PATENT DOCUMENT

Publication Number: US-9279189-B2
Application Number: US-201414585021-A
Country: US
Kind Code: B2

Title: Methods for forming defect-free anodized parts

Abstract:
Manufacturing methods related to anodizing of metal parts are described. In particular, pre-anodizing and post-anodizing methods for forming a consistent and defect-free interface between metal and non-metal sections of a part are described. Methods involve preventing residues from various manufacturing processes from entering a gap or space at the interface between the metal and non-metal section of the part and that can disrupt subsequent anodizing and anodic film dyeing processes. In particular embodiments, methods involve forming a barrier layer or filler layer between the metal and non-metal sections. Portions of the barrier layer or filler layer can be removed prior to anodizing. The resultant part has a well-defined and uniform space between the metal and non-metal sections that is free from visual defects.

Claims:
What is claimed is:  
     
       1. A method of forming a housing for an electronic device, the housing including an anodizable section and non-anodizable section, the method comprising:
 forming a boundary layer on the anodizable section, the boundary layer configured to prevent exposure of the anodizable section to a chemical agent that causes the anodizable section to form a corrosion product that is associated with defects; 
 molding the non-anodizable section onto the boundary layer such that the boundary layer is situated between the anodizable section and non-anodizable section at a junction region; 
 removing a portion of the boundary layer exposing a surface of the anodizable section; and 
 converting the exposed surface to a metal oxide layer, wherein the boundary layer prevents formation of the corrosion product at the junction region during one or more of the molding, removing, and converting such that the junction region is defect-free. 
 
     
     
       2. The method of  claim 1 , wherein the boundary layer has a uniform thickness. 
     
     
       3. The method of  claim 1 , wherein the metal oxide layer is a first metal oxide layer and the boundary layer is a second metal oxide layer, wherein forming the boundary layer comprises:
 converting exposed surfaces of the anodizable section to the second metal oxide layer. 
 
     
     
       4. The method of  claim 1 , further comprising:
 after the converting, infusing a dye into the metal oxide layer, wherein the corrosion product disrupts infusion of the dye at the junction region. 
 
     
     
       5. The method of  claim 4 , further comprising:
 prior to infusing dye into the metal oxide layer, cleaning the housing using one or more acidic solutions. 
 
     
     
       6. The method of  claim 5 , wherein cleaning the housing comprises:
 rinsing the housing in a series of different acidic solutions. 
 
     
     
       7. The method of  claim 5 , wherein sonic vibration is applied to the one or more acidic solutions to provide a cleaning action that assists cleaning of the housing. 
     
     
       8. The method of  claim 1 , wherein forming the boundary layer comprises:
 electrocoating the boundary layer onto the anodizable section. 
 
     
     
       9. The method of  claim 8 , wherein the boundary layer is comprised of a polymer. 
     
     
       10. The method of  claim 1 , further comprising:
 prior to forming the boundary layer, forming an interlock feature on the anodizable section, the interlock feature having engagement surfaces that engage with the non-anodizable section and secure the non-anodizable section to the anodizable section. 
 
     
     
       11. The method of  claim 10 , wherein the interlock feature is a recess within the anodizable section, wherein molding the non-anodizable section onto the anodizable section includes depositing a portion of the non-anodizable section within the recess. 
     
     
       12. The method of  claim 10 , wherein the interlock feature has a low aspect ratio such that substantially no voids are formed between the non-anodizable section and the boundary layer. 
     
     
       13. A method of forming a housing for an electronic device, the housing including a metal section and a plastic section, the method comprising:
 forming a boundary layer on the metal section, wherein a first portion of the boundary layer is formed on a first surface of the metal section and a second portion of the boundary layer is formed on a second surface of the metal section, wherein the boundary layer is configured to prevent exposure of the metal section to a chemical agent that causes the metal section to form a corrosion product that is associated with defects; 
 molding the plastic section onto the first portion of the boundary layer such that the boundary layer is situated between the metal section and plastic section at a junction region; 
 removing the second portion of the boundary layer exposing a surface of the metal section; and 
 converting the exposed surface to a metal oxide layer, wherein the boundary layer prevents formation of the corrosion product at the junction region during one or more of the molding, removing, and converting such that the junction region is defect-free. 
 
     
     
       14. The method of  claim 13 , wherein the first surface and the second surface of the metal section meet at corner, wherein the junction region is at corner. 
     
     
       15. The method of  claim 13 , wherein the metal oxide layer corresponds to an exterior surface of the housing. 
     
     
       16. The method of  claim 13 , wherein removing the second portion comprises:
 cutting off the second portion of the boundary layer and a portion of the plastic section. 
 
     
     
       17. A housing for an electronic device, the housing comprising:
 a metal section having a first surface and a second surface that meet at a corner, wherein the first surface has a boundary layer positioned thereon and the second surface has a metal oxide layer positioned thereon, wherein the boundary layer has a substantially uniform thickness, wherein an exposed surface of the metal oxide layer corresponds to an exterior surface of the housing; and 
 a plastic section directly adjacent the boundary layer such that the boundary layer is positioned between the plastic section and the first surface of the metal section. 
 
     
     
       18. The housing of  claim 17 , wherein the first surface of the metal section includes an interlock feature and the boundary layer conforms to a shape of the interlock feature, wherein the plastic section engages with boundary layer at the interlock feature securing the plastic section to the metal section. 
     
     
       19. The housing of  claim 18 , wherein the shape of the interlock feature is characterized as having a low aspect ratio. 
     
     
       20. The housing of  claim 18 , wherein the electronic device includes a radio frequency antenna, wherein the plastic section is comprised of a radio frequency transparent material that allows radio frequency waves to pass there through to or from the radio frequency antenna.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This is a continuation of International Application PCT/US14/72567, with an international filing date of Dec. 29, 2014, entitled “Methods For Forming Defect-Free Anodized Parts”, which claims priority to U.S. Provisional Application No. 61/988,807 filed May 5, 2014 entitled “Methods For Forming Defect-Free Anodized Parts”, each of which is incorporated herein by reference in its entirety. 
    
