IPC-TM-650 EN 2022 试验方法.pdf - 第574页

1 Scope These methods are designed for use in determin- ing the dielectric strength of solid electrical insulating materi- als. 2 Applicable Documents None 3 Test Specimens 3.1 Dimensions The specimens shall be of such a…

7.2

Report

the minimum value in percent of requirement if it

is below the requirement for average electric strength.

7.3

Report the actual thickness range of the material tested

including the minimum and maximum individual thickness

measurements.

7.4

Report

any anomalies in the test or any variations from

the prescribed procedures or tolerances.

8.0 Notes

8.1 This

test method may be modified to an air medium to

predict performance in normal environments more accurately,

however, unless the electrode is effectively guarded, the

breakdown will generally occur in air.

8.2

For

testing the effect of copper foil on clad laminate

under 0.005 inch it is suggested that two inch circular elec-

trodes be left on the 4 inch X 4 inch specimen by etching. The

ground electrode may be slightly larger to assure registration.

8.3

For

materials which are compressible, a standard pres-

sure of 25 PSI is to be used for determining specimen thick-

ness.

IPC-TM-650

Number

2.5.6.2

Subject

Electric

Strength of Printed Wiring Material

Date

8/97

Revision

age3of3

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Scope

These

methods are designed for use in determin-

ing the dielectric strength of solid electrical insulating materi-

als.

Applicable Documents

None

Test Specimens

3.1 Dimensions

The

specimens shall be of such a diam-

eter that flashover will not occur. This usually means that the

diameter should be 76 mm or more.

3.2

Thick Solid Materials

The

breakdown voltage of thick

solid materials may be so high that special test specimens cut

or molded in reduced thickness may be required.

3.3

At Various Thicknesses

When

it is desired to deter-

mine the dielectric strength for different thicknesses of a mate-

rial, it is necessary to test each different thickness, unless the

variation due to thickness is already known.

3.4

Exceptional Conditions

The

special sizes of speci-

mens required for determining dielectric strength under

exceptional conditions shall be as specified in the material

specification.

Equipment/Apparatus

4.1 Transformer

The

desired test voltage may be most

readily obtained by a step-up transformer energized from a

variable low-voltage source. The transformer and its control-

ling equipment shall be of such size and design that the test

specimen in circuit, the crest factor (ratio of maximum to

mean effective) of the test voltage shall not differ by more than

± 5% from that of a sinusoidal wave over the upper half of the

range of test voltage. The crest factor may be checked by

means of a sphere gap or peak-reading voltmeter in conjunc-

tion with a r.m.s. voltmeter. For test specimens of small

capacitance, a testing transformer as small as 500-volt-

ampere rating must be used. Where the wave-form cannot be

determined conveniently, a transformer having a rating of not

less than 2 kilovolt amperes shall be used for voltages not

exceeding 50,000 volts. Tests shall be made at commercial

power frequencies. When a transformer is used at voltages

lower than its full rating, the current drawn from the high-

voltage winding should not exceed the full-load full-voltage

current rating.

4.2

Circuit Breaker

The

test transformer circuit shall be

protected by an automatic circuit-breaking device designed to

open instantaneously on the current produced by breakdown

of the test specimen. Excessive flow of current at the time of

breakdown causes pitting and heating of the electrodes and

thereby increases the work of electrode maintenance and time

of testing.

4.3

Voltage Control

The

rate of voltage rise shall not, for

short time tests, vary more than ± 25% from the specified

rate. Control of voltage may be secured in one of several

ways:

a. Variable-ratio autotransformer

b. Resistance-potential divider

c. Generator-field regulation

d. Induction regulator

Preference should be given to equipment having an approxi-

mately straight-line voltage-time curve over the desired oper-

ating range. Motor drive with variable speed control should be

preferred to manual drive because of the difficulty in maintain-

ing reasonable uniform rate of voltage rise with the latter.

4.4

Voltmeter

The

voltage shall be measured by an

approved method, which gives root-mean-square values,

preferably by means of

a. A voltmeter connected to the secondary of a separate

potential transformer

b. An electrostatic voltmeter in the secondary circuit

c. A voltmeter connected to a well-designed tertiary coil in the

test transformer. A voltmeter connected to the primary side

of the testing transformer may be used only if the ratio of

transformer does not change appreciably with load.

