PATENT DOCUMENT

Publication Number: US-9402303-B2
Application Number: US-201313908280-A
Country: US
Kind Code: B2

Title: Flexible printed circuit cables with slits

Abstract:
An electronic device contains electrical circuits. The circuits may include circuitry on printed circuit boards and components such as a touch screen display and buttons. Signal paths for routing signals between the electrical circuits may be formed from metal traces on flexible printed circuit cables. The flexible printed circuit cables may be bent around one or more bend axes. A flexible printed circuit cable may be formed from a flexible polymer substrate having one or more layers of polymer. Upper and lower ground layers may be supported by the flexible polymer substrate. The metal traces for the signal paths may lie between the upper and lower ground layers. Longitudinal slits within the flexible printed circuit may be formed that pass through the ground layers and the polymer layers. Vias may be formed that couple the ground layers together. The vias may run along the edges of the slits.

Claims:
What is claimed is: 
     
       1. A flexible printed circuit cable, comprising:
 a flexible polymer substrate with a bend around a bend axis; 
 metal signal line traces supported by the flexible polymer substrate; and 
 at least one slit that passes through the flexible polymer substrate, wherein the at least one slit overlaps the bend axis, wherein the flexible printed circuit cable has a Y-shape with first and second branches, wherein the first branch bends around the bend axis and is coupled to a first component, and wherein the second branch bends around an additional bend axis that is different than the bend axis and is coupled to a second component that is different than the first component. 
 
     
     
       2. The flexible printed circuit cable defined in  claim 1  wherein the flexible polymer substrate comprises at least one layer of polyimide and wherein the at least one slit divides the metal signal line traces into multiple sets of signal line traces. 
     
     
       3. The flexible printed circuit cable defined in  claim 1  further comprising upper and lower ground layers supported by the flexible polymer substrate, wherein the metal signal line traces lie between the upper and lower ground layers. 
     
     
       4. The flexible printed circuit cable defined in  claim 3  wherein the at least one slit passes through the upper and lower ground layers. 
     
     
       5. The flexible printed circuit cable defined in  claim 4  wherein the flexible polymer substrate is an elongated flexible polymer substrate that extends along a longitudinal axis and wherein the at least one slit comprises a plurality of slits that extend parallel to the longitudinal axis. 
     
     
       6. The flexible printed circuit cable defined in  claim 5  further comprising a plurality of conductive vias that are coupled between the upper and lower ground layers. 
     
     
       7. The flexible printed circuit cable defined in  claim 6  wherein the slits have edges and wherein the vias include vias that run along the edges of the slits. 
     
     
       8. The flexible printed circuit cable defined in  claim 7  wherein the flexible polymer substrate comprises at least one polymer layer having a width extending between opposing edges and wherein the flexible polymer substrate comprises at least one recess that locally narrows the width. 
     
     
       9. The flexible printed circuit cable defined in  claim 4  wherein the flexible polymer substrate has a width extending between opposing edges and wherein the flexible polymer substrate comprises at least one recess that locally narrows the width. 
     
     
       10. The flexible printed circuit cable defined in  claim 9  wherein the flexible polymer substrate comprises multiple layers of polymer. 
     
     
       11. A flexible printed circuit cable, comprising:
 at least one layer of polymer with a bend around a bend axis; 
 at least one metal signal trace on the layer of polymer; 
 a slit that passes through the layer of polymer, wherein the slit has edges, wherein the slit overlaps the bend axis; and 
 vias that run along the edges of the slit, wherein each via passes through the layer of polymer, wherein the flexible printed circuit cable has a first branch that bends around the bend axis and is coupled to a display, and wherein the flexible printed circuit cable has a second branch that bends around an additional bend axis that is different than the bend axis and is coupled to a touch sensor. 
 
     
     
       12. The flexible printed circuit cable defined in  claim 11  further comprising upper and lower ground layers, wherein the vias extend between the upper and lower ground layers and wherein the at least one metal signal trace comprises multiple metal signal traces running in parallel with each other. 
     
     
       13. The flexible printed circuit cable defined in  claim 11  further comprising stress relief openings at opposing ends of the slit. 
     
