PATENT DOCUMENT

Publication Number: US-9485862-B2
Application Number: US-201414472223-A
Country: US
Kind Code: B2

Title: Electronic devices with carbon nanotube printed circuits

Abstract:
An electronic device has structures such as substrates and internal housing structures. The substrates may be rigid substrates such as rigid printed circuit boards and flexible substrates such as flexible printed circuits, flexible touch sensor substrates, and flexible display substrates. Carbon nanotubes may be patterned to form carbon nanotube signal paths on the substrates. The signal paths may resist cracking when bent. A flexible structure such as a flexible printed circuit may have carbon nanotube signal paths interposed between polymer layers. Openings in a polymer layer may expose metal solder pads on the carbon nanotube signal paths. A stiffener may be provided under the metal solder pads. Polymer materials in the flexible structure may be molded to form bends. Bends may be formed along edges of a touch sensor or display or may be formed in a flexible printed circuit.

Claims:
What is claimed is: 
     
       1. A carbon nanotube flexible printed circuit, comprising:
 a first polymer layer; 
 carbon nanotube signal paths on the first polymer layer; 
 metal solder pads on portions of the carbon nanotube signal paths, wherein the metal solder pads are in direct contact with the carbon nanotube signal paths; and 
 a second polymer layer on the first polymer layer, wherein the metal solder pads comprise first and second metal solder pads on respective first and second opposing ends of one of the carbon nanotube signal paths, wherein the second polymer layer has first and second openings that are respectively aligned with the first and second metal solder pads, and wherein the first and second polymer layers comprise molded portions that maintain a bend in the carbon nanotube signal paths. 
 
     
     
       2. The carbon nanotube flexible printed circuit defined in  claim 1  wherein the carbon nanotube signal paths are interposed between the first polymer layer and the second polymer layer. 
     
     
       3. The carbon nanotube flexible printed circuit defined in  claim 2  wherein the metal solder pads comprise electroplated metal. 
     
     
       4. The carbon nanotube flexible printed circuit defined in  claim 3  further comprising a stiffener under at least some of the metal solder pads. 
     
     
       5. The carbon nanotube flexible printed circuit defined in  claim 4  wherein the stiffener comprises a layer of metal attached to the first polymer layer with a layer of adhesive. 
     
     
       6. The carbon nanotube flexible printed circuit defined in  claim 1  further comprising a first layer of adhesive between the first polymer layer and the carbon nanotube signal paths and a second layer of adhesive between the second polymer layer and the carbon nanotube signal paths. 
     
     
       7. A carbon nanotube flexible printed circuit, comprising:
 a first polymer layer with first and second opposing sides; 
 a carbon nanotube signal path on the first side of the first polymer layer, wherein the carbon nanotube signal path has first and second ends; 
 a first metal solder pad on the first end of the carbon nanotube signal path; 
 a second metal solder pad on the second end of the carbon nanotube signal path, wherein the carbon nanotube signal path electrically connects the first metal solder pad to the second metal solder pad; and 
 a stiffener formed under at least the first metal solder pad, wherein the stiffener is formed on the second side of the first polymer layer. 
 
     
     
       8. The carbon nanotube flexible printed circuit defined in  claim 7 , further comprising:
 a second polymer layer on the first polymer layer, wherein the carbon nanotube signal path is interposed between the first and second polymer layers. 
 
     
     
       9. The carbon nanotube flexible printed circuit defined in  claim 8 , wherein the second polymer layer has a first opening that is aligned with the first metal solder pad and a second opening that is aligned with the second metal solder pad. 
     
     
       10. The carbon nanotube flexible printed circuit defined in  claim 7 , wherein the first and second metal solder pads are in direct contact with the carbon nanotube signal path. 
     
     
       11. The carbon nanotube flexible printed circuit defined in  claim 8 , wherein the first and second polymer layers comprise molded portions that maintain a bend in the carbon nanotube signal path. 
     
     
       12. The carbon nanotube flexible printed circuit defined in  claim 8 , wherein the first and second polymer layers have a bend and wherein the carbon nanotube signal path is bent along the bend.

