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EIA-364-1 09

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EIA-364-1 09

    EIA

    STANDARD

    TP-109

    LOOP INDUCTANCE

    MEASUREMENT TEST

    PROCEDURE FOR ELECTRICAL

    CONNECTORS

    (1 nH 10 nH)

    EIA-364-1 09

    May 2003 ELECTRONIC COMPONENTS, ASSEMBLIES & MATERIALS

    ASSOCIATION

    THE ELECTRONIC COMPONENTS SECTOR OF THE ELECTRONIC INDUSTRIES

    ALLIANCE

ANSI/EIA-364-109-2003

Approved: May 20, 2003

EIA-364-109

    NOTICE

    EIA Engineering Standards and Publications are designed to serve the public interest

    through eliminating misunderstandings between manufacturers and purchasers,

    facilitating interchangeability and improvement of products, and assisting the purchaser

    in selecting and obtaining with minimum delay the proper product for his particular need.

    Existence of such Standards and Publications shall not in any respect preclude any

    member or nonmember of EIA from manufacturing or selling products not conforming to

    such Standards and Publications, nor shall the existence of such Standards and

    Publications preclude their voluntary use by those other than EIA members, whether the

    standard is to be used either domestically or internationally.

    Standards and Publications are adopted by EIA in accordance with the American

    National Standards Institute (ANSI) patent policy. By such action, EIA does not assume

    any liability to any patent owner, nor does it assume any obligation whatever to parties

    adopting the Standard or Publication.

    This EIA Standard is considered to have International Standardization implication, but

the International Electrotechnical Commission activity has not progressed to the point

    where a valid comparison between the EIA Standard and the IEC document can be made.

    This Standard does not purport to address all safety problems associated with its use or

    all applicable regulatory requirements. It is the responsibility of the user of this Standard

    to establish appropriate safety and health practices and to determine the applicability of

    regulatory limitations before its use.

    (From Standards Proposal No. 4831, formulated under the cognizance of the ECA CE-2.0

    Committee on National Connector Standards.

    Published by

    ?ELECTRONIC INDUSTRIES ALLIANCE 2003

    Technology Strategy & Standards Department

    2500 Wilson Boulevard

    Arlington, VA 22201

    PRICE: Please refer to the current

    Catalog of EIA Electronic Industries Alliance Standards and Engineering Publications

    or call Global Engineering Documents, USA and Canada (1-800-854-7179)

    International (303-397-7956)

    All rights reserved

    Printed in U.S.A.

    i

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    U.S.A. and Canada 1-800-854-7179, International (303) 397-7956

    CONTENTS

    Clause Page

    1 Introduction ............................................................................................................... 1

    1.1 Scope ......................................................................................................................... 1

    1.2 Object ........................................................................................................................ 1

    1.3 Definitions ................................................................................................................ 1

    2 Test resources ........................................................................................................... 3

    2.1 Equipment ................................................................................................................. 3

    2.2 Fixture ....................................................................................................................... 3

3 Test specimen ............................................................................................................ 5

    3.1 Description ................................................................................................................ 5

    4 Test procedure ........................................................................................................... 5

    5 Details to be specified ............................................................................................... 6 6 Test documentation ................................................................................................... 7 Figure

    A.1 Example of test equipment setup for loop inductance measurements ......................

    A-1

    A.2 Example of fixture loop inductance measurements setup ......................................... A-2

    A.3 Example of loop inductance measurements setup .................................................... A-3

    A.4 Diagram of probes contacting the bottom side of the printed circuit board test

    fixture ................................................................................................................. A-4

    B.1 Short reference trace ................................................................................................. B-2

    B.2 Open reference trace ................................................................................................. B-2

    B.3 Fifty ohm load reference trace .................................................................................. B-3

    B.4 Transmission reference trace .................................................................................... B-3

    C.1 Microstrip (a) and stripline (b) geometries ...............................................................

    C-1

    C.2 Buried microstrip geometry ......................................................................................

    C-2

    D.1 Example of mutual inductance coupling coefficient measurement setup .................

    D-3

    E.1 Conductor arrangement and current path convention for description of inductance E-2

    ii

    Annex Page

    A Loop inductance measurement setup (normative) .................................................... A-1 B Calibration standards and test board reference traces (informative) ........................ B-1 C Printed circuit board design considerations for electronics measurements

    (informative) .............................................................................................................