    
     FIELD 
     This disclosure relates generally to anodizing techniques and anodized structures. In particular, methods for anodizing parts having metal and non-metal sections are described. The methods can be used to form a consistent and defect-free interface between the metal and non-metal sections. 
     BACKGROUND 
     Anodizing is a process used in many manufacturing product lines to provide protective and cosmetically appealing surfaces to metal portions of a part. During an anodizing process, a part is exposed to an electrolytic process whereby the part acts as an anode. The process forms a metal oxide layer or anodic film on surfaces of a part. The metal oxide layer can enhance the durability and corrosion resistance of the part. In addition, the metal oxide layer has a porous structure that can accept any of a number of dyes. These dyes can be infused within the porous structures of the metal oxide to give the part a particular color. 
     In addition to anodizing, products typically undergo a number of other manufacturing processes. For instance, the part can undergo any of a number of metal shaping processes such as machining (e.g., cutting, milling, etc.), forging, extruding. In addition, the part typically undergoes any of number of surface treatment processes, such as polishing, etching and blasting procedures. Many times, consumer products are composite parts that include metal and non-metal sections, such as plastic or glass sections. Residues from the various manufacturing processes, such as chemical residues, can get trapped within gaps and crevices between the metal and non-metal sections, which can detrimentally affect a subsequent anodizing process and cause defects in the resultant metal oxide film. In some cases, these defects can be visible, especially if the metal oxide film is dyed. 
     SUMMARY 
     This paper describes various embodiments that relate to treating metal substrates and electroplating onto metal substrates. 
     According to one embodiment, a method of forming a housing for an electronic device is described. The housing includes an anodizable section and non-anodizable section. The method includes forming a boundary layer on the anodizable section. The boundary layer is configured to prevent exposure of the anodizable section to a chemical agent that causes the anodizable section to form a corrosion product that is associated with defects. The method also includes molding the non-anodizable section onto the boundary layer such that the boundary layer is situated between the anodizable section and non-anodizable section at a junction region. The method further includes removing a portion of the boundary layer exposing a surface of the anodizable section. The method additionally includes converting the exposed surface to a metal oxide layer. The boundary layer prevents formation of the corrosion product at the junction region during one or more of the molding, removing, and converting such that the junction region is defect-free. 
     According to another embodiment, a method of forming a housing for an electronic device is described. The housing includes a metal section and a plastic section. The method includes forming a boundary layer on the metal section. A first portion of the boundary layer is formed on a first surface of the metal section and a second portion of the boundary layer is formed on a second surface of the metal section. The boundary layer is configured to prevent exposure of the metal section to a chemical agent that causes the metal section to form a corrosion product that is associated with defects. The method additionally includes molding the plastic section onto the first portion of the boundary layer such that the boundary layer is situated between the metal section and plastic section at a junction region. The method also includes removing the second portion of the boundary layer exposing a surface of the metal section. The method further includes converting the exposed surface to a metal oxide layer. The boundary layer prevents formation of the corrosion product at the junction region during one or more of the molding, removing, and converting such that the junction region is defect-free. 
     According to a further embodiment, a housing for an electronic device. The housing includes a metal section having a first surface and a second surface that meet at a corner. The first surface has a boundary layer positioned thereon and the second surface has a metal oxide layer positioned thereon. The boundary layer has a substantially uniform thickness. An exposed surface of the metal oxide layer corresponds to an exterior surface of the housing. The housing also includes a plastic section directly adjacent the boundary layer such that the boundary layer is positioned between the plastic section and the first surface of the metal section. 
     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, and in which: 
         FIGS. 1A-1F  show cross-section views of a portion of a part at various stages of a gap filling and anodizing process in accordance with described embodiments. 
         FIGS. 2A-2G  show cross-section views of a portion of a part, which includes two non-anodizable sections, at various stages of a gap filling and anodizing process in accordance with described embodiments. 
         FIG. 3  shows a flowchart indicating a gap filling and anodizing process in accordance with described embodiments. 
         FIG. 4  shows a flowchart indicating a process for forming a metal filler layer in accordance with described embodiments. 
         FIG. 5  shows a graph illustrating voltage and current density changes during an electrolytic metal filler layer removal process in accordance with described embodiments. 
         FIGS. 6A-6F  show cross-section views of a portion of a part at various stages of manufacture using a boundary layer in accordance with some embodiments. 
         FIGS. 7A-7E  show cross-section views of portions of anodizable sections having different shaped interlock features in accordance with some embodiments. 
         FIG. 8  shows a flowchart indicating a process for forming a composite part using a boundary layer in accordance with embodiments described with reference to  FIGS. 6A-6F  and  7 A- 7 E. 
     
    
    
