PATENT DOCUMENT

Publication Number: US-8804363-B2
Application Number: US-201213683997-A
Country: US
Kind Code: B2

Title: Printed circuit boards with embedded components

Abstract:
Printed circuit boards are provided with embedded components. The embedded components may be mounted within recesses in the surface of a printed circuit board substrate. The printed circuit board substrate may have grooves and buried channels in which wires may be mounted. Recesses may be provided with solder pads to which the wires may be soldered or attached with conductive adhesive. An integrated switch may be provided in an opening within a printed circuit board substrate. The integrated switch may have a dome switch member that is mounted within the opening. A cover member for the switch may be formed from a flexible layer that covers the dome switch member. Terminals for the integrated switch may be formed from conductive structures in an interior printed circuit board layer. Interconnects may be used to electrically connect embedded components such as switches, integrated circuits, solder pads for wires, and other devices.

Claims:
What is claimed is: 
     
       1. Apparatus, comprising:
 a printed circuit board substrate; 
 a conductive planar contact pad in an opening in the printed circuit board substrate; 
 a wire that is connected to the contact pad; and 
 an embedded switch in the printed circuit board substrate. 
 
     
     
       2. The apparatus defined in  claim 1  further comprising a stiffener connected to the printed circuit board substrate under the embedded switch. 
     
     
       3. The apparatus defined in  claim 1  further comprising a buried channel in the printed circuit board substrate, wherein the wire passes through the buried channel. 
     
     
       4. The apparatus defined in  claim 3  further comprising conductive adhesive with which the wire is connected to the contact pad. 
     
     
       5. The apparatus defined in  claim 1  further comprising a wire opening in the printed circuit board substrate in which the wire is located and further comprising solder that connects the wire to the contact pad. 
     
     
       6. The apparatus defined in  claim 1 , wherein the wire comprises an insulating coating. 
     
     
       7. Apparatus, comprising:
 a printed circuit board substrate; 
 a solder pad recessed in an opening in the printed circuit board substrate; and 
 a wire that is soldered to the solder pad; and 
 an embedded dome switch in the printed circuit board substrate. 
 
     
     
       8. The apparatus defined in  claim 7 , further comprising an integrated circuit embedded in the printed circuit board substrate, wherein the integrated circuit is electrically connected to the solder pad. 
     
     
       9. The apparatus defined in  claim 7 , wherein the opening in the printed circuit board substrate has an open-top well shape. 
     
     
       10. The apparatus defined in  claim 7 , wherein the opening in the printed circuit board substrate has inner surfaces, the apparatus further comprising adhesive over the wire, wherein the adhesive binds to the inner surfaces of the opening. 
     
     
       11. The apparatus defined in  claim 7 , further comprising a via in the printed circuit board substrate, wherein the via is connected to the solder pad. 
     
     
       12. The apparatus defined in  claim 7 , wherein at least a portion of the wire is routed within a groove-shaped opening in the printed circuit board substrate. 
     
     
       13. The apparatus defined in  claim 7 , wherein at least a portion of the wire is routed within a buried channel in the printed circuit board substrate. 
     
     
       14. The apparatus defined in  claim 10 , wherein the opening comprises sidewalls that laterally confine the adhesive and prevent the adhesive from interfering with adjacent structures. 
     
     
       15. The apparatus defined in  claim 12 , further comprising a covering layer of printed circuit material that covers the wire and the groove-shaped opening. 
     
     
       16. The apparatus defined in  claim 13 , further comprising a conductive adhesive and a conductive material that are located within the buried channel, and wherein the conductive material electrically connects the wire to the solder pad via the conductive adhesive. 
     
     
       17. The apparatus defined in  claim 7 , wherein the wire is entirely located within the opening. 
     
     
       18. The apparatus defined in  claim 7 , wherein a portion of the wire protrudes above a top surface of the printed circuit board substrate.

Description:
This application is a division of patent application Ser. No. 12/832,885, filed Jul. 8, 2010, which is hereby incorporated by referenced herein in its entirety. 
    
