PATENT DOCUMENT

Publication Number: US-9710023-B2
Application Number: US-201514834315-A
Country: US
Kind Code: B2

Title: Treatment of substrate sub-surface

Abstract:
Perforated structures and methods for forming perforated structures are disclosed. The perforated structures include partial holes or blind-holes that pass partially through the substrate. The partial holes can be positioned proximate to through-holes that pass entirely through the substrate. The partial holes add mechanical strength to the perforated substrate. Described are methods for modifying the optical appearance of the partial holes such that the partial holes appear indistinguishable from the through-holes, which allows for flexibility in designing cosmetically appealing patterns within the perforated structures.

Claims:
What is claimed is: 
     
       1. A housing for an electronic device, the housing comprising:
 a wall defining an internal cavity and having a perforated region at an exterior surface of the wall, the perforated region comprising:
 a through-hole having a through-hole opening at the exterior surface, the through-hole connecting the through-hole opening to the internal cavity, and a blind-hole having a blind-hole opening at the exterior surface, the blind-hole formed partially through the wall and terminating at a terminal surface opposite the blind-hole opening, the terminal surface having a coating that absorbs light passing through the blind-hole opening and incident upon the coating. 
 
 
     
     
       2. The housing of  claim 1 , wherein light incident upon the through-hole opening passes through the through-hole and into the internal cavity such that substantially no light reflects back through the through-hole resulting in the through-hole opening having a darkened appearance with respect to the exterior surface, wherein substantially no light incident upon the coating reflects back through the blind-hole such that the blind-hole opening is perceived as having the darkened appearance of the through-hole opening. 
     
     
       3. The housing of  claim 1 , wherein the housing is comprised of a metal material having a metallic color, wherein the blind-hole opening is perceived as having a darker color than the metallic color. 
     
     
       4. The housing of  claim 1 , wherein the through-hole provides access to a speaker housed within the internal cavity, the through-hole allowing sound from the speaker to pass therethrough. 
     
     
       5. The housing of  claim 1 , wherein the coating comprises black ink. 
     
     
       6. The housing of  claim 1 , wherein the coating comprises multiple ink layers, wherein one of the multiple ink layers is a protective layer deposited on at least one layer of black ink. 
     
     
       7. The housing of  claim 6 , wherein the protective layer prevents loss of the black ink from the blind-hole. 
     
     
       8. The housing of  claim 1 , wherein the through-hole opening has the same diameter as the blind-hole opening. 
     
     
       9. The housing of  claim 8 , wherein the diameter is about 0.5 mm or less. 
     
     
       10. The housing of  claim 1 , wherein the perforated region includes a number of blind-holes and a number of through-holes, the blind-holes and through-holes arranged approximately equidistantly with respect to each other. 
     
     
       11. The housing of  claim 1 , wherein the electronic device is a portable computing device, tablet computer, desktop computer or mobile phone. 
     
     
       12. A method of forming a perforated structure, the method comprising:
 forming through-holes within a substrate having a first surface and an opposing second surface, the through-holes formed through the first surface and the second surface; 
 forming blind-holes within the substrate, the blind-holes formed through the first surface and not through the second surface such that the blind-holes have terminal surfaces; and 
 camouflaging the blind-holes to appear as through-holes by darkening the terminal surfaces of the blind-holes. 
 
     
     
       13. The method of  claim 12 , wherein camouflaging the blind-holes includes depositing an ink coating on the terminal surfaces. 
     
     
       14. The method of  claim 13 , wherein depositing the ink coating includes depositing multiple layers of ink. 
     
     
       15. The method of  claim 13 , further comprising:
 depositing a protective layer on the ink coating, the protective layer preventing loss of the ink coating from the blind-holes. 
 
     
     
       16. The method of  claim 13 , wherein depositing the ink coating comprises:
 selectively depositing the ink coating within the blind-holes without substantially depositing the ink coating on the first surface. 
 
     
     
       17. The method of  claim 13 , wherein depositing the ink coating comprises:
 depositing the ink within the blind-holes and on the first surface; and 
 after the depositing, cleaning the first surface. 
 
     
     
       18. The method of  claim 12 , wherein darkening the terminal surfaces of the blind-holes comprises:
 masking the first surface of the substrate, and 
 depositing an ink coating on at least the terminal surfaces of the blind-holes. 
 
     
     
       19. A perforated structure, comprising:
 a substrate having a first surface and opposing second surface, the substrate comprising:
 a number of through-holes formed through the first surface and the second surface, and a number of partial holes formed through the first surface and not through the second surface such that inner walls define the partial holes, 
 
 wherein the inner walls have an ink coating that imparts a dark appearance to the partial holes. 
 
     
     
       20. The perforated structure of  claim 19 , wherein the partial holes further include a protective layer formed on the ink coating that prevents loss of the ink coating from the partial holes.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims the benefit of U.S. Provisional Application No. 62/101,826, entitled “TREATMENT OF SUBSTRATE SUB-SURFACE” filed Jan. 9, 2015, the content of which is incorporated herein by reference in its entirety for all purposes. 
    
    
     FIELD 
     This disclosure relates generally to systems and methods for treating perforated structures, such as speaker grids for electronic devices. In particular, systems and methods for improving the cosmetics and enhancing physical characteristics of perforated structures are described. 
     BACKGROUND 
     Many consumer electronic devices have sound systems that include acoustic speakers. The speakers are often contained within a housing of the electronic device, with through-holes provided through a portion of the housing that let acoustic sound from the speakers to pass through the housing and reach a user of the electronic device. 
     In some cases, these speaker holes are visible features of the housing. In order to make the speaker holes cosmetically appealing, the speaker holes can be arranged in appealing patterns. In some cases, this includes drilling more holes through the housing than required for adequate sound quality in order to provide a desired cosmetically appealing pattern. However, drilling more holes means removing more material from the housing, which can compromise the mechanical strength and structural integrity of the housing. 
     SUMMARY 
     This paper describes various embodiments that relate to perforated structures and methods for manufacturing the same. The perforated structures can make up portions of consumer products, such as housing for electronic devices. The methods described can be utilized in a manufacturing setting where a number of perforated structures as part of a product line are produced. 
     According to one embodiment, a housing for an electronic device is described. The housing includes a wall defining an internal cavity and having a perforated region at an exterior surface of the wall. The perforated region includes a through-hole having a through-hole opening at the exterior surface, the through-hole connecting the through-hole opening to the internal cavity. The perforated region also includes a blind-hole having a blind-hole opening at the exterior surface, the blind-hole formed partially through the wall and terminating at a terminal surface opposite the blind-hole opening. The terminal surface has a coating that absorbs light passing through the blind-hole opening and incident upon the coating. 
     According to another embodiment, a method of forming a perforated structure is described. The method includes forming through-holes within a substrate having a first surface and an opposing second surface. The through-holes are formed through the first surface and the second surface. The method also includes forming blind-holes within the substrate. The blind-holes are formed through the first surface and not through the second surface such that the blind-holes have terminal surfaces. The method further includes camouflaging the blind-holes to appear as through-holes by darkening the terminal surfaces of the blind-holes. 
     According to a further embodiment, a perforated structure is described. The perforated structure includes a substrate having a first surface and opposing second surface. The substrate includes a number of through-holes formed through the first surface and the second surface. The substrate also includes a number of partial holes formed through the first surface and not through the second surface such that inner walls define the partial holes. The inner walls have an ink coating that imparts a dark appearance to the partial holes. 
     These and other embodiments will be described in detail below. 
    
