IPC-TM-650 EN 2022 试验方法.pdf - 第431页

5.4.2 Record the capacitance of the air filled cell as C 1 to the nearest .01 pf (or nearest .001 pf if the 0-20 pf scale is used). 5.4.3 Remove the specimen from the humidity controlled environment. 5.4.4 Insert the fir…

4.3

Test Leads

RG 58/U coax cables approximately

304.8 mm [12 in] long with suitable connectors for the bridge.

One lead shall have a banana plug (high lead) and the low lead

should have a GR874

the cell end. (Note: The use of a

G874-QBJA

instead

of the standard GR874 will permit a

BNC

connector

to be used for the cell connection of the low

lead, reducing the chances of damaging the 874 connector.)

4.4

Flask

with stopper (for silicone fluid storage).

4.5

Beaker

for cell overflow.

4.6

Funnel.

4.7

Filter

paper (coarse).

4.8

Centistoke Dow Corning 200 Fluid (500 ml minimum).

Note: Fluid must be at the same ambient temperature as the

test cell and should be stored in close proximity to the test

cell.

4.9

Forceps

or large tweezers.

5.0

Procedure

5.1 Conditioning

All

materials which are affected by mois-

ture, including all reinforced laminates and most films, should

be conditioned at 23°C ± 2°C50±5% RH for a minimum of

24 hours prior to testing. If required by the specification,

specimens may be tested after humidity or water immersion

or tested after desiccation.

5.2

Test Conditions

For

ambient temperature tests the

temperature should be 23°C ± 2°C.

Note: Variation should not exceed 1°C during the test. Ambi-

ent humidity is not critical for most materials. The exception is

very thin, very hydroscopic material such as polyimide film,

where moisture content may be well over 1%. Such material

must be tested at the desired humidity since the dielectric

constant will increase measurably with moisture content and

changes may occur very rapidly after removal from a con-

trolled environment. For materials which experience glass

transitions in the room temperature region, e.g., PTFE, some

acrylics, the temperature should be 23°C ± 1°C.

5.3

Set Up

5.3.1

Open

the electrode on the cell. Blow out the cell using

clean compressed air to remove any dust or silicone fluid.

5.3.2

Warm

up the bridge for at least the minimum amount

of time recommended by the manufacturer.

5.3.3

Attach

the low lead to the guarded electrode of the

cell and the bridge.

5.3.4

Attach

the high lead to the bridge and place the

banana plug in the vicinity of, but not touching, the banana

plug jack of the test cell.

Note: Be certain the shielding on the high lead does not con-

tact the banana plug.

5.3.5

Set

the bridge up on appropriate ranges:

Capacitance: 200 pf (or 100 pf)

Conductance: microsiemens

0-2 PTFE and very low loss material.

0-20 Epoxy and other moderate loss materials.

0-200 Some phenolic and very high loss materials.

Note: For very thick specimens >3.18 mm [>0.125 in] the 0 to

20 pf range can often be used, increasing the precision of the

measurement. All values must be obtained on the same range

for both capacitance and conductance.

5.3.6

Set

the cell spacing on the LD-3 to approximately

125% of the material thickness 0.51 mm minimum to 7.62

[0.020 in minimum to 0.3 in] Note: The spacing may be as

little as 10% or as much as 50% greater than specimen thick-

ness without a significant effect on results.

5.3.7

Zero

the bridge for both capacitance and conduc-

tance.

5.4

Measurement

5.4.1

Connect

the banana plug of the high lead to the cell.

GR874—Catalogue #874-9414 Gilbert Engineering, Glendale, AZ, (602) 245-1050

4. G874-QBJA—Catalogue #874 QBJA Gilbert Engineering, Glendale, AZ

5. BNC—Catalogue #999-225 Amphenol

IPC-TM-650

Number

2.5.5.3

Subject

Permittivity

(Dielectric Constant) and Loss Tangent (Dissipation

Factor) of Materials (Two Fluid Cell Method)

Date

12/87

Revision

age2of4

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5.4.2

Record

the capacitance of the air filled cell as C

the

nearest .01 pf (or nearest .001 pf if the 0-20 pf scale is

used).

5.4.3 Remove the specimen from the humidity controlled

environment.

5.4.4

Insert

the first specimen to be tested with the marked

corner remaining in the upper left and the right side of the test

specimen against one side of the test cell. Note: This will

ensure that subsequent measurements are taken using the

same area of the specimen.

