Patent Publication Number: US-9431699-B2

Title: Structures for forming conductive paths in antennas and other electronic device structures

Description:
This application is a division of patent application Ser. No. 13/024,300, filed Feb. 9, 2011, which claims the benefit of provisional patent application No. 61/431,520, filed Jan. 11, 2011, which are hereby incorporated by reference herein in its entirety. This application claims the benefit of and claims priority to patent application Ser. No. 13/024,300, filed Feb. 9, 2011 and provisional patent application No. 61/431,520, filed Jan. 11, 2011. 
    
    
     BACKGROUND 
     This relates generally to electronic devices, and, more particularly, to conductive electronic device structures such as structures that form conductive paths for antennas and other electronic device structures. 
     Electronic devices such as cellular telephones and other devices often contain wireless communications circuitry. The wireless communications circuitry may include, for example, cellular telephone transceiver circuits for communicating with cellular telephone networks. Wireless communications circuitry in an electronic device may also include wireless local area network circuits and other wireless circuits. Antenna structures are used in transmitting and receiving wireless signals. 
     To satisfy consumer demand for small form factor wireless devices, manufacturers are continually striving to implement wireless communications circuitry such as antennas using compact arrangements. At the same time, it may be desirable to include conductive structures such as metal device housing components in an electronic device. Because conductive components can affect radio-frequency performance, care must be taken when incorporating antennas into an electronic device that includes conductive structures. In some arrangements, it may be desirable to use conductive housing structures in forming antenna structures for a device. Doing so may entail formation of electrical connections between different portions of the device. For example, it may be desirable to form an electrical connection between internal device components and a conductive peripheral housing member. 
     The presence of wireless communications circuitry in environments that contain cameras and other electrical components that can generate interference also poses challenges. If care is not taken, signals from an electronic component source can disrupt the operation of the wireless circuitry. 
     In view of these challenges, it may be desirable to be able to form electrical connections between different portions of an electronic device. It may, for example, be desirable to bridge a gap in an antenna or to form ground paths that help ground conductive portions of a device and thereby suppress interference. 
     SUMMARY 
     Electronic devices may be provided that contain conductive paths. A conductive path may be formed from an elongated metal member that extends across a dielectric gap in an antenna. The elongated metal member may be a strip of stainless steel that is welded to conductive structures at either end using a laser welding process that is suitable for volume manufacturing. 
     The antenna may be formed from conductive structures that form an antenna ground and conductive structures that are part of a peripheral conductive housing member in the electronic device. The conductive structures that form the antenna ground may include planar metal housing structures. The gap may separate the peripheral conductive housing member from the planar metal housing structures. 
     A conductive path may also be formed using one or more springs. A spring may be welded to a conductive member and may have prongs that press against an additional conductive member when the spring is compressed. The prongs may have narrowed tips to accentuate the force produced by the tips on opposing metal surfaces, thereby ensuring satisfactory electrical contact. Curved prong shapes and burrs on the spring prongs may also help form a satisfactory electrical contact between the spring prongs and opposing metal surfaces. 
     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 of the type that may be provided with antenna structures in which an electrical connection is made to a conductive housing structure such as a conductive peripheral housing member and in which signal paths may be formed using conductive structures such as springs in accordance with an embodiment of the present invention. 
         FIG. 2  is a top interior view of an electronic device of the type shown in  FIG. 1  in which electrical connections are made to a conductive peripheral housing member in accordance with an embodiment of the present invention. 
         FIG. 3  is a diagram showing illustrative structures that may be used in forming an electrical connection between an internal housing structure such as a ground plate member and a conductive peripheral housing member in accordance with an embodiment of the present invention. 
         FIG. 4  is a top view of the illustrative structures of  FIG. 3  in accordance with an embodiment of the present invention. 
         FIG. 5  is a side view of a portion of an electronic device showing how a conductive member that is connected to the upper surface of a ground plane member may bridge a dielectric gap between the ground plane member and a peripheral conductive housing member in accordance with an embodiment of the present invention. 
