PATENT DOCUMENT

Publication Number: US-9164159-B2
Application Number: US-201213715648-A
Country: US
Kind Code: B2

Title: Methods for validating radio-frequency test stations

Abstract:
A manufacturing system for assembling wireless electronic devices is provided. The manufacturing system may include test stations for testing the radio-frequency performance of components that are to be assembled within the electronic devices. A reference test station may be calibrated using calibration coupons having known radio-frequency characteristics. The calibration coupons may include transmission line structures. The reference test station may measure verification standards to establish baseline measurement data. The verification standards may include circuitry having electrical components with given impedance values. Many verification coupons may be measured to enable testing for a wide range of impedance values. Test stations in the manufacturing system may subsequently measure the verification standards to generate test measurement data. The test measurement data may be compared to the baseline measurement data to characterize the performance of the test stations to ensure consistent test measurements across the test stations.

Claims:
What is claimed is: 
     
       1. A method of validating a plurality of inspection test stations, the method comprising:
 with a plurality of calibration reference structures, calibrating at least one master test station that is different from the plurality of inspection test stations; 
 testing a plurality of verification reference structures with the at least one master test station after calibrating the at least one master test station with the plurality of calibration reference structures; and 
 using the plurality of verification reference structures that have been tested with the at least one master test station, determining whether each inspection test station in the plurality of inspection test stations has satisfactory performance. 
 
     
     
       2. The method defined in  claim 1 , wherein the verification reference structures comprise impedance modeling circuitry and conductive contacts formed on a substrate, the method further comprising:
 removing systematic errors associated with the substrate and the conductive contacts of the verification reference structures by calibrating the at least one master test station with the plurality of calibration reference structures. 
 
     
     
       3. The method defined in  claim 1 , wherein determining whether each inspection test station in the plurality of inspection test stations has satisfactory performance comprises:
 with each inspection test station in the plurality of inspection test stations, providing test signals to the verification reference structures; and 
 with each inspection test station in the plurality of inspection test stations, measuring scattering parameters associated with the verification reference structures. 
 
     
     
       4. The method defined in  claim 1 , further comprising:
 obtaining baseline measurement data by testing the plurality of verification reference structures with the at least one master test station; 
 obtaining test measurement data by testing the plurality of verification test structures with each inspection test station in the plurality of inspection test stations; and 
 comparing the test measurement data to the baseline measurement data to determine whether each inspection test station in the plurality of inspection test stations has satisfactory performance. 
 
     
     
       5. The method defined in  claim 4 , wherein each inspection test station in the plurality of inspection test stations includes a vector network analyzer and a test fixture and determining whether each inspection test station in the plurality of inspection test stations has satisfactory performance comprises:
 removing systematic errors associated with the vector network analyzer and the test fixture of each inspection test station in the plurality of inspection test stations prior to comparing the test measurement data to the baseline measurement data. 
 
     
     
       6. The method defined in  claim 1 , wherein each inspection test station in the plurality of inspection test stations includes a test host, the method further comprising:
 with the test host, generating offset data to calibrate an inspection test station in the plurality of inspection test stations that has unsatisfactory performance. 
 
     
     
       7. The method defined in  claim 1 , wherein the calibration reference structures each include a transmission line structure and calibrating the at least one master test station comprises:
 with the at least one master test station, measuring radio-frequency characteristics associated with the transmission line structure. 
 
     
     
       8. The method defined in  claim 7 , wherein each calibration reference structure has a respective transmission line structure and measuring the radio-frequency characteristics associated with the transmission line structure comprises:
 measuring the radio-frequency characteristics of the respective transmission line structure in each of the plurality calibration reference structures. 
 
     
     
       9. The method defined in  claim 8 , further comprising:
 measuring the radio-frequency characteristics of the respective transmission line structure in each calibration reference structure using a THRU-REFLECT-LINE (TRL) approach. 
 
     
     
       10. The method defined in  claim 7 , wherein the radio-frequency characteristics include scattering parameters associated with the calibration reference structures and calibrating the at least one master test station further comprises:
 measuring the scattering parameters associated with calibration reference structures using the at least one master test station. 
 
     
     
       11. A method of calibrating a master test station, the method comprising:
 sequentially coupling the master test station to each passive reference test structure of a plurality of passive reference test structures; 
 with the master test station, obtaining calibration measurement data by testing each of the passive reference test structures of the plurality of passive reference test structures while the passive reference test structures are coupled to the master test station; and 
 calibrating the master test station using calibration data generated by comparing the obtained calibration measurement data to reference data. 
 
     
     
       12. The method defined in  claim 11 , wherein obtaining the calibration measurement data comprises:
 with the master test station, measuring radio-frequency characteristics associated with each passive reference test structure in the plurality of passive reference test structures. 
 
     
     
       13. The method defined in  claim 12 , wherein the reference data includes predetermined radio-frequency characteristics associated with each passive reference test structure in the plurality of passive reference test structures and comparing the calibration measurement data to the reference data comprises:
 comparing the measured radio-frequency characteristics to the predetermined radio-frequency characteristics. 
 
     
     
       14. The method defined in  claim 12 , further comprising:
 with an additional master test station, measuring radio-frequency characteristics associated with each passive reference test structure in the plurality of passive reference test structures to obtain additional test data, wherein comparing the calibration measurement data to the reference data comprises comparing the calibration measurement data the to the additional test data. 
 
     
     
       15. The method defined in  claim 13 , wherein the measured radio-frequency characteristics comprise scattering parameters associated with each passive reference test structure in the plurality of passive reference test structures and the predetermined radio-frequency characteristics comprise predetermined scattering parameters associated with each passive reference test structure in the plurality of passive reference test structures, the method further comprising:
 comparing the measured scattering parameters to the predetermined scattering parameters. 
 
     
     
       16. A method of validating a plurality of inspection test stations, the method comprising:
 sequentially coupling each inspection test station of the plurality of inspection test stations to each passive reference test structure of a plurality of passive reference test structures; 
 with each inspection test station in the plurality of inspection test stations, obtaining verification measurement data by performing radio-frequency testing on each of the passive reference test structures of the plurality of passive reference test structures while each of the passive reference test structures of the plurality of passive reference test structures is coupled to that inspection test station; and 
 determining whether each inspection test station in the plurality of inspection test stations has satisfactory performance by comparing the verification measurement data to reference data. 
 
     
     
       17. The method defined in  claim 16 , wherein the reference data is generated by a master test station using the plurality of passive reference test structures and determining whether each inspection test station in the plurality of inspection test stations has satisfactory performance comprises:
 comparing the verification measurement data to reference data generated by the master test station. 
 
     
     
       18. The method defined in  claim 16 , wherein obtaining the verification measurement data comprises:
 with the inspection test stations, measuring scattering parameters associated with each passive reference test structure in the plurality of passive reference test structures. 
 
     
     
       19. The method defined in  claim 18 , wherein the passive reference test structures include circuitry and conductive contacts coupled to the circuitry, the circuitry comprises one or more electrical components connected between the conductive contacts in a shunt configuration, and measuring the scattering parameters associated with each passive reference test structure comprises:
 measuring the scattering parameters associated with the one or more electrical components connected between the conductive contacts in the shunt configuration. 
 
     
     
       20. The method defined in  claim 18 , wherein the passive reference test structures include circuitry and conductive contacts coupled to the circuitry, the circuitry comprises one or more electrical components connected between the conductive contacts in a series configuration, and measuring the scattering parameters associated with each passive reference test structure comprises:
 measuring the scattering parameters associated with the one or more electrical components connected between the conductive contacts in the series configuration.

