PATENT DOCUMENT

Publication Number: US-8686297-B2
Application Number: US-201113220230-A
Country: US
Kind Code: B2

Title: Laminated flex circuit layers for electronic device components

Abstract:
An electronic device may have a housing in which an antenna and a proximity sensor formed from flex circuit structures are mounted. The flex circuit structures may include first and second flex circuit layers. The first and second flex circuit layers may include metal antenna structures and metal proximity sensor electrode structures. Solder may be used to attach electrical components to the flex circuit layers and may be used to electrically connect metal structures on the first and second flex circuit layers to each other. The first and second flex circuit layers may be laminated together using a compressive fixture. The compressive fixture may have a first fixture with a convex surface and a second fixture with a concave surface so that the laminated flex circuit layers are provided with a bend.

Claims:
What is claimed is: 
     
       1. A flex circuit structure, comprising:
 a first flex circuit layer comprising one or more conductive trace layers configured to form a first layer of patterned conductive material; 
 a second flex circuit layer comprising one or more conductive trace layers configured to form a second layer of patterned conductive material, wherein
 the first and the second layers of patterned conductive material are laminated together, and formed on opposing sides of the flex circuit structure and at least a portion of each is electrically isolated from each other by a dielectric layer to form a parallel plate capacitor, and wherein 
 below a first frequency, the parallel plate capacitor has a high impedance value such that the corresponding portions of the first and second layers of patterned conductive material serve as independent first and second proximity sensor capacitor electrodes, and 
 above a second frequency associated with a radio-frequency (RF) antenna signal, the impedance of the parallel plate capacitor is such that the first and the second layers of patterned conductive material are effectively shorted to each other to operate together as a unitary patterned conductor to act as an antenna resonating element, further wherein 
 the first proximity sensor capacitor electrode is disposed on a first surface of the flex circuit structure and the second proximity sensor capacitor electrode is disposed on a second surface of the flex circuit structure; and 
 
 an adhesive layer between the first and second layers of patterned conductive material, the adhesive layer including air paths. 
 
     
     
       2. The flex circuit structure as recited in  claim 1 , wherein the first frequency is about 1 MHz and wherein the second frequency is about 100 MHz. 
     
     
       3. The flex circuit structure as recited in  claim 1  wherein at least one of the first flex circuit layer and the second flex circuit layer comprises an antenna trace. 
     
     
       4. The flex circuit structure as recited in  claim 1 , wherein the first flex circuit layer comprises at least one component connected to the first layer of patterned conductive material. 
     
     
       5. The flex circuit structure as recited in  claim 4 , wherein the at least one component connected to the first layer of patterned conductive material is electrically interconnected to the second layer of patterned conductive material using an electrical interconnect. 
     
     
       6. The flex circuit structure as recited in  claim 1 , wherein the first surface is outwardly directed and the second surface is inwardly directed. 
     
     
       7. The flex circuit structure as recited in  claim 1 , wherein the first and second patterned conductive layers of the flex circuit structures are shaped in the form of an inverted-F antenna resonating element. 
     
     
       8. The flex circuit structure as recited in  claim 7 , wherein the first and second patterned conductive layers of the flex circuit structures shaped in the form of the inverted-F antenna resonating element comprise:
 a first branch; 
 a second branch to provide additional frequency resonances and/or broadened antenna bandwidth; 
 a short circuit branch; and 
 a feed branch. 
 
     
     
       9. The flex circuit structure as recited in  claim 7 , wherein the inverted-F antenna further comprises at least one additional arm, the additional arm being shaped as a bend, or as a curve. 
     
     
       10. The flex circuit structure as recited in  claim 9 , the flex circuit structure further comprising a first positive antenna feed terminal and a first ground antenna feed terminal, the first positive antenna feed terminal arranged to receive an RF signal from an RF transceiver by way of a positive signal line at a second positive antenna feed terminal coupling the first positive antenna feed terminal and the RF transceiver. 
     
     
       11. The flex circuit structure as recited in  claim 10 , the first ground antenna feed terminal coupled to a ground signal line at a second ground antenna feed terminal. 
     
     
       12. The flex circuit structure as recited in  claim 11 , wherein the second positive antenna feed terminal is coupled to the first positive antenna feed terminal via a capacitor Cfp. 
     
     
       13. The flex circuit structure as recited in  claim 10 , wherein the first positive antenna feed terminal is connected to an antenna resonating element branch. 
     
     
       14. The flex circuit structure as recited in  claim 11 , wherein the second ground antenna feed terminal is coupled to the first ground antenna feed terminal via a capacitor Cfg, wherein
 capacitors Cfg and Cfp form a high pass filter configured to prevent low frequency noise from interfering with an RF antenna operation of the flex circuit structure. 
 