         FIG. 6  is a side view of a portion of an electronic device showing how a conductive member that is connected to the lower surface of a ground plane member may bridge a dielectric gap between the ground plane member and a peripheral conductive housing member in accordance with an embodiment of the present invention. 
         FIG. 7  is a perspective view of a bracket on which a pair of multi-prong springs has been mounted in accordance with an embodiment of the present invention. 
         FIG. 8  is a cross-sectional side view of a portion of an electronic device that includes a component such as camera that has been mounted within a bracket that is grounded using multi-prong springs in accordance with an embodiment of the present invention. 
         FIG. 9  is a cross-sectional side view of an illustrative conductive member such as a bracket having a pair of multi-prong springs in their uncompressed state in accordance with an embodiment of the present invention. 
         FIG. 10  is a cross-sectional side view of an illustrative conductive member such as a bracket having a pair of multi-prong springs in their compressed state in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices may be provided with conductive structures. For example, electronic devices may be provided with conductive structures that form antennas, electromagnetic shields, and other components. Conductive paths may be formed between the conductive structures. For example, a conductive member may be used to bridge a dielectric gap in an antenna and conductive spring structures may be provided that help form electrical connections between conductive parts of an electronic device such as grounded metal structures. 
     An illustrative electronic device of the type that may contain conductive structures such as these is shown in  FIG. 1 . Device  10  of  FIG. 1  may be a notebook computer, a tablet computer, a computer monitor with an integrated computer, a desktop computer, or other electronic equipment. If desired, electronic device  10  may be a portable device such as a cellular telephone, a media player, other handheld devices, a wrist-watch device, a pendant device, an earpiece device, or other compact portable device. 
     As shown in  FIG. 1 , device  10  may have a housing such as housing  11 . Housing  11  may be formed from materials such as plastic, metal, carbon fiber and other fiber composites, ceramic, glass, wood, other materials, or combinations of these materials. Device  10  may be formed using a unibody construction in which some or all of housing  11  is formed from a single piece of material (e.g., a single cast or machined piece of metal, a single piece of molded plastic, etc.) or may be formed from frame structures, housing sidewall structures, and other structures that are assembled together using fasteners, adhesive, and other attachment mechanisms. In the illustrative arrangement shown in  FIG. 1 , housing  11  includes conductive peripheral housing member  12 . Conductive peripheral housing member  12  may have a ring shape that runs around the rectangular periphery of device  10 . One or more gaps such as gaps  30  may be formed in conductive peripheral housing member  12 . Gaps such as gaps  30  may be filled with dielectric such as plastic and may interrupt the otherwise continuous shape of conductive peripheral housing member. Conductive peripheral housing member may have any suitable number of gaps  30  (e.g., more than one, more than two, three or more, less than three, etc.). 
     Conductive peripheral housing member  12  may be formed from a durable material such as metal. Stainless steel may be used for forming housing member  12  because stainless steel is aesthetically appealing, strong, and can be machined during manufacturing. Other metals may be used if desired. The rear face of housing  11  may be formed from plastic, glass, metal, ceramic composites, or other suitable materials. For example, the rear face of housing  11  may be formed form a plate of glass having regions that are backed by a layer of internal metal for added strength. Conductive peripheral housing member  12  may be relatively short in vertical dimension Z (e.g., to serve as a bezel for display  14 ) or may be taller (e.g., to serve as the sidewalls of housing  11  as shown in the illustrative arrangement of  FIG. 1 ). 
     Device  10  may include components such as buttons, input-output port connectors, ports for removable media, sensors, microphones, speakers, status indicators, and other device components. As shown in  FIG. 1 , for example, device  10  may include buttons such as menu button  16 . Device  10  may also include a speaker port such as speaker port  18  (e.g., to serve as an ear speaker for device  10 ). 
