PATENT DOCUMENT

Publication Number: US-9560749-B2
Application Number: US-201414216916-A
Country: US
Kind Code: B2

Title: Electronic devices having stress concentrators for printed circuit boards

Abstract:
An electronic device may have circuitry mounted on a printed circuit board. The circuitry may include electronic components such as integrated circuits, sensors, and switches that are sensitive to bending-induced stress in the printed circuit board. An overmolded plastic stress concentrator may be overmolded over the printed circuit board and the circuitry on the printed circuit board. A flexible plastic body may be used to enclose the stress concentrator and printed circuit board. The plastic body, stress concentrator, and printed circuit board may be elongated along a longitudinal axis. The stress concentrator may have unbent regions in which the printed circuit board is prevented from flexing and enhanced flexibility regions. Sensitive circuitry may be located in the unbent regions to prevent the sensitive circuitry from being exposed to bending stress.

Claims:
What is claimed is: 
     
       1. Apparatus, comprising:
 a printed circuit board; 
 circuitry mounted on a surface of the printed circuit board, wherein the circuitry includes a dome switch that is soldered to the printed circuit board; and 
 a stress concentrator with an enhanced flexibility region, wherein the stress concentrator restricts bending of the printed circuit board to the enhanced flexibility region, wherein the stress concentrator comprises plastic overmolded over the printed circuit board such that the plastic is in direct contact with the surface and the circuitry, wherein the dome switch is covered by the plastic, wherein the printed circuit board is elongated along a longitudinal axis, wherein the printed circuit board has a uniform height along the length of the longitudinal axis, and wherein the printed circuit board has a uniform rigidity along the length of the longitudinal axis. 
 
     
     
       2. The apparatus defined in  claim 1  wherein the stress concentrator is elongated along the longitudinal axis. 
     
     
       3. The apparatus defined in  claim 2  wherein the stress concentrator has transverse dimensions that are perpendicular to the longitudinal axis and wherein the stress concentrator has at least one locally narrowed transverse dimension in the enhanced flexibility region. 
     
     
       4. The apparatus defined in  claim 3  wherein the stress concentrator comprises unbent regions and wherein the enhanced flexibility region is more flexible than the unbent regions. 
     
     
       5. The apparatus defined in  claim 4  wherein the stress concentrator comprises an additional enhanced flexibility region at a different location along the longitudinal axis from the enhanced flexibility region. 
     
     
       6. The apparatus defined in  claim 4  wherein the circuitry comprises electrical components in the unbent regions, wherein the enhanced flexibility region is free of any electrical components. 
     
     
       7. The apparatus defined in  claim 4  wherein the circuitry comprises integrated circuits in the unbent regions and does not have integrated circuits in the enhanced flexibility region. 
     
     
       8. The apparatus defined in  claim 2  wherein the stress concentrator has a first material and a second material, wherein the second material is located in the enhanced flexibility region, wherein the first material comprises a first plastic, and wherein the second material comprises a second plastic that is more flexible than the first plastic. 
     
     
       9. The apparatus defined in  claim 2  further comprising a plastic body that surrounds the stress concentrator. 
     
     
       10. The apparatus defined in  claim 9  wherein the plastic body comprises flexible plastic that deforms when a user presses the plastic body to use the dome switches. 
     
     
       11. The apparatus defined in  claim 10  wherein the stress concentrator comprises unbent regions, wherein the enhanced flexibility region is more flexible than the unbent regions, and wherein the enhanced flexibility region is located between the unbent regions. 
     
     
       12. The apparatus defined in  claim 1 , wherein the printed circuit board is embedded in the plastic such that the plastic completely surrounds the printed circuit board and the dome switch. 
     
     
       13. The apparatus defined in  claim 1 , wherein the enhanced flexibility region has a narrowed ring-shape region. 
     
     
       14. The apparatus defined in  claim 1 , wherein the dome switch is completely covered by and in direct contact with the plastic. 
     
     
       15. The apparatus defined in  claim 1 , wherein the printed circuit board is a rigid printed circuit board. 
     
     
       16. Apparatus, comprising:
 a printed circuit board; 
 electronic components soldered to the printed circuit board; and 
 a stress concentrator with unbent regions separated by an enhanced flexibility region that is more flexible than the unbent regions, wherein the stress concentrator prevents bending of the printed circuit board in the unbent regions and allows bending of the printed circuit board in the enhanced flexibility region, wherein the unbent regions are formed from only a first material, wherein the enhanced flexibility region is formed from only a second material, wherein the second material is more flexible than the first material, wherein the first material has a first thickness, and wherein the second material has a second thickness that is the same as the first thickness. 
 
