PATENT DOCUMENT

Publication Number: US-9274142-B2
Application Number: US-201113097847-A
Country: US
Kind Code: B2

Title: Testing system with capacitively coupled probe for evaluating electronic device structures

Abstract:
Conductive electronic device structures such as a conductive housing member that forms part of an antenna may be tested during manufacturing. A test system may be provided that has a capacitive coupling probe. The probe may have electrodes. The electrodes may be formed from patterned metal structures in a dielectric substrate. A test unit may provide radio-frequency test signals in a range of frequencies. The radio-frequency test signals may be applied to the conductive housing member or other conductive structures under test using the electrodes. Complex impedance data, forward transfer coefficient data, or other data may be used to determine whether the structures are faulty. A fixture may be used to hold the capacitive coupling probe in place against the conductive electronic device structures during testing.

Claims:
What is claimed is: 
     
       1. A test system for testing conductive electronic device structures under test, comprising:
 a test unit; 
 a fixture with a cavity that receives the conductive electronic device structures under test, wherein the fixture surrounds the conductive electronic device structures under test and the conductive electronic device structures under test comprise a conductive housing member that forms part of an antenna; and 
 at least one capacitively coupled probe that is coupled to the test unit, wherein the capacitively coupled probe has a metal layer that forms at least a portion of an electrode that is configured to capacitively couple to the conductive electronic device structures under test and a dielectric layer that covers the metal layer and is interposed between the metal layer and the conductive electronic device structures under test when the conductive electronic device structures under test are received within the fixture, and the metal layer and the dielectric layer are interposed between the fixture and the conductive electronic device structures under test. 
 
     
     
       2. The test system defined in  claim 1  further comprising a biasing member interposed between the fixture and the capacitively coupled probe that biases the capacitively coupled probe against the conductive electronic device structures under test such that the at least one dielectric layer is in direct contact with the conductive electronic device structures under test. 
     
     
       3. The test system defined in  claim 2  wherein the biasing member comprises foam. 
     
     
       4. The test system defined in  claim 1  further comprising:
 biasing structures that bias the at least one pin towards the metal layer. 
 
     
     
       5. The test system defined in  claim 1  wherein the fixture comprises biasing structures that hold the conductive electronic device structures under test within the fixture and the biasing structures bias the conductive electronic device structures under test towards the dielectric layer such that the conductive electronic device structures under test are in direct contact with the dielectric layer. 
     
     
       6. The test system defined in  claim 5  wherein the biasing structures comprise movable retention members. 
     
     
       7. The test system defined in  claim 6  further comprising levers that move the movable retention members. 
     
     
       8. The test system defined in  claim 7  further comprising springs coupled to the movable retention members. 
     
     
       9. The test system defined in  claim 1  wherein the test unit is configured to measure test data with the capacitively coupled probe and wherein the test data is selected from the group consisting of: inductance data, impedance data, and capacitance data. 
     
     
       10. The test system defined in  claim 1 , wherein the at least one capacitively coupled probe comprises at least one positive pin and at least one ground pin, wherein the fixture has an asymmetric opening and wherein the probe has a mating shape to ensure that the probe is inserted in the opening with a desired polarity. 
     
     
       11. The test system defined in  claim 1 , wherein the dielectric layer electrically isolates the metal layer from the conductive electronic device structures under test. 
     
     
       12. The test system defined in  claim 1 , wherein the test unit comprises a vector network analyzer. 
     
     
       13. The test system defined in  claim 1 , wherein the test unit is configured to generate and receive radio-frequency test signals. 
     
     
       14. The test system defined in  claim 1 , wherein the dielectric layer has a thickness of 20 to 30 microns. 
     
     
       15. A test system for testing conductive electronic device structures under test, comprising:
 a test unit; 
 a test fixture having a cavity for receiving the conductive electronic device structures under test; and 
 a test probe that is coupled to the test unit and that is capacitively coupled to the conductive electronic device structures under test via an electrode, wherein the test unit is configured to convey test signals over the test probe and the electrode, the test probe comprises at least one positive pin and at least one ground pin that protrude through an asymmetric opening in the test fixture, and the test probe has a mating shape to ensure that the test probe is inserted in the asymmetric opening with a desired polarity. 
 
     
     
       16. The test system defined in  claim 15 , further comprising a dielectric layer interposed between the electrode and the conductive electronic device structures under test, wherein the dielectric layer contacts the electrode and the conductive electronic device structures under test during testing. 
     
     
       17. The test system defined in  claim 15 , wherein the test probe is capacitively coupled to a first side of the conductive electronic device structures under test, further comprising:
 biasing structures formed in the test fixture at a second side of the conductive electronic device structures under test that opposes the first side, wherein the biasing structures are configured to hold the conductive electronic device structures under test within the fixture. 
 