     
       14. The flexible printed circuit cable defined in  claim 1 , wherein the flexible polymer substrate has a thickness extending between opposing upper and lower surfaces and wherein the flexible polymer substrate comprises at least one recess that locally thins the thickness. 
     
     
       15. The flexible printed circuit cable defined in  claim 1 , wherein the flexible polymer substrate is an elongated flexible polymer substrate that extends along a longitudinal axis, and wherein the longitudinal axis is perpendicular to the bend axis. 
     
     
       16. The flexible printed circuit cable defined in  claim 11 , wherein the at least one layer of polymer has a width extending between opposing edges and wherein the at least one layer of polymer comprises a plurality of recesses that locally narrow the width. 
     
     
       17. The flexible printed circuit cable defined in  claim 16 , wherein the bend around the bend axis is one of a plurality of bends around respective bend axes, and wherein each recess overlaps a respective bend axis. 
     
     
       18. The flexible printed circuit cable defined in  claim 1 , wherein the additional bend axis is parallel to the bend axis, wherein the first branch comprises a first portion of the flexible printed circuit cable that is bent to overlap a second portion of the flexible printed circuit cable, and wherein the second branch comprises a third portion of the flexible printed circuit cable that is bent to overlap a fourth portion of the flexible printed circuit cable. 
     
     
       19. The flexible printed circuit cable defined in  claim 18 , wherein the first component comprises a display, wherein the second component comprises a touch sensor, wherein the first branch is coupled to the display with a first connector, and wherein the second branch is coupled to the touch sensor with a second connector. 
     
     
       20. The flexible printed circuit defined in  claim 11 , wherein the additional bend axis is parallel to the bend axis, wherein the first branch is coupled to the display with a first connector, wherein the second branch is coupled to the touch sensor with a second connector, and wherein the first and second branches are both coupled to a printed circuit board with a third connector.