     
     
       17. The apparatus defined in  claim 16  wherein the electronic components include a component selected from the group consisting of: an integrated circuit, a sensor, and a switch and wherein the electronic components have contacts that are soldered to solder pads on the printed circuit board. 
     
     
       18. The apparatus defined in  claim 16 , wherein at least one of the electronic components is soldered to the printed circuit board in the enhanced flexibility region. 
     
     
       19. A headset controller, comprising:
 a printed circuit board; 
 a molded plastic stress concentrator on the printed circuit board; and 
 a housing in which the printed circuit board and molded plastic stress concentrator are mounted, wherein the molded plastic stress concentrator is elongated along a longitudinal axis, wherein the molded plastic stress concentrator has planar regions characterized by first and second transverse dimensions that are perpendicular to the longitudinal axis and has enhanced flexibility regions characterized by third and fourth transverse dimensions that are narrowed with respect to the first and second transverse dimensions of the planar regions, and wherein the enhanced flexibility regions enable the planar regions to be bent in a first direction and a second direction that is perpendicular to the first direction. 
 
     
     
       20. The headset controller defined in  claim 19  further comprising electronic components mounted on the printed circuit board in the planar regions. 
     
     
       21. The headset controller defined in  claim 20  wherein the printed circuit board is free of stress-sensitive electronic components in the enhanced flexibility region, wherein the electronic components include switches, and wherein the housing is flexible to allow a user to depress the switches. 
     
     
       22. The headset controller defined in  claim 19 , wherein the first and second transverse dimensions are perpendicular, wherein the third transverse dimension is parallel to the first transverse dimension, and wherein the fourth transverse dimension is parallel to the second transverse dimension.