     
     
       15. The flex circuit structure as recited in  claim 10 , wherein the RF transceiver is disposed within a housing of a portable electronic device, the housing formed of RF opaque material, the housing further comprising an opening suitably sized to accommodate an RF transparent structure. 
     
     
       16. The flex circuit structure as recited in  claim 11 , wherein the flex circuit structure is disposed within the housing in proximity to the opening. 
     
     
       17. The flex circuit structure as recited in  claim 16 , wherein the flex circuit structure conforms to an inside surface of the housing. 
     
     
       18. The flex circuit structure as recited in  claim 17 , wherein the flex circuit structure is laminated and bent to conform to the inside surface. 
     
     
       19. The flex circuit structure as recited in  claim 1  wherein at least one of the first flex circuit layer and the second flex circuit layer is formed from sheets of polyimide. 
     
     
       20. The flex circuit structure as recited in  claim 1  wherein the first and second flex circuit layers are soldered to each other.

Description:
BACKGROUND 
     This relates generally to electronic devices, and, more particularly, to flexible structures in electronic devices. 
     Electronic devices such as portable computers and handheld electronic devices are becoming increasingly popular. Devices such as these are often provided with wireless communications capabilities. For example, electronic devices may use long-range wireless communications circuitry to communicate using cellular telephone bands. Electronic devices may use short-range wireless communications links to handle communications with nearby equipment. Electronic devices are also often provided with sensors and other electronic components. 
     It can be difficult to incorporate antennas, sensors, and other electrical components successfully into an electronic device. Some electronic devices are manufactured with small form factors, so space for components is limited. In many electronic devices, the presence of conductive structures can influence the performance of electronic components, further restricting potential mounting arrangements for components. 
     It would therefore be desirable to be able to provide improved ways in which to incorporate components in electronic devices. 
     SUMMARY 
     An electronic device may have integral antenna resonating element and proximity sensor capacitor electrode structures formed from conductive structures such as conductive flexible printed circuit (“flex circuit”) structures. 
     The flex circuit structures may include first and second flex circuit layers. The first and second flex circuit layers may include metal antenna structures and metal proximity sensor electrode structures. Solder may be used to attach electrical components such as surface mount technology (SMT) components to the flex circuit layers. Solder may also be used to electrically connect metal structures on the first and second flex circuit layers to each other. The solder may be formed from a patterned solder paste or from solder ball structures that are held in place with solder resin before solder joint formation. 
     The first and second flex circuit layers may be laminated together using a compressive fixture. The compressive fixture may have a first fixture with a convex surface and a second fixture with a corresponding concave surface. The first fixture may be formed from a rigid material. The second fixture may be formed from an elastomeric material. The flex circuit layers may be laminated together between the convex and concave surfaces using adhesive. The adhesive may be patterned to form air gaps. The air gaps may allow gas to escape during solder joint formation. The bent shape of the convex and concave surfaces may be used to form a bend in the laminated flex circuit layers. 
     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 front perspective view of an illustrative electronic device of the type that may be provided with component structures in accordance with an embodiment of the present invention. 
         FIG. 2  is a rear perspective view of an illustrative electronic device such as the electronic device of  FIG. 1  in accordance with an embodiment of the present invention. 
         FIG. 3  is a cross-sectional side view of a portion of the electronic device of  FIGS. 1 and 2  in accordance with an embodiment of the present invention. 
         FIG. 4  is a top view of an illustrative integrated antenna and proximity sensor in an electronic device in accordance with an embodiment of the present invention. 
         FIG. 5  is a perspective view of an electronic component formed from conductive traces on a flexible substrate with a bend to accommodate mounting within an electronic device in accordance with an embodiment of the present invention. 
         FIG. 6  is a diagram showing how components such as the component of  FIG. 5  may be formed by combining multiple flexible layers in accordance with an embodiment of the present invention. 
         FIG. 7  is a cross-sectional side view of an illustrative electronic component formed from two flex circuit substrates that have been interconnected using patterned solder paste in accordance with an embodiment of the present invention. 
         FIG. 8  is a cross-sectional side view of an illustrative electronic component formed from two flex circuits that have been interconnected using a solder ball in accordance with an embodiment of the present invention. 