    C-1

    D Mutual inductance coupling coefficient (informative) ............................................. D-1 iii EIA-364-109 Page 1

    TEST PROCEDURE No. 109

    LOOP INDUCTANCE MEASUREMENT TEST PROCEDURE FOR ELECTRICAL

    CONNECTORS (1 nH 10 nH)

    (From EIA Standards Proposal No. 4831, formulated under the cognizance EIA CE-2.0

    Committee on National Connector Standards.)

    1 Introduction

    1.1 Scope

    This procedure applies to interconnect assemblies, such as electrical connectors and

sockets.

    1.2 Object

    This standard describes a test method to measure the loop inductance (1 nH 10 nH

    range) in the frequency domain using probes and vector network analyzer.

    NOTE ? This test method is written for test professionals who are

    knowledgeable in the electronics field and are trained to use the

    referenced equipment. Because the measurement values are heavily

    influenced by the fixture and equipment this method cannot describe

    all of the possible combinations. The major equipment manufacturers

    provide Application Notes for more in-depth technical description of

    how to optimize the use of their equipment. It is imperative that the

    referencing document include the necessary description and sketches

    for the test professional to understand how to setup and perform the

    requested measurements. 1.3 Definitions

    1.3.1 Specimen environment impedance

    The impedance presented to the signal conductors by the fixture. This impedance is a

    result of transmission lines, termination resistors, attached receivers or signal sources,

    and fixture parasitics.

    1.3.2 Inductance

    The property of a circuit or circuit element that opposes a change in current flow.

    Inductance causes current changes to lag behind voltage changes. It is measured in

    Henrys.

    EIA-364-109 Page 2

    1.3.3 Self inductance (L)

    The inductance of a single conductor.

    1.3.4 Mutual inductance (L) mThe common property of two electric conductors whereby a voltage (electromotive force)

    is induced across one conductor by a change of current in the other conductor.

    1.3.5 Loop inductance (L) LoopThe inductance of two or more conductors in which the current flows into one conductor

    and returns through the other(s). The loop is defined as the current path inscribed by the

    ‗drive‘ and ‗return‘ path in the conductors.

where: L= self inductance of the driven conductor 1

    L= self inductance of the return path conductor(s) 2

    L= mutual inductance between the drive and return path conductors. m

    1.3.6 Mutual inductance coupling coefficient (K) m

    The measure of degree of magnetic coupling between two conductors. It is a unitless

    parameter and is defined as follows:

1.3.7 Inductive reactance

    The resistance presented to an alternating current (ac) due to the inductance of a

    connector and is measured in ohms. It is also the imaginary term of the impedance and is

    directly proportional to the inductance and to the frequency of the applied voltage. 1.3.8 Termination (electronics usage)

    An impedance connected to the end of a transmission line, typically to minimize reflected energy on the line.

    EIA-364-109 Page 3

    2 Test resources

    2.1 Equipment

    A vector network analyzer shall be used. Microprobes, semi-rigid coax, or similar high frequency test hardware shall be used to minimize fixture influence on the measurement results. It is recommended that a precision x-y positioning station be used to prevent probe damage and provide precision, consistent probe placement. See annex A for sketches of the probes and test equipment set up.

    NOTES

    1 The test professional should be aware of the frequency limitations of the fixture.

    2 The test professional should be aware of any limitations of any mathematical

    functions performed (e.g. normalization, inverse FFT, or software filtering.)

    2.2 Fixture

    The generic term ―probe(s)‖ is used throughout the procedure to refer to semi-rigid coax,

    commercially available microprobes, or similar test hardware.

    The ―fixture‖ shall consist of either the probes alone or the probes in conjunction with a

    test board.

    2.2.1 General

    2.2.1.1 The fixture shall provide a low inductance path to the specimen. It is recommended that the fixture inductance be less than the specimen inductance. This can be aided by keeping the trace lengths as short as possible, and the traces as wide as possible.

    2.2.1.2 The specimen may be probed directly or through a test board. It is recommended that the specimen be probed directly (without a test board) to minimize measurement error. Test boards, when used, shall provide pads such that the probes may contact the board. Measurement variations can be minimized by keeping the pads as small as possible as this will allow repeatable microprobe placement and more uniform pad thickness.