Description:
BACKGROUND 
     This relates generally to electronic devices, and, more particularly, to structures for preventing damage to electronic device circuitry. 
     Electronic devices include components such as buttons, integrated circuits, and other electrical components. These components are mounted to printed circuit boards. Devices may be exposed to external forces during use. For example, a user of a device may intentionally or unintentionally apply force to a device housing. The applied force can stress internal components. For example, the force applied to a device may bend printed circuit boards within the device. 
     If care is not taken, devices that are subjected to external forces can become damaged. If a printed circuit or other substrate is bent excessively, stress may develop in the printed circuit that causes sensitive circuitry on the printed circuit to become damaged. For example, sensitive integrated circuits and other electronic components may become damaged, solder joints that are used in mounting electrical components to the printed circuit may fail, and other sensitive structures may be adversely affected by excess stress arising from a bent substrate. 
     It would therefore be desirable to be able to provide structures for protecting electronic devices from damage due to printed circuit stress. 
     SUMMARY 
     An electronic device may have circuitry mounted on a printed circuit board. The circuitry may include electronic components such as integrated circuits, sensors, and switches that are sensitive to bending-induced stress in the printed circuit board. A plastic stress concentrator may be molded over the printed circuit board and the circuitry on the printed circuit board. A flexible plastic body may be used to enclose the stress concentrator and printed circuit board. The plastic body, stress concentrator, and printed circuit board may be elongated along a longitudinal axis. 
     The stress concentrator may have unbent regions in which the printed circuit board is prevented from flexing and may have enhanced flexibility regions that are more flexible than the unbent regions. The enhanced flexibility regions allow the printed circuit board to bend to accommodate application of external forces to the electronic device. Sensitive circuitry may be located in the unbent regions. The unbent regions are stiffer than the regions of enhanced flexibility and resist bending. This prevents the sensitive circuitry from being exposed to bending stress. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an illustrative electronic device that may be provided with a stress concentrator for preventing damage to circuitry on a printed circuit due to externally applied force in accordance with an embodiment. 
         FIG. 2  is a perspective view of a system environment in which electronic equipment such as a headset with a headset controller is used with a portable electronic device in accordance with an embodiment. 
         FIG. 3  is a cross-sectional side view of the headset controller of  FIG. 2  in accordance with an embodiment. 
         FIG. 4  is a cross-sectional side view of a portion of a printed circuit showing how electronic components may be mounted to the printed circuit in accordance with an embodiment. 
         FIG. 5  is a cross-sectional side view of an illustrative printed circuit that has been bent sufficiently to exhibit a bend characterized by a radius of curvature. 
         FIG. 6  is a cross-sectional side view of an illustrative printed circuit that has been provided with a stress concentrator in accordance with an embodiment. 
         FIG. 7  is a cross-sectional side view of the illustrative printed circuit and stress concentrator of  FIG. 6  following application of an external force that produces a bend in accordance with an embodiment. 
         FIG. 8  is a perspective view of an illustrative printed circuit that has been populated with electronic components such as switches, integrated circuits, and other potentially sensitive circuitry in accordance with an embodiment. 
         FIG. 9  is a cross-sectional side view of an illustrative printed circuit that has been covered with overmolded plastic that forms a stress concentrator to concentrate stress from bending the printed circuit into particular locations along the length of the printed circuit that are devoid of sensitive circuitry in accordance with an embodiment. 
         FIG. 10  is a cross-sectional side view of the printed circuit and stress concentrator of  FIG. 9  during the application of external stress that bends the printed circuit in accordance with an embodiment. 
         FIG. 11  is a perspective view of an illustrative stress concentrator formed from overmolded plastic with one-sided vertical indentations in accordance with an embodiment. 
         FIG. 12  is a perspective view of an illustrative stress concentrator formed from overmolded plastic with two-sided vertical indentations on opposing sides of an embedded printed circuit in accordance with an embodiment. 
         FIG. 13  is a perspective view of an illustrative stress concentrator formed from horizontal indentations at two different locations along the length of an embedded printed circuit in accordance with an embodiment. 
         FIG. 14  is a perspective view of an illustrative stress concentrator formed from ring-shaped indentations that run around the body of an overmolded stress concentrator at two different locations along the length of an embedded printed circuit in accordance with an embodiment. 
         FIG. 15  is a cross-sectional side view of an illustrative stress concentrator formed from multiple overmolded shots of plastic with different flexibilities or other materials with different flexibilities in accordance with an embodiment. 