         FIG. 9  is a cross-sectional top view of an illustrative adhesive pattern that may be used to provide air gap channels that accommodate escaping gas when connecting multiple flex circuit layers with solder in accordance with an embodiment of the present invention. 
         FIG. 10  is a perspective view of an illustrative flex circuit of the type that may be connected to another flex circuit to form an electronic component in accordance with an embodiment of the present invention. 
         FIG. 11  is a perspective view of part of an illustrative flex circuit lamination tool and a flex circuit of the type that may be coupled to the flex circuit of  FIG. 10  to form an electronic component in accordance with an embodiment of the present invention. 
         FIG. 12  is a cross-sectional side view of an illustrative tool for assembling flex circuit structures together just prior to compression of the flex circuit structures between upper and lower tool pieces in accordance with an embodiment of the present invention. 
         FIG. 13  is a cross-sectional side view of an illustrative tool for assembling flex circuit structures together during compression of the flex circuit structures between upper and lower tool pieces in accordance with an embodiment of the present invention. 
         FIG. 14  is a side view of flex circuit structures of the type shown in  FIGS. 10 and 11  during compression of the flex circuit structures between mating tool pieces such as rigid and elastomeric compressive fixtures in accordance with an embodiment of the present invention. 
         FIG. 15  is a perspective view of a tool being used to form a bend in flex circuit structures in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices may be provided with antennas, sensors, and other electronic components. It may be desirable to form these components from flexible structures. For example, it may be desirable to form components for electronic devices from flexible printed circuit structures. Flexible printed circuits, which are sometimes referred to as flex circuits, may include patterned metal traces on flexible substrates such as layers of polyimide or other flexible polymer sheets. Flex circuits may be used in forming antennas, capacitive sensors, assemblies that include antenna and capacitive sensor structures, other electronic device components, or combinations of these structures. 
     An illustrative electronic device in which electronic components may be used is shown in  FIG. 1 . Portable device  10  may include one or more antenna resonating elements, one or more capacitive proximity sensor structures, one or more components that include antenna structures and proximity sensor structures, other electronic components, etc. Illustrative arrangements in which an electronic device such as device  10  of  FIG. 1  is provided with electronic components such as antenna structures and/or proximity sensor structures that are formed from multiple flex circuit layers are sometimes described herein as an example. In general, electronic devices may be provided with any suitable flex-circuit-based electronic components. The electronic devices may be, for example, desktop computers, computers integrated into computer monitors, portable computers, tablet computers, handheld devices, cellular telephones, wristwatch devise, pendant devices, other small or miniature devices, televisions, set-top boxes, or other electronic equipment. 
     As shown in  FIG. 1 , device  10  may be a relatively thin device such as a tablet computer (as an example). Device  10  may have display such as display  50  mounted on its front (top) surface. Housing  12  may have curved portions that form the edges of device  10  and a relatively planar portion that forms the rear surface of device  10  (as an example). A radio-frequency (RF) window (sometimes referred to as an antenna window) such as RF window  58  may be formed in housing  12 . Antenna and proximity sensor structures for device  10  may be formed in the vicinity of window  58 . 
     Device  10  may have user input-output devices such as button  59 . Display  50  may be a touch screen display that is used in gathering user touch input. The surface of display  50  may be covered using a dielectric member such as a planar cover glass member. The central portion of display (shown as region  56  in  FIG. 1 ) may be an active region that displays images and that is sensitive to touch input. The peripheral regions of display  50  such as regions  54  may be inactive regions that are free from touch sensor electrodes and that do not display images. 
     A layer of material such as an opaque ink or plastic may be placed on the underside of display  50  in peripheral regions  54  (e.g., on the underside of the cover glass). This layer may be transparent to radio-frequency signals. The conductive touch sensor electrodes in region  56  may tend to block radio-frequency signals. However, radio-frequency signals may pass through the cover glass and opaque layer in inactive display regions  54  (as an example). In the opposite direction, radio-frequency signals may pass through antenna window  58 . Lower-frequency electromagnetic fields also pass through window  58 , so capacitance measurements for a proximity sensor may be made through antenna window  58 . 
     Housing  12  may be formed from one or more structures. For example, housing  12  may include an internal frame and planar housing walls that are mounted to the frame. Housing  12  may also be formed from a unitary block of material such as a cast or machined block of aluminum. Arrangements that use both of these approaches may also be used if desired. 
