PATENT DOCUMENT

Publication Number: US-10542628-B2
Application Number: US-201715821789-A
Country: US
Kind Code: B2

Title: Enclosure for an electronic device having a shell and internal chassis

Abstract:
A housing or enclosure for an electronic device is formed from a shell and chassis may positioned along an interior of the shell. The shell may be formed from a hard or cosmetic material and the chassis may be formed from a machinable material. The chassis may define one or more machined surfaces that are configured to receive or mount a component of the electronic device.

Claims:
What is claimed is: 
     
       1. An electronic device, comprising:
 a shell forming an exterior surface of the electronic device, the shell comprising a first material; 
 a chassis formed along an interior of the shell and defining a machined shelf, the chassis comprising a second material; 
 a display positioned at least partially within the shell; and 
 a transparent cover positioned over the display and compliantly coupled to the machined shelf to form a seal between the transparent cover and the machined shelf. 
 
     
     
       2. The electronic device of  claim 1 , wherein the chassis is formed from a chassis material having a machinability that is greater than a machinability of the shell. 
     
     
       3. The electronic device of  claim 1 , wherein:
 the shell includes a back surface opposite the transparent cover; 
 the back surface defines an opening; 
 the chassis defines an attachment feature within the opening; 
 a back cover is coupled to the attachment feature of the chassis; and 
 an additional seal is formed between the attachment feature and the back cover by a compliant engagement of the attachment feature with the back cover. 
 
     
     
       4. The electronic device of  claim 1 , wherein the transparent cover is press fit within the machined shelf. 
     
     
       5. The electronic device of  claim 1 , wherein:
 the chassis further comprises a set of threaded mounts; and 
 the electronic device further comprises a circuit board attached to the set of threaded mounts. 
 
     
     
       6. The electronic device of  claim 1 , wherein:
 the shell defines a first portion of an opening configured to receive a component; and 
 the chassis defines a second portion of the opening configured to receive the component. 
 
     
     
       7. The electronic device of  claim 6 , wherein:
 the component is a compressible button; and 
 the second portion of the opening defines a surface configured to receive the compressible button. 
 
     
     
       8. The electronic device of  claim 7 , further comprising:
 an O-ring positioned between the second portion of the opening and the compressible button and configured to form a button seal between the chassis and the compressible button. 
 
     
     
       9. The electronic device of  claim 1 , wherein:
 the shell comprises a ceramic material; and 
 the chassis comprises at least one of: aluminum, machine steel, or plastic. 
 
     
     
       10. An electronic device, comprising:
 a ceramic shell forming an external surface of the electronic device and defining a display opening and a first portion of a component opening formed along the external surface; 
 a display positioned within the display opening; 
 a machined chassis formed from a material different than the ceramic shell and coupled to an interior surface of the shell, the machined chassis defining a second portion of the component opening; and 
 a component positioned within the component opening. 
 
     
     
       11. The electronic device of  claim 10 , wherein the second portion of the component opening defines a contoured surface. 
     
     
       12. The electronic device of  claim 11 , wherein:
 the component opening extends along a length of the shell; and 
 the second portion of the component opening has a maximum width that is greater than an opening width of the first portion along the external surface. 
 
     
     
       13. The electronic device of  claim 11 , wherein:
 the machined chassis defines a shelf along a perimeter of the display opening; 
 the electronic device further comprises a transparent cover positioned over the display; and 
 the shelf and the transparent cover cooperate to form a seal configured to prevent ingress of contaminants into the electronic device by a compliant engagement of a surface of the shelf with the transparent cover.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application No. 62/540,345, filed on Aug. 2, 2017, and entitled “Enclosure for an Electronic Device Having a Shell and Internal Chassis,” which is incorporated by reference as if fully disclosed herein. 
    
    
     FIELD 
     The described embodiments relate generally to electronic devices. More particularly, the present embodiments relate to enclosures having a shell and a machinable layer or chassis formed within the shell. 
     BACKGROUND 
     Many modern electronic devices are complex in design, having a great number of features within a small package. Mobile and wearable electronic devices in particular may require multiple components to be precisely designed and constructed to meet customer needs including high portability. 
     Components for mobile and wearable devices may be made from various materials. Some materials may have desirable attributes for device performance and/or appearance, but may at the same time be difficult and/or costly to produce with the precision necessary for inclusion within highly portable devices. 
     SUMMARY 
     Embodiments described herein relate to precisely machined components for electronic devices made from brittle materials. Brittle components of an electronic device may be formed from ceramic or other materials which are difficult to machine due to hardness, brittleness, and/or other properties. To reduce the cost and increase effectiveness of machining brittle components, a machinable material may be deposited onto the brittle component. The machinable material may then be machined or otherwise processed to produce a finished surface. 
     In one aspect, an electronic device may include a shell forming an exterior surface of the electronic device, a chassis formed along an interior of the shell, a display positioned at least partially within the shell, and a transparent cover positioned over the display. The chassis defines a machined shelf and the transparent cover is coupled to the machined shelf. A seal is formed between the transparent cover and the machined shelf. 
     The chassis may be formed from a chassis material with a greater machinability than the shell. In some examples, the shell includes a back surface opposite the transparent cover. The back surface defines an opening, and the chassis defines an attachment feature within the opening. A back cover is coupled to the attachment feature of the chassis, and an additional seal is formed between the attachment feature and the back cover. 
     In some examples, the transparent cover is press fit within the machined shelf. The chassis may include a set of threaded mounts, and a circuit board may be attached to the set of threaded mounts. In some examples, the shell defines a first portion of an opening configured to receive a component. The chassis defines a second portion of the opening configured to receive the component. The component may be a compressible button and the second portion of the opening may define a surface configured to receive the compressible button. 
     In further examples, an O-ring is positioned between the second portion of the opening and the compressible button. The O-ring forms a button seal between the chassis and the compressible button. The shell may include a ceramic material, a hardened steel, stainless steel, or other difficult to machine material, and the chassis may include at least one of aluminum, machine steel, brass or plastic that is more machinable than the shell. 
     In another aspect, a housing for an electronic device includes a shell. A machinable layer is deposited over an interior surface of the shell, and the machinable layer includes at least one of a metal or a plastic. The machinable layer defines a mounting surface configured to mount a component of the electronic device. 
     In some examples, the shell defines an opening, and a portion of the machinable layer is positioned at least partially within the opening. The portion of the machinable layer defines a machined surface within the opening. The machined surface may form a bearing surface configured to receive a rotatable shaft within the opening. In other examples, the shell defines a first portion of a recess into a side of the housing. The machinable layer defines a second portion of the recess, and the recess is configured to receive a watch crown. 
     In still other examples, the mounting surface defines a threaded aperture. The component may be attached to the housing by a fastener secured to the threaded aperture. The machinable layer may include an aluminum material cast into an interior portion of the shell. 
     In another aspect, an electronic device includes a ceramic shell forming an external surface of the electronic device. The shell defines a display opening and a first portion of a component opening formed along the external surface. A display is positioned within the display opening. A machined chassis is coupled to an interior surface of the shell and defines a second portion of the component opening. A component is positioned within the component opening. 
     In some examples, the second portion of the opening defines a contoured surface. The component opening may extend along a length of the shell, and the second portion of the component opening may have a maximum width which is greater than an opening width of the first portion along the external surface. In some examples, the machined chassis defines a shelf along a perimeter of the display opening. The electronic device includes a transparent cover positioned over the display, and the shelf and the transparent cover cooperate to form a seal configured to prevent ingress of contaminants into the electronic device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like elements. 
         FIG. 1  depicts an example electronic device in the form of a watch incorporating one or more brittle components, such as a shell for a housing, according to the present disclosure. 
         FIG. 2A  depicts a perspective view of a shell for a housing of an electronic device. 
         FIG. 2B  depicts a cross-sectional view of the shell depicted in  FIG. 2A , taken along line A-A. 
         FIG. 2C  depicts a perspective view of a shell for a housing, with a machinable material deposited over an attachment point. 
         FIG. 2D  depicts a cross-sectional view of the shell depicted in  FIG. 2C , taken along line B-B. 
         FIG. 2E  depicts a perspective view of a shell after processing of the machinable material. 
         FIG. 2F  depicts a cross-sectional view of the shell depicted in  FIG. 2E , taken along line C-C. 
         FIG. 2G  depicts a perspective view of a shell after fitting a transparent cover within the finished attachment point. 
         FIG. 2H  depicts a cross-sectional view of the shell depicted in  FIG. 2G , taken along line D-D. 
         FIG. 3A  depicts a perspective view of a shell for a housing, formed with openings for attachment. 
         FIG. 3B  depicts a cross-sectional view of the shell depicted in  FIG. 3A , taken along line E-E. 
         FIG. 3C  depicts a cross-sectional view of the shell depicted in  FIG. 3A , taken along line F-F. 
         FIG. 3D  depicts a perspective view of a shell, after a machinable material is deposited and processed. 
         FIG. 3E  depicts a cross-sectional view of the shell depicted in  FIG. 3D , taken along line G-G. 
         FIG. 3F  depicts a cross-sectional view of the shell depicted in  FIG. 3D , taken along line H-H. 
         FIG. 4A  depicts a perspective view of a shell formed with an opening along a length of the component. 
         FIG. 4B  depicts a front view of the shell of  FIG. 4A . 
         FIG. 4C  depicts a side view of the shell of  FIG. 4A . 
         FIG. 4D  depicts a perspective view of a shell over which a complex interface geometry has been formed. 
         FIG. 4E  depicts a cross-sectional view of the shell depicted in  FIG. 4D , taken along line J-J. 
         FIG. 4F  depicts a cross-sectional view of the shell depicted in  FIG. 4D , taken along line K-K. 
         FIG. 4G  depicts a cross-sectional view of the shell depicted in  FIG. 4D , taken along line L-L. 
         FIG. 5A  depicts a perspective view of a shell formed from a brittle material for a housing of an electronic device. 
         FIG. 5B  depicts the housing after a machinable material has been added to the shell and processed. 
         FIG. 5C  depicts a cross-sectional view of the housing depicted in  FIG. 5B , taken along line M-M. 
         FIG. 5D  depicts a cross-sectional view of the housing depicted in  FIG. 5B , taken along line N-N. 
         FIG. 5E  depicts a cross-sectional view of the housing depicted in  FIG. 5B , taken along line O-O. 
         FIG. 5F  depicts a cross-sectional view of the housing depicted in  FIG. 5B , taken along line U-U, illustrating an example technique for forming a mounting feature. 
         FIG. 5G  depicts a cross-sectional view of the housing depicted in  FIG. 5B , taken along line U-U, illustrating an example technique for forming a mounting feature. 
         FIG. 5H  depicts a cross-sectional view of the housing depicted in  FIG. 5B , taken along line U-U, illustrating an example technique for forming a mounting feature. 
         FIG. 5I  depicts a cross-sectional view of the housing depicted in  FIG. 5B , taken along line U-U, illustrating an example technique for forming a mounting feature. 
         FIG. 5J  depicts a cross-sectional view of the housing depicted in  FIG. 5B , taken along line U-U, illustrating an example technique for forming a mounting feature. 
         FIG. 5K  depicts a cross-sectional view of the housing depicted in  FIG. 5B , taken along line U-U, illustrating an example technique for forming a mounting feature. 
         FIG. 5L  depicts the housing of  FIG. 5B , illustrating additional components which interface with the processed machinable material. 
         FIG. 6  depicts another example electronic device in the form of a portable electronic device incorporating a shell for a housing according to the present disclosure. 
         FIG. 7A  depicts a perspective view of a housing of an electronic device formed from a brittle material. 
         FIG. 7B  depicts the electronic device housing after a machinable material has been added and processed. 
         FIG. 7C  depicts a cross-sectional view of the housing depicted in  FIG. 7B , taken along line P-P. 
         FIG. 7D  depicts a cross-sectional view of the housing depicted in  FIG. 7B , taken along line Q-Q. 
         FIG. 7E  depicts a cross-sectional view of the housing depicted in  FIG. 7B , taken along line R-R. 
         FIG. 7F  depicts a perspective view of the housing of an electronic device including a transparent cover and a back cover. 
         FIG. 7G  depicts a cross-sectional view of the housing depicted in  FIG. 7F , taken along line S-S. 
         FIG. 7H  depicts a housing for an electronic device including an insulating material coupled to the housing by a machinable material. 
         FIG. 7I  depicts a cross-sectional view of the housing depicted in  FIG. 7H , taken along line T-T. 
     