     Wireless communications circuitry in electronic device  10  may be used to support wireless communications in one or more wireless communications bands. Antenna structures in electronic device  10  may be used in transmitting and receiving radio-frequency signals. 
     One or more antennas may be formed in device  10 . The antennas may, for example, be formed in locations such as locations  24  and  26  to provide separation from the conductive elements of display  14 . Antennas may be formed using single band and multiband antenna structures. Examples of communications bands that may be covered by the antennas include cellular telephone bands (e.g., the bands at 700 MHz, 850 MHz, 900 MHz, 1800 MHz, 1900 MHz, and 2100 MHz), satellite navigation bands (e.g., the Global Positioning System band at 1575 MHz), wireless local area network bands such as the IEEE 802.11 (WiFi®) bands at 2.4 GHz and 5 GHz, the Bluetooth band at 2.4 GHz, etc. Examples of antenna configurations that may be used for the antennas in device  10  include monopole antennas, dipole antennas, strip antennas, patch antennas, inverted-F antennas, coil antennas, planar inverted-F antennas, open slot antennas, closed slot antennas, loop antennas, hybrid antennas that include antenna structures of multiple types, or other suitable antenna structures. 
     Device  10  may include one or more displays such as display  14 . Display  14  may be a liquid crystal display (LCD), an organic light-emitting diode (OLED) display, a plasma display, an electronic ink display, etc. A touch sensor may be incorporated into display  14  (i.e., display  14  may be a touch screen). The touch sensor may be an acoustic touch sensor, a resistive touch sensor, a piezoelectric touch sensor, a capacitive touch sensor (e.g., a touch sensor based on an array of indium tin oxide capacitor electrodes), or a touch sensor based on other touch technologies. 
     Display  14  may be covered by a transparent planar conductive member such as a layer of glass or plastic. The cover layer for display  14 , which is sometimes referred to as a cover glass layer or cover glass, may extend over substantially all of the front face of device  10 , as shown in  FIG. 1 . The rectangular center portion of the cover glass (surrounded by dashed line  20  in  FIG. 1 ) contains an array of image pixels and is sometimes referred to as the active portion of the display. The peripheral outer portion of the cover glass (i.e., rectangular peripheral ring  22  of  FIG. 1 ) does not contain any active image pixels and is sometimes referred to as the inactive portion of display  14 . A patterned opaque masking layer such as a peripheral ring of black ink may be formed under inactive portion  22  to hide interior device components from view by a user. 
       FIG. 2  is a top view of the interior of device  10  showing how antennas  40 L and  40 U may be implemented within housing  11  and housing member  12 . As shown in  FIG. 2 , ground plane G may be formed within housing  11  and may be surrounded by peripheral conductive housing member  12 . Ground plane G may form antenna ground for antennas  40 L and  40 U. Because ground plane G may serve as antenna ground, ground plane G may sometimes be referred to as antenna ground, ground, or a ground plane element (as examples). One or more printed circuit boards or other mounting structures may be used to mount components  31  in device  10 . Components  31  may include radio-frequency transceiver circuits that are coupled to antennas  40 U and  40 L using transmission lines  52 L and  52 U, processors, application-specific integrated circuits, cameras, sensors, switches, connectors, buttons, and other electronic device components. 
     In central portion C of device  10 , ground plane G may be formed by conductive structures such as a conductive housing midplate member (sometimes referred to as an internal housing plate or planer internal housing structures). The structures of ground plane G may be connected between the left and right edges of member  12 . Printed circuit boards with conductive ground traces (e.g., one or more printed circuit boards used to mount components  31 ) may form part of ground plane G. 
     The midplate member may have one or more individual sections (e.g., patterned sheet metal sections) that are welded together. Portions of the midplate structures may be covered with insert-molded plastic (e.g., to provide structural support in portions of the interior of device where no conductive ground is desired, such dielectric-filled portions of antennas  40 U and  40 L in regions  24  and  26 ). 