     Housing  12  may be formed of any suitable materials including plastic, wood, glass, ceramics, metal, fiber-based composites such as carbon fiber composites, other suitable materials, or a combination of these materials. In some situations, portions of housing  12  may be formed from a dielectric or other low-conductivity material, so as not to disturb the operation of conductive antenna elements that are located in proximity to housing  12 . In other situations, housing  12  may be formed from metal elements. An advantage of forming housing  12  from metal or other structurally sound conductive materials is that this may improve device aesthetics and may help improve durability and portability. 
     With one suitable arrangement, housing  12  may be formed from a metal such as aluminum. Portions of housing  12  in the vicinity of antenna window  58  may be used as antenna ground. Antenna window  58  may be formed from a dielectric material such as polycarbonate (PC), acrylonitrile butadiene styrene (ABS), a PC/ABS blend, or other plastics (as examples). Window  58  may be attached to housing  12  using adhesive, fasteners, or other suitable attachment mechanisms. To ensure that device  10  has an attractive appearance, it may be desirable to form window  58  so that the exterior surfaces of window  58  conform to the edge profile exhibited by housing  12  in other portions of device  10 . For example, if housing  12  has straight edges  12 A and a flat bottom surface, window  58  may be formed with a right-angle bend and vertical sidewalls. If housing  12  has curved edges  12 A, window  58  may have a similarly curved surface. 
       FIG. 2  is a rear perspective view of device  10  of  FIG. 1  showing how device  10  may have a relatively planar rear surface  12 B and showing how antenna window  58  may be rectangular in shape with curved portions that match the shape of curved housing edges  12 A. 
     A cross-sectional view of device  10  taken along line  1300  of  FIG. 2  and viewed in direction  1302  is shown in  FIG. 3 . As shown in  FIG. 3 , structures  200  may be mounted within device  10  in the vicinity of RF window (antenna window)  58 . Structures  200  may serve as an antenna resonating element for an antenna. The antenna may be fed using transmission line  44 . Transmission line  44  may have a positive signal conductor that is coupled to positive antenna feed terminal  76  and a ground signal conductor that is coupled to antenna ground (e.g., housing  12  and other conductive structures) at ground antenna feed terminal  78 . 
     The antenna resonating element formed from structures  200  may be based on any suitable antenna resonating element design (e.g., structures  200  may form a patch antenna resonating element, a single arm inverted-F antenna structure, a dual-arm inverted-F antenna structure, other suitable multi-arm or single arm inverted-F antenna structures, a closed and/or open slot antenna structure, a loop antenna structure, a monopole, a dipole, a planar inverted-F antenna structure, a hybrid of any two or more of these designs, etc.). Housing  12  may serve as antenna ground for an antenna formed from structure  200  or other conductive structures within device  10  may serve as ground (e.g., conductive components, traces on printed circuits, etc.). 
     Conductive structures  200  may form one or more proximity sensor capacitor electrodes. With one suitable arrangement, structures  200  may be formed from a flex circuit structure. The flex circuit structure may include at least first and second layers of patterned conductive material. The first and second layers of patterned conductive material may be formed on opposing sides of the flex circuit structure (e.g., top and bottom sides). At frequencies associated with antenna signals, the first and second layers may be effectively shorted to each other and may form an antenna resonating element. At lower frequencies, the first and second layers may serve as first and second proximity sensor capacitor electrodes (e.g., an inwardly directed electrode and an outwardly directed electrode). 
     Structures  200  may be implemented by laminating together two or more flex circuit layers to form a composite flex circuit structure. By incorporating multiple flex circuit layers into structures  200 , potentially complex patterns of conductive traces (e.g., traces on three or more different metal layers) may be formed. Components may be mounted on the flex circuit layers and interconnected to the patterns of conductive traces. Lamination tools may be used in forming the composite flex circuit structure. The lamination tools may bend the flex circuit layers prior to lamination to help minimize built-in stress relative to flex circuit structures formed by bending a single layer of flex circuit material. 
     If desired, structures  200  may include integrated circuits, discrete components such as resistors, inductors, and capacitors, and other electronic devices. Structures  200  may also include conductive traces for forming antenna resonating element patterns, transmission lines, and proximity sensor electrode patterns (as examples). 
     Structures  200  may be formed from a first flex circuit layer and a second flex circuit layer. A first layer of patterned conductive material in structures  200  may be formed from one or more conductive trace layers in the first flex circuit layer. A second layer of patterned conductive material in structures  200  may be formed from one or more conductive trace layers in the second flex circuit layer. Conductive paths may be formed between the first and second layers using solder or other conductive materials (e.g., anisotropic conductive film, etc.). 
