IPC-TM-650 EN 2022 试验方法.pdf - 第465页

An alternate method for trimming the copper strip is to use a sharp scalpel. However, this can smear the copper across that the specimen end surface, especially with thin speci- mens, and may introduce end fringing error…

This

method is best suited for measurements at ambient tem-

peratures in a controlled laboratory atmosphere. It may be

possible to adapt it for measurements at other temperatures.

6.1.1

The

steel clamping bars, copper clamping plates, and

the specimen assembly with copper foil are stacked with the

help of a jig (Figure 5) to assure the following:

a) One side surface or edge of each steel bar, copper plate,

specimen card, and ground plane copper foil lie in a

common plane.

b) The end surfaces of the steel bars lie in a common plane

within a 0.1 mm tolerance.

c) The ends of the copper plates extend beyond the steel

bars equally on both ends within a 0.1 mm tolerance.

d) The ends of copper plates, specimen cards, and copper

foil ground planes lie in a vertical plane within a 0.1 mm

tolerance.

e) In the case of specimen type A, the center conductor,

whose length extends enough beyond both ends of the

specimen cards to be gripped in tension and positioned,

is centered across the width of the specimen cards.

6.1.2

The

stack formed in 6.1.1 is clamped with a specified

total force. For a selected specimen length of 153 mm or less,

the force is applied through a force gage in a line centered on

the outer faces of the steel bars. For greater lengths, the force

should be distributed through force gages at two or more

positions not further than 153 mm apart along the length to

get uniformity of force per unit length along the specimen

length with minimal deflection of the steel bars. Thus, for a

304.8 mm length, apply equal forces at the 76.2 mm and

228.6 mm positions. If a 381 mm was used, apply force at the

63.5 mm, 190.5 mm, and 317.5 mm positions.

6.1.3

Remove

the alignment jig used in 6.1.1.

6.1.4

For

type A specimens, the center copper strip will still

be extending beyond the plane formed by the surfaces of the

copper plates, ground foil, and specimen end. This is clipped

off cleanly flush with that plane. One preferred method for

doing this is to use a lever-action toe nail clipper with a con-

vex shaped cutting pattern modified by grinding so that the

metal extending beyond the cutting edges is removed so that

the cutting edges are able to reach to the specimen edge for

cutting the copper strip.

IPC-25551-9

Figure

9 Probe Assembly Position (See 6.1.5) for One End of the Clamped Stack

Note: This figure shows coaxial probe with fitting and Be-Cu alloy wire for ground continuity without showing supporting mechanical

structures and adjustments.

IPC-TM-650

Number

2.5.5.5.1

Subject

Stripline

Test for Complex Relative Permittivity of Circuit Board

Materials to 14 GHz

Date

3/98

Revision

age7of11

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alternate method for trimming the copper strip is to use a

sharp scalpel. However, this can smear the copper across

that the specimen end surface, especially with thin speci-

mens, and may introduce end fringing errors on short L val-

ues.

6.1.5

Fasten

the probe assemblies to the clamped stack at

both ends so that the coaxial cable probe end is centered on

the stripline resonator center line. Adjust the assembly so the

contact areas on the soldered copper fitting make firm electri-

cal contact by the wires to both top and bottom copper

plates. Figure 9 shows by vertical and horizontal sectional

views through the stripline resonator centerline this relation-

ship among:

• the copper ground plates (see 5.1.2).

• the specimen with conductors (see 3.0).

• the coaxial cable with extended center conductor end (see

5.2.1).

• the copper fitting (see 5.2.2) soldered to the coaxial cable.

• the wire connection (see 5.2.3).

For the purpose of this method horizontal orientation is paral-

lel to the plane of the specimen surface in the fixture. See

three requirements under 5.2.4.

6.1.6

Adjust

the position of the coaxial cable probe ends so

the air gaps they form with the stripline resonator element are

equal. This may be done with the help of a network analyzer

set for lowest frequency by adjusting the gaps smaller until

each causes a sudden shift in reflected or transmitted power,

then adjusting them back to a small gap value, equal on both

ends.

6.1.7

With

the probe’s longitudinal position set to a small air

gap such as 0.05 mm, use an appropriate means with the

electronic instrumentation to identify the approximate location

of the lowest resonant frequency (the fundamental where the

resonator length is half the wavelength in the material being

tested) and a series of resonances (harmonics) up to the high-

est frequency of interest. Ideally harmonic resonances occur

at each integer multiple of the fundamental resonance. The

integer multiples are the values of n in formula 1 of section

7.1. Select which of these resonances will be measured as

discussed in section 6.3, 6.4, or 6.5.

6.2

Adjustment of Air Gap for Each Resonance

Before

the

measurement at each resonance, adjust the air gaps at

each probe an equal amount to get the dB insertion loss at

the maximum transmission to a recommended value between

49.5 and 51.5 dB. As resonant frequency is increased from

resonance to resonance for a given specimen, the gap

required for a nominal 50 dB insertion loss at resonance tends

to increase. A high value dB minimizes the correction for

unloaded Q and makes this correction less sensitive to poor

data on the baseline dB of the instrumentation. Too high a dB

value will put the measurements down in the noise region of

the instrumentation, making results less certain and less

reproducible.

6.3

Manual Measurement of the Specimen

The

follow-

ing procedure is most applicable where only equipment as

described in 4.1 is available. The equipment of 4.2 could also

be operated manually.

6.3.1

The

resonant frequency shall be found by scanning

frequency over the expected transmission range of the test

resonator. The frequency shall be precisely adjusted to get a

maximum reading of power in dB.

