PATENT DOCUMENT

Publication Number: US-8654537-B2
Application Number: US-95829310-A
Country: US
Kind Code: B2

Title: Printed circuit board with integral radio-frequency shields

Abstract:
Electrical components such as integrated circuits may be mounted on a printed circuit board. To prevent the electrical components from being subjected to electromagnetic interference, radio-frequency shielding structures may be formed over the components. The radio-frequency shielding structures may be formed from a layer of metallic paint. Components may be covered by a layer of dielectric. Channels may be formed in the dielectric between blocks of circuitry. The metallic paint may be used to coat the surfaces of the dielectric and to fill the channels. Openings may be formed in the surface of the metallic paint to separate radio-frequency shields from each other. Conductive traces on the surface of the printed circuit board may be used in connecting the metallic paint layer to internal printed circuit board traces.

Claims:
What is claimed is: 
     
       1. Apparatus, comprising:
 a printed circuit board substrate having a plurality of integrated circuits; 
 a dielectric encapsulant that encapsulates the integrated circuits; 
 at least one channel in the dielectric encapsulant between adjacent integrated circuits; 
 a conductive material that at least partly fills the channel and that coats the dielectric encapsulant to form radio-frequency shields for each of the integrated circuits; and 
 at least one isolating channel that substantially surrounds at least a given one of the radio-frequency shields and that electrically separates the at least given one of the radio-frequency shields from at least another one of the radio-frequency shields, wherein the at least one isolating channel comprises an opening that extends through the layer of conductive material and the dielectric encapsulant. 
 
     
     
       2. The apparatus defined in  claim 1  wherein the printed circuit board comprises traces that interconnect the integrated circuits and wherein at least some of the traces comprise substantially planar regions that extend lower portions of at least one of the radio-frequency shields at least partly underneath at least one of the integrated circuits. 
     
     
       3. The apparatus defined in  claim 1  wherein the integrated circuits include a first integrated circuit and a second integrated circuit, wherein the channel is interposed between the first and second integrated circuits, and wherein the printed circuit board includes interconnect traces that interconnect the first and second integrated circuit and that pass under the channel. 
     
     
       4. The apparatus defined in  claim 3  wherein the printed circuit board has a surface on which the first and second integrated circuits are mounted and at least one trace on the surface that lies under the channel. 
     
     
       5. The apparatus defined in  claim 4  wherein the conductive material in the channel contacts the trace on the surface of the printed circuit board. 
     
     
       6. The apparatus defined in  claim 5  wherein the conductive material comprises silver paint. 
     
     
       7. The apparatus defined in  claim 6  wherein the printed circuit board comprises a sawed edge that is at least partly covered by some of the conductive material. 
     
     
       8. The apparatus defined in  claim 1  wherein the channel comprises a laser-cut channel that surrounds at least one of the integrated circuits. 
     
     
       9. The apparatus defined in  claim 1  wherein the at least one channel comprises at least first and second channels at least partly filled by the conductive material, wherein the printed circuit board substrate lies in a plane, wherein the first and second channels each have a height dimension that is perpendicular to the plane, and wherein the height of the first channel is less than the height of the second channel. 
     
     
       10. The apparatus defined in  claim 1  wherein the at least one channel comprises at least first and second channels at least partly filled by the conductive material, wherein the printed circuit board has a surface on which the integrated circuits are mounted, wherein the first channel extends from above the surface of the printed circuit board to below the surface of the printed circuit board, and wherein the second channel does not extend below the surface of the printed circuit board.