    
    
     The use of cross-hatching or shading in the accompanying figures is generally provided to clarify the boundaries between adjacent elements and also to facilitate legibility of the figures. Accordingly, neither the presence nor the absence of cross-hatching or shading conveys or indicates any preference or requirement for particular materials, material properties, element proportions, element dimensions, commonalities of similarly illustrated elements, or any other characteristic, attribute, or property for any element illustrated in the accompanying figures. 
     Additionally, it should be understood that the proportions and dimensions (either relative or absolute) of the various features and elements (and collections and groupings thereof) and the boundaries, separations, and positional relationships presented therebetween, are provided in the accompanying figures merely to facilitate an understanding of the various embodiments described herein and, accordingly, may not necessarily be presented or illustrated to scale, and are not intended to indicate any preference or requirement for an illustrated embodiment to the exclusion of embodiments described with reference thereto. 
     DETAILED DESCRIPTION 
     Reference will now be made in detail to representative embodiments illustrated in the accompanying drawings. It should be understood that the following descriptions are not intended to limit the embodiments to one preferred implementation. To the contrary, the described embodiments are intended to cover alternatives, modifications, and equivalents as can be included within the spirit and scope of the disclosure and as defined by the appended claims. 
     The following disclosure relates to portable electronic devices having precisely machined components, such as a shell for a housing of the device, formed from a brittle or otherwise difficult to machine material. Such brittle or difficult to machine components may be costly to manufacture with a high degree of precision, requiring additional machining time and causing additional wear to machining tools. This disclosure is directed to methods, systems, and devices in which such costs and difficulties of manufacturing may be reduced. 
     A variety of brittle and difficult to process materials may be used to form components of electronic devices. Such materials may contain properties which are desirable for use within an electronic device. For example, a brittle material, such as a ceramic material, may form an outer shell or enclosure of an electronic device. A brittle material like a ceramic may be particularly suitable due to the material&#39;s hardness, appearance, durability, impact resistance, transmissivity of electromagnetic radiation, and so on. Similarly, an outer shell may be formed from a hardened steel, stainless steel, or other material that is difficult to machine or process but provides a desirable appearance, durability, and/or surface hardness for the electronic device. 
     While such brittle or otherwise difficult to process materials may have desirable properties, the material may also be costly to manufacture into a finished component. This drawback may be particularly disadvantageous when producing highly portable devices, such as wearable electronics, in which the size of the device requires components to be manufactured with a high level of precision to maintain portability, form water tight seals, have small gaps between parts, and provide other fine features that enhance a user experience. 
     The present disclosure advantageously reduces the cost of producing components made from brittle materials for use within portable electronic devices. In a first example, a shell for a housing may be formed from a ceramic material. Example ceramic materials may include zirconia, zirconium dioxide, partially stabilized zirconia, alumina, aluminum oxides, glass, and other similar materials. In some instances, a ceramic shell is formed by placing a slurry or paste into a mold or similar shaping mechanism. The ceramic material is partially cured in order to yield a green body. This green body is then sintered, in which the green body is heated, removing any remaining moisture and hardening the green body into a ceramic shell. After sintering, the ceramic shell may be machined to form an exterior surface of the electronic device. 
     A sintered ceramic component, such as a ceramic housing, may be difficult and costly to machine (e.g., the ceramic material may have a low machinability). For example, the chosen ceramic material may have a high hardness rating, such that only expensive equipment may be used for cutting, grinding, and other machining. The ceramic material may additionally increase wear on machining equipment, further increasing cost. Many ceramics are brittle and can only be shaped through techniques which subtract only small portions of the ceramic material at a time, further increasing the time and cost of machining components. Other suitable shell materials including high carbon steel, stainless steel, and other metal alloys may also be difficult or costly to machine. 
     In high-precision applications, such as housings for portable electronic devices, the ceramic manufacturing process may further add cost to producing a final, machined component. Edges of a component which mate with surrounding parts may require very close tolerances. However, the curing and sintering processes for manufacturing ceramics generally result in volumetric shrinking toward a final product. Thus, sintered ceramic components are traditionally produced with excess material which must to be removed in order to yield finished components within required tolerances. 
     With the present disclosure, a high-precision surface may be produced by depositing a machinable material onto a brittle or difficult to machine component, such as a ceramic shell for a housing. The machinable material may be deposited by an appropriate technique, such as casting, molding, plating, brazing, soldering, coating (e.g., plasma spray, thermal spray, cold spray), vapor deposition, chemical deposition, insert molding, overmolding, or 3-D printing. The machinable material may then be processed by grinding, cutting, turning, boring, drilling, tapping, and so on to produce a precise finished surface for fitting with other parts. 
     In one example, an external housing for an electronic device may be formed from a ceramic material. The shell may be shaped to hold device components, including an electronic display. A transparent cover may be placed over the electronic display, and one or more edges of the transparent cover may interface with the housing. The interface between the housing and the transparent cover requires a precise fit. 
     In order to achieve a precise fit for the transparent cover, the housing may include a shell forming an exterior surface of the electronic device. The shell may be molded, cured, and sintered to produce a cover attachment point, such as a shelf. However, the ceramic shelf may not be produced within the tolerances required for the finished electronic device. Thus, a machinable material, such as a softer or more machinable metal, plastic, or other similar material may be deposited on and/or around the shelf. Portions of the machinable material are then removed from the shelf to produce a precise, machined surface. The transparent cover may then be coupled to the machined surface, such as by press fitting or by bonding using an adhesive or bonding agent. 
     In another example, a ceramic housing for an electronic device may interface with a number of internal and/or external components. The components may be rigidly or otherwise mounted to the housing, requiring the housing to include multiple internal and/or external mounting surfaces. Traditionally, a ceramic housing may be directly machined to produce each of the required mounting surfaces, which may require a costly, multi-step machining process. 
     Instead, a machinable material, such as a machinable metal or plastic, may be deposited over an interior surface of a shell and machined to form a chassis for attachment of components. In some examples, a block of machinable material may be cast into (or otherwise attached to) an interior surface of the shell. Portions of the block of material may then be selectively removed to generate a machined chassis, defining holes, protrusions, threads, planes, and other mounting surfaces and features. 
     In other examples, a layer of machinable material may be deposited over all or a portion of the shell, and mounting features may be added to the deposited layer. Other portions of the layer of machinable material may be selectively removed to produce additional mounting features for parts of the electronic device. It should be understood that these methods may be combined in a variety of ways to produce the finished surfaces desired for attaching device components to the shell of the housing. 
     These and other embodiments are discussed below with reference to  FIGS. 1-7G . However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these figures is for explanatory purposes only and should not be construed as limiting. 
       FIG. 1  depicts an example electronic device in the form of a watch incorporating one or more brittle components, such as a shell for a housing, according to the present disclosure. The electronic device  100  includes a housing  102  surrounding a display  104 . The display  104  can provide a visual output to the user. The display  104  can be implemented with any suitable technology, including, but not limited to: a liquid-crystal display (LCD) element, an organic light emitting diode (OLED) element, an electroluminescent (EL) display, and the like. 
