equidistant spots  516  within oxide layer  514  that are spaced an average distance  519  apart from each other. Pitch  519  can be adjusted in accordance with an amount of whiteness desired, with a smaller pitch  519  corresponding to whiter appearing oxide layer  514 .  FIG. 5C  shows a top view of part  520  having equidistant spots  526  within oxide layer  524  that are arranged in a staggered configuration spaced an average distance  529  apart from each other. Distance  529  can be adjusted in accordance with an amount of whiteness desired, with smaller distances  529  corresponding to whiter appearing oxide layer  524 . Note that the patterns of spots shown in  FIGS. 5A-5C  are merely exemplary and that any suitable pattern of spots can be formed within an oxide layer. For example, in other embodiments, the spots are spaced a substantially random distances from each other. 
       FIG. 6A  shows part  600 , which includes oxide layer  604  disposed on substrate  602 . Oxide layer  604  has a substantially continuous line  606  that includes a continuous crystalline metal oxide portions or continuous line of cracks. Line  606  can be formed using a continuous laser beam or a pulsed laser beam. For example, a continuous laser beam can be continuously scanned across top surface  608  to form continuous line  606 . A pulsed laser beam can be scanned incrementally over top surface  608  forming a substantially continuous line  606 .  FIGS. 6B and 6C  show top views of parts  610  and  620 , respectively, having different patterns of lines of crystalline metal oxide portions or cracks.  FIG. 6B  shows a top view of part  610  having equidistant parallel lines  616  within oxide layer  612 . Adjacent lines  626  may be equidistant with respect to each other. Lines  616  are spaced an average distance  614  apart from each other. Distance  614  can be chosen such that the overall appearance of oxide layer  612  is white as viewed from a top surface of oxide layer  612 . Distance  614  can be adjusted in accordance with an amount of whiteness desired, with smaller distances  614  corresponding to whiter appearing oxide layer  612 . 
       FIG. 6C  shows a top view of part  620  having equidistant lines  626  of crystalline metal oxide portions or cracks that are arranged in a crosshatched pattern. Lines  626  are spaced an average distance  624  apart from each other, with some of the lines  626  arranged in a parallel orientation with respect to each other and other lines  626  arranged in a perpendicular orientation with respect to each other, thereby forming the crosshatched pattern. Distance  624  can be chosen such that the overall appearance of oxide layer  622  is white as viewed from a top surface of oxide layer  622 . Distance  624  can be adjusted in accordance with an amount of whiteness desired, with smaller distances  624  corresponding to whiter appearing oxide layer  622 . Note that the patterns of lines of crystalline metal oxide portions or cracks shown in  FIGS. 6A-6C  are merely exemplary and that any suitable pattern of lines can be formed within an oxide layer. For example, in other embodiments, the lines are spaced at substantially random distances from each other. 
     The crystalline metal oxide portions or cracks can be positioned at any suitable depth within an oxide layer. To illustrate,  FIGS. 7A-7C  show cross section views of different parts  700 ,  710 , and  720 , respectively, which have spots of crystalline metal oxide portions or cracks at different depths within oxide layers.  FIG. 7A  shows a cross section view of part  700  having spots  706  within oxide layer  704 , which is positioned over substrate  702 . Spots  706  are situated an average distance or depth  709  from top surface  708  of oxide layer  704 . Depth  709  can be adjusted in accordance with an amount of whiteness desired of oxide layer  704 . In some embodiments, the smaller depths  709  correspond to a whiter appearing oxide layer  704 .  FIG. 7B  shows a cross section view of part  710  having spots  716  of crystalline metal oxide portions or cracks within oxide layer  714 , which is positioned over substrate  712 . Spots  716  are situated an average depth  719  as measured from top surface  718  of oxide layer  704 . As shown, spots  716  are positioned at a farther depth within oxide layer  714  with respect to top surface  718  compared to spots  706  of part  700 . In some embodiments, the larger average depth  719  will result in oxide layer  714  of part  710  having a less white appearance compared to oxide layer  704  of part  700 . This can be due to different observer viewing angles of spots  706  and spots  716  as viewed from top surfaces  708  and  718 , respectively. 