     
     
       18. A test system for testing conductive electronic device structures under test of an electronic device, comprising:
 a test unit configured to generate test signals; 
 a first test probe that is capacitively coupled to the conductive electronic device structures under test via a first electrode, wherein the conductive electronic device structures under test comprise a conductive housing member that runs around the periphery of the electronic device, the first test probe is capacitively coupled to the conductive housing member, and the first test probe is configured to provide the test signals to the conductive housing member; and 
 a second test probe that is capacitively coupled to the conductive housing member via a second electrode, wherein the second test probe is configured to receive the test signals from the conductive housing member. 
 
     
     
       19. The test system defined in  claim 18 , further comprising:
 a test fixture in which the conductive electronic device structures under test are placed during testing. 
 
     
     
       20. The test system defined in  claim 18 , wherein the electronic device has planar front and rear surfaces and the conductive housing member surrounds a periphery of the planar front and rear surfaces. 
     
     
       21. The test system defined in  claim 18 , wherein the electronic device has a display. 
     
     
       22. The test system defined in  claim 18 , wherein the conductive housing member forms part of an antenna for the electronic device. 
     
     
       23. The test system defined in  claim 22 , wherein the conductive housing member has a gap filled with dielectric, the gap has first and second opposing sides, the first test probe is capacitively coupled to the conductive housing member at the first side of the gap, and the second test probe is capacitively coupled to the conductive housing member at the second side of the gap.