5.4.5

Read

and record the value of capacitance with the

specimen in the cell as C

5.4.6

Remove

the first specimen and obtain C

for

any other

specimens to be measured with same cell spacing.

5.4.7

After

removing the last specimen from the cell, fill the

cell with Dow Corning 200 Fluid using the funnel and a filter to

remove any small particles from the fluid and collect any

excess fluid from the overflow pipe on the cell with the small

beaker.

5.4.8

Allow

a few seconds for the temperature of the cell

and fluid to equilibrate and record the capacitance of the liq-

uid filled cell as C

Note: If

the capacitance is drifting consistently in one direc-

tion, the fluid is not at equilibrium.

5.4.9

Record

the conductance of the fluid filled as cell G

Note: The

value obtained will vary somewhat with cell spacing

and humidity but should not exceed 500 microsiemen (200

microsiemen if low loss material, with a loss tangent under

.001 is being tested). Values beyond this are generally indica-

tive of problems with the leads, contamination of the fluid or

bridge error and must be corrected if correct dissipation fac-

tor is to be determined.

5.4.10

Insert

the first specimen in the fluid filled cell exactly

as in the dry reading and record the value of the capacitance

as C

and

the value of the conductance as G

Note: Values

should stabilize within a few seconds after speci-

men insertion. If they do not there is very likely air trapped in

the cell. This is quite common if multiple thin specimens are

used to form one test specimen. If this occurs presoaking the

specimen with fluid before immersion and inserting one ply at

a time should eliminate the problem.

5.4.11

Remove

the first specimen and insert each subse-

quent specimen in the same order as the dry values were

obtained and record the C

and

values

for each.

5.4.12 After

the last specimen is measured and removed

from fluid, check and record the values of the capacitance

and conductance.

Note: If the level of the fluid with the specimen removed does

not cover the electrodes, fill the cell before checking the final

values. This check on C

will

be used to verify the amount of

influence that changes in ambient temperature have had on

the values obtained.

6.0

Calculation

6.1

Calculate

the value of the permittivity (dielectric constant)

of each specimen tested using the equation:

DK =

1.00058

(C3−C1)(C2−C1) C4

(C3−C1) C4 −(C4−C2) C3

Round

the value obtained to the nearest .01.

6.2

Calculate

the value of the loss tangent (dissipation fac-

tor) of each specimen tested using the equation:

DF =

6.2832

* .99942 C1−C4

C4−C2

6.2832

−

6.2832

Round

the value to the nearest .0001.

Note: Values should be calculated using a computer and must

not be rounded prematurely.

6.3

the value of C

changed

during the course of the mea-

surements, use the final values of C

and

the value of C

and

the values on the last specimen for C

and

recalcu-

late the DK and Df of the final specimen. If the difference in DK

values is significant, the temperature of the cell must be con-

trolled more precisely during the measurement period.

6.4

Calculate

the average permittivity (dielectric constant) (if

more than one specimen was tested).

6.5

Calculate

the average loss tangent (dissipation factor) (if

more than one specimen was tested).

7.0

Report

IPC-TM-650

Number

2.5.5.3

Subject

Permittivity

(Dielectric Constant) and Loss Tangent (Dissipation

Factor) of Materials (Two Fluid Cell Method)

Date

12/87

Revision

age3of4

电子技术应用　　　　　　　ｗｗｗ．ＣｈｉｎａＡＥＴ．ｃｏｍ

7.1

Report

the minimum, maximum and average values of

the permittivity (dielectric constant).

7.2

Report the average value of the loss tangent (dissipation

factor).

7.3 Report the specimen preconditioning, e.g., C-24/23/50.

7.4 Report

the actual test conditions for temperature and

humidity.

7.5

Report

if the specimen was built up.

7.6

Report

the approximate cell spacing.

7.7

Report

any anomalies in the test or variations from the

prescribed procedures or tolerances.

IPC-2553-1

Figure

IPC-TM-650

Number

2.5.5.3

Subject

Permittivity

(Dielectric Constant) and Loss Tangent (Dissipation

Factor) of Materials (Two Fluid Cell Method)

Date

12/87

Revision

age4of4

电子技术应用　　　　　　　ｗｗｗ．ＣｈｉｎａＡＥＴ．ｃｏｍ