Description:
BACKGROUND 
     This relates generally to wireless communications circuitry, and more particularly, to electronic devices having wireless communications circuitry. 
     Wireless electronic devices such as portable computers and cellular telephones are often provided with wireless communications circuitry that includes a number of electric components. The electric components are assembled in a manufacturing system to produce the wireless communications circuitry. A given electric component is typically tested using a test station in the manufacturing system prior to assembly within an electronic device. To expedite the manufacturing process, many test stations can be used to test the given electric component in parallel (i.e., to determine whether the electric component under test has been manufactured properly or whether the electric component under test satisfies design criteria). 
     Each test station that is used to test the given component typically experiences measurement variation due to variations between individual test stations. The behavior of each test station is typically unique, as it is challenging to manufacture test stations that are exactly identical to one another. It is challenging to limit variation between test stations within a single manufacturing system as well as across a number of manufacturing systems formed at different locations. Variations between individual test stations make it difficult to provide consistent testing for each component under test. 
     It would therefore be desirable to be able to provide improved test systems for testing wireless electronic devices 
     SUMMARY 
     A wireless electronic device may include a number of components such as wireless communications circuitry, antenna circuitry, and storage and processing circuitry. The components in the wireless electronic device may be assembled using a manufacturing system. The manufacturing system may include test stations to test the performance of components under test before fully assembling the wireless electronic device. 
     The test stations may perform radio-frequency testing on a number of passive reference test structures. The passive reference test structures may include calibration reference structures and verification reference structures. Calibrated test stations may be referred to as reference test stations or master test stations. At least one reference test station may be calibrated using a number of calibration reference structures (sometimes referred to as calibration “coupons”) having reference data such as predetermined radio-frequency characteristics. The calibration coupons may include conductive contacts, transmission line structures, and a group of electrical components formed on a substrate. The reference test stations may include a tester that measures radio-frequency characteristics of the calibration coupons using test probes. The reference test station may measure radio-frequency characteristics associated with the transmission line structures and the group of electrical components. 
     A number of different calibration coupons each having different transmission line structures and/or different groups of electrical components may be tested by the reference test station. The radio-frequency characteristics associated with the transmission line structures and/or the groups of electrical components in the calibration coupons may be measured using a THRU-REFLECT-LINE (TRL) method. The radio-frequency characteristics associated with the calibration coupons may be scattering parameters. The reference test stations may be calibrated to remove systematic errors associated with the tester and test probes. The measured radio-frequency characteristics of the calibration coupons may be compared to the predetermined radio-frequency characteristics (e.g., predetermined scattering parameters) of the calibration coupons to calibrate the reference test station. 
     In another arrangement, an additional reference test station at a different location may also measure the radio-frequency characteristics associated with each calibration coupon to obtain additional test data. The additional test data measured by the additional reference test station may be compared to the measured radio-frequency characteristics (e.g., calibration measurement data) obtained by a given reference test station to calibrate the given reference test station. 
     The calibrated reference test stations may test a number of verification reference structures (sometimes referred to as verification coupons) to establish baseline measurement data. The baseline measurement data may serve as reference data for verifying the performance of the test stations. The verification coupons may include conductive contacts and impedance modeling circuitry formed on a substrate. The impedance modeling circuitry may include electrical components that model the impedance of a component under test. The electrical components may be connected between the conductive contacts in shunt configurations, series configurations, or shunt and series configurations. 
     Each test station may obtain test measurement data (sometimes referred to as verification measurement data) by testing the verification coupons. The test measurement data may include scattering parameters associated with the verification coupons that are measured after test signals are applied to the verification coupons. The verification coupons may be used to determine whether each test station is capable of obtaining accurate test measurement data by comparing the test measurement data to the baseline measurement (reference) data. The reference test station may remove systematic errors associated with the substrate and the conductive contacts of the verification coupons by calibrating the reference test stations with the calibration coupons. 
     Further features of the present invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an illustrative electronic device with wireless communications circuitry in accordance with an embodiment of the present invention. 
         FIG. 2  is a diagram showing how radio-frequency transceiver circuitry may be coupled to antennas within an electronic device of the type shown in  FIG. 1  in accordance with an embodiment of the present invention. 
         FIG. 3  is diagram of an illustrative assembly line for testing and assembling an electronic device in accordance with an embodiment of the present invention. 
         FIG. 4  is a flow chart of illustrative steps for testing the performance of inspection test stations using calibration and verification coupons in accordance with an embodiment of the present invention. 
         FIG. 5  is a diagram of an illustrative master test station that is calibrated using a calibration coupon in accordance with an embodiment of the present invention. 
         FIGS. 6A-6D  are diagrams of calibration coupons that may be formed with different transmission line structures for calibrating a master test station in accordance with an embodiment of the present invention. 
         FIG. 7  is a flow chart of illustrative steps for calibrating a master test station using calibration coupons having predetermined radio-frequency performance characteristics in accordance with an embodiment of the present invention. 
         FIG. 8  is a flow chart of illustrative steps for calibrating a master test station using calibration coupons by comparing calibration measurements at multiple master test stations in accordance with an embodiment of the present invention. 
         FIG. 9  is a diagram showing how test reference planes may be shifted using the steps of  FIGS. 7 and 8  in accordance with an embodiment of the present invention. 
         FIG. 10  is a diagram of an illustrative inspection test station that is tested using a verification coupon mounted to a coupon support structure in accordance with an embodiment of the present invention. 
         FIGS. 11A-11D  are diagrams of verification coupons that may be formed having electrical components in a series configuration for testing inspection test stations at a wide range of impedances in accordance with an embodiment of the present invention. 
         FIG. 12A-12C  are diagrams of verification coupons that may be formed having electrical components in a series configuration for testing inspection test stations at a wide range of impedances in accordance with an embodiment of the present invention. 
         FIG. 13  is a flow chart of illustrative steps for testing the performance of inspection test stations using verification coupons in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices such as device  10  of  FIG. 1  may be provided with wireless communications circuitry. The wireless communications circuitry may be used to support long-range wireless communications such as communications in cellular telephone bands. Examples of long-range (cellular telephone) bands that may be handled by device  10  include the 800 MHz band, the 850 MHz band, the 900 MHz band, the 1800 MHz band, the 1900 MHz band, the 2100 MHz band, the 700 MHz band, and other bands. The long-range bands used by device  10  may include the so-called LTE (Long Term Evolution) bands. The LTE bands are numbered (e.g., 1, 2, 3, etc.) and are sometimes referred to as E-UTRA operating bands. Long-range signals such as signals associated with satellite navigation bands may be received by the wireless communications circuitry of device  10 . For example, device  10  may use wireless circuitry to receive signals in the 1575 MHz band associated with Global Positioning System (GPS) communications. Short-range wireless communications may also be supported by the wireless circuitry of device  10 . For example, device  10  may include wireless circuitry for handling local area network links such as WiFi® links at 2.4 GHz and 5 GHz, Bluetooth® links at 2.4 GHz, etc. 
     As shown in  FIG. 1 , device  10  may include storage and processing circuitry  28 . Storage and processing circuitry  28  may include storage such as hard disk drive storage, nonvolatile memory (e.g., flash memory or other electrically-programmable-read-only memory configured to form a solid state drive), volatile memory (e.g., static or dynamic random-access-memory), etc. Processing circuitry in storage and processing circuitry  28  may be used to control the operation of device  10 . This processing circuitry may be based on one or more microprocessors, microcontrollers, digital signal processors, application specific integrated circuits, etc. 