     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 as defined by the appended claims. 
     The following disclosure pertains to techniques related to anodizing of metal parts. In particular, pre-anodizing and post-anodizing methods for forming a consistent interface between metal and non-metal sections of a part are described. In addition, the interface between the metal and non-metal section are free from visible defects related to dyeing of an anodic film. Methods described involve preventing residues from various manufacturing processes from entering a gap or space at the interface between the metal and non-metal section of the part. If left within the gaps, these residues can disrupt subsequent anodizing and anodic film dyeing processes. In particular embodiments, methods involve filling the gap with a filler material or filler layer prior to exposure to the various manufacturing processes. The filler material can then be removed prior to anodizing and anodic film dyeing. 
     The methods described herein are well suited for providing both protective and attractive surfaces to visible portions of consumer products. For example, methods described herein can be used to provide protective and cosmetically appealing exterior portions of metal housings and casings for electronic devices, such as those manufactured by Apple Inc., based in Cupertino, Calif. In particular embodiments, the methods are used to form protective coatings for exterior metallic surfaces of computers, portable electronic devices and/or accessories for electronic devices. 
     These and other embodiments are discussed below with reference to  FIGS. 1-8 . 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. 
     Many consumer products are composite parts that include metal portions and non-metal sections. Forming these composite parts can involve any of a number of shaping, machining, molding and surface treatment processes. Residues, such as chemical residues, from these various manufacturing process can get caught within gaps between the metal and non-metal sections and remain within the gaps during subsequent anodizing and dyeing processes. In some cases, the residues include chemical agents used in chemical polishing (e.g., phosphoric acid) and/or agents from electrolytic processes (e.g., phosphoric acid and/or sulfuric acid). These trapped residues can be released out of the gaps during subsequent processes and cause visible defects in the part. For example, the residues can disrupt the intake of dye within a metal oxide layer in localized areas at the interface between the metal and non-metal sections of the part, causing visible defects along this interface. Methods described herein involve filling the gaps with a filler material prior to exposing the part to pre-anodizing processes, thereby preventing residues from entering the gaps. 
       FIGS. 1A-1F  show cross-section views of a portion of part  100  at various stages of a gap filling and anodizing process in accordance with described embodiments. At  FIG. 1A , part  100  includes anodizable section  102 . Anodizable section  102  includes an anodizable metal, such as aluminum and/or titanium. In some embodiments, anodizable section  102  includes a metal alloy of an anodizable metal, such as an aluminum alloy. Part  100  includes cut out section  104 , having a shape and size configured to accept a non-anodizable section using, for example, a molding process. Cut out section  104  can be formed using any suitable technique. For example, one or more machining processes can be used to form cut out section  104 . In some embodiments, part  100  is a portion of a housing for a consumer product, such as a housing for an electronic device. In some embodiments, surface  108  corresponds to an exterior surface of a housing. 
     At  FIG. 1B , filler layer  106  is deposited on a surface of part  100  corresponding to cut out section  104 . Filler layer  106  can be made of any material suitable for preventing material from entering within a gap formed between anodizable section  102  and a subsequently formed non-anodizable section. In some embodiments, filler layer  106  is made of a metal material, such as nickel and/or copper. Filler layer  106  can be deposited using any suitable technique. In some embodiments, filler layer  106  is deposited using a plating process. In some embodiments, surface  108  of part  100  is masked prior to forming filler layer  106  onto part  100 . After filler layer  106  is deposited, the mask can be removed. In other embodiments, filler layer  106  is initially deposited onto exposed surfaces of part  100 , including surface  108 . Then, portions of filler layer  106  on surface  108  are removed. 
     The inset view of  FIG. 1B  shows a close-up view of a portion of part  100 . As shown in the inset view, in some embodiments, filler layer  106  can include sub-layers. That is, filler layer  106  can include first layer  110 , directly deposited on anodizable section  102 , and second layer  112 , deposited on first layer  110 . In some embodiments, second layer  112  has a porous structure that includes pores  114 . In some embodiments, the average diameter of pores  114  is about 5 micrometers or greater. Pores  114  can engage with a subsequently deposited non-anodizable section, which will be described in detail below. In some embodiments, second layer  112  has a rough topology that includes a number of engagement surfaces that can also engage with a subsequently deposited non-anodizable section. In some embodiments, second layer  112  includes a rough topology and pores  114 . In some embodiments, first layer  110  is an electrolessly deposited metal, such as electrolessly deposited nickel. Any suitable electroless disposition process can be used. Electrolessly depositing generally provides a first layer  110  that adheres well to anodizable section  102  and gives first layer  110  a uniform thickness distribution. In some embodiments, second layer  112  is an electroplated metal. Any suitable electroplating process can be used. Electroplating generally provides a thicker layer of metal than electroless deposition. In some embodiments, second layer  112  is an electroplated porous nickel layer that includes pores  114 . The electroplating process conditions can be optimized to give second layer  112  a substantially uniform thickness. This way, a subsequently formed gap between anodizable section  102  and a subsequently formed non-anodizable section is uniform and cosmetically appealing. 
     The thicknesses of each of first layer  110  and second layer  112 , as well as the overall thickness of filler layer  106 , can vary depending on particular design requirements. First layer  110  deposited using electroless deposition is generally thinner than second layer  112  deposited using plating techniques. In some case, it is desirable that the thickness of filler layer  106  be thick enough to provide a wide enough space for sufficient cleaning during a post-anodizing cleaning process, which will be described in detail below. However, for cosmetic reasons, filler layer  106  should have a suitably small thickness variation such that resulting space between anodizable section  102  and an adjacent non-anodizable section has a consistent width. However, it can be difficult to form a very thick second layer  112  with small thickness variation using electroplating techniques. That is, the thicker second layer  112  is electroplated on, the more thickness variation second layer  112  will have. Thus, a balance between providing a filler layer  106  that is thick enough for sufficient cleaning during a post-anodizing cleaning process and thin enough such that filler layer  106  has a small thickness variation should be considered. As describe above, to minimize thickness variation of filler layer  106 , in some embodiments an electroless plating process (e.g., electroless nickel) can be used to deposit first layer  110 . Since there is no current in electroless plating, there is no current density variation across the part, which drives growth rate differences. In some embodiments, substantially all of filler layer  106  is deposited using electroless plating. In some embodiments, filler layer  106  has a thickness ranging from about 5 to 30 micrometers. In some embodiments, filler layer  106  has a thickness ranging from about 10 to 20 micrometers. Note that in some embodiments filler layer  106  is made of a single layer and not two layers, as shown in  FIG. 1B . In other embodiments, filler layer  106  includes three or more layers. 
     At  FIG. 1C , non-anodizable section  116  is incorporated into part  100 . Non-anodizable section  116  is generally made of a material that does not form an oxide layer when exposed to an anodizing process. Non-anodizable section  116  can correspond, for example, to a plastic, ceramic or glass portion of part  100 . In some embodiments, non-anodizable section  116  is made of a radio frequency transparent material (e.g., radio frequency transparent plastic) that allows radio frequency waves to pass there through. This can be useful in applications where part  100  corresponds to a housing for an electronic device having a radio frequency antenna and portions of the housing should allow for radio frequency communication to and/or from the radio frequency antenna. In some embodiments, non-anodizable section  116  is formed using a molding process wherein a molten material, such as melted plastic, is deposited within cut out section  104  and allowed to harden. In this way, non-anodizable section  116  can take on a shape corresponding to cut out section  104 . As shown in the inset view, in embodiments where second layer  112  has pores  114 , portions of non-anodizable section  116  can deposit within pores  114  of second layer  112 . After non-anodizable section  116  hardens, the portions of non-anodizable section  116  deposited within pores  114  engage with the side walls of pores  114 , thereby securing non-anodizable section  116  to second layer  112  and to anodizable section  102 . In addition, this can create a tight seal between non-anodizable section  116  and second layer  112  that helps prevent entrance of residues during subsequent manufacturing processes. Note that in embodiments where second layer  112  has a rough topology instead of or in addition to pores  114 , the engagement surfaces of the rough topology can also engage with non-anodizable section  116 . That is, non-anodizable section  116  engages with the engagement surfaces of second layer  112 . 
