PATENT DOCUMENT

Publication Number: US-10375853-B2
Application Number: US-201715682291-A
Country: US
Kind Code: B2

Title: Electronic device with cooling fan

Abstract:
In an exemplary electronic device with a cooling fan, a fan assembly is attached to a keyboard assembly of the electronic device. The fan assembly includes an impeller at least partially inside a fan enclosure. The fan enclosure has, on a surface, an inlet opening and an external protrusion. The electronic device further includes a bottom case. The fan assembly is positioned between the keyboard assembly and the bottom case and oriented such that the inlet opening and the external protrusion face the bottom case. The external protrusion maintains a passage between the fan enclosure and the bottom case that allows air to enter the inlet opening and also resists interference between the rotating impeller and the stationary bottom case.

Claims:
What is claimed is: 
     
       1. An electronic device having an internal cooling fan, the electronic device comprising:
 a fan assembly attached to a keyboard assembly, the fan assembly comprising:
 a fan enclosure having, on a surface, an inlet opening and an external protrusion; and 
 an impeller at least partially inside the fan enclosure; and 
 
 a bottom case, the fan assembly positioned between the keyboard assembly and the bottom case and oriented such that the inlet opening and the external protrusion face the bottom case, 
 wherein the external protrusion maintains a passage between the fan enclosure and the bottom case that allows air to enter the inlet opening, wherein the entire external protrusion is positioned on a side of the inlet opening that is opposite of a diffuser portion of the fan enclosure, and wherein at least a portion of the passage extends continuously from an inner surface of the bottom case to a surface of the external protrusion closest to the inner surface of the bottom case. 
 
     
     
       2. The device of  claim 1 , wherein a cross-section of the external protrusion has a teardrop shape. 
     
     
       3. The device of  claim 2 , wherein the cross-section of the external protrusion tapers toward the inlet opening. 
     
     
       4. The device of  claim 1 , wherein the external protrusion is separated from the bottom case by a gap. 
     
     
       5. The device of  claim 1 , wherein the external protrusion is positioned closer to a sidewall of the fan enclosure than the inlet opening, and wherein at least a portion of the sidewall of the fan enclosure is parallel to a rotation axis of the impeller. 
     
     
       6. The device of  claim 1 , wherein a portion of the impeller extends out from within the fan enclosure through the inlet opening. 
     
     
       7. The device of  claim 1 , wherein at least a portion of a wall on which the surface is disposed increases in thickness radially outward from the inlet opening. 
     
     
       8. The device of  claim 1 , wherein the inlet opening is disposed on a wall of the fan enclosure, wherein the impeller comprises a plurality of blades, each blade of the plurality of blades includes an edge proximate to a portion of the wall surrounding the inlet opening, and wherein the edge of each blade of the plurality of blades is sloped away from a rotation axis of the impeller. 
     
     
       9. The device of  claim 8 , wherein an inner surface of the portion of the wall surrounding the inlet opening is parallel to the edge of each blade of the plurality of blades. 
     
     
       10. The device of  claim 9 , wherein the edge of each blade of the plurality of blades is positioned no more than 0.6 mm from the inner surface of the portion of the wall surrounding the inlet opening. 
     
     
       11. The device of  claim 1 , wherein the diffuser portion comprises:
 a diffuser channel; and 
 an outlet opening through which air exits the fan assembly, the outlet opening disposed at an end of the diffuser channel, 
 wherein the diffuser channel diverges toward the outlet opening with respect to a plane of rotation of the impeller. 
 
     
     
       12. The device of  claim 11 , wherein at least a wall of the diffuser channel diverges toward the outlet opening at an angle of 5-7 degrees with respect to the plane of rotation of the impeller. 
     
     
       13. The device of  claim 11 , wherein:
 an inner surface of the diffuser portion is linearly sloped toward the outlet opening and with respect to the plane of rotation of the impeller. 
 
     
     
       14. The device of  claim 11 , wherein:
 a height of a cross-section of the outlet opening is perpendicular to a width of the cross-section of the outlet opening; and 
 the height of the cross-section of the outlet opening varies across the width of the cross-section of the outlet opening. 
 
     
     
       15. The device of  claim 11 , wherein:
 a thickest portion of a wall of the diffuser portion is disposed between opposite sidewalls of the diffuser portion; and 
 a thickness of the wall of the diffuser portion tapers from the thickest portion toward each sidewall of the opposite sidewalls. 
 
     
     
       16. The device of  claim 15 , wherein an inner surface of the wall of the diffuser portion has a topography that is independent of a topography of an outer surface of the wall of the diffuser portion. 
     
     
       17. The device of  claim 1 , wherein the fan enclosure comprises at least two discrete pieces. 
     
     
       18. The device of  claim 1 , wherein the fan enclosure consists of a first piece and a second piece that are attached to each other using one or more attaching components. 
     
     
       19. The device of  claim 1 , further comprising a motherboard, wherein the fan assembly is disposed between the keyboard assembly and the motherboard. 
     
     
       20. The device of  claim 19 , wherein:
 the fan enclosure comprises a first piece and a second piece that are disposed on opposite sides of the impeller; 
 the first piece of the fan enclosure has the inlet opening; and 
 the motherboard is directly attached to the first piece of the fan enclosure. 
 
     
     
       21. The device of  claim 19 , wherein:
 the fan enclosure comprises a first piece and a second piece that are disposed on opposite sides of the impeller; 
 the first piece of the fan enclosure has the inlet opening; and 
 the motherboard is directly attached to the second piece of the fan enclosure without being directly attached to the first piece of the fan enclosure. 
 
     
     
       22. The device of  claim 1 , wherein the fan enclosure includes a second wall disposed on a side of the fan enclosure opposite of the inlet opening, and wherein the second wall of the fan enclosure is directly attached to a bottom surface of the keyboard assembly. 
     
     
       23. The device of  claim 22 , wherein
 a majority of an outer surface of the second wall of the fan enclosure is positioned flush against the bottom surface of the keyboard assembly. 
 
     
     
       24. The device of  claim 23 , wherein:
 the fan assembly includes a flexible printed circuit configured to transmit a back electromotive force signal generated by a motor of the fan assembly; 
 the flexible printed circuit is disposed between the outer surface of the second wall of the fan enclosure and the bottom surface of the keyboard assembly; and 
 the flexible printed circuit does not include an electromagnetic interference (EMI) shielding layer. 
 
     
     
       25. The device of  claim 1 , wherein:
 a base layer of the keyboard assembly includes a plurality of openings configured to allow air to pass through the base layer; and 
 a recessed portion of the base layer and an outer surface of the fan enclosure form a venting channel, the venting channel coupling two or more openings of the plurality of openings. 
 
     
     
       26. The device of  claim 25 , wherein an edge of the recessed portion of the base layer extends beyond a perimeter of the fan assembly. 
     
     
       27. The device of  claim 2 , wherein a first end of the cross-section of the external protrusion is positioned closer to the inlet opening than a second end of the cross-section of the external protrusion, and wherein a diameter at the second end is greater than a diameter at the first end. 
     
     
       28. The device of  claim 1 , wherein the external protrusion is entirely disposed between the inlet opening and an external sidewall of the fan enclosure opposite of the diffuser portion.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from U.S. Provisional Ser. No. 62/384,041, filed on Sep. 6, 2016, entitled ELECTRONIC DEVICE WITH COOLING FAN, and from U.S. Provisional Ser. No. 62/413,395, filed on Oct. 26, 2016, entitled ELECTRONIC DEVICE WITH COOLING FAN, which are hereby incorporated by reference in their entirety for all purposes. 
    