         FIG. 16  is a cross-sectional side view of an illustrative printed circuit onto which electronic components that are sensitive to bending damage and that are insensitive to bending damage have been mounted showing how an overmolded stress concentrator may concentrate stress on the insensitive components in accordance with an embodiment. 
         FIG. 17  is a cross-sectional side view of an illustrative printed circuit assembly for an electronic device in which an overmolded stress concentrator has been configured to create a neutral stress plane that is aligned with electrical components mounted on a printed circuit in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices may be provided with electrical components that are mounted on substrates such as printed circuits. For example, electrical components may be mounted on a printed circuit using solder or conductive adhesive. To prevent damage to the printed circuit during application of external stress to a device, a stress concentrator can be formed on the printed circuit. When external stress is applied to the device, the printed circuit will tend to bend. The stress concentrator ensures that any bending of the printed circuit will take place only at locations along the printed circuit that are free of sensitive circuitry. 
     A perspective view of an illustrative electronic device that may be provided with one or more printed circuits is shown in  FIG. 1 . An electronic device such as electronic device  10  of  FIG. 1  may be an accessory such as a controller for a headset, a laser pointer, an electronic stylus for use with a tablet computer or electronic drawing surface, all or part of a laptop computer, a computer monitor containing an embedded computer, a tablet computer, a cellular telephone, a media player, or other handheld or portable electronic device, a smaller device such as a wrist-watch device, a pendant device, a headphone or earpiece device, or other wearable or miniature device, a television, a computer display that does not contain an embedded computer, a gaming device, a navigation device, an embedded system such as a system in which electronic equipment with a display is mounted in a kiosk or automobile, equipment that implements the functionality of two or more of these devices, accessories used with this equipment, or other electronic equipment. 
     In the illustrative configuration of  FIG. 1 , device  10  has a body  16  that is elongated along longitudinal axis  18 . In particular, device  10  has a length L along longitudinal axis  18  that is larger than lateral dimensions such as width W (i.e., longitudinal dimension L is significantly larger than transverse dimensions such as width W). Elongated devices such as device  10  of  FIG. 1  tend to be more susceptible to bending during the application of external force than other devices, due to the lever arm produced by length L. As an example, if a user were to apply force F to device  10  in downward direction  20 , the middle of device  10  would tend to bend downward relative to the ends of device  10 . This type of external force may be applied to device  10  intentionally (e.g., when a user is pressing on device  10  with the user&#39;s fingers to actuate a button) or may be applied to device  10  unintentionally (e.g., when device  10  is located in the clothing of a user and the user sits on device  10  or leans on device  10 ). 
     Device  10  and the components and substrates of device  10  may have any suitable shapes. Configurations of the type shown in  FIG. 1  in which device  10  has an elongated shape are sometimes described herein as an example. In elongated device arrangements, device  10  may have a housing that is box-shaped (e.g., a shape with six planar sides), cigar-shaped, an ellipsoid, a shape with one or more flat sides and one or more smoothly curved surfaces, a shape with a triangular cross-section and rounded ends, or other suitable shape. 
     Device  10  may contain electronic components  14  mounted on one or more substrates such as substrate  12 . Components  14  may include buttons, switches, integrated circuits, discrete components such as resistors, inductors, and capacitors (e.g., surface mount technology components), electrical connectors, optical sensors, pressure sensors, accelerometers, capacitive sensors, touch sensors, speakers, microphones, microelectromechanical systems (MEMS) devices, wires with solder joints, and other circuitry. Substrate  12  may be a printed circuit such as a rigid printed circuit board (e.g., a printed circuit board formed from a rigid printed circuit board material such as fiberglass-filled epoxy), a flexible printed circuit (e.g., a printed circuit formed from patterned metal traces on a flexible substrate such as a layer of polyimide or a sheet of other flexible polymer), a “rigid flex” substrate (i.e., a rigid printed circuit board with flexible printed circuit tails), a ceramic layer, a glass layer, a molded plastic carrier, or other dielectric substrate. Printed circuits may contain one or more laminated layers of dielectric and/or vias and one or more layers of patterned metal traces that form signal lines. Configurations for device  10  in which substrate  12  is a printed circuit such as a rigid printed circuit board are sometimes described herein as an example. This is, however, merely illustrative. Substrate  12  may be formed from any suitable dielectric structures for supporting circuitry  14 . 
     Body  16  of device  10  may sometimes be referred to as a case or housing. Body  16  may be formed of materials such as plastic (e.g., flexible plastic that allows a user to press switches located on a printed circuit board under body  16 ), glass, ceramics, carbon-fiber composites and other fiber-based composites, metal (e.g., machined aluminum, stainless steel, or other metals), other materials, or a combination of these materials. Device  10  may be formed using a unibody construction in which most or all of body  16  is formed from a single structural element (e.g., a piece of machined metal or a piece of molded plastic) or may be formed from multiple housing structures (e.g., outer housing structures that have been mounted to internal frame elements or other internal housing structures). 