Description:
BACKGROUND 
     This relates to structures for providing electromagnetic shielding for circuits such as radio-frequency circuits. 
     Electronic devices such as computers, cellular telephones, and other devices often contain circuitry that requires electromagnetic shielding. For example, some electronic devices include radio-frequency transceiver circuits. Electronic devices may also include memory and other components that use clocks. If care is not taken, signals from one circuit may interfere with the proper operation of another circuit. For example, a clock signal or a clock signal harmonic that falls within the operating band of a radio-frequency receiver may cause undesirable interference for the receiver. 
     To prevent disruption from electromagnetic interference, circuits such as transceivers may be enclosed within metal radio-frequency (RF) shielding cans. The metal of the shielding cans blocks radio-frequency signals and helps shield the enclosed components from electromagnetic interference (EMI). In a typical configuration, integrated circuits are covered by RF shielding cans after being mounted on a printed circuit board. 
     Conventional arrangements in which RF shielding cans are mounted to a printed circuit board can help to reduce electromagnetic interference, but may be undesirably bulky. This may limit the effectiveness of RF shielding can arrangements in complex board designs in which numerous sections of the board require individual shielding. 
     It would therefore be desirable to provide improved radio-frequency shielding structures. 
     SUMMARY 
     Electrical components such as integrated circuits and associated discrete components may be organized into blocks of circuitry on a printed circuit board. The blocks of circuitry may be encapsulated in a layer of dielectric. Channels may be formed in the dielectric between the blocks of circuitry and surrounding the periphery of each block to be shielded. Each block of circuitry may be provided with an integral radio-frequency shielding structure formed from a conductive coating such as layer of metallic paint. The metallic paint may coat the planar surface of the dielectric layer and may form conductive shielding structure sidewalls by partly or completely filling the channels in the dielectric that surround the blocks. 
     The channels in the dielectric may be formed by applying laser light to the dielectric or by using mechanical removal techniques such as sawing. To facilitate material removal using laser light and to help prevent excess material from being removed, metal traces may be formed on the surface of the printed circuit board under the regions where the channels are to be formed. The laser light tends to reflect from the metal traces, rather than penetrate into the printed circuit board substrate. When complete, the channels can be filled with conductive material that forms conductive sidewall structures for the radio-frequency shields. Individual shielding structures may be formed by cutting openings in the conductive coating layer using a laser or other cutting tool. 
     A spring may be attached to the conductive coating layer. The spring may be used electrically connect the radio-frequency shielding structures to a conductive housings structure such as a conductive housing wall. 
     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 perspective view of an illustrative electronic device in which a printed circuit board and components that are shielded with radio-frequency shielding structures may be mounted in accordance with an embodiment of the present invention. 
         FIG. 2  is a circuit diagram of an electronic device in accordance with an embodiment of the present invention. 
         FIG. 3  is a cross-sectional side view of an illustrative printed circuit board substrate on which components have been mounted and covered with resin. 
         FIG. 4  is a cross-sectional side view of the printed circuit board substrate of  FIG. 3  following sawing to form a groove around and between respective components and following deposition of a metallic paint such as silver paint as a coating on the resin. 
         FIG. 5  is a cross-sectional side view of the printed circuit board substrate of  FIG. 4  following sawing operations to divide the substrate into individual pieces. 
         FIG. 6  is a top view of a printed circuit board substrate with electrically connected or electrically isolated shielding structures for different blocks of circuitry in accordance with an embodiment of the present invention. 
         FIG. 7  is a cross-sectional side view of an illustrative printed circuit board on which components have been mounted using a mounting tool in accordance with an embodiment of the present invention. 
         FIG. 8  is a cross-sectional side view of the printed circuit board of  FIG. 7  following encapsulation of blocks of circuitry within a dielectric encapsulant layer in accordance with an embodiment of the present invention. 
         FIG. 9  is a cross-sectional side view of the substrate of  FIG. 8  following removal of portions of the encapsulant with a dielectric removal tool to form channels in accordance with an embodiment of the present invention. 
         FIG. 10  is a cross-sectional side view of the substrate of  FIG. 9  following deposition of a coating layer to cover the channel sidewalls and exposed planar surfaces of the encapsulant regions in accordance with an embodiment of the present invention. 
         FIG. 11  is a cross-sectional side view of a printed circuit board having encapsulant that has been formed with two different thicknesses on the printed circuit board in accordance with an embodiment of the present invention. 