    
     FIELD 
     This relates generally to electronic devices, and more specifically, to electronic devices with internal cooling fans. 
     BACKGROUND 
     As recent models of electronic devices are becoming increasingly faster and more powerful, they are also becoming sleeker and smaller in size. Consumer preferences and demands tend to drive both of these trends toward faster and smaller. Electronic device makers are thus faced with the challenges of incorporating faster and more powerful electronic chips and circuitry into smaller electronic device offerings. 
     Electronic devices contain components that produce heat during normal operation. Fans, heat sinks, and/or other heat management components are used to reduce heat. But increasingly faster and more powerful chips and integrated circuitry can generate more heat than previous generations of electronics. Placement of these components into smaller overall volumes can create new challenges. 
     SUMMARY 
     In an exemplary electronic device with a cooling fan, a fan assembly is attached to a keyboard assembly of the electronic device. The fan assembly includes an impeller at least partially inside a fan enclosure. The fan enclosure has, on a surface, an inlet opening and an external protrusion. The electronic device further includes a bottom case. The fan assembly is positioned between the keyboard assembly and the bottom case and oriented such that the inlet opening and the external protrusion face the bottom case. The external protrusion maintains a passage between the fan enclosure and the bottom case that allows air to enter the inlet opening. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  illustrates a front perspective view of an electronic device, according to various examples. 
         FIG. 1B  illustrates a partial plan view of an interior region of a base portion of an electronic device with a cooling fan, according to various examples. 
         FIG. 1C  illustrates a cross-sectional view of a portion of an electronic device with an internal cooling fan, according to various examples. 
         FIGS. 2A-2B  illustrate top perspective views of a cooling fan of an electronic device, according to various examples. 
         FIG. 2C  illustrates a bottom perspective view of a cooling fan of an electronic device, according to various examples. 
         FIG. 2D  illustrates a cross-sectional view of a cooling fan of an electronic device, according to various examples. 
         FIG. 3  illustrates a magnified perspective view of an external protrusion on the surface of a cooling fan, according to various examples. 
         FIG. 4  illustrates simulated airflow around an external protrusion of a cooling fan, where the external protrusion has a teardrop-shaped cross-section, according to various examples. 
         FIG. 5  illustrates simulated airflow around an external protrusion of a cooling fan, where the external protrusion has a circular cross-section, according to various examples. 
         FIG. 6  illustrates a cross-sectional view of a diffuser portion of a cooling fan, according to various examples. 
         FIG. 7  illustrates a cover portion of a fan enclosure of a cooling fan, according to various examples. 
         FIG. 8  illustrates a base plate of a fan enclosure of a cooling fan, according to various examples. 
         FIGS. 9A-9B  illustrate cross-sectional perspective views of a cover portion of a fan enclosure of a cooling fan, according to various examples. 
         FIG. 10  illustrates a cross-sectional view of an electronic device where the motherboard is attached to a cover portion of a fan enclosure of a cooling fan, according to various examples. 
         FIG. 11  illustrates a cross-sectional view of an electronic device where the motherboard is attached to a base plate of a fan enclosure of a cooling fan, according to various examples. 
         FIG. 12A  illustrates a top-down view of a cooling fan attached to a base layer of a keyboard assembly, according to various examples. 
         FIG. 12B  illustrates a top-down view of a base plate of a fan enclosure of a cooling fan attached to a base layer of a keyboard assembly, according to various examples. 
         FIG. 13  illustrates a top-down view of a portion of an electronic device where cooling fans are attached to a keyboard assembly that has one of several possible configurations, according to various examples. 
         FIG. 14A  illustrates a cross-sectional view of a portion of an electronic device where a cooling fan is attached to a keyboard assembly via a base plate of the cooling fan, according to various examples. 
         FIG. 14B  illustrates a cross-sectional view of a portion of an electronic device where a motherboard is attached a base plate of a cooling fan, according to various examples. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is presented to enable a person of ordinary skill in the art to make and use the various embodiments. Descriptions of specific devices and applications are provided only as examples. Various modifications to the examples described herein will be readily apparent to those of ordinary skill in the art, and the general principles defined herein may be applied to other examples and applications without departing from the spirit and scope of the various embodiments. Thus, the various embodiments are not intended to be limited to the examples described herein and shown, but are to be accorded the scope consistent with the claims. 
     Electronic devices contain components that produce heat during normal operation. As such, fans, heat sinks, and other heat diversion components are used to manage operating temperatures in some electronic devices. Heat-producing components generate heat at increasing levels, and ongoing consumer demands require that devices become smaller and thinner, such that fans and other components need to be smaller and more efficient. However, integrating fans into smaller or thinner devices can result in the fans being more susceptible to damage during user handling events. In particular, fans that are integrated into smaller or thinner devices can have components that are positioned very close together. This increases the likelihood that stationary and moving components in the fan rub against each other and cause damage or unwanted noise during user handling events. For example, force exerted on the keyboard or external case of an electronic device can transfer to the fan and cause stationary components of the fan (e.g., the fan enclosure) to rub against moving components of the fan (e.g., the impeller). Furthermore, fans that are integrated into smaller or thinner devices can be more susceptible to localized obstruction to airflow, which can result in higher friction losses, more turbulent airflow, vortex shedding, and increased aeroacoustic noise. There is thus a desire for improved fan designs that occupy less space, have sufficient structural support and margin to resist user handling events, and/or produce reduced aeroacoustic noise while still delivering acceptable levels of device heat management. 
     In accordance with at least some of the embodiments set forth herein, various structures and arrangements for cooling fans of electronic devices are described that address the challenges discussed above. In one exemplary electronic device, a fan assembly is attached to a keyboard assembly of the electronic device. The fan assembly includes an impeller at least partially inside a fan enclosure. The fan enclosure has, on a surface, an inlet opening and an external protrusion. The electronic device further includes a bottom case. The fan assembly is positioned between the keyboard assembly and the bottom case and oriented such that the inlet opening and the external protrusion face the bottom case. The external protrusion maintains clearance between the fan assembly and the bottom case during user handling events to ensure proper fan operation. 
       FIG. 1A  illustrates a front perspective view of an exemplary electronic device. In various embodiments, an electronic device suitable for use with the disclosed cooling fan can include a desktop computing device with a built-in display, a portable computing device, or a video-streaming device, for example. In the example shown in  FIG. 1A , electronic device  100  can be a consumer electronic device such as a laptop computer. As shown, electronic device  100  includes display housing  102  coupled with base portion  104 , allowing display housing  102  to pivot with respect to base portion  104 . In some examples, display housing  102  and base portion  104  are formed from a metal, such as aluminum. In other examples, display housing  102  and base portion  104  are formed from plastic. Display housing  102  includes display panel  106  designed to provide visual content. Base portion  104  includes top case  112  coupled with a bottom case (e.g., bottom case  122  shown in  FIG. 1C ). Top case  112  and the bottom case define a space designed to receive several components of electronic device  100 , such as processor circuits, memory circuits, and one or more battery modules. Also, base portion  104  includes several components allowing a user to input one or more controls to the electronic device  100 , such as touch pad  116  and keyboard assembly  118 . 
     During use of electronic device  100 , some of the several components enclosed within the space defined by the top and bottom cases convert electrical energy into heat, thereby causing an increase in the temperature of electronic device  100 . To reduce the temperature, base portion  104  can include an internal cooling fan. For example,  FIG. 1B  illustrates a partial plan view of an interior region of base portion  104  of electronic device  100 , according to various examples. The bottom case of base portion  104  is removed to show cooling fan  200  disposed within base portion  104 . In the perspective view shown in  FIG. 1B , keys  124  of keyboard assembly  118  are oriented into the plane of the drawing and cooling fan  200  is positioned over the bottom surface of keyboard assembly  118 . Cooling fan  200  includes fan enclosure  202  and impeller  206  disposed at least partially inside fan enclosure  202 . Fan enclosure  202  forms an exterior surface for the fan and defines inlet opening  212  and outlet opening  210  of cooling fan  200 . Heat from at least some of the several components of electronic device  100  can be transported via a heat pipe (not shown) to cooling fins  120  that are disposed adjacent to outlet opening  210 . A motor (not shown) of cooling fan  200  is configured to rotate impeller  206  to draw air into inlet opening  212  and expel air through outlet opening  210  into cooling fins  120 , thereby removing heat from cooling fins  120  and cooling electronic device  100 . 
       FIG. 1C  illustrates a cross-sectional view of a portion of electronic device  100  with cooling fan  200 , according to various examples. Specifically,  FIG. 1C  is a cross-sectional view of electronic device  100  taken along the portion indicated by dotted line  123  on  FIG. 1B . Bottom case  122  of base portion  104  is included in the depiction of electronic device  100  in  FIG. 1C . As shown, keyboard assembly  118  and cooling fan  200  are disposed at least partially between top case  112  and bottom case  122  of bottom portion  104 . Keyboard assembly  118 , in some examples, is attached to top case  112 . Cooling fan  200  is attached to base layer  126  of keyboard assembly  118  and is oriented such that inlet opening  212  and external protrusion  214  face bottom case  122 . Cooling fan  200 , in some examples, does not directly contact bottom case  122 . As shown in  FIG. 1C , external protrusion  214  protrudes from outer surface  204  of fan enclosure  202 . External protrusion  214  is separated from bottom case  122  by gap  130  and thus does not directly contact bottom case  122 . In some examples, height  134  of gap  130  is approximately 0.8-1.2 mm. In a specific example, height  134  of gap  130  is approximately 1.0 mm. 
     External protrusion  214  can serve to increase the amount of force that cooling fan  200  can sustain from user handling of electronic device  100  before damage is incurred. For example, during user handling of electronic device  100 , top case  112  and/or bottom case  122  can experience compressive forces that cause bottom case  122  to translate toward cooling fan  200  or vice versa. During such events, external protrusion  214  resists inner surface  132  of bottom case  122  from directly contacting impeller  206 . Direct contact of bottom case  122  with impeller  206  is undesirable as it can interfere with the rotation of impeller  206 , which can generate undesirable frictional noise and also cause damage to cooling fan  200 . 