     In some embodiments, the type of material for non-anodizable section  116  is chosen, in part, based on the ability to flow and deposit within pores  114 . For example, plastics with lower viscosities will generally flow more easily within pores  114 . However, other factors such as durability should be taken into account when choosing the material for non-anodizable section  116 . In particular, lower viscosity plastics may flow more easily but may not provide sufficient durability when hardened compared to higher viscosity plastics. Thus, these considerations should be taken into account when choosing materials for non-anodizable section  116 . In some embodiments, pores  114  have a large enough average diameter to accommodate higher viscosity plastics. As described above, in some embodiments, pores  114  have an average diameter of about 5 micrometers or more. 
     After non-anodizable section  116  is incorporated into part  100  (e.g., plastic has hardened), part  100  can undergo one or more manufacturing processes. Filler layer  106  can prevent residues and other artifacts from these manufacturing processes from entering between anodizable section  102  and non-anodizable section  116 . Typical manufacturing processes can include shaping, machining and surface treatment processes. For example, surface  108  of anodizable section  102  and surface  118  of non-anodizable section  116  can be co-finished using a polishing process to form a continuous smooth surface for composite part  100 . In some cases, one or both of surfaces  108  and  118  are exposed to a texturing process, such as a blasting process. A masking process can be used to cover one or both of surface  108  and  118  during any of these surface finishing procedures, if suitable. 
     At  FIG. 1D , a portion of filler layer  106  is removed leaving gap  120  between anodizable section  102  and non-anodizable section  116 . In particular, a portion of filler layer  106  that is near exposed surfaces  108  and  118  is removed. In some embodiments, gap  120  corresponds to a channel that runs around a perimeter of anodizable section  102 . As shown, a portion of filler layer  106  remains within part  100  tightly securing non-anodizable section  116  to anodizable section  102 . In other embodiments, substantially all of filler layer  106  is removed. The amount of filler layer  106  removed and the depth  122  of gap  120  can depend on the removal technique and process parameters of the removal technique. As described above, the width  124  of gap  120  will depend on the thickness of filler layer  106 . 
     In embodiments wherein filler layer  106  includes a metal, an electrolytic process can be used to dissolve the removed portion of filler layer  106  into an electrolytic bath. In some embodiments, an electrolytic bath suitable for an anodizing process can be used. In a particular embodiment, a sulfuric acid electrolytic bath is used. In some embodiments, the electrolytic process includes using a relatively low applied voltage compared to a typical anodizing process. That is, the applied voltage is kept at a sufficiently high voltage for efficient removal of filler layer  106  but sufficiently low voltage to avoid anodizing of anodizable section  102  once filler layer  106  is removed. In some embodiments, the process parameters for electrolytically removing filler layer  106  are optimized for providing a gap  120  with a large and consistent depth  122 . Details regarding some electrolytic processes suitable for removing filler layer  106  are described below with reference to  FIG. 5 . 
     After a portion or all of filler layer  106  is removed, part  100  can optionally undergo one or more additional manufacturing processes. For example, one or more surface treatments, such as chemical polishing, can be performed after removal of filler layer  106 . If any residues become trapped within gap  120  during these additional manufacturing processes, they can be removed during a subsequent post-anodizing cleaning process that will be described below. In other embodiments, part  100  goes straight to an anodizing process without undergoing additional manufacturing processes. 
     At  FIG. 1E , part  100  is exposed to an anodizing process converting a surface portion of anodizable section  102  to metal oxide layer  126 . In some embodiments, surface  118  of non-anodizable section  116  is masked prior to exposure to the anodizing process in order to protect degradation of non-anodizable section  116 . In other embodiments, non-anodizable section  116  is made of a material sufficiently durable to withstand an anodizing process without degrading. Metal oxide layer  126  can provide a durable protective layer for anodizable section  102 . For example, if anodizable section  102  is made of aluminum or aluminum alloy, metal oxide layer  126  can correspond to a protective aluminum oxide layer. Anodizing generally provides a conformal metal oxide layer  126  having a consistent thickness. 
     As shown in the inset view, in some embodiments, metal oxide layer  126  does not fully fill the width  124  of gap  120 . That is, the thickness of metal oxide layer  126  can be less than the width  124  of gap  120 , forming space  128  between metal oxide layer  126  and non-anodizable section  116 . Note that in other embodiments, metal oxide layer  126  substantially fills gap  120  without forming a substantial space. The width of space  128  can depend on the thickness of metal oxide layer  126  and the width of gap  120 . As described above, controlling the thickness of which filler layer  106  is deposited can determine the width  124  of gap  120 . In some embodiments, a post-anodizing cleaning process is used to clean any further residue accumulated within space  128  prior to a dyeing process. The post-anodizing cleaning process can include, for example, exposing part  100  to an acidic solution that can chemically react with and cause the residues to dissolve in acidic solution. Thus, in some embodiments, space  128  can be designed to be sufficiently wide in order to provide thorough cleaning of space  128  during the post-anodizing cleaning process. Thus, the processes described above can be used to create a junction region or interface region  129  between anodizable section  102  and non-anodizable section  116  will have a consistent width. In addition, metal oxide layer  126  will be substantially free of visible defects. 
     At  FIG. 1F , part  100  is optionally exposed to a dyeing process wherein one or more dyes are infused within metal oxide layer  126 . As a result, metal oxide layer  126  takes on a color corresponding to the dye/dyes. Substantially no residues will remain on or within metal oxide layer  126  at region  130  proximate non-anodizable section  116  that can inhibit the uptake of dye within metal oxide layer  126 . Thus, region  130  will have a consistent color and be substantially free of visible defects. 
     In some cases, a part includes two or more non-anodizable sections.  FIGS. 2A-2G  show cross-section views of a portion of part  200 , which includes two non-anodizable sections, at various stages of a gap filling and anodizing process in accordance with described embodiments. At  FIG. 2A , opening  204  is formed within anodizable section  202 . In some embodiments, part  200  is a metal housing with exterior surfaces  206  and opening  204  corresponds to a channel that runs along perimeters of metal portions of the housing. Opening  204  can be formed using any suitable process, including one or more machining, molding and shaping processes. Anodizable section  202  includes interlock features  208  that can help secure a subsequently formed non-anodizable section within opening  204 . Interlock features  208  can have any suitable shapes. In some embodiments, interlock features  208  have tapered edges such that a subsequently formed non-anodizable section can engage with interlock features  208  in a dovetail design. In some embodiments, interlock features  208  have an undercut shape. According to some embodiments, a key criterion as to the shape of features  208  is that they can be completely filled by a subsequently formed non-anodizable section using, for example, an injection molding process. This can prevent forming difficult to clean voids where residues can be trapped. 
     At  FIG. 2B , first non-anodizable section  210  is formed within opening  204 . As shown, first non-anodizable section  210  does not fully fill opening  204 , but instead fills the bottom portion of opening  204 . First non-anodizable section  210  can be made of any suitable material including plastic, glass and/or ceramic. In some applications, non-anodizable section  210  is made of a radio frequency transparent material (e.g., radio frequency transparent plastic) that allows radio frequency waves to pass there through to and/or from a radio frequency antenna. First non-anodizable section  210  can act as a structurally supportive portion within opening  204 . Thus, in some embodiments, first non-anodizable section  210  can be made of a structurally rigid material such as a hard plastic. First non-anodizable section  210  can be formed using any suitable method. In some embodiments, first non-anodizable section  210  is molded while in molten form within opening  204  and allowed to harden, securing first non-anodizable section  210  to anodizable section  202 . 
     At  FIG. 2C , filler layer  212  is deposited on anodizable section  202  along internal surfaces of opening  204 . As described above with reference to part  100 , filler layer  212  can be made of any material suitable for preventing material from entering within a gap formed between anodizable section  202  and a subsequently formed second non-anodizable section. In some embodiments, filler layer  212  is made of a metal material, such as nickel and/or copper and is deposited using plating techniques. In some embodiments, filler layer  212  includes two or more sub-layers. For example, filler layer  212  can include a first layer that is a thin conformal and uniform layer that is deposited electrolessly and a second layer that is a bulk metal layer that is deposited using electroplating techniques. The second layer can have a porous structure that provides engagement surfaces for a subsequently deposited second non-anodizable section to engage with. In some embodiments, surface  206  of part  200  is masked prior to forming filler layer  212 . After filler layer  212  is deposited, the mask can be removed exposing surface  206 . In other embodiments, filler layer  212  is initially deposited onto exposed surfaces of part  100 , including surface  206 . Then, portions of filler layer  212  on surface  206  are removed. 