     A transparent cover  118  may be positioned over the front surface (or a portion of the front surface) of the electronic device  100 . A touch and/or force sensor may be positioned below the transparent cover  118 , and enable least a portion of the transparent cover  118  to function as an input surface that receives touch and/or force inputs. The transparent cover  118  may be formed from a sheet of glass, plastic, sapphire, or combinations thereof. The transparent cover  118  may also be a laminate or composite of multiple materials. In one embodiment, the transparent cover  118  covers the display  104 . 
     Various layers of a display stack (such as the transparent cover  118 , display  104 , touch sensor layer, and so on) may be adhered together with an optically transparent adhesive and/or may be supported by a common frame or portion of the housing  102 . A common frame may extend around a perimeter, or a portion of the perimeter, of the layers, may be segmented around the perimeter, or a portion of the perimeter, or may be coupled to the various layers of the display stack in another manner. 
     In some embodiments, each of the layers of the display stack may be attached or deposited onto separate substrates that may be laminated or bonded to each other. The display stack may also include other layers for improving the structural or optical performance of the display  104 , including, for example, polarizer sheets, color masks, and the like. Additionally, the display stack may include a touch sensor for determining the location of one or more touches on the transparent cover  118  of the electronic device  100 . 
     In many cases, the electronic device  100  can also include a processor, memory, power supply and/or battery, network connections, sensors, input/output ports, acoustic components, haptic components, digital and/or analog circuits for performing and/or coordinating tasks of the electronic device  100 , and so on. For simplicity of illustration, the electronic device  100  is depicted in  FIG. 1  without many of these components, each of which may be included, partially and/or entirely, within the housing  102 . 
     The electronic device may be operable to receive additional input from a user, such as through a button  108 . The electronic device  100  may also be operable to perform various actions in response to input received via a watch crown  106  or similar input structure. The watch crown  106  may be operable to receive rotational and other inputs, such as force inputs to the watch crown  106 . 
     As a wearable device, the electronic device  100  may be compact, lightweight, and durably constructed. Accordingly, components of the electronic device  100  may be precisely shaped and fitted together in order to reduce overall size, reduce mass, and/or increase performance of the electronic device  100 . The compact nature of the electronic device  100  may increase the challenge of precisely machining components to create a final product. 
     Some components of the electronic device  100 , such as the housing  102 , may interact with a variety of other components, requiring the components to have multiple precision interfaces. The housing  102 , for example, may interface with a transparent cover  118  over the display  104 , the watch crown  106 , one or more buttons  108 , the watch band  105 , and various other internal and external components of the electronic device  100  (e.g., the display stack or common frame may be coupled to and supported by the housing  102 ). Each of these interfaces may require precise machining to yield desired performance. 
     In some embodiments, the electronic device  100  may be constructed to be resistant to entry of liquids (e.g., water) and other contaminants. In such embodiments, the need for precision machining may be heightened. For example, the interface between the housing  102  and the transparent cover  118  may be a press fit or may otherwise resist the entry of contaminants into the housing  102 . A compressible seal or structure may be placed between the watch crown  106  and the housing  102  that resists passage of contaminants into internal portions of the watch crown  106  and/or the electronic device  100  while allowing the watch crown  106  to receive rotational inputs. Portions of the compressible seal may collapse and/or bend to allow translational movement of the watch crown  106 . The compressible seal may require a precise interface between the housing  102  and the watch crown  106 . A similar seal may be included between the button  108  and the housing  102 . In general, any opening in the housing  102  may require precision machining to ensure the electronic device  100  remains sealed to prevent or reduce ingress of external contaminants. 
     These precision components may be formed from brittle or difficult to machine materials, such as ceramics, hardened metals, high hardness metals, sapphire, thermoplastics, composites, and so on. Difficult to machine materials may be desirable for components of the electronic device  100  for particular material properties, such as durability. In particular, it may be desirable to form external surfaces of the electronic device  100  from a hard or durable brittle material or materials. For example, the housing  102  of the electronic device  100  and/or the transparent cover  118  over the display  104  may be formed from a hard or durable material that may be characterized as a brittle material. 
     In the example of the housing  102  of an electronic device  100 , certain brittle materials may be selected for desirable properties, such as appearance, hardness, and durability. For example, by forming the housing  102  from such materials, the electronic device  100  may be less susceptible to damage from contact with other objects while the electronic device  100  is worn by a user. In addition, the electronic device  100  may transmit electromagnetic signals, and a ceramic housing  102  may allow for clear transmission of electromagnetic signals, where a metal would interfere with such transmission. Other materials including hardened steel, stainless steel, titanium or other metal alloys may also provide desirable as appearance, hardness, and durability but also provide desired conductive properties and/or metallic exterior finish. 
     However, as previously noted, the housing  102  must interface with a number of other components, and each interface may require a level of precision which cannot be achieved during the process of molding and sintering the ceramic material. Accordingly, the housing  102  may include a hard (e.g., ceramic) shell, and a more machinable material (e.g., aluminum, brass, plastic, steel) may be deposited into at least a portion of the shell. The machinable material may then be processed to yield the required precision-machined interface surfaces, as further described below with respect to  FIGS. 2A-5L . 
     The electronic device is shown in  FIG. 1  as a wearable electronic device. However, it is understood that this is an example. In various implementations, an electronic device may be any kind of electronic device that uses a difficult to machine component for a high-precision application. Sample electronic devices include a laptop computer, a desktop computer, a mobile computer, a smart phone, a tablet computer, a fitness monitor, a personal media player, a display, audiovisual equipment, and so on. An additional example of an electronic device with a housing formed from a ceramic or otherwise difficult to machine material is illustrated below with respect to  FIGS. 6-7G . 
       FIGS. 2A-2H  depict an example of a shell of a housing, formed from a brittle or difficult to machine material, as a machinable material is added to an interface to yield a precision interface.  FIG. 2A  depicts a perspective view of a shell for a housing of an electronic device.  FIG. 2B  depicts a cross-sectional view of the shell depicted in  FIG. 2A , taken along line A-A. 
     As depicted in  FIG. 2A , a component for an electronic device may be formed from a brittle or otherwise difficult to machine material. The brittle component may be a shell  212  for a housing of the electronic device formed from a ceramic material, such as zirconium dioxide, aluminum oxide, silicon carbide, tungsten carbide, porcelain, and any other suitable ceramic material. In other embodiments, a different component may be formed, and/or the component may be formed from another brittle and/or difficult to machine material, such as glass (e.g., soda lime glass, borosilicate glass), glass ceramics, fiber composites (e.g., fiberglass, carbon fiber), hardened metals, hardened steel, high carbon steel, titanium, and so on. 
     In the case of a ceramic material, a shell  212  is generally produced by mixing the ceramic material into a slurry with water, binder, and deflocculant. The slurry may be placed into a mold, slip, or similar shaping mechanism and pressed to produce a green body (a weakly bound ceramic body, possessing the general shape of the desired product, but not yet hardened). The green body may include structural features of the shell  212 , such as a shelf  214 , which may be intended as an attachment point for interfacing with another component of the electronic device. 
     After the green body is formed, it may be sintered to produce the shell  212 . In the sintering process, the green body may first be heated at a relatively low temperature to remove binders. Then the green body may be placed under high temperature and other forces, such as pressure and/or electrical current to complete the sintering process. During sintering, the green body may be subject to volumetric shrinking to yield the ceramic shell  212 . 
     After sintering, the shell  212  may be hard and have low machinability. Machinability is a measure of how long a machining tool lasts when processing a particular material. Machinability may be expressed in comparison to another material, such as steel. For example: 
     