     External protrusion  214  maintains passage  128  between fan enclosure  202  and bottom case  122  that allows air to enter the inlet opening  212 . Specifically, during most user handling events where compressive forces are applied to top case  112  and/or bottom case  122 , inner surface  132  of bottom case  122  can directly contact external protrusion  214  without inner surface  132  of bottom case  122  directly contacting impeller  206  or portion  216  of fan enclosure  202 . External protrusion  214  thus increases the amount of force that top case  112  and/or bottom case  122  can sustain before bottom case  122  interferes with the rotation of impeller  206 . This can enable base portion  104  to have a thinner design because less clearance between bottom case  122  and fan enclosure or between blades  222  and portion  216  of fan enclosure  202  would need to be provided. Additionally, external protrusion  214  enables cooling fan  200  to be positioned closer to bottom case  122  because external protrusion  214  serves to limit the motion of cooling fan  200  during a shock event (e.g., electronic device is dropped and impacts a surface). This is desirable because reducing the motion of cooling fan  200  reduces the amount of strain that cooling fan  200  experiences. In some examples, height  136  of passage  128  between portion  216  and bottom case  122  is approximately 1.8-2.0 mm. In some examples, distance  138  between the hub of impeller  206  and bottom case  122  is approximately 1.5-1.8 mm. Additional details regarding external protrusion  214  are described below with reference to  FIGS. 2A-D  and  FIGS. 3-5 . 
     As depicted in  FIG. 1C , cooling fan  200  is positioned between keyboard assembly  118  and bottom case  122 . Cooling fan  200  is attached to base layer  126  of keyboard assembly  118  and keyboard assembly  118  is attached to top case  112 , in some examples. In addition to base layer  126 , keyboard assembly  118  includes keys  124 , support mechanisms  110 , and electronics package  108 . Each key  124  is supported by support mechanism  110  that translates key  124  vertically in response to a downward force on key  124  during a keystroke event. In some examples, each electronics package  108  includes a switch attached to a flexible printed circuit board. The switch of electronics package  108  biases key  124  to be in its natural, non-depressed position. When key  124  is placed in a depressed position by a keystroke event, the switch can cause the keystroke event to be registered by circuitry associated with the switch or by other circuitry contained within electronics package  108 . In some examples, each electronics package  108  further includes a light source (e.g., light-emitting diode) for backlighting the respective key  124 . Support mechanisms  110  and electronics packages  108  are attached to base layer  126  of keyboard assembly  118 . Base layer  126  can provide the platform for the components contained within the keyboard assembly. In some examples, base layer  126  includes openings (e.g., openings  1206  shown in  FIGS. 12A-B ) that extend from a top surface to a bottom surface of base layer  126 . The openings enable air under key  124  to vent through base layer  126  into an internal region of base portion  104  when key  124  is depressed. Base layer  126  includes one or more layers. For example, base layer  126  includes one or more of a feature plate, a circuit board, an illumination panel, or a sensor membrane. One skilled in the art would recognize that base layer  126  can include other layers necessary for the function of keyboard assembly  118 . In some examples, base layer  126  includes an electromagnetic inference (EMI) shielding layer for shielding the electronic components of keyboard assembly  118  (e.g., electronics packages  108  or the circuit board of base layer  126 ) from EMI generated by components within bottom portion  104 . The EMI shielding layer also shields EMI generated by components within bottom portion  104 , thereby reducing the amount of EMI escaping into free-space. The EMI shielding layer, in some examples, is the bottommost layer of base layer  126  adjacent to cooling fan  200 . In some examples, the EMI shielding layer includes a metal film that extends across base layer  126 . The EMI shielding layer can be grounded. In a specific example, the EMI shielding layer includes an aluminized Mylar layer. 
     In the present example, cooling fan  200  is directly attached to keyboard assembly  118 . Specifically, cooling fan  200  is directly attached to the bottom surface of keyboard assembly  118  such that a majority of an outer surface of back wall  232  is positioned substantially flush against the bottom surface of keyboard assembly  118 . The majority of the outer surface of back wall  232  is thus in direct contact with the bottom surface of keyboard assembly  118 . In the present example, the bottom surface of keyboard assembly  118  corresponds to the bottom surface of base layer  126 . Specifically, the bottom surface of base layer  126  is oriented toward bottom case  122  and away from keys  124 . Back wall  232  of fan enclosure  202  is disposed on a side of the fan enclosure  202  opposite of inlet opening  212 . Back wall  232  is thus oriented toward top case  112 . Positioning back wall  232  of fan enclosure  202  directly against the bottom surface of keyboard assembly  118  can be desirable to reduce the vertical space occupied by the fan, which enables a thinner base portion  104  of electronic device  100 . Additionally, the amount of noise generated during operation of cooling fan  200  is reduced. Specifically, when back wall  232  is positioned directly against base layer  126  of keyboard assembly  118 , the vibration of back wall  232  caused by the rotation of the motor and impeller  206  is dampened by base layer  126  and other components of keyboard assembly  118 . This reduces the amplitude of vibration generated by cooling fan  200 . In contrast, if cooling fan  200  were attached to keyboard assembly  118  with spacers that maintain a gap (e.g., greater than 0.2 mm gap) between the outer surface of back wall  232  and the bottom surface of keyboard assembly  118 , back wall  232  is less supported and various vibration modes can develop on back wall  232  during operation of cooling fan  200 . This could result in increased vibrational noise from cooling fan  200 . Additional aspects regarding positioning back wall  232  of cooling fan  200  against the bottom surface of keyboard assembly  118  are described below with reference to  FIGS. 12A-B . 
     Various aspects of cooling fan  200  are now described in detail with reference to  FIGS. 2A-D .  FIGS. 2A-B  illustrate top perspective views of cooling fan  200 , according to various examples.  FIG. 2C  illustrates a bottom perspective view of cooling fan  200 , according to various examples.  FIG. 2D  illustrates a cross-section view of cooling fan  200  with the motor and bearing not shown, according to various examples. The cross-sectional view of cooling fan  200  in  FIG. 2D  is taken along dotted line  240  shown in  FIG. 2B . Cooling fan  200  can also be referred to as a fan assembly. 
     In the present example, cooling fan  200  is a centrifugal fan designed to draw air through inlet opening  212  into the center of the fan and drive the air radially outward from the center of the fan and out through outlet opening  210  of the fan. Cooling fan  200  includes fan enclosure  202  that forms an exterior surface for the fan and impeller  206  that is disposed at least partially inside fan enclosure  202 . Fan enclosure  202  also defines a fan cavity that at least partially houses impeller  206 . Impeller  206  includes a plurality of blades  222  positioned around hub  238 . A portion of impeller  206  extends out from the interior of fan enclosure  202  through inlet opening  212 . Specifically, as shown in  FIGS. 2A-D , hub  238  of impeller  206  extends at least partially out through inlet opening  212 . It should be recognized that in other examples, the impeller can be entirely disposed within the fan enclosure such that the hub of the impeller does not extend beyond the plane of inlet opening  212 . Although in the present example, cooling fan  200  is a centrifugal fan, it should be recognized that at least some of the features of cooling fan  200  described herein are applicable to other mechanical fan configurations. 
     Cooling fan  200  further includes a motor and bearing (not shown) disposed within fan hub  238  that rotates impeller  206  with respect to rotation axis  226  that is aligned to the center of hub  238 . Power is transmitted to the motor via flexible printed circuit (FPC)  236  of cooling fan  200  (shown in  FIG. 2C ). As the motor turns, the motor emits a back electromotive force (EMF) signal that is transmitted through FPC  236  to a driver circuit separate from cooling fan  200 . FPC  236  is thus configured to transmit a back EMF signal generated by the motor of cooling fan  200  to the driver circuit. The back EMF signal indicates the rotational speed of the motor. One end of FPC  236  is attached to the motor within fan enclosure  202 . FPC  236  extends out from fan enclosure  202  through opening  237  (e.g., similar or identical to opening  802  shown in  FIG. 8 ) on back wall  232 . An external portion of FPC  236  is positioned along the outer surface of back wall  232  of fan enclosure  202 . 
     Fan enclosure  202  includes front wall  224  disposed on one side of impeller  206  and back wall  232  disposed on an opposite side of impeller  206 . Fan housing  202  also includes sidewalls  234  that surround most of the perimeter of impeller  206 . Sidewalls  234  couple back wall  232  to front wall  224 . In the present example, front wall  224  and side wall  234  are formed integrally as one part. Front wall  224  defines inlet opening  212  for allowing air to enter into fan enclosure  202  of cooling fan  200 . In some examples, a second inlet opening for allowing air into the fan enclosure can be included on the back wall of the fan enclosure. Fan enclosure  202  further includes diffuser portion  230  disposed on one side of cooling fan  200 . During operation of cooling fan  200 , air is directed through a diffuser channel (e.g., diffuser channel  606  shown in  FIG. 6 ) of diffuser portion  230  and expelled out from outlet opening  210 . Outlet opening  210  is disposed at the end of the diffuser channel and is oriented approximately perpendicularly to inlet opening  212 . It should be recognized that various alternative air inlet and air outlet arrangements may also be used. 
     The dimensions of fan enclosure  202  are suitably designed to address the challenges discussed above. In one aspect, the vertical profile of fan enclosure is small to enable a thinner and sleeker electronic device. For instance, in some examples, distance  248  from outer surface  204  of front wall  224  adjacent to blade  222  to outer surface of back wall  232  is approximately 4.0-4.4 mm, distance  252  from outer surface  204  of front wall  224  at outlet opening  210  to outer surface of back wall  232  at outlet opening is approximately 5.0-6.0 mm, and distance  250  from end surface of external protrusion  214  to outer surface of back wall  232  is approximately 5.0-6.0 mm. 