Description:
BACKGROUND 
     This relates generally to electronic devices and, more particularly, to structures such as printed circuits for electronic devices. 
     Printed circuits are often used to route signals within electronic devices such as cellular telephones, computers, and other electronic equipment. Electrical components can be mounted to a printed circuit using solder. Because printed circuits are relatively thin, the use of printed circuits to route signals between components in an electronic device can help minimize the size and weight of the device. 
     In some situations, it can be difficult to satisfactorily mount printed circuits within an electronic device. Flexible printed circuits often have bends and can be subjected to numerous bending and unbending cycles during operation of a device. If care is not taken, a flexible printed circuit will be bent too much. This can lead to cracks in signal lines on the flexible printed circuit and poor reliability. Although cracks can be reduced and reliability enhanced by placing restrictions on the amount of bending that is imposed on a flexible printed circuit, this can create undesired bulk and undesired limitations on the movement of the flexible printed circuit. 
     It would therefore be desirable to be able to provide improved structures such as printed circuits for electronic devices. 
     SUMMARY 
     An electronic device has structures such as substrates and internal housing structures. The substrates may include rigid substrates such as rigid printed circuit boards and flexible substrates such as flexible printed circuits, flexible touch sensor substrates, and flexible display substrates. The internal housing structures may include a carbon nanotube midplate that extends between opposing housing walls to lend structural support to an electronic device. 
     Carbon nanotubes may be patterned to form carbon nanotube signal paths on the substrates. The signal paths may resist cracking when bent. A bent portion of a carbon nanotube signal path may be formed in a portion of a flexible substrate that traverses a hinge or other flexible portion of an electronic device. 
     A flexible structure such as a flexible printed circuit may have a carbon nanotube layer interposed between polymer layers. The carbon nanotube layer may be patterned to form carbon nanotube signal paths that are covered by a polymer layer. Openings in the polymer layer may be formed to expose metal solder pads on the carbon nanotube signal paths. 
     A stiffener may be attached to the flexible printed circuit with adhesive under the metal solder pads. Polymer materials in the flexible structure may be molded to form bends. Bends may be formed along edges of a touch sensor or display, may be formed in a flexible printed circuit, or may be formed within other carbon nanotube flexible substrate structures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an illustrative electronic device in accordance with an embodiment. 
         FIG. 2  is a perspective view of an illustrative electronic device that bends along a flexible portion such as a flexible seam associated with a hinge in accordance with an embodiment. 
         FIG. 3  is a cross-sectional side view of an illustrative electronic device having a flexible printed circuit with a bend in accordance with an embodiment. 
         FIG. 4  is a cross-sectional side view of an illustrative electronic device having a display such as a touch sensor display with a bend in accordance with an embodiment. 
         FIG. 5  is a cross-sectional side view of an illustrative carbon nanotube layer in which carbon nanotubes are being supported by a substrate in accordance with an embodiment. 
         FIG. 6  is a cross-sectional side view of an illustrative carbon nanotube layer in which a layer of carbon nanotubes and a metal layer or other layer has been formed on a substrate in accordance with an embodiment. 
         FIG. 7  is a cross-sectional side view of an illustrative carbon nanotube layer in which a layer of adhesive on a substrate has been used to attach a layer of carbon nanotubes to the substrate in accordance with an embodiment. 
         FIG. 8  is a cross-sectional side view of an illustrative carbon nanotube layer in which carbon nanotubes have been embedded in a matrix such as a polymer binder in accordance with an embodiment. 
         FIG. 9  is a diagram of illustrative equipment involved in forming carbon nanotube structures for an electronic device in accordance with an embodiment. 
         FIG. 10  is a diagram of illustrative operations and equipment involved in forming carbon nanotube structures for a flexible substrate such as a flexible printed circuit in accordance with an embodiment. 
         FIGS. 11A, 11B, 11C, 11D, and 11E  are perspective views of an illustrative printed circuit with carbon nanotubes during various phases of fabrication in accordance with an embodiment. 
         FIG. 12  is a cross-sectional side view of an illustrative carbon nanotube printed circuit with a stiffener in accordance with an embodiment. 
         FIG. 13  is a flow chart of illustrative steps involved in forming carbon nanotube structures such as carbon nanotube printed circuits in accordance with an embodiment. 
         FIG. 14  is a side view of illustrative roller-based equipment for laminating layers together for a carbon nanotube printed circuit in accordance with an embodiment. 
         FIG. 15  is a side view of illustrative stamping equipment such as roller-based stamping equipment of the type that may be used to form carbon nanotube structures in accordance with an embodiment. 
         FIG. 16  is a cross-sectional side view of an illustrative carbon nanotube structure during molding and bending operations in accordance with an embodiment. 
         FIG. 17  is a perspective view of an illustrative carbon nanotube structure with a right-angle bend in accordance with an embodiment. 
         FIG. 18  is a cross-sectional side view of an illustrative carbon nanotube structure coupled to another structure using conductive material in accordance with an embodiment. 
         FIG. 19  is a cross-sectional side view of an illustrative electronic device that has a structural housing member such as a midplate member formed from carbon fiber material in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices may be provided with carbon nanotube structures or other structures based on carbon (e.g., graphene structures, carbon-fiber structures having carbon fibers other than carbon nanotubes, etc.). Configurations in which the carbon-based structures are carbon nanotube structures are sometimes described herein as an example. 