    
     BACKGROUND 
     This relates to assemblies of electrical and mechanical components for electronic devices, and, more particularly, to ways in which to incorporate components into printed circuit board structures. 
     Electronic devices use integrated circuits and electrical components such as switches. These components are typically mounted to the surface of a printed circuit board using solder. 
     Printed circuit boards may be formed from substrates such as fiberglass-filled epoxy. In complex designs, multiple board layers may be laminated to form a multilayer printed circuit board. 
     In a typical printed circuit board arrangement, parts are attached to the surface of the outermost board layer. Vias may be formed to interconnect board layers. Some boards have included embedded microphones. 
     Switches and other components such as the wires are generally attached only to the surface of printed circuit boards. While this approach is sometimes acceptable, problems can arise when it is desired to form robust and compact structures. Traditional component mounting approaches may result in boards that are not sufficiently strong or that have awkwardly protruding components. Traditional approaches may also raise concerns with environmental sealing, the strength with which structures are attached to a board, and manufacturability. 
     It would therefore be desirable to be able to provide improved printed circuit board structures such as printed circuit board structures with embedded switches and other electrical components and improved methods for manufacturing such boards. 
     SUMMARY 
     Compact and robust electrical device accessories and other equipment may be formed using printed circuit boards with embedded components. Printed circuit board substrates may be formed from one or more layers of dielectric material. In multilayer substrates multiple printed circuit board layers may be laminated together. Conductive layers may be patterned to form interconnects. Interconnects may also be formed by drilling vias. Vias may be drilled mechanically or using laser drilling. 
     Embedded components may be mounted within recesses in the surface of a printed circuit board substrate and other openings. The openings may be well-shaped recesses such as square recesses that penetrate partway into the printed circuit board substrate or may have the shapes of grooves or buried channels. Switches such as tact switches may be mounted within printed circuit board substrate openings. Vias may be used to form connections to the terminals of embedded switches. 
     Grooves and buried channels in a printed circuit board substrate may be used to mount wires. Surface recesses and other openings may be provided with solder pads to which the wires may be soldered or attached with conductive adhesive. Adhesive may be used to seal solder pad structures. 
     An integrated switch may be formed in a recess within a printed circuit board substrate. The integrated switch may have a dome switch member that is mounted within the recess. A cover member for the switch may be formed from a flexible layer that covers the dome switch member. Terminals for the integrated switch may be formed from conductive structures in an interior printed circuit board layer. Interconnects that include patterned printed circuit board conductor layers and vias formed by machining and laser drilling may be used to electrically connect embedded components such as tact switches, integrated domes switches, microphones, integrated circuits, solder pads for wires, and other devices. 
     Further features of the invention, its 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 cross-sectional side view of an illustrative printed circuit board containing an embedded switch in accordance with the embodiment of the present invention. 
         FIG. 2  is a cross-sectional side view of an illustrative printed circuit board showing how the printed circuit board may be provided with vias of different types to interconnect components and printed circuit board layers in accordance with an embodiment of the present invention. 
         FIG. 3  is an exploded perspective view of an illustrative printed circuit board showing how layers of the printed circuit board may be provided with holes, slots, and other openings to accommodate embedded components in accordance with an embodiment of the present invention. 
         FIG. 4  is a cross-sectional side view of an illustrative printed circuit board in which a packaged switch and an integrated circuit have been embedded in accordance with an embodiment of the present invention. 
         FIG. 5  is a cross-sectional side view of a printed circuit board with embedded components such as a top-vented microphone, a switch, and an integrated circuit in accordance with an embodiment of the present invention. 
         FIG. 6  is a cross-sectional side view of a printed circuit board with embedded components such as a bottom-vented microphone, a switch, and an integrated circuit in accordance with an embodiment of the present invention. 
         FIG. 7  is a cross-sectional side view of a printed circuit board showing how wires may be connected to the printed circuit board using different arrangements in accordance with an embodiment of the present invention. 
         FIG. 8  is a cross-sectional side view of an illustrative printed circuit board showing how a wire that runs along the surface of the printed circuit board may be attached to the printed circuit board using a recessed solder pad in accordance with an embodiment of the present invention. 
         FIG. 9  is a cross-sectional side view of an illustrative printed circuit board showing how a wire that is partly recessed in the board using a groove in the upper surface of the board may be attached to the printed circuit board using a recessed solder pad in accordance with an embodiment of the present invention. 
         FIG. 10  is top view of an illustrative printed circuit board showing how a wire that runs along the surface of the printed circuit board or that is partly recessed in a groove in the surface of the printed circuit board may be attached to the printed circuit board using a recessed solder pad in accordance with an embodiment of the present invention. 