       FIG. 7C  shows a cross section view of part  720  having a first layer of spots  726  of crystalline metal oxide portions or cracks and a second layer of spots  727  of crystalline metal oxide portions or cracks within oxide layer  724 , which is positioned over substrate  722 . First layer of spots  726  are situated an average depth  731  from top surface  728  of oxide layer  724 . Second layer of spots  727  are situated an average depth  732 , larger than average depth  731 , from top surface  728  of oxide layer  724 . In some embodiments, oxide layer  724  of part  720  will have a larger amount of crystalline metal oxide portions or cracks and appear whiter than each of oxide layer  714  of part  710  and oxide layer  704  of part  700 . First layer of spots  726  can be arranged in a staggered or parallel orientation with respect to second layer of spots  727 . Note that the depth of the spots of crystalline metal oxide portions or cracks shown in  FIGS. 7A-7C  are merely exemplary and that any suitable depth and number of layers of spots can be formed within an oxide layer. For example, in other embodiments, three or more layers of spots are formed within an oxide layer. 
       FIG. 8  shows flowchart  800  indicating a method for forming a white oxide layer using melting processes in accordance with described embodiments. At  802 , at least a portion of an oxide layer is melted. The oxide layer can be formed using any suitable technique and can have any suitable microstructure. In some embodiments, the oxide layer is formed using an anodizing process to form a largely amorphous metal oxide structure. The oxide layer can be formed at any suitable thickness. In some embodiments, the oxide layer has a thickness ranging from about 5 micrometers and about 60 micrometers. In some embodiments, the oxide layer has a thickness ranging from about 10 micrometers and about 30 micrometers. In some embodiments, the oxide layer is planarized in order to form a uniform top surface to the oxide layer. The melting can be performing using any suitable process. In some embodiments, the melting occurs by directing a laser beam at the oxide layer such that a localized portion of the oxide layer is heated at a temperature sufficient to reach a melting temperature of the metal oxide material. 
     At  804 , the at least one melted portion of the oxide layer is allowed to cool, thereby forming light diffusing surfaces within the oxide layer. In some embodiments, the cooling process causes the metal oxide material to re-solidify in crystalline form. In some embodiments, the cooling process causes the metal oxide material to crack. In some embodiments, the cooling process forms both crystalline metal oxide and forms cracks. The crystalline metal oxide and/or cracks have surfaces that can cause light incident on the top surface of the oxide layer to diffusely reflect, imparting a white appearance to the oxide layer. In some embodiments, the crystalline metal oxide or cracks are formed beneath the top surface of the oxide layer, thereby leaving a continuous, un-affected and un-cracked top surface. The crystalline metal oxide portions or cracks can be formed in any suitable pattern within the oxide layer and at any suitable depth within the oxide layer. In some embodiments, the depth and pattern of crystalline metal oxide portions or cracks is chosen to achieve a predetermined whiteness of the oxide layer. 
     As described above, specular reflection involves reflection of light in one direction. Objects that specularly reflect light will have a mirror-like quality. In contrast, diffuse reflection involves scattering of light resulting in objects appearing white. In some applications, it can be desirable for an oxide film to both diffusely and specularly reflect visible light, resulting in a white and bright appearance. The relative amount of diffuse reflection and specular reflection can be adjusted to accomplish a particular white and bright appearance. To illustrate,  FIG. 9A  shows a cross section view of part  900 , which includes oxide layer  904  positioned on substrate  902 . Oxide layer  904  includes first portion  910  and second portion  912 . First portion  910  has spots  906  of crystalline metal oxide or cracks that diffusely reflect incoming visible light. For instance, light ray  914  entering top surface  908  of oxide layer  904  reflects off spots  906  and exits top surface  908  at a first angle. Light ray  916  entering top surface  908  of oxide layer  904  reflects off spots  906  and exits top surface  908  at a second angle that is different than the first angle. In this way, spots  906  diffusely reflect light incident top surface  908  and impart a white appearance to first portion  910  of oxide layer  904 . 