     Carbon nanotube structures may include single-wall carbon nanotubes, multiple-wall carbon nanotubes, or mixtures of single-wall and multiple-wall carbon nanotubes. Carbon nanotubes can form conductive paths for printed circuits or other flexible substrates such as substrates associated with touch sensors and displays and can form structural components in an electronic device. 
     Conductive carbon nanotube paths can form signal paths that are flexible and resistant to cracking The carbon nanotube structures may be incorporated into signal cables such as flexible printed circuit cables, rigid printed circuit boards, printed circuits that include rigid portions with flexible tails (sometimes referred to as “rigid flex”), portions of display structures, portions of touch sensors such as capacitive touch sensor arrays for displays or track pads, camera structures, antenna structures, housing structures, internal device structures, electrical components, substrates, brackets, housing walls, other structures, or combinations of these structures. 
       FIG. 1  is a perspective view of an illustrative electronic device of the type that may include carbon nanotube structures. Electronic device  10  may be a computing device such as 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, a device embedded in eyeglasses or other equipment worn on a user&#39;s head, 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, or other electronic equipment. In the illustrative configuration of  FIG. 1 , device  10  is a portable device such as a cellular telephone, media player, tablet computer, or other portable computing device. Other configurations may be used for device  10  if desired. The example of  FIG. 1  is merely illustrative. 
     In the example of  FIG. 1 , device  10  includes display  14 . Display  14  has been mounted in 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. 
     Display  14  may include an array of pixels formed from liquid crystal display (LCD) components, an array of electrophoretic pixels, an array of plasma display pixels, an array of organic light-emitting diode pixels, an array of electrowetting pixels, or 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 speaker port  18 . Openings may be formed in housing  12  to form communications ports, holes for buttons, and other structures. 
     If desired, device  10  may have a hinge or other bendable joint. An illustrative device that bends along a flexible seam is shown in  FIG. 2 . As shown in  FIG. 2 , device  10  may have two or more portions such as portions  12 A and  12 B that rotate with respect to each other in directions  24  about axis  22 . Device  10  may be a laptop computer, a case for a tablet computer, a portable device with a flexible display, or other flexible device. There is a single bend axis in the example of  FIG. 2  that allows device  10  to bend along a single flexible joint. Configurations for device  10  with multiple flexible regions may also be used. 
     Device  10  may contain components  20 A and  20 B in portions  12 A and  12 B, respectively. Portions  12 A and  12 B may be housing portions, may be portions of a case (e.g., a plastic cover for a device that is separate from the case), or may be other suitable structures. Components  20 A and  20 B may be respective halves of a display that flexes along the bendable joint that is aligned with axis  22 , may be a keyboard and display, respectively, may be a keyboard or other component in a case and a table computer or other component mounted in the case, or may be other components in device  10 . 
     Devices such as device  10  of  FIGS. 1 and 2  may use carbon nanotube structures to form signal paths. The signal paths may be formed within a printed circuit or other structure. For example, carbon nanotube traces may be formed within a flexible substrate such as a flexible printed circuit, a flexible display, or a flexible touch sensor layer. Due to the strength and flexibility of carbon nanotubes, a carbon nanotube flexible substrate may be bent abruptly to form a thin device (see, e.g., device  10  of  FIG. 1 ) and may be bent repeatedly to accommodate repeated bending of device  10  (e.g., when the carbon nanotube flexible substrate traverses a flexible joint such as the flexible portion of device  10  along bend axis  22  of  FIG. 2  or otherwise bridges device portions that bend with respect to each other). Carbon nanotube signal paths may be less prone to cracking than metal traces in flexible printed circuits and other flexible substrates and may therefore be used to help enhance reliability in devices with bent flexible substrates. 
     A cross-sectional side view of an illustrative electronic device of the type that may include carbon nanotube structures is shown in  FIG. 3 . As shown in  FIG. 3 , display  14  of device  10  may be formed from a display module such as display module  42  mounted under a cover layer such as display cover layer  40  (as an example). Display  14  (display module  42 ) may be a liquid crystal display, an organic light-emitting diode display, a plasma display, an electrophoretic display, a display that is insensitive to touch, a touch sensitive display that incorporates and array of capacitive touch sensor electrodes or other touch sensor structures, or may be any other type of suitable display. Display cover layer  40  may be layer of clear glass, a transparent plastic member, a transparent crystalline member such as a sapphire layer, or other clear structure. Display layers such as the layers of display module  42  may be rigid and/or may be flexible (e.g., display  14  may be flexible). 
     Display  14  may be mounted to housing  12 . Device  10  may have inner housing structures that provide additional structural support to device  10  and/or that serve as mounting platforms for printed circuits and other structures. Structural internal housing members may sometimes be referred to as housing structures and may be considered to form part of housing  12 . 
     Electrical components  48  may be mounted within the interior of housing  12 . Components  48  may be mounted to printed circuits such as printed circuit  46 . Printed circuit  46  may be a rigid printed circuit board (e.g., a printed circuit board formed from fiberglass-filled epoxy or other rigid printed circuit board material) or may be a flexible printed circuit (e.g., printed circuit formed from a sheet of polyimide or other flexible polymer layer). Patterned conductive traces within printed circuit board  46  may be used to form signal paths between components  48 . The conductive traces may be formed from conductive materials such as metal and/or carbon nanotubes. 