         FIG. 11  is a cross-sectional side view of an illustrative printed circuit board showing how a wire that is routed through an interior cavity in the printed circuit board may be attached to the printed circuit board using a recessed solder pad in accordance with an embodiment of the present invention. 
         FIG. 12  is a top view of a printed circuit board that has fully embedded wires of the type shown in  FIG. 11  in accordance with an embodiment of the present invention. 
         FIG. 13  is a cross-sectional side view of an illustrative printed circuit board showing how a wire may be connected to a contact pad located in the interior of the printed circuit board in accordance with an embodiment of the present invention. 
         FIG. 14  is an exploded perspective view showing how a wire may be embedded within a printed circuit board in accordance with an embodiment of the present invention. 
         FIG. 15  is a top view of a printed circuit board showing how a wire channel may be provided with strain relief features in accordance with an embodiment of the present invention. 
         FIG. 16  is a cross-sectional side view of a conventional dome switch without a protective housing. 
         FIG. 17  is a cross-sectional side view of a conventional dome switch encased within a protective housing. 
         FIG. 18  is a cross-sectional side view of an illustrative printed circuit board with an integrated dome switch and embedded integrated circuit in accordance with an embodiment of the present invention. 
         FIG. 19  is a top view of an illustrative electronic device that includes a printed circuit board with embedded components in accordance with an embodiment of the present invention. 
         FIG. 20  is a flow chart of illustrative steps involved in forming printed circuit boards with embedded components in accordance with an embodiment of the present invention. 
         FIG. 21  is a cross-sectional side view of an illustrative printed circuit board with an integrated dome switch and embedded integrated circuit that may include a stiffener in accordance with an embodiment of the present invention. 
         FIGS. 22A and 22B  are perspective views of illustrative stiffeners that may provide mechanical support for a dome switch that is integrated into a printed circuit board of the type shown in  FIG. 21  in accordance with embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     This relates to substrates for mounting components. The substrates may be, for example, printed circuit board substrates. The components that are mounted may include electrical components such as switches and wires and may include mechanical components such as supports or housing structures. Illustrative arrangements in which electrical components are mounted using printed circuit board substrates are sometimes described herein as an example. 
     Components may be embedded in printed circuit board substrates by forming grooves or other recesses in the surface of a board. Components may also be embedded within the interior of a printed circuit board. Combinations of these approaches may be used if desired. 
     Grooves and other openings in a printed circuit board may be formed by milling or machining using drills routers or other mechanical tools or using laser machining equipment. For example, lasers may be used to drill vias in printed circuit boards. 
     The components that are embedded in a printed circuit board may include switches, wires, integrated circuits, connectors, microphones, speakers, light-emitting diodes and other components that can serve as displays and status indicators, or other suitable structures and electrical components. Configurations in which components such as switches, wires, integrated circuits, and microphones are embedded in printed circuit boards are sometimes described herein as an example. This is merely illustrative. Any suitable components may be embedded in a printed circuit board if desired. 
     Printed circuit boards in which components have been embedded may be used in electronic devices such as desktop computers, portable computers, cellular telephones, media players, televisions, displays, headsets, adapters, cables, speakers, radios, and other suitable equipment and accessories. When used in devices of these types, the use of an embedded component arrangement may help save space, may help allow board dimensions to be adjusted to satisfy design constraints (e.g., to increase board thickness without unnecessarily increasing the overall height of a printed circuit board assembly, to decrease board thickness, etc.), may improve environmental sealing, may improve structural strength, etc. Manufacturability may also be enhanced (e.g., by allowing more components to be assembled in an integrated fashion, thereby reducing part counts). 
     A cross-sectional side view of an illustrative printed circuit board with embedded components is shown in  FIG. 1 . In the example of  FIG. 1 , switch  14  and integrated circuit  24  have been embedded within printed circuit board  12 . Printed circuit board  12  may contain one or more layers. Components that are embedded within printed circuit board  12  may be embedded within an interior cavity of board  12  or may be embedded in a board recess (i.e., an opening that penetrates only partway into board  12 ). Integrated circuit  12  represents an example of a component that is embedded within an internal cavity in board  12 . Switch  14  represents an example of a component embedded in a recess in board  12 . 
     As shown in  FIG. 1 , switch  14  may be a packaged dome switch having a housing that encloses dome switch member  22 . This type of packaged dome switch is sometimes referred to as a “tact” (tactile) switch. Other types of switches may be embedded within printed circuit boards if desired. Switch  14  may have a structure such as structure  18  that a user may actuate with the tip of finger  16  or other external object. When finger  16  is pressed downwards in direction  20 , member  18  may move downwards to compress domes switch member  22  and thereby close switch  14 . 
     The recesses in which components such as switch  14  are mounted may have the shapes of circles, squares, elongated groove-like shapes, etc. Interior openings (buried cavities) in board  12  may be cube-shaped or may have other suitable shapes. In some arrangements, more complex openings in printed circuit board  12  may be formed. For example, grooves, via-shaped recesses, interior cavities, and other openings may be combined to help attach and mount more complex structures such as wires or components that require venting (e.g., microphones and speakers). 