Description:
BACKGROUND 
     This relates generally to electronic devices and, more particularly, to electronic devices with flexible printed circuit cables. 
     Electronic devices include electrical components. Signals are often routed between electrical components using cables formed from flexible printed circuits. Flexible printed circuit cables are compact and lightweight and can be bent to accommodate tight spaces within an electronic device housing. 
     As signal routing needs for electronic devices become increasingly complex, there is a desire to create flexible printed circuit cables with more signal lines. At the same time, printed circuit board real estate concerns encourage the use of shorter cables. 
     To accommodate concerns about increasing routing complexity while maintaining a compact size for a flexible printed circuit cable, designers may create shorter and wider flexible printed circuit cables. Use of this type of cable poses challenges. If care is not taken, cables may become stiff and resistant to flexing. As a result, manufacturing variations in the locations of the components being coupled using a flexible printed circuit cable can give rise to excessive stresses in the flexible printed circuit cable. These stresses may cause connectors to pull apart or can lead to other potential failures. 
     It would therefore be desirable to be able to provide electronic devices with improved flexible printed circuit cables. 
     SUMMARY 
     An electronic device contains electrical circuits. The circuits may include circuitry on printed circuit boards and components such as a touch screen display and buttons. The touch screen display may have a display formed from an array of display pixels and a two-dimensional capacitive touch sensor array that forms a touch sensor overlapping the array of display pixels. 
     Signals paths for routing signals between the electrical circuits may be formed from metal traces on flexible printed circuit cables. The flexible printed circuit cables may be bent around one or more bend axes. A flexible printed circuit cable may have one end that is coupled to a printed circuit board and another end that branches into first and second branches. The first branch may be coupled to a touch sensor in the display. The second branch may be coupled to an array of display pixels in the display. 
     A flexible printed circuit cable may be formed from a flexible polymer substrate having one or more layers of polymer. Upper and lower ground layers may be supported by the flexible polymer substrate. The metal traces for the signal paths may lie between the upper and lower ground layers. Longitudinal slits within the flexible printed circuit may be formed that pass through the ground layers and the polymer layers. Vias may be formed that couple the ground layers together. The vias may run along the edges of the slits. 
     Further features, their nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an illustrative electronic device of the type that may be provided with flexible printed circuit cabling having slits running along the length of the flexible printed circuit cabling in accordance with an embodiment. 
         FIG. 2  is a cross-sectional side view of an electronic device with a flexible printed circuit cable of the type that may be provided with slits in accordance with an embodiment. 
         FIG. 3  is a perspective view of an illustrative flexible printed circuit cable having slits and having a split that divides the flexible printed circuit cable into two parallel flexible printed circuit cable branches in accordance with an embodiment. 
         FIG. 4  is a top view of an illustrative flexible printed circuit cable having slits that run parallel to each other along the length of the flexible printed circuit cable and that have signal lines of the type that may be organized to segregate different types of signals from each other in accordance with embodiment. 
         FIG. 5  is a cross-sectional side view of an illustrative flexible printed circuit cable having layers of signal and ground traces embedded within layers of polymer and having vias in accordance with an embodiment. 
         FIG. 6  is a cross-sectional side view of a portion of an illustrative flexible printed circuit showing how ground plane traces in different layers of the flexible printed circuit may be coupled using vias in accordance with an embodiment. 
         FIG. 7  is a cross-sectional side view of an illustrative flexible printed circuit cable having a ground layer that includes a layer of conductive adhesive in accordance with an embodiment. 
         FIG. 8  is a cross-sectional side view of a portion of an illustrative flexible printed circuit of the type shown in  FIG. 7  showing how electrical connections may be made between layers in accordance with an embodiment. 
         FIG. 9  is a top view of an illustrative flexible printed circuit cable having multiple sets of parallel slits at different respective locations along the length of the flexible printed circuit cable in accordance with an embodiment. 
         FIG. 10  is a cross-sectional side view of a portion of an electronic device showing how a flexible printed circuit cable may have multiple bends of the type that may overlap slits in accordance with an embodiment. 
         FIG. 11  is a top view of an illustrative flexible printed circuit cable with edge recesses that are configured to locally decrease the width of the flexible printed circuit cable at various locations along the length of the flexible printed circuit cable and thereby enhance flexibility of the flexible printed circuit cable at those locations in accordance with an embodiment. 