     One or more substrates such as substrate  12  may be mounted within body (housing  16 ). As shown in the illustrative arrangement of  FIG. 1 , device  10 , body  16 , and at least one printed circuit  12  in device  10  may have an elongated shape with a longitudinal axis that is aligned with longitudinal axis  18  of device  10 . Printed circuit  12  may, for example, have a length that extends along axis  18  and lateral (transverse) dimensions (like width W of device  10 ) that are perpendicular to longitudinal axis  18 . Mounting arrangements like this may allow printed circuit  12  and components  14  to be mounted efficiently, but may expose printed circuit  12  to potential bending upon application of external forces to device  10 . 
       FIG. 2  is a diagram of an illustrative system of the type that may include an electronic device (component) such as device  10  of  FIG. 1 . In the example of  FIG. 2 , device  10  is a controller for headset  22 . Headset  22  plugs into electrical equipment  30  (e.g., a computer, cellular telephone, etc.), so that music and other audio content on equipment  30  can be played for a user. As shown in  FIG. 2 , headset  22  includes speakers  24  such as ear-bud speakers for presenting sound to a user&#39;s ears. Cables  26  include one or more wires for routing electrical signals between speakers  24 , controller  10 , and audio plug  27 . Audio plug  27  plugs into mating audio jack  28  on electronic device  30 . Electrical device  30  may be a computer, a television, a tablet computer, a music player, or other electrical equipment. In the illustrative example of  FIG. 2 , device  30  has touch screen display  36 , menu button  32 , and speaker port  34 . Other types of electrical equipment may be provided with audio jacks such as audio jack  28  to mate with audio plug  27  of headset  22 , if desired. The configuration of  FIG. 2  is merely illustrative. 
     Controller  10  of  FIG. 2  has buttons such as buttons  38 ,  40 , and  42  formed at different locations along the length of device body  16  (i.e., at different positions along longitudinal axis  18  of device  10 ). A user may press on buttons  38 ,  40 , and  42  to control device  30  and therefore the audio content being presented to the user through speakers  24 . There may be three buttons in device  10 , may be fewer than three buttons in device  10 , or may be more than three buttons in device  10 . The housing of device  10  may be formed from an elastomeric material that can be depressed by a user&#39;s fingers to actuate underlying switches mounted to printed circuit board  12  or may be formed from other suitable materials. 
     A cross-sectional side view of headset controller  10  of  FIG. 2  is shown in  FIG. 3 . As shown in  FIG. 3 , dome switches such as dome switches  14 A,  14 B, and  14 C may be soldered or otherwise mounted on printed circuit  12  at different locations along longitudinal device axis  18  to form buttons  38 ,  42 , and  40 , respectively. Body  16  of device  10  may be formed from an elastomeric housing material that allows body  16  to flex when pressed downwards in direction  20  by user&#39;s finger  44 . Wires  26  may be coupled to the opposing ends of device  10  and may extend through the interior of device  10  to connect to circuitry on printed circuit  12 . Solder may be used in coupling wires  26  to solder pads formed from the traces on printed circuit  12 . Solder may also be used in mounting electrical components  14  to printed circuit  12 . 
     A cross-sectional side view of an illustrative printed circuit onto which components have been mounted in shown in  FIG. 4 . As shown in  FIG. 4 , printed circuit board  12  may contain signal paths for routing traces between components  14 . The signal paths may be formed from patterned metal traces on printed circuit  12  such as embedded signal lines  46 , surface signal lines such as signal line  48 , and contacts (solder pads) such as contacts  50 . Components  14  may have contacts (solder pads  52 ). Solder  54  may be used to solder contacts  52  to contacts  50 , thereby electrically connecting components  14  to the signal paths of printed circuit  12  and mechanically mounting components  14  to printed circuit  12 . 
     Solder joints such as the printed circuit solder joints formed from solder  54  can connect components  14  to the signal paths of printed circuit  12 , but can be subject to damage if there is excessive bending of printed circuit  12 . When printed circuit  12  bends, stress is produced in the printed circuit and the spacing between solder joints changes. This can cause a solder joint to become loose. This effect is particularly noticeable in components  14  such as integrated circuits that have a sizable distance between respective contacts  52  (e.g., 1 mm or more or other suitable maximum pad-to-pad spacing along longitudinal axis  18 ). Certain signal lines on printed circuit  12  may also be damaged if printed circuit  12  bends excessively. On the other hand, some signal lines in printed circuit  12  may be robust (e.g., by using thinned metal and/or wider trace layouts). 
     Avoidance of all bending in printed circuit  12  is generally impractical, because it would involve making housing  16  and other structures overly complex and bulky. Nevertheless, care should be taken to avoid creating undesired levels of stress in printed circuit board  12 , particularly in regions of printed circuit board  12  that contain sensitive circuitry. With one suitable arrangement, which is described herein as an example, a stress concentrator is attached to printed circuit board  12 . The stress concentrator allows some bending and stress in printed circuit board  12  in areas that are free of sensitive circuitry such as components  14  to accommodate externally applied force, but maintains other areas of printed circuit board  12  in an unbent configuration to protect sensitive circuitry in those areas from bending-stress-induced damage. 