     Printed circuit board  12  may include one or more layers of dielectric and one or more layers of conductor. Typical printed circuit boards may have core layers that are formed from dielectrics. Examples of suitable materials that may be used in forming a printed circuit board include dielectrics such as fiberglass-filled epoxy (e.g., in a rigid printed circuit board) and polyimide (e.g., in a flexible printed circuit board of the type sometimes referred to as a flex circuit). For example, printed circuit boards may be formed from FR-2 (phenolic cotton paper), FR-3 (cotton paper and epoxy), FR-4 (woven glass and epoxy), FR-5 (woven glass and epoxy), FR-6 (matte glass and polyester), G-10 (woven glass and epoxy), CEM-1 (cotton paper and epoxy), CEM-2 (cotton paper and epoxy), CEM-3 (woven glass and epoxy), CEM-4 (woven glass and epoxy), CEM-5 (woven glass and polyester), paper impregnated with phonolic resin, polystyrene, polyimide, polytetrafluoroethylene (PTFE), plastic, other polymers, ceramics, or other suitable dielectrics. 
     In multilayer printed circuit boards, core layers may be attached to each other using attachment layers such as layers of prepreg (i.e., pre-impregnated layers of fiber and resin). Layers of copper or other conductive materials may be formed on the surfaces of the printed circuit board core layers and prepreg layers. For example, a core layer may have upper and lower surfaces that are covered with a layer of metal such as copper. 
     A cross-sectional side view of printed circuit board  12  showing how board  12  may be formed from multiple printed circuit board core layers C alternated with interposed layers of prepreg P is shown in  FIG. 2 . The core layers may be attached to the prepreg layer and to each other by curing the prepreg (e.g., by application of heat and pressure while the layers are in proper lateral alignment). 
     As shown in the example of  FIG. 2 , printed circuit board  2  may include multiple printed circuit core layers C each of which includes a printed circuit board core dielectric layer  30  (e.g., FR4) interposed between respective upper and lower metal layers  32  (e.g., layers of copper on the surfaces of core  30 ). Each prepreg layer P may include prepreg dielectric  26 . The exposed upper and lower surfaces of board  12  (i.e., the upper surface of the upper most prepreg layer P and the lower surface of the bottommost prepreg layer P in the orientation of  FIG. 2 ) may be coated with patterned conductor (e.g., patterned metal  28 ). Other layups may be used if desired. The number of layers and the makeup of the layers in printed circuit board  12  of  FIG. 2  is merely illustrative. 
     The metal layers of printed circuit board such as layers  28  and  32  may be patterned using photolithography, laser etching, foil stamping, screen printing, pad printing, shadow masking, or other suitable conductor patterning techniques. In a typical scenario, copper layers  32  may be patterned by screen printing a masking layer onto the surface of each layer, etching to remove unprotected metal, and removing the masking layer. The patterned conductive material of layers  28  and  32  may be used to form signal lines, contact pads, and other conductive structures. These structures, which are sometimes collectively referred to as interconnects, may be formed on the upper surface and lower surface of board  12  and in interior layers of board  12 . 
     Vertical conductive structures called vias may be used to electrically connect layers of interconnects in board  12 . As shown in  FIG. 2 , different types of vias  34  may be formed in board  12 . 
     Vias such as via V 1  that are contained entirely within the interior of board  12  and that do not make direct electrical connection to the outside layers of board  12  are sometimes referred to as buried vias. In the example of  FIG. 2 , buried via V 1  is used to connect the upper and lower copper layers on the lowermost core layer C of board  12 . 
     Vias such as via V 2  that are used to connect conductive structures on an exterior surface of board  12  to an interior conductive layer in board  12  are sometimes referred to as blind vias. In the example of  FIG. 2 , blind via V 2  is used to connect the lowermost surface of board  12  to one of the copper layers on the lowermost core layer in board  12 . Vias such as via V 3  that pass through the entire thickness of board  12  are sometimes referred to as through vias. As shown in  FIG. 2 , via V 3  (and the other vias  34  in board  12 ) may be coated with an interior conductive layer such as plated copper layer  36 . As illustrated by laser beam  38  and laser-drilled via V 4 , vias  34  can be formed by laser drilling. Vias can also be formed using mechanical drilling (i.e., with a drill bit) or other mechanical machining techniques. Via holes may be filled using metal (e.g., copper) plating techniques, by filling a via hole with conductive paste, by filling a via hole with conductive adhesive, or by filling a via hole with other conductive material. 
     To accommodate components of different shapes and sizes, it may be desirable to form a variety of different openings in the materials that make up printed circuit board  12 . These openings may take the form of squares, rectangles, circles, shapes with curved and straight sides, elongated groove-like and slot-like shapes, etc. A perspective view of a printed circuit board showing some of the types of openings that may be formed in the layers of the printed circuit board is shown in  FIG. 3 . As shown in  FIG. 3 , printed circuit board  12  may include multiple layers such as layers  12 A,  12 B, and  12 C. Only three layers are shown in  FIG. 3 , but, in general, board  12  may have any suitable number of layers (e.g., one layer, two layers, three layers, four layers, more than four layers, more than twenty layers, fewer than twenty layers, etc.). Layers  12 A,  12 B, and  12 C may, for example, be alternating layers of prepreg and core material (e.g., FR4) or other suitable dielectric layers and may have associated patterned metal layers for forming interconnects. The metal layers are not shown in  FIG. 3  to avoid over-complicating the drawing. 