    
     
       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. 
         FIGS. 1A and 1B  show perspective views of devices having perforated substrates. 
         FIG. 2  shows a section view of a perforated substrate that includes through-holes and blind-holes. 
         FIGS. 3A and 3B  show front views of a top case of a portable computing device before and after a blind-hole darkening procedure. 
         FIGS. 4A-4D  show section views of a perforated substrate undergoing a selective ink depositing process. 
         FIGS. 5A-5D  show section views of a perforated substrate undergoing a flood printing process. 
         FIG. 6  shows a flowchart indicating an ink coverage process for darkening blind-holes in accordance with  FIGS. 4A-4D and 5A-5D . 
         FIGS. 7A-7D  show section views of a perforated substrate undergoing a masking and flood printing process. 
         FIGS. 8A-8D  show section views of a perforated substrate undergoing a masking and selective ink depositing process. 
         FIG. 9A  shows a flowchart indicating an ink coverage process for masking and darkening blind-holes in accordance with  FIGS. 7A-7D and 8A-8D . 
         FIG. 9B  shows a bottom view of the portable computing device shown in  FIG. 1B  illustrating a non-perforated structure that can be darkened using the methods described herein. 
         FIGS. 10A and 10B  show images of substrate samples with through-holes and blind-holes prior to a darkening process. 
         FIGS. 11A and 11B  show images of substrate samples with through-holes and blind-holes that were printed with one layer of black ink. 
         FIGS. 12A and 12B  show images of substrate samples with through-holes and blind-holes that were deposited with two layers of black ink. 
         FIGS. 13A and 13B  show images of substrate samples with through-holes and blind-holes that were deposited with one layer of a CMYK ink mixture. 
         FIGS. 14A and 14B  show images of a substrate covered with a layer of pure black ink and a substrate covered with multiple layers of black ink followed by a clear ink layer, respectively. 
         FIG. 15  shows an image of a substrate sample with blind-holes drilled with a 130 degree drill bit and deposited with multiple layers of black ink followed by a clear ink layer. 
         FIG. 16  shows cross section views of substrate samples with blind-holes drilled with a 130 degree drill bit and deposited with multiple layers of black ink followed by a clear ink layer. 
         FIG. 17  shows an image of a substrate sample with blind-holes drilled with a 150 degree drill bit and deposited with multiple layers of black ink followed by a clear ink layer. 
         FIG. 18  shows cross section views of substrate samples with blind-holes drilled with a 150 degree drill bit and deposited with multiple layers of black ink followed by a clear ink layer. 
     
    
    