         FIG. 12  is a cross-sectional side view of an illustrative printed circuit board showing how a layer of conductive coating material may fill substantially all of a channel in an encapsulant layer 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 conductive coating material may conformally coat the sidewall surfaces of channels in an encapsulant layer to form radio-frequency shielding structure sidewalls in accordance with an embodiment of the present invention. 
         FIG. 14  is a cross-sectional side view of the illustrative printed circuit board of  FIG. 13  after removing a portion of the conductive material to separate the radio-frequency shielding structures for two adjacent blocks of circuitry in accordance with an embodiment of the present invention. 
         FIG. 15  is a cross-sectional side view of a printed circuit board following attachment of components, encapsulation of the components with a layer of encapsulant, and formation of a channel between blocks of circuitry each of which is formed from one or more of the components in accordance with an embodiment of the present invention. 
         FIG. 16  is a cross-sectional side view of the printed circuit board of  FIG. 15  following deposition of a layer of conductive material to fill the channel between the components in accordance with an embodiment of the present invention. 
         FIG. 17  is a cross-sectional side view of the printed circuit board of  FIG. 17  following application of an additional layer of conductive material to the exposed planar upper surfaces of the encapsulated components on the printed circuit board in accordance with an embodiment of the present invention. 
         FIG. 18  is a cross-sectional side view of a printed circuit board with integral radio-frequency shielding structures and a conductive spring structure that facilitates the formation of an electrical connection between the shielding structures and a conductive housing wall in accordance with an embodiment of the present invention. 
         FIG. 19  is a cross-sectional side view of an illustrative printed circuit board having integral radio-frequency shielding structures with filled channels and coated end regions 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 integral radio-frequency shielding structures in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     This relates to radio-frequency shielding structures for electrical components. The electrical components that are shielded by the radio-frequency shielding structures may be electronic devices such as integrated circuits that operate in radio-frequency bands (e.g., transceiver integrated circuits, memory circuits and other circuits with clocks that produce signals with fundamentals or harmonics in radio-frequency bands, etc.). Shielded components may also include circuitry formed from one or more discrete components such as inductors, capacitors, and resistors, switches, etc. The electrical components that are shielded may be aggressors (components that produce radio-frequency signal interference) and/or victims (components that are sensitive to interference that is received from external sources). 
     The radio-frequency (RF) shielding structures may help to reduce interference from electromagnetic signals and may therefore sometimes be referred to as electromagnetic interference (EMI) shielding structures. 
     Electronic components with radio-frequency shielding and other electronic components may be mounted on one or more printed circuit boards in an electronic device. The printed circuit boards may be formed from rigid printed circuit board materials such as fiberglass-filled epoxy (e.g., FR4), flexible printed circuits (e.g., printed circuits formed from flexible sheets of polymer such as polyimide), and rigid flex circuits (e.g., printed circuits that contain both rigid portions and flexible tails). 
     Printed circuit boards having shielded components may be used in electronic devices such as desktop computers, laptop computers, computers built into computer monitors, tablet computers, cellular telephones, media players, gaming devices, television set top boxes, audio-video equipment, handheld devices, miniature devices such as pendant and wristwatch devices, or other electronic equipment. An illustrative electronic device that may contain electromagnetic shielding structures is shown in  FIG. 1 . As shown in  FIG. 1 , electronic device  10  may have a housing such as housing  12 . Housing  12  may be formed from metal, plastic, fiber-composite materials such as carbon fiber materials, glass, ceramics, other materials, or combinations of these materials. Housing  12  may be formed from a single piece of machined metal (e.g., using a unibody-type construction) or may be formed from multiple structures that are attached together such as an internal housing frame, a bezel or band structure, housing sidewalls, planar housing wall members, etc. 
     As shown in the example of  FIG. 1 , device  10  may have a display such as display  14 . Display  14  may be a liquid crystal display (LCD), a plasma display, a light-emitting diode (LED) display such as an organic light-emitting diode (OLED) display, an electronic ink display, or a display using other display structures. A capacitive touch screen array or other touch sensor may be integrated into display  14  to form a touch screen for device  10 . A user may supply input for device  10  using a touch screen display or using other user input-output interface structures such as one or more buttons (see, e.g., menu button  16 ). Input-output ports may be formed in housing  12 . For example, input-output ports may be formed to receive digital signaling cables, audio plugs, and cables associated with other devices. The illustrative configuration of device  10  that is shown in  FIG. 1  is merely illustrative. Device  10  may, in general, be any suitable electronic device. 