    2.2.1.3 The fixture shall allow one signal line to be driven at a time. The fixture shall allow one or more return path conductors to be connected to the measuring equipment. The fixture(s) shall allow for enough measurements throughout the specimen such that variations in geometries, materials, transmission paths, etc. may be demonstrated and provide a representative sampling of specimen performance.

    EIA-364-109 Page 4

    NOTE ? The fixture geometry and materials will impact the measurements due to

    the fixture parasitics. Usually the product's intended use dictates the most meaningful

    way to fixture it.

    2.2.1.4 The far end of the driven line should be terminated in a low inductance electrical short circuit to the return conductor(s). The short circuit may be achieved by using a copper block or by shorting together all contacts on the test board.

    2.2.2 Specimen environment impedance

Unless otherwise specified in the referencing document, the specimen environment

    impedance shall match the impedance of the test equipment. Typically this will be 50

    ohms.

    2.2.3 Calibration features

    NOTE ? The term ―calibration‖ used in this document is not to be confused with

    the periodic factory equipment calibration. Calibration is used in the sense of

    characterizing the fixture so that when the ―fixture plus specimen‖ measurement is

    taken, the characteristics of the specimen alone can be accurately determined. 2.2.4.1 Equipment calibration standard

    For calibration of the vector network analyzer, calibration standards shall be used to

    conduct the open, short, and load calibration. When probes are used the calibration shall

    be conducted such that the calibration plane is at the tip of the probes. For example a

    ceramic substrate with open, short, and load standards may be used.

    NOTE ? Other calibration techniques such as through-reflect-line may be used.

    The calibration standard and fixture shall incorporate features appropriate to the

    calibration method(s) being used.

    2.2.4.2 Test board characterization structure

    The test board, if used, shall provide a reference structure such that a loop inductance

    measurement

    EIA-364-109 Page 5

    can be conducted. This structure shall be identical to that used for the measurement of the specimen, except that a short circuit is included between the driven and return paths

    where the specimen would otherwise be located. It is recommended that a ground plane

    be used as the return path to provide the lowest possible inductance, to minimize the

    effect of the fixture on the measurement result. See annex C for a discussion of

    calibration and reference traces.

    EIA-364-109 Page 6

    3 Test specimen

    3.1 Description

    For this test procedure the test specimen shall be as follows:

    3.1.1 Connectors

    A connector or mated connector pair.

    3.1.2 Sockets

    A socket and test device.

    4 Test procedure

    for loop inductance. 4.1 Set the vector network analyzer to measure S11

    4.2 Calibrate the equipment and fixture according to the manufacturer‘s specifications

    using the calibration standard. The calibration plane is to be directly at the probe interface to the fixture; see 2.2.4.1 for more detailed information. Unless otherwise specified in the referencing document it is recommended that the following equipment settings be used:

    ? Smith chart format,

    ? set network analyzer to display inductance values,

    ? minimum of 401 measurement points,

    ? frequency span conduct both wideband and narrowband sweeps,

    ? no smoothing,

    ? averaging set to 16 or higher.

    NOTE ? ―Wideband‖ sweep is typically the full range of the network analyzer

    and ―narrowband‖ sweep is over a limited range (for example 100

    MHz wide). EIA-364-109 Page 7

    4.3 Fixture measurement

    Position the probes to touch the interface pads of the test board characterization structure.

    Measure and record the loop inductance of the fixture from the Smith chart at the

    frequency(s) of interest.

    NOTE ? A loop inductance vs. frequency graph may be generated through the

    use of data acquisition software and spreadsheet software, if specified

    in the referencing document. EIA-364-109 Page 8

    4.4 Specimen measurement

    4.4.1 Connect the probe to the fixture interface pad of the driven line with the specimen

    installed as shown in figure A.1. Terminate the far end of the driven line in an electrical

    short circuit to the return conductor(s).

    4.4.2 Place the specimen a minimum of 5 cm from any object that may introduce error

    into the measurement.

    4.4.3 Measure and record the loop inductance over the specified test frequency range or

    discrete frequencies.

    4.4.4 Calculate the specimen loop inductance by subtracting the fixture loop inductance,

    (see 4.3) from the specimen plus fixture loop inductance, see 4.4.3.

    NOTE If specified in the referencing document, a loop inductance vs.

    frequency graph may be generated through the use of data acquisition

    software and spreadsheet software. 4.4.5 If requested, repeat 4.4.1 through 4.4.4 on multiple conductors throughout the

    specimen.