     Second portion  912  does not substantially include any spots of crystalline metal oxide or cracks and is substantially translucent or transparent. As such, at least some light incident top surface  908  can travel through second portion  912  and reflect off top surface  922  of substrate  902 . If top surface  922  is a specularly reflective surface, such as a polished shiny metal surface, light will reflect off of top surface  922 . For instance, light ray  918  entering top surface  908  travels through oxide layer  904 , reflects off top surface  922 , and exits top surface  908  at a first angle. Light ray  920  entering top surface  908  travels through oxide layer  904 , reflects off top surface  922 , and exits top surface  908  also at the first angle. In this way, the specularly reflective top surface  922  of substrate  902  can be visible through second portion  912  of oxide layer  904  and impart a shiny mirror-like shine to the portion of part  900  corresponding to second portion  912 . This combination of diffuse and specular reflection gives part  900  a white and bright appearance. The relative amount of diffuse and specular reflection can be adjusted by choosing an amount of portions of oxide layer  904  having spots  906 . The amount of specular reflection of part  900  can be measured using any of a number of light reflection measurement techniques. In some embodiments, a spectrometer configured to measure specular light intensity at specified angles can be used. The measure of specular light intensity is associated with an amount of lightness and L value, as described above. In some embodiments, the amount of specular reflection is compared against a standard to achieve a predetermined amount of specular reflection for part  900 . 
       FIG. 9B  shows flowchart  950  indicating a method for tuning a melting process for producing a white oxide film having a target amount of diffuse and specular reflectance. At  952 , crystalline metal oxide or cracks are formed within an oxide film creating a white oxide film. In some embodiments, a laser melting procedure is used. The laser will have a set of parameters, such as wavelength, spot size and depth of focus, appropriate for melting metal oxide material within the oxide layer and forming crystalline metal oxide portions or cracks. At  954 , the amount of specular reflectance of the white oxide film is measured. A spectrometer may be used. The spectrometer can measure the spectral reflectance at a defined angle and generate a corresponding reflectance spectrum. At  956 , the measured specular reflectance of the white oxide film is compared to a target specular reflectance measurement. The target specular reflectance measurement will correspond to a white oxide film having a desired amount of specular and diffuse reflection. 
     At  958 , it is determined from the comparison whether the amount of specular reflectance of the white oxide film is too high. If the specular reflectance is too high, at  960 , a new cracking process is designed that has an increased amount of diffuse reflectance. The amount of diffuse reflectance can be increased by increasing the amount of crystalline metal oxide portions or cracks within the oxide film, or changing the positions of the crystalline metal oxide portions or cracks within the oxide film, such as described above with reference to  FIGS. 5-7 . Then, returning to  952 , an additional white oxide film is formed using the new melting process parameters. If the specular reflectance is not too high, at  962 , it is determined from the comparison whether the amount of specular reflectance of the white oxide film is too low. If the specular reflectance is too low, at  964 , a new melting process is designed that has a decreased amount of diffuse reflectance. The amount of diffuse reflectance can be decreased by decreasing the amount of crystalline metal oxide portions or cracks within the oxide film, or changing the positions of the crystalline metal oxide portions or cracks within the oxide film, such as described above with reference to  FIGS. 5-7 . Then, returning to  952 , an additional white oxide film is formed using the new melting process parameters. If the specular reflectance is not too low, the white oxide film has a target amount of diffuse and specular reflectance. 