     Storage and processing circuitry  28  may be used to run software on device  10 , such as internet browsing applications, voice-over-internet-protocol (VOIP) telephone call applications, email applications, media playback applications, operating system functions, functions related to communications band selection during radio-frequency transmission and reception operations, etc. To support interactions with external equipment (e.g., a radio-frequency base station, radio-frequency test equipment, etc.), storage and processing circuitry  28  may be used in implementing communications protocols. Communications protocols that may be implemented using storage and processing circuitry  28  include internet protocols, wireless local area network protocols (e.g., IEEE 802.11 protocols—sometimes referred to as WiFi®), protocols for other short-range wireless communications links such as the Bluetooth® protocol, IEEE 802.16 (WiMax) protocols, cellular telephone protocols such as the “2G” Global System for Mobile Communications (GSM) protocol, the “2G” Code Division Multiple Access (CDMA) protocol, the “3G” Universal Mobile Telecommunications System (UMTS) protocol, the “4G” Long Term Evolution (LTE) protocol, MIMO (multiple input multiple output) protocols, antenna diversity protocols, etc. Wireless communications operations such as communications band selection operations may be controlled using software stored and running on device  10  (i.e., stored and running on storage and processing circuitry  28  and/or input-output circuitry  30 ). 
     Input-output circuitry  30  may include input-output devices  32 . Input-output devices  32  may be used to allow data to be supplied to device  10  and to allow data to be provided from device  10  to external devices. Input-output devices  32  may include user interface devices, data port devices, and other input-output components. For example, input-output devices may include touch screens, displays without touch sensor capabilities, buttons, joysticks, click wheels, scrolling wheels, touch pads, key pads, keyboards, microphones, cameras, buttons, speakers, status indicators, light sources, audio jacks and other audio port components, digital data port devices, light sensors, motion sensors (accelerometers), capacitance sensors, proximity sensors, etc. 
     Input-output circuitry  30  may include wireless communications circuitry  34  for communicating wirelessly with external equipment. Wireless communications circuitry  34  may include radio-frequency (RF) transceiver circuitry formed from one or more integrated circuits, power amplifier circuitry, low-noise input amplifiers, passive RF components, one or more antennas, transmission lines, and other circuitry for handling RF wireless signals. Wireless signals can also be sent using light (e.g., using infrared communications). 
     Wireless communications circuitry  34  may include radio-frequency transceiver circuitry  90  for handling various radio-frequency communications bands. For example, circuitry  90  may include transceiver circuitry  36 ,  38 , and  42 . Transceiver circuitry  36  may handle 2.4 GHz and 5 GHz bands for WiFi® (IEEE 802.11) communications and may handle the 2.4 GHz Bluetooth® communications band. Circuitry  34  may use cellular telephone transceiver circuitry  38  for handling wireless communications in cellular telephone bands such as at 850 MHz, 900 MHz, 1800 MHz, 1900 MHz, and 2100 MHz and/or the LTE bands and other bands (as examples). Circuitry  38  may handle voice data and non-voice data traffic. 
     Transceiver circuitry  90  may include global positioning system (GPS) receiver equipment such as GPS receiver circuitry  42  for receiving GPS signals at 1575 MHz or for handling other satellite positioning data. In WiFi® and Bluetooth® links and other short-range wireless links, wireless signals are typically used to convey data over tens or hundreds of feet. In cellular telephone links and other long-range links, wireless signals are typically used to convey data over thousands of feet or miles. 
     Wireless communications circuitry  34  may include one or more antennas  40 . Antennas  40  may be formed using any suitable antenna types. For example, antennas  40  may include antennas with resonating elements that are formed from loop antenna structures, patch antenna structures, inverted-F antenna structures, slot antenna structures, planar inverted-F antenna structures, helical antenna structures, hybrids of these designs, etc. Different types of antennas may be used for different bands and combinations of bands. For example, one type of antenna may be used in forming a local wireless link antenna and another type of antenna may be used in forming a remote wireless link antenna. 
     As shown in  FIG. 1 , wireless communications circuitry  34  may also include baseband processor  88 . Baseband processor may include memory and processing circuits and may also be considered to form part of storage and processing circuitry  28  of device  10 . 
     Baseband processor  88  may be used to provide data to storage and processing circuitry  28 . Data that is conveyed to circuitry  28  from baseband processor  88  may include raw and processed data associated with wireless (antenna) performance metrics for received signals such as received power, transmitted power, frame error rate, bit error rate, channel quality measurements based on received signal strength indicator (RSSI) information, channel quality measurements based on received signal code power (RSCP) information, channel quality measurements based on reference symbol received power (RSRP) information, channel quality measurements based on signal-to-interference ratio (SINR) and signal-to-noise ratio (SNR) information, channel quality measurements based on signal quality data such as Ec/Io or Ec/No data, information on whether responses (acknowledgements) are being received from a cellular telephone tower corresponding to requests from the electronic device, information on whether a network access procedure has succeeded, information on how many re-transmissions are being requested over a cellular link between the electronic device and a cellular tower, information on whether a loss of signaling message has been received, information on whether paging signals have been successfully received, and other information that is reflective of the performance of wireless circuitry  34 . This information may be analyzed by storage and processing circuitry  28  and/or processor  88  and, in response, storage and processing circuitry  28  (or, if desired, baseband processor  58 ) may issue control commands for controlling wireless circuitry  34 . For example, baseband processor  88  may issue commands that direct transceiver circuitry  90  to switch into use desired transmitters/receivers and antennas. 
     Antenna diversity schemes may be implemented in which multiple redundant antennas are used in handling communications for a particular band or bands of interest. In an antenna diversity scheme, storage and processing circuitry  28  may select which antenna to use in real time based on signal strength measurements or other data. In multiple-input-multiple-output (MIMO) schemes, multiple antennas may be used in transmitting and receiving multiple data streams, thereby enhancing data throughput. 
     Illustrative locations in which antennas  40  may be formed in device  10  are shown in  FIG. 2 . As shown in  FIG. 2 , electronic device  10  may have a housing such as housing  12 . Housing  12  may include plastic walls, metal housing structures, structures formed from carbon-fiber materials or other composites, glass, ceramics, or other suitable materials. Housing  12  may be formed using a single piece of material (e.g., using a unibody configuration) or may be formed from a frame, housing walls, and other individual parts that are assembled to form a completed housing structure. The components of device  10  that are shown in  FIG. 1  may be mounted within housing  12 . Antenna structures  40  may be mounted within housing  12  and may, if desired, be formed using parts of housing  12 . For example, housing  12  may include metal housing sidewalls, peripheral conductive members such as band-shaped members (with or without dielectric gaps), conductive bezels, and other conductive structures that may be used in forming antenna structures  40 . 
     As shown in  FIG. 2 , antenna structures  40  may be coupled to transceiver circuitry  90  by paths such as paths  45 . Paths  45  may include transmission line structures such as coaxial cables, microstrip transmission lines, stripline transmission lines, etc. Impedance matching circuitry, filter circuitry, and switching circuitry may be interposed in paths  45  (as examples). Impedance matching circuitry may be used to ensure that antennas  40  are efficiently coupled to transceiver circuitry  90  in desired frequency bands of interest. Filter circuitry may be used to implement frequency-based multiplexing circuits such as diplexers, duplexers, and triplexers. Switching circuitry may be used to selectively couple antennas  40  to desired ports of transceiver circuitry  90 . For example, a switch may be configured to route one of paths  45  to a given antenna in one operating mode. In another operating mode, the switch may be configured to route a different one of paths  45  to the given antenna. The use of switching circuitry between transceiver circuitry  90  and antennas  40  allows device  10  to switch particular antennas  40  in and out of use depending on the current performance associated with each of the antennas. 
     In a device such as a cellular telephone that has an elongated rectangular outline, it may be desirable to place antennas  40  at one or both ends of the device. As shown in  FIG. 2 , for example, some of antennas  40  may be placed in upper end region  42  of housing  12  and some of antennas  40  may be placed in lower end region  44  of housing  12 . The antenna structures in device  10  may include a single antenna in region  42 , a single antenna in region  44 , multiple antennas in region  42 , multiple antennas in region  44 , or may include one or more antennas located elsewhere in housing  12 . 
     Antenna structures  40  may be formed within some or all of regions such as regions  42  and  44 . For example, an antenna such as antenna  40 T- 1  may be located within region  42 - 1  or an antenna such as antenna  40 T- 2  may be formed that fills some or all of region  42 - 2 . Similarly, an antenna such as antenna  40 B- 1  may fill some or all of region  44 - 2  or an antenna such as antenna  40 B- 2  may be formed in region  44 - 1 . These types of arrangements need not be mutually exclusive. For example, region  44  may contain a first antenna such as antenna  40 B- 1  and a second antenna such as antenna  40 B- 2 . 
     Transceiver circuitry  90  may contain transmitters such as radio-frequency transmitters  48  and receivers such as radio-frequency receivers  50 . Transmitters  48  and receivers  50  may be implemented using one or more integrated circuits (e.g., cellular telephone communications circuits, wireless local area network communications circuits, circuits for Bluetooth® communications, circuits for receiving satellite navigation system signals, power amplifier circuits for increasing transmitted signal power, low noise amplifier circuits for increasing signal power in received signals, other suitable wireless communications circuits, and combinations of these circuits). 