     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, they are intended to cover alternatives, modifications, and equivalents as can be included within the spirit and scope of the described embodiments. 
     Described herein are methods for providing perforated structures. The methods include providing an arrangement of different types of holes within a substrate such that the arrangement of holes is cosmetically appealing and the substrate retains a structural integrity. In particular embodiments, the methods involve providing a combination of through-holes that pass all the way through the substrate and blind-holes that pass partially through the substrate. The blind-holes allow more substrate material to remain intact and provide extra mechanical strength to the substrate than it would otherwise have with only through-holes. In some embodiments, the blind-holes are treated so that the blind-holes appear indistinguishable from the through-holes, which can improve the cosmetics of the perforated structure. In some cases, the treatment involves modifying inner surfaces of the blind-holes such that the inner surfaces appear darker. 
     In some embodiments, the perforated structures serve as speaker grids or microphone grids as part of a housing for an electronic device. The through-holes allow sound to pass through the housing to and/or from a user of the electronic device. The blind-holes can be arranged in a pattern amongst the through-holes to provide mechanical strength to the speaker grid. In some cases, the blind-holes hide one or more components housed within the housing. When treated, the blind-holes can be darkened and camouflaged to look like the through-holes, resulting in a uniform and cosmetically appealing arrangement of similar looking holes. 
     In some embodiments, ink is deposited on the inner surfaces of the blind-holes to give the blind-holes a darkened appearance. This can be accomplished using printing techniques, such as inkjet printing techniques. Inkjet printing is generally a non-contact printing technique where droplets of ink are propelled through a nozzle toward the substrate. This allows for accurate placement of the ink on the substrate and can also allow for small amounts of ink to be deposited and effectively cured at a time. The ink is printed onto inner surfaces of the blind-holes, such as the bottom or terminal surfaces of the blind-holes. In some embodiments, one or more ink layers are deposited. In some embodiments, the ink is selectively printed within the blind-holes without substantially depositing ink elsewhere on the substrate. In other embodiments, the ink is printed on an entire surface of the substrate, including within the blind-holes. This can be referred to as a flood printing technique. In some cases, a mask is used to mask off certain surfaces of the substrate. The ink can be dispensed either selectively into an area within and encircling the blind-holes or over the entire masked substrate surface. The mask can then be peeled off to reveal a clean substrate surface. In some cases, in addition to changing the optical properties of the blind-holes, the printing changes the thermal, mechanical and/or chemical properties of the substrate. Various types of inks can be used, such as a single colored ink, a mixture of colored ink and clear ink, or a multilayered ink that includes a clear ink layer over one or more colored ink layers. 
     As used herein, the terms “hole,” “opening,” “perforation” and “aperture” are used interchangeably and can refer to any suitable opening that is formed partially or fully through a substrate. The term “through-hole” refers to passageway that passes completely through a substrate. The terms “blind-hole” and “partial hole” refer to passageways that are formed a partial distance through a substrate and do not pass completely through the substrate. 
     Methods described herein are well suited for providing cosmetically appealing surface structures and designs for consumer products. For example, the methods described herein can be used to form cosmetically appealing perforated structures, such as speaker or microphone grids or grids for housing or enclosures for portable electronic devices, desktop computers, mobile electronic devices and electronic device accessories, such as those manufactured by Apple Inc., based in Cupertino, Calif. 
     These and other embodiments are discussed below with reference to  FIGS. 1A-18 . 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. 
       FIGS. 1A and 1B  show front facing perspective views of portable computing devices  100  and  130 , respectively, in accordance with some embodiments.  FIG. 1A  shows portable computing device  100  that can include base portion  102 , which can be pivotally connected to lid portion  104  by way of clutch assembly  106  hidden from view. Lid portion  104  can be moved with the aid of clutch assembly  106  from a closed position to remain in an open position and back again. Lid portion  104  can include display  108  and rear cover  110  that can add a cosmetic finish to lid portion  104  and also provide structural support to display  108 . Base portion  102  can define an internal chamber or cavity that houses internal components of portable computing device  100 . Thus, base portion  102  can function as a housing. In some cases, base portion  102  includes bottom case  112  that is fastened to top case  114 . Base portion  102  can be made of any suitable material, such as metal, plastic, ceramic or suitable combinations thereof. In some cases, base portion  102  is made of a metal alloy that provides a cosmetically appealing look to base portion  102  while providing structural integrity to base portion  102 . Top case  114  can be configured to accommodate various user input devices such as keyboard  116  and touchpad  118 , which can be configured to receive finger gesturing input from a user. 
     Top case  114  can include speaker grids  120  that port audio from speakers  122  enclosed within base portion  102 . Speaker grids  120  are perforated regions within top case  114  that include a number of holes for allowing sound from speakers  122  to pass through base portion  102  and out of portable computing device  100 . The holes of speaker grids  120  can be any suitable size and can be visible to a user of portable computing device  100 . The holes of speaker grids  120  can be arranged in a cosmetically appealing pattern, such as a uniformly spaced array, and can be arranged to form any suitable design, such as a rectangular shape shown in  FIG. 1A . In some cases, more holes are formed within speaker grids  120  than necessary for providing adequate sound passage in order to provide a cosmetically appealing design. However, providing more holes within top case  114  removes material from top case  114 , which can mechanically weaken top case  114 . For example, if top case  114  is made of a metal material, providing too many through-holes within speaker grids  120  can cause the metal material to lose mechanical strength and be more susceptible to bending, denting or other deformation. If top case  114  is made of a more brittle material, too many through-holes within speaker grids  120  can cause the material forming speaker grids  120  to be susceptible to breaking or cracking. Bending, denting, breaking, cracking or other deformation of top case  114  can compromise the structural integrity as well as detrimentally affect the cosmetic appearance of top case  114 . 
       FIG. 1B  shows portable computing device  130  that includes similar features as portable computing device  100 . In particular, portable computing device  130  includes base portion  132  pivotally connected to lid portion  134  by way of clutch assembly  136  hidden from view. Lid portion  134  can include display  138  and rear cover  140 , and base portion  132  can define an internal chamber or cavity that houses internal components of portable computing device  130 . Base portion  132  includes bottom case  142  that is fastened to top case  144 . Top case  144  can include keyboard  146  and touchpad  148 . However, speaker grid  150  of portable computing device  130  is located in a different area than speaker grid  120  of portable computing device  100 . In particular, speaker grid  150  is positioned over one or more speakers  152  located near clutch assembly  136 . As shown, the holes of speaker grid  150  are arranged to have a different design or shape (a long rectangular shape) than the holes of speaker grid  150 . As with the speaker grids  120  of portable computing device  100 , providing too many through-holes within speaker grid  150  can make speaker grid  150  susceptible to bending, denting, breaking, cracking or other deformation. 
     Methods described herein can be used to overcome problems associated with through-holes within perforated structures, such as speaker grids  120  and  150 . The methods involve replacing some of the through-holes within speaker grids  120  or  150  with partial holes that are formed partially though the substrate, sometimes referred to as blind-holes.  FIG. 2  shows a section view of a portion of substrate  200 , which includes a combination of through-holes  202  and blind-holes  204 , in accordance with some embodiments. Substrate  200  can correspond to a portion of speaker grids  120  or  150 . Thus, substrate  200  can correspond to an exterior wall or housing (e.g., top case  114  or  144 ), with exterior surface  206  corresponding to an exterior surface of a housing and interior surface  208  corresponding to an interior surface of the housing. Through-holes  202  are formed through an entire thickness  214  of substrate  200  to allow sound from one or more speakers to pass through substrate  200 . Blind-holes  204  are formed partially through substrate  200  such that support portion  210  of substrate  200  remains intact. Support portion  210  can be characterized as having a thickness  212 . The extra material provided by support portion  210  can provide more mechanical strength compared to a substrate that has through-holes  202  in place of blind-holes  204 . This can make speaker grids  120  or  150  more resistance to deformation when exposed to an impact event, such as a drop event or by an object falling onto speaker grids  120  or  150 . 