     Openings  40  may be formed in layers  12 A,  12 B, and  12 C. Openings  40  may pass completely through the layer in which they are formed (see, for example, square opening  40 D, which passes completely through layer  12 A) or may be provided in the form of recesses that pass only partway through a layer (see, for example, groove  40 C, which passes through the upper half of layer  12 C, but which does not pass through the lower half of layer  12 C). To accommodate components that require openings through more than one layer, openings in respective layers can be aligned and stacked one on top of the next (see, for example, laterally aligned openings  40 A and  40 B, which are formed in adjacent layers  12 A and  12 B). When printed circuit board  12  is formed by laminating layers  12 A,  12 B, and  12 C together, openings  40 A and  40 B will combine to form a larger opening (i.e., an opening with a larger vertical dimension) than would be possible by forming a hole in a single one of these layers. 
     The components that are embedded in printed circuit board  12  may be stand-alone components. For example, components such as packaged integrated circuit die and packaged switches may be embedded in board  12 . The components that are embedded in printed circuit board  12  may also be fabricated using an integrated approach (i.e., by forming parts of the housing for the components from the printed circuit board material itself). 
     An example of an arrangement that involves the mounting of stand-alone components is shown in  FIG. 4 . As shown in  FIG. 4 , tact switch  14  may be embedded in a recess in printed circuit board  12  and integrated circuit  24  may be mounted in an internal cavity in printed circuit board  12 . Tact switch  14  may have conductive terminals (leads)  42 . Vias  34  such as laser-drilled vias or other vias may be used to form electrical connections to terminals  42  and contact pads  44  on integrated circuit  24 . Interconnects such as interconnects  46  may be used to form electrical routing pathways for printed circuit board  12  (e.g., to interconnect metal structures such as contacts  44 , vias  34 , and terminals  42 ). 
     Integrated circuit  24  may be a microprocessor, a microcontroller, an audio chip, an application-specific integrated circuit, or other integrated circuit. If desired, discrete electrical components (e.g., resistors, inductors, capacitors, and transistors) may be mounted in internal cavities in printed circuit board  12  or multiple integrated circuits may be mounted in internal cavities in printed circuit board  12 . Different types of stand-alone components may also be embedded in printed circuit board  12  if desired. The example of  FIG. 4  is merely illustrative. 
     As shown in  FIG. 5 , components such as microphones (e.g., microphone  50 ) may be embedded in printed circuit board  12  with other components such as switch  14  and integrated circuit  24 . Interconnects such as horizontal interconnect structures  46  and vias  34  may be used to interconnect terminals  44  on microphone  50  with terminals  44  on integrated circuit and terminals on switch  14 . Microphone  50  may have an input port such a microphone port  48  that receives sound from the ambient environment. As shown in  FIG. 6 , a channel such as acoustic channel  54  may be formed in printed circuit board  12 . This type of acoustic microphone channel arrangement (which is used in some conventional printed circuit boards to form microphone ports) may be used in board  12  to allow sound to exit from a speaker or other acoustic component or may be used to allow sound to reach a microphone. 
     In the  FIG. 6  example, microphone  50  has been mounted port-side down. If desired, microphone  50  may be mounted port-side up ( FIG. 5 ) or may have other orientations. Speakers (e.g., audio-quality speakers or buzzers or other sound-generating components that are embedded within board  12 ) may be provided with one or more acoustic channels such as channel  54  that couple the input-output port of the speaker or other acoustic component to the exterior surface of printed circuit board  12 . 
     Some types of electrical equipment include wires. Wires may be used, for example, to connect a battery to power terminals or to connect headphone speakers to an integrated circuit. To accommodate designs such as these, printed circuit board  12  may be provided with wire openings that receive wires. A cross-sectional view of an illustrative printed circuit board showing different ways in which wires  52  may be mounted to printed circuit board  12  are shown in  FIG. 7 . 
     Wires  52  may be insulated wires (e.g., wires that are coated with plastic or other insulating material along at least some of their length) or may uncoated (bare) wires. Wires  52  may be formed from solid metal (e.g., solid copper) or may be formed from intertwined filaments of metal (e.g., copper strands). 
     Wires  52  may have ends that are soldered to solder pads formed on the outermost surface of printed circuit board  12  or to solder pads that are formed within openings in printed circuit board  12  (e.g., on the bottom surfaces of recess that penetrate only partway through board  12 ). The solder pads may be planar pads that are formed from square planar conductive contact pad structures or may be formed from contact pad structures of other suitable shapes. 
     Before reaching a solder pad, a wire may run along the surface of printed circuit board  12  (as illustrated by wire  52 C in the  FIG. 7  example), may be routed through an interior opening in board  12  (as with wire  52 D, which is routed through tunnel  40 G), or may be routed within a recess (as with wire  52 A in square-shaped recess  40 E and wire  52 B in rounded recess  40 F). Combinations of these arrangements may also be used. Moreover, recess-shaped openings such as grooves  40 E and  40 F and tunnel-shaped openings such as internal cavity  40 G may run vertically or diagonally as well as horizontally. Adhesive, portions of printed circuit board layers, clamps, solder, welds, fasteners, connectors, and other suitable supporting structures may be used to help hold wires  52  in place on printed circuit board  12 . 