     As briefly discussed above, fan enclosure  202  includes external protrusion  214  that protrudes from outer surface  204  of fan enclosure  202 . In some examples, external protrusion  214  is approximately perpendicular to outer surface  204  of fan enclosure  202 . External protrusion  214  is configured to resist bottom case  122  from directly contacting impeller  206  or outer surface  204  of fan enclosure  202 , thereby increasing the amount of force that cooling fan  200  can sustain during user handling events before damage or unwanted rubbing noise is incurred. In particular, during most user handling events, passage  128  is maintained between outer surface  204  of fan enclosure  202  and bottom case  122  and allows air to enter inlet opening  212 . At the same time, because external protrusion  214  protrudes from outer surface  204 , external protrusion can partially obstruct airflow toward inlet opening  212 . Excessive obstruction to the airflow can cause the formation of turbulent airflow upstream of inlet opening  212 . The turbulent airflow can be intensified by impeller  206  after entering inlet opening and can cause airflow exiting outlet opening  210  to become even more turbulent. Turbulent airflow entering or exiting cooling fan  200  is undesirable as it produces undesirable aeroacoustic noise. In order to reduce the formation of turbulent airflow through passage  128 , external protrusion  214  can be positioned away from areas where airflow is the strongest. For example, external protrusion  214  can be positioned on outer surface  204  where airflow toward inlet opening  212  is minimal. In the present example, airflow toward inlet opening  212  is the strongest near diffuser portion  230  and near inlet opening  212 . Thus, as shown in  FIGS. 2A-B , external protrusion  214  is positioned proximate to a side opposite of diffuser portion  230  such that inlet opening  212  is positioned between external protrusion  214  and diffuser portion  230 . Additionally, external protrusion  214  is positioned proximate to sidewall  234  and thus away from inlet opening  212  where airflow is stronger. Specifically, external protrusion  214  is positioned closer to sidewall  234  of fan enclosure  202  than inlet opening  212 . 
     In the present example, as shown in  FIG. 2D , at least a portion of external protrusion  214  directly overlaps with a portion of sidewall  234 . Positioning external protrusion  214  at the perimeter of outer surface  204  and above sidewall  234  can be desirable for providing greater support and strength to external protrusion  214 . A force applied to external protrusion  214  by bottom case  122  would thus be distributed through sidewall  234  rather than cause front wall  224  to translate toward blades  222 . This is advantageous for providing further resistance against front wall  224  contacting blades  222 . 
     In some examples, the external protrusion is aerodynamically-shaped to further reduce the formation of undesirable air flow structures such as vortices or turbulent wakes around the external protrusion.  FIG. 3  illustrates a magnified perspective view of external protrusion  214  on outer surface  204  of cooling fan  200 , according to various examples. As shown, the cross-section of external protrusion  214  has a teardrop shape to reduce the disturbance to the surrounding air flow field caused by external protrusion  214 . In the present example, the teardrop-shaped cross-section is symmetric, with its axis of symmetry aligned with the local air flow direction. In other examples, the teardrop shaped cross-section can be asymmetric. The cross-section of external protrusion  214  is tapered toward the inlet opening  212 . Specifically, the wider end of the teardrop cross-section is proximate to sidewall  234  and the narrower end of the teardrop cross-section is proximate to inlet opening. Both the wider end and the narrower end of external protrusion  214  are rounded. In some examples, diameter  306  at the wider rounded end of external protrusion  214  is 1.5-3.0 mm and diameter  308  at the narrower rounded end of external protrusion  214  is 0.5-1.5 mm. In some examples, long dimension  302  of external protrusion  214  is aligned radially with respect to the center of impeller  206  or the center of inlet opening  212 . In other examples, long dimension  302  of external protrusion  214  is aligned with the local direction of the air flow, which is towards the center of impeller  206  or the center of inlet opening  212 . In some examples, long dimension  302  of external protrusion  214  is approximately 5-7 mm, and height  304  of external protrusion  214  is approximately 1-3 mm. It should be recognized that various other similar aerodynamic designs can be implemented for external protrusion  214 . For example, external protrusion  214  can generally have an elongated cross-section with a narrow end and a wider end. In other examples, external protrusion  214  has an elliptical cross-section with narrower opposite ends and a wider middle portion. 
     The aerodynamic shape of external protrusion  214  can be advantageous to reduce the formation undesirable airflow structures or increased turbulence.  FIG. 4  illustrates simulated airflow around external protrusion  402  of a cooling fan, where external protrusion  402  has a teardrop-shaped cross-section. As air flows around external protrusion  402 , only a relatively small region  404  of separated wake flow is formed downstream of the narrow end of external protrusion  402 . In contrast,  FIG. 5  illustrates simulated airflow around external protrusion  502  of a cooling fan, where external protrusion  502  has a circular cross-section. As air flows around external protrusion  502 , the flow separates extensively from the circular cross-section and causes a significantly larger region of separated wake flow and alternating vorticity (represented by arrows  504 ) downstream of external protrusion  502 . Thus, as illustrated by  FIGS. 4 and 5 , an aerodynamically shaped (e.g., teardrop-shaped) external protrusion can be advantageous as it reduces the formation of unsteady and turbulent airflow in its wake and thus reduces the amount of aeroacoustic noise generated by the cooling fan. 
     Although in the present example, cooling fan  200  is depicted as having only one external protrusion  502  on surface  204  of fan enclosure  202 , it should be recognized that in some examples, the cooling fan can have more than one external protrusion on the surface of the fan enclosure. In some examples, more than one external protrusion can be desirable to distribute any applied force over a larger surface. This may, for example, reduce the likelihood that any applied force would cause an external protrusion to damage (e.g., cause an indentation or crack in) the bottom case of the electronic device. The additional structural support from multiple external protrusions may also reduce the likelihood that a user handling event would cause the bottom case to directly contact the impeller or front wall  224  of the fan enclosure. In addition, the external protrusion(s) can act together with the raised diffuser portion  230  with height  252  to provide additional support against deflection of bottom case  122 . In other examples, having more than one external protrusion may not be desirable from an aerodynamic point of view. The additional external protrusions can cause additional obstruction and produce significant undesirable air flow structures or turbulent airflow that generates excessive aeroacoustic noise. In these examples, the cooling fan  200  has only one external protrusion on an outer surface of the fan enclosure. 
     With reference back to  FIGS. 1C and 2D , front wall  224  of fan enclosure  202  adjacent to blades  222  is discussed in greater detail. Specifically, front wall  224  of fan enclosure  202  adjacent to blades  222  may not have a uniform thickness. In some examples at least a portion  216  of front wall  224  of fan enclosure  202  increases in thickness radially outward from the inlet opening  212 . As shown, portion  216  includes the portion of front wall  224  surrounding inlet opening  212  and adjacent to blades  222  of impeller. The thickness variation can be desirable to improve clearance  228  between inner surface  218  of portion  216  of front wall  224  and blades  222 . Specifically, during a keystroke event where a force is applied to keyboard assembly  118 , the applied force can cause base layer  126  of keyboard assembly  118  to deflect toward cooling fan  200 , which can in turn cause back wall  232  of fan enclosure  202  to translate impeller  206  toward portion  216  of front wall  224 . The thickness variation of portion  216  of front wall  224  increases clearance  228  between front wall  224  and impeller  206 , which increases the amount of force required to cause impeller  206  to contact front wall  224  and reduces the likelihood that impeller  206  contacts front wall  224 . 
     In some examples, each blade  222  of impeller  206  is tapered such that height  254  of each blade decreases toward the perimeter of impeller  206  along the length of the blade. Specifically, each blade  222  includes edge  220  proximate to portion  216  of front wall  224 . Edge  220  of each blade  222  is sloped away from a rotation axis  226  of impeller  206  to form a tapered blade. In some examples, edge  220  has a linear slope. The thickness of portion  216  of front wall  224  varies such that inner surface  218  of portion  216  of front wall  224  has a slope that is similar to edge  220  of each blade. For example, inner surface  218  of portion  216  of front wall  224  is approximately parallel to edge  220  of each blade  222 , in that the slope of the taper to inner surface  218  matches the slope of the taper to edge  220  of blade  222 . In some examples, inner surface  218  of portion  216  has a linear slope in a radial direction with respect to a center of inlet opening  212 . In some examples, inner surface  218  of portion  216  is sloped in a radial direction with respect to a center of inlet opening  212  at an angle of approximately 5-9 degrees with respect to the plane of rotation of impeller  206 . Additionally, in some examples, edge  220  of each blade  222  is positioned no more than approximately 0.6 mm from inner surface  218  of portion  216  of front wall  224 . In some examples, edge  220  of each blade  222  is positioned approximately 0.3-0.6 mm from inner surface  218  of portion  216  of front wall  224 . In some examples, the average distance of edge  220  of each blade  222  to inner surface  218  of portion  216  of front wall  224  is approximately 0.4-0.6 mm. 
     Further, in some examples, the outer surface of portion  216  of front wall  224  has a slope that is different than inner surface  218  of portion  216  of front wall  224 . Specifically, the slope of the outer surface of portion  216  of front wall  224  can be configured based on aesthetic considerations or aerodynamic considerations of airflow over the outer surface  204 . In some examples, outer surface of portion  216  has a curved slope. The outer surface of portion  216  of front wall  224  can be sloped in a manner that reduces the thickness profile of cooling fan  200 . In some examples, the outer surface of portion  216  of front wall  224  is approximately parallel to the rotation plane of impeller  206 . In other examples, the outer surface of portion  216  of front wall  224  is sloped toward rotation axis  226 . In some examples, thickness  256  of portion  216  at inlet opening  212  is 0.3-0.5 mm and thickness  258  of portion  216  at the perimeter of impeller  206  is 0.4-0.6 mm. 
     Turning now to  FIG. 6 , diffuser portion  230  of cooling fan  200  is described in greater detail.  FIG. 6  illustrates a cross-section view of diffuser portion  230  of cooling fan  200 , according to various examples. As discussed briefly above, diffuser portion  230  channels airflow out through outlet opening  210 . Diffuser portion  230  includes the portion of fan enclosure  202  that extends from an outer edge of impeller  206  to outlet opening  210 . Diffuser portion  230  includes diffuser channel  606  that is defined by front wall  224 , sidewall  234 , and back wall  232  of fan enclosure  202 . Outlet opening  210  is disposed at an end of diffuser channel  606 . Diffuser portion  230  and outlet opening  210  are suitably designed to reduce the use of space (e.g., in the horizontal direction with fan  200  lying on back wall  232 ). Diffuser portion  230  and outlet opening  210  are suitably designed to reduce the occurrence of flow separation from wall surfaces, or formation of turbulent airflow while providing sufficient volume of airflow to cool the cooling fins. In some examples, length  612  of diffuser channel  606  is less than the radius of impeller  206 . Specifically, in some examples, length  612  of diffuser channel  606  is 6-11 mm. In some examples, the width (not shown) of diffuser channel  606  is greater than the diameter of impeller  206 . In the context of  FIG. 6 , the width of diffuser channel  606  is perpendicular to the plane of the drawing and parallel to the plane of rotation of impeller  206 . The width of diffuser channel  606  refers to the distance between opposite sidewalls of diffuser channel  606 . In some examples, the cross-section of diffuser channel  606  along a plane perpendicular to the drawing of  FIG. 6  has an aspect ratio of greater than 12, where the aspect ratio is the ratio of the width of the diffuser channel to the height of the diffuser channel. 