     One of the problems associates with forming blind-holes  204  is that blind-holes  204  can appear different than through-holes  202  by observer  222  viewing exterior surface  206 . This can be due to different behavior of light reflected from through-holes  202  versus blind-holes  204 . For example, if substrate  200  corresponds to top case  114  or  144  (portable computing devices  100  and  130 , respectively) light can enter and pass all the way through through-holes  202  and reach the internal chamber or cavity, generally giving through-holes  202  a black or otherwise dark color. In contrast, light entering blind-holes  204  can be reflected off of surfaces of inner walls  207  that define blind-holes  204 , such as terminal surfaces  220 . Terminal surfaces  220  are at the end or bottom of blind-holes and can correspond to surfaces that are most viewable from observer  222 . Terminal surfaces  220  can be referred to as sub-surfaces due to the position of terminal surfaces  220  relative to exterior surface  206 . If substrate  200  is made of a metallic material, terminal surfaces  220  can be especially reflective and appear light in color compared to the darker through-holes  202 . This visual distinction between through-holes  202  and blind-holes  204  can adversely affect the cosmetic appearance of substrate  200 . For example, some of the holes of speaker grids  120  or  150  may appear lighter than others, giving speaker grids  120  or  150  a non-uniform appearance. 
     To address this issue, described herein are methods for modifying the appearance of blind-holes  204  such that blind-holes  204  appear indistinguishable from through-holes  202  when viewed by observer  222 . In particular embodiments, the methods involve darkening blind-holes  204  so that they appear to provide access to the internal chamber of base portion  102  like through-holes  202 . To illustrate,  FIGS. 3A and 3B  show exterior views of top case  144  disassembled from portable computing device  130  shown in  FIG. 1B .  FIG. 3A  shows top case  144  before darkening of blind-holes  204  and  FIG. 3B  shows top case  144  after darkening of blind-holes  204 , in accordance with described embodiments. Note that the embodiments described below with reference to  FIGS. 3A and 3B  can also be used to form modified blind-holes within top case  114  of portable computing device  100  shown in  FIG. 1A , or any other suitable consumer electronic device casing such as a casing for a tablet computer, desktop computer or mobile phone. The methods described herein can also be used to form other types of perforated structures, such as microphone grids that allow access to one or more microphones as part of a housing. In some embodiments, the perforated structures are cosmetic portions of the housing and do not serve to provide access to a particular component within the housing. The perforated structure can be an integral part of the housing itself or can constitute a separate piece that can be coupled to a housing. 
     Top case  144  can be divided into various areas, such as keyboard area  302 , touchpad area  304  and speaker grid  150 . In some cases, top case  144  is made of a singular material, such as a metal or metal alloy material. In a particular embodiment, top case  144  is made of an aluminum alloy. In some embodiments, keyboard area  302  can include openings  306  for accommodating keys of portable computing device  130 . Touchpad area  304  can be configured to accommodate a touchpad assembly. As shown in close-up inset view  310 , speaker grid  150  can include through-holes  202  and blind-holes  204  that combine to form a pattern of holes within top case  144 . In this case, through-holes  202  and blind-holes  204  are arranged approximately equidistant from each other and have substantially the same diameters, forming a rectangular shaped grid pattern. Blind-holes  204  are arranged around groups  308  of through-holes  202  within speaker grid  150 . Through-holes  202  can allow sound from underlying speakers to pass through top case  144 . In this particular embodiment, speaker grid  150  includes four groups  308  of through-holes  202 , with each group  308  having a rectangular shape. Blind-holes  204  do not pass all the way through top case  144 , thereby forming support portion  210  (shown in  FIG. 2 ) that provide more mechanical strength to speaker grid  150  compared to a speaker grid having only through-holes  202 . This can make speaker grid  150 , and top case  144 , more resistant to deformation, as described above. 
     Note that groups  308  are exemplary arrangements of through-holes  202  and are not meant to limit the scope of possibilities within the scope of described embodiments. For example, groups  308  can each have a circular shape, square shape, triangular shape, etc. In addition, any number of groups  308  can be formed within speaker grid  150 . In some embodiments, through-holes  202  are arranged in rows and/or columns within speaker grid  150 . In some cases, groups  308  are positioned to hide one or more components housed within base portion  132 . In some cases, groups  308  are positioned away from corner or edge regions of a perforated structure to provide stiffness at the corner or edge regions. In some embodiments, through-holes  202  are not arranged in distinct clusters, but scattered amongst blind-holes  204 . In some embodiments, through-holes  202  are provided only where needed and the rest of the holes are blind-holes  204 . That is, the number of through-holes  202  can be minimized. In some embodiments, blind-holes  204  are arranged on non-flat (three-dimensional) surfaces, such as substrates having curved or stepped surfaces. 
     When top case  144  is assembled within portable computing device  130 , through-holes  202  provide access to an internal chamber that houses one or more speakers. In this way, through-holes  202  can allow sound from the one or more speakers to pass through top case  144  and to a user of portable computing device  130 . Unfortunately, blind-holes  204  can appear lighter than through-holes  202 . As described above, this can be due to light reflecting off of inner surfaces of blind-holes  204 . If top case  144  is made of a metal material, the inner surfaces of blind-holes  204  can be especially reflective due to the light reflective qualities of many metal materials.  FIG. 3B  shows top case  144  after inner surfaces of blind-holes  204  have been modified. For example, the inner surfaces of blind-holes  204  can be darkened with a surface modification process or covered with one or more darkening agents to reduce or eliminate reflectance of light that reaches the inner surfaces of blind-holes  204 . This results in a uniform appearing and cosmetically appealing speaker grid  150  from the perspective of the user. 
     Described below are different methods for modifying the appearance of blind-holes  204  such that they appear identical to or similar to through-holes  202 . According to some embodiments, the methods involve darkening blind-holes  204  using a laser. For example, a laser beam from a laser can be directed toward blind-holes  204  impinging on surfaces of the inner walls of blind-holes  204 . The laser beam can have a laser beam energy sufficient to chemically modify and darken the surfaces of inner walls  207 . In some embodiments, the laser beam oxidizes carbon-containing material within substrate  200  creating a black colored surface within blind-holes  204 . It may be difficult, however, to laser darken some substrate materials, such as those that do not contain carbon. In addition, the use of a laser generally requires accurately directing the laser beam within each blind-hole  204 , which can be time consuming and impractical when substrate  200  contains many blind-holes  204 . 
     In some cases, a faster and more versatile darkening technique involves covering the inner surfaces within the blind-holes  204  with one or more materials, such as a dark colored ink. Described below are details of different ink depositing methods used to darken the appearance of blind-holes  204 . Note that the methods described below are not meant to limit the scope of possible methods for modifying and darkening blind-holes  204  and that other suitable methods can be used. In addition, the methods below can be used in any suitable combination in order to achieve a desired appearance of blind-holes  204  and/or through-holes  202 . In some embodiments, the ink depositing methods are combined with other darkening methods, such as the laser darkening methods described above. Those of skill in the art can appreciate that in addition to changing the appearance (optical properties) of blind-holes  204  and/or through-holes  202 , the methods described herein can be applied to change the thermal, mechanical, and chemical properties of substrate  200 . 
       FIGS. 4A-4D  show section views of perforated substrate  400  undergoing a selective ink coverage process, in accordance with some embodiments.  FIG. 4A  shows substrate  400  after one or more hole forming processes to form through-holes  402  and blind-holes  404 . Inner walls  407  define boundaries and shapes of blind-holes  404 . Substrate  400  can correspond to an exterior wall or housing (e.g., top case  114  or  144 ), with exterior surface  406  corresponding to an exterior surface of a housing and interior surface  408  corresponding to an interior surface of the housing. Substrate  400  can be made of any suitable material, including metal, plastic, ceramic, glass or a combination thereof. In some embodiments, substrate  400  is made of a metal alloy, such as an aluminum alloy. In some embodiments, substrate  400  is anodized prior to or after forming through-holes  402  and blind-holes  404 . Thus, the surface of substrate  400  can be anodized and different than inner metal surfaces of blind holes  404 , such as terminal surfaces  420 . 
     Through-holes  402  and blind-holes  404  can be formed using any suitable method, including drilling (e.g., mechanical or laser drilling). In some embodiments, through-holes  402  and blind-holes  404  are formed using computer numerical control (CNC) methods. In some embodiments, through-holes  402  and blind-holes  404  are formed in a single process, such as a single drilling process. In other embodiments, through-holes  402  and blind-holes  404  are formed in separate drilling processes. The size and shape of each of through-holes  402  and blind-holes  404  can vary depending on design requirements and on manufacturing processes. In some embodiments, blind-holes  404  have curved or non-planar terminal surfaces  420 , which can be a product of the drilling process. For example, if a mechanical drill is used to form blind-holes  404 , terminal surfaces  420  can be associated with a shape of the drill bit that is used. In some embodiments, through-holes  402  and blind-holes  404  are drilled using a drilling machine with drill bit point angle of 130 degrees or 150 degrees. In other embodiments, terminal surfaces  420  have a different shape, such as a substantially flat shape that can be formed using, for example, a laser drilling process. In some cases it is found that shallower or flatter terminal surfaces  420  results in better ink coverage and improved darkening of blind-holes  404 . 