     The first layer of patterned conductive material may face outwards in direction  300  and the second patterned conductive layer may face inwards into housing  12  in direction  302  (as an example). The two layers of patterned conductive material may be electrically isolated from each other by interposed dielectric to form a parallel plate capacitor. At frequencies below about 1 MHz, the parallel plate capacitor may have a relatively high impedance (e.g., forming a DC open circuit), so that the patterned coating layers may serve as independent first and second proximity sensor capacitor electrodes. At frequencies above 1 MHz (e.g., at frequencies above 100 MHz or above 1 GHz), the impedance of the parallel plate capacitor is low, so the patterned conductive layers may be effectively shorted together. This allows both of the layers to operate together as a unitary patterned conductor in an antenna resonating element. 
     During operation of the antenna formed form structures  200 , radio-frequency antenna signals can be conveyed through dielectric window  58 . Radio-frequency antenna signals associated with structures  200  may also be conveyed through a display cover member such as cover glass  60 . Display  50  may have an active region such as region  56  in which cover glass  60  has underlying conductive structure such as display panel module  64 . The structures in display panel  64  such as touch sensor electrodes and active display pixel circuitry may be conductive and may therefore attenuate radio-frequency signals. In region  54 , however, display  50  may be inactive (i.e., panel  64  may be absent). An opaque layer such as plastic or ink  62  may be formed on the underside of transparent cover glass  60  in region  54  to block the antenna resonating element from view. Opaque material  62  and the dielectric material of cover member  60  in region  54  may be sufficiently transparent to radio-frequency signals that radio-frequency signals can be conveyed through these structures in directions  70 . 
       FIG. 4  illustrates how structures  200  may be located in an opening in a portion of conductive housing structures  12  (as an example). Window  58  of  FIG. 3  is not shown in  FIG. 4 . The opening in  FIG. 4  has the shape of a rectangular recess along one edge of housing structures  12 . Openings of other shapes may be used if desired. As shown in  FIG. 4 , the patterned conductive layers of structures  200  may have the shape of an inverted-F antenna resonating element. In particular, structures  200  may have a main branch such as branch  200 - 1 , one or more additional branches such as branch  200 - 2  (e.g., to provide additional frequency resonances and/or broadened antenna bandwidth), a short circuit branch such as branch  200 - 4 , and a feed branch such as branch  200 - 3 . Other branches (arms), features such as bends, curved edges, and other shapes may be included if desired. 
     Transmission line  44  may be coupled between structures  200  and associated radio-frequency transceiver circuitry. Transmission line  44  may have a positive signal line that is connected to positive antenna feed terminal  76  and a ground signal line that is connected to ground antenna feed terminal  78 . Positive antenna feed terminal  76  may be coupled to positive antenna feed terminal  76 ′ on antenna resonating element branch  200 - 3  via capacitor Cfp. Ground antenna feed terminal  78  may be coupled to ground antenna feed terminal  78 ′ on antenna resonating element branch  200 - 4  via capacitor Cfg. 
     The capacitance values for capacitors Cfp and Cfg are preferably of sufficient size to ensure that the impedance of these capacitors is low and does not disrupt antenna operation at frequencies associated with wireless signals in device  10 . For example, if path  44  is being used to handle signals at frequencies of 100 MHz or more (e.g., cellular telephone signals, wireless local area network signals, etc.), the values of Cfp and Cfg may be 10 pF or more, 100 pF or more (e.g., 100s of pF), or may have other suitable sizes that ensure that transmitted and received antenna signals are not blocked. At lower frequencies, the impedance of capacitors Cfp and Cfg is preferably sufficiently large to prevent interference from reaching the antenna resonating element formed from structures  200 . 
     Proximity sensor circuitry may be coupled to structures  200  through inductor(s)  202 . For example, proximity sensor circuitry such as capacitance-to-digital converter circuitry  136  or other control circuitry may be used to make capacitance measurements using one or more capacitor electrodes formed from the patterned conductive layer(s) of structures  200 . Inductor(s)  202  may have impedance values (e.g., impedances of 100s of nH) that prevent radio-frequency antenna signals (e.g., antenna signals at frequencies of 100 MHz or more) from reaching capacitance-to-digital converter  136  or other proximity sensor circuitry while allowing AC proximity sensor signals (e.g., signals with frequencies below 1 MHz) to pass between structures  200  and the proximity sensor circuitry. 
     Capacitors Cfp and Cfg form a high pass filter. By using high-pass circuitry such as capacitors Cfp and Cfg, low frequency noise can be prevented from interfering with antenna operation for structures  200 . Inductor(s)  202  form a low-pass filter. By using low-pass circuitry such as inductor(s)  202 , radio-frequency noise from antenna signals can be prevented from interfering with proximity sensor operation for structures  200 . If desired, other types of high-pass and low-pass filters may be interposed between structures  200  and the radio-frequency transceiver circuitry and proximity sensor circuitry that is associated with structures  200 . The arrangement of  FIG. 4  is merely illustrative. 