     Diffuser channel  606  diverges such that the height of diffuser channel  606  increases towards outlet opening  210  (e.g., from the edge of impeller  206 ). For example, height  614  of diffuser channel  606  at the edge of impeller  206  is 3.1-3.8 mm and height  616  of diffuser channel  606  at outlet opening  210  is approximately 4.1-5.1 mm. A diverging diffuser channel can enable outlet opening  210  to be suitably adapted to the height of cooling fins  120  ( FIG. 1B ) while keeping the vertical profile of the remainder of cooling fan thin so that air can enter the fan inlet with reduced impedance. In the present example, front wall  224  along diffuser channel  606  diverges toward outlet opening  210  with respect to back wall  232 . Specifically, in some examples, inner surface  602  of front wall  224  diverges at an angle of 5-10 degrees, 5-7 degrees, or 6-7 degrees with respect to the plane of rotation of impeller  206 . In other examples, inner surface  602  of front wall  224  diverges at an angle of 5-10 degrees, 5-7 degrees, or 6-7 degrees with respect to the plane of back wall  232 . The plane of rotation of impeller  206  is perpendicular to rotation axis  226 . It should be recognized that in other examples, back wall  232  along diffuser channel  606  can (additionally or alternatively) diverge toward outlet opening  210  with respect to front wall  224 . 
     Diffuser portion  230  diverges in a manner that reduces flow separation within diffuser channel  606  and thus reduces turbulent airflow exiting outlet opening  210 . Less turbulent airflow can result in less aeroacoustic noise. For example, as shown in  FIG. 6 , inner surface  602  of diffuser portion  230  is linearly sloped toward the outlet opening and with respect to the plane of rotation of the impeller. In contrast, a curved slope for inner surface  602  can, in some examples, cause undesirable flow separation. Additionally, a gradual divergence angle can be desirable to reduce flow separation. For example, the linear slope of inner surface is 5-10 degrees, 5-7 degrees, or 6-7 degrees. In some examples, the slope of inner surface  602  of diffuser portion  230  is different from the slope of inner surface  218  of portion  216  of front wall  224 . Specifically, in the present example, the transition between inner surface  218  of portion  216  and inner surface  602  of diffuser portion  230  is substantially abrupt rather than gradual where a distinct inflection region  608  exists adjacent to outer edge  610  of impeller between inner surface  218  of portion  216  and inner surface  602  of diffuser portion  230 . In some examples, the slope of outer surface  604  of front wall  224  at portion  216  and diffuser portion  230  is independent from the slope of inner surfaces  218  and  602  of front wall  224 . The slope of outer surface  604  of front wall  224  is aerodynamically optimized for airflow toward inlet opening  212 . For example, outer surface  604  of front wall  224  gradually slopes from inlet opening  212  to outlet opening and does not have an inflection region. Additionally, outer surface  604  of front wall  224  has a gradual curved slope rather than a linear slope along diffuser portion  230 . 
     Turning now to  FIGS. 7 and 8 , portions that form fan enclosure  202  of cooling fan  200  are described.  FIG. 7  illustrates a perspective view of cover portion  700  of fan enclosure  202 , according to various examples. The perspective view of  FIG. 7  shows the surface of cover portion  700  that corresponds to the inner surface of fan enclosure  202 .  FIG. 8  illustrates base plate  800  of fan enclosure  202 , according to various examples. The perspective view of  FIG. 8  shows the surface of base plate  800  that corresponds to the inner surface of fan enclosure  202 . In the present example, fan enclosure  202  of cooling fan  200  is constructed of only two discrete pieces: cover portion  700  and base plate  800  which are attached to each other using one or more attaching components (e.g., one or more of fasteners, adhesive, etc.) Specifically, cover portion  700  and base plate  800  form front wall  224 , sidewalls  234 , and back wall  232  of cooling fan  200  that define the fan cavity in which impeller  206  is at least partially housed. Cover portion  700  and base plate  800  are each single-piece members. For example, neither cover portion  700  nor base plate  800  is constructed of two or more parts connected together. It should be recognized that in other examples, the fan enclosure can be constructed with two or more discrete pieces. In those examples, the cover portion or the base plate of the fan enclosure can include two or more parts connected together. In some examples, each of cover portion  700  and base plate  800  is formed from a single material. For example, cover portion  700  is formed from die-cast aluminum or injection molded plastic. Base plate  800  is formed from steel or aluminum. 
     Base plate  800  includes wall  806  that forms the back wall of the fan enclosure (e.g., back wall  232  of fan enclosure  202 ). Inner surface of wall  806  is, in some examples, substantially planar. In some examples, outer surface (not shown in  FIG. 8 ) of wall  806  includes a recessed channel for the FPC (e.g., recessed channel  268  for FPC  236  shown in  FIG. 2C ). In some examples, the recessed channel is recessed by approximately 0.10-0.16 mm. Wall  806  includes opening  802  through which FPC  236  connects to the motor of the cooling fan. In some examples, the thickness of wall  806  is approximately 0.4-0.6 mm. In a specific example, the thickness of wall  806  is approximately 0.5 mm. In some examples, wall  806  has a substantially uniform thickness (excluding the recessed channel). In examples where base plate  800  is formed using two or more parts connected together, base plate  800  can include a spacer layer attached to a main layer. In these examples, the spacer layer can include an opening that defines the recessed channel when attached to the main layer. The spacer layer can comprise a plastic film and the main layer can comprise a metal plate. 
     Base plate  800  further includes one or more vertical tabs  808  that each extend from an edge along the perimeter of base plate  800 . Vertical tabs  808  are adapted to fit into slots  714  of cover portion  700 , thereby increasing the stiffness and strength of the adhesive joint between cover  700  and base plate  800 . Base plate  800  also includes one or more horizontal tabs  804   a - b . In some examples, horizontal tabs  804   a  are adapted to attach a motherboard (sometimes called a main board, main logic board, or MLB) to base plate  800 . For example, as shown in  FIG. 8 , horizontal tabs  804   a  include protruding threaded inserts to which a motherboard can be attached using one or more attaching components (e.g., one or more fasteners). In some examples, horizontal tabs  804   b  are adapted to attach base plate  800  to the base layer (e.g., base layer  126 ) of the keyboard assembly. In the present example shown in  FIG. 8 , horizontal tabs  804   b  do not include protruding threaded inserts. 
     Cover portion  700  includes front wall  702  and sidewalls  704 , which form, for example, front wall  224  and sidewalls  234  of fan enclosure  202 . Front wall  702  and sidewalls  704  are integrally formed as a single-piece member and are not two discrete pieces that are connected together. Because front wall  702  and sidewalls  704  are integrated as a single piece and not assembled together from two separate pieces, additional tolerance or margin need not be provided for assembly. This enables cover portion  700  to be constructed with a smaller thickness  706  and enables a reduced clearance  228 . Cover portion  700  also occupies a smaller horizontal area since additional attaching components (e.g., fasteners, flanges, rivets, adhesives, etc.) to connect front wall  702  and sidewalls  704  are not needed. Moreover, because front wall  702  and sidewalls  704  are integrally formed as one piece, cover portion  700  is, as a whole, structurally stiffer. This enables cover portion  700  to better support base plate  800  to resist translation of the impeller against the front wall of the fan enclosure during keystroke events on the keyboard. Cover portion  700  also includes tabs  708  that are adapted to attach cover portion  700  to base plate  800  or to base layer  126  of keyboard assembly  118  using one or more attaching components (e.g., one or more fasteners or adhesives). 
     In some examples, cover portion  700  is die-casted to integrate front wall  702  and sidewalls  704  as a single-piece member. Die-casting can be desirable to form the inner surface of cover portion  700  independent from the outer surface of cover portion  700 . For example, the inner surface of cover portion  700  can be optimized for the airflow characteristics within the fan enclosure whereas the outer surface of cover portion  700  can be optimized for aesthetics and for airflow characteristics toward the inlet opening of the fan enclosure. Specifically, as discussed in greater detail below with respect to  FIGS. 9A-B , the inner and outer surfaces of diffuser portion  710  of cover portion  700  can be independently shaped. Furthermore, forming cover portion  700  with die-casting can be desirable to integrate the external protrusion (e.g., external protrusion  214 ) on the outer surface of cover portion  700 . Such integration enables greater strength and stiffness of front wall  702  when a load is applied to the external protrusion. Injection molding of cover portion  700  using a plastic material can provide similar benefits, though the stiffness tends to be less than that associated with die-cast materials (e.g., metal). 
       FIGS. 9A-B  illustrate cross-sectional perspective views of cover portion  700 , according to various examples. In particular,  FIG. 9B  is a cross-sectional perspective view of cover portion  700  along dotted line  902  indicated on  FIG. 9A . As shown in  FIGS. 9A-B , the thickness of sidewall  704  is greater than the thickness of front wall  702 . A thicker sidewall  704  can be desirable for providing greater structural support and stiffness whereas a thinner front wall  702  can be desirable to reduce the overall thickness of cooling fan, thereby enabling a thinner electronic device. The thickness gradually reduces and tapers from sidewall  704  to front wall  702 . The gradual taper can be desirable for improved mold flow and manufacturing process yield during die-casting. Additionally, the gradual taper can provide improved aerodynamic airflow and thus less aeroacoustic noise. In particular, the inner and outer surfaces of cover portion  700  transition smoothly from sidewalls  704  to front wall  702  and do not include any gap or interface that would be characteristic of front wall  702  and sidewalls  704  being two separate pieces that are joined together. For example, with reference to  FIG. 9B , internal and external corners  914  and  912  between front wall  702  and sidewalls  704  are smooth and gradually rounded (e.g., with radius of 1-3 mm). 
     As shown in  FIG. 9A , the thickness of front wall  702  varies from one sidewall to the opposite sidewall of cover portion  700  at diffuser portion  710 . As a result, the height of the diffuser channel (e.g., diffuser channel  606  of  FIG. 6 ) in the diffuser portion of the fan enclosure (e.g., diffuser portion  230  of  FIGS. 2A-2B ) varies across the outlet opening. For example, as shown in  FIG. 2B , height  242  of outlet opening  210  varies across width  244  of outlet opening  210 , where height  242  is perpendicular to width  244 . Width  244  is parallel to the plane of rotation of impeller  206 . Varying the thickness of front wall  702  of cover portion  700  and thus the height of the diffuser channel across the width of the diffuser channel can be desirable to optimize the aerodynamics of the diffuser channel. This in turn can reduce the generation of aeroacoustic noise. In particular, airflow proximate to the center portion of the diffuser channel between the opposite sidewalls of fan enclosure  202  may have a strong cross-flow component due to the tangential velocity induced by the rotation of impeller  206 . The cross-flow component can lead to flow separation along the inner surface of diffuser portion  230 . Increasing the thickness of front wall  702  of cover portion  700  and thus reducing height  242  of outlet opening  210  proximate to the center of the diffuser channel can reduce flow separation by accelerating the flow in that region and thus reduce the formation of turbulence. 