Description:
BACKGROUND 
     This relates generally to testing, and more particularly, to testing electronic device structures for manufacturing faults. 
     Electronic devices such as portable computers and cellular telephones are often provided with wireless communications capabilities. For example, electronic devices may use long-range wireless communications circuitry such as cellular telephone circuitry and short-range wireless communications circuitry such as wireless local area network circuitry. 
     In some devices, conductive housing structures may form part of an electronic device antenna. The performance of this type of antenna may depend on how accurately the conductive housing structures are manufactured. Excessive variations in the size and shape of conductive electronic device housing structures may have a negative impact on the performance of antennas formed using the structures. Variations in conductive electronic device structures of other types may also impact device performance. 
     It would therefore be desirable to be able to provide ways to test electronic device structures such as conductive electronic device structures that form parts of antennas and other structures. 
     SUMMARY 
     Electronic devices may include conductive structures such as conductive housing structures and structures associated with device components. Conductive housing structures may form part of an antenna, part of an electromagnetic shielding can, part of a printed circuit pad, or other structures. 
     To ensure that conductive electronic device structures have been fabricated properly, conductive electronic device structures may be tested during manufacturing. A test system may be provided that has a capacitive coupling probe. The capacitive coupling probe may have first and second electrodes. A probe having first and second pins may be used to couple a test unit to the capacitive coupling probe. 
     The electrodes in the capacitive coupling probe may be formed from patterned metal pad structures in a dielectric substrate such as a flexible printed circuit substrate. A test fixture may receive the conductive electronic device structures during testing. A layer of foam in the test fixture or other biasing structures may be used to bias the capacitive coupling probe against the conductive electronic device structures. The test fixture may contain retention members that help hold the conductive electronic device structures under test within the test fixture. 
     A test unit may provide radio-frequency test signals in a range of frequencies. The radio-frequency test signals may be transmitted through the conductive housing member or other conductive structures under test using the first and second capacitively coupled electrodes. Complex impedance data, forward transfer coefficient data, or other data may be used to determine whether the structures are faulty. 
     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 include conductive housing structures that may be tested in accordance with an embodiment of the present invention. 
         FIG. 2  is a top view of an illustrative electronic device of the type shown in  FIG. 1  showing the locations of gaps in a peripheral conductive housing member and the locations of possible antennas within the electronic device in accordance with an embodiment of the present invention. 
         FIG. 3A  is a top view of a portion of a conductive electronic device housing structure being tested using an electrically connected probe in accordance with an embodiment of the present invention. 
         FIG. 3B  is a top view of a portion of a conductive electronic device housing structure being tested using a capacitive coupling probe in accordance with an embodiment of the present invention. 
         FIG. 4  is a circuit diagram of a circuit that is formed with a probe that is capacitively coupled to a peripheral conductive housing member with a gap in accordance with an embodiment of the present invention. 
         FIG. 5  is an exploded perspective view of illustrative electronic device structures under test in a test system in accordance with an embodiment of the present invention. 
         FIG. 6  is an exploded perspective view of a portion of a peripheral conductive housing member with a gap and an associated capacitive coupling probe and a probe with mating spring-loaded pins in accordance with an embodiment of the present invention. 
         FIG. 7  is a cross-sectional top view of test system components and associated electronic device structures under test in accordance with an embodiment of the present invention. 
         FIG. 8  is an exploded perspective view of an illustrative test fixture in accordance with an embodiment of the present invention. 
         FIG. 9  is a graph of illustrative impedance magnitude data of the type that may be gathered using a test system in accordance with an embodiment of the present invention. 
         FIG. 10  is a graph of illustrative impedance phase data of the type that may be gathered using a test system in accordance with an embodiment of the present invention. 
         FIG. 11  is a graph of a subsection of the impedance magnitude data of  FIG. 9  showing how the measured impedance may vary as a function of the size of a gap in a peripheral conductive housing structure in accordance with an embodiment of the present invention. 
         FIG. 12  is a flow chart of illustrative steps involved in using a test system of the type shown in  FIG. 5  in testing electronic device structures in accordance with an embodiment of the present invention. 
         FIG. 13  is a perspective view showing how flex circuit electrodes in a capacitively coupled probe may conform to an electronic device structure having compound curves in accordance with an embodiment of the present invention. 
         FIG. 14  is a perspective view of a portion of a test system showing how a connector may be mounted on a flex circuit probe in a fixture in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices may be provided with wireless communications circuitry such as antennas and associated transceiver circuits. The wireless communications circuitry may be used to support wireless communications in multiple wireless communications bands. The wireless communications circuitry may include one or more antennas. 
     The antennas can include loop antennas, inverted-F antennas, strip antennas, planar inverted-F antennas, slot antennas, hybrid antennas that include antenna structures of more than one type, or other suitable antennas. Conductive structures for the antennas may, if desired, be formed from conductive electronic device structures. The conductive electronic device structures may include conductive housing structures. The housing structures may include a peripheral conductive member that runs around the periphery of an electronic device. The peripheral conductive member may serve as a bezel for a planar structure such as a display, may serve as sidewall structures for a device housing, or may form other housing structures. Gaps in the peripheral conductive member may be associated with the antennas. 