       FIG. 8  is a cross-sectional side view of a printed circuit board showing how a wire that runs along the surface of the printed circuit board may be connected to interconnect structures in the board using a recessed solder pad. As shown in  FIG. 8 , wire  52  may have an insulating coating  64 . End  62  may be uncoated with insulating coating  64 , to facilitate formation of a solder connection with solder pad  56 . Solder pads such as solder pad  56 , which may sometimes be referred to as contacts, contact pads, or interconnect structures, may be formed from patterned conductor layers in printed circuit board  12  (e.g., layers such as layers  32  of  FIG. 2 ) or other suitable conductive structures. Solder pads  56  may, for example, be formed form copper or copper plated with gold or other materials. Solder pads  56  may be electrically connected to the interconnects of printed circuit board  12  (e.g., using vias such as vias  34 , using parts of horizontal interconnects  46 , etc.). 
     During solder attachment, tip  62  of wire  52  may be soldered to solder pad  56  using solder  58 . Adhesive  60  such as ultraviolet (UV) glue (e.g., UV-cured epoxy) may be used to seal solder  58 . In a given printed circuit board  12 , numerous openings  40  may be formed with the open-top well shape of  FIG. 8 , each of which may receive a respective wire  52 . This helps improve isolation between respective solder pads  56  on board  12 . The use of recesses such a recess  40  of  FIG. 8  also allows adhesive  60  to be used to help hold wire  52  in place. As shown in  FIG. 8 , adhesive  60  may bind to the inner surfaces of recess  40  (e.g., the sidewalls of recess  40  in the  FIG. 8  example), which helps attach wire  52  to printed circuit board  12  and relieves stress from solder  58 . The presence of the sidewalls of well  40  laterally confines adhesive  60  and prevents adhesive  60  from interfering with adjacent structures. 
     In the illustrative arrangement of  FIG. 9 , wire  52  has been routed within a groove-shaped opening. Groove shaped opening  40  may, for example, have a profile of the type shown by recess  40 E or recess  40 F of  FIG. 7 . The depth of groove  40  may be relatively deep so that none of wire  52  protrudes above the top surface of printed circuit board  12  (as with wire  52 A in groove  40 E of  FIG. 7 ) or may be relatively shallow so that some of wire  52  protrudes above the top surface of printed circuit board  12  (as with wire  52 B in groove  40 F of  FIG. 7 ). 
     As shown in the top view of printed circuit board  12  of  FIG. 10 , wires  52  may form part of a wire bundle such as wire bundle  64 . Wire bundle  64  may, for example, include twisted wires  52  and, if desired, strengthening fibers and ground shielding housed within a plastic cable jacket. Wires  52  in the example of  FIG. 10  may be routed along the top surface of printed circuit board  12  or may be routed within grooves  40  such as grooves  40 E and  40 F of  FIG. 7 . 
       FIG. 11  is a cross-sectional side view of printed circuit board  12  showing how wire  52  may be routed to recessed solder pad  56  using buried channel  40 G in printed circuit board  12  (i.e., using a tunnel). 
       FIG. 12  is a top view of a printed circuit board structure of the type shown in  FIG. 11 . As shown in  FIG. 12 , wires  52  may be routed through buried channels  40 G and may be attached at their ends to solder pads  56  ( FIG. 11 ) using solder  58  (and adhesive  60 , as shown in  FIG. 11 ). Wires  52  may be placed in channels  40 G after channels  40 G have been formed (e.g., by inserting each wire  52  into channel  40 G through the opening formed where channel  40 G exits the sidewall of printed circuit board  12 ) or may be formed by placing wire  52  into a groove-shaped opening in board  12  and, once wire  52  is in place, covering wire  52  and groove  40 G with a covering layer of printed circuit board material. 
     If desired, conductive adhesive or other conductive materials may be used in forming solder joint  58  (e.g., conductive paste, etc.). 
       FIG. 13  is a side view of an illustrative printed circuit board showing how wire  52  may be connected to contact pad  56  using conductive adhesive  58 . Adhesive  60  (e.g., UV glue) may be used to help secure wire  52  in buried channel  40 G. Solder pad (contact pad)  56  need not be formed at the bottom of an open well structure (as with the example of  FIG. 11 ), but rather may be formed in an interior cavity in board  12 . Wire  52 , conductive material  58  and adhesive  60  may be inserted into channel  40 G before channel  40 G is laminated with covering layers of printed circuit board  12  or may be inserted into channel  40 G after printed circuit board  12  has been formed.  FIG. 14  is a perspective view of wire  52  in a configuration in which buried channel  40 G is formed from a groove-shaped recess in layer  12 B that is enclosed by covering wire  52  and recess  40 G with upper printed circuit board layer  12 A. If desired, channels such as buried channel  40 G may be formed entirely within a single layer of printed circuit board material (e.g., by using horizontal mechanical or laser drilling). 
     Openings  40  such as the openings that are used to receive wire  52  may be provided with bends, as shown by bends  66  in  FIG. 15 . Bends  66  may be provided in buried wire channels such as channel  40 G of  FIG. 7  or recessed grooves such as grooves  40 E and  40 F. Bends  66  may help retain wire  52  within printed circuit board  12  and may therefore serve as a strain relief structure. 
     It may be desirable to integrate the components that are embedded in printed circuit board  12  into printed circuit board  12 . Component integration approaches may be used, for example, to reduce part counts, to minimize size, to improve environmental sealing, etc. With one suitable arrangement, switch structures such as dome switch structures can be integrated into board  12 . 
       FIG. 16  is a cross-sectional side view of a conventional dome switch. Dome switch  80  has a dome member  70 . Dome member  70  is mounted to the surface of circuit board  68 . Central contact  82  forms a first switch terminal for dome switch  80 . Ring-shaped outer contact  72  forms a second switch terminal for dome switch  80 . Interconnects  74  (i.e., traces in board  68 ) are used to connect the switch terminals of dome switch  80  to circuitry that processes switch signals. When a user presses surface  76  of dome  70  in direction  78  with finger  16 , dome  70  collapses. Dome  70  has a conductive inner surface. When dome  70  collapses, the conductive inner surface of dome  70  shorts terminals  72  and  82  together, thereby closing switch  80 . 