     Additionally, varying the thickness of front wall  702  of cover portion  700  and thus the height of the diffuser channel can enable airflow to exit outlet opening  210  with a more uniform velocity across width  244  of outlet opening  210 . Specifically, as shown in  FIG. 2B , height  242  of outlet opening  210  can be greatest where airflow rate is the greatest and smallest where airflow rate is the lowest at outlet opening  210 . In the present example, height  242  of outlet opening  210  is the greatest adjacent to sidewalls  234  and smallest at position  246  of outlet opening  210  that is between sidewalls  234 . Height  242  gradually reduces from sidewalls  234  toward position  246  of outlet opening  210 . In some examples, height  242  of outlet opening adjacent to sidewalls is approximately 3.5-4.2 mm and height  242  of outlet opening at position  246  is approximately 2.5-3.5 mm. Position  246  is disposed between sidewalls  260  and  262  of outlet opening  210 . In particular, position  246  is disposed closer to sidewall  260  than to sidewall  262 . Sidewall  260  is closer to impeller  206  than sidewall  262 . In some examples, the ratio of the distance between position  246  and sidewall  260  to the distance between position  246  and sidewall  262  is 0.20-0.40. Alternatively, in other examples (not shown), height  242  of outlet opening  210  is approximately uniform across width  244 , where height  242  of outlet opening  210  is not reduced at position  246 . 
     Returning to  FIG. 9A , thickest portion  916  of front wall  702  in diffuser portion  710  is where dotted line  902  intersects with edge  904  of cover portion  700 . As shown, the thickness of front wall  702  in diffuser portion  710  tapers from thickest portion  916  toward each sidewall of opposite sidewalls  704 . Additionally, as shown in  FIG. 9B , the thickness of front wall  702  in diffuser portion  710  increases from inlet opening  712  to thickest portion  916 . In some examples, the inner surface of front wall  702  in diffuser portion  710  has a topography that is independent of the topography on the outer surface of front wall  702  in diffuser portion  710 . In particular, as shown in  FIGS. 9A-B , the inner surface of front wall  702  in diffuser portion  710  slopes away from thickest portion  916  toward sidewalls  704  and inlet opening  712 . In contrast, the topography on the outer surface of front wall  702  in diffuser portion  710  is more uniform and is not dependent on the position of thickest portion  916 . 
     Turning now to  FIGS. 10 and 11 , two different mounting configurations with respect to a cooling fan in an electronic device are described.  FIG. 10  illustrates a cross-sectional view of electronic device  1000  where motherboard  1006  is attached to cover portion  1008  of the fan enclosure of cooling fan  1004 , according to various examples.  FIG. 11  illustrates a cross-sectional view of electronic device  1100  where motherboard  1106  is attached to base plate  1110  of the fan enclosure of cooling fan  1104 , according to various examples. In both mounting configurations, the cooling fan is disposed between the keyboard assembly and the motherboard where the motherboard is mounted to the cooling fan and the cooling fan is mounted to the keyboard assembly. The cooling fan is thus a mounting point for the motherboard and functions as an integral structural component for the motherboard. This can be advantageous for more efficiently integrating the internal components of the electronic device into a smaller space, thereby enabling a thinner and sleeker electronic device. The motherboard includes at least a printed circuit board and a plurality of electrical components that include at least a central processing unit (CPU) and memory. 
     As shown in  FIG. 10 , the fan enclosure of cooling fan  1004  is constructed of two separate pieces: cover portion  1008  and base plate  1010 , which can be similar or identical to cover portion  700  and base plate  800 , respectively. In this example, motherboard  1006  is attached to cover portion  1008  of cooling fan  1004 . Specifically, cover portion  1008  includes one or more tabs  1016  that extend from the main body of cover portion  1008 . One or more tabs  1016  can be similar or identical to tabs  708  of cover portion  700  ( FIG. 7 ). Motherboard  1006  is directly attached to one or more tabs  1016  of cover portion  1008  without directly contacting any portion of base plate  1010 . In some examples, one or more attaching components  1018  (e.g., one or more fasteners or adhesives) directly attach: motherboard  1006  to cooling fan  1004 , cooling fan  1004  to keyboard assembly  1002  (via base layer  1020 ), and keyboard assembly  1002  to top case  1012 . Motherboard  1006  and cooling fan  1004  are disposed between top case  1012  and bottom case  1014 . 
     In other examples (not shown), base plate  1010  is directly attached to keyboard assembly  1002  and top case  1012  using one or more attaching components via one or more tabs of base plate  1010  (e.g., tabs  804   b  of  FIG. 8 ). Additionally, motherboard  1006  is directly attached to cover portion  1008  using one or more attaching components via one or more tabs of cover portion  1008  (e.g., tabs  708  of  FIG. 7 ). In some examples, motherboard  1006  is directly attached to one or more tabs of cover portion  1008  without being directly attached to base plate  1010 . 
     With reference to  FIG. 11 , electronic device  1100  is similar to electronic device  1000  except that cover portion  1108  and base plate  1110  have a different mounting configuration with respect to motherboard  1106 . In this example, motherboard  1106  is attached to base plate  1110  of the fan enclosure of electronic device  1100  without being directly attached to cover portion  1108 . Specifically, base plate  1110  includes one or more tabs  1116  that extend from the main body of base plate  1110 . One or more tabs  1116  can be similar or identical to tabs  804   a  of base plate  800 . In the present example, one or more tabs  1116  include threaded inserts  1118 . Motherboard  1106  is attached to one or more tabs  1116  of base plate  1110  via threaded inserts  1118  without directly contacting cover portion  1108 . In other examples, the threaded inserts can be optional. In some examples, one or more attaching components  1120  (e.g., one or more fasteners or adhesives) directly attach: motherboard  1106  to cooling fan  1104 , cooling fan  1104  to keyboard assembly  1102  (via base layer  1122 ), and keyboard assembly  1102  to top case  1112 . In some examples, attaching components  1120  are positioned through tabs  1116  of base plate  1110  without being positioned through cover portion  1108 . Motherboard  1106  and cooling fan  1104  are disposed between top case  1112  and bottom case  1114 . 
     Turning now to  FIGS. 12A-B , additional aspects of attaching a cooling fan against a bottom surface of a keyboard assembly are described.  FIG. 12A  illustrates a top-down view of cooling fan  1202  attached to base layer  1204  of a keyboard assembly, according to various examples. Cooling fan  1202  and base layer  1204  are similar or identical to cooling fan  200  and base layer  126  of  FIG. 1C , respectively. In the top-down view of  FIG. 12A , the bottom surface of base layer  1204  is shown. The keys (not shown) of the keyboard assembly are facing into the plane of the drawing. Base layer  1204  includes plurality of openings  1206  that extend from the top surface to the bottom surface of base layer  1204 . Plurality of openings  1206  can serve to allow air to vent through base layer  1204  into the interior of the electronic device during, for example, a keystroke event. In the present example, cooling fan  1202  has a fan enclosure that includes cover portion  1214  and base plate  1208 . 
       FIG. 12B  illustrates a similar configuration as  FIG. 12A , except that most of the components of cooling fan  1202  (including cover portion  1214  and the impeller) have been removed to more clearly show the features between base layer  1204  of the keyboard assembly and base plate  1208  of cooling fan  1202 . As shown, only base plate  1208  and FPC  1210  of cooling fan  1202  remain. The top-down view of base plate  1208  in  FIG. 12B  shows the inner surface of base plate  1208  and the bottom surface of base layer  1204 . The outer surface (not shown) of base plate  1208  is oriented toward the bottom surface of base layer  1204 . Cooling fan  1202  is attached to the keyboard assembly such that a majority of the outer surface of base plate  1208  is positioned substantially flush against the bottom surface of base layer  1204 . FPC  1210  is disposed between base plate  1208  and base layer  1204  such that FPC  1210  directly contacts the outer surface of base plate  1208  and the bottom surface of base layer  1204 . Because base plate  1208  is positioned directly against base layer  1204 , base plate  1208  and base layer  1204  provide EMI shielding to FPC  1210 . For example, each base plate  1208  and base layer  1204  comprises a metal layer that inherently shields FPC  1210  from EMI generated by the electronic components within the electronic device. As a result of this configuration, FPC  1210  need not include a separate EMI shielding layer. Specifically, in the present example, FPC  1210  does not include an EMI shielding layer, such as a metal layer. This is advantageous for enabling a thinner FPC, which results in a thinner overall system. A thinner FPC also enables the recessed channel (e.g., recessed channel  268 ) of base plate  1208  to be shallower, which can reduce the extent that the recessed channel detracts from the stiffness of base plate  1208 . A stiffer base plate  1208  is desirable for resisting against deflection under user loading and associated rubbing between the impeller and the cover portion. 
     As shown in  FIG. 12B , base layer  1204  includes recessed portion  1212 . In some examples, recessed portion  1212  has a recessed depth of 0.1-0.2 mm with respect to bottom surface of base layer  1204 . Two or more openings  1206   a  of plurality of openings  1206  coincide with recessed portion  1212 . Recessed portion  1212  and the outer surface of base plate  1208  form a venting channel. One or more edges  1216  of recessed portion  1212  extend beyond a perimeter of base plate  1208 . The one or more edges  1216  thus form openings  1218  with base plate  1208  to allow air to exit from venting channel. The venting channel couples two or more openings  1206   a  such that during keystroke events, air can vent through each of two or more openings  1206   a  into the venting channel and out through the one or more openings  1218  at edges  1216  of recessed portion  1212 . Venting channel can be desirable to provide a desirable tactile response to the user when the user depresses a key positioned directly above cooling fan  1202 . Additionally, it enables the keys positioned directly above cooling fan  1202  to have a similar tactile response as other keys on the keyboard assembly, which improves the user experience. 
     Further, recessed portion  1212  can be advantageous for reducing movement of base plate  1208  during a keystroke event. This reduces the likelihood that base plate  1208  would cause the impeller to directly contact the cover portion of the fan assembly. In particular, recessed portion  1212  is positioned to correspond to one or more components of the keyboard assembly that coincide with a load path during a keystroke event. When a key directly above cooling fan  1202  is depressed, a load is transmitted from the key through the one or more components to a portion of base layer  1204  that corresponds to recessed portion  1212 . The load causes base layer  1204  to locally depress toward base plate  1208  of cooling fan  1202 . However, due to the presence of recessed portion  1212 , base layer  1204  locally deforms into the venting channel, which reduces the likelihood that base plate  1208  is translated by the key depression event. This in turn reduces the likelihood that the impeller is forced into the cover portion. 
     In some examples, at least part of recessed portion  1212  coincides with the path along which FPC  1210  is routed between base plate  1208  and base layer  1204 . In these examples, FPC  1210  is routed through the channel formed by recessed portion  1212  and base plate  1208 . The depth of the recessed channel (e.g., recessed channel  268 ) of base plate  1208  can thus be reduced or, alternatively, the recessed channel of base plate  1208  can be completely eliminated. Eliminating the recessed channel (or reducing its depth) of base plate  1208  can be desirable for improving the overall stiffness of base plate  1208 , which enables base plate  1208  to better resist against deflection under user loading and associated rubbing between the impeller and the cover portion. 