     At  FIG. 2D , second non-anodizable section  214  is deposited into opening  204  and incorporated into part  200 . Second non-anodizable section  214  can be made of any suitable material including plastic, glass and/or ceramic. In some embodiments, top surface  216  corresponds to an exterior surface of part  200 . Thus, in some embodiments, second non-anodizable section  214  acts as a cosmetic portion of the part and does not necessarily have the structural properties of first non-anodizable section  210 . For example, second non-anodizable section  214  can be made of a less rigid but more aesthetically appealing plastic material than first non-anodizable section  210 . Second non-anodizable section  214  can be formed using any suitable method, including molding of second non-anodizable section  214  while in molten form within opening  204  and on top of first non-anodizable section  210 . Portions of second non-anodizable section  214  can mold within and conform to the shape of interlock features  208 , thereby securing second non-anodizable section  214  to part  200 . In embodiments where filler layer  212  includes a porous structure, portions of second non-anodizable section  214  can deposit within the pores of filler layer  212 , similar to shown in  FIG. 1C . This can further secure second non-anodizable section  214  to part  200 . In addition, this creates a tight seal between second non-anodizable section  214  and filler layer  212 , thereby assuring that residues will not enter between second non-anodizable section  214  and filler layer  212 . 
     After second non-anodizable section  214  is hardened, part  200  can undergo one or more manufacturing processes. Filler layer  212  can prevent residues and other artifacts from these manufacturing processes from entering between anodizable section  202  and second non-anodizable section  214 . Typical manufacturing processes can include shaping, machining and surface treatment processes. For example, surface  206  of anodizable section  202  and surface  216  of second non-anodizable section  214  can be co-finished using a polishing process to form a continuous smooth surface for composite part  200 . Other surface treatment processes can include a texturing process, such as a blasting process. 
     At  FIG. 2E , a portion of filler layer  212  is removed leaving gaps  218  between anodizable section  202  and second non-anodizable section  214 . In particular, a portion of filler layer  212  that is near exposed surfaces  206  and  216  is removed. In the embodiment shown in  FIG. 2E , a portion of filler layer  212  remains within part  200 . This can help tightly secure second non-anodizable section  214  to part  200 . In other embodiments, substantially all of filler layer  212  is removed. The amount of filler layer  212  removed, i.e., the depth of gap  218 , can depend upon the removal technique and process parameters. The width of gap  218  will depend on the thickness of filler layer  212 . In embodiments wherein filler layer  212  includes a metal, an electrolytic process can be used to dissolve the removed portion of filler layer  212  into an electrolytic bath. Details of some electrolytic processes suitable for removing filler layer  106  are described below with reference to  FIG. 5 . After a portion or all of filler layer  212  is removed and gap  218  is formed, part  100  can optionally undergo one or more additional manufacturing processes. For example, one or more surface treatments, such as chemical polishing, can be performed. 
     At  FIG. 2F , part  200  is exposed to an anodizing process converting a surface portion of anodizable section  202  to metal oxide layer  220 . In some embodiments, metal oxide layer  220  substantially fills gap  218 . In other embodiments, metal oxide layer  220  does not fully fill gap  218 , and instead, leaves a space between metal oxide layer  220  and second non-anodizable section  214 , similar to space  128  shown in  FIG. 1E . As described above, controlling the thickness metal oxide layer  220  and/or the thickness of filler layer  212  can control the width of the space between metal oxide layer  220  and second non-anodizable section  214 . In some embodiments, a post-anodizing cleaning process is used to clean any further residue accumulated within this space prior to a dyeing process. The post-anodizing cleaning process can include, for example, exposing part  200  to an acidic solution. 
     At  FIG. 2G , part  200  is exposed to a dyeing process where one or more dyes are infused within metal oxide layer  126 . Substantially no residues will remain on or within metal oxide layer  220  at regions  222  proximate second non-anodizable section  214  that can inhibit the dyeing of metal oxide layer  220 . Thus, regions  222  will have a consistent color and be substantially free of visible defects. 
       FIG. 3  shows high-level flowchart  300  indicating a gap filling and anodizing process in accordance with described embodiments. At  302 , a filler layer is deposited on a surface of an anodizable section of a part. The anodizable section generally includes a material that forms a metal oxide film when exposed to an anodizing process. Suitable anodizable materials include aluminum, titanium and combinations thereof. In some embodiments, the filler layer includes a metal that is deposited using one or more plating processes. In particular embodiments, the filler layer is made of nickel and/or copper. The choice of filler layer material can depend, in part, on the chemical resistance of the material. For example, in some embodiments, nickel is found to be more chemically resistant to some surface treatment processes compared to copper. As described above, the thickness of the filler layer defines a width of a gap between the anodizable section and a subsequently formed non-anodizable section of the part. Thus, one can control the width of the gap by controlling the thickness of the filler layer. The filler layer can also protect the surface of the anodizable section during manufacturing processes, such as surface treatment and machining processes. When the filler layer is removed, a fresh surface of the anodizable section is provided for an anodizing process. 
     In some embodiments, the filler layer includes sub-layers. For example, the filler layer can include a thin electrolessly deposited first layer (e.g., electroless nickel layer) that adheres well to the anodizable section and has a conformal and uniform thickness. The filler layer can also include electrolytically deposited porous second layer (e.g., porous nickel layer) that makes up the bulk of the filler layer. A metal filler layer depositing process that includes a first layer and second layer is described in detail below with reference to  FIG. 4 . Using a metal filler layer with these multiple layers can provide at least two benefits: 1) when removed, it can help create a consistent gap for effective cleaning after anodizing, and 2) it can improve adhesion of the non-anodizable and anodizable sections of the part. 
     At  304 , a non-anodizable section of the part is formed such that the filler layer fills a gap between the anodizable section and the non-anodizable section. The non-anodizable section generally includes a material that does not form a metal oxide film when exposed to an anodizing process. Suitable non-anodizable materials include plastic, ceramic, glass and combinations thereof. In some embodiments, the non-anodizable section is formed by molding a non-anodizable material in molten form onto a surface of the filler layer. In some embodiments, portions of the molten non-anodizable material deposit within pores of the porous bulk layer. Once hardened, the non-anodizable material engages with the porous bulk layer securing the non-anodizable section to the filler layer and to the part. 
     At  306 , the part is exposed to one or more manufacturing processes. The manufacturing processes can include a surface treatment process and/or a machining process. In some embodiments, a surface of the anodizable section and a surface of the non-anodizable section are co-finished. For example, a polishing process can be used to polish surfaces of both the anodizable and non-anodizable sections. Some of these finishing treatments include slurries and other chemicals that can get trapped in gaps and crevices of the part. The filler layer prevents residues from the surface treatment and/or other manufacturing processes from entering the gap between the anodizable and non-anodizable sections. 
     At  308 , at least a portion of the filler layer is removed, exposing a surface of the anodizable section within the gap. The process for removal of the filler layer will depend, in part, on the type of material of the filler layer. In some embodiments where the filler layer is made of metal, an electrolytic removal process is used. During the electrolytic removal process, a voltage is applied to the part and a portion of the metal filler layer dissolves within an electrolytic bath. In some embodiments, the electrolytic process involves using a bath suitable for an anodizing process, such as a sulfuric acid or phosphoric acid bath. The electrolytic process can involve applying a relatively low voltage (compared to anodizing) to the part such that the filler layer is removed without substantially anodizing the part. The electrolytic process can be optimized to provide a gap having a large and consistent depth. Details of factors involved in optimizing an electrolytic metal filler layer removal process are described below with reference to  FIG. 5 . In some embodiments, the electrolytic removal process for removing a nickel filler layer includes using a voltage of about 6 V or less. In some embodiments, a voltage between about 1 V and 6 V is used. 
     At  310 , the part is optionally exposed to one or more manufacturing processes. For example, one or more surface treatments, such as chemical polishing, can be performed. Any residues trapped within gap can be removed during a subsequent post-anodizing cleaning process. In other embodiments, part goes straight to an anodizing process without undergoing additional manufacturing processes. 
     At  312 , a portion of the exposed anodizable section is converted to a metal oxide layer using an anodizing process. In some embodiments, the anodizing process is performed in the same electrolytic bath as the filler layer removal process at  308 . In other embodiments, the anodizing process is performed in a different bath than the filler layer removal process at  308 . In some embodiments, the portion of the metal oxide layer formed within the gap has a thickness that is less than the width of the gap, thereby forming a space between the metal oxide layer and the non-anodizable section. The width of this space can be designed to be narrow enough to provide a cosmetically appealing interface between the anodizable and non-anodizable sections of the part but wide enough to allow for efficient cleaning during a subsequent post-anodizing cleaning process. 