     The size of the gaps that is produced during manufacturing can influence the electrical properties of the antennas that are formed using the peripheral conductive housing members. To ensure that the gaps are formed appropriately, it may be desirable to electrically test the peripheral conductive housing member during manufacturing. The electrical test measurements may reveal undesired manufacturing variations in the gaps. Other conductive electronic device structures may also be tested in this way if desired. 
     An illustrative electronic device of the type that may be provided with conductive electronic device structures such as a peripheral conductive housing member that forms part of one or more antennas is shown in  FIG. 1 . Electronic device  10  may be a portable electronic device or other suitable electronic device. For example, electronic device  10  may be a laptop computer, a tablet computer, a somewhat smaller device such as a wrist-watch device, pendant device, headphone device, earpiece device, or other wearable or miniature device, a cellular telephone, a media player, etc. 
     Device  10  may include a housing such as housing  12 . Housing  12 , which may sometimes be referred to as a case, may be formed of plastic, glass, ceramics, fiber composites, metal (e.g., stainless steel, aluminum, etc.), other suitable materials, or a combination of these materials. In some situations, parts of housing  12  may be formed from dielectric or other low-conductivity material. In other situations, housing  12  or at least some of the structures that make up housing  12  may be formed from metal elements. 
     Device  10  may, if desired, have a display such as display  14 . Display  14  may, for example, be a touch screen that incorporates capacitive touch electrodes. Display  14  may include image pixels formed from light-emitting diodes (LEDs), organic LEDs (OLEDs), plasma cells, electronic ink elements, liquid crystal display (LCD) components, or other suitable image pixel structures. A cover glass layer may cover the surface of display  14 . Buttons and speaker port openings may pass through openings in the cover glass. 
     Housing  12  may include structures such as housing member  16 . Member  16  may run around the rectangular periphery of device  10  and display  14 . Member  16  or part of member  16  may serve as a bezel for display  14  (e.g., a cosmetic trim that surrounds all four sides of display  14  and/or helps hold display  14  to device  10 ). Member  16  may also, if desired, form sidewall structures for device  10 . 
     Member  16  may be formed of a conductive material and may therefore sometimes be referred to as a peripheral conductive housing member or conductive housing structures. Member  16  may be formed from a metal such as stainless steel, aluminum, or other suitable materials. One, two, or more than two separate structures may be used in forming member  16 . 
     It is not necessary for member  16  to have a uniform cross-section. For example, the top portion of member  16  may, if desired, have an inwardly protruding lip that helps hold display  14  in place. If desired, the bottom portion of member  16  may also have an enlarged lip (e.g., in the plane of the rear surface of device  10 ). In the example of  FIG. 1 , member  16  has substantially straight vertical sidewalls. This is merely illustrative. The sidewalls of member  16  may be curved or may have any other suitable shape. In some configurations (e.g., when member  16  serves as a bezel for display  14 ), member  16  may run around the lip of housing  12  (i.e., member  16  may cover only the edge of housing  12  that surrounds display  14  and not the rear edge of the sidewalls of housing  12 ). 
     Display  14  may include conductive structures such as an array of capacitive electrodes, conductive lines for addressing pixel elements, driver circuits, etc. Housing  12  may include internal structures such as metal frame members, a planar housing member (sometimes referred to as a midplate) that spans the walls of housing  12  (i.e., a sheet metal structure that is welded or otherwise connected between the opposing right and left sides of member  16 ), printed circuit boards, and other internal conductive structures. These conductive structures may be located in center of housing  12  (as an example). 
     In regions  20  and  22 , openings may be formed between the conductive housing structures and conductive electrical components that make up device  10 . These openings may be filled with air, plastic, and other dielectrics. Conductive housing structures and other conductive structures in device  10  may serve as a ground plane for the antennas in device  10 . The openings in regions  20  and  22  may serve as slots in open or closed slot antennas, may serve as a central dielectric region that is surrounded by a conductive path of materials in a loop antenna, may serve as a space that separates an antenna resonating element such as a strip antenna resonating element or an inverted-F antenna resonating element from the ground plane, or may otherwise serve as part of antenna structures formed in regions  20  and  22 . 
     Portions of member  16  may be provided with gap structures  18 . Gaps  18  be filled with dielectric such as polymer, ceramic, glass, etc. Gaps  18  may divide member  16  into one or more peripheral conductive member segments. There may be, for example, two segments of member  16  (e.g., in an arrangement with two gaps), three segments of member  16  (e.g., in an arrangement with three gaps), four segments of member  16  (e.g., in an arrangement with four gaps, etc.). The segments of peripheral conductive member  16  that are formed in this way may form parts of antennas in device  10 . 
     A top view of an interior portion of device  10  is shown in  FIG. 2 . If desired, device  10  may have upper and lower antennas (as an example). An upper antenna such as antenna  40 U may, for example, be formed at the upper end of device  10  in region  22 . A lower antenna such as antenna  40 L may, for example, be formed at the lower end of device  10  in region  20 . The antennas may be used separately to cover separate communications bands of interest or may be used together to implement an antenna diversity scheme or a multiple-input-multiple-output (MIMO) antenna scheme. 