     If desired, components such as connectors may be mounted to printed circuit  46 . As shown in  FIG. 3 , for example, a cable such as flexible printed circuit cable  54  may couple display module  42  to connector  52 . Flexible printed circuit cable  54  (and other flexible substrates in device  10 ) may be formed from flexible polymer substrates such as polyimide layers and may have conductive traces formed from conductive material such as metal and/or carbon nanotubes. Connector  52  may mate with corresponding connector  50 . Connectors  52  and  50  may be board-to-board connectors. Connector  52  may be soldered to flexible printed circuit  54  or may be attached to flexible printed circuit  54  using other techniques. Connector  50  may be soldered to printed circuit  46  or may be otherwise connected to printed circuit  46 . When coupled as shown in  FIG. 3 , signals may pass from signal lines in flexible printed circuit  54  (e.g., display signals associated with operation of display  42 ) and signal lines in printed circuit  46 . 
     To form a connection such as the signal path connection provided by flexible printed circuit  54 , it may be desirable to bend flexible printed circuit  54  at one or more locations along the length of flexible printed circuit  54 . In the example of  FIG. 3 , flexible printed circuit  54  has been bent once to form bend  56 . Configurations in which flexible structures such as flexible printed circuit  54  are bent multiple times and/or in which a flexible substrate such as flexible printed circuit, flexible display, or flexible touch sensor are bent back and forth repeatedly during operation of a device with a hinge may also be used. 
       FIG. 4  is a cross-sectional side view of device  10  in an illustrative configuration in which display module  42  is formed from one or more flexible display layers having bent edge portions  42 E. Display module  42  may be, for example, a flexible organic light-emitting diode display formed from flexible polymer substrate layers such as one or more layers of polyimide or other flexible substrate materials. A flexible touch sensor may be incorporated into display  42 , if desired. 
     Bent edge portions  42 E may be located along the right and/or left sides of device  10  or elsewhere in device  10 . In the example of  FIG. 4 , bent edge portions  42 E have been formed by bending display module (display layer)  42  at right angles, so that both the left edge and the right edge form a right-angle bend with respect to the main active area of display module  42  under display cover layer  40 . Displays with 180° bends and bends of other shapes may also be used. Display module  42  may be attached to the inner surfaces of device  10  such as display cover layer  40  and/or may be supported using structures such as structures  58 . Structure  58  may be a support structure, internal device component(s) such as a battery or other circuitry, an internal housing structure, or other portions of device  10 . 
     If desired, display modules such as illustrative display module  42  may include a touch sensor such as capacitive touch sensor or a touch sensor formed using other touch technologies. A capacitive touch sensor may have an array of capacitive touch sensor electrodes. When combined with a display, the capacitive touch sensor electrodes may be formed from transparent conductive material. For example, a touch sensor may be formed from an array of transparent indium tin oxide electrodes. Touch sensors such as these may be implemented using touch sensor substrates such as flexible polymer layers. The flexible touch substrate layers may be integrated into display module  42  or may be separate from display module  42  and may bend along edges such as edges  42 E. 
     Structures in device  10  such as printed circuits (e.g., flexible printed circuit  54  of  FIG. 3  and/or printed circuit  46  of  FIG. 3 ), displays (e.g., flexible display layer(s)  42  of  FIG. 4 ), touch sensors (e.g., a flexible touch sensor array in display layers  42  of  FIG. 4  having active and/or inactive portions bent along edges  42 E), and other structures in device  10  may be provided with carbon nanotubes. The carbon nanotubes may be patterned to form conductive signal paths that are resistant to damage when flexed. 
     An illustrative carbon nanotube structure is shown in  FIG. 5 . In the example of  FIG. 5 , carbon nanotubes  62  have been provided in a layer on top of substrate  64  to form carbon nanotube layer (sheet)  60 . Carbon nanotubes  62  may be single wall nanotubes and/or multiple-wall nanotubes. Nanotubes  62  may be grown in a furnace using chemical vapor deposition techniques or may be grown using other suitable techniques. Nanotubes  62  may be grown directly on substrate  64  or may be grown on a separate substrate before being transferred to substrate  64  (e.g., in a liquid, in a powder, etc.). Substrate  64  may be a layer of metal foil, a polymer layer (e.g., a sheet of polyimide or other flexible polymer, a rigid polymer layer, etc.), a ceramic layer, a glass layer, a layer of polymer or other material to which carbon-fibers, glass fibers, or other fibers have been added, a rigid printed circuit board layer (e.g., a layer of fiberglass-filled epoxy), a layer of other materials, or a combination of two or more of these layers. Substrate  64  may have flexible portions and/or may have rigid portions. 
     As shown in  FIG. 6 , carbon nanotube layer  60  may have a layer of carbon nanotubes  62  formed on a substrate such as substrate  64  that has a coating layer such as coating  66 . Substrate  62  may be a metal layer, a rigid or flexible polymer layer, a ceramic layer, a glass layer, a fiber-based composite layer, a layer of rigid printed circuit board material, other layers, or combinations of these layers. Layer  66  may be interposed between layer  64  and layer  62 . Layer  66  may be a metal layer, a polymer layer, a ceramic layer, a glass layer, a fiber-based composite layer, a layer of rigid printed circuit board material, other layers, or combinations of these layers. As an example, layer  64  may be a flexible polymer substrate layer and layer  66  may be a metal layer (e.g., a metal coating) formed on the surface of polymer layer  64 . Carbon nanotube layer  62  may be grown on the surface of coating layer  66  or carbon nanotubes for layer  62  may be grown elsewhere and transferred to layer  66 . 