     In accordance with an embodiment of the present invention, electronic devices  10  may be manufactured using a manufacturing system such as manufacturing system  178  as shown in  FIG. 3 . Manufacturing system  178  may manufacture a number of electronic devices  10  simultaneously (e.g., many electronic devices  10  may each be assembled on a respective assembly line in parallel). There may be multiple manufacturing systems  178  at a number of different geographical locations for manufacturing electronic devices  10 . Manufacturing system  178  may manufacture electronic devices  10  by assembling different components within production devices (e.g., components such as transceiver circuitry  90 , antennas  40 , wireless communications circuitry  34 , etc.). Manufacturing system  178  may also test the performance of components for use in electronic devices  10 . 
     In order to test the performance of many components for use in electronic devices  10  simultaneously, manufacturing system  178  may include a number of assembly lines  184  that each convey a respective component  180  to inspection test stations  182  in parallel (e.g., a first assembly line  184 - 1  conveys a first component  180 - 1  to a first inspection test station  182 - 1 , a second assembly line  184 - 2  conveys a second component  180 - 2  to a second inspection test station  182 - 2 , etc.). Components  180  that are tested by inspection test stations  182  may sometimes be referred to as components under test. 
     Inspection test stations  182  may be any suitable test stations for characterizing the performance of components under test  180 . For example, inspection test stations  182  may test the radio-frequency performance of components under test  180 . Components under test  180  that have sufficient radio-frequency performance may be labeled as “passing” components. Components under test  180  that have insufficient radio-frequency performance may be labeled as “failing” components. Passing components may be conveyed to assembly equipment  186  via assembly lines  184  for further assembly, whereas failing components may be discarded or reworked. 
     Assembly equipment  186  may further assemble components  180  within a corresponding electronic device  10 . Assembly equipment  186  may, for example, modify components  180 , attach components  180  to additional components, combine multiple components  180 , etc. In the scenario where components  180  are a part of wireless circuitry  34 , assembly equipment  186  may attach components  180  to antenna circuitry such as antennas  40  ( FIG. 1 ). Devices  10  with assembled components may be further tested by other test stations, if desired. 
     During testing of components under test (CUT)  180 , each inspection test station  182  may experience measurement variation due to variations between individual inspection test stations  182  (e.g., process, voltage, and temperature variations that may affect the operation of each test station  182 ). The behavior of each inspection test station  182  is typically unique, because it is challenging to manufacture test stations that are exactly identical to one another. For example, the behavior of inspection test station  182 - 1  may be different from the behavior of inspection test station  182 - 2  while performing tests on components under test  180 . In addition, it is challenging to limit variation between inspection test stations  182  across multiple manufacturing systems  178  at different locations. Variations between individual inspection test stations  182  make it difficult to provide consistent testing for each component under test  180 . It may therefore be desirable to be able to provide a test standard for ensuring that test results are consistent across multiple inspection test stations  182  at different test sites (locations). 
     A reference standard such as standard  188  (sometimes referred to herein as passive reference test structure, a reference coupon, or a “coupon”) may be used to ensure consistent testing across multiple inspection test stations  182 . Reference coupon  188  may be provided with similar physical form factor to components under test  180 . Reference coupon  188  may include a number of conductive contacts  228  formed on a substrate such as carrier substrate  227 . Reference coupon  188  may also include circuitry  100  formed on carrier substrate  227 . In addition, reference coupon  188  may include transmission line structures and groups of electrical components formed on carrier substrate  227 . Contacts  228  may, for example, be formed from solder bumps on substrate  227  (e.g., bumps sometimes referred to as controlled collapse chip connection (C4) bumps or “flip-chip” bumps). Contacts  228  may allow signals to be passed to and from circuitry  100 . Carrier substrate  227  may be a semiconductor substrate, dielectric substrate, or any other suitable substrate for conductive contacts  228  and circuitry  100 . 
     Test stations in manufacturing system  178  may, for example, test a number of radio-frequency parameters associated with components under test  180 . If desired, multiple reference coupons such as reference coupon  188  may be provided to test stations in manufacturing system  178 . Each reference coupon  188  may be formed to allow radio-frequency testing of a respective subset of the radio-frequency parameters associated with components under test  180  when provided to test stations in manufacturing system  178 . 
     Each manufacturing system  178  may have a “golden” reference test station such as master test station  200 . Master test station  200  may be an inspection test station that has been carefully calibrated using a well-known reference standard. Master test station  200  may perform testing operations on reference coupons  188 . Reference coupons  188  may be configured as calibration coupons or verification coupons. 
     Reference coupons  188  that are configured as calibration coupons may serve to provide the well-known reference standard used to calibrate master test station  200 . Reference coupons  188  that are configured as calibration coupons may be referred to herein as calibration coupons  226  (see, e.g., calibration coupon  226  of  FIG. 5 ). Calibration coupons  226  may be formed with transmission lines structures and/or groups of electrical components that are coupled to a number of conductive contacts  228 . Calibration coupons  226  may have predetermined radio-frequency performance characteristics. During calibration of master test station  200 , master test station  200  may measure radio-frequency performance characteristics associated with calibration coupons  226  (e.g., radio-frequency performance characteristics associated with the transmission line structures, groups of electrical components, contacts  228 , and substrate  227 ). The measured performance characteristics of calibration coupons  226  may be compared to the predetermined performance characteristics to suitably calibrate master test station  200 . 
     Reference coupons  188  that are configured as verification coupons may be provided to master test station  200  after calibration. Reference coupons  188  that are configured as verification coupons may be referred to herein as verification coupons  326  (see, e.g., verification coupon  326  of  FIG. 10 ). Verification coupons  326  may include circuitry  100  that is formed to model the electrical behavior (e.g., impedance characteristics) of components under test  180 . Verification coupons  326  may be measured by master test station  200  to establish baseline test measurements. Verification coupons  326  may be subsequently measured by inspection test stations  182 . The measurements performed by inspection test stations  182  may be compared to the baseline test measurements to characterize the performance of individual inspection test stations  182 . Characterizing the performance of individual inspection test stations  182  in this way serves to ensure consistent behavior across all inspection test stations  182 . 
     A flow chart of illustrative steps that may be performed by a manufacturing system such as manufacturing system  178  to test the performance of inspection test stations  182  is shown in  FIG. 4 . 
     At step  240 , one or more calibration coupons  226  having well-known radio-frequency performance characteristics are provided to master test station  200 . The radio-frequency performance characteristics of the calibration coupons  226  may be determined through simulation, modeling, or any other suitable method for characterizing calibration coupons  226 . Calibration coupons  226  may also be provided to other master test stations  200  at other locations for master test station calibration. Master test stations  200  may perform measurements on calibration coupons  226  to obtain calibration measurement data. The calibration measurement data may be compared with the known measurement characteristics of calibration coupons  226  to calibrate master test stations  200 . In this way, master test stations  200  at many different locations may be calibrated using the same reference standard. 
     At step  242 , one or more verification coupons  326  are provided to master test station  200 . Circuitry  100  in verification coupons  326  may have electrical characteristics such as impedance values that are similar to impedance values of components under test  180 . Master test station  200  may perform measurements on verification coupons  326  to obtain baseline test measurement data. A number of verification coupons  326  having different impedance values may be measured by master test station  200  (e.g., circuitry  100  on verification coupons  326  may be formed having different impedance values). In this way, master test stations  200  may obtain baseline measurement data for verification coupons  326  with circuitry having a wide range of impedance values. This process may occur across multiple manufacturing systems  178  at different locations in parallel. 
     At step  244 , verification coupons  326  that are measured by master test station  200  may be supplied to an inspection test station such as inspection test station  182 -( FIG. 3 ). Inspection test station  182 - 1  may perform the same measurements on verification coupons  326  that are performed by master test stations  200  in order to obtain test station measurement data associated with inspection test station  182 - 1 . The test station measurement data may be compared to the baseline test measurement data to validate the performance of inspection test station  182 - 1 . For example, if the test station measurement data varies significantly from the baseline test measurement data, test station  182 - 1  may be characterized as having unacceptable performance. Test stations  182  that are characterized as having unacceptable performance may be labeled “failing” test stations. If the test station measurement data sufficiently matches the baseline test measurement data, test station  182 - 1  may be characterized as having acceptable performance. Test stations  182  that are characterized as having acceptable performance may be labeled “passing” test stations. This process may be repeated at all inspection test stations  182 . The performance of inspection test stations  182  may be consistently tested across different manufacturing systems  178  at different locations because each manufacturing system  178  is calibrated using the same calibration coupons  226  (i.e., the same reference standards are used to calibrate master test stations at each manufacturing system  178 ). 