     Antenna  40 L may be formed from the portions of midplate  58  and peripheral conductive housing member  16  that surround dielectric-filled opening  56 . Antenna  40 L may be fed by transmission line  50 , which is coupled to positive feed terminal  54  and ground feed terminal  52 . Other feed arrangements may be used if desired. The arrangement of  FIG. 2  is merely illustrative. 
     Antenna  40 U may be formed from the portions of midplate  58  and peripheral conductive housing member  16  that surround dielectric-filled opening  60 . Member  16  may have a low-band segment LBA that terminates at one of gaps  18  and a high-band segment HBA that terminates at another one of gaps  18 . Antenna  40 U may be fed using transmission line  62 . Transmission line  62  may be coupled to positive antenna feed terminal  66  and ground antenna feed terminal  64  (as an example). Conductive member  68  may span opening  60  to form an inverted-F antenna short-circuit path. Segments LBA and HBA may form low-band and high-band cellular telephone inverted-F antennas (as an example). 
     Gaps  18  separate respective portions of peripheral conductive housing member  16  from each other so that these portions of conductive housing member  16  form parallel plate capacitors. The capacitance associated with a typical gap may be, for example, about 1 pF. With one suitable arrangement, the width of each gap (i.e., the dimension of the gap along the longitudinal dimension of peripheral conductive housing member  16 ) may be nominally about 0.7 mm. 
     Due to manufacturing variations, there will generally be a variation in the widths of gaps  18  from device to device. In some situations, one of gaps  18  will be narrower than desired, leading to an excessive gap capacitance Cm. In other situations, a gap may be wider than desired, leading to a value of gap capacitance Cm for that gap that is lower than desired. 
     Variations in capacitance and other electrical parameters associated with conductive device structures such as peripheral conductive housing member  16  and gaps  18  can have a significant impact on the performance of device  10 . For example, variations in the width of gaps  18  may affect the frequencies in which antennas such as antennas  40 U and  40 L operate. 
     If desired, testing may be performed on structures other than conductive housing members. For example, conductive structure  16  may be associated with a conductive component structure such as an electromagnetic shielding can, may be associated with a printed circuit board pad, may be associated with conductive traces on other substrates, may be associated with other conductive components in device  10 , etc. Structures with dielectric regions  18  other than gaps can affect radio-frequency characteristics of structures  16 . For example, holes or other openings in conductive structure  16  may affect the electrical properties of structure  16 . A conductive structure such as structure  16  may be formed form two sheets of metal that are separated by a thin dielectric layer  18 . In this type of configuration or any other configuration where the size and shape of dielectric  18  relative to conductive material  16  affects radio-frequency signal propagation, device performance may be characterized by performing radio-frequency characterization measurements. 
     To ensure that gaps  18  or other conductive electronic device structures have been formed properly, a test system may be used to measure the electrical properties of the electronic device structures. For example, the capacitance of gaps  18  may be measured or other parameters such as series inductance and impedance may be measured. 
     As shown in  FIG. 3A , one way in which the capacitance Cm of gap  18  may be measured is by making electrical contact with the portions of peripheral conductive housing member  16  on opposing sides of the gap using contacts  70 . Contacts  70  may be exposed patterned metal pads on a substrate such as a flexible printed circuit substrate (dielectric substrate  80 ) or may be spring-loaded pins. In some situations, peripheral conductive housing member  16  may be formed from a metal (e.g., stainless steel) that has a non-negligible contact resistance when probed by spring-loaded pins or other contact-based probes. The surface of member  16  may also be susceptible to scratching when probed using pins. It may therefore be desirable to use a capacitively coupled probe arrangement of the type shown in  FIG. 3B . 
     In the  FIG. 3B  configuration, first and second probe terminals  72  and  74  are electrically connected to respective first and second probe pads  76  and  78  (sometimes referred to as first and second electrodes) in dielectric  80  of capacitive coupling probe  100 . Probe terminals  72  and  74  may be placed in contact with first and second probe pads  76  and  78  using a robot or other computer-controlled positioner or manually. If desired, terminals  72  and  74  may be wires or other conductive paths associated with a cable and may be soldered directly to pads  76  and  78  without using a probe. Dielectric  80  may be, for example, a sheet of polymer such as a polyimide sheet in a flexible printed circuit (“flex circuit”). Probe pads  76  and  78  may be formed from metal traces in the flex circuit. When placed against peripheral conductive housing member  16 , pad  76  and member  16  form a first parallel plate capacitor and pad  78  and peripheral conductive housing member  16  form a second parallel plate capacitor. Because pins are not used to directly probe member  16 , member  16  will generally not be scratched during testing, which may be helpful when member  16  has a cosmetic surface that should not be damaged during testing. Dielectric  80  covers electrodes  76  and  78  and, when probe  100  is placed against conductive member  16  during testing, dielectric  80  electrically isolates (insulates) electrodes  76  and  78  from conductive member  16 . Because electrical coupling is achieved without requiring direct metal-to-metal contact between the probe electrodes and member  16 , satisfactory electrical coupling can be achieved at radio-frequencies even in the presence of an oxide or other coating that may give rise to a non-negligible contact resistance when probing the conductive structure with pins. 
     As shown in  FIG. 3B , member  16  may, if desired, be covered with a dielectric coating such as coating  160 . For example, member  16  may be a metal member coated with a layer of plastic (i.e., coating  160  may be plastic and may be associated with a protective coating, a logo on a housing member, a cosmetic trim, or other structures), a native oxide such as a native oxide on stainless steel or other metals having a thickness of less than 5 microns, or other dielectric films. Interior portions of conductive structures, exterior portions (i.e., cosmetic exterior portions), combinations of interior and exterior portions, or other suitable areas on conductive structures such as member  16  may be probed if desired. 