         FIG. 12  is a cross-sectional side view of an illustrative flexible printed circuit cable with recesses that are configured to locally decrease the thickness of the flexible printed circuit cable at various locations along the length of the flexible printed circuit cable and thereby enhance flexibility of the flexible printed circuit cable at those locations in accordance with an embodiment. 
         FIG. 13  is a top view of an illustrative flexible printed circuit cable having slits with stress relief features in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Flexible printed circuits are formed from layers of flexible polymer or other dielectric and patterned metal traces. Substrates that may be used in forming flexible printed circuits include layers of polyimide and sheets of other flexible polymer materials. Metal traces on flexible printed circuits may be formed from metals such as copper or other traces that can be patterned into signal lines and ground plane structures. Metal flexible printed circuit traces may be patterned using blanket physical vapor deposition followed by photolithographic patterning, by depositing metal lines using ink-jet printing or screen printing techniques, using laser-based processing (e.g., using laser light to selectively activate substrate regions followed by electroplating to grow metal on the activated regions), or by using other suitable patterning techniques. 
     The metal traces on flexible printed circuits can be used to form serial and parallel digital data signal paths and analog signal paths. Flexible printed circuits that contain signal lines for conveying analog and/or digital signals are sometimes referred to as flexible printed circuit buses or flexible printed circuit cables. As an example, a flexible printed circuit may contain a signal bus containing tens or hundreds of parallel signal lines. A flexible printed circuit of this type may be used as a cable to route signals between electrical components on a printed circuit board and components such as display or touch sensor components. Flexible printed circuit cables may also be used to route signals between printed circuits, between a printed circuit and components such as buttons and other input-output devices, between a camera and other circuitry in an electronic device, or between other circuits. 
     An illustrative electronic device that may include flexible printed circuit cabling is shown in  FIG. 1 . Electronic devices such as device  10  of  FIG. 1  may be cellular telephones, media players, other handheld portable devices, somewhat smaller portable devices such as wrist-watch devices, pendant devices, or other wearable or miniature devices, gaming equipment, tablet computers, notebook computers, desktop computers, televisions, computer monitors, computers integrated into computer displays, or other electronic equipment. 
     In the example of  FIG. 1 , device  10  includes a display such as display  14 . Display  14  has been mounted in a housing such as housing  12 . Housing  12 , which may sometimes be referred to as an enclosure or case, may be formed of plastic, glass, ceramics, fiber composites, metal (e.g., stainless steel, aluminum, etc.), other suitable materials, or a combination of any two or more of these materials. Housing  12  may be formed using a unibody configuration in which some or all of housing  12  is machined or molded as a single structure or may be formed using multiple structures (e.g., an internal frame structure, one or more structures that form exterior housing surfaces, etc.). 
     Display  14  may be a touch screen display that incorporates a layer of conductive capacitive touch sensor electrodes or other touch sensor components (e.g., resistive touch sensor components, acoustic touch sensor components, force-based touch sensor components, light-based touch sensor components, etc.) or may be a display that is not touch-sensitive. Capacitive touch screen electrodes may be formed from an array of indium tin oxide pads or other transparent conductive structures. A capacitive touch sensor may be formed from an array of capacitive electrodes that are formed on a layer of glass or plastic or other substrate material. The substrate may be a clear material to allow the touch sensor to overlap a display such as display  14 . The capacitive touch sensor in a touch screen display may be formed form a substrate that is attached to display layers with adhesive or may be formed as part of a display arrangement with integrated touch sensor and display structures (as examples). 
     Display  14  may include an array of display pixels formed from liquid crystal display (LCD) components, an array of electrophoretic display pixels, an array of plasma display pixels, an array of organic light-emitting diode display pixels, an array of electrowetting display pixels, or display pixels based on other display technologies. 
     Display  14  may be protected using a display cover layer such as a layer of transparent glass or clear plastic. Openings may be formed in the display cover layer. For example, an opening may be formed in the display cover layer to accommodate a button such as button  16 . An opening may also be formed in the display cover layer to accommodate ports such as a speaker port or other components. 