     At step  246 , failing inspection test stations  182  may optionally generate calibration data to correct for unacceptable performance. For example, the calibration data may be used to obtain offset settings that compensate for the test measurement data obtained by failing inspection test stations  182  to help sufficiently match the baseline measurement data. 
     In accordance with an embodiment of the present invention, master test station  200  may be calibrated using a reference standard such as calibration coupon  226 . Calibration coupon  226  may include a number of transmission lines structures (e.g., microstrip transmission lines, stripline transmission lines, etc.) and resistive loads coupled between one or more conductive contacts  228 . A number of calibration coupons  226  may be formed each having different respective transmission lines structures and groups of electrical components (e.g., resistive loads). The selected transmission lines structures and groups of electrical components in calibration coupon  226  may be chosen to allow master test station  200  to calibrate systematic errors associated with conductive contacts  228 , various transmission line structures, and groups of electrical components on carrier substrate  227 . Calibration coupon  226  may be formed to replicate the physical form factor of components under test  180 . In general, using calibration coupon  226  having physical dimensions similar to those of components under test  180  can help improve calibration accuracy. 
     As shown in  FIG. 5 , master test station  200  may include a test host such as test host  202  (e.g., a personal computer, laptop computer, tablet computer, etc.), a radio-frequency tester such as radio-frequency tester  204 , control circuitry, network circuitry, cabling, and other test equipment. 
     Radio-frequency tester  204  may be, for example, a vector network analyzer. Tester  204  may have a first port  216 - 1  to which a first radio-frequency cable  218 - 1  is connected and a second port  216 - 2  to which a second radio-frequency cable  216 - 2  is connected. Radio-frequency cables  218 - 1  and  218 - 2  may be, for example, coaxial cables. In particular, first cable  218 - 1  may have a first end that is connected to tester port  216 - 1  and a second end terminating at a first radio-frequency connector  220 - 1 . Similarly, second cable  218 - 2  may have a first end that is connected to tester port  216 - 2  and a second end terminating at a second radio-frequency connector  220 - 2 . Radio-frequency connectors  220 - 1  and  220 - 2  may be, for example, SubMiniature Version A (SMA) connectors or any other suitable radio-frequency connectors. First radio-frequency connector  220 - 1  may be coupled to radio-frequency test probe  222 - 1 . Similarly, second radio-frequency connector  220 - 2  may be coupled to radio-frequency test probe  222 - 2 . Radio-frequency test probes  222 - 1  and  222 - 2  may have probe contacts  224  (sometimes referred to as conductive probe tips or probe pins). 
     During calibration, first port  216 - 1  of tester  204  may be coupled to a first group  229  of conductive contacts  228  on calibration coupon  226  (e.g., by touching probe contacts  224  of test probe  222 - 1  to first group  229  of conductive contacts  228 ), whereas second port  216 - 2  of tester  204  may be coupled to a second group  231  of conductive contacts  228  (e.g., by touching probe contacts  224  of test probe  222 - 2  to second group  231  of contacts  228 ). Radio-frequency tester  204  may receive commands from test host  202  via path  230  that direct tester  204  to gather desired radio-frequency measurements from calibration coupon  226 . If desired, test data can be provided from tester  204  to test host  202  via path  230 . 
     Radio-frequency tester  204  may be configured to produce radio-frequency test signals that are applied to coupon  226  via cables  218  and probes  222 . Tester  204  may apply radio-frequency test signals to one or more probe contacts  224 . Tester  204  may also provide a path to ground to one or more probe contacts  224 . Calibration coupon  226  may emit radio-frequency signals when being energized by the test signals generated using tester  204 . As electromagnetic test signals are transmitted by tester  204  and applied to calibration coupon  226  through test cable  218 - 1 , corresponding emitted electromagnetic signals may be received through test cable  218 - 2  (as an example). Tester  204  may also receive reflected signals via cable  218 - 1  (i.e., signals that were reflected from calibration coupon  226  in response to the signals transmitted through test cable  218 - 1 ). 
     The reflected signals gathered in this way may be used to compute a reflection coefficient (sometimes referred to as an S11 parameter or S11 scattering parameter). The transmitted signals on cable  218 - 1  and corresponding received signals on cable  218 - 2  may be used to compute a forward transfer coefficient (sometimes referred to as an S21 parameter or S21 scattering parameter). The S11 and S21 data may include magnitude and phase components. 
     Similarly, tester  204  may also transmit test signals to calibration coupon  226  through test cable  218 - 2 . As test electromagnetic signals are transmitted by tester  204  and applied to calibration coupon  226  through test cable  218 - 2 , corresponding emitted electromagnetic test signals may be received through test cable  218 - 1 . Tester  204  may also receive reflected signals via cable  218 - 2  (i.e., signals that were reflected from calibration coupon  226  in response to the signals transmitted through test cable  218 - 2 ). The emitted and reflected signals gathered in this way may be used to compute reflection coefficient data (sometimes referred to as an S22 scattering parameter) and forward transfer coefficient data (sometimes referred to as an S12 scattering parameter) and forward transfer coefficient data (sometimes referred to as an S12 scattering parameter). 
     The S11, S12, S22, and S21 parameters (collectively referred to as scattering parameters or S parameters) measured using tester  204  may collectively be used as measurement data that is representative of the radio-frequency performance characteristics of master test station  200 . Calibration coupon  226  may have well-known, predetermined radio-frequency characteristics such as predetermined S parameters. The predetermined radio-frequency characteristics of calibration coupon  226  may be determined, for example, through detailed simulation and modeling of calibration coupon  226 . Calibration coupon  226  may be precisely manufactured (e.g., by laser-trimming) to exhibit the predetermined radio-frequency characteristics associated with calibration coupon  226 . 
     The predetermined characteristics of calibration coupon  226  may establish a baseline reference (e.g., baseline S parameters) for calibrating master test station  200 . Assuming that systematic errors associated with master test station  200  (including errors associated with tester  204 , ports  216 , cables  218 , radio-frequency connectors  220 , test probes  222 , and probe contacts  224 ) have been calibrated, the measurement data may be compared to the baseline reference obtained by master test station  200  during calibration operations to calibrate master test station  200 . For example, offset settings may be generated for master test station  200  during calibration operations. The offset settings may be provided to tester  204  to enable the measurement data obtained by master test station  200  to suitably match the baseline reference. Calibrating master test station  200  in this way may calibrate systematic errors associated with contacts  228  and carrier substrate  227  of calibration coupon  226 . 
     Master test station  200  as shown in  FIG. 5  is merely illustrative and does not serve to limit the scope of the present invention. If desired, master test station  200  may include other means of controlling and monitoring the operation of tester  204 , may include other types of radio-frequency testers for measuring the characteristics of coupon  226 , and may include other suitable test equipment. Calibration coupon  226  may include any number of conductive contacts  228  and test probes  222  may include any suitable number of corresponding probe contacts  224 . 
     A number of different calibration coupons  226  each formed with different transmission lines structures and groups of electrical components may be sequentially measured by master test station  200 . Transmission line structures in calibration coupon  226  may have associated properties that affect the impedance of the transmission line structures (e.g., transmission line widths, transmission line lengths, etc.). The radio-frequency characteristics of the transmission line structures may be selected (e.g., by forming transmission lines structures with suitable dimensions) to allow master test station  200  to calibrate systematic errors associated with conductive contacts  228  and carrier substrate  227 . 
       FIG. 6A-6D  are diagrams of calibration coupons  226  having different transmission lines structures (e.g., calibration coupon  226  may have a first configuration of transmission line structures shown by calibration coupon  226 - 1  of  FIG. 6A , calibration coupon  226  may have a second configuration shown by calibration coupon  226 - 2  of  FIG. 6B , etc.). 
     In one suitable embodiment of the present invention, calibration coupon  226 - 1  may include a transmission line  232  that forms an electrical short between a number of signal contacts  228 - 1  as shown in  FIG. 6A . In the example of  FIG. 6A , calibration coupon  226 - 1  has a transmission line short  232  formed between conductive signal contacts  228 - 1  and ground contacts  228 - 2 . Transmission line short  232  may be formed having a selected width W to provide short  232  with suitable impedance. During calibration of master test station  200 , first group  229  of contacts  228  are coupled to test probe  222 - 1  and second group  231  of contacts  228  are coupled to test probe  222 - 2  via probe contacts  224  (see  FIG. 5 ). Tester  204  may provide radio-frequency test signals at signal contacts  228 - 1  and a path to ground at ground contacts  228 - 2 . Transmission line short  232  may thereby provide an electrical short to ground for radio-frequency test signals provided at signal contacts  228 - 1  from tester  204 . 