     In some embodiments, each of through-holes  402  has substantially the same diameter and each of blind-holes  404  has substantially the same diameter. In some embodiments, average diameter  416  of through-holes  402  is substantially the same as average diameter  418  of blind-holes  404 . In other embodiments, average diameter  416  of through-holes  402  is different than average diameter  418  of blind-holes  404 . In some applications, the average diameter  416  of through-holes  402  and average diameter  418  of blind-holes  404  are each less than about 1 mm, such as about 0.5 mm or less. In a particular embodiment, average diameter  416  of through-holes  402  and average diameter  418  of blind-holes  404  are each around 0.35 mm. The average depth  409  of blind-holes  404  can vary depending on design requirements as well as a desired average thickness  412  of support portion  410 . In some embodiments, blind-holes  404  have substantially the same depth while in other embodiments blind-holes  404  have varying depths. Thickness  414  of substrate  400  can vary depending on design. In some embodiments, blind-holes  404  are formed about halfway through thickness  414  of substrate  400 . In some embodiments, depth  409  of blind-holes  404  is at least about 100 micrometers. In a particular embodiment, the thickness substrate is about 600 micrometers, depth of blind-holes  404  ranges between about 200 micrometers and 300 micrometers, resulting in support portion  410  having a thickness  414  ranging between about 300 micrometers and 400 micrometers. 
       FIG. 4B  shows substrate after coating  422  is selectively deposited onto surfaces of inner walls  407  that define blind-holes  404 , such as terminal surfaces  420 . Coating  422  covers terminal surfaces  420  so as to darken the appearance of blind-holes  404  as viewed by an observer viewing exterior surface  406 . This is because coating  422  can be configured to absorb light entering blind-holes  404  and incident coating  422  such that a darkened appearance of the blind-holes  404  is perceived as the darkened appearance of through-holes  402 . For example, light incident upon the through-hole openings of through-holes  202  passes through through-holes  202  and into an internal cavity of housing  144  such that substantially no light reflects back through through-holes  202 . This results in the through-hole openings of through-holes  202  having a darkened appearance with respect to an exterior surface of housing  144 . In addition, substantially no light incident upon coating  422  reflects back through blind-holes  404  such that the blind-hole openings of blind-holes  404  are perceived as having the darkened appearance of the through-hole openings of through-holes  202 . In this way, blind-holes  404  can be camouflaged as through-holes  402 . 
     Coating  422  can be made of any suitable material, such as ink. If a printing process is used, the selective coating operation can be referred to as a selective printing process. Note that in some embodiments coating  422  can also cover portions of other surfaces within blind-holes  404 , such as sidewalls  424 . In some embodiments, the selective depositing avoids depositing coating  422  onto exterior surface  406 . This can be accomplished using an ink printer that is designed to accurately dispense ink in predetermined two-dimensional locations. For example, ink-dispensing nozzles of an inkjet type printer can be scanned or passed over exterior surface  406  of substrate  400  to selectively deposit coating within blind-holes  404 . In a particular embodiment, an adjustable X-Y translation stage is attached to a printer table of the printer in order to obtain accurate control of ink depositing. In one embodiment, a camera is used to capture an image of patterns of ink dots deposited onto test samples and displayed on a monitor. Test samples can be analyzed to determine the sizes (e.g., diameters) and X-Y locations of the each of ink dots such that each ink dot is accurately deposited within each blind-hole  404 . 
     The method used to deposit coating  422  can depend in part on the size (i.e., diameters) of blind-holes  404 . For example, the deposition technique should be able to form droplets of ink that are small enough to fit within blind-holes  404 . If blind-holes  404  have small diameters, some spraying techniques may not be able to form ink droplets small enough to provide adequate displacement of air from blind-holes  404  during the deposition process, resulting in the ink not getting deposited within blind-holes  404 . Thus, the method used should be able to provide ink droplets sufficiently small to overcome any surface tension created when deposited within blind-holes  404  and allow dislocation of air trapped within blind-holes  404  during the depositing. In some embodiments, the ink droplet size is less than about 100 microliters, and in a particular embodiment, between about 10 and 100 microliters. In some embodiments, this involves the use of ink jet dispenser systems where small droplets of ink are propelled through a nozzle. Examples of suitable equipment include flatbed printers, such those manufactured by Canon Inc. (Japan), Fujifilm (Japan), and Roland DG Corporation (Japan), which can produce droplets in the scale of picoliters. Other equipment can include piezoelectric style jet dispensers, such as PICO® Piezoelectric jet dispensing systems manufactured by Nordson Corporation (headquartered in Westlake, Ohio, U.S.), which can produce droplets as small as 2 nanoliters. 
     The angle at which the ink droplets deposit within blind-holes  404  can be controlled to some extent by the speed of the ink dispenser (e.g., ink jet nozzle) passing over substrate  400 . In some embodiments, the speed of passing the ink dispenser is slow enough such that the ink droplets are directed substantially straight down toward substrate  400  (i.e., substantially normal to exterior surface  406 ). Faster speeds can cause the ink droplets to fall at non-normal angles with respect to substrate  400  such that the ink deposits more on one side of terminal surfaces  420 , resulting in non-uniform coverage of terminal surfaces  420 . Even faster speeds can result in ink accumulations along sidewalls  424 . 
     Coating  422  can be made of any suitable colorant or combination of colorants. If coating  422  is made of ink, the ink should be sufficiently harden so that coating  422  does not run or drip out of blind-holes  404 . In some embodiments, an ink that can be used in inkjet printers is used, such as various water-based inks, solvent based inks, latex inks, and UV/LED curable inks UV/LED curable inks can be particularly suitable when substrate  400  is part of a manufacturing product line (such as portable computing devices  100  and  130 ) since these inks generally cure very quickly at relatively low temperatures. Any suitable UV/LED curable inkjet printers can be used to dispense the inks, including some Arizona 400 series printers manufactured by Canon Inc. (Japan) and some UJF-3042 series LED curable inkjet printers manufactured by Mimaki Engineering Co., Ltd. (Japan). 
     In some embodiments, a dark colored and opaque ink is used, such as black ink. The black ink can be made either from a pure black ink (e.g., black  265 ) or from a mixture of colors, such as a CMYK (cyan, magenta, yellow, and black) mixture. In some embodiments, other combinations of inks with different colors are used. In some embodiments, the ink is mixed with a filler or binder material that provides more volume to coating  422  to ensure full coverage of terminal surfaces  420 . The filler or binder material can itself have a color or can be substantially colorless. If an inkjet printer is used, the filler or binder material can be dispensed at the same time as the black ink using a separate ink jet nozzle so that a thicker layer of ink can be deposited per pass. In some embodiments, the filler or binder material is a clear colored ink, such as clear inks used to provide glossy appearance to prints. In a particular embodiment, a black colored ink is mixed with a clear colored ink. The viscosity of the ink should be sufficient to form small enough droplets of ink, as described above, but also to provide a good opaque color. Note that coating  422  can have any color and is not limited to black or dark colored ink material. For example, coating  422  can have a predetermined color to match a color of an object positioned on or near interior surface  408  and visible through through-holes  402 . 
     In some cases, coating  422  is not deposited to a thickness great enough to sufficiently darken blind-holes  404 . That is, coating  422  may be thin enough to allow some light to reflect off terminal surfaces  420 , making blind-holes  404  still appear lighter than through-holes  402 . Thus, it may be useful to measure the darkness of blind-holes  404  in comparison to through-holes  402 . In some embodiments, optical images of blind-holes  404  and through-holes  402  are measure using a digital microscope, such as a Dino-LITE digital microscope manufactured by AnMo Electronics Corporation. Some images showing differences between blind-holes, through-holes and ink covered holes are described in the Examples provided below with reference to  FIGS. 10A-18 . 
     If it is determined that coating  422  is not thick enough to sufficiently darken blind-holes  404 , at  FIG. 4C  coating  422  is thickened by depositing one or more additional layers of ink within blind-holes  404 . For example, the ink dispensing nozzle of the printer can be passed one or more additional times over substrate  400  to dispense one or more additional layers of ink. The additional layers of ink can include one or more types of ink. Examples of some particular embodiments where a black and clear layer, followed by another black and clear layer, followed by a black layer of ink are deposited are described below with reference to  FIGS. 10A-18 . The type of coverage provided by coating  422  required to adequately darken inner surfaces  407  can depend on the depth  409  of blind-holes. For example, if average depth  409  of blind-holes  404  is shallow, it may only be necessary to cover terminal surfaces  420  without much coverage required over sidewalls  424  since it would be difficult for an observer to view sidewalls  424  from outside of exterior surface  406 . However, if average depth  409  of blind-holes  404  is large (high aspect ratio), it may be necessary to provide coverage of some of sidewalls  424 . This can be accomplished by thickening coating  422  to an extent that a sufficient amount of sidewalls  424  are covered. 