       
         
           
             
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               × 
               100 
             
           
         
       
     
     Other measures of machinability may take into account the type of cutting tool required (and its cost), the geometry of the tool, the clamping method required, number of cycles required, the complexity of the finished surface, and so on. Many brittle materials, including ceramics, such as zirconium dioxide and aluminum oxide, have low machinability, requiring a greater amount of time and expense over machinable materials such as aluminum and medium-carbon steel. As an example, the shell may have a machinability index that ranges between 0 and 60% as compared to standard steel (e.g., 1212 carbon steel). In general and as discussed below, the machinability index of the shell is lower than the machinability index of a chassis formed from a machinable material. As an example, the machinable material may have a machinability index that may be approximately 50% or higher as compared to standard steel (e.g., 1212 carbon steel). If the machinable material is more machinable than standard steel (e.g., 1212 carbon steel), the machinability index may be greater than 100%. 
     The forming and sintering process of a ceramic material may further make achieving precise finished surfaces difficult and costly. As noted above, a green body may be formed from a mold that includes geometric features desired in the shell  212 , such as a shelf  214  for attaching another part. When the green body is sintered, it is subject to volumetric shrinking, and the shelf  214  may be produced within a relatively wide variance. 
     Traditionally, as a result of the limitations of molding and sintering, the green body may be formed with excess material, which material is then removed through machining to produce a finished shelf. As the ceramic material may have a low machinability, even producing a simple shelf within tolerances may be costly and time-consuming. 
     In order to reduce the cost and time involved to produce finished edges, surfaces, and attachment points, such as the shelf  214 , the green body may instead be formed with slightly less material than needed at those points. The green body is sintered to produce the shell  212  with a shelf  214 , which may need additional material to meet final specifications for the shell  212 . 
     As depicted in  FIGS. 2C and 2D , a machinable material may be added to the component of  FIGS. 2A and 2B .  FIG. 2C  depicts a perspective view of a shell with a machinable material deposited over a shelf, which may serve as an attachment point.  FIG. 2D  depicts a cross-sectional view of the shell depicted in  FIG. 2C , taken along line B-B. 
     After the shell  212  is produced, a machinable material  216  may be deposited over the shell  212  (e.g., over an interior surface of the shell  212 ). The machinable material  216  may be any material having a higher machinability than the material (e.g., ceramic) forming the shell  212 . For example, the machinable material may be aluminum, brass, machinable steel, medium-carbon steel, brass, plastics, and so on. In general, the machinable material may have a machinability index that may be approximately 50% or higher as compared to standard steel. If the machinable material is more machinable than standard steel, the machinability index may be greater than 100%. In some embodiments, the machinable material may be selected for additional properties, such as conductivity, insularity, capacitance, compliance, stiffness, and other properties which may be desirable for a given application. 
     The machinable material  216  may be deposited over the shell  212  through an appropriate method. For example, the machinable material  216  may be coupled to the shell by brazing, casting, coating (e.g., plasma spray, thermal spray, cold spray), soldering, plating, vapor deposition, chemical deposition, insert molding, overmolding, 3-D printing, and any other appropriate techniques. In some embodiments, the machinable material  216  may be deposited onto the entire shell  212 , and in other embodiments the machinable material  216  may be deposited onto a target area, such as the shelf  214 . 
     In some embodiments, a bond between the machinable material  216  and the shell  212  may be facilitated through an appropriate technique. For example, a surface of the shell  212 , such as an interior surface, may be roughened through grinding, etching, or similar techniques prior to addition of the machinable material  216 . In another example, an adhesive may facilitate bonding between the machinable material  216  and the shell  212 . In another example, the shell may be plated or clad with another material (e.g., a softer material or a material with a lower melting point), which may facilitate forming a bond between the machinable material  216  and the shell  212 . 
     As depicted in  FIGS. 2E and 2F , the machinable material may be processed to produce a finished surface.  FIG. 2E  depicts a perspective view of a shell after processing of the machinable material.  FIG. 2F  depicts a cross-sectional view of the shell depicted in  FIG. 2E , taken along line C-C. 
     After the machinable material is deposited over the shell  212 , the material may be machined or otherwise processed to produce a finished surface, the machined shelf  216 ′. For example, the machinable material over the shelf  214  may be selectively removed by milling, grinding, polishing, or otherwise removing portions of the machinable material until the machined shelf  216 ′ is achieved. In some embodiments, the machined shelf  216 ′ may be at least a portion of a machined chassis, which may additionally couple to other components. 
     Once the machined shelf  216 ′ is produced, another component may be coupled to the shell  212  at the machined shelf  216 ′.  FIG. 2G  depicts a perspective view of a shell after fitting a transparent cover within an attachment point, such as a machined shelf.  FIG. 2H  depicts a cross-sectional view of the shell depicted in  FIG. 2G , taken along line D-D. 
     With the machined shelf  216 ′ prepared, the shell  212  may be coupled to another component of the electronic device. For example, the machined shelf  216 ′ may function as a bezel or other retaining mechanism for retaining a transparent cover  218  (e.g., a transparent cover  118  over a display  104 , such as depicted in  FIG. 1 ). Accordingly, once the machined shelf  216 ′ is prepared, a transparent cover  218  may be coupled to, bonded to, or otherwise attached to the machined shelf  216 ′. 
     In some embodiments, a seal may be formed between the transparent cover  218  and the machined shelf  216 ′. In some cases, the machinable material of the machined shelf  216 ′ may be a sufficiently compliant material to facilitate a seal. In some cases, a compliant material is positioned on the machined shelf  216 ′ and is configured to interface with the transparent cover  218  to form a seal or barrier. The seal or barrier may reduce or prevent the ingress of external materials including, for example, liquid, moisture, dust, and other potential contaminants. The use of a compliant material for the machined shelf  216 ′ or on the machined shelf  216 ′ may additionally provide impact resistance to one or both of the shell  212  and the transparent cover  218 . In some embodiments, the transparent cover  218  may be press fit into a cavity or opening defined, in part, by the machined shelf  216 ′. 
     In some embodiments, the machined shelf  216 ′ may additionally or alternatively include a groove, beveled edge, or other attachment feature to facilitate retention of the transparent cover  218 . In some embodiments, the transparent cover  218  may be coupled to the machined shelf  216 ′ by another appropriate means, such as application of an adhesive, a retention clip, and so on. 
     In some embodiments, the machinable material for the machined shelf  216 ′ may be selected for other performance characteristics. For example, the shell  212  and the transparent cover  218  may each be a dielectric material, while the machined shelf  216 ′ may be conductive (e.g., a metal). The machined shelf  216 ′ may in these cases additionally serve as an antenna, conductive material for a sensor, or another purpose. 
     In some embodiments, the shell  212  may also be shaped to receive a back cover  241 . Thus a back shelf  239  may be formed in the shell  212  opposite the shelf  214 . A machinable material (e.g., the same or a different machinable material as the machined shelf  216 ′) may be deposited over the back shelf  239  and machined to form an attachment feature, such as a machined back shelf  240 . In some embodiments, the machined back shelf  240  may form at least a portion of a machined chassis, which may also include the machined shelf  216 ′. The back cover  241  may then be coupled to the machined back shelf  240  in a manner such as described above with respect to the transparent cover  218 . 
       FIGS. 3A-3F  depict an example of a shell for a housing of an electronic device as a machinable material is added to multiple openings to yield precision interfaces.  FIG. 3A  depicts a perspective view of a shell for a housing, formed with openings for attachment.  FIG. 3B  depicts a cross-sectional view of the shell depicted in  FIG. 3A , taken along line E-E.  FIG. 3C  depicts a cross-sectional view of the shell depicted in  FIG. 3A , taken along line F-F. 
     As depicted in  FIG. 3A , a component, such as a shell  312 , for an electronic device may be formed from a brittle or otherwise difficult to machine material. The shell  312  may be formed from a ceramic material in a manner similar to that described above with respect to  FIGS. 2A-2F , though the shell  312  can be formed of any difficult to machine material (e.g., hardened steel, stainless steel, titanium). In the example of  FIG. 3A , the shell  312  may additionally be molded to define an oblong opening  320  on a first face of the shell  312 . A round opening  324  surrounded by a recess  322  may be defined on a second face of the shell  312 . 
     Each of the oblong opening  320  and the round opening  324  may require a precise finish for fitting to other parts (e.g., receiving a component or accessory) of an electronic device. For example, the oblong opening  320  may facilitate a depressible button. The round opening  324  and surrounding recess  322  may facilitate a crown or similar component, which may be rotatable. 
     The precision surfaces required for the oblong opening  320  and the round opening  324  may be difficult and costly to achieve through molding and machining a housing from ceramic or another brittle material. Accordingly, shell  312  for the housing may be formed, and a machinable material may be deposited in and/or around the oblong opening  320  and the round opening  324  in order to produce precise machined surfaces. 
       FIG. 3D  depicts a perspective view of a shell, after a machinable material is deposited and processed.  FIG. 3E  depicts a cross-sectional view of the shell depicted in  FIG. 3D , taken along line G-G.  FIG. 3F  depicts a cross-sectional view of the shell depicted in  FIG. 3D , taken along line H-H. 