     In another suitable arrangement of the present invention, calibration coupon  226 - 2  may be formed in an open circuit configuration as shown in  FIG. 6B  (e.g., none of contacts  228  are connected via transmission line structures). During calibration of master test station  200 , first group  229  of contacts  228  are coupled to test probe  222 - 1  and second group  231  of contacts  228  are coupled to test probe  222 - 2  via probe contacts  224 . In such an arrangement, probes  222  are provided with an open circuit. 
     In another suitable arrangement of the present invention, calibration coupon  226 - 3  may include an electrical component such as a resistive load as shown in  FIG. 6C . In such an arrangement, resistive structures such as resistors  236  may be coupled to signal contacts  228 - 1  via transmission lines  234 . Transmission lines  234  may be formed having a selected length L and a selected width W to provide transmission lines  234  with suitable impedance. Resistors  236  may be interposed between transmission lines  234  and ground  237 . Ground  237  may be formed in a lower layer within carrier substrate  227  (e.g., ground  237  may be formed as conductive ground plane within carrier substrate  227 ). During calibration operations, tester  204  may provide radio-frequency test signals at signal contacts  228 - 1  via test probes  222  that are conveyed to ground  237  via transmission lines  234  and resistors  236 . 
     In yet another suitable arrangement, calibration coupon  226 - 4  may include a through path between a number of signal contacts  228 - 1  as shown in  FIG. 6D . In the example of  FIG. 6D , coupon  226 - 4  is formed with transmission line  240  that serves as an electrical through path between two signal contacts  228 - 1 . Transmission line  240  may be formed having a selected width W to provide transmission line path  240  with suitable impedance. During calibration operations, tester  204  may provide radio-frequency test signals at signal contacts  228 - 1 . Transmission line  240  provides a through path for the test signals provided at signal contacts  228 - 1 . 
     Calibration coupons  226  of  FIG. 6  are merely illustrative. If desired, calibration coupons  226  may be configured with any suitable transmission line structures and groups of electrical components between any number of contacts  228  (e.g., between any number of signal contacts  228 - 1  and ground contacts  228 - 2 ). The transmission line structures shown in  FIG. 6  may be suitably combined or altered to affect the radio-frequency performance characteristics of calibration coupon  226 . 
     Master test station  200  may measure radio-frequency characteristics of calibration coupon  226  such as S parameters for each of the calibration coupon configurations shown in  FIG. 6  (e.g., for calibration coupons  226 - 1 ,  226 - 2 , etc.). The measured S parameters for each configuration of calibration coupon  226  may be compared to baseline S parameters to provide calibration data for master test station  200 . The baseline S parameters may be determined by detailed simulation and modeling of each configuration of calibration coupon  226 . Alternatively, the baseline S parameters may be determined by comparing the measured S parameters for many master test stations such as master test station  200  at different locations (e.g., for master test stations  200  in manufacturing systems  178  formed at different geographical locations). Assuming systematic errors associated with master test station  200  have been removed, the measured S parameters may be compared to the baseline S parameters to calibrate systematic errors associated with contacts  228  and carrier substrate  227 . 
     A flow chart of illustrative steps for calibrating master test station  200  is shown in  FIG. 7 . In calibrating master test station  200 , it may be desirable to separate the effects associated with the transmission medium (e.g., the effects associated with test cables  218 , test probe  222 , and probe contacts  224 ) from circuitry formed internal to conductive contacts  228  (e.g., circuitry that receives signals from probes  222  via conductive contacts  228 ). At radio-frequencies, systematic effects such as signal leakage and impedance mismatch can affect measured data. In a stable calibration environment, such types of systematic effects are repeatable and can be characterized and removed via calibration. As an example, calibration coupons  226  can be connected to tester  204  during calibration. Systematic effects may then be quantified by computing the difference between measured and known responses associated with calibration coupon  226 . This process of removing systematic effects associated with master test station  200  is sometimes referred to as error correction. 
     At step  250 , radio-frequency tester  204  may be calibrated to remove potential errors that are associated with radio-frequency tester  204  and coaxial cables  218  (i.e., cables  218 - 1  and  218 - 2 ). For example, vector network analyzer  204  may be calibrated at the coaxial ports using known coaxial standards (e.g., using conventional open, short, load, and thru coaxial standards) to ensure that vector network analyzer  204  is initialized to desired test settings. Once this step is complete, measurements gathered using tester  204  will only reflect the behavior of structures coupled to the ends of coaxial cables  218  (e.g., ports  216 - 1  and  216 - 2  of tester  204  are virtually extended to the ends of cables  218  so that a new reference plane  302  is established, as shown in  FIG. 9 . 
     Test probes  222  (i.e., test probes  222 - 1  and  222 - 2 ) and probe contacts  224  may also be calibrated to de-embed systematic effects that are associated with test probes  222  and probe contacts  224 . For example, probes  222  and probe contacts  224  may be calibrated at probe contacts  224  using known probe standards (e.g., using conventional open, short, load, and thru probe standards). Once this step is complete, measurements gathered using tester  204  will only reflect the behavior of structures coupled to probe contacts  224  (e.g., ports  216 - 1  and  216 - 2  of tester  204  are virtually extended to the ends of probe contacts  224  so that a new reference plane  304  is established). 
     At step  252 , a number of calibration coupons  226  each having different transmission line structures and groups of electrical components may be coupled to master test station  200  (e.g., calibration coupons such as  226 - 1 ,  226 - 2 ,  226 - 3 , and  226 - 4  of  FIGS. 6A-6D  may be coupled to master test station  200 ). During calibration, conductive contacts  228  of each calibration coupon  226  are coupled to probe contacts  224 . Master test station  200  may measure radio-frequency characteristics such as S parameters for calibration coupons  226  having each transmission line configuration. 
     In one suitable arrangement, calibration coupons  226  having the configurations shown in  FIGS. 6A-6D  (e.g., calibration coupons  226 - 1 ,  226 - 2 , etc.) may be measured to calibrate master test station  200  using a THRU-REFLECT-LINE (TRL) approach. The TRL approach is a two-port calibration procedure that relies on testing different transmission line structures on a substrate such as substrate  227  to fully characterize the systematic errors associated with substrate  227  and contacts  228 . 
     For example, a reference standard such as calibration coupon  226  having different types of transmission line structures (e.g., calibration coupons  226 - 1 ,  226 - 2 ,  226 - 3 , and  226 - 3  of  FIGS. 6A-6D ) may be coupled to radio-frequency tester  204  during step  252 . In this example, the TRL approach involves sequentially coupling tester  204  to contacts  228  on each of calibration coupons  226 - 1 ,  226 - 2 ,  226 - 3 , and  226 - 4 . 
     During the THRU calibration step, calibration coupon  226 - 4  of  FIG. 6  may be coupled to tester  204  while obtaining desired two-port measurements (i.e., first group  229  and second group  231  of contacts  228  on calibration coupon  226 - 4  may be coupled to probe contacts  224  of test probes  222 ). During a first half of the REFLECT calibration step, tester  204  may be coupled to calibration coupon  226 - 2  while obtaining a first set of reflection coefficient measurements associated with an open circuit response (i.e., first group  229  and second group  231  of contacts  228  on calibration coupon  226 - 2  may be coupled to probe contacts  224  of test probes  222 ). During a second half of the REFLECT calibration step, tester  204  may be coupled to calibration coupon  226 - 3  while obtaining a second set of reflection coefficient measurements associated with a resistive load circuit response (i.e., first group  229  and second group  231  of contacts  228  on calibration coupon  226 - 3  may be coupled to probe contacts  224  of test probes  222 ). During the LINE calibration step, tester  204  may be coupled to calibration coupon  226 - 4  formed with transmission line  240  between signal contacts  228 - 1  while obtaining a set of two-port measurements (i.e., first group  229  and second group  231  of contacts  228  on calibration coupon  226 - 4  may be coupled to probe contacts  224  of test probes  222 ). 
     Measurements gathered from calibration coupons  226  can then be applied to tester  204  to remove any effects associated with carrier substrate  227  and contacts  228 . Once the TRL calibration is complete, measurements performed by tester  204  on any additional reference standards  188  such as verification coupons  326  having circuitry  100  will only reflect the behavior of internal circuitry  100  (e.g., ports  216 - 1  and  216 - 2  of tester  204  will be virtually extended to the edge of circuitry  100 , shifting the test reference plane to position  306  as shown in  FIG. 9 ). If desired, any suitable variation of the TRL approach can be used during step  252 . 
     At step  254 , the S parameters measured by master test station  200  may be compared to known characteristics (e.g., to well-known, predetermined baseline S parameters) of calibration coupons  226  to calibrate master test station  200 . Once master test station  200  has been calibrated, any subsequent measurements gathered using tester  204  from additional reference standards  188  such as verification coupons  326  will only reflect the behavior of internal circuitry  100  (e.g., ports  216 - 1  and  216 - 2  of tester  204  will be virtually extended to the edge of circuitry  100 , shifting the test reference plane to position  306 ). At this point, all errors associated with master test station  200 , contacts  228 , and carrier substrate  227  have been calibrated for. 
     At step  256 , calibration coupons  226  may be passed to master test stations  200  at other locations. For example, coupons  226  may be passed to master test stations  200  in manufacturing systems  178  formed at other geographic locations. Master test stations  200  in manufacturing systems  178  formed at other locations may be similarly calibrated with calibration coupons  226  using the steps of  FIG. 7 . 
