Abstract:
A housing for an electronic device includes a metal substrate and a ceramic coating directly formed on at least portions of the substrate, the coated portions of the substrate having a rough surface. A method for fabricating the housing comprises roughening predetermined portions of the substrate; thermally spraying a ceramic coating on the roughened portions of the substrate, fixing the substrate on a tool having cold water circularly running there within during the thermal spraying; and grinding and polishing the ceramic coating.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present disclosure relates to housings for electronic devices and a fabrication method thereof. 
         [0003]    2. Description of Related Art 
         [0004]    Metals such as stainless steel, aluminum alloy, magnesium alloy, or titanium alloy, are usually applied for shells of portable electronic devices such as MP3 players, personal digital assistances (PDAs), and mobile phones. 
         [0005]    Metal shells are usually electroplated or sprayed by paint to form decorative layers. However, these decorative layers have insufficient wear-resistance. 
         [0006]    Therefore, there is room for improvement within the art. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    Many aspects of the present housing and fabrication method thereof can be better understood with reference to the drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present housing and fabrication method thereof. 
           [0008]      FIG. 1  is a schematic cross-section view of a housing according to a first exemplary embodiment. 
           [0009]      FIG. 2  is a schematic cross-section view of a metal substrate of a housing according to a second exemplary embodiment. 
           [0010]      FIG. 3  is a schematic view showing one manufacturing process in the method of forming a ceramic coating on the metal substrate according to the second exemplary embodiment. 
           [0011]      FIG. 4  is a schematic cross-section view of the housing according to the second exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]      FIG. 1  shows a housing  10  for electronic devices (such as mobile phones) according to a first exemplary embodiment. The housing  10  includes a metal substrate  12  and a ceramic coating  14  formed on the substrate  12 . 
         [0013]    The substrate  12  may be stainless steel, aluminum, aluminum alloy, magnesium, magnesium alloy, or titanium alloy. The substrate  12  may have a thickness of about 0.4 mm to about 0.6 mm. In this exemplary embodiment, the substrate  12  may be stainless steel and have a thickness of about 0.5 mm. The substrate  12  has an outer surface  122  and an opposite inner surface  124 . The outer surface  122  is roughened and has a roughness (Ra) of about 1.3 μm to about 2.0 μm. 
         [0014]    The ceramic coating  14  is directly formed on the entire outer surface  122 . The ceramic coating  14  may be comprised of an oxide ceramic, such as aluminum oxide (Al 2 O 3 ), ferroferric oxide (Fe 3 O 4 ), or titanium oxide (TiO 2 ). Since the above referred materials have different colors, the material comprising the ceramic coating  14  may be selected according to a desired color. The ceramic coating  14  has a surface roughness (Ra) of about 0.1 μm to about 0.3 μm, and has a thickness of about 0.12 mm to about 0.14 mm. 
         [0015]    An exemplary method for making the housing  10  may include the following steps. 
         [0016]    A metal substrate  12  is provided. The substrate  12  has the outer surface  122  and the inner surface  124 . 
         [0017]    The outer surface  122  may be roughened, for example by sandblasting. Exemplary materials of sandblasting material include silicon carbide, ferrochromium alloy, copper ore, ceramic, alumina and glass. In this exemplary embodiment, silicon carbide particle of 60 mesh size is used for the blasting. The outer surface  122  processed by this step achieves a roughness (Ra) of about 1.3 μm to about 2.0 μm. 
         [0018]    A ceramic coating  14  is formed on the outer surface  122  by thermal spraying, such as flame spraying or plasma spraying. It may be preferable to implement the thermal spraying approximately 4 hours after the roughening step. An oxide ceramic material such as aluminum oxide (Al 2 O 3 ), ferroferric oxide (Fe 3 O 4 ), or titanium oxide (TiO 2 ) may be sprayed to form the ceramic coating. Because the substrate  12  has a small thickness of about 0.4 mm to about 0.6 mm and may be overheated and deformed during the thermal spraying, the substrate  12  may be fixed on a tool having cold water circularly running there within to cool and prevent the substrate  12  from deforming. The ceramic coating  14  has an initial surface roughness (Ra) of about 2.1 μm to about 2.3 μm. 