       FIG. 2  is a circuit diagram showing illustrative circuit components that may be used in device  10 . As shown in  FIG. 2 , device  10  may include control circuitry  18 , radio-frequency transceiver circuitry  26 , and additional components  32  (e.g., a display such as display  14  of  FIG. 1 , audio circuits such as audio codec chips, speakers, and microphones, etc.). Control circuitry  18  may include one or more processing circuits  22 . Processing circuits  22  may include microprocessors, digital signal processors, application-specific integrated circuits, and processing circuitry in other integrated circuits (e.g., processing circuitry in a power management unit, processing circuitry in communications chips, etc.). Processing circuits  22  may run software code that is stored in memory  20 . Memory  20  may include volatile memory such as static random-access memory, dynamic random access memory, flash memory, hard drive storage, etc. 
     Processors  22  and memory  20  may be clocked using one or more clock signals from clock circuits such as clock circuitry  24 . For example, a clock circuit may receive a reference clock from a clock source such as a crystal oscillator and may produce one or more associated clock signals. These clock signals may be applied to electronic components in device  10 , as illustrated by the application of clock signals to memory  20  and processors  22  in the  FIG. 2  example. 
     Radio-frequency transceiver circuitry  26  may include receivers  28  and transmitters  30 . Radio-frequency transceiver circuitry  26  may include wireless communications circuits that operate in cellular telephone bands (e.g., the bands at 850 MHz, 900 MHz, 1800 MHz, 1900 MHz, and 2100 MHz), wireless local area network bands (e.g., the IEEE 802.11 bands at 2.4 GHz and 5 GHz), the Bluetooth® band at 2.4 GHz, satellite navigation bands such as the Global Positioning System (GPS) band at 1575 MHz, wireless circuits for receiving radio signals such as frequency-modulation (FM) signals, etc. 
     Components  32  may include display drivers circuits for driving display signals into display  14  ( FIG. 1 ), audio circuitry (e.g., circuitry that includes analog-to-digital and digital-to-analog converters), and other components. Clock circuitry  24  may distribute clocks to components  32  (e.g., clocks for clocking display driver circuits, clocks for operating analog-to-digital and digital-to-analog circuitry, etc.). 
     The operation of the circuitry of device  10  involves the use of clocks and other signals that have the potential to interfere with one another. For example, a clock circuit such as circuit  24  may generate a clock signal for clocking a processor or display component. The fundamental or harmonics of these clocks may fall within the operating band of one of receivers  28  (as an example) and may therefore represent a source of interference for that receiver. Signals that are generated by one of transmitters  30  may likewise serve as a source of interference for other circuitry in device  10 . 
     To ensure that the circuitry of device  10  operates properly, it may be desirable to electromagnetically shield blocks of circuitry in device  10  from each other. For example, it may be desirable to shield a wireless communications integrated circuit so that system noise (e.g., from clocks or other noise sources) will not interfere with proper receiver operation. It may also be desirable to shield an audio circuit so that the audio circuit does not pick up noise from another circuit on device  10  or to shield memory circuits and processor circuits so that their clocks do not cause interference. 
     With conventional RF shielding can arrangements, each device that is to be shielded is provided with a separate metal radio-frequency shielding can. To avoid the bulk associated with conventional radio-frequency shielding cans, some integrated circuits are available with shielding structures formed from a coating of silver paint. The formation of this type of conventional radio-frequency shielding structure is shown in  FIGS. 3 ,  4 , and  5 . As shown in  FIG. 3 , integrated circuits  34  or other electrical components may be mounted on rigid printed circuit board  38  (e.g., using solder). Resin  36  may be used to encapsulate circuits  34 . Printed circuit board  38  may include one or more conductive layers such as ground plane layer  40  of  FIG. 3 . Ground planer layer  40  may serve as a lower layer of radio-frequency shielding. 
     After encapsulating integrated circuits  34  with resin  36 , a saw can be used to cut channels such as channel  42  of  FIG. 4  that surround all four sides of each integrated circuit  34 . The depth of each channel  42  may be sufficient to penetrate board  38  past the depth of layer  40 , so that edges  50  of layer  38  are exposed. 
     After forming channel  42  in a rectangle surrounding each integrated circuit  34  on board  38 , a coating of silver paint  44  may be screen printed onto the surface of resin  36 . This coats upper planar surfaces  46  of resin  36  and channel sidewalls  48  with silver paint and forms an electrical connection between coating  44  and layer  40  at edges  50 . 
     Following application of silver paint coating  44  of  FIG. 4 , a saw may be used to cut away any remaining printed circuit board material at the bottom of channel  42 . This separates the individual integrated circuits  34  on board  38  from each other to form individual integrated circuit structures of the type shown in  FIG. 5 . Because coating  44  and layer  38  are conductive, the structures of  FIG. 5  form a conductive radio-frequency shielding structure for integrated circuit  34 . The structures of  FIG. 5  may be mounted to a logic board (e.g., using solder). Conductive vias  52  may form electrical paths between the solder on the logic board and the input-output pads on integrated circuit  34 . 