     A flow chart of illustrative steps for calibrating master test station  200  in another suitable embodiment of the present invention is shown in  FIG. 8 . 
     At step  260 , master test station  200  may be calibrated using step  250  of  FIG. 7 . Once this step is complete, measurements gathered using tester  204  will only reflect the behavior of structures coupled to probe contacts  224  (e.g., ports  216 - 1  and  216 - 2  of tester  204  are virtually extended to the ends of probe contacts  224  so that a new reference plane  304  is established, as shown in  FIG. 9 ). 
     At step  262 , master test station  200  may measure S parameters of a number of calibration coupons  226  each having different transmission line configurations (e.g., calibration coupons  226 - 1 ,  226 - 2 ,  226 - 3 , and  226 - 4  of  FIG. 6 ) using step  252  of  FIG. 7 . The calibration coupons  226  measured at step  262  may not have well-known predetermined S parameters. 
     At step  264 , calibration coupons  226  may be passed to master test stations  200  at other locations (e.g., master test stations  200  in manufacturing systems  178  formed at other geographic locations). Master test stations  200  at other locations may perform step  262  to measure the S parameters of calibration coupons  226  having each transmission line configuration. 
     At step  266 , the measured S parameters for each master test station  200  used to measure calibration coupons  266  are compared to one another to establish baseline S parameters. For example, the baseline S parameters may be established by averaging the S parameters measured at all master test stations  200  or by any other suitable algorithm that operates on the S parameters measured at a number of master test stations  200 . The S parameters measured at each master test station  200  may be compared to the baseline S parameters to calibrate each master test station  200  up to reference plane  306  as shown in  FIG. 9 . 
     Once master test station  200  has been calibrated up to reference plane  306 , any further reference coupons  188  that are measured by master test station  200  such as verification coupons  326  may thereby be calibrated up to reference plane  306  (e.g., the effects of all errors associated with master contacts  228  and carrier substrate  227  have been calibrated for). After calibration, master test station  200  may measure verification coupons  326  to establish a baseline test reference with which to characterize the performance of inspection test stations  182  (see  FIG. 3 ). 
     Master test station  200  may measure radio-frequency characteristics such as S parameters of verification coupons  326  to establish the baseline test reference (e.g., baseline S parameters). Verification coupons  326  may be passed to inspection test stations  182  to test the radio-frequency performance of inspection test stations  182 . 
     In accordance with an embodiment of the present invention, the performance of inspection test stations such as inspection test station  182  may be tested using a test standard such as verification coupon  326  as shown in  FIG. 10 . Conductive contacts  228  and carrier substrate  227  of verification coupons  326  may be described by the same systematic errors associated with calibration coupons  226 . 
     As shown in  FIG. 10 , inspection test station  182  may include a test host such as test host  302  (e.g., a personal computer, laptop computer, tablet computer, etc.), a radio-frequency tester such as radio-frequency tester  304 , test structures such as test fixture  310  and probing structure  312 , control circuitry, network equipment, cabling, and other test equipment. Verification coupon  326  may be mounted on a support structure such as coupon support structure  308  (e.g., a printed circuit board) during testing. Support structure  308  may secure verification coupon  326  in a known fixed position during test operations. 
     Probing structure  312  may be supported by test fixture  310 . Test fixture  310  may be a plastic support structure or other dielectric substrate, a rigid printed circuit board substrate, or other substrate material. Probing structure  312  may, for example, be constructed using a flexible printed circuit (“flex circuit”) formed from a sheet of polyimide or other flexible polymer, or other substrate material. 
     Probing structure  312  may include contacts such as conductive probe tips  324  configured to mate with corresponding contacts  228  on verification coupons  326 . Probe tips  324  may be coupled to test connectors  320 . Probe tips  324  may be coupled to test connectors  320  using any suitable radio-frequency transmission line formed within test fixture  310 . Test signals may be conveyed to and from verification coupon  326  via such traces that are coupled to probe tips  314 . In another suitable arrangement, probe tips  324  may be formed directly on test fixture  310 . 
     Radio-frequency tester  304  in inspection test station  182  may be, for example, a vector network analyzer. Tester  304  may have a first port  316 - 1  to which a first radio-frequency cable  318 - 1  is connected and a second port  316 - 2  to which a second radio-frequency cable  316 - 2  is connected. Radio-frequency cables  318 - 1  and  318 - 2  may be, for example, coaxial cables. In particular, first cable  318 - 1  may have a first end that is connected to tester port  316 - 1  and a second end terminating at a first radio-frequency connector  320 - 1 . Similarly, second cable  318 - 2  may have a first end that is connected to tester port  316 - 2  and a second end terminating at a second radio-frequency connector  320 - 2 . Radio-frequency connectors  320 - 1  and  320 - 2  may be, for example, SubMiniature Version A (SMA) connectors or any other suitable radio-frequency connectors. 
     During testing operations, ports  316 - 1  and  316 - 2  of tester  304  may be coupled to conductive contacts  228  on verification coupon  326  (e.g., by touching probe tips  324  to conductive contacts  228 ). Radio-frequency tester  304  may receive commands from test host  302  via path  330  that direct tester  304  to gather desired radio-frequency measurements from calibration coupon  326 . If desired, test data can be provided from tester  304  to test host  302  via path  330 . When conductive contacts  228  are coupled to probe tips  324 , circuitry  100  in verification coupon  326  may be electrically coupled to radio-frequency tester  304 . 
     Tester  304  may be calibrated to remove potential errors that are associated with radio-frequency tester  304  and coaxial cables  318 . Tester  304  may measure radio-frequency performance characteristics such as S parameters of circuitry  100  in verification coupon  326 . The measured S parameters may be representative of the radio-frequency performance of inspection test station  182 . 
     Assuming that systematic errors associated with inspection test station  182  have been removed (including errors associated with tester  304 , ports  316 , cables  318 , radio-frequency connectors  320 , test fixture  310 , probing structure  312 , and probe tips  324 ), the radio-frequency performance characteristics measured by inspection test station  182  may be compared to the baseline reference (e.g., baseline S parameters) determined by the calibrated master test station  200 . 
     If measured radio-frequency performance characteristics (e.g., measured S parameters) do not acceptably match the baseline reference, the radio-frequency performance of the associated inspection test station  182  may be characterized as being unsatisfactory. An inspection test station  182  that has unsatisfactory radio-frequency performance may be labeled as a “failing” test station. If a measured performance characteristic acceptably matches the baseline performance characteristic, the radio-frequency performance of the associated inspection test station  182  may be characterized as satisfactory. An inspection test station  182  that has satisfactory radio-frequency performance may be labeled as a “passing” test station. An inspection test station  182  may be labeled as a “failing” test station if the associated radio-frequency performance characteristics measured by inspection test station  182  in response to testing one or more verification coupons  326  do not acceptably match the corresponding baseline reference. 
     A failing inspection test station  182  may be optionally calibrated (e.g., by providing the failing test station  182  with offset data generated by test host  202 ) to sufficiently match the measured radio-frequency performance characteristics to the baseline radio-frequency performance characteristics. For example, a failing inspection test station  182  may be calibrated by generating offset data with test host  202  to be supplied to tester  204 . 
     Circuitry  100  on verification coupons  326  may include components that model radio-frequency characteristics (e.g., impedances) of components under test  180 . For example, circuitry  100  in verification coupon  326  may include one or more capacitors, resistors, inductors, shorts, or any other suitable electric component connected together in series or shunt configurations between contacts  228  of verification coupon  326 . Components in circuitry  100  may be formed so that circuitry  100  has selected impedance characteristics. The selected impedance characteristics may be chosen to match the impedance characteristics of a particular component under test  180 . 
     A number of different verification coupons  326  each formed with respective circuitry  100  having different impedance characteristics may be sequentially measured by master test station  200  and inspection test stations  182 . The impedance characteristics of circuitry  100  may be selected (e.g., by forming circuitry  100  with suitable electrical components) to allow master test station  200  and inspection test stations  182  to measure verification coupons  326  having a wide range of impedance characteristics. In general, measuring verification coupons  326  having a wide range of impedance characteristics ensures that inspection test stations  182  can perform accurate measurements on components under test having different impedance characteristics. 
       FIGS. 11A-11D  are diagrams of verification coupons  326  formed with circuitry  100  having different electrical components arranged in a series configuration between signal contacts  228 - 1  (e.g., verification coupon  326  may have a first configuration of circuitry  100  shown by verification coupon  326 - 1  of  FIG. 11A , verification coupon  326  may have a second configuration shown by verification coupon  326 - 2  of  FIG. 11B , etc.). During test operations, test signals may be provided to/from signal contacts  228 - 1  (e.g., test signals may be received from tester  204  in master test station  200  and tester  304  in inspection test stations  182 ). Measuring verification coupons  326 - 1 ,  326 - 2 ,  326 - 3 , and  326 - 4  with master test station  200  and inspection test stations  182  may provide testing for a wide range of impedance characteristics. 