6.3.2

Determine

half power points by adjusting frequency to

give three dB readings both above and below the maximum

transmission frequency. Measure each frequency with the fre-

quency meter and record the results:

•f1-3dBdown, below the maximum transmission fre-

quency.

•f2-3dBdown, above the maximum transmission fre-

quency.

6.4

Automated Measurement of the Specimen

For

automated system to be used in performing the measure-

ment, computer software is needed that will collect paired

values of frequency and transmitted power. From this data,

the frequency for maximum power transmission and the fre-

quencies of the half power points are determined. The com-

puter program may optionally include computation of permit-

tivity and loss tangent as described in section 7.0. Results and

collected data may be displayed on the screen, stored in a

disk file, sent to a printer, or any combination of these.

In one possible mode of operation, with the equipment

described in 4.2, the sequence of steps described in 6.4.1

through 6.4.4 is performed as many times as necessary to get

enough data to complete the test procedure. The computer is

designated as the controller on the GPIB.

IPC-TM-650

Number

2.5.5.5.1

Subject

Stripline

Test for Complex Relative Permittivity of Circuit Board

Materials to 14 GHz

Date

3/98

Revision

age8of11

电子技术应用　　　　　　　ｗｗｗ．ＣｈｉｎａＡＥＴ．ｃｏｍ

6.4.1

The

computer sets the sweeper to a selected carrier

wave frequency without an AM or FM audio signal and to a

desired output power level, such as 10 dBm.

6.4.2 The same frequency is given to the synchronizer with

instructions to lock the frequency of the sweeper to the speci-

fied value.

6.4.3

The

computer checks the synchronizer for status until

the status value indicates the frequency is locked.

6.4.4

The

power meter reading is obtained by the computer.

Since it takes a finite amount of time for the power sensor to

stabilize, either a delay is used or the reading may be taken

repeatedly until consecutive readings meet a given require-

ment for stability.

6.5

Use of the Network Analyzer for Measurement of

the Specimen

automated network analyzer may be

used either by operating the front panel controls manually or

under computer control with suitable specialized software.

The fixture with the specimen is connected by test cables and

adapters as a device under test. Set up the instrument so the

Cartesian screen display shows the S21 parameter, the

transmission/incident power ratio, in negative dB vertical scale

units versus frequency on the horizontal scale. Select the start

and stop frequency range to sweep across the resonance

peak and at least 3 dB below the peak. Adjust the start and

stop frequency values as narrowly as possible, but still include

the resonant peak and the portions of the response curve on

both sides of it that extend 3 dB downward.

6.5.1 The

first option is to get the three points (f

and

)

described in 6.3 or 6.4. Determine the resonant dB

and

frequency

values

for the highest point (maximum) on the

response curve. With manual operation, instrument program

features may be available to do this very quickly. On the

response curve to the left and right of f

locate the f

and

points

as near as possible to 3 dB below dB

These

may then be used in the calculations shown in 7.2.

6.5.2

second option requires a computer external to the

instrument. Collect from the network analyzer all of the f, dB

data points represented by the response curve between f

and

apply non-linear regression analysis tech-

niques to determine statistically values for Q

loaded

and

that

best fit the f

paired

data points to the formula.

-1

0log

(10)

log

(

1+4Q

loaded

-1

)

[1]

where 10 log

(10)

is the constant for converting from log

dB.

This formula may be derived from formula 5 with the rea-

sonable assumption that f

-f

equals

-f

The statistically

derived values for f

and

Q would then be used in formulas 2

of section 7.1, formula 3 of section 7.2, and formula 6 of sec-

tion 7.3 respectively.

This has been found to fit the collected data points very well

at all regions across the entire f

range.

It is a simplified

version of the non-linear regression method for complex S21

parameters described by Vanzura

7.0

Calculations

7.1 Stripline Permittivity

Use

special care to assign the

correct n value for each resonance measured.

At resonance, the electrical length of the resonator circuit is an

integral number of half wavelengths. The effective stripline

permittivity, ε

can be calculated from the frequency of maxi-

mum transmission as follows:

nC/(2f

+ ∆L))]

[2]

where

n is the number of half wavelengths along the resonant

strip of length L in mm, ∆L is the total effective increase in

length of the resonant strip due to the fringing field at the ends

of the resonant strip, C (the speed of light) is 2.9978z10

mm/s,

and f

Hz (or cycles/s) is the measured resonant

(maximum transmission) frequency.

The resonator ends coincide with the end edges of both the

dielectric and the ground planes. The relative fringing field at

the ends becomes extremely small. It has been the practice

with this method to ignore this fringing field and consider the

∆L value to be zero in the calculation of stripline permittivity.

7.2

Calculation of Effective Dielectric Loss Tangent

tan δ =

1/Q

unloaded

1/Q

[3]

where:

1/Q

the loss factor of the conductor

1/Q

unloaded

the total loss factor of the unloaded resonator

due only to the dielectric, copper, and copper-dielectric inter-

face, and does not include loss due to coupling of the probes.

7.2.1

The resonator loss factor

The

measurement of the

resonance gives a value for the loss factor of the resonator

with loading due to probe coupling (1/Q

loaded

IPC-TM-650

Number

2.5.5.5.1

Subject

Stripline

Test for Complex Relative Permittivity of Circuit Board

Materials to 14 GHz

Date

3/98

Revision

age9of11

电子技术应用　　　　　　　ｗｗｗ．ＣｈｉｎａＡＥＴ．ｃｏｍ