     In the center of display  14 , display  14  may contain an array of active display pixels. This region is sometimes referred to as the active area of the display. A rectangular ring-shaped region surrounding the periphery of the active display region may not contain any active display pixels and may therefore sometimes be referred to as the inactive area of the display. The display cover layer or other layers in display  14  may be provided with an opaque masking layer in the inactive region to hide internal components from view by a user. Windows in inactive edge portions of display  14 , housing  12 , and other portions of device  10  may be used to accommodate components such as a proximity sensor, ambient light sensor, microphone, camera, and antennas. 
     A cross-sectional side view of device  10  is shown in  FIG. 2 . As shown in the illustrative configuration of  FIG. 2 , device  10  may have a display such as display  14  that is mounted on the front face of device  10  in housing  12 . Display  14  may have a display cover layer  18  and a display module such as display module  20 . Display cover layer  18  may be formed from a clear glass layer, a layer of transparent plastic, or other cover layer material. A layer of ink (e.g., black ink or white ink or ink of other colors) may form a rectangular ring-shaped opaque masking layer in an inactive border region of display  14 . 
     Display module  20  may be, for example, a liquid crystal display module or an organic light-emitting diode display layer (as examples). Display module  20  may include an array of display pixels in one or more display layers (shown as display layers  20 A—also sometimes referred to as display pixel array  20 A or display  20 A) and a two-dimensional touch sensor such as a capacitive touch sensor or a touch sensor formed using other touch technologies (shown as touch sensor layer  20 B). The structures of display layers  20 A and touch sensor layers  20 B may be laminated to each other using adhesive or may be formed as integral portions of a common touch screen display assembly. 
     Device  10  may include components such as components  24  that are mounted on one or more substrates such as substrate  22 . Substrate  22  may be a dielectric carrier such as a molded plastic carrier or may be a printed circuit. For example, substrates  48  may be a printed circuit such as a rigid printed circuit board formed from a dielectric material such as fiberglass-filled epoxy or may be a flexible printed circuit formed from a dielectric layer such as a sheet of polyimide or other flexible polymer layer. Metal interconnect paths may be provided on within substrate  22  to allow substrate  22  to covey signals between components mounted on substrate  22 . With one illustrative configuration, which may sometimes be described herein as an example, substrate  22  is a rigid printed circuit substrate. 
     Electrical components such as components  24  may be mounted on printed circuit  22  and may be electrically connected to conductive paths in printed circuit  22 . Components  24  may be, for example, integrated circuits, discrete components such as capacitors, resistors, and inductors, switches, connectors, sensors, input-output devices such as status indicators lights, audio components, or other electrical and/or mechanical components for device  10 . Components  24  may be attached to printed circuit  22  using solder, welds, anisotropic conductive film or other conductive adhesives, or other conductive connections. 
     Flexible printed circuit cables such as flexible printed circuit cable  26  may be used to route signals within device  10 . For example, a flexible printed circuit cable may be used to couple two different printed circuits together, may be used to couple a printed circuit to a component, may be used to interconnect components, or may otherwise be used in providing routing paths between circuits in device  10 . 
     Flexible printed circuit cable  26  and other printed circuits in device  10  such as printed circuit board  22  may contain signal paths. The printed circuit signal paths may sometimes be referred to as lines, traces, or interconnects and may be formed from conductive materials such as metal (e.g., copper, gold, aluminum, etc.). Using these printed circuit paths, components  22  may be interconnected with each other and may be interconnected with other components in device  10  such as touch sensor  20 B and display  20 A in touch screen display  14 . 
     The metal traces in flexible printed circuit cable  26  may be coupled to display  14  and substrates such as substrate  22  or other circuits in device  10  using anisotropic conductive film or other conductive adhesive, using solder, or using other coupling mechanisms. As shown in  FIG. 2 , for example, flexible printed circuit  26  may have an end such as end  28  that is coupled to traces in printed circuit  22  using connector  30 . Connector  30  may be a printed circuit connector such as a board-to-board connector or a zero-insertion-force connector (as examples). Flexible printed circuit  26  may have a Y-shape with two branches that extend away from end  28  to form ends  32 A and  32 B. The metal traces in flexible printed circuit  26  at ends  32 A and  32 B may be coupled to circuits such as circuits in display  14  or other components or printed circuits. As an example, end  32 A of flexible printed circuit  26  may be coupled to display (display pixel array)  20 A using connector structures  36  and end  32 B of flexible printed circuit  26  may be coupled to touch sensor  20 B using connector structures  34 . Connector structures  34  and  36  may include anisotropic conductive film connections, zero-insertion-force connectors, board-to-board connector structures, printed circuits, welds, solder connections, or other coupling structures and circuitry. As an example, structures  36  may include a printed circuit board and circuitry that is coupled to display  20 A using anisotropic conductive film and structures  34  may include a connector that is coupled to touch sensor  20 B. 