     When assembled, conductive structures  200  may appear as shown in  FIG. 5  (as an example). As shown in  FIG. 5 , conductive structures  200  may be bent. Conductive structures  200  may be formed from a composite flex circuit structure that includes at least first and second laminated flex circuits. The bend in the composite flex circuit structure of  FIG. 5  may be formed by laminating the first and second flex circuits to each other while the first and second flex circuits are maintained in a bent configuration. Bending the flex circuits to a desired bend radius or to a tighter bend radius associated with over-bending before completing the lamination process may help reduce residual stress in the resulting composite flex circuit structure. 
     As shown in the  FIG. 5  example, one of the edges of conductive structures  200  may be bent back along its length to form bent edge  200 B. Bent edge  200 B may allow structures  200  to fit within housing  12  so that bent edge  200 B rests under inactive region  54  of display cover glass  60 , as shown in  FIG. 3 . This is merely an illustrative configuration that may be used for mounting conductive structures  200  within housing  12  of device  10 . Other configurations may be used if desired. 
     To help accommodate shapes for structures  200  that allow structures  200  to fit within housing  12  such as shapes with one or more bends, it may be desirable to form structures  200  using a lamination process. During the lamination process, two or more substrate layers such as two or more flex circuit layers may be attached to each other using adhesive. 
     Flex circuit layers for forming structures  200  may be formed from sheets of polyimide or other flexible polymer layers. Conductive patterned materials such as traces of metal may be used in forming antenna structures, component interconnects, transmission lines, sensor electrodes, and other conductive structures on the flex circuits. The flex circuits may contain one or more layers of metal traces with one or more layers of intervening dielectric (e.g., one or more intervening layers of polyimide or other flex circuit substrate materials). 
     During lamination, adhesive, heat, and/or pressure may be used in connecting multiple flex circuit layers together. Solder or other conductive materials (e.g., anisotropic conductive film, etc.) may be used in electrically connecting the metal traces on one flex circuit layer to another. Solder connections may be formed by reflowing solder paste structures in a reflow oven, by reflowing balls of solder in a reflow oven, by heating solder paste or solder balls using a localized heat source such as a heat bar (hot bar) or heat gun, or using other suitable solder reflow techniques. 
       FIG. 6  is a diagram of equipment and processes involved in forming structures such as structures  200  of  FIG. 5 . Substrates such as substrates  306  and  308  may be used in forming structures  200 . Substrates  306  and  308  may be, for example, flex circuit substrates formed from sheets of polyimide or other flexible polymers. Metal structures (e.g., one or more patterned layers of copper or other metals) may be formed on each flex circuit substrate. 
     Solder paste may be deposited on the surfaces of substrates  306  and  308  using solder paste patterning tool  310 . Tool  310  may include screen printing equipment or other equipment that can deposit a desired pattern of solder paste onto one or more surfaces of each flex circuit substrate. Patterned metal traces in substrates  306  and  308  may be used in forming solder pads. During solder paste deposition operations with tool  310 , solder paste may be screen printed or otherwise deposited on top of the solder pads on substrates  306  and  308 . In  FIG. 12 , solder paste patterns are shown as solder paste  312  on substrate  306  and solder paste  314  on substrate  308 . If desired, solder for forming solder connections may be deposited on a flex circuit substrate in the form of one or more balls of solid solder. Solid solder balls may be temporarily held in place on a substrate using solder resin (see, e.g., solder ball  316  of  FIG. 6 , which is being held in place by resin  318 ). 
     If desired, integrated circuits, discrete components such as resistors, inductors, capacitors, switches, and other electrical components may be mounted on solder paste  312  and  314  (see, e.g., illustrative electrical component  322  on solder paste  312  on substrate  306  in the example of  FIG. 6 ). These components may be, for example, surface mount technology (SMT) components that are attached to the flex circuit substrates using a pick and place tool (as an example). 
     Following placement of components  322  on substrate  306  using pick and place tool  320 , a heat source such as reflow oven  324  may be used to reflow the solder on substrate  306 . During the reflow process, the heat produced by oven  324  or other suitable heat source can convert the solder paste into solder connections with components  322  and/or solder balls on exposed solder pads. 