     Dome switches such as dome switch  80  of  FIG. 16  are generally not well sealed against environmental intrusions, so dust and moisture can adversely affect switch operation. To provide environmental sealing, dome switches are therefore sometimes enclosed within housings. A conventional dome switch that is packaged within a housing is shown in  FIG. 17 . As shown in  FIG. 17 , packaged dome switch  90  has a housing such as housing  84 . Dome member  70  and contacts  72  and  82  may be housed within housing  84 . Flexible cover  88  may be attached to the top of housing  84  using adhesive  86 . Flexible cover  88  may help seal switch  90 , while still allowing finger  16  to compress dome member  70  to actuate switch  90 . However, the presence of housing walls  84  tends to add undesired bulk and height to dome switch  90 . 
     A printed circuit board with an integrated dome switch is shown in  FIG. 18 . As shown in  FIG. 18 , printed circuit board  12  may be provided with a cavity such as dome switch opening  102  (e.g., a recess that penetrates only partway through board  12  and that has a bottom surface). Dome switch  104  may be integrated with printed circuit board  12  by mounting dome switch components directly within cavity  102  (e.g., without using a separate housing member to enclose these components). 
     Switch  104  may have contacts such as central contact  95  and ring-shaped outer contact  92 . Contacts  95  and  92  may be formed from patterned conductive layers in printed circuit board  12  (e.g., patterned layers of conductor  32 ). Vias  34  (e.g., laser-formed vias) and horizontal interconnect structures  46  may form electrical connections with terminals  95  and  92  and may be used to interconnect terminals  92  and  95  with circuitry within integrated circuit  24  or other suitable circuitry. Dome switch  104  may have a dome member such as dome member  94 . Dome member  94  may be formed from metal or may be formed from other substances (e.g., plastic) that have an inner conductive layer such as an inner layer of metal. Member  96 , which may be formed from plastic, may be interposed between dome member  94  and cover  98 . Cover  98  may be a rectangular or circular flexible sheet formed from plastic, polyimide, polytetrafluoroethylene, or other suitable polymers or flexible materials. Flexible member  98  may be sealed around its periphery to the upper surface of printed circuit board  12  using adhesive  100 . The width W of adhesive  100  about the periphery of flexible layer  98  may be, for example, about 0.5 to 5 mm (as an example). When a user presses downwards on surface  106  of flexible cover  98 , member  96  and dome  94  are pressed downwards in direction  108 . When dome  94  is compressed, its inner conductive surface shorts contacts  95  and  92  together, thereby closing switch  104 . Because of the presence of the peripheral seal around the periphery of flexible member  98 , switch  104  may be well sealed against the environment. Flexible member  98  may therefore help prevent the intrusion of dust and moisture into switch cavity  102  and under dome member  94 . 
     Printed circuit boards  12  may be used in any suitable electronic device such as an electronic accessory (e.g., a headset with speakers and a microphone), a cellular telephone, a tablet computer, a portable computer, a pendant device, a portable music player, a handheld device, a wristwatch device, etc.  FIG. 19  is a top view of an illustrative electronic device that may include a printed circuit board with embedded components. As shown in  FIG. 19 , electronic device  110  may have a housing such as housing  114  that encases printed circuit board  12 . Printed circuit board  12  may include surface mount technology (SMT) components, discrete components such as capacitors, resistors, inductors, and connectors, and may include integrated circuits. Components such as switches, speakers, sensors, light-emitting diodes, microphones, and other devices may be mounted on printed circuit board  12  (e.g., using solder pads, wire bonding, ball-grid array packaging, and other suitable mounting techniques). Preferably, at least some of the devices that are mounted on printed circuit board  12  may be embedded in printed circuit board  12 . In the example of  FIG. 19 , printed circuit board  12  includes an integrated (and embedded) dome switch (switch  104 ), embedded wires  52  with recessed (embedded) solder pads  56  and solder  58 , embedded integrated circuit (circuit  24 ), and additional embedded components  112  (e.g., an embedded microphone with an associated acoustic port opening within board  12 , an embedded speaker, an embedded tact switch, other components, multiple components of these types, etc.). These embedded components may be formed within openings  40  in printed circuit board  12  and may be interconnected using interconnects  46  (e.g., horizontal interconnects and vias). 
     Illustrative steps and equipment involved in forming printed circuit boards with embedded components are shown in  FIG. 20 . As shown in  FIG. 20 , unlaminated (individual) layers  116  of core and prepreg printed circuit board material may be obtained and provided to machining tools  118 . Machining tools  118  may include mechanical tools such as mechanical drilling and milling tools and stamping tools. Machining tools  118  may also include laser drilling tools. Tools  118  may be used to form openings  40  in one or more of printed circuit board layers  116 , producing patterned unlaminated printed circuit board layers  120 . Openings may pass completely though layers  120  or may pass partially through each layer  120 . 
     Layers  120  may be patterned (e.g., the conductive layers on the surfaces of layers  120  may be patterned using screen printing, etching, etc.). Patterned layers  120  may be laminated using laminating tools  124 . During the lamination process, components may be embedded within some of openings  40 . For example, wires  52  may be enclosed within buried channels in printed circuit board  12 , integrated circuit  24  may be encased within an interior cavity  40  in printed circuit board  12 , components may be embedded in recesses that pass partway through board  12 , etc. 