         [0019]    The ceramic coating  14  is ground and polished to achieve a surface roughness of about 0.1 μm to about 0.3 μm. The grinding and polishing process may include the following steps: 
         [0020]    The substrate  12  with the ceramic coating  14  is preliminary ground by sandblasting to remove the outermost rough layer of the ceramic coating  14 . An abrasive belt having pyramidal carborundum grain attached may be used. During the grinding, cold water may be sprayed on the substrate  12  to prevent deformation. The preliminary ground ceramic coating  14  has a surface roughness (Ra) of about 1.0 μm to about 1.4 μm. 
         [0021]    The preliminary ground ceramic coating  14  is finely ground to wipe off the trace on the ceramic coating  14  produced by the preliminary grinding. This step is similar with the preliminary grinding except that an abrasive belt having alumina grain and not carborundum grain attached is used in this step. The finely ground ceramic coating  14  has a surface roughness (Ra) of about 0.5 μm to about 0.8 μm. 
         [0022]    A rock grinding process may be used to remove the trace on the ceramic coating  14  produced by the fine grinding. This step can be carried out in a rock grinder using a conical abrasive. The rock ground ceramic coating  14  achieves a surface roughness (Ra) of about 0.1 μm to about 0.3 μm. 
         [0023]    The substrate  12  with the ceramic coating  14  may be further processed by roll grinding to improve the brightness of the ceramic coating  14 . Walnut shell powder may be used as the abrasive. 
         [0024]      FIG. 4  shows a housing  20  for electronic devices according to a second exemplary embodiment. The housing  20  which is similar with the housing  10  and includes a metal substrate  22  and a ceramic coating  24  formed on the substrate  22 . Referring to  FIG. 2 , the substrate  22  has an outer surface  222  and an opposite inner surface  224 . The difference to the first exemplary embodiment includes the outer surface  222  has recesses  225  and protrusions  226 . The bottoms  2251  of the recesses  225  have a surface roughness (Ra) of about 1.3 μm to about 2.0 μm. The ceramic coating  24  is formed in the recesses  225 . The ceramic coating  24  is ultimately coplanar with the protrusions  226  to cooperatively form the exterior surface of the housing  20 . The ceramic coating  24  may form patterns, logos, or characters on the housing  20 . 
         [0025]    An exemplary method for making the housing  20  may include the following steps. 
         [0026]    A metal substrate  22  is provided. The substrate  22  has the outer surface  222  and the inner surface  224 . 
         [0027]    Predetermined portions of the outer surface  222  are etched by, for example chemical etching or laser etching, to form recesses  225 . The other portions of the outer surface  222  not etched form the relative protrusions  226 . In this exemplary embodiment, chemical etching is used. 
         [0028]    The recesses  225  may be processed by sandblasting to increase the roughness of their bottoms  2251 . Because the bottoms  2251  of the recesses  225  may have not enough roughness for facilitating the bonding between the subsequently formed ceramic coating  24  and the substrate  22 , the sandblasting process may increase the roughness of the recesses  225 . The sandblasted bottoms achieve the roughness (Ra) of about 1.3 μm to about 2.0 μm. 
         [0029]    Referring to  FIG. 3 , a ceramic coating  24  is formed on the substrate  22  using a method similar with the method for forming the ceramic coating  14  in the first exemplary embodiment. The ceramic coating  24  covers the entire outer surface  222 , including all the recesses  225  and the protrusions  226 . 
         [0030]    The ceramic coating  24  is ground and polished to achieve a surface roughness of about 0.1 μm to about 0.3 μm. The grinding process may include preliminary grinding, fine grinding, rock grinding, and roll grinding which are carried out in sequence similar with the first exemplary embodiment. Unlike the first exemplary embodiment, the preliminary grinding processing removes the outermost rough layer of the ceramic coating  24  and also exposes the protrusions  226 . Therefore, the exterior surface of the housing  20  is comprised of two distinct materials, metal and ceramic, and patterns or logos may be formed thereby. 
         [0031]    The exposed protrusions  226  may be further processed by sandblasting to achieve a matted appearance, thus the ceramic coating  24  is noticeable. 
         [0032]    It is to be understood, however, that even though numerous characteristics and advantages of the present exemplary embodiments have been set forth in the foregoing description, together with details of the structures and functions of the exemplary embodiments, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.