     If desired, adhesive (e.g., polymer) may be used in attaching carbon nanotubes  62  to substrate  64 . As shown in  FIG. 7 , for example, substrate  64  may be coated with a layer of adhesive such as polymer adhesive layer  68 . Carbon nanotubes  62  (e.g., carbon nanotube powder) may be deposited on the surface of substrate  64  while adhesive  68  is in a tacky state (e.g., uncured liquid adhesive, tacky pressure sensitive adhesive, etc.). If desired, adhesive  68  may then be cured by application of ultraviolet light, by application of heat, by application of catalyst, etc. When deposited in this way, lower portion  62 ′ of carbon nanotube layer  62  will become embedded within adhesive layer  68 , thereby attaching carbon nanotube layer  62  to the surface of substrate  64 . If desired, a layer of material may be interposed between adhesive layer  68  and substrate  64 . The interposed layer may be a layer of metal foil, a polymer layer (e.g., a sheet of polyimide or other flexible polymer, a rigid polymer layer, etc.), a ceramic layer, a glass layer, a layer of polymer or other material to which carbon-fibers, glass fibers, or other fibers have been added, a rigid printed circuit board layer (e.g., a layer of fiberglass-filled epoxy), a layer of other materials, or a combination of two or more of these layers. 
     As shown in  FIG. 8 , carbon nanotube layer  60  may be formed by embedding carbon nanotubes  62  within polymer matrix  70 . Some of nanotubes  62  may protrude from one or more of the surfaces of layer  60  or nanotubes  62  may be contained within polymer matrix  70 . Polymer matrix  70  may be formed from a polymer that is initially liquid. While in a liquid state, carbon nanotubes  60  may be added to the liquid polymer. Solvent may then be evaporated from the liquid polymer or the liquid polymer may be cured (e.g., by application of ultraviolet light, heat, catalyst, etc.) to form a solid polymer matrix with embedded carbon nanotubes. Carbon nanotubes  62  may be sufficiently dense to form conductive paths within matrix  70  (i.e., carbon nanotube layer  60  may be conductive). 
     Carbon nanotubes  62  in  FIGS. 5, 6, and 7  may be sufficiently dense to form conductive signal paths. If desired, other structures may be used to form carbon nanotube layer  60 . The configurations of  FIGS. 5, 6, 7, 8  are merely illustrative. 
     Illustrative equipment for forming electronic device structures such as structures with carbon nanotubes is shown in  FIG. 9 . As shown in  FIG. 9 , equipment  70  may be used in forming structures with carbon nanotube paths such as structures  84 . The carbon nanotube paths may be used as signal lines in displays, touch sensors, flexible printed circuit cables, and other electronic device structures. 
     Molding tool  72  may be used to apply heat and pressure to plastic parts. The plastic parts may include polymer substrate layers, plastic carrier structures, injection-molded structures, and other molded polymer structures. Carbon nanotube paths may be incorporated into the molded polymer structures before molding, after molding, or both before and after molding operations. 
     Deposition equipment  74  may be used in depositing carbon nanotubes for forming carbon nanotube paths, metal layers for patterned metal traces that are separate from or combined with the carbon nanotube paths, layers of dielectric for isolating signal paths and other conductive structures, and other materials. Deposition equipment  74  may include physical vapor deposition equipment, chemical vapor deposition equipment, ink-jet printing tools, screen printing equipment, tools for pad printing, nozzles for spraying or dripping material, electrochemical deposition equipment (e.g., equipment for electroplating metals onto carbon nanotubes or other materials), and other equipment for depositing materials. 
     Patterning equipment  76  may include photolithographic tools for patterning blanket films (e.g., equipment that uses masks, etching, etc. to pattern blanket films such as films with carbon nanotubes, metal layers, dielectric layers, etc.). 
     Lamination tool  78  may be used to attach layers of material to each other (e.g., metal films, polymer layers, layers of adhesive, carbon nanotube layers, etc.). Lamination tool  78  may include presses or other equipment that press layers together (e.g., so that adhesive layers or other layers are bonded together). 
     Cutting tools  80  may include laser cutting equipment, knife blades (e.g., a blade that is controlled by a computer-controlled positioner), laser patterning equipment, die stamping tools (e.g., die stamping structures mounted on a press, a stamping die mounted on a rotating drum or other roller-based stamping and/or embossing equipment, etc.). 
     Soldering tools and other equipment  82  may be used in forming electrical connections. Equipment  82  may include equipment for activating conductive bonds formed from anisotropic conductive adhesive and other conductive adhesive, equipment for reflowing solder such as an oven, hot bar, or lamp, equipment for forming connections from metallic paint, conductive adhesive, or other conductive materials, or other electrical connection formation equipment. 
       FIG. 10  is a diagram showing how carbon nanotubes may be used in forming signal paths on a substrate. In the example of  FIG. 10 , carbon nanotube layer  60  includes a layer of carbon nanotubes  62  on substrate layer  64  (e.g., a flexible printed circuit substrate layer such as a layer of flexible polyimide or a sheet of other flexible polymer). Patterning tool  76  may be used to pattern nanotubes  62  to form one or more carbon nanotube signal paths (paths  62 ′). Patterning tool  76  may, for example, include photolithography equipment and equipment for removing undesired portions of nanotubes  62  (e.g., etching equipment). 
     After patterning nanotube layer  60  to form individual carbon nanotube signal paths  62 ′ on the upper surface of substrate  64 , a dielectric cover layer (coverlay) such a layer  86  may be formed on top of carbon nanotube signal paths  62 ′. With one suitable arrangement, layer  86  is formed from a liquid polymer that is deposited using screen printing tool  74  or other suitable deposition tool. Using tool  74 , layer  86  may be deposited in a pattern that forms one or more openings  88 . Openings  88  may be aligned with signal paths  62 ′ (e.g., openings  88  may expose regions for solder pads or other contacts formed from underlying portions of paths  62 ′). With another suitable arrangement, lamination tool  78  or equipment for depositing a blanket layer of dielectric may be used to form dielectric layer  86  on the upper surface of substrate  64  over carbon nanotube signal lines  62 ′. Laser  80  or other equipment may then be used to form openings  88 . If desired, metal may be deposited in openings  88  before or after forming layer  86  (e.g., to help form contacts suitable for receiving solder joints). Substrate  64 , carbon nanotube signal paths  62 ′, and other layers such as dielectric cover layer  86  may form a flexible printed circuit, a rigid printed circuit, or other suitable structure. 