     As shown in  FIG. 2 , flexible printed circuit cable  26  may be bent around bend axis  38 . Bend axis  38  may extend into the page in the orientation of  FIG. 2  (i.e., parallel to the X axis). To ensure that flexible printed circuit cable  26  is sufficiently flexible to accommodate shifts in the locations of components in display  14  and substrate  22  (i.e., manufacturing variations that affect the angular orientation of flexible printed circuit cable  26  in the X-Y plane and lateral locations of the ends of flexible printed circuit cable  26  along the X and Y axis), flexible printed circuit cable  26  may be provided with one or more slits. The slits may run along the length of flexible printed circuit cable  26  (i.e., the flexible printed circuit cable may have a longitudinal axis along which the flexible printed circuit cable extends and the slits may run partway along the length of the flexible printed circuit cable parallel to the longitudinal axis). 
       FIG. 3  is a perspective view of an illustrative flexible printed circuit cable with slits. As shown in  FIG. 3 , flexible printed circuit cable  26  may have end  28  and a Y-shape that branches into ends  32 A and  32 B. With this type of arrangement, one branch of flexible printed circuit cable  26  may split off from end  28  and may terminate in end  32 B and another branch of flexible printed circuit cable  26  may split off from end  28  to terminate at end  32 A. The branch of flexible printed circuit cable  26  that extends between end  28  and end  32 A may be bent around bend axis  38 A. The branch of flexible printed circuit cable  26  that extends between end  28  and end  32 B may be bent around bend axis  38 B. 
     Slits may be formed in either or both branches of flexible printed circuit cable  26  of  FIG. 3 . As shown in  FIG. 3 , for example, slits  40  may be formed in the branch of flexible printed circuit cable  26  that extends from end  28  to end  32 A. Each of slits  40  has an elongated shape that runs parallel to the longitudinal axis of elongated flexible printed circuit cable  26 . The shape of each slit  40  may be, for example, a rectangle with a width that is narrower than its length (e.g., a rectangular opening with a length that is ten times as large as its width or more). Slits  40  may pass completely through the dielectric and conductive layers of flexible printed circuit  26  and may be filled with air. There are two slits  40  in  FIG. 3 , but, in general, there may be any suitable number of slits in flexible printed circuit  26  (e.g., one or more slits, two or more slits, two to five slits, three or more slits, more than five slits, etc.). Slits  40 , which may sometimes be referred to as elongated openings, slots, or gaps, may allow portions of flexible printed circuit cable  26  to move relative to other portions of flexible printed circuit cable  26 . This may help prevent flexible printed circuit cable  26  from becoming overly stiff, which could lead to stresses that could cause connectors and other electrical joints to become disconnected. 
     Interconnection cables such as flexible printed circuit cable  26  may carry analog signals, digital signals, direct-current (DC) power and data signals, alternating current (AC) signals, high speed data signals, low speed data signals, or other signals. To prevent excessive interference, it may be desirable to segregate high-speed lines from low-speed lines and/or to segregate signals that produce potential interference (sometimes referred to as aggressors) from signals that are sensitive to potential interference (sometimes referred to as victims). 
       FIG. 4  is a top view of an illustrative flexible printed circuit cable with slits  40 . In the example of  FIG. 4 , flexible printed circuit  26  extends along longitudinal axis  46  between first end  28  and second end  32 . Other layouts may be used for flexible printed circuit cable  26  if desired. The  FIG. 4  example is merely illustrative. 
     As shown in  FIG. 4 , flexible printed circuit cable  26  may have multiple metal signal traces such as signal traces  44 . Signal traces  44  and slits  40  may run parallel to longitudinal axis  46  (i.e., slits  40  may each have a longitudinal axis that runs parallel to longitudinal axis  46 ). Slits  40  may overlap bend axis  38 . Due to the presence of slits  40 , flexible printed circuit cable  26  will not be overly stiff and will be able to bend around bend axis  38  when installed within electronic device  10 . 
     Slits  40  may divide metal traces  44  into sets or groups of metal traces such as set S 1 , set S 2 , set S 3 , and set S 4 . There are four sets of metal traces  44  in the example of  FIG. 4 , separated by three respective slits  40 . Other numbers of slits  40  and sets of metal traces  44  may be used in flexible printed circuit cable  26  if desired. Moreover, there are no branches in flexible printed circuit cable  26  of  FIG. 4 , because flexible printed circuit cable  26  extends in an undivided fashion between opposing ends  28  and  32 . As shown in  FIG. 3 , flexible printed circuit cable  26  may, if desired, have a division that forms two respective branches, may have multiple splits to form three or more branches, may have branches at either opposing end of flexible printed circuit cable  26 , or may have other suitable shapes. 