     With reference back to  FIGS. 7 and 8 , tabs  708  of cover portion  700  or tabs  804   b  of base plate  800  are, in some examples, configured to enable the cooling fan to be attached to approximately the same location of the keyboard regardless of the mechanical layout (e.g., ANSI, ISO, or JIS) of the keys of the keyboard and without having to customize tabs  708  or  804   b  for each mechanical layout. For example,  FIG. 13  illustrates a top-down view of a portion of electronic device  1300  where cooling fans  1304 ,  1306  are attached to keyboard assembly  1308  that has one of three possible configurations. Cooling fans  1304 ,  1306  are similar or identical to cooling fan  200 , described above. In this example, keys  1302  of keyboard assembly  1308  are facing into the plane of the drawing and cooling fans  1304 ,  1306  are disposed over keyboard assembly  1308  such that the inlet opening of each cooling fan is facing away from keyboard assembly  1308 . In  FIG. 13 , three possible mechanical layouts (e.g., ANSI, ISO, or JIS) of the keys  1302  of keyboard assembly  1308  are shown overlapping together. Specifically, solid lines  1312  depict the configuration of the keyboard web of the top case (e.g., top case  112 ) of electronic device  1300  surrounding the keys  1302  of keyboard assembly for the ANSI keyboard layout. Dotted lines  1310  depict differences in the configuration of the keyboard web of the top case for ISO and JIS keyboard layouts relative to the ANSI keyboard layout. In this example, the overall area occupied by each keyboard layout (ANSI, ISO, or JIS) is approximately the same. 
     As shown in  FIG. 13 , the base plate of each cooling fan  1304 ,  1306  includes four tabs (e.g., tabs  1314  of cooling fan  1304  and tabs  1316  of cooling fan  1306 ). Tabs  1314 ,  1316  are similar or identical to tabs  804   b , described above with reference to  FIG. 8 . Each of tabs  1314 ,  1316  includes an opening for receiving a fastener (e.g., fastener  1416  shown in  FIG. 14A ). In some examples, the openings of one or more of tabs  1314 ,  1316  have an elliptical shape to provide flexibility for the mounting position to the keyboard web. Each tab of tabs  1314 ,  1316  is configured such that the center of each opening coincides with a respective mounting point on the keyboard web of the top case. Specifically, the mounting points are positioned where a horizontal portion (e.g.,  1318 ) and a vertical portion (e.g.,  1320 ) of the keyboard web intersect between keys  1302  of keyboard assembly  1308 . Notably, the same mounting points are chosen such that they are present on the keyboard web regardless of the keyboard layout (e.g., ANSI, ISO, or JIS) that is implemented. As a result, cooling fans  1304 ,  1306  can be attached at approximately the same location with respect to keyboard assembly  1308  for multiple keyboard layouts (e.g., ANSI, ISO, or JIS) using the same fan configuration. This is technically desirable as it beneficially reduces manufacturing variations for the cooling fan and the electronic device. 
     In a specific example of cooling fan  1304 , the openings of tabs  1314  are aligned with fourth specific mounting points on the keyboard web that are position between specific keys  1302  of keyboard assembly  1308 , which has an ANSI (American English) layout. In this example, a first mounting point is disposed at an intersection in the keyboard web between three keys  1302  corresponding to the number “1,” the symbol “˜,” and the “tab” function, respectively. A second mounting point is disposed at an intersection in the keyboard web between three keys  1302  corresponding to the letters “E” and “R” and the number “4”, respectively. A third mounting point is disposed at an intersection in the keyboard web between three keys  1302  corresponding to the letters “D,” “S,” and “X,” respectively. Finally, a fourth mounting point is disposed at an intersection in the keyboard web between three keys  1302  corresponding to the “shift,” “control,” and “option” functions, respectively. 
     In a specific example of cooling fan  1306 , the openings of tabs  1316  are aligned with fourth specific mounting points on the keyboard web that are position between specific keys  1302  of keyboard assembly  1308 , which has an ANSI (American English) layout. In this example, a first mounting point is disposed at an intersection in the keyboard web between three keys  1302  corresponding to the numbers “9” and “0” and the letter “O,” respectively. A second mounting point is disposed at an intersection in the keyboard web between three keys  1302  corresponding to the symbols “]” and “\” and the “delete” function, respectively. A third mounting point is disposed at an intersection in the keyboard web between three keys  1302  corresponding to the letter “L” and the punctuation marks “.” and “;”, respectively. Finally, a fourth mounting point is disposed at an intersection in the keyboard web between three keys  1302  corresponding to the “shift,” “left arrow,” and “up/down arrow” functions, respectively. 
     Although the cooling fans  1304 ,  1306  shown in  FIG. 13  each have four tabs  1314 ,  1316  for attaching cooling fans  1304 ,  1306  to keyboard assembly  1308 , it should be recognized that in other examples, the number of tabs  1314 ,  1316  can vary. Furthermore, although in the present example, cooling fans  1304 ,  1306  are attached to keyboard assembly  1308  via tabs  1314 ,  1316  extending from the base plate of the cooling fans, it should be appreciated that in other examples, the configuration describe above with respect to  FIG. 13  can similarly be implemented using tabs (e.g., tabs  708  in  FIG. 7 ) extending from the cover portion of the cooling fans. For example, tabs  1314 ,  1316  can extend from the cover portion rather than from the base plate of the cooling fans. 
     Turning now to  FIGS. 14A-B , cross-sectional views of a portion of electronic device  1400  are shown, according to various examples. Specifically,  FIG. 14A  illustrates an exemplary mounting configuration of cooling fan  1403  in electronic device  1400 , and  FIG. 14B  illustrates an exemplary mounting configuration of motherboard  1408  to cooling fan  1403 . As shown in  FIG. 14A , cooling fan  1403  includes base plate  1406  that is attached to cover portion  1404  by fastener  1410 . Base plate  1406  includes one or more tabs  1412   b  that are similar or identical to tabs  804   b  of  FIG. 8 . Fastener  1416  attaches cooling fan  1403  through an opening of tab  1412   b  and threads into a portion of keyboard web  1414  of the top case. The portion of keyboard web  1414  that receives fastener  1416  corresponds to one of the mounting points on the keyboard web discussed above in  FIG. 13 . As shown in  FIG. 14A , the portion of keyboard web  1414  includes mini boss  1415  that extends toward tab  1412   b . Mini boss  1415  serves to increase the threading and thus strengthen the threaded joint. Mini boss  1415  is in clearance to tab  1412   b  of base plate  1406  such that cooling fan  1403  is fixed against base layer  1407  of keyboard assembly  1401 , thereby clamping keyboard assembly  1401  against keyboard web  1414  of the top case. In some examples, tab  1412   b  is laser etched around the opening of tab  1412   b  such that fastener  1416  creates a conductive path between cooling fan  1403  and the top case of electronic device  1400 . 
     In some examples, motherboard  1408  is structurally tied to the top case of electronic device  1400  through one or more tabs  1412   a  of base plate  1406 . This is a desirable design feature that enables flexibility for mounting motherboard  1408  in electronic device  1400  and allows more efficient layout of motherboard  1408  within electronic device  1400 . In contrast, if motherboard  1406  were to be mounted to keyboard web  1414  of the top case rather than to tabs  1412   a  of base plate  1406 , the mounting points of motherboard  1408  would need to align with common intersections on keyboard web  1414  for various keyboard layouts, thereby restricting the mounting options for motherboard  1408 . As shown in  FIG. 14B , motherboard  1408  is attached to tab  1412   a  of base plate  1406  using fastener  1418 . Specifically, fastener  1418  passes through an opening in motherboard  1408  and ties into threaded insert  1420  that is attached to tab  1412   b  of base plate  1406 . In some examples, a circular piece of conductive foam is disposed between tab  1412   a  and base layer  1407  of keyboard assembly  1401 . The conductive foam creates an additional conductive path between cooling fan  1403  and base layer  1407  of keyboard assembly  1401 . 
     The foregoing description should be understood to include embodiments of cooling fans and electronic devices with cooling fans that include any combination of the features described herein. For example, one embodiment of a cooling fan includes a single-piece cover portion (e.g., cover portion  700 ) having independently optimized aerodynamic internal and external surfaces. The cover portion includes sidewalls (e.g., sidewall  704 ) that gradually taper to the front wall (e.g., front wall  702 ). The cover portion also includes a sloped portion surrounding the inlet opening (e.g., inner surface  218  of portion  216 ) to provide additional margin to the blades of the impeller. An external protrusion (e.g., external protrusion  214 ) extends from an external surface of the cover portion. Further, the cover portion includes a diffuser portion (e.g., diffuser portion  710 ) with an internal surface topography designed to reduce localized flow separation. The slope of the inner surface of the diffuser portion is independent of the slope of the outer surface of the diffuser portion. 
     Another embodiment of an electronic device includes a cooling fan that is directly mounted to a keyboard assembly such that a majority of the outer surface of the base plate (e.g., base plate  1208 ) is flush against the base layer (e.g., base layer  1204 ) of the keyboard assembly. The FPC (e.g., FPC  236 ) of the cooling fan is disposed within a recessed channel (e.g., recessed channel  268 ) on the base plate of the cooling fan. The FPC is further positioned between the base layer of the keyboard assembly and the base plate of the cooling fan. The FPC is shielded from EMI by being positioned between the base plate and the base layer and does not have a separate EMI shielding layer. The cooling fan is attached to the keyboard assembly via tabs (e.g., tabs  708 ) that extend from the cover portion of the cooling fan. Alternatively, the cooling fan is attached to keyboard assembly via tabs (e.g., tabs  804 ) that extend from the base plate of the cooling fan. The tabs of the cover portion or the base portion include threaded inserts. The base layer of the keyboard assembly includes a recessed portion (e.g., recessed portion  1212 ) that forms a venting channel with the base plate of the cooling fan. 
     The terminology used in the description of the various described examples herein is for the purpose of describing particular examples only and is not intended to be limiting. As used in the description of the various described examples and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that the term “and/or” as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items. It will be further understood that the terms “includes,” “including,” “comprises,” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     The foregoing description, for purpose of explanation, has been described with reference to specific embodiments. However, the illustrative discussions above are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in view of the above teachings. The embodiments were chosen and described in order to best explain the principles of the techniques and their practical applications. Others skilled in the art are thereby enabled to best utilize the techniques and various embodiments with various modifications as are suited to the particular use contemplated. 
     Although the disclosure and examples have been fully described with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art. Such changes and modifications are to be understood as being included within the scope of the disclosure and examples as defined by the claims.