     When it is determined that terminal surfaces  420  of blind-holes  404  are sufficiently darkened, at  FIG. 4D  protective layer or coating  426  is optionally deposited onto coating  422 . Protective coating  426  can prevent coating  422  from being dislodged from blind-holes  404  or prevent coating  422  from exposure to chemicals, such as chemicals used to clean substrate  400 , and that can lead to loss or discoloration of coating  422  from blind-holes  404 . In some embodiments, protective coating  426  can also reduce point reflection of coating  422 , thereby providing a darker color to blind-holes  404 . In some embodiments, protective coating  426  is substantially water resistant. Protective coating  426  can be made of any suitable material. In some embodiments, protective coating  426  is made of a clear ink, such as the clear ink that is mixed with a black ink for depositing coating  422  in some embodiments described above. 
     The selective printing process described above allows for selective coverage of coating  422  and protective coating  426  into blind-holes  404 . This process can require accurate alignment, which can make the selective printing process challenging, especially when substrate  400  has many blind-holes  404  or when blind-holes  404  are located relatively far distances apart from each other. An alternative to selective printing is flood printing, which involves depositing ink over an entire surface portion of a substrate.  FIGS. 5A-5D  show perforated substrate  500  undergoing a flood printing process, in accordance with some embodiments. 
     At  FIG. 5A  through-holes  502  and blind-holes  504  are formed within substrate  500 . Blind-holes  504  include inner walls  507  that define blind-holes  504 , which include terminal surfaces  520 . Any suitable hole forming process can be used, as described above with reference to  FIG. 4A . Exterior surface  506  can correspond to an exterior surface of a housing, such as an exterior surface of top case  114  or  144 .  FIG. 5B  shows substrate  500  after coating  522  is deposited onto surfaces of inner walls  507 , such as terminal surfaces  520 , as well as exterior surface  506 . Coating  522  can be made by depositing multiple layers of ink until coating  522  sufficiently covers terminal surfaces  520 , as described above with reference to  FIGS. 4B and 4C . In some embodiments, portions of coating  522  pass through through-holes  502  and collect at interior surface  508  proximate to through-holes  502 . 
       FIG. 5C  shows substrate  500  after protective coating  526  is optionally applied over coating  522 . Protective coating  526  can prevent exposure of coating  522  to chemicals and can be made of any suitable material, as described above with reference to  FIG. 4D . In some embodiments, portions of protective coating  526  pass through through-holes  502  and collect near interior surface  508  proximate to through-holes  502 . Note that in some embodiments, depositing coating  522  ( FIG. 5B ) or depositing protective coating  526  ( FIG. 5C ) involves a selective depositing within blind-holes  504  without substantially depositing onto exterior surface  506  and/or interior surface  508 . 
       FIG. 5D  shows portions of coating  522  and/or protective coating  526  removed from exterior surface  506  and interior surface  508 , leaving coating  522  and protective coating  526  on terminal surfaces  520  of blind-holes  504 . In some embodiments, the removal is accomplished by pressing an adhesive tape onto each of exterior surface  506  and interior surface  508  and removing the adhesive tape with portions of coating  522  and protective coating  526  adhered thereon. In some embodiments, the removal is accomplished by wiping each of exterior surface  506  and interior surface  508  using a solvent, such as an alcohol solvent. In some embodiments, a combination of adhesive tape and solvent wiping are used. 
       FIG. 6  shows flowchart  600  indicating an ink coverage process for darkening blind-holes, in accordance the methods described above with reference to  FIGS. 4A-4D and 5A-5D . At  602 , one or more blind-holes are formed within a substrate. The substrate can be made of any suitable material including metal, plastic, ceramic, glass or a combination thereof. The blind-holes can be formed using any suitable process, including a mechanical drilling process, a laser drilling process or a combination thereof. The blind-holes can be situated adjacent to through-holes such that the blind-holes and through-holes are arranged in a predetermined cosmetically appealing pattern. 
     At  604 , in some embodiments ink is selectively printed into the blind-holes without being substantially printed onto the surface of the substrate. This can be accomplished using a positioning device that adjusts the relative position of the substrate with respect to the printer, and a detection device (e.g., camera) that can detect the position of the blind-holes within the substrate. The ink can be deposited to a predetermined thickness. The predetermined thickness can be associated with an amount of coverage of inner surfaces of the blind-holes sufficient to darken the appearance of the blind-holes to a predetermined amount when viewed from a top surface of the substrate. The darkness of the blind-holes can be measured using an imaging device such as a digital microscope. In some embodiments, the ink is deposited in multiple layers so as to accomplish the predetermined darkness. In some embodiments, a protective coating is deposited over the ink in order to keep the ink within the blind-holes and to prevent exposure of the ink from chemicals, such as chemicals used to clean the substrate. 
     At  606 , in alternate embodiments ink is flood printed within the blind-holes and onto the surface of the substrate. Flood printing does not necessarily involve as accurate of substrate positioning and ink depositing as selective printing  604 , and can therefore be more easily implemented than selective printing  604 . As with selective printing  604 , the ink can be deposited to a predetermined thickness associated with a predetermined appearance of the blind-holes. At  608 , the ink is cleaned off the surface of the substrate such that ink remains within the blind-holes. The cleaning can involve use of an adhesive tape, solvent wiping, or both. 
     In some embodiments, a mask is used to mask off portions of a substrate prior to depositing ink. The mask can be positioned on the substrate prior to the hole forming process to assure accurate alignment of edges of the mask and the edges of the holes. To illustrate,  FIGS. 7A-7D  show perforated substrate  700  undergoing an ink depositing process that includes use of a mask, in accordance with some embodiments.  FIG. 7A  shows mask  701  formed on exterior surface  706  of substrate  700 . Mask  701  should be deposited thick enough to provide substantially uniform coverage of exterior surface  706  and thin enough to avoid interference with a subsequent ink depositing process. Mask  701  should be durable enough to withstand degradation and peeling away from substrate  700  during a subsequent drilling process. In one embodiment, mask  701  is made of a laminated material that includes a plastic film, a pressure sensitive adhesive layer, and optionally a release liner. The release liner is removed prior to application. The plastic film should have enough strength so that it does not deform during a subsequent hole forming process. In a particular embodiment, mask  701  includes a plastic film made of a polyethylene terephthalate (PET) having a thickness ranging between about 25 micrometers and about 200 micrometers. In one embodiment, mask  701  includes a plastic PET film having a thickness ranging between about 50 micrometers and about 150 micrometers. In one embodiment, mask  701  includes a plastic PET film having a thickness ranging between about 75 micrometers and about 125 micrometers. The plastic film can be optically clear, translucent or opaque. 
     Mask  701  can be attached to substrate  700  by an adhesive layer, such as a pressure sensitive adhesive. In embodiments where mask  701  remains on exterior surface  706  during a subsequent hole forming process, the adhesive layer should have enough bonding strength so that mask  701  remains firmly in place on exterior surface  706  during the hole forming process. In addition, the adhesive layer should be easily removable from exterior surface  706  after ink depositing without leaving substantial residues on exterior surface  706 . In some embodiments, the adhesive layer is chosen based on a peel value. In one embodiment, an adhesive layer having a peel value ranging between about 1N/25 mm and 6N/25 mm as measured on stainless steel ranges is used. In one embodiment, an adhesive layer having a peel value ranging between about 1.5 N/25 mm and 3N/25 mm as measured on stainless steel ranges is used. In one embodiment, the adhesive layer has a thickness ranging between about 5 grams per square meter (gsm) and 50 gsm. In one embodiment, the adhesive layer has a thickness ranging between about 10 gsm and 30 gsm. In one embodiment, the adhesive layer has a thickness ranging between about 15 gsm and 25 gsm. In some embodiments, more than one mask  701  is used within a single hole forming process. 
     Mask  701  can have different colors either by using a colored plastic film or a colored adhesive layer. Examples of suitable masks include certain paint masks, such as those manufactured by Avery Dennison Corp. (based in Pasadena, Calif.) and some R grade films manufactured by Worldmark International Ltd. (based in Glasgow, United Kingdom). In another embodiment, the mask  701  includes a dry adhesive layer. Examples of suitable dry adhesive layers include synthetic papers, such as some products manufactured by YUPO Synthetic Papers and Gecko grip materials pioneered by University of Massachusetts Amherst, Carnegie Mellon University, University of California in Berkeley, Karlsruhe Institute of Technology and others. 