     In some systems, it may be desirable to provide shielding for multiple components on a single printed circuit board, while using shielding structures that have the potential to reduce system size and improve shielding performance. An illustrative layout showing how a printed circuit board in device  10  of  FIG. 1  may be provided with individual compact radio-frequency shielding structures for respective circuit blocks is shown in  FIG. 6 . 
     As shown in  FIG. 6 , printed circuit board  56  may be populated with multiple blocks  54  of circuitry such as a power management unit (PMU) block, a system-on-chip (SOC) block, a radio-frequency (RF) transceiver block, an audio circuit (AUDIO) block, and a frequency modulation (FM) block (e.g., for receiving FM radio signals). Other blocks of circuitry may be provided on printed circuit board  56  if desired. The example of  FIG. 6  is merely illustrative. 
     Each block of circuitry  54  on printed circuit board  56  may include one or more components (e.g., one or more integrated circuits, one or more discrete components, etc.). Circuit blocks typically include at least one integrated circuit, but may, if desired, contain only discrete components. In a typical block that contains an integrated circuit, one or more associated discrete components may be included (e.g., to form a circuit network that supports the operation of the integrated circuit). 
     Each circuit block  54  on printed circuit board  56  generally has the potential to generate radio-frequency interference and has the potential to be disrupted by radio-frequency interference from other circuit blocks. Accordingly, it may be desirable to provide all or at least some of circuit blocks  54  on printed circuit board  56  with corresponding radio-frequency shields. The radio-frequency shields on printed circuit board  56  may be formed from coatings of conductive material (e.g., silver paint or other metallic paint) and may therefore form shielding structures that are integral with board  56  (sometimes referred to as integral shielding structures). If desired, one or more regions of board  56  may be left unshielded. 
       FIGS. 7 ,  8 ,  9 , and  10  are cross-sectional side views of an illustrative printed circuit board during various stages of assembly and fabrication of integrated RF shielding structures. As shown in  FIG. 7 , a pick-and-place tool or other suitable automated or manually controlled component mounting equipment may be used in mounting components  86  on printed circuit board  56 . Components  86  may be clustered so as to form circuit blocks  54  of the type shown in  FIG. 6 . In some situations, a shielded circuit block will contain only one component  86  (e.g., an integrated circuit). In other situations, a shielded circuit block will contain multiple components (e.g., one, two, or more than two integrated circuits and one, two, or more associated discrete components). Individual components  86  are shown in the circuit blocks of the cross-sectional views of  FIGS. 7 ,  8 ,  9 , and  10  to avoid over-complicating the drawings. 
     Printed circuit board  56  may be a rigid printed circuit board (e.g., a fiberglass-filled epoxy board such as an FR4 board), a rigid flex board that has flex circuit tails (e.g., tails formed from polyimide sheets or other flexible polymer sheets), or other suitable substrate material. Components  86  may be mounted to board  56  using solder, conductive adhesive, connectors, or other attachment mechanisms (illustrated schematically as solder balls  62  in  FIG. 7 ). Components  86  may have input-output pads (contacts). Printed circuit board  56  may have mating contacts. When soldered (or otherwise connected) to board  56 , the input-output pads of components  86  are electrically connected to the mating contacts of printed circuit board  56 . 
     Board  56  may contain one or more layers of printed circuit board material and one or more corresponding layers of traces such as illustrative trace  64  of  FIG. 7 . The traces may be formed from copper, other metals, or other conductive materials. Vias (vertical conductive segments) may be used to interconnect traces on respective layers of board  56 . Some of the traces on board  56  may be used in routing signals between components  86 . For example, the output of one integrated circuits on board  56  may be routed to the input of another integrated circuit on board  56  using a bus formed from multiple parallel traces  64 . The traces of board  56  may also be used in forming planar sections that serve as ground planes. One or more of these planar regions of conductor in printed circuit board  56  may form a lower portion of a radio-frequency shield for components  86 . 
     During fabrication of board  56 , patterned surface traces such traces  66  may be formed on the exposed upper surface of board  56 . Traces  66  may be formed from copper or other metals (as an example). Traces  66  may be interconnected with other traces on board  56  (i.e., traces  64 ) using vias and other conductive structures). Traces  66  may be formed in the shape of rectangular rings or other shapes that surround circuit blocks  54  of  FIG. 6 . If, for example, an integrated circuit and several discrete components are to be shielded, a rectangular ring-shaped trace (one of traces  66  of  FIG. 7 ) may surround the integrated circuit and the discrete components. 