     As depicted in  FIGS. 3D-3F , a machinable material is deposited onto the shell  312  and processed to produce a button interface  326  within the oblong opening  320 , which interfaces with and retains a button or other component. The machinable material also forms a crown shaft interface  328  within the round opening  324 , which may function as a bearing surface for a rotatable shaft of a crown and otherwise retain and interface with the crown. In some cases, the machinable material may include a brass, lubricated alloy, or other material suitable for use in a plane or journal bearing. 
     The oblong opening  320  and the button interface  326  may cooperate as a first and a second portion of an opening. The oblong opening  320  may be the first portion of this opening, which allows a compressible button (e.g., button  108 ) or other component to be at least partially recessed within the opening. The button interface  326  may be the second portion of this opening, which provides a planar surface within the first portion of the opening and a more precise opening for attachment of the button (or other component) and related components. 
     The shape of this opening, including the first portion of the oblong opening  320  and the second portion of the button interface  326 , may be difficult to mold or machine from the material of the shell  312  (e.g., ceramic). Accordingly, it may significantly reduce cost to form the first portion, the oblong opening  320 , with the ceramic shell  312 , and form the second portion, the button interface  326 , from a machinable material (e.g., aluminum, brass, machinable steel, plastic, etc.). 
     Similarly, the round opening  324  and the crown shaft interface  328  may cooperate to form a precise through-hole (e.g., opening) for retaining a rotatable crown. The precise size and shape for the through-hole may be similarly difficult to mold or machine from the material of the shell  312 . Accordingly, the shell  312  may be molded with the round opening  324  being slightly larger than needed for the crown, and a machinable material may be deposited within the round opening  324 . The machinable material may then be machined to form a machined surface, or crown shaft interface  328 . 
     The machined surface of the crown shaft interface  328  may form a bearing, such as a plane bearing or bearing surface, to accommodate a rotatable crown shaft within the round opening  324 . In some cases, the machinable material along the crown shaft interface  324  may include a brass, lubricated alloy, or other material suitable for use in a plane or journal bearing. The crown shaft interface  328  may also form a contoured interior surface, which may accommodate internal components of the crown, such as a nut, retaining clip, O-ring, or other retaining or sealing component to facilitate retention of a crown within the shell  312 . 
     In some embodiments, the button interface  328  and/or the crown shaft interface  328  may form at least a portion of a machined chassis. The machined chassis may include additional features for mounting to components of the electronic device. 
     In some embodiments, the button interface  326  and crown shaft interface  328  may be formed by depositing a block of machinable material onto the shell  312  through an appropriate technique, such as described above with respect to  FIGS. 2C and 2D . The block of material may be deposited immediately around each of the oblong opening  320  and the round opening  324 , or the block of material may be deposited around the entire shell  312 . After the block of machinable material is deposited, the material may be milled, ground, drilled, polished, or otherwise machined to form the button interface  326  and the crown shaft interface  328 . 
     In other embodiments, the button interface  326  and crown shaft interface  328  may each be formed and machined prior to inclusion with the shell  312 . The button interface  326  may then be coupled to the shell  312  at or near the oblong opening  320  through an appropriate technique, such as brazing or soldering. The crown shaft interface  328  may similarly be coupled at or near the round opening  324 . 
     In some embodiments, a layer of machinable material may be deposited over an area of the shell  312 , such as the interior of the shell  312 . The machinable layer may be deposited through an appropriate technique, such as vapor deposition or plating, and form a base for other components to couple to. For example, the button interface  326  may be pre-formed and coupled to the layer of machinable material through brazing or soldering. 
       FIGS. 4A-4G  depict an example of a shell on which a complex interface geometry is formed.  FIG. 4A  depicts a perspective view of a shell formed with an opening along a length of the component.  FIG. 4B  depicts a front view of the shell of  FIG. 4A .  FIG. 4C  depicts a side view of the shell depicted in  FIG. 4A . 
     As depicted in  FIGS. 4A-4C , a component  412  for an electronic device may be formed from a brittle or otherwise difficult to machine material. The shell  412  may be formed from a ceramic material in a manner similar to that described above with respect to  FIGS. 2A-2F , though the shell can be formed of any difficult to machine material (e.g., stainless steel, hardened steel, high-carbon steel, titanium). In the example of  FIGS. 4A-4D , the shell  412  may additionally be molded to define an opening  430  along its length. 
     The opening  430  may be included to facilitate receiving a component or accessory, such as a watch band, within the shell  412 . The opening  430  may require a complex geometry which could not be molded into the shell  412 . Such a complex geometry may additionally be very costly to obtain by machining the shell  412 . 
     Accordingly, the shell  412  may be shaped to include the opening  430  along its length. As depicted in  FIG. 4C , in some embodiments the opening  430  may be molded or machined to include an undercut, wherein an interior width of the opening  430  is greater than the width of the opening  430  at the external surface. Additional complex geometry of the opening may be supplied through the addition of a machinable material. 
       FIG. 4D  depicts a perspective view of a shell over which a complex interface geometry has been formed using a machinable material.  FIG. 4E  depicts a cross-sectional view of the shell of  FIG. 4D , taken along line J-J.  FIG. 4F  depicts a cross-sectional view of the shell depicted in  FIG. 4D , taken along line K-K.  FIG. 4G  depicts a cross-sectional view of the shell depicted in  FIG. 4E , taken along line L-L. 
     As depicted in  FIGS. 4E-4H , a machinable material is deposited onto the shell  412  and processed to produce a contoured surface  432 , an internal chassis  434  (e.g., a machined chassis), attachment features  436 , additional mounting points  438  (e.g., a screw boss, a bracket with a threaded aperture, and so on), and a ledge  437 . The contoured surface  432  may be formed within the opening  430  along the length of the shell  412 . The internal chassis  434  may be formed from the same material (e.g., from a same block of material) on the interior of the shell  412 . 
     The contoured surface  432  may form a precise shape to which a component or accessory of the electronic device attaches, such as a watch band (e.g., watch band  105  depicted in  FIG. 1 ). The contoured surface  432  may have a maximum interior width which is greater than a width at the surface of the opening  430 , and the shape of the contoured surface  432  may be difficult and/or costly to mold or machine from the material of the shell  412 . Accordingly, the cost of producing the contoured surface  432  in a precise shape may be significantly reduced by forming a first portion of an opening by the opening  430  in the shell  412  (e.g., by molding and/or simple machining processes), and to form a second portion of the opening, the shape of the contoured surface  432 , from a machinable material. 
     The difficulty of machining the shell  412 , may be compounded by the need for forming an internal chassis  434  on the internal surface of the shell  412  opposite the opening  430 . The internal chassis  434  may include attachment features  436 , such as threaded apertures to which internal components of the electronic device (e.g., components of the display stack, sensors, input/output ports, acoustic components, haptic components, digital and/or analog circuits) are mounted. One or more recesses, such as a ledge  437 , may also be included to facilitate placement of internal components of the electronic device. 
     The geometry of the internal chassis  434  may require a multi-stage and costly machining process, in which a great deal of brittle material may need to be removed at a relatively slow pace. By creating a shell  412  with the simple opening  430 , however, the machining cost may be greatly reduced as both the contoured surface  432  and the internal chassis  434  are formed and machined from a more machinable material (e.g., aluminum or machine steel). 
     In some embodiments, the contoured surface  432  and internal chassis  434  may be formed by depositing a block of machinable material onto the interior of the shell  412  through an appropriate technique, such as described above with respect to  FIGS. 2C and 2D . The block of material may be deposited immediately around the opening  430 , or the block of material may be deposited around the entire shell  412 . After the block of machinable material is deposited, the material may be milled, ground, drilled, polished, or otherwise machined to form the contoured surface  432  and internal chassis  434 . 
     In other embodiments, the contoured surface  432  and internal chassis  434  may be formed and machined prior to inclusion with the shell  412 . The part including the contoured surface  432  and internal chassis  434  may then be coupled to the shell  412  at or near the opening  430  through an appropriate technique, such as brazing or soldering. 
     In some embodiments, a layer of machinable material may be deposited over an area of the shell  412 , such as the interior surface of the shell  412 . The layer of machinable material may be deposited through an appropriate technique, such as vapor deposition or plating, and form a base for other components to couple to and/or be machined from. For example, the contoured surface  432  and internal chassis  434  may be machined into the layer of machinable material. Additional mounting points  438  (e.g., screw bosses, brackets, or the like) may be formed integral with the layer of machinable material, or may be pre-formed and coupled to the layer of machinable material through brazing, soldering, or similar techniques (see, e.g.,  FIGS. 5F-5K ). The additional mounting points  438  may couple to an internal support frame, a circuit board, or other internal components of the electronic device. 
       FIGS. 5A-5L  depict an example of a housing of an electronic device, including a shell formed from a brittle material.  FIG. 5A  depicts a perspective view of the shell formed from the brittle material.  FIG. 5B  depicts the housing after a machinable material has been added to the shell and processed. 