     At ends  24  and  26  of device  10 , the shape of ground plane G may be determined by the shapes and locations of conductive structures that are tied to ground. Ground plane G in the simplified layout of  FIG. 2  has a straight upper edge UE and a straight lower edge LE. In actual devices, the upper and lower edges of ground plane G and the interior surface of peripheral conductive housing member  12  generally have more complex shapes determined by the shapes of individual conductive structures that are present in device  10 . Examples of conductive structures that may overlap to form ground plane G and that may influence the shape of the inner surface of member  12  include housing structures (e.g., a conductive housing midplate structure, which may have protruding portions), conductive components (e.g., switches, cameras, data connectors, printed circuits such as flex circuits and rigid printed circuit boards, radio-frequency shielding cans, buttons and conductive button mounting structures), and other conductive structures in device  10 . In the illustrative layout of  FIG. 2 , the portions of device  10  that are conductive and tied to ground to form part of ground plane G are shaded and are contiguous with central portion C. 
     Openings such as openings  138  and  140  (sometimes referred to as gaps) may be formed between ground plane G and respective portions of peripheral conductive housing member  12 . Openings  138  and  140  may be filled with air, plastic, and other dielectrics and are therefore sometimes referred to as dielectric-filled gaps or openings. Openings  138  and  140  may be associated with antenna structures  40 U and  40 L. 
     Lower antenna  40 L may be formed by a loop antenna structure having a shape that is determined at least partly by the shape of the lower portions of ground plane G and conductive housing member  12 . In the example of  FIG. 2 , opening  138  is depicted as being rectangular, but this is merely illustrative. In practice, the shape of opening  138  may be dictated by the placement of conductive structures in region  26  such as a microphone, flex circuit traces, a data port connector, buttons, a speaker, etc. 
     Lower antenna  40 L may be fed using an antenna feed made up of positive antenna feed terminal  58 L and ground antenna feed terminal  54 L. Transmission line  52 L may be coupled to the antenna feed for lower antenna  40 L. Gap  30 ′ may form a capacitance that helps configure the frequency response of antenna  40 L. If desired, device  10  may have conductive housing portions, matching circuit elements, and other structures and components that help match the impedance of transmission line  52 L to antenna  40 L. 
     Antenna  40 U may be a two-branch inverted-F antenna. Transmission line  52 U may be used to feed antenna  40 U at antenna feed terminals  58 U and  54 U. Conductive structures  150  may form a shorting path that bridges dielectric opening  140  and electrically shorts ground plane G to peripheral housing member  12 . Conductive structure  148  (which may be formed using structures of the type used in forming structures  150  or other suitable structures) and matching circuit M may be used to connect antenna feed terminal  58 U to peripheral conductive member  12  at point  152 . Conductive structures such as structures  148  and  150  (which are sometimes referred to as conductive paths) may be formed by flex circuit traces, conductive housing structures, springs, screws, welded connections, solder joints, brackets, metal plates, or other conductive structures. 
     Gaps such as gaps  30 ′,  30 ″, and  30 ′″ (e.g., gaps  30  of  FIG. 1 ) may be present in peripheral conductive member  12 . A phantom gap may be provided in the lower right-hand portion of device  10  for aesthetic symmetry if desired. The presence of gaps  30 ′,  30 ″, and  30 ′″ may divide peripheral conductive housing member  12  into segments. As shown in  FIG. 2 , peripheral conductive member  12  may include first segment  12 - 1 , second segment  12 - 2 , and third segment  12 - 3 . 