     Signals may be assigned to the different sets of metal traces  44  in a way that minimizes interference. For example, with one suitable arrangement, all (or nearly all) signals with more than a particular data rate (i.e., high-speed signals) may be assigned to set S 2 , whereas all (or nearly all) signals with less than that particular data rate (low-speed signals) may be assigned to sets S 1 , S 3 , and S 4 . With another illustrative configuration, aggressors may be assigned to one set (e.g., set S 3 ), whereas victims may be assigned to other sets (e.g., S 1 , S 2 , and S 4 ). 
     Flexible printed circuit cable  26  may have ground structures that are coupled by vertically extending structures such as vias  42 . Vias  42  may extend vertically in dimension Z to couple respective ground layers together or to otherwise short together metal traces in flexible printed circuit cable  26 . Signal interference can be minimized by arranging vias  42  in a pattern that forms grounded edges on both sides of each set of signal lines. For example, a series of vias  42 - 1  may run along left edge  26 L of flexible printed circuit cable  26  parallel to dimension Y and a series of vias  42 - 2  may run along right edge  26 R of flexible printed circuit cable  26  parallel to dimension Y. Vias  42 ′ may run parallel to dimension Y along the edges  40 ′ of slits  40 . In this way, set S 1  of metal traces  44  is electromagnetically isolated from interference by a left-hand ground path formed from vias  42 - 1  and a right-hand ground path formed from the group of vias  42 ′ along the leftmost edge  40 ′. Other sets of metal traces  44  are likewise bordered by grounding structures that run along their right and left edges. By bordering the edges of printed circuit cable  26  and the edges of slits  40  with grounding vias, interference between signals on different sets of metal traces  44  and external signal interference may be reduced. 
     As shown in the cross-sectional side view of  FIG. 5 , flexible printed circuit cable  26  may have ground layers such as layers G 1  and G 2  (e.g., ground layers formed from copper or other metal) and a signal layer of patterned metal traces such as layer  44 . Metal traces in layer  44  may lie above lower ground layer G 1  and above upper ground layer G 2 . These conductive structures may be supported by substrate layers such as dielectric layers  48  (e.g., multiple layers of polyimide or other flexible polymer layers that make up the polymer substrate for flexible printed circuit cable  26 ). 
       FIG. 6  is a cross-sectional side view of a portion of flexible printed circuit cable  26  of  FIG. 5  showing how a via such as via  42  may short lower ground G 1  to upper ground G 1 . 
     In the illustrative configuration of flexible printed circuit cable  26  that is shown in  FIG. 7 , flexible printed circuit cable  26  has ground layers such as layers G 1  and G 2  and a signal layer of patterned metal traces such as layer  44  that lies between layers G 1  and G 2 . These conductive layers may be supported by substrate layers such as dielectric layers  48  (e.g., layers of polyimide or other flexible polymer layers in a polymer substrate for cable  26 ). Ground layer G 1  may be formed from a layer of copper (as an example). Ground layer G 2  may have a layer of conductive adhesive such as layer G 2 - 1  and may have a conductive layer such as layer G 2 - 2 . Layer G 2 - 2  may be a copper foil, silver, or other conductive material. 
       FIG. 8  is a cross-sectional side view of a portion of flexible printed circuit cable  26  of  FIG. 8  showing how a vertical connection through opening  48 V may be formed by a portion of conductive adhesive G 2 - 1 . Structures such as the vertical structure of  FIG. 8  may be used in forming vias  42  to short together ground layers G 1  and G 2 . 
     As shown in  FIG. 9 , flexible printed circuit cable  26  may have multiple sets of slits  40  each of which is located at a different respective position along the length of flexible printed circuit cable  26  and longitudinal axis  46  of flexible printed circuit cable  26 . There are three illustrative bend axis locations in  FIG. 9 . Slits  40 - 1  overlap bend axis  38 - 1 . Slits  40 - 2  overlap bend axis  38 - 2 . Slits  40 - 3  overlap bend axis  38 - 3 . 
       FIG. 10  is a cross-sectional side view of illustrative flexible printed circuit cable  26  of  FIG. 9  showing how cable  26 - 3  may be bent around each of the bend axes  38 - 1 ,  38 - 2 , and  38 - 3  while coupling structures  50  and  52 . Flexible printed circuit cable  26  may have ends that are coupled to structures  50  and  52  using coupling structures  54 . Coupling structures  54  may include anisotropic conductive film, welds, solder, connectors, printed circuit boards, or other signal path coupling structures. Structures  50  and  52  may be printed circuits, display  14 , a touch sensor, a display pixel array in display  14 , buttons, or other circuits. 
     If desired, flexible printed circuit cable  26  may be provided with a variable width. As shown in  FIG. 11 , for example, flexible printed circuit cable  26  may be characterized by a width W extending between opposing respective left and right edges  26 L and  26 R of cable  26 . The width W of flexible printed circuit cable  26  may be locally narrowed to enhance flexibility in flexible printed circuit cable  26 . As an example, flexible printed circuit cable  26  may be provided with recesses (notches) on one or both edges  26 R and  26 L of cable  26 . These recesses may locally narrow the width of flexible printed circuit cable  26  where cable  26  overlaps bend axes. 