     At  314 , the space between the anodizable and non-anodizable sections is optionally cleaning using a post-anodizing cleaning process. In some embodiments, the post-anodizing cleaning process involves exposing the part to an acidic solution for a sufficient time to dissolve any remaining residues trapped within the space between the anodizable and non-anodizable sections. In a particular embodiment, the part is exposed to an acidic solution for a time period ranging from about 5 minutes to about 40 minutes. At  316 , the metal oxide layer is optionally dyed using a dyeing process. Any suitable dye or combination of dyes can be used, including one or more organic, inorganic and/or metal dyes. The metal oxide layer takes on a color corresponding to the dye/dyes. The resulting part will have clean, visible defect-free and cosmetically attractive interface between the anodizable and non-anodizable sections. 
       FIG. 4  shows flowchart  400  indicating a process for forming a metal filler layer having two sub-layers, in accordance with described embodiments. At  402 , a first layer of the metal filler layer is deposited on a surface of an anodizable section of a part. In some embodiments, the first layer is made of nickel, copper or a combination thereof. In some embodiments, the first layer is deposited using an electroless deposition process. Electroless deposition generally relies on chemical reactions at the surface of the substrate (anodizable section) in contrast to electroplating, which relies on electric current through an electrolyte in order to deposit material on a substrate. Electroless deposition generally forms a well-adhered thin conformal metal layer that generally has a more uniform thickness compared to a metal layer formed using electroplating. 
     At  404 , a second layer of the metal filler layer is deposited on a surface of the first layer. In some embodiments, the second layer is made of nickel, copper or a combination thereof. In some embodiments, the second layer is deposited using an electroplating process. Electroplating can generally form a thicker layer than electroless deposition. Thus, in some embodiments, the second layer has a greater average thickness than the first layer. The second layer can be plated to a large enough thickness to provide a large enough space for post-anodizing cleaning, described above. However, it can be difficult to form uniform metal layer using electroplating. The thicker the metal layer, the greater the thickness variation. Too much thickness variation will result in a gap that is uneven and cosmetically unappealing. Thus, in some embodiments, the second layer is deposited to a small enough thickness to provide a second layer with a sufficiently cosmetically appealing uniform thickness. 
     In some embodiments, the second layer has a porous structure in order to enhance adhesion to a subsequently deposited non-anodizable section of the part. Process conditions for forming the filler layer can vary depending on a number of factors including the material of the filler layer, size of the part and desired thickness and porosity. In some embodiments, process conditions for plating a porous second layer are tuned such that the porous second layer has an average pore size sufficient for accepting portions of a particular material of the non-anodizable section. In some embodiments, the average pore size is about 5 micrometers or greater. In particular embodiments, plating of a porous nickel layer includes using a current density ranging from about 0.5 A/dm 2  to about 8 A/dm 2 , a plating bath temperature ranging from about 35 degrees C. to about 55 degrees C., and a nickel concentration ranging from about 100 g/L to about 500 g/L. 
     At  406 , a non-anodizable section of the part is deposited on the second layer. In embodiments where the second layer is porous, portions of the non-anodizable section deposit within the pores of the second layer and engage with the pore walls, thereby securing the non-anodizable section to the part. In addition, having the non-anodizable section so securely adhered to the second layer can assure that residues from subsequent manufacturing processes do not enter between the non-anodizable section and the second layer. These aspects are as described above in detail with reference to  FIGS. 1B and 1C . 
     As described above, in some embodiments the filler layer is a metal filler layer that can be removed using an electrolytic process. Process parameters for the electrolytic metal filler layer removal process can be tuned to control the amount of metal removed and the depth of the resulting gap.  FIG. 5  shows graph  500  illustrating voltage and current density changes during an electrolytic metal filler layer removal process in accordance with described embodiments. Graph  500  shows removal of a metal filler layer that includes an electrolessly deposited first metal layer and a electrolytically deposited bulk second metal layer, as described above in some embodiments. The voltage during the removal process corresponds to the amount of voltage from the power supply that is applied to the part. The current density corresponds to the amount of current per area of the part (typically measured in A/dm 2 ). Graph  500  shows a current density curve indicating relative changes in current density over the electrolytic process, shown as a thin line. Graph  500  also shows a voltage curve indicating relative changes in applied voltage over the electrolytic process, shown as a thick line. 
     Graph  500  shows time period  502  (from time t 1  to time t 3 ) corresponding to dissolving of the bulk second metal layer, followed by time period  504  (from time t 3  to time t 5 ) corresponding to dissolving of the electrolessly deposited first metal layer. During time period  502 , the current density increases when voltage is applied at t 1  and reaches a peak at t 2 . During the time period between t 1  and t 2  the majority of the bulk second metal layer is removed. From time t 2  to t 3 , the current density decreases as the bulk second metal layer get thinner and resistance increases. Finally at t 3  the second metal layer is completely dissolved within electrolytic bath. During time t 3  to t 4 , the current density remains substantially constant as the majority of the electrolytically deposited first metal layer is dissolved. From time t 4  to t 5 , the current density decreases as the first metal layer gets thinner and resistance increases. Finally at t 5  the electrolytically deposited first metal layer is completely dissolved within the electrolytic bath. At t 6 , the voltage is increased and the current density also increases as anodizing begins and the metal substrate starts to convert to metal oxide. 
     During time periods  502  and  504 , corresponding to the removal of the first and second metal layers, the applied voltage is kept substantially constant. The voltage is also kept relatively low compared to the voltage at t 6  when anodizing begins. Note that in some embodiments, the voltage can be increased and decreased during the time periods  502  and  504 ; however, the voltage will preferably remain relatively low compared to the voltage applied at t 6 . Thus, an electrolytic removal process can be designed for applying a high enough voltage to efficiently remove the first and second metal layers and low enough to substantially avoid the start of anodizing. In some embodiments where the first layer is an electrolessly deposited nickel layer and the second layer is an electrolytically deposited porous nickel layer, the voltage during removal of the first and second metal layers (time periods  502  and  504 ) is kept below about 6 V. In some embodiments, the voltage is kept below about 3 V. In some embodiments, the voltage is kept between about 1 V and 6 V. In some embodiments, the voltage at t 6 , corresponding to the start of anodizing, is increased to about 15 V or higher. 
     The anodizing process can occur in the same electrolytic bath or in a different electrolytic bath than the electrolytic metal filler layer removal process. That is, in some embodiments, after the first and second metal layers are dissolved, the part is transferred to a second electrolytic bath for anodizing. This can prevent particles from the electrolytic metal filler layer removal process from disrupting the anodizing process and creating defects within the resultant metal oxide layer. In some embodiments, the part is transferred to an intermediate bath after the electrolytic metal layer removal bath and prior to transferring into the anodizing bath. This intermediate bath can remove particles on the surface of the part accumulated from the electrolytic metal layer removal process. As described above, in some embodiments, the part undergoes a surface treatment process, such as a chemical polishing or degreasing process, between the electrolytic metal layer removal bath and the anodizing bath. In some embodiments, the part is prevented from being exposed to solutions capable of oxidizing the metal substrate (anodizable section) after the metal filler layer is removed. In some embodiments, the part is transferred between baths in an inert environment, such as a nitrogen or argon environment. 
     According to some embodiments, a boundary layer is formed on surfaces of an anodizable section of a part that a non-anodizable section is molded onto. This boundary layer can act as a corrosion barrier that prevents corrosion products from developing within gaps between the anodizable and non-anodizable sections. To illustrate,  FIGS. 6A-6F  show cross-section views of a portion of part  600  at various stages of a process that includes formation of a boundary layer, in accordance with some embodiments. At  6 A, opening  604  is formed within anodizable section  602 . Anodizable section  602  includes an anodizable metal, such as aluminum and/or titanium. In some embodiments, anodizable section  602  is made of an aluminum alloy. In some embodiments, part  600  is a housing with exterior surfaces  606  and opening  604  corresponds to a channel that runs along perimeters of metal portions of the housing. 
     Opening  604  can be formed using any suitable process, including one or more machining, molding and shaping processes. Anodizable section  602  includes interlock features  608  that are designed to secure a subsequently formed non-anodizable section within opening  604 . Interlock features  608  can have any suitable shapes, such as those having tapered edges so the subsequently formed non-anodizable section can engage with interlock features  608  in a dovetail manner. In some embodiments, interlock features  608  have an undercut shape. According to some embodiments, the shape of interlock features  608  are optimized so that they can be completely filled by the subsequently formed non-anodizable section without substantially any voids that can trap residues. Some of these shapes are described in detail below with reference to  FIGS. 7A-7E . 