     Segment  12 - 1  may form antenna resonating element arms for antenna  40 U. In particular, a first portion (segment) of segment  12 - 1  may extend from point  152  (where segment  12 - 1  is fed) to the end of segment  12 - 1  that is defined by gap  30 ″ and a second portion (segment) of segment  12 - 1  may extend from point  152  to the opposing end of segment  12 - 1  that is defined by gap  30 ′″. The first and second portions of segment  12 - 1  may form respective branches of an inverted F antenna and may be associated with respective low band (LB) and high band (HB) antenna resonances for antenna  40 U. The relative positions of structures  148  and  150  along the length of member  12 - 1  may affect the response of antenna  40 U and may be selected to tune antenna  40 U. Antenna tuning adjustments may also be made by adjusting matching circuit M, by adjusting the configuration of components used in forming paths  148  and  150 , by adjusting the shapes of opening  140 , etc. Antenna  40 L may likewise be adjusted. 
     With one illustrative arrangement, antenna  40 L may cover the transmit and receive sub-bands in five communications bands (e.g., 850 MHz, 900 MHz, 1800 MHz, 1900 MHz, and 2100 MHz). Antenna  40 U may, as an example, be configured to cover a subset of these five illustrative communications bands. For example, antenna  40 U may be configured to cover a two receive bands of interest and, with tuning, four receive bands of interest. 
     Illustrative structures that may be used to form shorting path  150  of  FIG. 2  (e.g., the electrical path in antenna  40 U that spans peripherally enclosed dielectric opening  140  and to short conductive peripheral housing member  12  to ground plane G) are shown schematically in  FIG. 3 . As shown in  FIG. 3 , path  150  may include one or more components such as conductive member  104  that bridge dielectric gap  140 . One end of conductive member  104  may be connected to the underside of lip portion  12 ′ of peripheral conductive housing member  12 . The other end of conductive member  104  may have a portion such as portion  102  that is connected to ground structures G (e.g., a conductive metal housing midplate member or other conductive housing structures). Portion  102  of member  104  may have an opening such as a circular hole or other engagement feature that engages with a mating engagement feature associated with ground plane structures G. For example, a nut, post, or other part (shown as engagement member  106  in the  FIG. 3  example) may form a protruding structure that is configured to pass through a circular opening in portion  102  of member  104 . Member  106  may be formed from a material such as metal (as an example). This type of engagement feature arrangement may facilitate device assembly. 
     Conductive member  104  and engagement feature  106  may be formed from a metal such as stainless steel. Welds, conductive adhesive, solder, or other attachment mechanisms may be used in connecting engagement feature  106  to ground structures G and may be used in connecting the ends of conductive member  104  to device  10 . For example, welds may be used to weld conductive member  104  to lip  12 ′ in peripheral conductive housing member  12  and welds may be used to weld portion  102  of conductive member  104  to ground structures G and/or engagement feature  106 . 
       FIG. 4  is a top view of the components of  FIG. 3  showing how a portion of conductive member  104  such as portion  104 ′ (shown in dashed lines) may be enlarged to ensure that there is adequate surface area at the attachment point between conductive member  104  and peripheral conductive housing member  12 . The main elongated body portion of conductive member  104  may be formed from a strip of stainless steel or other metal. Conductive member  104  may, for example, have an elongated body portion with a thickness of about 0.03 to 0.8 mm and a width of about 0.05 to 2 mm (as examples). 
       FIG. 5  is a side view of a portion of device  10  showing how conductive member  104  may span dielectric gap  140  between ground structures G and peripheral conductive housing member  12  in antenna  40 U. In the configuration of  FIG. 5 , member  104  has been attached to upper surface  112  of ground structures G using welds  108 . Engagement structure  106  (e.g., a nut, metal post, or other suitable structure that mates with the hole or other engagement feature on conductive member  104 ) may be welded to lower surface  114  of ground structures G using welds  110 . Welds  116  may be used to weld portion  104 ′ of conductive member  104  to lower surface  118  of portion  12 ′ of peripheral conductive housing member  12 . 
     Welds  108 , welds  110 , welds  116 , and the other welds used in device  10  may be laser welds or welds formed using other suitable welding technologies. 