    4.4.6 When additional measurements with different test frequencies or ranges are

    required perform the calibration step defined in 4.2, then repeat 4.4.1 through 4.4.5 as

    necessary.

    5 Details to be specified

    The following details shall be specified in the referencing document:

    5.1 Measurement frequency range and/or discrete frequency(s)

    5.2 Special requirements with respect to the fixture, and the short circuit, (see 2.2.1.4)

    construction and electrical properties of each.

    5.3 Signal/ground pattern, including the number and location of signal and grounds. It is

    recommended that enough locations within the specimen be measured to take into

    account the varying loop inductances within the specimen

    5.4 Location of the drive signal connection point, location of the return signal connection

    point and connections to be made to adjacent pins, if any

    5.5 Specimen environment impedance if other than 50 ohms

    5.6 Plots, if desired, and Smith charts or loop inductance vs. frequency graphs

    EIA-364-109 Page 9

    6 Test documentation

    Documentation shall contain the details specified in clause 5, with any exceptions, and the following:

    6.1 Title of test

    6.2 Test equipment used, and date of last and next calibration

    6.3 Description of test fixture and associated calibration structures

    6.4 Values and observations

    6.5 Representative graphs, if available

    6.6 Name of operator and date of test

    EIA-364-109 Page A-1

    Annex

    A Loop inductance measurement setup (normative)

    A.1 Figure A.1 shows an example of a typical test equipment setup for loop inductance measurements including the equipment, cables, probes, and fixture.

    Figure A.1 - Example of test equipment setup for loop inductance measurements

    EIA-364-109 Page A-2

    A.2 Figure A.2 shows an example of the measurement set up for measuring the loop inductance of a fixture with a ground plane return path. The signal and ground vias are shorted together with a copper surface. The test fixture should be designed such that the signal trace, pad interface, and copper surface provide the lowest inductance path from the probe tip to the signal and ground vias. This reference trace and pad interface should represent the same structures and geometries that will be used for the specimen measurement.

    Figure A.2 - Example of fixture loop inductance measurement setup

    EIA-364-109 Page A-3

    A.3 Figure A.3 shows an example of the measurement set up for measuring the loop inductance of the fixture plus specimen. The figure shows an example of the probe, pads, shorting block, and a specimen consisting of an edgecard connector. The ground pad is connected to the test board ground plane (not shown) that is in turn connected to the specimen ground contacts. It is important that the shorting block connect the specified return path conductors, but not adjacent signal pins.

    Figure A.3 - Example of loop inductance measurement setup

    EIA-364-109 Page A-4

    A.4 Figure A.4 shows a drawing of a microprobe contacting the bottom side of the PCB test fixture and the specimen mounted on the opposite side of the PCB. The test professional should be aware that this type of fixture may be used, but that all vias and traces should be taken into consideration when conducting the calibration procedures. Figure A.4 - Diagram of microprobes contacting the bottom side of the printed circuit

    board test fixture

    EIA-364-109 Page B-1

    B Calibration standards and test board reference traces (informative)

    B.1 Calibration standards

    B.1.1 For the equipment calibration, a traceable calibration impedance standard should be used for a reference baseline. Specific equipment calibration should be performed according to the manufacturer‘s instructions. However, care should be taken as to what standards or other fixtures are used for the calibration procedure.

    NOTE ? The term ―calibration‖ used in this document is not to be confused with

    the periodic factory equipment calibration. Calibration is used in the sense of

    characterizing the fixture so that when the ―fixture plus specimen‖ measurement is

    taken, the characteristics of the specimen alone can be accurately determined. B.1.2 When possible the fixture should be designed to allow the attachment of the

    calibration standard as close to the specimen as possible. Reflections from fixture

    imperfections increase measurement error.

    B.1.3 Printed circuit test boards should not be used as calibration standards. Because of different printed circuit board technologies, fabrication control, and material variations, it becomes difficult to insure that different board designs or fabrication techniques will have the same calibration reference for the impedance measurements. The impedance

    value of ―controlled impedance traces‖ on a printed circuit board is typically ? 10% or

    ? 5% of the target value. In measurements and applications, this may be an acceptable tolerance to hold, however, for calibration purposes, this should not be used as a baseline. B.1.4 The use of the traceable standard termination at the end of the test cable will allow the test fixture printed circuit board effects to be measured more accurately. The test professional will be able to accurately measure the impedance or transmission

    characteristic of the printed circuit board fixture, and not allow the test equipment to try to compensate for any fixture discontinuities.