Metadata:
Filing Date: 20170821
Publication Date: 20190806
Grant Date: 20190806
Priority Date: 20160906
Inventors: AIELLO, ANTHONY J.
BERK, Jonathan L.
CHENG, KAREN
DYBENKO, JESSE T.
EDMONDS, TREVOR
FLEISCHMAN, KWONIL D.
HERMS, RICHARD A.
KNOPF, ERIC A.
NAGHIB LAHOUTI, ARASH
PATTON, BRAD L.
Assignee: APPLE INC
CPC Classifications: [{"code": "H01L23/467", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L23/4006", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/1662", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/1658", "inventive": true, "first": false, "tree": "[]"}, {"code": "F04D25/0613", "inventive": true, "first": false, "tree": "[]"}, {"code": "F04D17/16", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/203", "inventive": true, "first": false, "tree": "[]"}, {"code": "F04D25/0613", "inventive": true, "first": false, "tree": "[]"}, {"code": "F04D29/441", "inventive": true, "first": false, "tree": "[]"}, {"code": "F04D17/16", "inventive": true, "first": false, "tree": "[]"}, {"code": "F04D29/441", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L23/4006", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L23/467", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/1662", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/203", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K7/20145", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F1/20", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L23/467", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/1662", "inventive": true, "first": false, "tree": "[]"}, {"code": "F04D17/16", "inventive": true, "first": false, "tree": "[]"}, {"code": "F04D29/441", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/20", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/1658", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/203", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K7/20145", "inventive": true, "first": true, "tree": "[]"}, {"code": "F04D25/0613", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L23/4006", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/1658", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 59799484