     As shown by the illustrative configuration of  FIG. 6 , conductive member  104  may, if desired, be attached to the lower surface of ground structures G. In the  FIG. 6  arrangement, upper surface  126  of engagement structure  106  (e.g., a nut, alignment post, or other engagement member) has been mechanically and electrically attached to lower surface  114  of ground structures G using welds  122 . Conductive member  104  has been welded to lower surface  120  of member  106  using welds  124 . 
     Using an arrangement of the type shown in  FIG. 5 , using an arrangement of the type shown in  FIG. 6 , or using other suitable configurations, conductive member  104  may form a conductive path in antenna  40 U such as conductive path  150  of  FIG. 2 . 
     If desired, electronic device may include conductive paths that form part of an electromagnetic shielding structure. For example, device  10  may have conductive structures such as structures  216  of  FIG. 7 . Conductive structures  216  may include a metal member such as bracket  204  and one or more springs such as springs  200 . 
     Bracket  204  may have legs  206  with rounded portions that engage mating features on other structures in device  10 . Bracket  204  may be attached to portions of grounding structures G ( FIG. 2 ) or other suitable housing structures. If desired, conductive structures  216  may be formed from other types of conductive members. The example of  FIG. 7  in which springs  200  are mounted to bracket  204  is merely illustrative. 
     Springs  200  may be attached to bracket  204  (or other suitable conductive structures) using welds such as welds  214 . Engagement features such as holes  202  may be provided in springs  200  for use in positioning springs  200  properly during assembly by fabrication equipment. 
     Springs  200  may have one or more prongs such as prongs  208 . In the illustrative configuration of  FIG. 7 , springs  200  have multiple prongs  208 , so that each respective pair of adjacent prongs  208  is separated by a respective one of gaps (air gaps)  212 . 
     Prong tips  210  may have a tapered shape (i.e., a shape in which the tips are narrower than the width of the main elongated body portions of prongs  208 ). In the example of  FIG. 7 , prong tips  210  are curved (rounded). Other tapered prong tip shapes that may be used in springs  200  include pointed tips with straight sides (e.g., triangular tips), trapezoidal tips, oval-shaped tips, and tip shapes with combinations of curved and straight edges. 
     Prongs  208  may be curved upwards to form the concave profile exhibited in  FIG. 7 . This may help ensure that tips  210  of spring  200  wipe along the surface of any member against which spring  200  is pressed during spring compression. The metal member that tips  210  of spring  200  press against may be, for example, a metal plate on an electrical device component, a planar metal housing structure, or other conductive planar member with which it is desired to form an electrical contact. 
       FIG. 8  shows how the conductive structures of  FIG. 7  may be used in mounting an electronic device component such as component  236  within device  10 . 
     In the example of  FIG. 8 , component  236  is a camera. The lens of the camera is mounted in alignment with opening  236  in ink layer  232  on the inner surface of transparent display cover layer  230  (e.g., the cover glass for display  14 ). Plastic bracket  234  may be attached to cover layer  230  using adhesive (as an example). 
     Ground structures G may have bent portions with openings such as openings  240  that receive bent portions of bracket legs  206 . This holds bracket  204  in place. A flex circuit such as flex circuit  226  may contain conductive traces such as traces  228 . Traces  228  may include signal and power traces for conveying signals and power to camera  236 . Traces  228  may include a ground trace that is grounded to metal flex circuit ground pad  224 . A conductive member such as stainless steel stiffener  222  may optionally be interposed between the lower one of springs  200  on bracket  204  and ground member (trace)  224 . The upper one of springs  200  may be interposed between bracket  204  and trace  218  on printed circuit board  217 . Trace  218  on printed circuit board  217  may be formed from a gold pad or other conductive member. 