     In the  FIG. 11  example, flexible printed circuit cable  26  has recesses  56 - 1  that narrow flexible printed circuit cable  26  where flexible printed circuit cable  26  overlaps bend axis  38 - 1 . Flexible printed circuit cable  26  of  FIG. 11  also has recesses  56 - 2  that narrow flexible printed circuit cable  26  where flexible printed circuit cable  26  overlaps bend axis  38 - 2  and has recesses  56 - 3  that narrow flexible printed circuit cable  26  where flexible printed circuit cable  26  overlaps bend axis  38 - 3 . 
     As shown in  FIG. 12 , flexible printed circuit cable  26  may be provided with a variable thickness. As shown in  FIG. 12 , flexible printed circuit cable  26  may be characterized by a thickness T extending between upper surface  26 T and opposing lower surface  26 B of cable  26 . The thickness T of flexible printed circuit cable  26  may be locally thinned to enhance flexibility in flexible printed circuit cable  26 . As an example, flexible printed circuit cable  26  may be provided with recesses on one or both surfaces of cable  26  such as upper surface  26 T and lower surface  26 B. Flexible printed circuit cable  26  may, for example, be provided with recesses such as recesses  60 - 1  on upper surface  26 T and lower surface  26 B to locally reduce the thickness of flexible printed circuit cable  26  in a location that overlaps bend axis  38 - 1 , recess  60 - 2  on upper surface  26 T to locally reduce the thickness of flexible printed circuit cable  26  in a location that overlaps bend axis  38 - 2 , and recess  60 - 3  on lower surface  26 B to locally reduce the thickness of flexible printed circuit cable  26  in a location that overlaps bend axis  38 - 3 . Recesses to thin the thickness of flexible printed circuit cable  26  may extend into one or more of the polymer layers that form the substrate of flexible printed circuit cable  26 . 
     In general, flexible printed circuit cable  26  may have one or more sets of slits  40  in combination with optional features such as optional horizontal width narrowing recesses and/or optional thickness narrowing recesses to form bendable regions overlapping one or more, two or more, three or more, or four or more bend axes. 
     Slits  40  may be formed by removing material from flexible printed circuit cable  26  (e.g., using die cutting, using a movable cutting head such as a drill, using a laser-cutting scheme, or using other material removal techniques). Slits  40  may also be formed by cutting flexible printed circuit cable  26  using a knife or other tool that does not remove material (i.e., using a knife to form a slit by forming a cut line in cable  26  without removing material along the cut line). Slits  40  formed by removing a portion of flexible printed circuit cable  26  and/or slits  40  that are formed by cutting lines into flexible printed circuit  26  using a knife may be susceptible to tearing at their ends. Stress relief features such as circular openings or openings of other shapes may be formed in flexible printed circuit  26  to help prevent tearing. As shown in the top view of  FIG. 13 , for example, slits  40  may have main portions  40 C (i.e., openings in flexible printed circuit that are formed from cut lines with no removed material and/or slits that are formed from elongated openings created by removing material). Main portions  40 C may have the shape of straight lines. At opposing ends of each main portion  40 C, slits  40  may be provided with stress relief openings  40 E. Stress relief openings  40 E may, for example, be formed by drilling holes in flexible printed circuit  26  at opposing ends of each slit  40 . 
     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: 20130603
Publication Date: 20160726
Grant Date: 20160726
Priority Date: 20130603
Inventors: QIAN AMY
PETERSON CARL R.
FRANKLIN JEREMY C.
ALVERSON JOSEPH F.
GIBBS KEVIN D.
Assignee: APPLE INC
CPC Classifications: [{"code": "H05K2201/09618", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2201/0715", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2201/09145", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F1/1658", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K2201/10128", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2201/042", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K1/147", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2201/09236", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K1/0221", "inventive": true, "first": true, "tree": "[]"}, {"code": "H05K1/028", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K2201/09063", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K1/0221", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F1/1658", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K1/147", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2201/0715", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2201/09063", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2201/09145", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2201/09236", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2201/10128", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2201/042", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2201/09618", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K1/028", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 51984707