     As shown in  FIG. 4 , signal path  82  (e.g., a coaxial cable or other transmission line) may have positive conductor  72  and ground conductor  74  (coupled to terminals  72  and  74  respectively in  FIG. 3B ). Transmission line path  82  may convey signals to and from the probe of  FIG. 3B  during testing. Capacitor C 1  represents the capacitance formed by pad  76  and peripheral conductive housing member  16 . Capacitor C 2  represents the capacitance formed by pad  78  and peripheral conductive housing member  16 . Capacitance Cm may be associated with gap  18 . In a typical configuration, the magnitudes of capacitors C 1  and C 2  may be about five to ten times greater or more than the capacitance 
     Cm, so the behavior of the series capacitance measured between terminals  72  and  74  will tend to be dominated by the behavior of the capacitance Cm of gap  18 . Series capacitance measurements between terminals  72  and  74  other electrical measurements such as complex impedance measurements that are affected by capacitance Cm may therefore be used in evaluating the size of gap  18 . Information on the size of gap  18  may be used in determining whether the conductive electronic device structures under test (e.g., member  16  with gap  18 ) or an antenna resonating element or other conductive structures have been manufactured satisfactorily. 
       FIG. 5  is a perspective view of an illustrative test system in which device structures under test  84  are being tested in test fixture  86 . Device structures under test  84  may include structures used in forming an electronic device such as electronic device  10  of  FIGS. 1 and 2 . For example, device structures under test  84  may include conductive housing structures such as peripheral conductive housing member  16 . Member  16  may have one or more dielectric-filled gaps  18 . Testing of device structures under test  84  may reveal whether member  16  contains a fault (e.g., whether or not gaps  18  are sized appropriately). 
     Fixture  86  may have a fixture base such as base  140 . Base  140  may be formed from a dielectric such as plastic (as an example). Base  140  may have a cavity such as cavity  142  that receives device structures under test  84  during testing. 
     When device structures under test  84  are placed within cavity  142 , levers  88  may be moved downwards in direction  90  around pivot  120 . This causes movable retention members  92  to move inwardly in direction  94  to serve as biasing structures that press against surface  96  of device structures under test  84 . When surface  96  is pressed in direction  94 , surface  98  is held firmly against probes  100  in cavity  142  of base  140 , ensuring satisfactory capacitive coupling between capacitive coupling probes  100  and member  16  during testing. Probes  100  may, if desired, have screen-printed alignment marks between their respective electrodes to help align structures  84  and probes  100 . 
     Base  140  may have openings such as openings  102 . Openings  102  may be configured to receive mating spring-loaded probes  104 . For example, openings  102  may have an interior shape that matches the exterior shape of probes  104 . Each probe  104  may have a positive spring-loaded pin such as spring loaded pin  106  and a ground spring-loaded pin such as pin  108 . The shapes of openings  102  and probes  104  may be asymmetric (“keyed”) to ensure that probes  104  are inserted within openings  102  using a desired polarity. When moved in direction  112  by biasing structures  110 , probes  104  may be received within openings  102  of fixture base  140 , so that pins  106  and  108  mate with respective contact pads on probe  100  (i.e., pins  106  and  108  may be shorted to pads  76  and  78  of  FIG. 3B , respectively). 
     Biasing structures  110  may include a solenoid-based actuator, a pneumatic actuator, spring members to apply biasing force in direction  112 , or other suitable biasing structures. These structures may be passive (e.g., fixed springs) or may be manually or automatically controlled. For example, biasing structures  110  may be coupled to test unit  118  by control paths  116 . Test unit  118  may contain one or more computers or other computing equipment that issues commands to biasing structures  110  using paths  116 . Fixture  140  may slide on rails such as rails  101 . The position of fixture  140  may be adjusted manually or using a positioner such as computer-controlled positioner  103  that can be adjusted using computers in test unit  118 . Using positioner  103  and/or positioners  110 , test structure  16  and probes  104  may be moved relative to each other to obtain optimal probe compression and placement. 
     Cables  114  may be coaxial cables or other transmission lines that are capable of transmitting and receiving radio-frequency signals. Cables  114  may be coupled between probes  104  and test unit  118 . Test unit  118  may include a network analyzer such as a vector network analyzer (VNA) or other test equipment that is capable of generating and receiving radio-frequency test signals. Radio-frequency test measurements made on device structures under test  84  using test unit  118 , probes  104 , and probes  100  may be analyzed using computing equipment in a network analyzer or using associated computing equipment such as an associated computer or network of computers. The computing equipment may include input-output devices such as a keyboard, mouse, and display. When testing reveals that device structures under test  84  are performing satisfactorily, an operator of the test system may be provided with a visible alert using a display in test unit  118  or other suitable actions may be taken. An operator may also be alerted in this way when testing reveals that device structures under test  84  contain a fault and are therefore not performing satisfactorily. 
     The arrangement of  FIG. 5  includes a pair of probes  104 . These probes may be used individually or may be operated simultaneously. Additional capacitive coupling probes and other types of probes may be used in test fixture  86  if desired. 
     An exploded perspective view of some of the components of the test system of  FIG. 5  is shown in  FIG. 6 . As shown in  FIG. 6 , probe  104  may include contacts such as spring-loaded pins  106  and  108  and a cable such as cable  114  having positive and ground conductive lines coupled respectively to pins  106  and  108 . Probe  100  may have a dielectric substrate such as a flex circuit substrate (substrate  80 ). Openings such as openings  122  may be used to expose contact pads in probe  100  (i.e., contact pads that allow gold-plated tips  124  of pins  106  and  108  to electrically connect with respective pads  76  and  78  of  FIG. 3B ). During testing, probe  100  may be placed against outer surface  98  of member  16  to capacitively couple probe  100  to member  16 . 