     At  FIG. 6B , boundary layer  610  is formed on surfaces of anodizable section  602 . In some embodiments, first portion  610   a  of boundary layer  610  is formed on internal surfaces of opening  604  and second portion  610   b  of boundary layer  610  is formed on exterior surfaces  606 . Boundary layer  610  acts as a barrier in that it that keeps residues from one of more subsequent manufacturing processes from reaching anodizable section  602  and causing anodizable section  602  to corrode. This prevents any corrosion products from forming at an interface between anodizable section  602  and a subsequently formed non-anodizable section. As described above, corrosion products can get trapped between anodizable section  602  and a subsequently formed non-anodizable section, which can ultimately disrupt the intake of an anodizing dye and create visible defects in part  600 . 
     In some embodiments, boundary layer  610  is a substantially uniformly thick layer that conforms with and preserves surface features of anodizable section  602 . In one embodiment, boundary layer  610  is a metal oxide layer that is formed by anodizing anodizable section  602 . Any suitable type of anodizing process can be used. The anodizing process should form a metal oxide layer that is adequately thick to protect anodizable section  602  from exposure to chemicals during the one or more subsequent process that can corrode anodizable section  602 . In some cases, the one or more subsequent processes involve exposure of boundary layer  610  to chemicals and/or mechanical abrasion that can erode some or boundary layer  610 . This means boundary layer  610  should be relatively thick and/or robust so as to prevent exposure of anodizable section  602 , even if some of boundary layer  610  is worn away. In a particular embodiment, boundary layer  610  has a thickness ranging from about 18 micrometers and about 20 micrometers. Boundary layer  610  is generally not used for cosmetic purposes since a majority or all of the visible portion (second portion  610   b ) will be removed during a subsequent removal process. Therefore, boundary layer  610  is typically not dyed or polished. In some embodiments, boundary layer  610  is sealed using an anodic sealing process to make boundary layer  610  less porous and susceptible to damage, thereby improving the erosion resistance of boundary layer  610  and protection of anodizable section  602 . 
     In some embodiments, boundary layer  610  is an electrocoating (e-coating). E-coating generally involves the use of electric current to deposit a paint or coating onto a part. The e-coating process can involve placing part  600  in a solution having a suspended coating material and applying a voltage to the solution so that the coating material adheres onto surfaces of part  600 . In some cases part  600  is then heated or baked after the coating process is complete. In some embodiments, the coating material is a polymer material, such as a urethane material. One difference between a boundary layer  610  made of a polymer e-coat material versus a metal oxide material is that a polymer e-coating can be made of a compliant polymer that is less brittle than a metal oxide material. A compliant polymer e-coating can be less susceptible to chipping damage during, for example, a subsequent machining process of part  600 . After boundary layer  610  is deposited, part  600  can optionally undergo one or more manufacturing processes, such as one or more machining, shaping and finishing processes. Boundary layer  610  prevents exposure of anodizable section  602 , thereby preventing formation of any corrosion products related to the exposure of anodizable section  602  to corrosive chemical agents. 
     At  FIG. 6C , non-anodizable section  612  is deposited into opening  604  making part  600  a composite part. Non-anodizable section  612  is deposited onto surfaces of first portion  610   a  of boundary layer  610  and defines a border or boundary of anodizable section  602 . Non-anodizable section  612  can be made of any suitable material including plastic, glass and/or ceramic. In some applications, part  600  corresponds to a housing for an electronic device and non-anodizable section  612  is made of a radio frequency transparent material (e.g., radio transparent frequency plastic) so that radio frequency waves can pass to and/or from an antenna positioned within the housing. In some cases non-anodizable section  612  is molded into opening  604  using, for example, an injection molding process. In some embodiments, non-anodizable section  612  acts as a cosmetic portion of part  600  in that non-anodizable section  612  corresponds to a visible portion of part  600 . In some embodiments, part  600  also includes piece  614 , which can be another non-anodizable section made of plastic, glass and/or ceramic. Piece  614  can act as a structural support to non-anodizable section  612  and therefore can be made of a more rigid material than non-anodizable section  612 , such as a hard plastic. In some embodiments, piece  614  is also radio frequency transparent. Piece  614  can be formed using any suitable method, such as a molding process. 
     Since boundary layer  610  covers anodizable section  602 , non-anodizable section  612  is deposited onto surfaces of boundary layer  610 . Thus, boundary layer  610  is sandwiched between anodizable section  602  and non-anodizable section  612 . Boundary layer  610  prevents exposure of anodizable section  602  to chemical agents during the depositing of non-anodizable section  612  that may cause formation of corrosion products. As non-anodizable section  612  is deposited within opening  604 , portions of non-anodizable section  612  are deposited within and engage with interlock features  608 , thereby securing non-anodizable section  612  to anodizable section  602 . This can keep non-anodizable section  612  from being dislodged from opening  604  and falling out of part  600  when part  600  is manipulated or inverted. In some embodiments, the shapes of interlock features  608  are designed to minimize or eliminate formation of voids between non-anodizable section  612  and anodizable section  602 . Other interlock feature shapes are described below with reference to  FIGS. 7A-7E . 
     After non-anodizable section  612  is deposited and sufficiently hardened, part  600  can undergo one or more shaping processes.  FIG. 6D  shows part  600  after a portion of boundary layer  610  is removed. In particular, second portion  610   b  of boundary layer  610  is removed, resulting in part  600  having exposed surfaces  616  and  618 . This can be accomplished using a machining process whereby second portion  610   b  and some of non-anodizable section  612  are cut off. In some cases, some of anodizable section  602  is also cut off. In some embodiments, surfaces  616  and  618  are co-finished using a polishing process to form a continuous smooth exterior surface for composite part  600 . Other surface treatment processes can include a texturing process, such as a blasting process. 
     In some embodiments, the one or more machining, polishing and other operations after forming non-anodizable section  612  can be optimized to prevent entrapment of chemicals and other residues from forming on part  600  and within crevices/gaps of part  600 , such as at interface region or junction region  620  between anodizable section  602  and non-anodizable section  612 . The one or more machining, polishing and other operations can also be optimized to assure that boundary layer  610  doesn&#39;t get damaged since such damage could cause corrosion of anodizable section  602 , which can leach into junction region  620 . For example, if a machining process is too aggressive, corners of boundary layer  610  can experience chipping or other damage. Thus, the machining process can be optimized to minimize potential chipping while still providing a predetermined surface quality, such as a predetermined amount of polish or texture (e.g., blasted texture) for surfaces  616  and/or  618 . It should be noted that any of the processes described above with respect to  FIGS. 6A-6D  can be adjusted and optimized to prevent formation of corrosion products and other residues at junction region  620  in order to provide an acceptable mass production yield of composite part  600 . 
     After non-anodizable section  612  is formed and composite part  600  is machined or otherwise processed, part  600  can be cleaned using one or more cleaning processes to remove any residues that may have formed on part  600 , and particularly at junction region  620 . Note that part  600  can also be cleaned after any of the processes described above with respect to  FIGS. 6A-6C  in order to provide an acceptable mass production yield of composite part  600 . 
     At  FIG. 6E , part  600  is exposed to an anodizing process converting exposed surface portions of anodizable section  602  to metal oxide layer  622 . In some embodiments, surface  618  of non-anodizable section  612  is masked prior to exposure to the anodizing process in order to protect degradation of non-anodizable section  612 . In other embodiments, non-anodizable section  612  is made of a material sufficiently durable to withstand an anodizing process without degrading. Metal oxide layer  622  can provide a durable protective layer for anodizable section  602 . For example, if anodizable section  602  is made of aluminum or aluminum alloy, metal oxide layer  622  can correspond to a protective aluminum oxide layer. The thickness of metal oxide layer  622  can vary depending on application requirements. In some embodiments, metal oxide layer  622  has a thickness ranging between about 8 micrometers and about 10 micrometers. 
     After metal oxide layer  622  is formed, it may be important to clean part  600  to remove any residues, especially prior to an anodic dyeing process to make sure there are no chemicals or other residues that could disrupt the uptake of the dye. In some embodiments, this involves rinsing part  600  in a series of acidic solutions, such as sulfonic acid solutions. In some embodiments, ultrasonic vibration is applied to one or more of the acidic solutions to provide extra cleaning action. In some embodiments, part  600  is rinsed in water between each of the acidic solution cleanings. In some embodiments, part  600  is additionally exposed to a desmutting solution, such as a nitric acid solution, to provide a cleaning solution that has a different viscosity than a sulfonic acid solution, which can help remove residues within crevices of part  600 . 
     At  FIG. 6F , part  600  is optionally exposed to a dyeing process where one or more dyes are infused within metal oxide layer  622 . As a result, metal oxide layer  622  takes on a color corresponding to the dye/dyes. Since processes described above have been optimized to eliminate the presence of residues (e.g., corrosion products) at junction region  620 , metal oxide layer  622  is clean enough to evenly uptake the dye/dyes. Thus part  600  has consistent color and is substantially free of visible defects, including at junction region  620 . In addition, since boundary layer is substantially uniform in thickness, boundary layer provides a consistent and uniform border for anodizable section  602 , giving part  600  clean and consistent lines. 