     In some embodiments, the underlying substrate surface has a different surface quality than a specularly reflective shine. For example, the underlying substrate can have a roughened surface that absorbs incident light and therefore has a dark or black appearance.  FIG. 10  shows a cross section view of part  1000 , which includes oxide layer  1004  positioned on substrate  1002 , which has rough top surface  1022 . Rough top surface  1022  can be formed using any suitable process, such as a laser marking technique. In a laser marking technique, the laser wavelength and other process parameters are tuned to travel through oxide layer  1004  and roughen rough top surface  1022  of substrate  1002 . Rough top surface  1022  can absorb anywhere from some light to substantially all light incident top surface  1008 . For instance, light rays  1014  and  1016  entering top surface  1008  travel through oxide layer  1004  and become absorbed by rough top surface  1022 . Oxide layer  1004  also includes spots  1006  of crystalline metal oxide portions or cracks that can diffusely reflect incoming visible light. For instance, light ray  1018  entering top surface  1008  reflects off spots  1006  and exits top surface  1008  at a first angle. Light ray  1020  entering top surface  1008  reflects off spots  1006  and exits top surface  1008  at a second angle that is different than first angle. The combination of light absorption and light diffuse gives part  1000  a unique color and appearance that can be adjusted by modifying the amount of roughness of rough top surface  1022  and the amount of spots  1006  within oxide layer  1004 . 
     In some embodiments, the cracks are formed in a pattern such that a portion of the part appears white while other portions of the part appear as a different color.  FIG. 11  shows a top view of part  1100  having different colored portions in accordance with described embodiments. Part  1100  includes an oxide layer  1104  that has a top surface corresponding to a top surface of part  1100 . Oxide layer  1104  includes first portion  1102 , which has a different appearance than surrounding second portion  1103 . First portion  1102  has spots  1106  of crystalline metal oxide portions or cracks that give first portion  1102  a white appearance. In some embodiments, first portion  1102  is in the shape of a design or logo. In some embodiments, second portion  1103  does not substantially include any spots of crystalline metal oxide portions or cracks and, therefore, has a different color than first portion  1102 . In some embodiments, second portion  1103  includes spots of crystalline metal oxide portions or cracks and has a different shade of white compared to first portion  1102 . Note that in embodiments where a laser beam is used to form spots  1106 , spots  1106  can be formed without the use of a masking process. That is, the laser system can be tuned to scan or raster select portions of an oxide layer, such as first portion  1102 , without the use of a mask. 
     In some embodiments, second portion  1103  is substantially translucent or transparent, thereby allowing the underlying metal substrate to show. In some embodiments, the underlying substrate is an aluminum or aluminum alloy and has a silver or grey color that can at least be partially visible through second portion  1103 . In some embodiments, the underlying substrate has a reflective surface (e.g., mirror-like shine) that is at least partially visible through second portion  1103 , as described above. In some embodiments, second portion  1103  has one or more coloring agents to impart a color to second portion  1103 . For example, second portion  1103  can include one or more dye, metal, or metal oxide agents infused within the pores of the oxide material of second portion  1103 . In some embodiments, first portion  1102  includes one or more coloring agents that can enhance its white color. For example, first portion  1102  can have one or more dye, metal, and metal oxide agents infused within the pores of the oxide material of first portion  1102 . 
     In some embodiments, the cracks are formed subsequent to an oxide film dyeing process such that forming the cracks modifies the color of the dye and results in an oxide film having a different color than imparted by the dye itself. To illustrate,  FIG. 12  shows a top view of part  1200  having different dyed portions in accordance with described embodiments. Part  1200  includes an oxide layer  1204  that has a top surface corresponding to a top surface of part  1200 . Oxide layer  1204  includes first portion  1202 , which has a different appearance than surrounding second portion  1203 . In some embodiments, first portion  1202  is in the shape of a design or logo. Both first portion  1202  and second portion  1203  have one or more of the same dye infused therein. However, first portion  1202  has spots  1206  of crystalline metal oxide portions or cracks. During the formation of spots  1206 , portions of the metal oxide material within first portion  1202  are heated and melted, as described above. This localized heating can cause the infused dye within first portion  1202  to change color. In some embodiments, the localized heating causes bleaching or lightening of the dye, thereby giving first portion  1202  a lighter color compared to surrounding second portion  1203 . As a result, part  1200  has a varied colored look. 