     As shown in  FIG. 5 , if printed circuit board  12  is not provided with a stress concentrator and is subjected to sufficient external lateral (downward) force F, printed circuit board  12  will bend in a relatively uniform manner. Board  12  may, for example, be characterized by a bend that exceeds a minimum bend radius R at all points along the length of board  12 . The uniform bending behavior of printed circuit board  12  may cause sensitive areas of board  12  to be subjected to more bending and therefore more localized stress than is acceptable for the sensitive circuitry in those areas. 
     This challenge can be addressed by providing printed circuit board  12  with a stress concentrator that ensures that most or all bending of board  12  will occur only in one or more predefined locations along the length of board  12 . The bend locations can be treated as “keep-out” regions that are maintained free of integrated circuits, dome switches, and other sensitive components  14  soldered to board  12 . For example, board  12  can be populated with sensitive components  14  that are located in the unbendable portions of board  12  whereas stress-insensitive metal traces and other robust circuitry can be located in the bendable portions of board  12 . By allowing board  12  to bend in the predefined bending locations, external forces on device  10  and board  12  can be accommodated without forming excessively bulky stiffening structures for the entire board length. 
       FIG. 6  is a cross-sectional side view of an illustrative printed circuit board  12  that has been provided with a stress concentrator structure. The stress concentrator structure may be formed from metal, plastic, or other material and may be attached to one or more sides of printed circuit board  12 . As an example, the stress concentrator may be formed from plastic that is injection molded over some or all of printed circuit board  12 . Stress concentrator  56  and the printed circuit board in stress concentrator  56  may be mounted within housing  16  of device  10 . 
     As shown in  FIG. 6 , stress concentrator structure  56  (e.g., an overmolded plastic member) may be provided with portions such as portion  58  that are relatively stiff and portions such as portions  60  that are thinner (i.e., that have narrower transverse dimensions) or that are otherwise locally weakened and are therefore more flexible than portions  58 . Printed circuit board  12  may be embedded within stress concentrator  56  of  FIG. 6  so that the longitudinal axis of printed circuit board  12  is aligned with the longitudinal axis of stress concentrator  56  and device  10 . 
     Sensitive circuitry  14  may be mounted on printed circuit board  12  within less flexible unbent regions  58 , whereas regions  60 , which have enhanced flexibility, may be left free of sensitive circuitry. When subjected to external force, the structures of  FIG. 7  will bend in enhanced flexibility regions  60 , as shown in  FIG. 7 . The stiffness of stress concentrator  56  within regions  58  is preferably sufficient to maintain the portion of printed circuit board  12  that lies within regions  58  in a straight and relatively unbent configuration. The enhanced flexibility of stress concentrator  56  within enhanced flexibility regions  60  relative to regions  58  allows stress concentrator  56  and printed circuit board  12  within stress concentrator  56  to bend in regions  60 , as shown in  FIG. 7 . Regions  60  do not contain any sensitive circuitry such as integrated circuits or other sensitive electrical components  14 , so the bends formed in regions  60  will not cause any solder joint failures or other damage to printed circuit board  12  and the circuitry on board  12 . 
     The amount of bending in regions  60  is greater than the amount of bending in straight unbent regions  58 . For example, regions  58  may exhibit a relatively large bend radius (e.g., a bend radius of 50 cm or larger—effectively making regions  58  perfectly straight and unbent), whereas regions  60  may be characterized by a bend radius of less than 50 cm, less than 10 cm, or less than 2 cm (as examples). When bent as shown in  FIG. 7 , adjacent portions  58  such as portion  58 A and  58 B may be separated by a bend such as bend  66  having an angle A of 0.1-2°, 1-30°, 5-20°, 3-30°, less than 15° less than 7°, or other suitable angle. Straight portions  58  are essentially unbent (e.g., the largest angle between two portions of a segment of a straight region  58  is less than 1°, less than 0.2°, or has another suitable narrow angle value). 
       FIG. 8  is a perspective view of an illustrative printed circuit that has been populated with electronic components such as buttons, integrated circuits, wires, and other potentially sensitive circuitry  14 . As shown in  FIG. 8 , wires such as wires  26  may be soldered to contacts  50  on printed circuit board  12  using solder  54 . Stress-sensitive electronic components such as switches  14 A,  14 B, and  14 C and other sensitive circuitry  14  may be soldered or otherwise mounted to traces such contacts  50  on printed circuit board  12 . Circuitry that is not sensitive to stress from bending such as illustrative trace  48  of  FIG. 8  may be located in enhanced flexibility regions  60  (i.e., regions where a subsequently formed stress concentrator will allow bending). Sensitive circuitry  14  may be located in unbent regions  58  (i.e., regions where the stress concentrator will not allow bending). 