     Trace  218  may form printed circuit ground  220 . Pad  224  and stiffener  222  may form camera ground  242 . Ground structures G may form housing ground  238 . When springs  200  are compressed as shown in  FIG. 8 , a reliable and low-resistance pathway is formed between member  218  and bracket  204  (by the upper spring) and between bracket  204  and members  222  and  224  (by the lower spring). This ensures that grounds  220 ,  242 , and  238  are shorted together, thereby forming an electromagnetic shielding structure that helps prevent interference from camera  236  from reaching wireless circuitry in device  10 . 
       FIGS. 9 and 10  show how springs  200  may move during compression of springs  200  against adjoining conductive structures. Springs  200  are shown in their uncompressed state in  FIG. 9 . Following compression, springs  200  appear as shown in  FIG. 10 . Arrangements of the type shown in  FIG. 10  are typically present following assembly of springs  200  into a finished electronic device such as device  10 . 
     In the configuration shown in  FIG. 9 , springs  200  are uncompressed, so prongs  208  are curved away from bracket  204 . Burrs such as burrs  244  may be formed as a result of stamping springs  200  from sheet metal. Burrs  244  are preferably oriented to face the opposing conductive members against which prongs  208  press during spring compression to aid in breaking through any insulating coatings on these conductive members. 
     When member  218  is pressed downwards in direction  246 , springs  200  are compressed between member  222  and member  218 . This causes tips  210  of springs  200  to move outwards in directions  248 . When moving outwards, tips  210  of the upper one of springs  200  wipe (scrape) along lower surface  250  of member  218  and tips  210  of the lower one of springs  200  wipe along the upper surface of member  222 . This wiping action and the presence of burrs  244  helps tips  210  break through any oxides or other insulating materials that may be present on the surfaces of members  218  and  222 . The breaking force of tips  210  may be accentuated by the narrowed shape of tips  210  (i.e., tips that are narrower than the elongated body portions of the prongs), because the reduced surface area associated with the narrowed tips helps to increase the pressure exerted by the tips per unit area. The use of a relatively large number of narrow-tip prongs (e.g., four or more, six or more, etc.) for each spring rather than using fewer prongs with larger tips therefore helps form satisfactory ohmic contacts between springs  200  and members  218  and  222 . 
     Another factor that enhances the performance of springs  200  relates to the curved shape of prongs  208 . This shape helps to ensure that tips  210  travel along a relatively large distance on the surfaces of member  218  and  222  and therefore form a satisfactory wiping motion to break through oxides and other insulating coatings that may be present. 
     The lateral dimensions of springs  200  may be on the order of 1-10 mm (as an example). The thickness of springs  200  may be, for example, 0.05 to 0.2 mm. The amount of vertical travel that is experienced by the tips of springs  210  during compression may be about 0.5 to 3 mm (as an example). 
     In a typical configuration, the ratio of the vertical compression distance to the thickness of the spring (sometimes referred to as the spring&#39;s dynamic range) may be about 5 to 20. In contrast, conventional conductive foam pads may have a dynamic range of 0.75. The surface of the metal parts that are contacted by conventional conductive foam pads may also be subject to corrosion, leading to deterioration of the ohmic contact formed between the foam and the metal parts over time. 
     Springs  200  may therefore be advantageous in configurations in which thin reliable electrical contacts are desired. The use of multiple prongs with narrowed tips, curved prong shapes, and burrs may establish a satisfactory wiping action when springs  200  are compressed. The use of upper and lower springs that are identical may help stabilize springs  200  and the structures to which springs  200  are attached during spring compression and may help balance spring forces. The use of springs that have a symmetric outline (e.g., the use of a laterally symmetric spring shape having three prongs that extend outward from one side of the spring and having three prongs that extend in the opposite direction from an opposing side of the spring) may help ensure stability and prevent tilting that might reduce the effectiveness of the spring tips in wiping the surface of the adjacent metal. 
     Although sometimes described in connection with forming grounding structures for a component such as a camera, springs  200  may be used in any configuration within device  10  or elsewhere in which an electrical connection between multiple conductive structures is desired. 
     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.