       FIG. 7  contains a cross-sectional view of probe  100 . As shown in  FIG. 7 , the dielectric substrate of probe  100  may include one or more layers such as layers  80 - 1 ,  80 - 2 , and  80 - 3 . Layers  80 - 1 ,  80 - 2 , and  80 - 3  may be polymer layers (sub-layers) such as layers of polyimide in a flex circuit layer. Layer  80 - 3  may have a thickness of about 20-30 microns (as an example). Layers  80 - 2  and  80 - 1  may have thicknesses of about 20-70 microns (as an example). One or more metal layers such as metal layers  130  may be patterned to form pads for probe  100  such as pads  76  and  78  of  FIG. 3B . In configurations with multiple metal layers, intervening vias such as metal vias  132  may be used to short the metal layers together to form unitary pad structures. Opening  122  in outermost polymer layer  80 - 1  may be used to allow contact with pins  106  and  108  when pins  106  and  108  are moved in direction  112  by biasing structures  110 . A coating of metal such as gold  123  may be used on metal  130  to reduce contact resistance and prevent oxidation. 
     Test measurement accuracy may be enhanced by ensuring that probe  100  is placed in firm contact with surface  98  of member  16 . This helps ensure that the distance between metal  130  and the metal of member  16  is uniform and is dictated by the known thickness of dielectric layer  80 - 3 . With one suitable biasing arrangement, which may be helpful when biasing probe  100  against a curved portion of member  16 , a compressible elastomeric substance such as polymer foam  128  may be interposed between the wall of fixture base  140  and probe  100  as shown in  FIG. 7 . When device structures under test  84  ( FIG. 5 ) are inserted into test fixture  86 , foam  128  will be compressed and will bias probe  100  in direction  112  towards surface  98 . If desired, other biasing structures may be used between probe  100  and the inner surface of fixture base  140  (e.g., springs, spring-based and actuator-based pushing mechanisms, levers, etc.). The biasing structures may be formed from plastic, metal, other materials, combination of these materials, etc. The use of a foam biasing member is merely illustrative. 
     An exploded perspective view of test fixture  86  is shown in  FIG. 8 . As shown in  FIG. 8 , test fixture  86  may include base  140 . Base  140  may have a cavity such as a substantially rectangular cavity (cavity  142 ) for receiving device structures under test  84  ( FIG. 5 ). Retention members  92  may have holes or other features that allow retention members to slide along rails  134  in base  140 . Springs  135  bias retention members  92  in direction  150 . When assembled, pivot members  120  are placed in holes  136  of rails  134  (passing through holes  152  in levers  88 ). Springs  135  push retention member  92  in direction  150  and create space within cavity  142  for structure  84 . When levers  88  are moved downward in direction  90 , levers  88  push retention member  92  in direction  152  and hold device structures under test  84  firmly against probes  110  within cavity  142 . 
       FIGS. 9 ,  10 , and  11  show illustrative test measurements that may be made using a test system of the type shown in  FIG. 5 . In general, any suitable characterizing electrical measurements may be made on structures  84  (impedance, capacitance, inductance, etc.). Radio-frequency measurements that are sensitive to the size of gap  18  may, for example, be made to reveal whether or not gaps  18  and member  16  have been manufactured properly. With one suitable arrangement, which is sometimes described herein as an example, radio-frequency complex impedance measurements (sometimes referred to as S 11  parameter measurements) are made by transmitting signals and measuring how much of the transmitted signals are reflected. Phase and magnitude impedance measurements may be made. If desired, radio-frequency signals may be transmitted using one of the electrodes (e.g., electrode  76 ) and received using another of the electrodes (e.g., electrode  78 ) to make S 21  measurements (sometimes referred to as forward transfer coefficient measurements). An example of a situation in which S 21  measurements may be made is when testing a cosmetic surface that runs along an exterior portion of an electronic device. The use of flex circuit electrodes such as electrodes  76  and  78  helps prevent scratches to the cosmetic surface. The S 21  measurement may be made by placing electrode  76  at one end of the cosmetic surface and by placing electrode  78  at another end of the cosmetic surface. The cosmetic surface may form a ground structure, part of an antenna, or other structure in an electronic device. The S 21  measurements may reveal defects that might affect antenna performance or other device operations. 
     In the graph of  FIG. 9 , complex impedance magnitude has been measured as a function of signal frequency over a frequency range of 0 to 5 GHz. In making these measurements, test unit  118  (e.g., a vector network analyzer) transmits radio-frequency signals and measures the reflected radio-frequency signals from the device structures under test. In the graph of  FIG. 10 , complex impedance phase (i.e., S 11  phase) has been measured over the illustrative 0 to 5 GHz frequency range.  FIG. 11  is a complex impedance magnitude plot covering a subset of the frequencies of  FIG. 9 . In particular, the data of  FIG. 11  spans the frequency range of about 0.25 GHz to 0.9 GHz. Other frequency ranges may be used when gathering complex impedance data, if desired. For example, complex impedance data (or other suitable electrical characterization data) may be gathered over a frequency range of at least 0.4 to 0.8 GHz, over a frequency range of at least 0.6 to 0.8 GHz, etc. 
     Two different sets of conductive electronic device structures under test were measured to obtain the curves of  FIGS. 9 ,  10 , and  11 . In the first set of device structures under test, member  16  has a gap that is 0.08 mm larger than the nominal 0.7 mm width of gap  18 . The 0.08 mm extra width of gap  18  in this situation may represent the largest allowable gap size that will result in acceptable performance for device  10  when gap  18  and member  16  are incorporated into an antenna in a finished device. Data corresponding to these device structures under test is represented by curves  144 . In the second set of device structures under test, member  16  has a gap that is 0.08 mm smaller than its nominal 0.7 mm width. Data for the smaller-than-normal gaps is represented by curves  146 . 