     Following patterning of traces  66  and  64 , formation of board  56 , and mounting of components  86  to board  56  using mounting tool  58 , the surface of board  56  may be covered with a layer of dielectric such as layer  68  of  FIG. 8 . Dielectric layer  68  may be formed from a resin such as epoxy or other suitable encapsulant (sometimes referred to as potting material). Layer  68  may help form an environmental seal that protects components  86  from exposure to dust and moisture. 
     Layer  68  may also form a substrate for subsequent deposition of one or more layers of conductive coating materials to form radio-frequency shields for the blocks of circuits  54  on board  56 . In the example of  FIG. 8 , there are two blocks of circuitry  54  (block  54 A and block  54 B). As described in connection with  FIG. 6 , printed circuit board  56  may have additional blocks of circuitry  54  (e.g., three or more blocks  54 , four or more blocks  54 , five or more blocks  54 , etc.). 
     Layer  68  may be based on a material that is initially in a liquid state and may be formed by spin coating, by spraying, by screen printing, by dipping, by ink-jet printing, by pad printing, by dripping, or using other coating techniques. One or more sub-layers may be applied to printed circuit board  56  to form layer  68 . To harden layer  68 , layer  68  may be dried (cured). Examples of treatments that may be used to solidify layer  68  include application of ultraviolet (UV) light (e.g., to UV-cure a UV epoxy), application of heat (e.g., to cure a thermally cured epoxy), and room temperature exposure (e.g., to allow a chemically cured dielectric material to harden and form dielectric layer  68 ). 
     After layer  68  has solidified, tools  70  may be used to form channels  74 , as shown in  FIG. 9 . Channels  74  may be formed in ring shapes that surround each separate block  54  of components  86  (see, e.g., the illustrative blocks of components in  FIG. 6 ). Channels  74  may, for example, be formed in rectangular ring shapes surrounding respective rectangular areas on board  56  (as an example). 
     Tools  70  may include a laser that produces light (illustrated by dashed lines  72 ) or may include a saw or other mechanical removal tool. Channels  74  may also be formed using masks and etching or other fabrication techniques. When a laser is used, the wavelength of light that is produced by the laser may be selected so that the laser light removes material  68  from channel  74  without removing a significant amount of underlying material in trace  66 . An advantage of using a laser rather than a mechanical removal tool such as a saw is that trace  66  may serve as a stop layer that helps restrict the depth of channel  74  and prevents channel  74  from extending excessively (e.g., to a depth that might damage the pattern of interconnect traces  64  within the layers of board  56 ). Laser removal tools may also be able to form narrower channels (e.g., channels with lateral dimensions of 50-500 microns or less) than saws (which may typically produce cuts of about 600 microns in width). If desired, tools  70  may include dry etching equipment (e.g., a plasma etch tool) to help remove residual particles from the surface of trace  66  following coarse material removal operations with a laser or saw. 
     Channels  74  are preferably formed in alignment with traces  66 , so that channel sidewalls  76  are formed above and overlapping respective portions of traces  66 . 
     After channels  74  have been formed, tools  78  may be used to deposit one or more layers of conductive coating  82  on the exposed surface of dielectric layer  68 , as shown in  FIG. 10 . Coating  82  may be formed from a conductive material such as silver paint or other suitable conductive material. Coating  82  may be deposited by screen printing, pad printing, dripping, spraying, dipping, ink-jet printing, evaporation, sputtering, other deposition techniques, and combinations of these techniques. Coating  82  may, if desired, be deposited using a conformal deposition process that allows coating  82  to coat sidewalls  76  of channels (grooves)  74 . 
     As shown in  FIG. 10 , printed circuit board  56  may include conductive traces  64 . Traces  64  may be formed from copper, other metals, or other conductive materials and may mate with traces  66  on the surface of board  56 . Traces  66 , which may be formed from copper, other metals, or other conductive materials, may be electrically connected to traces  64 . Traces  64  may, for example, include substantially uninterrupted planar regions (e.g., ground planes) and may serve as the lower portion of radio-frequency shielding structures for board  56 . 
     As shown in  FIG. 10 , some of traces  64  may be formed between traces  66  and adjacent components  86  and some of traces  64  may run under traces  66  and may be used in interconnecting components  86  in different (and separately shielded) blocks of circuitry. For example, some of traces  66  (e.g., the traces in region  80 ) may run under channels  74  and may be used in connecting components  86  in circuit block  54 A with corresponding components  86  in circuit block  54 B. Traces  64  may be formed in one or more layers of printed circuit board  56 . Board  56  may have any suitable number of layers (e.g., 1-10 layers or more). Conductive structures such as vias  84  (which may be considered to form part of interconnect traces  64 ) may be used to interconnect input-output pads on components  86  and solder balls  62  to traces  64 . 