     Stress concentrator  56  may be formed by overmolding plastic over printed circuit board  12 . Flexibility enhancement features such locally thinned portions of the overmolded plastic material may be formed in regions  60 . An illustrative configuration for stress concentrator  56  is shown in  FIG. 9 . As shown in  FIG. 9 , stress concentrator  56  may be formed by overmolding plastic onto printed circuit board  12 , so that some plastic is formed above and below printed circuit board  12 . In this type of configuration, printed circuit board  12  will be embedded within the plastic of stress concentrator  56 . For example, stress concentrator  56  may have an upper portion such as portion  56 A that overlaps circuitry  14  on the upper surface of printed circuit board  12  and may have a lower portion on the opposing lower surface of printed circuit board  12  such as illustrative lower portion  56 B. Portions  56 A and  56 B may form parts of an integral molded plastic piece or may be separate layers of plastic. Electronic components  14  may be mounted on the upper surface of printed circuit board  12  as shown in  FIG. 9  and/or may be mounted on the opposing lower surface of printed circuit board  12 . 
     The thickness and other stiffness attributes of stress concentrator  56  may be locally adjusted to promote bending in regions  60  over regions  58 . As shown in  FIG. 9 , stress concentrator  56  may have a transverse dimension (i.e., a dimension perpendicular to longitudinal axis  18 ) such as thickness T 2 . Thickness T 2  is sufficient to maintain printed circuit board  12  and sensitive circuitry  14  in unbent regions  58  in a straight (unbent) configuration. In enhanced flexibility regions  60 , the transverse dimensions of stress concentrator  56  relative to longitudinal axis  18  may be decreased (narrowed) relative to the transverse dimensions of stress concentrator  56  in straight regions  58 . For example, the thickness of stress concentrator  56  in regions  60  may be decreased to a minimum of T 1 , where T 1  is less than minimum thickness value T 2  in regions  58 . Because less stress concentrator material is present in regions  60  than regions  58 , regions  60  will be more flexible than regions  58 . This concentrates flexing (and printed circuit board stress) into regions  60 , thereby ensuring that sensitive circuitry  14  on printed circuit board  12  in regions  58  will not bend and will not be exposed to excessive stress. 
       FIG. 10  is a cross-sectional side view of illustrative stress concentrator  56  of  FIG. 9  following bending. As shown in  FIG. 10 , stiff unbent regions  58  remain straight, whereas enhanced flexibility regions  60  allow stress concentrator  56  and embedded printed circuit board  12  to bend more than in regions  58  when external force is applied to device  10  (e.g., body  16  and/or other portions of device  10 ) and thereby to stress concentrator  56  in device  10 . 
     Enhanced flexibility regions  60  in stress concentrator  56  may be provided by local vertical thinning of the top surface of stress concentrator  56 , as shown in the illustrative single-sided thinning arrangement of  FIG. 11 . Due to the presence of vertical notches on the top surface of stress concentrator  56 , thickness T 1  of stress concentrator  56  in enhanced flexibility regions  60  is less than thickness T 2  of stress concentrator  56  in regions  58  while width W is the same for both regions  58  and  60 . 
       FIG. 12  shows how enhanced flexibility regions  60  may be formed by thinning stress concentrator  56  using notches on opposing upper and lower surfaces of stress concentrator  56  while leaving width W the same for both regions  58  and  60 . As shown in  FIG. 12 , by providing aligned notches on the upper and lower surfaces, reduced thickness T 1  (i.e., a reduced vertical transverse dimension perpendicular to longitudinal axis  18 ) is created in regions  60  relative to thickness T 2  in regions  58 . This enhances the flexibility of stress concentrator  58  in regions  60 . 
     If desired, horizontal narrowing of stress concentrator  56  may be used to create locally reduced transverse dimensions (see, e.g., reduced horizontal transverse dimension T 1  of  FIG. 13  from horizontally extending notches). Because transverse dimension T 1  of stress concentrator  56  in regions  60  is less than transverse dimension T 2  in regions  58 , stress concentrator  56  of  FIG. 13  (and therefore the printed circuit board embedded within stress concentrator  56 ) may flex more in regions  60  than in regions  58 , thereby preventing damage to sensitive circuitry  14  in regions  58 . 
       FIG. 14  is a perspective view of an illustrative stress concentrator in which material has been removed from the stress concentrator to narrow the stress concentrator in both vertical and horizontal transverse dimensions. As shown in  FIG. 14 , stress concentrator  56  has a narrowed ring-shaped region in each enhanced flexibility region  60 . 
     If desired, enhanced flexibility regions  60  of stress concentrator  56  can be formed by incorporating material into regions  60  that is more flexible than the material in regions  58 . For example, stress concentrator  56  may be provided with a first material in regions  58  and a second material in regions  60 . The material in regions  60  may be more flexible than the material in regions  58 , thereby enhancing the flexibility of stress concentrator  56  in regions  60  relative to regions  58 .  FIG. 15  is a cross-sectional side view of stress concentrator  56  in this type of configuration. As shown in  FIG. 15 , regions  58  may contain overmolded plastic  56 - 1  and regions  60  may contain overmolded plastic  56 - 2 . Plastic  56 - 1  and plastic  56 - 2  may be formed from different types of plastic, from plastic containing different types of filler structures, from plastic treated in different ways to change its flexibility, etc. Printed circuit board  12  and sensitive electrical components  14  may be embedded within stress concentrator  56 . Sensitive circuitry  14  may be restricted to unbent regions  58 , to avoid damage from flexing of printed circuit board  12  in enhanced flexibility regions  60 . 