       FIGS. 11A, 11B, 11C, 11D, and 11E  show another illustrative technique for forming carbon nanotube signal paths (e.g., signal paths on a printed circuit). 
       FIG. 11A  shows how substrate  64  may initially be devoid of carbon nanotube structures. Substrate  64  may be a layer of dielectric such as a sheet of flexible or rigid polymer. 
     To form carbon nanotube paths, a blanket layer of carbon nanotubes (layer  62 ) is deposited on substrate  64  and openings  90  are formed (e.g., using cutting tools  80  such a cutting die), as shown in  FIG. 11B . The portions of carbon nanotube layer  62  that are not removed when forming openings  90  are used to form signal path portions  62 ′. If desired, carbon nanotube layer  60  may be formed using other arrangements as described in connection with  FIGS. 5, 6, 7 , and  8 . 
       FIG. 11C  shows how conductive regions such as metal pads  92  may be formed on selected portions of signal paths  62 ′ such as the opposing ends of each path  62 ′. Metal pads  92  may be formed by evaporating metal through a shadow mask, by printing metallic paint onto portions of paths  62 ′, by electroplating copper and gold layers or other metal layers onto portions of path  62 ′, by etching or otherwise patterning blanket metal films, etc. 
     As shown in  FIG. 11D , after metal pads  92  have been formed on paths  62 ′, paths  62 ′ may be sandwiched between upper and lower polymer layers or other dielectric layers (e.g., flexible polyimide sheets or other flexible substrate material, etc.) such as upper dielectric cover layer  98  and lower dielectric layer  108 . Dielectric cover layer  98  may be formed on the upper surface of substrate  64  covering paths  62 ′. Layer  98  may include openings  100  that are aligned with respective pads  92 , so that pads  92  are exposed through openings  100 . Layer  98  may be formed from screen printed polymer, a photoimageable polymer that is patterned using photolithography, a laminated polymer sheet (e.g., a sheet of polymer attached to carbon nanotube layer  60  using adhesive), or other dielectric layer that has openings  100  over pads  92 . Layer  108  may be a flexible polymer layer such as a flexible polyimide layer or other polymer (as an example). Layer  108  may be attached to carbon nanotube layer  60  (i.e., paths  62 ′) using adhesive or other suitable bonding techniques. 
     As shown in  FIG. 11B , openings  90  to not extend across the entire width of layer  64  to ensure that paths  62 ′ are held together for subsequent processing steps. If each opening  90  extended across all of layer  64 , layer  64  (and layer  62  on layer  64 ) would be divided into a number of individual small pieces, which would make handling difficult or impossible. The presence of the uncut portions of layers  64  and  62  (layer  60 ) at opposing ends of paths  62 ′ allows these portions to serve as a temporary support structure that secures paths  62 ′ with respect to each other. 
     After the pad formation process of  FIG. 11C  and polymer layer attachment and patterning process of  FIG. 11D , the uncut edge portions of layer  60  may be removed. For example, a cutting die, knife, laser cutter, or other equipment may be used to cut away edge portions  102  of the structures of  FIG. 11D  by forming cuts along cut line  94  and along cut line  96 . 
     Flexible printed circuit  104  of  FIG. 11E  is formed by removing edge portions  102  of  FIG. 11D . After edge portions  102  have been removed, pads  92  will be exposed along the edges of flexible printed circuit  104 , leaving individual solder pads (contacts)  92  exposed. Each pair of pads (in the example of  FIG. 11E ) is coupled by a respective carbon nanotube signal path  62 ′ embedded within the layers of flexible printed circuit  104 . Because the edge portions have been removed, each signal path  62 ′ in the flexible printed circuit may be isolated from the others. Pads  92  may be located at opposing ends of each signal path  62 ′ and are available for bonding (e.g., soldering) to wires or other conductive paths in device  10 . 
       FIG. 12  is a cross-sectional side view of an illustrative printed circuit with carbon nanotube paths formed from carbon nanotube layer  60 . Printed circuit  104  may be flexible printed circuit, a rigid printed circuit, or a printed circuit with both rigid and flexible portions. In the example of  FIG. 12 , printed circuit  104  is flexible and has a stiffener such as stiffener  110  that locally stiffens flexible printed circuit  104 . The region in which stiffener  110  is located may be, for example, a region that overlaps contacts (solder pads) such as solder pad  92 . The presence of stiffener  110  under pads such as pad  92  may help prevent damage to solder joints formed on these pads that might otherwise arise from the flexing of flexible printed circuit  104 . Stiffener  110  may be created from a metal sheet (e.g., a thin stainless steel layer), a plastic layer, or other rigid layers of plastic, metal, etc. Stiffener  110  may be attached to flexible printed circuit  104  using a layer of adhesive  106 . 
     Layers of adhesive  106  may also be used in attaching together layers of material in printed circuit  104  such as dielectric layer  108 , carbon nanotube layer  60 , and dielectric layer  98 , as shown in  FIG. 12 . Dielectric layers  108  and  98  may be formed from polyimide or other polymer layers. Openings may be formed in polymer layer  98  such as opening  100 . Opening  100  may be aligned with metal solder pad  92  on carbon nanotube layer  60 . Carbon nanotube layer  60  may be patterned to form individual signal paths  62 ′ using an arrangement of the type shown in  FIGS. 11A, 11B, 11C, 11D, and 11E  or using other patterning techniques. 
     Illustrative steps involved in forming a flexible printed circuit of the type shown in  FIG. 12  are shown in  FIG. 13 . 
     At step  112 , carbon nanotube layer  60  may be fabricated. Carbon nanotube layer  60  may include carbon nanotubes and one or more supporting layers, as described in connection with  FIGS. 5, 6, 7, and 8 . 
     At step  114 , carbon nanotube layer  60  may be patterned to form carbon nanotube signal paths using cutting techniques, photolithography, etc. Electroplating or other metal deposition techniques may be used to selectively coat portions of the carbon nanotube signal paths with metal (e.g., opposing end portions may be plated with copper and gold, etc.). 