4.5

Electrodes

The

electrodes used for thin solid materials

(sheets and plates) shall be metal disks 5 mm in diameter and

25 mm in length, with the edges rounded to a radius of 6.4

mm. The electrodes used for thick solid materials shall be

metal disks 25 mm in diameter and 25 mm in length, with

edges rounded to a radius of 3.2 mm. The electrodes for

tapes and sheet materials to be compared with tapes shall be

The

Institute for Interconnecting and Packaging Electronic Circuits

2215 Sanders Road • Northbrook, IL 60062

IPC-TM-650

TEST

METHODS MANUAL

Number

2.5.6.3

Subject

Dielectric

Breakdown Voltage and Dielectric

Strength

Date

10/86

Revision

Originating Task Group

N/A

Material

in this Test Methods Manual was voluntarily established by Technical Committees of the IPC. This material is advisory only

and its use or adaptation is entirely voluntary. IPC disclaims all liability of any kind as to the use, application, or adaptation of this

material. Users are also wholly responsible for protecting themselves against all claims or liabilities for patent infringement.

Equipment referenced is for the convenience of the user and does not imply endorsement by the IPC.

age1of3

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opposing

cylindrical rods 6.4 mm in diameter, with edges

rounded to a radius of 0.75 mm. The upper movable elec-

trodes shall weigh 45.35g ± 2g. When 6.4 mm electrodes are

used, it is advisable that they be surrounded by guard elec-

trodes or shrouds.

4.5.1

The

dielectric strength of an insulating material varies

with the thickness of the material and the area and geometry

of the test electrodes, and these should be specified in the

specification. Tests made with different electrodes are not

comparable. Where materials are made up into forms of uni-

form thickness, such as sheets and plates, tests shall be

made upon that thickness of material. In other cases, a thick-

ness of the test specimen and diameter and shape of the

electrode have been selected, which are compatible with con-

venience of testing.

4.6

Equipment Testing Apparatus

4.6.1 For Tests Made in Air

Use

may be made of any well

designed oven of sufficient size to hold the test equipment. It

should be provided with some means of circulating air so that

approximately constant temperature is maintained around the

test specimen and with a thermometer or thermocouple for

measuring the temperature as near the point of test as prac-

ticable to the nearest 1°C.

4.6.2

For Test Under Oil

Use

may be made of an oil bath,

provided with some means for circulating the oil so that the

temperature is substantially uniform around the test speci-

mens and with a thermometer or thermocouple for measuring

the temperature as near the point of test as practicable to the

nearest 1°C.

Procedure

5.1 Test Medium

The

medium to be used in the tests

should be specified in the specification. In general, it is prefer-

able to test materials in the medium, whether air or oil, in

which they are to be used. Where conditions of use are not

well defined, materials should be tested in air up to the point

where the breakdown is so high that an excessive amount of

material is required to prevent flashover to excessive burning

of the surface. For specimens having a high breakdown, such

as the thicker and highgrade materials, it is usually necessary

to make dielectric strength tests under oil: however; it should

be understood that breakdown values obtained under oil are

not comparable with those obtained in air.

5.2

Preparing Specimens

5.2.1

the preparation of test specimens, care shall be

taken to have the surfaces adjacent to the electrodes parallel

and as plane and smooth as the material permits. The dielec-

tric strength of an insulating material varies with the thickness

of the test specimen. Therefore, tests on specimens of differ-

ent thicknesses are not comparable. The thickness used shall

be the average thickness of the sample measured as specified

in the specification involved.

5.2.2

The

dielectric strength of most insulating materials var-

ies with temperature and humidity. The test coiditions to be

used should be specified in the specification. Usually it is

desirable to determine the dielectric behavior of a material

over the range of temperature and humidity to which it is likely

to be subjected in use. When required, materials may be con-

ditioned in a suitably controlled chamber. The test specimen

shall be kept in the chamber long enough to reach a uniform

temperature and humidity prior to testing. When required, the

dielectric strength tests shall be made on the specimen while

still in the conditioning chamber. For purpose of tests, a high-

voltage conductor may be conveniently carried into the cham-

ber through an insulating bushing.

5.3

Positioning and Care of Electrodes

Electrodes

shall

be held truly coaxial. Where electrodes have flat test faces, the

latter shall be parallel to each other. The test faces shall be

kept smooth and polished and free from pitting.

5.4

Application of Voltage

5.4.1 Test for Specified Minimum Requirement

The

voltage

shall be applied and increased at a uniform rate from

zero to the value specified in the material specification and

shall be held at the value for the specified time. Unless other-

wise specified, the rate of rise per second shall be 5% of the

specified voltage. Note that this test is to check for ability to

withstand a specified voltage and not to determine the break-

down value.

5.4.2

Test to Breakdown, Short-time Test

The

voltage

shall be increased from zero to breakdown at a uniform rate.

The rate of rise shall be 0.5 or 1.0 kilovolts per second.

depending on the total test time required and the voltage-time

characteristic of the material. The rate of rise of voltage should

be specified in the material specification.

IPC-TM-650

Number

2.5.6.3

Subject

Dielectric

Breakdown Voltage and Dielectric Strength

Date

10/86

Revision

age2of3

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