       FIG. 7B  shows substrate  700  after formation of through-holes  702  and blind-holes  704 . Blind-holes  704  have inner walls  707  that define shapes and sizes of blind-holes  704 . Any suitable hole forming process can be used, such as those described above with reference to  FIGS. 4A and 5A . As shown, through-holes  702  and blind-holes  704  can be formed through mask  701  creating a corresponding pattern of holes within mask  701 . In this way, the edges (perimeters) of the holes within mask  701  accurately correspond to the edges (perimeters) of through-holes  702  and blind-holes  704 . Note that in some embodiments mask  701  is applied onto substrate  700  after through-holes  702  and blind-holes  704  are formed. In these embodiments, mask  701  can include openings corresponding to through-holes  702  and blind-holes  704 , with the openings within mask  701  having diameters the same size or substantially larger than the diameters of through-holes  702  and blind-holes  704 . 
       FIG. 7C  shows substrate  700  after coating  722  and optional protective coating  726  are deposited onto mask  701  and onto surfaces of inner walls  707  that define blind-holes  704 , such as terminal surfaces  720 . As described above, coating  722  can include one or more layers of ink. Each layer of ink can include one or more types and colors of ink and can include filler or binder material, such as a clear ink. Protective coating  726  can be optionally applied over coating  722 . Since mask  701  has holes with perimeters that accurately correspond to through-holes  702  and blind-holes  704 , mask  701  prevents coating  722  and protective coating  726  from depositing onto exterior surface  706 . In some embodiments, portions of coating  722  can be passed through through-holes  702  and become deposited on interior surface  708  (not shown). In these cases, interior surface  708  can be cleaned using one or both of an adhesive tape and solvent wiping, as described above with reference to  FIG. 5D . 
       FIG. 7D  shows substrate  700  after removal of mask  701 . In some embodiments, exterior surface  706  required no further cleaning after removal of mask  701 . In other embodiments, one or both of an adhesive tape and solvent wiping, as described above with reference to  FIG. 5D  is used to clean any ink residues from exterior surface  706 . 
     In some cases, a mask is used in conjunction with a selective depositing process, as shown in  FIGS. 8A-8D .  FIG. 8A  shows mask  801  formed on exterior surface  806  of perforated substrate  800 . Mask  801  can be made of any suitable material and can have any suitable thickness. In some embodiments, mask  801  is a laminated material with a plastic film, a pressure sensitive adhesive layer and optionally a release liner, as described above with reference to  FIG. 8A .  FIG. 8B  shows substrate  800  after formation of through-holes  802  and blind-holes  804 . Blind-holes  804  have inner walls  807  that define shapes and sizes of blind-holes  804 . Any suitable hole-formation process can be used, such as described above. The hole-formation process can also form corresponding holes within mask  801 . 
       FIG. 8C  shows substrate  800  after coating  822  and optional protective coating  826  are selectively deposited onto inner surfaces  807  of blind-holes  804 , such as terminal surfaces  820 . The selective depositing can be performed using a selective printing process, such as described above with reference to  FIG. 4B , which involves tuning print locations based on two-dimensional coordinates (X-Y). As described above, it can be difficult to accurately align substrate  800  with respect to a printer such that coating  822  only deposits within blind-holes  804 . However, since mask  801  has holes with perimeters that accurately correspond to through-holes  802  and blind-holes  804 , mask  801  can prevent deposition onto exterior surface  806  due to any misalignment of substrate  800  with respect to the printer. Thus, the combination of mask  801  with selective depositing can provide good coverage of terminal surfaces  820  of blind-holes  804  while minimizing ink waste and clean up.  FIG. 8D  shows substrate  800  after mask  801  is removed providing a clean and ink-free exterior surface  806 . 
       FIG. 9A  shows flowchart  900  indicating an ink coverage process for darkening blind-holes that includes use of a mask, in accordance with the methods described above with reference to  FIGS. 7A-7D and 8A-8D . At  902 , a mask is applied on a surface of a substrate. The substrate can be made of any suitable material including metal, plastic, ceramic, glass or a combination thereof. At  904 , one or more blind-holes are formed within a substrate. Since the mask is positioned on the substrate, one or more holes are also formed within the mask corresponding to the one or more blind-holes of the substrate. 
     At  906 , in some embodiments ink is selectively printed into the blind-holes. The presence of the mask covers the substrate surface along the perimeters of the blind-holes so that alignment of the selective printing is less critical compared to when no mask is used. This can provide good coverage within the blind-holes while minimizing ink waste. In some cases, multiple layers of ink are deposited within the blind-holes in order to provide adequate coverage and achieve a predetermined darkness of the blind-holes. In some embodiments, a protective coating is deposited over the ink in order to keep the ink within the blind-holes and prevent chemical exposure of the ink. At  908 , the mask is removed from the surface of the substrate. The result is a clean substrate surface with ink-darkened blind-holes. 
     At  910 , in alternate embodiments ink is flood printed within the blind-holes and the mask. As with selective printing  906 , the ink can be deposited to a predetermined thickness associated with a predetermined appearance of the blind-holes. At  912 , the mask is removed from the surface of the substrate taking along with it the excess ink deposited on the mask, resulting in a clean substrate surface with ink darkened holes. 
     Note that the methods described herein can be used to darken structures other than perforated structures. For example, the methods can be used to provide cosmetically appealing seams or outlines of features. To illustrate,  FIG. 9B  shows a bottom view of base portion  132  of the portable computing device  130  described above with respect to  FIG. 1B .  FIG. 9B  shows base portion  142 , which can include feet  154  that protrude from a surface of base portion  142 . Feet  154  can be configured to contact a support surface on which portable computing device  130  is placed. The perimeters of each of feet  154  can include gaps  156  that provide clean looking and cosmetically appealing outlines for feet  154 . In some cases, it can be difficult to form gap  156  such that it forms a consistent and uniform outline to feet  154 . The methods described above can also be used to darken gap  156  in order to provide clean looking outlines for feet  154 . For example, an inkjet printer can be arranged to print and form an ink coating within each of gaps  156 . The ink coatings can include multiple layers as well as a protective layer to prevent loss of the ink from within gaps  156 . As described above, the thickness of the ink coating and protective coating can depend on the depth of gaps  156 . Note that the outlining or darkening methods described herein are not limited to flat surfaces of substrates, but can also be applied to non-flat three-dimensional surfaces, such as curved or stepped surfaces. 
     EXAMPLES 
     Example 1 
     Imaging of Blind-Holes and Through-Holes 
       FIGS. 10A and 10B  show images of through-holes  1002  and blind-holes  1004  using a Dino-LITE digital microscope. Through-holes  1002  and blind-holes  1004  were drilled in an anodized aluminum substrate using a Hitachi ND-6Ni210E machine with a 130 degree drill bit. The diameter of each of through-holes  1002  and blind-holes  1004  is about 0.4 mm. The depth of through-holes  1002  is about 0.6 mm and the depth of the blind-holes  1004  ranges from 0.2 mm and 0.3 mm. The images of  FIGS. 10A and 10B  show how through-holes  1002  appear darker than blind-holes  1004 . In particular, blind-holes  1004  appear shiny due to the highly reflective terminal surface of blind-holes  1004 . 
     Example 2 
     Selective Printing Process 
     Through-holes and blind-holes were drilled in an anodized aluminum alloy substrate. Canon Arizona 480GT UV/LED printer was used to selectively print within the blind-holes. The printer has 8 color ink channels having CMYK, Lc, Lm, W, and W/C and two mercury lamps for curing. An adjustable X-Y translation stage was attached to the printer table via double-sided tape. A plastic film was attached to the X-Y translation stage via a double-sided adhesive. A CCD Camera was used to capture the image of the plastic film and displayed on a monitor. A template image including black dots matching the size of the blind-holes was printed onto the plastic film and displayed on the monitor. The plastic film was then removed and the substrate was mounted onto the X-Y translation stage via a double-sided adhesive tape. The position of the substrate was adjusted to match at least two of the blind-holes with the printed dots shown on the monitor. The template image was then printed and ink dispensed onto the blind-holes. 
     Example 3 
     Masked Printing Process Using One Black Ink Layer 
       FIGS. 11A and 11B  show images of through-holes  1102  and blind-holes  1104  that were deposited with one layer of black ink. The images were taken using a Dino-LITE digital microscope. The printing process involved applying a mask having a 100 micrometer thick polyethylene terephthalate (PET) film and a 20 micrometer thick removable acrylic pressure sensitive adhesive (F0418 manufactured by Avery Dennison Corporation) to the substrate. Blind-holes  1104  and through-holes  1102  were drilled in the substrate through the mask with a 130 degree drill bit. Black ink was flood printed onto the substrate and into blind-holes  1104  using the Canon Arizona 480GT UV/LED printer using the printing parameters provided in Table 1 below. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Parameter 
                 Value 
               