     At step  116 , dielectric layers (e.g., polyimide substrate layers or other flexible polymer sheets) may be attached to the upper and lower surfaces of the carbon nanotube layer. Adhesive layers such as adhesive layers  106  may be used, for example, to attach polymer layers  108  and  98  to the lower and upper surfaces of carbon nanotube layer  60 . Layer  98  may be provided with openings  100  that overlap respective contacts (solder pads)  92 , as shown in  FIG. 12 . 
     Following attachment of polymer layers  108  and  98 , stiffener  110  may be attached to flexible printed circuit  104  using adhesive  106  in a portion of flexible printed circuit  104  that overlaps pads  92  or other suitable portion of flexible printed circuit  104  (step  118 ). 
       FIG. 14  is a diagram of illustrative roller-based equipment that may be used in forming flexible printed circuit material with carbon nanotubes. As shown in  FIG. 14 , carbon nanotube layer  60  may be dispensed from roller  128 . Upper roller  120  may dispense upper flexible polymer layer  124  and lower roller  122  may dispense lower flexible polymer layer  126 . Rollers  130  may compress carbon nanotube layer  60  between layers  124  and  126  to form laminated layers  132 . Heat may be applied during lamination. In laminated layers  132  (e.g., flexible printed circuit material), carbon nanotube layer  60  may be sandwiched between respective polymer layers. 
     If desired, the polymer layers may be coated with adhesive to attach the polymer layers to the carbon nanotube layer. With one suitable arrangement, layers  124  and  126  may be layer such as layers  98  and  108  of  FIG. 12  and may be attached to carbon nanotube layer  60  using adhesive  106 . Carbon nanotube layer  60  may be patterned before lamination between layers  124  and  126  and/or after lamination between layers  124  and  126  (e.g., by die cutting, laser cutting, photolithography to pattern carbon nanotubes on a substrate layer, etc.). Carbon nanotube layer  60  may also be sandwiched between polymer layers for a flexible printed circuit using planar press structures (e.g., a heated metal press) in addition to or instead of using roller-based lamination systems. Dielectric coatings may also be formed by spraying, dipping, etc. The example of  FIG. 14  is merely illustrative. 
     As shown in  FIG. 15 , roller-based stamping equipment may be used to form carbon nanotube printed circuit structures. Roller  134  may dispense layer  132 . Layer  132  may be a layer of flexible substrate material (e.g., flexible printed circuit material) that includes a carbon nanotube layer such as layer  60  that has been laminated between respective polymer layers such as layers  124  and  126  ( FIG. 14 ) or may contain only layer  60  (as examples). Rollers  136  and  138  may have stamping features  139  that cut openings in layer  132 . Embossing rollers  140  may have protrusions such as protrusions  142 , mating recesses such as recesses  144 , or other embossing features. As layer  132  passes through rollers  140 , the features on rollers  140  create bends such as bends  146  and other features in layer  132 . Heat may be applied using rollers or other sources during embossing. The heat may help mold or otherwise shape the polymer of layer  132 . 
     Embossed layer  132  may be cut into individual sections using a cutter. For example, computer-controlled positioner  154  may press cutting head  148  against surface  150  of cutting block  152  repeatedly to cut layer  132  into respective embossed flexible printed circuit portions  156 . Portions  156  may contain one or more bends or other features. Flexible printed circuits  156  may then be installed within device  10 . If desired, layer  132  may include semi-rigid layers and the rollers or other equipment of system  15  may be heated to cure the semi-rigid layers following embossing. Printed circuits  156  may therefore be rigid printed circuits with carbon nanotube signal paths, if desired. 
     To ensure that a carbon nanotube flexible printed circuit can exhibit a tight bend radius, it may be desirable to mold carbon nanotube signal paths such as paths formed from carbon nanotube layer  60  within plastic. Roller-based equipment of the type shown in  FIG. 15  may be used. Alternatively, heated mold die may be used. This type of arrangement is shown in  FIG. 16 . As shown in  FIG. 16 , mold structures such as mold structure  158  and mold structure  160  may be pushed in directions  162  and  164 , respectively. This compresses flexible printed circuit  132  between the opposing inner surfaces of mold structures  158  and  160 . Polymer layers  124  and  126  may be formed from polymer material that is set into a desired shape under application of heat and pressure from mold structures  158  and  160 . When mold structures  158  and  160  are removed, the molded polymer portions will maintain their bent shape and will maintain the bent carbon nanotube signal paths in their bent shape. Flexible printed circuit  132  will therefore retain a desired shape (e.g. a semicircular bend shape in the example of  FIG. 16 ). The shape into which carbon nanotube flexible printed circuit material  132  is molded may have one bend, two bends, or more than two bends. The bends may be right angle bends such as the right-angle edge bends of portions  42 E in  FIG. 4 , may be 180° bends (as shown in  FIG. 16 ), or may have other suitable shapes. 
     To help prevent cracks in the signal lines traversing bent portions of a flexible substrate from disrupting signal flow, some or all of these signal lines may include carbon nanotubes. The carbon nanotubes may be patterned to form carbon nanotube traces  62 ′ as described in connection with  FIGS. 11 and 12 . Carbon nanotubes may also be combined with metal lines. Consider, as an example, the configuration of  FIG. 17 . As shown in  FIG. 17 , flexible substrate  182  may have a bend where flexible substrate  182  traverses angled edge  174  of support structure  180  between planar upper surface  176  of support structure  180  and planar side surface  178  of support structure  180 . Flexible substrate  182  may be a carbon nanotube flexible printed circuit, a flexible substrate in a display, a flexible touch sensor substrate, or other suitable flexible structure. Flexible substrate  182  may have signal paths formed on a flexible polymer layer such as polymer layer  186  (e.g., a polyimide layer, etc.). A dielectric cover layer may cover the surface of substrate  182 . 