       FIG. 16  is a cross-sectional side view of stress concentrator  56  and embedded printed circuit board  12  in an illustrative configuration in which circuitry  14  includes both sensitive circuitry S and insensitive circuitry N. Sensitive circuitry S includes integrated circuits and other components (e.g., components with solder joints that are separated by a pad-to-pad spacing that makes the components sensitive to stress-induced damage) and other circuitry that is prone to stress-induced failure in the event that printed circuit board  12  bends as shown in  FIG. 5  during use of device  10  by a user. Insensitive circuitry N is less sensitive to stress and can reliably withstand the bending conditions that cause sensitive circuitry S to be damaged. As shown in  FIG. 16 , the reduced sensitivity of the components of circuitry N relative to the components of circuitry S allows insensitive circuitry N to be mounted in enhanced flexibility regions  60 , while sensitive components in circuitry S are restricted to regions  58 . Examples of circuit components that are less sensitive to stress-induced failure and that therefore might be safely mounted in regions  60  in some usage scenarios include small discrete components (e.g., capacitors, inductors, resistors, etc.) and/or components that are mounted with contacts arranged along a transverse dimension perpendicular to longitudinal axis  18 . Components such as these do not tend to have widely spaced solder joints and therefore experience less solder joint displacement for a given amount of bend in printed circuit board  14  than larger components such as integrated circuits, switches, and other circuits (e.g., elongated components mounted parallel to longitudinal axis  18  of device  10 ) that have relatively large distances between solder joints. 
     If desired, the amount of stress concentrator material  56 A that is formed above the upper surface of printed circuit  14  and the amount of stress concentrator material  56 B that is formed below the lower surface of printed circuit  14  can be balanced to locate the neutral stress plane of stress concentrator  56  in alignment with components  14  on printed circuit board  12 . As shown in  FIG. 17 , for example, stress concentrator portion  56 A may have a different (e.g., larger) thickness than stress concentrator portion  56 B. When stress concentrator  56  (e.g., the portion of stress concentrator  56  associated with the left-hand enhanced flexibility region  60  in the  FIG. 17  example) moves downward in direction  20  relative to the remaining portions of stress concentrator  56 , upper portion  56 A of stress concentrator  56  at the bend will be under compressive stress, whereas lower portion  56 B and printed circuit board  12  will be under tensile stress. 
     Neutral stress plane  70  represents the plane along which stress is minimized during bending. Within neutral stress plane  70 , compressive stress on one side of the plane is balanced by the tensile stress on the other side of the plane. By configuring the thicknesses of layers  56 A and  56 B appropriately, neutral stress plane  70  can be aligned with the solder joints, surface traces, and other sensitive structures within circuitry  14  on printed circuit board  12 . By aligning neutral stress plane  70  with circuitry  14  in this way, stress-induced failures may be minimized due to flexing of stress concentrator  56  and printed circuit board  12  in enhanced flexibility regions  60 . If desired, wires such as wires  26  can be routed to pass though neutral stress plane  70  (either along the entire length of device  10  or locally in regions prone to bending such as enhanced flexibility regions  60 , as shown in  FIG. 17 ). 
     The foregoing is merely illustrative and various modifications can be made by those skilled in the art without departing from the scope and spirit of the described embodiments. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20140317
Publication Date: 20170131
Grant Date: 20170131
Priority Date: 20140317
Inventors: STANLEY CRAIG M.
QIAN PHILLIP
WANG ERIK L.
Assignee: APPLE INC
CPC Classifications: [{"code": "H05K2203/1316", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K1/148", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K3/284", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K1/118", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K1/0278", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K3/4691", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K1/11", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K1/14", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K1/028", "inventive": true, "first": true, "tree": "[]"}, {"code": "H05K2201/10053", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K1/147", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K1/147", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K1/028", "inventive": true, "first": true, "tree": "[]"}, {"code": "H05K1/11", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2203/1316", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K1/148", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K1/0278", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2201/10053", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K3/4691", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K1/14", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K1/118", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K3/284", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 54070593