     In one suitable embodiment of the present invention, circuitry  100  in verification coupon  326 - 1  may include a capacitive structure such as capacitor  332  connected in series between signal contacts  228 - 1  as shown in  FIG. 11A . In another suitable arrangement of the present invention, circuitry  100  in verification coupon  326 - 2  may include an inductive structure such as inductor  334  connected in series between signal contacts  228 - 1  as shown in  FIG. 11B . In another suitable arrangement, circuitry  100  in verification coupon  326 - 3  may include a resistive structure such as resistor  336  connected in series between signal contacts  228 - 1  as shown in  FIG. 11C . In yet another suitable arrangement, verification coupon  326 - 4  may include a transmission line such as transmission line  338  connected between signal contacts  228 - 1  as shown in  FIG. 11D . Transmission line  338  may be formed having a selected width W to provide transmission line  338  with suitable impedance. 
     Electrical components such as capacitor  332 , inductor  334 , resistor  336 , and transmission line  338  in circuitry  100  may provide the associated verification coupon  326  with respective impedance. Master test station  200  and inspection test stations  182  may perform measurements on each of verification coupon  326 - 1 ,  326 - 2 ,  326 - 3 , and  326 - 4  to characterize the performance of inspection test stations  182  at a wide range of tested impedances. 
       FIGS. 12A-12D  are diagrams of verification coupons formed with circuitry  100  having different electrical components arranged in a shunt configuration between signal contacts  228 - 1  (e.g., verification coupon  326  may have a first configuration of circuitry  100  shown by verification coupon  326 - 5  of  FIG. 12A , may have a second configuration shown by verification coupon  326 - 6  of  FIG. 12B , etc.). During test operations, test signals may be provided to/from signal contacts  228 - 1  (e.g., test signals may be received from tester  204  in master test station  200  and tester  304  in inspection test stations  182 ). Measuring verification coupons  326 - 5 ,  326 - 6 , and  326 - 7  with master test station  200  and inspection test stations  182  may provide testing for a wide range of impedance characteristics. 
     In one suitable embodiment of the present invention, circuitry  100  in verification coupon  326 - 5  may include a capacitive structure such as capacitor  340  connected in a shunt configuration between signal contacts  228 - 1  and ground  237  as shown in  FIG. 12A . In another suitable arrangement, circuitry  100  in verification coupon  326 - 6  may include an inductive structure such as inductor  334  connected in a shunt configuration between signal contacts  228 - 1  and ground  237  as shown in  FIG. 12B . In yet another suitable arrangement, circuitry  100  in calibration coupon  226 - 7  may include a resistive structure such as resistor  336  connected in a shunt configuration between signal contacts  228 - 1  and ground  237  as shown in  FIG. 12C . Electrical components such as capacitor  340 , inductor  342 , and resistor  344  in circuitry  100  may provide the associated verification coupon  326  with respective impedance. Master test station  200  and inspection test stations  182  may perform measurements on each of verification coupon  326 - 5 ,  326 - 6 , and  326 - 7  to characterize the performance of inspection test stations  182  at a wide range of impedance characteristics. 
     Inspection test station  182  may measure radio-frequency characteristics of verification coupon  326  such as S parameters for each configuration of verification coupon  326  shown in  FIGS. 11 and 12  (e.g., for verification coupons  326 - 1 ,  326 - 2 , etc.). The measured S parameters for each configuration of verification coupon  326  may be compared to baseline S parameters determined by calibrated master test station  200  to characterize the performance of inspection test station  182 . 
     Verification coupons  326  of  FIGS. 11 and 12  are merely illustrative. If desired, circuitry  100  in verification coupons  326  may include other components such as variable capacitors, variable resistive loads, variable inductors, radio-frequency switches, or any other suitable components. Circuitry  100  in verification coupons  326  may be formed with any number and combination of capacitors, resistors, inductors, and transmission lines connected in series or shunt configurations between any number of contacts  228  and ground  237  so that verification coupons  326  have suitable impedance characteristics. 
     A flow chart of illustrative steps for testing inspection test stations such as inspection test station  182  of  FIG. 10  is shown in  FIG. 13 . In testing inspection test station  182 , it may be desirable to separate the effects associated with the transmission medium (e.g., the effects associated with test cables  318 , test fixture  310 , probe structure  312 , and probe contacts  324 ) from circuitry  100  in verification coupons  326 . At radio-frequencies, systematic effects such as signal leakage and impedance mismatch can affect measured data. In a stable test environment, such types of systematic effects are repeatable and can be characterized and removed via calibration. 
     At step  270  (i.e., after calibrating master test station  200 ), calibrated master test station  200  may probe verification coupon  326  by coupling probe contacts  224  ( FIG. 5 ) to contacts  228  on verification coupon  326 . 
     At step  272 , calibrated master test station  200  may measure radio-frequency performance characteristics such as S parameters of verification coupon  326 . The S parameters measured by master test station  200  may establish baseline S parameters for the associated verification coupon  326 . The baseline S parameters may be used to test inspection test stations  182  in manufacturing system  178  ( FIG. 3 ). 
     At step  274 , verification coupon  326  may be mounted to a support structure such as coupon support structure  308  (e.g., a printed circuit board). 
     At step  276 , verification coupon  326  mounted to coupon support structure  308  may be passed to a selected inspection test station  182  (e.g., verification coupon  326  may be passed to inspection test station  182 - 1 , inspection test station  182 - 2 , etc.). Contacts  228  in verification coupon  326  may couple to probe tips  324  of inspection test station  182  during testing. 
     At step  278 , radio-frequency tester  304  may be calibrated to remove potential errors that are associated with radio-frequency tester  304 , coaxial cables  318  (i.e., cables  318 - 1  and  318 - 2 ), test fixture  310 , probe structure  312 , and probe tips  324  using step  250  of  FIG. 7  (e.g., by using the TRL approach or any other suitable calibration procedure). In another suitable arrangement, step  278  is performed prior to step  270 . Once this step is complete, measurements gathered using tester  304  will only reflect the behavior of structures coupled to probe tips  324  (e.g., ports  316 - 1  and  316 - 2  of tester  304  are virtually extended to the ends of probe tips  324  so that a new reference plane  322  is established as shown in  FIG. 10 ). 
     At step  280 , inspection test station  280  may measure radio-frequency performance characteristics such as S parameters of the mounted verification coupon  326 . The S parameters measured by inspection test station  182  may be compared to the baseline S parameters determined by master test station  200  during step  272 . 
     If the S parameters measured by inspection test station  182  do not acceptably match the baseline S parameters, inspection test station  182  may be labeled as a “failing” test station. If the S parameters measured by inspection test station  182  acceptably match the baseline S parameters, inspection test station  182  may be labeled as a “passing” test station. 
     If inspection test stations  182  in manufacturing system  178  remain to be tested using a given verification coupon  326 , processing may loop back to step  276  as shown by path  282 . If no inspection test stations  182  remain to be tested using the given verification coupon  326 , inspection test station  182  may test the performance of additional verification coupons  326 . For example, verification coupon  326 - 1  having a capacitor connected in series between signal contacts  228 - 1  (see  FIGS. 11A-11D ) may be used to test the radio-frequency performance of inspection test stations  182 . Once test operations are complete, verification coupon  326 - 2  having an inductor connected in series between two contacts  228  may be used to test the radio-frequency performance of inspection test stations  182 . In this way, the radio-frequency performance of each inspection test station  182  in manufacturing system  178  may be tested using a number of verification coupons having different impedance characteristics. 
     Master test system  200 , inspection test system  182 , calibration coupons  226 , and verification coupons  326  of  FIGS. 3-13  are merely illustrative. If desired, master test system  200  may include a test fixture such as test fixture  310  and probing structures such as probing structure  312  of  FIG. 10  for measuring the baseline S parameters of verification coupons  326 . Calibration coupons  226  and verification coupons  326  may have any number of contacts  228 . Master test system  200  and inspection test stations  182  may measure any suitable radio-frequency performance characteristic associated with calibration coupons  226  and verification coupons  326 . Master test station  200  may measure radio-frequency performance characteristics of a given verification coupon  326  while another verification coupon is being measured by inspection test stations  182 . Verification coupons  326  may be supplied to inspection test stations  182  by master test station  200  for measurement in parallel. 
     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. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20121214
Publication Date: 20151020
Grant Date: 20151020
Priority Date: 20121214
Inventors: NATH JAYESH
HAN LIANG
MOW MATTHEW A.
TSAI MING-JU
NICKEL JOSHUA G.
XU HAO
BEVELACQUA PETER
PASCOLINI MATTIA
SCHLUB ROBERT W.
CABALLERO RUBEN
Assignee: APPLE INC
CPC Classifications: [{"code": "G01R31/2822", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01R31/2879", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01R35/007", "inventive": true, "first": true, "tree": "[]"}, {"code": "G01R31/3191", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01R31/3191", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01R31/2822", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01R35/007", "inventive": true, "first": true, "tree": "[]"}, {"code": "G01R31/2879", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 50930170