     The signal paths on substrate  182  may be formed from metal and carbon nanotubes. In some situations, the signals paths on polymer layer  186  may be formed entirely from carbon nanotubes. In other situations, at least some of the signal paths may include metal. For example, a signal path may have metal portions  166  and carbon nanotube segment  168 . Metal signal lines  166  may have a gap in the portion of layer  186  that traverses the bend at edge  174 . This avoids metal signal line cracking To electrically connect metal signal lines  166  on either side of the bend with each other, carbon nanotube segment  168  may bridge the gap in metal signal lines  166 . With another suitable arrangement, a metal signal trace may be provided with a carbon nanotube coating and no metal signal trace gaps. For example, metal line  170  may have a carbon nanotube trace such as trace  172 . Carbon nanotube trace  172  may be formed from a carbon nanotube layer that has a linewidth comparable to the linewidth of metal line  170  and that covers some or all of line  170 . In the example of  FIG. 17 , carbon nanotubes  172  form a line segment that covers metal signal line  170  in a portion of line  170  that crosses over bent edge  174  of support structure  180  and the corresponding bend in flexible polymer layer  186 . Configurations of the type shown in  FIG. 17  may be used to allow signal lines to traverse a hinge or other flexible joint in device  12  (see, e.g., hinge axis  22  of  FIG. 2 ). 
     Carbon nanotubes are flexible and are therefore resistant to cracking and undesired open circuit conditions due to bends. By providing flexible substrate  182  with carbon nanotube paths that cover metal paths in at least the portion of the metal paths that bend, the likelihood of undesired open circuit conditions in the signal paths is reduced. 
       FIG. 18  shows how a flexible printed circuit or other flexible substrate may have carbon nanotubes that are coupled to a metal signal trace or other signal path on another substrate. As shown in  FIG. 18 , signal trace  188  may be formed on substrate  186 . Signal trace  188  may be formed from metal, carbon nanotubes, or both metal and carbon nanotubes. Substrate  186  may be a dielectric such as a polymer (e.g., a flexible printed circuit substrate material). Flexible printed circuit  190  may contain signal paths such as signal path  194 . Signal path  194  may be formed from carbon nanotubes and my, if desired, include metal (e.g., a plated metal solder pad). A dielectric cover layer may cover traces such as path  194 . At connection  198 , conductive material  196  may be used to couple signal path  194  to signal path  188 . Conductive material  196  may be solder, conductive adhesive, or other conductive material. 
       FIG. 19  is a cross-sectional side view of an illustrative electronic device showing how carbon nanotube material may be used in forming a structural component in device  10  such as an internal housing member. In the example of  FIG. 19 , device  10  has a display such as display  14  that is mounted in housing  12 . Display  14  includes display cover layer  40  and display module  42 . Electrical components  48  may be mounted on printed circuit  46  within housing  12 . Housing  12  may have rear housing wall  12 R and sidewalls  12 W. Sidewalls  12 W may be vertical sidewalls and/or may be curved sidewalls. Carbon nanotube structure  200  (e.g., a layer of carbon nanotubes such as carbon nanotube layer  60 , etc.) may extend between respective sidewalls  12 W and may span the interior of housing  12 . 
     Carbon nanotube structures  200  may, for example, form a carbon nanotube housing midplate. The carbon nanotube midplate may be formed from carbon nanotubes, a substrate (e.g., metal, plastic, etc.), metal layer(s), polymer layer(s), or other suitable materials (see, e.g.,  FIGS. 5, 6, 7, and 8 ). With one suitable arrangement, carbon nanotube structures  200  may form a planar sheet that is connected to housing sidewalls  12 W with connections  202 . Connections  202  may include mounting brackets, fasteners such as screws, welds, solder, adhesive, or other attachment mechanisms. The presence of carbon nanotube midplate in housing  12  may help provide housing  12  and device  10  with structural rigidity (e.g., torsional rigidity. Components may be packed into the interior spaces of device  10  above and below the carbon nanotube midplate and may help further enhance rigidity. 
     Carbon nanotubes can be strong and light, so the use of a carbon nanotube midplate may allow the size of device  10  to be minimized. If desired, carbon nanotubes may be provided in other electronic device structures to provide enhanced strength. Carbon nanotube layers may be patterned to form sheets and other thin layers, structures with curves (e.g., brackets), traces on dielectric support structures, and portions of other structural members in device  10 . The use of a carbon nanotube layer (e.g., layer  60 ) to form a structural midplate member in the housing of device  10  (e.g., a portable device such as a cellular telephone, etc.) is merely illustrative. 
     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: 20140828
Publication Date: 20161101
Grant Date: 20161101
Priority Date: 20140828
Inventors: KAMEI IBUKI
RASMUSSEN TIMOTHY J.
DO TRENT K.
Assignee: APPLE INC
CPC Classifications: [{"code": "H05K3/4007", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K1/111", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K1/118", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K1/0393", "inventive": true, "first": true, "tree": "[]"}, {"code": "H05K1/097", "inventive": true, "first": true, "tree": "[]"}, {"code": "H05K3/28", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K3/041", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K3/041", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K3/361", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2201/026", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K1/118", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K1/028", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2201/026", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K1/0393", "inventive": true, "first": true, "tree": "[]"}, {"code": "H05K1/028", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K1/111", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K2201/05", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2203/0759", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K3/28", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K3/361", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K3/4007", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K2201/05", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2203/0759", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K1/097", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 55404254