     To facilitate the formation of bends in structure  200 , substrates  306  and  308  may be bent prior to and/or during the lamination process. In this way, relatively thick structures can be formed with bends without introducing undesirably large amounts of stress. As shown in  FIG. 6 , for example, substrate  306  and substrate  308  may be laminated together using compressive fixtures and solder joint formation tool  324 . During lamination with tools  324 , substrate  306  and  308  may be compressed together and, during compression, may be held in a bent configuration. Solder joints may be formed using a heat bar, heat gun, oven, or other source of heat within tools  324 . Because substrates  306  and  308  are bent prior to lamination of substrate  306  to substrate  308 , structures  200  will tend to have minimal stress due to bending. Structures  306  and  308  may be relatively thin (e.g., 100 microns or less or 200 microns or less) and can therefore be bent without introducing excessive bending stress (e.g., when compared to bending pre-laminated substrates). 
     After the substrates have been bent into their desired shape, the lamination process can be used to attach substrates  306  and  308  together in their bent shape. Lamination may be performed using adhesive and heat and pressure (as an example). To minimize stress, it may be desirable to slightly over-bend substrates  306  and  308  within compressive fixtures  324 . Other configurations may also be used (e.g., bending substrates  306  and  308  to their desired final shape, under-bending substrates  306  and  308 , etc.). 
     Compressive fixtures  324  may include cavities such as rectangular recesses or recess with other shapes to accommodate protruding components (e.g., components such as components  322 ). Solder joints can be formed between substrates  306  during the use of tools  324 . For example, tools  324  may include heat bar equipment, an oven, or other heating equipment for reflowing solder  312 ,  314 , and/or  316 , thereby electrically connecting the traces in substrates  306  and  308 . 
     Following lamination of substrates  306  and  308  using tool  324 , substrates  306  and  308  have a desired bent shape and form structures  200 . Structures  200  may, if desired, be attached to a support structure such as carrier  326 . Carrier  326  may, for example, be formed from a dielectric such as plastic (e.g., to accommodate structures such as antenna structures, capacitive proximity sensor structures, and other structures that might potentially be affected by the presence of conductive support structures). Structures  200  may be attached to carrier  326  to form mounted structures  330  using adhesive or other suitable attachment mechanisms. 
     An illustrative set of material layers that may be used in forming substrates such substrate layers  306  and  308  of  FIG. 6  are shown in  FIG. 7 . As shown in  FIG. 7 , layer  306  may include coverlay (solder mask) layer  332 , adhesive layer  334 , a metal layer such as copper layer  336 , a polymer layer such as polyimide layer  336 , a metal layer such as copper layer  340  (which may be, if desired, shorted to layer  336  using vias through polyimide layer  338 ), adhesive layer  342 , and coverlay layer  344 . Layers  336  and  340  may, if desired, form patterned metal structures such as structures  200 L of  FIG. 5 . Layer  308  may include coverlay layer  350 , adhesive layer  352 , a metal layer such as copper layer  354 , a polymer layer such as polyimide layer  356 , and coverlay layer  358 . 
     As shown in  FIG. 7 , solder paste  312  may be patterned to mate with solder paste  314 . Following reflow operations, solder paste  312  and  314  can form a solder connection between conductive structures on layers  306  and conductive structures on layer  308  (e.g., metal layers such as layers  336 ,  340 , and  354 ). These connections may be used in forming signal paths for sensor signals, signal paths for antenna signals, and/or signal paths for other signals. Coverlay layers in layers  306  and  308  may serve as a solder mask. Adhesive  346  may be used to attach layers  306  and  308 . Adhesive  346  may be patterned to form air gaps such as air gaps  348 . Air gaps may also be formed from inspection holes within layers  306  and  308 . The inspection holes may be provided in the vicinity of solder joints to help determine whether solder joints have been formed properly. The presence of the air gaps may provide exit paths that allow gas to escape from solder paste  312  and  314  when solder paste  312  and  314  is heated. 
     In the arrangement for layers  306  and  308  that is shown in  FIG. 8 , solder  318  has been used to form a solder connection between the conductive structures on layers  306  and  308 . The thickness of each of layers  306  and  308  may be (for example) about 70-150 microns, about 40-200 microns, or other suitable thicknesses. 
       FIG. 9  is a top view of patterned adhesive  346  of  FIG. 9  (on an illustrative substrate layer shown as layer  360 ). Adhesive  346  may be patterned to form rectangular islands, elongated strips, other tiled structures, or other suitable shapes that form interspersed air gap paths  348 . Air gap paths  348  may serve as channels to allow gases to escape from structures  200  during solder reflow operations. 
       FIG. 10  is a perspective view of an illustrative substrate layer such as substrate layer  306 . As shown in  FIG. 10 , layer  306  may have alignment features such as portions  362  that form alignment holes  364 . Components  322  may be mounted on one or both sides of layer  306 . Tails such as tails  366  and  368  or other protruding structures may be used to interconnect the circuitry of layer  306  to other structures in device  10 . For example, tails  366  and  368  may be used in forming signal paths for radio-frequency signals (e.g., transmission line paths), signal paths for sensor signals, and signal paths for other signals. 