     With the configuration shown in  FIG. 10 , printed circuit board  56  contains multiple blocks  54  of circuitry each of which contains one or more components  86  and each of which has a respective radio-frequency shielding structure. The radio-frequency shielding structures are made up of the ground plane structures in board  56  (shown as traces  64 ) that lie under each block  54 , the traces  66  that surround each block  54  on board  56 , the sidewall portions of conductive layer  82  that coat sidewalls  76  of channels  74 , and the planar portion of coating  82  that covers each block  54 . In the portion of board  56  that is shown in  FIG. 10 , there are two complete shielding structures (the left-hand structure that is shielding block  54 A and the right-hand structure that is shielding block  54 B). If desired, board  56  may have additional shielding structures (e.g., three or more, four or more, five or more, etc.).  FIG. 6  shows an illustrative layout in which each of five different blocks of components  54  has a respective shielding structure. 
     As shown in  FIG. 11 , dielectric layer  68  may have portions with different heights. For example, dielectric layer portion  68 A may have a height (thickness) H 1  that is greater than the height (thickness) H 2  of dielectric layer portion  68 B. The lower height H 2  of region  68 B may help make it possible to install board  56  in a compact housing. Portion  68 B may be formed by removing some of the upper portion of a layer that was deposited at the same time as portion  68 A or layer  68 A may be built up with respect to portion  68 B (e.g., by adding an additional coating or using a mold with different heights). 
       FIG. 12  shows how channel  74  may be completely filled with portion  82 B of coating  82 . Portion  82 A of coating  82  may cover the planar upper surface of encapsulant  68 . Portions  82 A and  82 B may be formed during a single application of coating  82  (e.g., a single screen printing operation) or may be formed using a sequence of multiple separate coating operations each of which deposits a respective portion of coating  82 . 
     The radio-frequency shielding structures that are associated with each circuit block  54  may be electrically connected (grounded) to each other or may be electrically isolated from one another.  FIGS. 13 and 14  illustrate how an opening may be formed between adjacent radio-frequency shielding structures in a scenario in which it is desired to isolate the radio-frequency isolation structures from each other. Initially, a radio-frequency shielding configuration of the type shown in  FIG. 10  may be formed. Channels  74  may have coated sidewalls as shown in  FIG. 13  or may be completely filled with conductive material  82  as illustrated in  FIG. 12 . After forming the electrically connected shielding structures of  FIG. 13 , laser light  72  may be applied to form channel  740  of  FIG. 14  or other cutting mechanisms such as a saw may be used to form channel  740 . Channel  740  may run around the periphery of one or both of blocks  54 A and  54 B to form a continuous opening in shielding layer  82  that electrically separates the radio-frequency shielding structures of block  54 A from the radio-frequency shielding structures of block  54 B. 
       FIGS. 15 ,  16 , and  17  are cross-sectional side views of printed circuit board  56  showing how channels  74  may be filled using multiple layers of coating material  82 . Initially, channel  74  may be formed in dielectric layer  68 , as shown in  FIG. 15 . In a first deposition step (e.g., using screen printing or other suitable techniques), conductive material  82 B (e.g., silver paint or other metallic paint or conductive liquid coating material) may be deposited within channel  74 , as shown in  FIG. 16 . A low-viscosity material may be used to fill channel  74  (e.g., using a wicking action produced by the relatively narrow width of channel  74 ). Due to the viscosity of material  82 B (e.g., its potentially low viscosity), it may not be possible to uniformly coat the exposed surface of dielectric layer  68  during the first deposition step. In a second deposition step (e.g., using screen printing or other suitable technique with a potentially more viscous coating material), conductive material  82 A with a higher viscosity may therefore be deposited over the exposed surface of dielectric layer  68 , as shown in  FIG. 17 . 
     It may be desirable to form grounding contacts or other electrical connections between a radio-frequency shielding structure formed from conductive layer  82  and a conductive housing wall or other conductive structure in device  10 . This may be accomplished using a spring or other flexible conductive component that is mounted to coating  82 , as shown in  FIG. 18 . In the  FIG. 18  example, coating layer  82  is being used to form respective radio-frequency shielding structures for three blocks of circuitry (block  54 A, block  54 B, and block  54 C). Conductive structure  90  may have a flexible portion  92  that is biased upwards in direction  94 . Conductive structure  90  may be, for example, a sheet of metal and portion  92  may be a tab that extends upwards from the sheet of metal. Because portion  92  is biased upwards, the upper surface of portion  92  presses against interior (lower) surface  96  of metal housing wall  12  and forms an electrical contact. This type of arrangement may be used when it is desired to electrically connect the radio-frequency shielding structures formed from conductive coating  82  to conductive device structures such as conductive housing structure  12 . Structure  12  may be, for example, a planar wall that forms the rear of device  10  (when viewed in the orientation of  FIG. 1 ). Structure  90  may be connected to layer  82  by placing structure  90  on layer  82  when layer  82  is wet, using conductive adhesive  88 , or using other suitable attachment mechanisms. 