     The lamination process results in a laminated printed circuit board (i.e., a printed circuit board substrate having laminated layers  126 ). Printed circuit board  126  may be processed using post-processing tools  128  (e.g., board  126  may be machined using machining tools such as tool  118  to form openings, solder connections may be formed using soldering tools, processing may be performed using other tools, etc.). Additional components may be incorporated into board  12  (e.g., additional components such as switch components may be added to a well-shaped recess that was machined partway into the laminated layers using tools  128 , etc.). After all desired embedded components have been incorporated into laminated layers  126 , the printed circuit board is complete (i.e., finished printed circuit board  130  has been produced). Assembly tools  132  may be used to attach board  130  to other system components and may be used to mount board  130  into a device housing to produce completed device  134 . 
     Printed circuit board  12  may contain one or more support structures such as structure  140  that provide mechanical support for embedded components such as switch  104 . Structure  140  may help to increase the durability and reliability of printed circuit boards  12  that include embedded components. Structure  140  may be referred to herein as a stiffener or a stiffening component. Structure  140  may be formed from materials such as metal, copper, steel, aluminum, plastics, ceramics, glass, etc. 
     Support structure  140  may include a planar member (e.g., a metal sheet) such as head  142  and an optional shaft  144 . Head  142  of structure  140  may have a relatively large area that spreads force out over printed circuit board  12  so that head  142  of structure  140  is mechanically grounded to printed circuit board  12 . Shaft  144  of structure  140  may mechanically ground embedded components such as switch  104  to head  142  of structure  140  and to printed circuit board  12 . Head  142  and shaft  144  of structure  140  may be mechanically connected to printed circuit board  12  and component  104  with adhesive, welds, fasteners such as screws, clips, and springs, with other attachment mechanisms, or with combinations of these arrangements. If desired, shaft  144  can be omitted. 
     As shown in  FIG. 21 , head  142  of structure  140  may be flush mounted in printed circuit board  12 . If desired head  142  of structure  140  may be embedded in printed circuit board  12  as shown by dotted outline  148 . With another suitable arrangement, head  142  of structure  140  may be mounted to an exterior surface of printed circuit board  12  as shown by dotted outline  146 . 
     Structure  140  may extend over lateral dimensions such as lateral dimension  154  and component  104  may extend over lateral dimensions such as lateral dimension  152 . As examples, lateral dimension  154  may be less than approximately one-half of dimension  152 , less than approximately three-quarters of dimension  152 , less than approximately equal to dimension  152 , less than approximately one and a quarter times dimension  152 , less than approximately one and a half times dimension  152 , less than approximately one and three quarter times dimension  152 , less than approximately two times dimension  152 , less than approximately two and a half times dimension  152 , or less than approximately three times dimension  152 . With these types of arrangements, support structure  140  may provide mechanical support and stiffening of printed circuit board  12  in the vicinity of embedded component  104  without stiffening portions of printed circuit board  12  away from component  104  (e.g., without stiffening portions of board  12  that are not adjacent to component  104 ). 
     If desired, printed circuit board  12  may include an encapsulant such as encapsulant  150  on the perimeter of opening  102 . With this type of arrangement, cover  98  and encapsulant  150  may form a moisture-proof seal (i.e., a moisture-blocking recessed liner) that protects embedded components such as switch  104  from moisture. 
       FIGS. 22A and 22B  illustrate examples of support structure  140 . In the example of  FIG. 22A , head  142  and shaft  144  of support structure are circular. In the example of  FIG. 22B , head  142  and shaft  144  of support structure are rectangular. These are merely examples and, in general, support structure  140  may have other shapes. If desired, shaft  144  may be the same size as or even larger than head  142 . 
     The foregoing is merely illustrative of the principles of this invention and various modifications can be made by those skilled in the art without departing from the scope and spirit of the invention.

Metadata:
Filing Date: 20121121
Publication Date: 20140812
Grant Date: 20140812
Priority Date: 20100708
Inventors: MINOO JAHAN
BIDMEAD ANTHONY P. N.
NIKKHOO MICHAEL
Assignee: APPLE INC
CPC Classifications: [{"code": "H05K1/115", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R1/025", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K1/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K2201/10356", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2201/10356", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K1/183", "inventive": true, "first": true, "tree": "[]"}, {"code": "H05K2201/10053", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2201/0919", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K1/185", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K2201/10446", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K1/185", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K2201/10053", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2201/0919", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R1/04", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K1/181", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K2201/10083", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2201/10083", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K1/183", "inventive": true, "first": true, "tree": "[]"}, {"code": "H05K2201/10446", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 45438422