    B.1.5 Figures B.1 through B.4 show single ended test boards using SOLT

    (Short-Open-Load-Through) calibration trace structures. Calibration using other methods, for example TRL (Through-Reflect-Line), will require different structures.

    EIA-364-109 Page B-2

    Figure B.1 Short reference trace

    Figure B.2 Open reference trace

    EIA-364-109 Page B-3

    Figure B.3 Fifty ohm load reference trace

    Figure B.4 Transmission reference trace

    EIA-364-109 Page B-4

    B.2 Test board reference traces

    Test boards shall include reference traces for measuring the frequency domain

    characteristics of the fixture in order to correct for fixture effects (e.g., discontinuities in impedance). Recommended test fixture configurations include:

    B.2.1 A reference trace ending in a via which is shorted to the return path conductor(s). The length of this reference trace should be the same as that of the trace connected to the near end of the specimen.

    B.2.2 A reference trace ending in a via which is open with respect to the return path

    conductor(s). The length of this reference trace should be the same as that of the trace connected to the near end of the specimen.

    B.2.3 A reference trace terminated in the specimen environment impedance. The length

    of this reference trace should be the same as that of the trace connected to the near end of the specimen.

    B.2.4 A reference structure consisting of a through transmission trace whose length is

    equal to the total fixture trace length for a single path, (length of the near end and far end traces). The test fixture shall provide an identical coaxial cable or probe connection at both ends.

    NOTE 1 ? This reference structure should be designed with the same

    configuration in which the specimen would be used in a typical

    application (such as footprint pads, grounds, traces, vias, etc).

    NOTE 2 ? The calibration structures above are described as terminating in a via.

    This is appropriate for pin-in-hole terminations, but is not appropriate

    for all terminations, e.g. surface mount connectors. Ideally the

    reference trace should terminate in the same type of pad or connection

    as the actual connector would experience. EIA-364-109 Page C-1

    w

C Printed circuit board design considerations for electronics measurements (informative)

    This annex provides a general overview of circuit board design considerations for

    numerous electronics measurements, not just inductance. Although several clauses do not

    pertain to inductance measurements, the information is provided for the user who may

    design a single test board to perform multiple electronics measurements.

    C.1 The designer should take precautions in designing printed-circuit boards for

    high-speed testing for several reasons. These include reflections due to impedance

    mismatches, signal attenuation due to skin effect of the narrow conductors, resonance

    effects due to long traces, crosstalk between traces, and others. Printed circuit board

    features that may be of concern include vias, SMT pads, probe interface, etc. Electrical

    discontinuities caused by these features are unavoidable in the test fixture(s), and shall

    not be overlooked as they may affect the impedance results of the specimen. This annex

    can not in the space allotted cover these topics in detail, but will attempt to lay the

    groundwork for further analysis and design, and refer the reader to more detailed

    treatments of the subject. There are a number of excellent references on the subject,

    which are listed at the end of this annex.

    C.2 When the printed circuit board traces approach critical lengths (defined later in the

    document), it becomes essential to design the traces to match the impedance of the test

    equipment to avoid inaccurate results due to reflections. Controlling the line impedance

    of printed circuit board traces is difficult without the use of embedded reference planes in

    the board. The preferred reference plane is one connected to signal ground, but any low

    impedance reference will work (including a voltage plane) if it is sufficiently decoupled.

    The signal line impedance is determined by conductor geometry, including the trace

    width and thickness, distance from the ground or other reference plane or conductor, and

    the dielectric constant of the board material. In the case of differential trace pairs, the

    spacing between the two traces is also critical. Several formulas exist for calculation of

    printed circuit board trace impedance, and a number of impedance calculation software

    tools are also available. The choice of board impedance formula is based on the

    conductors‘ relative placement as well as their position in the board cross-section, some

    common examples of which are shown in the figures below.

    Figure C.1 - Microstrip (a) and stripline (b) geometries EIA-364-109 Page C-2

    C.2.1 In figure C.1 (a), a cross section of a microstrip transmission line is shown. The

    signal line of width w and thickness t lies on top of the surface of the dielectric layer with

    relative dielectric constant ε(typically between 4 and 5 for glass-epoxy boards) at a r

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