       FIG. 11  is a perspective view of an illustrative substrate layer such as layer  308 . In the configuration of  FIG. 11 , substrate layer  308  has been mounted on compressive fixture  376 . Compressive fixture  376  may form part of a two piece compressive fixture (e.g., tool  324  of  FIG. 6 ) that compresses and bends layers  306  and  308  during lamination. Fixture  376  may have a concave upper surface that mates with a convex lower surface of a mating compressive fixture. If desired, one of the compressive fixture structures may be formed from an elastomeric substance (e.g., silicone) and the other compressive fixture may be implemented using a rigid material (e.g., steel). 
     As shown in  FIG. 11 , layer  308  may have alignment features of the type provided in layer  306 . For example, layer  308  may have portions  370  with alignment holes  372 . Posts  374  of fixture  376  may protrude through holes  372 . When substrate layer  306  is placed over layer  308  for lamination, holes  364  may fit over posts  374  or other tool alignment structures. By providing layers  306  and  308  with matching alignment holes or other alignment features and by providing the compressive fixtures with mating alignment posts or other mating alignment features, layers  306  and  308  may be aligned with respect to the compressive fixtures and to each other during lamination. 
       FIGS. 12 and 13  show how layers  306  and  308  may be compressed together using compressive fixtures (tools  324 ). As shown in  FIG. 13 , layers  306  and  308  may be placed on top of each other on lower fixture  376  (e.g., using alignment features to ensure proper alignment). Fixture  376  may mate with fixture  378 . An oven or other heated chamber may be used to enclose fixture  376  and fixture  378  in tools  324  and/or other heat sources may be provided in tools  324  (e.g., a heat gun, a hot bar, etc.). The oven or other heat source may be used as a solder joint formation tool (i.e., the oven may be used to heat solder to its melting point to attach the solder structures within layers  306  and  308  to each other). Fixture  378  may be formed from a rigid material such as steel. Fixture  376  may be formed from a pliable elastomeric substance such as silicone that can conform to the shape of fixture  378  when fixture  378  is pressed against fixture  376  in direction  380 . 
     Fixture  376  may have a concave surface with a bend radius that is slightly larger than the desired bend radius for layers  306  and  308 . Fixture  378  may have a convex surface with a bend radius equal to the desired bend radius for layers  306  and  308  (i.e., a bend radius slightly smaller than the desired final bend radius for the bend in structures  200 ). When fixture  378  is pressed against fixture  376  in direction  380 , layers  306  and  308  are compressed against each other while the elastomeric material of fixture  376  allows the concave surface of fixture  376  to conform to the convex surface of fixture  378 . During the compression process, layers  308  and  306  are initially compressed together at the tip of fixture  378 . Following additional compression, the rest of layers  308  and  306  are compressed together. In this way, layers  306  and  308  are progressively compressed together starting at their centers and moving towards their peripheries. This progressive lateral compression arrangement helps to avoid formation of air bubbles between layers  306  and  308  during lamination. 
     If desired, the compressive fixtures may be provided with cavities to accommodate protruding components on structures  200 . As shown in  FIG. 14 , for example, compressive fixture  378  may be provided with cavities  382  to accommodate protruding components  322  on flex circuit layer  306 . Fixture  376  may also be provided with cavities to accommodate components. 
       FIG. 15  shows how tools  328  may be used to mount laminated flex circuit structures  200  to carrier  326 . 
     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: 20110829
Publication Date: 20140401
Grant Date: 20140401
Priority Date: 20110829
Inventors: SHIU BOON W.
JIANG YI
CHEN CHUN-LUNG
SCHLUB ROBERT W.
CABALLERO RUBEN
Assignee: APPLE INC
CPC Classifications: [{"code": "H05K2201/10151", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K3/363", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2201/10151", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01Q5/364", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K2203/167", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01Q5/364", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/243", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/38", "inventive": true, "first": true, "tree": "[]"}, {"code": "H05K3/363", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K1/028", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K1/147", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/44", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K2201/09063", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K1/147", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01Q1/38", "inventive": true, "first": true, "tree": "[]"}, {"code": "H05K2203/041", "inventive": false, "first": false, "tree": "[]"}, {"code": "Y10T156/1031", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K1/028", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K2203/167", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2203/041", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2201/09063", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01Q1/44", "inventive": true, "first": false, "tree": "[]"}, {"code": "Y10T156/1031", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 47741995