               
                   
                   
               
             
            
               
                   
                 Ink type 
                 Pure black 
               
               
                   
                 Print Density 
                 100% 
               
               
                   
                 Printing Mode 
                 High Definition 
               
               
                   
                 Number of passes 
                 1 
               
               
                   
                   
               
            
           
         
       
     
     As shown in  FIG. 11B , blind-holes  1104  are partially covered by the single layer of black ink. However, blind-holes  1104  still show some shiny appearance due to insufficient coverage of the terminal surfaces of the blind-holes  1104 . 
     Example 4 
     Masked Printing Process Using Two Black Ink Layers 
       FIGS. 12A and 12B  show Dino-LITE digital microscope images of through-holes  1202  and blind-holes  1204  that were deposited with two layers of black ink. After masking, the substrate was flood printed with black ink using the Canon Arizona 480GT UV/LED printer using the printing parameters provided in Table 2 below. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Parameter 
                 Value 
               
               
                   
                   
               
             
            
               
                   
                 Ink type 
                 Pure black 
               
               
                   
                 Print Density 
                 100% 
               
               
                   
                 Printing Mode 
                 High Definition 
               
               
                   
                 Number of passes 
                 2 
               
               
                   
                   
               
            
           
         
       
     
     Compared to the single ink layer of black ink shown in  FIG. 11B , the coverage of the blind-holes  1204  in  FIG. 12B  was significantly reduced with the two layers of black ink. In particular, only small white spots are observed in some of blind-holes  1204 . 
     Example 5 
     Masked Printing Process Using One CMYK Black Ink Layer 
     As described above, the black ink can be created from a CMYK mixture, which is different than a pure black ink.  FIGS. 13A and 13B  show images of through-holes  1302  and blind-holes  1304  that were deposited with one layer of CMYK mixture. The images were taken using a Dino-LITE digital microscope. After masking, the CMYK mixture was flood printed on the substrate in one pass using a Canon Arizona 480GT UV/LED printer using the printing parameters provided in Table 3 below. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 Parameter 
                 Value 
               
               
                   
                   
               
             
            
               
                   
                 Ink type 
                 CMYK 
               
               
                   
                 Print Density 
                 100% 
               
               
                   
                 Printing Mode 
                 High Definition 
               
               
                   
                 Number of passes 
                 1 
               
               
                   
                   
               
            
           
         
       
     
     Compared to blind-holes  1104  with the single ink layer of black ink shown in  FIG. 11B , blind-holes  1304  in  FIG. 13B  appear to show more of the underlying reflective substrate and appears lighter in color. Thus, in some cases the pure black ink may provide more effective darkening of blind-holes compared to CMYK in mixtures. 
     Example 6 
     Masked Process Using Multilayered Pure Black Ink and Clear Ink Layer 
     Multiple layers of black ink can be deposited followed by a clear ink layer in order to further reduce light reflection from within blind-holes.  FIG. 14A  shows an image of a substrate covered with a layer of pure black ink and  FIG. 14B  shows an image of a substrate covered with multiple layers of black ink followed by a clear ink layer. The images were taken using a Dino-LITE digital microscope. The black ink/clear ink deposition shown in  FIG. 14B  was deposited using Canon Arizona 480GT UV/LED printer using the multiple layered process provided in Table 4 below. 
     
       
         
           
               
               
             
               
                 TABLE 4 
               
               
                   
               
             
            
               
                 Layer 1 
                 Mixture of black ink 256 and clear ink; High definition mode 
               
               
                 Layer 2 
                 Black ink 256; High definition mode 
               
               
                 Layer 3 
                 Clear ink; Quality mode 
               
               
                   
               
            
           
         
       
     
     Comparison of  FIGS. 14A and 14B  shows that the mixture of black ink and clear ink in  FIG. 14B  results in a denser black color. The mixture of the black ink with clear ink (layer 1) allows for dispensing about two times more ink volume in the same pass. The pure black layer (layer 2) ensures sufficient density of the black ink to reduce light reflection. The clear ink layer (layer 3) reduces light reflection by eliminating point reflection from the black ink layer. In addition, the clear ink layer (layer 3) can protect the black ink against ink loss upon cleaning with chemical agents. 
       FIG. 15  shows a Dino-LITE digital microscope image of a substrate with blind-holes  1504  deposited with the multiple layered process of Table 4. As shown, blind-holes  1504  are substantially black with only tiny white spots  1505  associated with light reflection from the LED bulbs of the Dino-LITE microscope. 
       FIG. 16  shows cross section views of substrate samples having blind-holes  16 A- 16 H deposited with the multiple layered process of Table 4. Blind-holes  16 A- 16 H were each drilled with a 130 degree drill bit resulting in cone shaped terminal surfaces  1600 . As shown, the terminal surfaces  1600  of blind-holes  16 A- 16 H are fully covered by the multiple ink layers. For example, coating  1601  and protective coating  1603  fully cover terminal surface  1600 . 
     Example 7 
     Masked Process Using 150 Degree Drill Bit 
     The coverage of the terminal surfaces of the blind-holes can depend on the geometry of the terminal surfaces.  FIG. 17  shows a Dino-LITE digital microscope image of a substrate with blind-holes  1704  that were drilled using a 150 degree drill bit and printed using Canon Arizona 480GT UV/LED printer using the multiple layered printing process provided in Table 4. A 150 degree drill bit has a shallower point angle compared to a 130 degree drill bit, resulting in a blind-hole having flatter terminal surface compared to a blind-hole formed using a 130 degree drill bit.  FIG. 17  shows that the only lightness within blind-holes  1704  is in the form of tiny white spots  1705  associated with light reflection from the LED bulbs of the Dino-LITE microscope. 
       FIG. 18  shows cross section views of substrate samples having blind-holes  18 A- 18 H each drilled with a 150 degree drill bit and printed with the multiple layered process of Table 4. The terminal surfaces  1800  of blind-holes  18 A- 18 H are shallower or flatter than the terminal surfaces  1600  of blind-holes  16 A- 16 H formed using a 130 degree drill bit. As shown, the terminal surfaces of blind-holes  18 A- 18 H are fully covered by the multiple ink layers. For example, coating  1801  and protective coating  1803  fully cover terminal surface  1800 . In addition, the shallower geometry of terminal surfaces  1800  allow for more coverage of sidewall surfaces  1805  of blind-holes  18 A- 18 H compared to blind-holes  16 A- 16 H. In some cases, this can result in darker appearing blind-holes  18 A- 18 H compared to blind-holes  16 A- 16 H. 
     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 targeted 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: 20150824
Publication Date: 20170718
Grant Date: 20170718
Priority Date: 20150109
Inventors: SHI MING KUN
METTLER JASON O.
KWAN HILBERT T.
BRUNI CHRISTOPHER
TIAN QI
ZHANG JING
BUJTOR HOWARD E.
JAYANATHAN STEPHEN V.
FARAHANI HOUTAN R.
Assignee: APPLE INC
CPC Classifications: [{"code": "G06F1/1656", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F1/1688", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/1688", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/1656", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 56367549