     As shown by curves  144  and  146  of  FIGS. 9 ,  10 , and  11 , there is a measureable difference in the electrical properties of device structures under test  84  when device structures under test  84  are subjected to manufacturing variations. In the present example, variations in the width of gap  18  in member  16  that forms part of an antenna have been characterized. If desired, other types of manufacturing variations that affect the electrical properties of device structures under test  84  may be characterized (e.g., changes in the size and shape of other conductive housing members, changes in the size and shape of electrical components in device structures under test  84 , etc.). 
     Illustrative steps involved in testing device structures under test  84  using a test system of the type shown in  FIG. 5  are shown in  FIG. 12 . 
     At step  148 , a test system operator may place one or more versions of electronic device structures under test  84  that have known characteristics in test fixture  86  and may gather corresponding test results. For example, impedance measurements and/or forward transfer coefficient measurements (magnitude and/or phase) may be obtained over a range of frequencies, as described in connection with  FIGS. 9 ,  10 , and  11 . The structures that are measured in this way may include substantially perfect (fault-free) structures and/or structures that exhibit acceptable manufacturing variations. For example, the structures that are measured may be members  16  that include gaps  18  that are at or near the limit of allowed variations in size from a nominal size of 0.7 mm (e.g., +/−0.08 mm). The test measurement data that is gathered during the operations of step  148  may be stored in test unit  118  to serve as baseline data (sometimes referred to as reference data or calibration data) to which subsequent test data may be compared when testing device structures of unknown quality during manufacturing. 
     After gathering baseline data on device structures with known characteristics (e.g., known gap sizes and/or gap capacitances) during the operations of step  148 , device structures may be tested in a production environment. In particular, during the operations of step  150 , a test system operator may repeatedly place device structures under test  84  into test fixture  86  and, during the operations of step  152 , may gather test data on those structures. The test structures that are placed in test fixture  86  may include conductive structures such as band  16  with gaps  18  that form part of one or more electronic device antennas or may be other conductive device structures. When inserted into test fixture  86 , levers  90 , retention members  92 , and biasing structures such as foam  128  ( FIG. 7 ) may be used to hold capacitive coupling probes such as probe  100  of  FIG. 6  in place against band  16  (or other conductive structures being tested). Biasing structures  110  may be used to hold spring-loaded pin probes  104  in place. When gathering test data during the operations of step  152 , test unit  118  may transmit radio-frequency signals and may receive reflected radio-frequency signals. The transmitted and received signals may be processed (e.g., to compute magnitude and phase impedance measurements to estimate the gaps size and/or capacitance Cm associated with gaps  18 , etc.). Test unit  118  may also transmit radio-frequency signals with one probe structure and may gather radio-frequency signals with another probe structure (i.e., to gather forward transfer coefficient measurements). 
     At step  154 , the test data that has been gathered from the device structures under test may be compared to the reference data that was collected during the calibration operations of step  148 . In particular, the test data may be evaluated to determine whether or not the test data deviates by more than an acceptable amount from the baseline data gathered during the operations of step  148 . In response to a determination that the test data is within acceptable limits, test unit  118  may issue a corresponding alert to the test system operator (e.g., by displaying a “pass” message or other suitable information on a display in test unit  118  or by issuing an audio alert) or may take other suitable actions (step  156 ). In response to a determination that the test data has varied from the reference data by more than acceptable limits, test unit  118  may issue an alert that informs the system operator that the device structures under test have failed testing or may take other suitable action (step  158 ). Structures that have passed testing may, for example, be assembled into finished products and sold to customers. Structures that have failed testing may be reworked or scrapped. 
       FIG. 13  is a perspective view showing how flex circuit electrodes in a capacitively coupled probe may conform to an electronic device structure having compound curves (i.e., a surface that curves in an arc parallel to dimension x and dimension y in the  FIG. 13  example). As shown in  FIG. 13 , probe  100  may be formed form a flexible dielectric such as flex circuit  80  that contains capacitive electrodes for coupling with curved surfaces of conductive structures  16  (e.g., a surface of an electronic device housing with convex and/or concave compound curves).  FIG. 13  also shows how shunt components may be used in probe  100 . A resistor such as resistor R may, as an example, be used to bridge electrodes  76  and  78 . Resistor R may, if desired, be formed from a surface mounted component that is soldered to the flex circuit substrate that forms probe  100 . 
       FIG. 14  is a perspective view of a portion of a test system showing how a connector such as SMA (SubMiniature version A) connector  202  has been mounted on flex circuit probe  100 . Foam  200  may be used to bias probe  100  against the surface of conductive structure  16  ( FIG. 5 ) during testing. Connector  202  may be coupled to a mating connector at the end of a cable such as cable  114  of  FIG. 5 . 
     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: 20110429
Publication Date: 20160301
Grant Date: 20160301
Priority Date: 20110429
Inventors: NICKEL JOSHUA G.
SHEN JR-YI
Assignee: APPLE INC
CPC Classifications: [{"code": "G01R31/312", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01R1/07", "inventive": true, "first": true, "tree": "[]"}, {"code": "G01R31/312", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01R1/07", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 47067414