     Channels  74  may extend only to the surface of printed circuit board  56  or may extend partly into board  56 . The cross-sectional side view of printed circuit board  56  of  FIG. 19  shows how channels  74  may have different shapes in different regions of the same printed circuit board (as an example). In the  FIG. 19  example, channel  74 ′ has been formed through encapsulant layer  68  and partly into the interior of board  56 . Channel  74 ′ extends sufficiently into board  56  that the sidewalls of channel  74 ′ extend past edges  64 ′ of conductive trace layer  64  (e.g., one or more ground plane layers in board  56 ). This allows the conductive material that fills channel  74 ′ to form an electrical connection with layer  64 . Channel  74 ″ extends through layer  68 , but terminates at the surface of board  56  on trace  66 . Electrical connection between material  82 ″ in channel  74 ″ and layer  64  may be made by conductive structures such as via  84 . Structure  74 ′″ may be formed along the edge of board  56  (e.g., using a sawing technique of the type described in connection with  FIG. 5 ). This removes board portion  56 ′ from board  56  and leaves coating material  82 ′″ along the exposed edge of board  56 . Coating material  82 ′″ may form an electrical contact with edge  64 ″ of one or more ground plane layers  64  in board  56 . 
       FIG. 20  is a flow chart of illustrative steps involved in forming printed circuit boards with multiple integral radio-frequency shields each of which shields a respective block of circuit components such as blocks  54  of  FIG. 6 . 
     At step  98 , components  86  may be mounted on board  56 . Components  86  may be arranged using a layout of the type shown in  FIG. 6  in which functionally related circuit components are grouped together. For example, one block  54  of components  86  may form radio-frequency transceiver circuitry and another block  54  of components  86  may form processing circuitry. Components may be soldered to printed circuit board  56  (e.g., using an automated soldering tool and/or manual soldering techniques), may be mounted on board  56  using conductive adhesive, or may be otherwise attached to the surface of board  56 . 
     During the operations of step  100 , components  86  may be encapsulated in resin. For example, one or more coatings of epoxy or other dielectric material  68  may be deposited on components  86 . 
     At step  102 , a laser or other cutting tool may be used to form channels  74 . A laser may advantageously be used to remove portions of dielectric material  68  above traces  66  without removing traces  66  (e.g., due to the reflectively of traces  66 ). The laser that is used to remove material  68  may be an infrared laser, a ultraviolet laser, a visible laser, a pulsed laser, a continuous wave laser, etc. Reactive ion etching, plasma etching, or other operations for cleaning and removing excess material may be used in combination with laser patterning of layer  68  if desired. The pattern of channels  74  that is formed in layer  68  may surround each respective block  54  of components without separating printed circuit  56  into individual pieces and without damaging any of the traces  64  in board  56  that are used to interconnect the circuitry of respective blocks  54 . 
     At step  104 , conductive material  82  (e.g., silver paint or other metallic material) may be deposited in channels  74 . Screen printing or other deposition techniques may be used in filling channels  74 . One or more coating layers may be used in filling channels  74 . Channels  74  may be completely filled or may be partially filled (e.g., so that only the sidewalls of channels  74  are coated). 
     Following formation of the conductive material  82  in channels  74 , edge portions of board  56  may be sawed off (e.g., to remove board portion  56 ′ of  FIG. 19  while leaving portion  56  and edge portion  82 ′″ of coating layer  82  in place). In configurations in which it is desired to separate individual radio-frequency shields from each other, a laser or other cutting tool may be used to form openings in layer  82  such as opening  740  in  FIG. 14 . If desired, one or more spring structures such as structure  90  of  FIG. 18  may be attached to layer  82 . Board  56  may then be mounted in device  10  (e.g., so that structure  90  shorts the radio-frequency shielding structures to a metal housing wall or other conductive device structure). 
     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: 20101201
Publication Date: 20140218
Grant Date: 20140218
Priority Date: 20101201
Inventors: FISHER, JR. JOSEPH
MAYO SEAN
PYPER DENNIS R.
NANGERONI PAUL
MANTOVANI JOSE
Assignee: APPLE INC
CPC Classifications: [{"code": "H05K9/0084", "inventive": true, "first": true, "tree": "[]"}, {"code": "H05K9/0084", "inventive": true, "first": true, "tree": "[]"}, {"code": "H05K3/284", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K9/0092", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K2201/0715", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2201/09509", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L23/552", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L2924/15192", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/16225", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2924/12044", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K3/284", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K9/0092", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K2201/0715", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2201/09509", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L23/552", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L2924/15192", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2224/16225", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2924/12044", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 46162062