       FIG. 5C  depicts a cross-sectional view of the housing depicted in  FIG. 5B , taken along line M-M.  FIG. 5D  depicts a cross-sectional view of the housing depicted in  FIG. 5B , taken along line N-N.  FIG. 5E  depicts a cross-sectional view of the housing depicted in  FIG. 5B , taken along line O-O.  FIGS. 5F-5K  depict a cross-sectional view of the housing depicted in  FIG. 5B , taken along line U-U, illustrating example techniques for forming a mounting feature.  FIG. 5L  depicts the housing of  FIG. 5B , illustrating additional components which interface with the processed machinable material. 
     As depicted in  FIG. 5A , it may be desirable to form a housing  502  for an electronic device from a brittle or otherwise difficult to machine material. However, given the difficulty of machining a housing entirely from this material, the external surface of the housing  502  may be a shell  542  of brittle material. The shell  542  may be formed from a ceramic material in a manner similar to the shell described above with respect to  FIGS. 2A-2F , though the shell  542  can be formed of any difficult to machine material (e.g., stainless steel, hardened steel, high-carbon steel, titanium). 
       FIG. 5A  may illustrate, for example, a ceramic shell  542  of a housing  502  after the green body of the shell  542  has been sintered to form a hardened, durable external surface for an electronic device. The shell  542  has been shaped (e.g., cast or molded) with a substantially uniform cross-section to enclose features of the electronic device, having four sides and a back surface  543 . Various features may be included in the sintered ceramic shell  542 , such as openings  530  along the length of two opposing sides (e.g., openings for retaining a watch band, such as watch band  105  depicted in  FIG. 1 ). 
     An additional side of the shell  542  may include an oblong opening  520  (e.g., an opening for retaining a depressible button, such as button  108  depicted in  FIG. 1 ) and a round opening  524  surrounded by a recess  522  (e.g., for interfacing with a watch crown, such as watch crown  106  depicted in  FIG. 1 ). 
     In some embodiments, the shell  542  may include a back surface  543 . The back surface  543  may be continuous with each of the sides, and may provide structural support to the sides of the shell  542  and/or to internal components of the electronic device. The back surface may include one or more openings  544 , which may house sensors or other components of the electronic device (e.g., optical sensors forming an optical heart rate monitor). 
     The shell  542  may be formed with the above openings and other features to facilitate interaction with input/output components of the electronic device, and may additionally facilitate the formation of mounting points and other internal features needed to retain components of the electronic device. The geometry of the final interfaces and internal features around the features of the shell  542  may require complicated and/or precise geometries which may not be achieved through the forming of the shell  542  (e.g., by sintering). Accordingly, the final interfaces and internal features of the shell  542  may be supplied through the addition and processing of a machinable material. 
     As depicted in  FIGS. 5B and 5C , a machinable material is deposited into the shell  542  and processed to produce various final interfaces for the housing  502 . In many embodiments, the machinable material forms a machined chassis. The machined chassis may include a contoured surface  532  and an internal chassis  534  formed on two sides the shell  542 . The contoured surface  532  and internal chassis  534  may be formed within the opening  530  along the length of each side of the shell  542 . 
     The contoured surface  532  may form a precise shape to which a component or accessory of the electronic device attaches, such as a watch band (e.g., watch band  105  depicted in  FIG. 1 ). The shape of the contoured surface  532  (e.g., a curved indentation upward into the shell  542 , having a maximum width which is greater than a width at the surface of the opening  530 ) may be difficult and/or costly to mold or machine from the material of the shell  542  (e.g., a ceramic or otherwise difficult to machine material). Accordingly, the contoured surface  532  may be formed by depositing and machining a machinable material within a simple opening  530  in the shell  542 . Thus, an opening for retaining a watch band or other accessory may be formed with the opening  530  as a first portion of the opening, and the contoured surface  532  of the chassis as a second portion of the opening. 
     Similar to the embodiment depicted in  FIGS. 4D-4G , the contoured surface  532  may adjoin an internal chassis  534 . The geometry of the internal chassis  534  and the contoured surface  532  may require a multi-stage and costly machining process, in which a great deal of brittle material may need to be removed at a relatively slow pace. By creating a shell  542  for the housing  502  with the simple opening  530 , however, the machining cost may be greatly reduced as both the contoured surface  532  and the internal chassis  534  are formed and machined from a more machinable material (e.g., aluminum or machine steel). 
     The internal chassis  534  may also be shaped to include attachment features  536 , such as threaded apertures to which internal components of the electronic device (e.g., components of the display stack, sensors, input/output ports, acoustic components, haptic components, digital and/or analog circuits) are mounted. One or more recesses, such as a ledge  537 , may also be included to facilitate placement of internal components of the electronic device. The internal chassis  534  may include additional apertures, planar surfaces, shaped surfaces, protrusions, mounting points, and other features to facilitate the attachment of internal components to the housing  502 . 
     As another example, depicted in  FIGS. 5B-5E , a machinable material is deposited onto the shell  542  and processed to produce a machined chassis, including a button interface  526  within the oblong opening  520  and a crown shaft interface  528  within the round opening  524 . The button interface  526  and the crown shaft interface  528  may form shapes which are difficult to mold or machine from the material of the shell  542  (e.g., ceramic). Accordingly, it may significantly reduce cost to form the oblong opening  520  and the round opening  524 , and form the more complex button interface  526  from the machined chassis. 
     With the machined chassis coupled to the shell  542 , the oblong opening  520  and the button interface  526  may cooperate as a first and a second portion of an opening. The oblong opening  520  may be the first portion of this opening, which allows a compressible button (e.g., button  108 ) or other component to be at least partially recessed within the opening. The button interface  526  may be the second portion of this opening, which provides a planar surface within the first portion of the opening and a more precise opening for attachment of the button (or other component) and related components. 
     Similarly, the round opening  524  and the crown shaft interface  528  may cooperate to form a precise through-hole (e.g., opening) for retaining a rotatable crown. The shell  542  may be molded with the round opening  524  being slightly larger than needed for the crown, and the machined chassis may be formed within the round opening  524 . The machined chassis within the round opening may form a machined surface, or crown shaft interface  528 . 
     The machined surface of the crown shaft interface  528  may form a bearing, such as a plane bearing or bearing surface, to accommodate a rotatable crown shaft within the round opening  524 . The recess  522  may be formed at least partially from the machinable material of the machined chassis as well. For example, after the machinable material is deposited within the shell  542 , the shell  542  and the machinable material may be machined to form the recess  522 , which partially recesses a crown knob within the shell  542 . 
     The internal chassis  534  may also include a shelf  516  or other attachment point for coupling a transparent cover  518 , as depicted in  FIG. 5C . For example, the shelf  516  may be formed as a bezel or other retaining mechanism for retaining a transparent cover  518  (e.g., a transparent cover  118  over a display  104 , such as depicted in  FIG. 1 ). In some embodiments, the transparent cover  518  may be press fit within the shelf  516  formed in the internal chassis  534 . Accordingly, the machinable material of the shelf  516  and the machined chassis may be a sufficiently compliant material to facilitate a seal to reduce or prevent ingress of contaminants into the housing  502 . The shelf  516  may additionally or alternatively include a groove, beveled edge, or other attachment feature to facilitate retention of the transparent cover  518 . In some embodiments, the transparent cover  518  may be coupled to the internal chassis  534  by another appropriate means, such as application of an adhesive, retention clip, and so on. 
     The back surface of the shell  542  may include one or more sensor openings  544  to house sensors or other components of the electronic device (e.g., optical sensors forming an optical heart rate monitor). A machinable layer or machined chassis may be deposited over the back surface to form a sensor interface  546  within the sensor openings  544  to provide a mounting surface for the sensors. Additional mounting features  548  (e.g., mounting points, mounting surfaces, screw bosses, protrusions, and so on) may be formed on or coupled to the back surface in order to facilitate attachment of components to the housing  502 . 
     In some embodiments, the contoured surface  532 , internal chassis  534 , button interface  526 , crown shaft interface  528 , sensor interface  546 , and other machined features may be formed by depositing a block of machinable material onto the interior of the shell  542  through an appropriate technique, such as described above with respect to  FIGS. 2C and 2D . The block of material may be deposited around the internal surface of the shell  542 . In some embodiments, the block of material may additionally be deposited on the back surface of the shell  542 . After the block of machinable material is deposited, the material may be milled, ground, drilled, polished, or otherwise machined to form a machined chassis, including the contoured surface  532 , internal chassis  534 , button interface  526 , crown shaft interface  528 , sensor interface  546 , and other machined features of the housing  502 . 
     In other embodiments, all or portions of the machined chassis may be formed and machined prior to inclusion with the shell  542 . For example, the internal chassis  534  may be formed and then be coupled to the internal surface of the shell  542  through an appropriate technique, such as brazing or soldering. 