       FIG. 13  shows flowchart  1300  indicating a method for forming an oxide layer on a part having a particular optical quality using the melting methods described herein. The optical quality can be a desired color or a desired brightness. At  1302 , light diffusing crystalline metal oxide portions or cracks are formed within an oxide layer. The light diffusing crystalline metal oxide portions or cracks can be formed using any suitable method. In some embodiments, the light diffusing crystalline metal oxide portions or cracks are formed by directing a laser beam at a top surface of the oxide layer such that energy from the laser beam is transferred as heat to melt a portion of the metal oxide material within the oxide layer. Crystalline metal oxide portions or cracks form within the oxide layer as the metal oxide material cools and contracts. In some embodiments, the laser is focused such that the crystalline metal oxide portions or cracks form entirely below a top surface of the oxide layer leaving the top surface of the oxide layer substantially crack-free and continuous. In some embodiments, the oxide layer has a smooth and specularly reflective top surface. In some embodiments, the oxide layer has one or more dyes or other coloring agents infused therein. In some embodiments, the heat from the laser beam modifies the color of the dyes or other coloring agents, thereby modifying the color of the oxide layer. 
     At  1304 , an optical quality of the oxide layer is measured after the melting treatment. A color of the treated oxide layer can be measured using any suitable colorimetric methods including, but not limited to, use of a colorimeter, spectrometer and/or a spectrophotometer. The brightness can be measured using any suitable method including, but not limited to, photometric techniques and/or radiometric techniques. At  1306 , the optical quality measurement of the treated oxide layer is compared to a target optical quality measurement. In some embodiments, the target optical quality is obtained by measuring the optical quality measurements of a sample that has a predetermined desired optical quality, such as a predefined color or brightness measurement. At  1308 , it is determined whether the measured optical quality of the treated oxide layer has achieved the target optical quality. If the target optical quality has not been achieved, at  1310 , a new process is design wherein the amount or position of the light diffusing within an oxide layer is adjusted. Then, at  1302 , another oxide layer is formed using the new process. This process is repeated until at  1308 , the target optical quality is achieved and the process of flowchart  1300  is complete. 
     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 target 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: 20140424
Publication Date: 20171212
Grant Date: 20171212
Priority Date: 20131113
Inventors: MCDONALD DANIEL T.
NASHNER MICHAEL S.
RUSSELL-CLARKE PETER N.
TATEBE MASASHIGE
Assignee: APPLE INC
CPC Classifications: [{"code": "B23K26/53", "inventive": true, "first": false, "tree": "[]"}, {"code": "C25D11/04", "inventive": false, "first": false, "tree": "[]"}, {"code": "C25D11/18", "inventive": true, "first": false, "tree": "[]"}, {"code": "Y10T428/24471", "inventive": false, "first": false, "tree": "[]"}, {"code": "B23K26/53", "inventive": true, "first": false, "tree": "[]"}, {"code": "C25D11/04", "inventive": false, "first": false, "tree": "[]"}, {"code": "B23K26/354", "inventive": true, "first": true, "tree": "[]"}, {"code": "Y10T428/24471", "inventive": false, "first": false, "tree": "[]"}, {"code": "B23K26/354", "inventive": true, "first": true, "tree": "[]"}, {"code": "B23K26/0057", "inventive": true, "first": false, "tree": "[]"}, {"code": "Y10T428/24471", "inventive": false, "first": false, "tree": "[]"}, {"code": "C25D11/18", "inventive": true, "first": false, "tree": "[]"}, {"code": "B23K26/0081", "inventive": true, "first": true, "tree": "[]"}, {"code": "C25D11/04", "inventive": false, "first": false, "tree": "[]"}, {"code": "C25D11/18", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 53044041