     As described above, interlock features  608  are shaped to secure non-anodizable section  612  with anodizable section  602 . In some cases interlock features  608  have a dovetail design or an undercut design. In some embodiments, the shapes of the interlock features can be optimized to prevent formation of voids when a non-anodizable section is deposited within the interlock features.  FIGS. 7A-7E  show cross-section views of portions of anodizable sections having different shaped interlock features, in accordance with some embodiments. The shapes of interlocking features shown in  FIGS. 7A-7E  are exemplary and not meant to limit a size and shape of other possible shapes within the scope of the present disclosure. 
       FIG. 7A  shows anodizable section  702  having interlock feature  704 . A conformal boundary layer can be formed on surfaces of anodizable section  702 , including on surfaces of interlock feature  704 . A subsequently deposited non-anodizable section can then be deposited on the boundary layer. Interlock feature  704  has a cross-section that includes surfaces that meet at corners  706 . Note that corners  706  have angles that have lower aspect ratios (i.e. shallower) than the corners of interlock features  608  described above with respect to  FIGS. 6A-6F . That is, the surfaces of corners  706  have less acute angles compared to interlock features  608  described above. In some embodiments, angles  706  of interlock feature  704  are less than or equal to about 90 degrees. This way, the shape of interlock feature  704  more closely matches a shape or radius of the non-anodizable section as it is being deposited (e.g., injection molded) within interlock feature  704 . This will assure that the non-anodizable section will completely fill interlock feature  704  without forming voids between the non-anodizable section and the boundary layer where corrosion products and/or other residues can become trapped. Chemicals and other residues trapped within such voids can be difficult to clean out and can travel up to the junction region between the anodizable section and the non-anodizable section causing the visible defects described above. However, interlock feature  704  should still have a high enough aspect ratio to allow for a subsequently formed boundary layer to adequate engage with a non-anodizable section. 
       FIG. 7B  shows another embodiment of an interlock feature  710  formed within anodizable section  708 . Interlock feature  710  also has a low aspect ratio but has a different shape than interlock feature  704 . In some embodiments, angles  712  are less than or equal to about 90 degrees. In some embodiments, the interlock features have curved surfaces.  FIG. 7C  shows anodizable section  714  with interlock feature  716 , which has a curved surface.  FIG. 7D  shows anodizable section  718  with interlock feature  720 , which has a curved surface in a different arrangement than the curved surface of interlock feature  716 .  FIG. 7E  shows anodizable section  722  with interlock feature  724 , which has a curved surface having a different shape than the curved surfaces of interlock feature  716  and interlock feature  720 . In particular, interlock feature  724  has a symmetrical cross-section curved shaped surface. 
     The interlock features of  FIGS. 7A-7E  can be formed using any suitable method, including any suitable machining process. In other embodiments, the interlock features are in the form of protrusions rather than recesses within an anodizable section. The shape of the protrusions can likewise be optimized to prevent formation of voids where chemicals and other residues can become entrapped. In some cases the interlock features include a combination of recesses and protrusions. 
       FIG. 8  shows flowchart  800  indicating a process for forming a composite part using a boundary layer in accordance with embodiments described above with reference to  FIGS. 6A-6F  and  7 A- 7 E. At  802  a boundary layer is formed on a surface of an anodizable section of a part. The boundary layer prevents exposure of the anodizable section to one or more chemical agents that can cause the anodizable section to form corrosion products. In some embodiments, the boundary layer is a metal oxide layer formed using an anodizing process. In some embodiments, the boundary layer is an e-coating, such as a polymer layer deposited using an e-coating process. The boundary layer should be thick enough to prevent exposure of the anodizable section during subsequent manufacturing processes. The thickness of the boundary layer can define a width of a gap between the anodizable section and a subsequently formed non-anodizable section of the part. 
     At  804 , the composite part is formed by depositing a non-anodizable section on a surface of the boundary layer. The non-anodizable section generally includes a material that does not form a metal oxide film when exposed to an anodizing process, such as plastic, ceramic, glass or combinations thereof. In some embodiments, the non-anodizable section is deposited by molding a non-anodizable material in molten form onto the surface of the boundary layer. In some embodiments, the anodizable section has one or more interlock features that have surfaces that engage with the non-anodizable section. The interlock features can be in from of recesses, protrusion or a combination of recesses and protrusions. The interlock features can have surface geometries that are designed to prevent formation of voids when the non-anodizable section is deposited within the interlock features. For example, the interlock features can have a low aspect ratio cross-section. This way, substantially all surfaces of the boundary layer that formed within interlock feature  704  will be engaged with the non-anodizable section. 
     At  806 , a portion of the boundary layer is removed exposing a surface of the anodizable section. In some embodiments this involves co-machining the anodizable section and the non-anodizable section. At  808 , the machined surface of the part is optionally finished using one or more of a polishing or texturing process (e.g., blasting or etching). In some embodiments, a surface of the anodizable section and a surface of the non-anodizable section are co-finished. 
     At  810 , a metal oxide layer is formed on the exposed anodizable section. In some applications, the metal oxide layer corresponds to a protective and cosmetic exterior coating for the part. The thickness and the nature of the metal oxide layer can vary depending on application needs. At  812 , the part is cleaned to remove any residues, such as chemicals and/or particles that formed during one or more of the processes  802 - 810  described above. In some cases the cleaning involves exposing the part to a series of different cleaning solutions (e.g., sulfonic and nitric acid solutions) and rinsing solutions (e.g., water). In some embodiments, sonic vibration (e.g., ultrasonic vibration) is applied to the cleaning and/or rinsing solutions to provide a cleaning action to the solution and assure thorough cleaning of the part. 
     At  814 , the metal oxide layer is optionally dyed and/or polished. Any suitable dye or combination of dyes can be used, including one or more organic, inorganic and/or metal dyes. The polishing can be chosen to provide a polished and attractive exterior surface to one or both of the anodizable section and the non-anodizable section. The resulting composite part has clean and visible defect-free cosmetic surface. In addition, the gap or space between the anodizable section and the non-anodizable section is consistent and uniform. Note that one or all of the processes  802 - 814  described above can be optimized to reduce or eliminate formation of residues, such as corrosion products. Additionally, one or more cleaning and/or rinsing processes can be implemented between any two of the processes  802 - 814  in order to assure elimination of such residues. 
     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: 20141229
Publication Date: 20160308
Grant Date: 20160308
Priority Date: 20140505
Inventors: BROWNING LUCY ELIZABETH
TATEBE MASASHIGE
ZHANG SHI HUA
BARNSTEAD MICHAEL W.
BRETHERTON RICHARD M.
OSHIMA TAKAHIRO
BACKS SEAN A.
LE DUY P.
MESCHKE ANDREW J.
JOHANNESSEN THOMAS
Assignee: APPLE INC
CPC Classifications: [{"code": "Y10T428/31678", "inventive": false, "first": false, "tree": "[]"}, {"code": "Y10T428/24033", "inventive": false, "first": false, "tree": "[]"}, {"code": "C25D5/022", "inventive": true, "first": true, "tree": "[]"}, {"code": "H05K5/04", "inventive": true, "first": false, "tree": "[]"}, {"code": "C25D5/022", "inventive": true, "first": true, "tree": "[]"}, {"code": "C25D5/022", "inventive": true, "first": true, "tree": "[]"}, {"code": "C23C18/32", "inventive": false, "first": false, "tree": "[]"}, {"code": "C23C18/1605", "inventive": true, "first": false, "tree": "[]"}, {"code": "C23C18/1689", "inventive": false, "first": false, "tree": "[]"}, {"code": "C25D11/24", "inventive": true, "first": false, "tree": "[]"}, {"code": "C25D11/16", "inventive": false, "first": false, "tree": "[]"}, {"code": "C23C18/38", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K5/0243", "inventive": true, "first": false, "tree": "[]"}, {"code": "C25D5/48", "inventive": false, "first": false, "tree": "[]"}, {"code": "C25D11/26", "inventive": true, "first": false, "tree": "[]"}, {"code": "C25D11/243", "inventive": true, "first": false, "tree": "[]"}, {"code": "C23C18/1653", "inventive": true, "first": false, "tree": "[]"}, {"code": "C25D11/00", "inventive": true, "first": false, "tree": "[]"}, {"code": "Y10T428/31678", "inventive": false, "first": false, "tree": "[]"}, {"code": "C25D11/16", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K5/0243", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K5/04", "inventive": true, "first": false, "tree": "[]"}, {"code": "C23C18/38", "inventive": false, "first": false, "tree": "[]"}, {"code": "C23C18/1605", "inventive": true, "first": false, "tree": "[]"}, {"code": "Y10T428/24033", "inventive": false, "first": false, "tree": "[]"}, {"code": "C25D11/24", "inventive": true, "first": false, "tree": "[]"}, {"code": "Y10T428/31678", "inventive": false, "first": false, "tree": "[]"}, {"code": "C23C18/1653", "inventive": true, "first": false, "tree": "[]"}, {"code": "Y10T428/24033", "inventive": false, "first": false, "tree": "[]"}, {"code": "C25D5/48", "inventive": false, "first": false, "tree": "[]"}, {"code": "C25D11/26", "inventive": true, "first": false, "tree": "[]"}, {"code": "C25D11/243", "inventive": true, "first": false, "tree": "[]"}, {"code": "C23C18/32", "inventive": false, "first": false, "tree": "[]"}, {"code": "C23C18/1689", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 54354846