     In some embodiments, a layer of machinable material may be deposited over an area of the shell  542 , such as the interior surface and/or back surface of the shell  542 . The layer of machinable material may be deposited through an appropriate technique, such as vapor deposition or plating, and form a base for other components to couple to and/or be machined from. For example, the contoured surface  532  and internal chassis  534  may be machined into the layer of machinable material. Mounting points  538  (e.g., mounting points for coupling to an internal support frame or other internal components) and additional mounting features  548  may be formed integral with the layer of machinable material, or may be pre-formed and coupled to the layer of machinable material through brazing, soldering, or similar techniques (see, e.g.,  FIGS. 5F-5K ) 
       FIGS. 5F-5K  illustrate example techniques for forming a mounting feature, mounting point, or the like, depicted as example cross-sectional views of the housing depicted in  FIG. 5B , taken along line U-U. As depicted, various techniques for forming and/or attaching a mounting feature  548 . A mounting feature  548  may be a threaded boss, nut, collar, stud, pin, standoff, or similar fastener or feature that facilitates mounting or an interface with components of the electronic device. 
     An example mounting feature  548  may be a (threaded) boss, and may be integrally formed with the machinable layer  549 , as depicted in  FIG. 5F . The mounting feature  548  may be cast, molded, or otherwise formed as part of the machinable layer  549 . As discussed previously, the machinable layer  549  may be coupled to the shell  542 . In some embodiments, the machinable layer  549  may be deposited over the shell, and material may be removed from the machinable layer  549  through an appropriate technique to form or define the mounting feature  548 . 
     In some embodiments, a mounting feature  548  may be formed separately from the machinable layer  549  and coupled to the machinable layer  549 , as depicted in  FIGS. 5G-5K . In some cases, the mounting feature  548  may be soldered or brazed to the machinable layer  549 , as depicted in  FIG. 5G . In other cases, an adhesive  553  may couple the mounting feature  548  to the machinable layer  549 . The adhesive  553  may be an appropriate adhesive for bonding the mounting feature  548  and the machinable layer  549 , such as an epoxy, a pressure sensitive adhesive, a thermal set adhesive, or other similar type of bonding agent. 
     In some embodiments, the machinable layer  549  may be configured to facilitate a structural or mechanical interlock between the mounting feature  548  and the machinable layer  549 . For example, as depicted in  FIG. 5I , an undercut  551 , knurl, beveled edge, groove, or similar attachment feature or combination of attachment features may be formed within a recess. The undercut  551  or similar attachment feature may retain the mounting feature  548  to the machinable layer  549 . In some cases, the mounting feature  548  includes a combination of a structural interlock and an adhesive, braze, or other bonding agent to retain the mounting feature  548  to the machinable layer  549 . 
     In some embodiments, as depicted in  FIG. 5J , a threaded recess  555  may be formed in the machinable layer  549 . The mounting feature  548  may be coupled to the machinable layer by mating corresponding threads on the mounting feature  548  to the threaded recess  555 . In still other embodiments, a recess  557  may be formed with or without attachment features, as depicted in  FIG. 5K , and the mounting feature  548  may be press fit into the recess  557 . 
     It should be understood that the techniques for forming or attaching mounting features illustrated and described with respect to  FIGS. 5F-5K  are illustrative in nature. A variety of similar techniques may be employed in order to form a mounting feature and/or attach it to the machinable layer. Additionally, one or more of the examples of  FIGS. 5F-5K  may be used in combination in any particular implementation. 
     Turning to  FIG. 5L , the mounting points, mounting features, and precision interfaces formed in or attached to the processed machinable material may facilitate attachment of components to the housing. The housing  502  may be similar to the housing  502  depicted in  FIG. 5B , including a shell  542 , chassis  534 , and other features. The chassis and other features may be formed from a machinable material using techniques described above. 
     Once precision interfaces and mounting features are formed in the shell  542 , additional components may be coupled to the shell  542 . For example, a watch band  505  may couple to the contoured surface  532  formed within the opening  530 . Additional attachment features may retain the watch band  505  within the contoured surface  532 , such as a latch or pin. A button  508  may couple to the button interface  526 , and a watch crown  506  may couple to the crown shaft interface  528 . 
     In addition, internal components of the electronic device may be coupled to the housing  502 . For example, a circuit board  533  or similar component may couple to mounting points  538 . A support frame  535  may couple to the chassis  534 , such as through the ledge  537  and adjacent attachment features  536 . The support frame  535  may support the components of a display  504 , and may also add structural support to the housing  502 . 
     In some embodiments, a transparent cover  518  may be positioned over the display  504 . The transparent cover  518  may protect the display and internal components, and may additionally function as an input surface that receives touch and/or force inputs. As described above, the transparent cover  518  may couple to the shelf  516 , and may be press fit or otherwise retained within the shelf  516  (e.g., the shelf  516  may include a groove or beveled edge, an adhesive, or retention clip may be coupled the transparent cover  518  to the shelf  516 . 
     Some embodiments of the housing  502  may include fewer or more precision interfaces, mounting points, and other mounting features. For example, precision surfaces may be required on or around a camera assembly, connector opening, circuit board mounting, battery enclosure, SIM card receiver, and other interface points requiring high tolerances which may not be achieved through the process of forming the shell  542 . In addition, in some embodiments a compliant or other material may be deposited within openings in the shell  542  or otherwise coupled to the shell  542  to increase the performance of the housing  502  (e.g., increasing impact resistance, increasing environmental adaptability, pre-stressing the shell  542 ). 
       FIG. 6  depicts another example electronic device in the form of a portable electronic device incorporating a shell for a housing according to the present disclosure. As shown in  FIG. 6 , the electronic device  600  includes a housing  602  to retain, support, and/or enclose various components of the electronic device  600 , such as a display  604 . The display  604  can provide a visual output to the user. The display  604  can be implemented with any suitable technology, such as described above with respect to  FIG. 1 . 
     A transparent cover  618  may be positioned over the front surface (or a portion of the front surface) of the electronic device  600 . At least a portion of the transparent cover  618  can function as an input surface  606  that receives touch and/or force inputs. Various layers of a display stack (such as the transparent cover  618 , display  604 , touch sensor layer, and so on) may be adhered together with an optically transparent adhesive and/or may be supported by a common frame or portion of the housing  602 . The display stack may be similar to that described above with respect to  FIG. 1 . 
     In many cases, the electronic device  600  can also include a processor, memory, power supply and/or battery, network connections, sensors, input/output ports, acoustic components, haptic components, digital and/or analog circuits for performing and/or coordinating tasks of the electronic device  600 , and so on. For simplicity of illustration, the electronic device  600  is depicted in  FIG. 6  without many of these components, each of which may be included, partially and/or entirely, within the housing  602 . 
     The electronic device may be operable to receive additional input from a user, such as through an input/output device  610 . In some embodiments, the input/output device  610  may be implemented as a mechanical button, while in other embodiments the input/output device  610  may be implemented as a touch and/or force sensitive region of the electronic device  600 . Additional buttons, switches, and other input-output devices may also be included. 
     Similar to the electronic device  100  depicted in  FIG. 1 , the electronic device  600  may be compact, lightweight, and durably constructed. Accordingly, components of the electronic device  600  may be precisely shaped and fitted together in order to reduce overall size, reduce mass, and/or increase performance of the electronic device  600 . Components of the electronic device  600 , such as the housing  602 , may interact with a variety of other components, requiring the components to have multiple precision interfaces. 
     For example, the housing  602  may interface with a transparent cover  618  over the display  604 , a back cover, and/or various other internal and external components of the electronic device  600  (e.g., the display stack or common frame may be coupled to and supported by the housing  602 , external buttons, and so on). Each of these interfaces may require precise machining to yield desired performance. Similar to the electronic device  100  of  FIG. 1 , the electronic device  600  may be constructed to be resistant to entry of liquids and other contaminants. In such embodiments, the need for precision machining may be heightened in order to maintain the electronic device  600  sealed. 
     Precision components may be formed from brittle or difficult to machine materials, such as ceramics. Accordingly, a more machinable material may be deposited over at least a portion of brittle components (such as the housing  602 ), which may then be processed to yield the required precision-machined interface surfaces, as further described below with respect to  FIGS. 7A-7G . 
       FIGS. 7A-7E  depict an example of a housing of an electronic device, including a shell formed from a brittle material.  FIG. 7A  depicts a perspective view of the shell formed from the brittle material.  FIG. 7B  depicts the housing after a machinable material has been added to the shell and processed.  FIG. 7C  depicts a cross-sectional view of the housing depicted in  FIG. 7B , taken along line P-P.  FIG. 7D  depicts a cross-sectional view of the housing depicted in  FIG. 7B , taken along line Q-Q.  FIG. 7E  depicts a cross-sectional view of the housing depicted in  FIG. 7B , taken along line R-R. 
     As depicted in  FIG. 7A , it may be desirable to form a housing  702  for an electronic device from a brittle or otherwise difficult to machine material. However, given the difficulty of machining a housing entirely from this material, the external surface of the housing  702  may be a shell  742  of brittle material. The shell  742  may be formed from a ceramic material in a manner similar to the shell described above with respect to  FIGS. 2A-2F , though the shell  742  can be formed of any difficult to machine material. 
       FIG. 7A  may illustrate, for example, a ceramic shell  742  of a housing  702  after the green body of the shell  742  has been sintered to form a hardened, durable external surface for an electronic device. The shell  742  has been shaped (e.g., molded) with a substantially uniform cross-section to enclose features of the electronic device, having four sides. The sintered ceramic shell  742  may define various features, such as an aperture  750  and a group of apertures  752  along a side of the shell  742 . 
     As depicted in  FIGS. 7B-7E , a machinable material is deposited into the shell  742  and processed to produce various final interfaces for the housing  702 . In many embodiments, the machinable material forms a machined chassis  734 . The machined chassis  734  may include various features, such as one or more mounting points  738  (e.g., mounting points for coupling to an internal support frame or other internal components), a microphone mounting region  758  around the aperture  750 , and a speaker mounting region  756  around the group of apertures  752 . 
     A microphone mounting region  758  may be formed in the machined chassis deposited around the aperture  750 . The microphone mounting region  758  may include a planar recess within the machinable material, and may additionally include threaded apertures  760 . The microphone mounting region  758  may facilitate attachment of a microphone, circuitry, and similar components within the electronic device, which may be coupled to the housing  702  via the threaded apertures  760 . 
     A speaker mounting region  756  may similarly be formed in the machined chassis deposited around a group of apertures  752 . The speaker mounting region  756  includes an ovular recess to facilitate attachment of a speaker, circuitry, and similar components within the electronic device. In some embodiments, the microphone mounting region  758  and/or the speaker mounting region  756  may further facilitate an O-ring, gasket, or similar liquid-sealing mechanism. 
     In some embodiments, the machined chassis  734  may also include a machined shelf  716  around a perimeter of the shell  742 . The machined shelf  716  may be an attachment point for coupling a transparent cover, such as described below with respect to  FIGS. 7F and 7G . The machined chassis  734  may further include a machined back shelf  740  around a perimeter of the shell  742  opposite the machined shelf  716 . The machined back shelf  740  may be an attachment point for a back cover, such as described below with respect to  FIGS. 7F and 7G . 
       FIG. 7F  depicts a perspective view of the housing of an electronic device after fitting a transparent cover and a back cover to attachment points, such as machined shelves.  FIG. 7G  depicts a cross-sectional view of the housing depicted in  FIG. 7F , taken along line S-S. 
     The machined shelf  716  may couple the shell  742  of the housing  702  to another component of the electronic device, such as the transparent cover  718  (e.g., a transparent cover  118  over a display  104 , such as depicted in  FIG. 1 ). Similarly, the machined back shelf  740  may couple the shell  742  to a back cover  741 . The back cover may function as an external surface of the electronic device, and may be transparent or opaque. The back cover can be formed with any suitable material, such as metal, glass, plastic, sapphire, or combinations thereof. 
     The machined shelf  716  and machined back shelf  740  may each function as a bezel or other retaining mechanism for the covers  718 ,  741 . A seal may be formed between the transparent cover  718  and the machined shelf  716 , and another seal may be formed between the back cover  741  and the machined back shelf  740 . In some embodiments, the machinable material of the machined shelf  716  and machined back shelf  740  may be a sufficiently compliant material to facilitate a seal. In some embodiments, one or both of the transparent cover  718  and the back cover  741  may be press fit into a respective shelf  716 ,  740 . 
     In some embodiments, one or both of the machined shelf  716  and the machined back shelf  740  may additionally or alternatively include a groove, beveled edge, or other attachment feature to facilitate retention of the transparent cover  718  and/or the back cover  741 . In some embodiments, the transparent cover  718  and/or the back cover  741  may be coupled to the housing  702  by another appropriate means, such as application of an adhesive, a retention clip, and so on. 
     In some embodiments, the machinable material of the machined chassis  734  may be selected for other performance characteristics, such as conductivity. Accordingly, one or both of the machined shelf  716  and the machined back shelf  740  may function as an antenna or other conductor. 
     In some embodiments, one or more mounting points  738  (e.g., a screw boss, bracket, or the like) may be formed on or coupled to the machined chassis  734  (see, e.g.,  FIGS. 5F-5K ). An internal component  762  of the electronic device (e.g., a circuit board, internal support frame, and so on) may be coupled to each mounting point  738  through a fastener  764  (e.g., a screw, rivet, clip, pin, and so on) secured to the mounting point (e.g., secured to a threaded aperture such as a screw boss). 
       FIG. 7H  depicts a housing for an electronic device including an insulating material coupled to the shell of the housing by a machinable material. In some embodiments, it may be desirable to isolate portions of the shell  742 , such as for electrical insulation. For example, the shell  742  may be formed from a metal which is difficult to machine. An insulating insert  768  may be coupled between segments of the shell  742  in order to form an antenna using the conductive material of the shell  742 . In some embodiments, the insulating insert  768  may facilitate transmission and/or reception of electromagnetic signals from internal components of the electronic device through the insulating insert  768 . 
     The insulating insert  768  may be formed from an appropriate material, such as plastic, acrylic, nylon, polycarbonate, polyurethane, and so on. A machinable material may be formed on an interior surface of the housing  742 , which may provide attachment features to retain the insulating insert  768  to the housing  742 . 
       FIG. 7I  depicts a cross-sectional view of the housing depicted in  FIG. 7H , taken along line T-T. As depicted in  FIG. 7I , the housing includes a shell  742  formed from a difficult to machine material (e.g., a high hardness metal, stainless steel, or ceramic). The shell  742  may define one or more splits  770 , which may divide the shell  742  into one or more segments. An insulating insert  768  may be coupled between the segments of the shell  742 , electrically isolating the segments. 
     In certain embodiments, an insulating insert  768  may be insert molded, injection molded, or otherwise formed within a split  770  in the shell  742 . In order to facilitate attachment of the insulating insert  768 , a machinable chassis  734  may be formed on an interior surface of the shell  742 . The machinable chassis  734  may be machined or otherwise shaped to include one or more attachment features  766 . 
     An attachment feature  766  may include multiple protrusions with a keyhole  770  or similar undercut between, in order to facilitate a mechanical interlock between the insulating insert  768  and the attachment feature  766 . In some embodiments, an attachment feature  766  may be formed in the machined chasses  734  adjacent each side of a split  770  to further interlock each segment of the shell  742  together through the insulating insert  768 . 
     The above description referenced brittle materials, and in particular sintered ceramic materials and other materials that may be difficult to machine (e.g., stainless steel, hardened steel, high-carbon steel, titanium). It should be understood that the present embodiment is not limited to such materials. Embodiments encompassed within the present disclosure include components for electronic devices formed from any material, in particular any material which has low machinability or for other reasons is costly to machine to produce finished surfaces and attachment features. 
     The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the described embodiments. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the described embodiments. Thus, the foregoing descriptions of the specific embodiments described herein are presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the embodiments to the precise forms disclosed. It will be apparent to one of ordinary skill in the art that many modifications and variations are possible in view of the above teachings.

Metadata:
Filing Date: 20171123
Publication Date: 20200121
Grant Date: 20200121
Priority Date: 20170802
Inventors: PREST, CHRISTOPHER D.
ELY, COLIN M.
MATSUYUKI, NAOTO
POOLE, Joseph C.
Assignee: APPLE INC
CPC Classifications: [{"code": "H05K5/0217", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/1633", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K5/0017", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K5/0095", "inventive": true, "first": true, "tree": "[]"}, {"code": "H05K7/1417", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/1637", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/163", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/163", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F1/1656", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K5/0247", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/1626", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K5/03", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K5/006", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K5/0017", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K5/03", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K5/0013", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/163", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K5/0247", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/1656", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K7/1417", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/1626", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K5/0095", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F1/1637", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/1633", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K5/006", "inventive": true, "first": false, "tree": "[]"}, {"code": "G04G17/08", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K5/0217", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K5/15", "inventive": true, "first": false, "tree": "[]"}, {"code": "G04G17/08", "inventive": true, "first": true, "tree": "[]"}, {"code": "G04G17/08", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/1633", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/1637", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/163", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/1626", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/1656", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 63108491