IPC-TM-650 EN 2022 试验方法.pdf - 第573页

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 individu…

4.7

Large

beaker or pan filled with ambient temperature dis-

tilled water.

4.8

Rack

for supporting and separating specimens in the

50°C water bath.

4.9

Lint

free paper towels.

5.0

Procedure

5.1 Preconditioning

Unless

otherwise specified, the

specimen shall be conditioned for 48 hours (+2 hours –0

hours) in distilled water maintained at 50°C ± 2°C.

Following this the specimen shall be immersed in the ambient

temperature distilled water for 30 minutes minimum, 4 hours

maximum, to achieve temperature equilibrium without signifi-

cant changes in moisture content.

5.2

Test Conditions

The

test should be performed at

ambient temperature, 23°C ± 5°C. Relative humidity is not

significant as the tests are performed under oil.

5.3

Equipment Set Up

5.3.1

Set

the high voltage tester in accordance with the

manufacturer’s instructions so that the voltage range will be

adequate for the material being tested.

5.3.2

Set

up the control for testing using a 500 volt per sec-

ond rate of rise.

5.3.3

Attach

the leads (if not permanently wired) such that

the high lead is connected to one electrode and the ground

lead is connected to the other electrode.

5.4

Test

5.4.1

Remove

a preconditioned specimen from the ambient

temperature water and wipe dry with a lint free paper towel.

5.4.2

Determine

and record the thickness of the specimen

at four locations 1 inch from the edge at the midpoint of each

side.

5.4.3 Insert

the specimen into the test fixture centering it to

reduce chances of flashover.

5.4.4

Operate

the tester such that the voltage is applied with

a 500 volts per second increase and observe the point at

which the tester indicates a breakdown.

5.4.5 Record the breakdown voltage to the nearest .1 KV

for values over 10 KV and to at least the nearest 5% for all

lower values.

5.4.6

Remove

the specimen from the oil medium and verify

that a breakdown has occurred. If none is apparent reinsert

the specimen, carefully centering it, and retest as in 5.4.4 and

5.4.5. Note: If flashover occurs, either a larger specimen or

new oil must be used.

4.7

Test

the remaining two specimens as in 5.4.1 through

5.4.6.

6.0

Calculations

6.1

Calculate

the average thickness for each specimen from

the four individual values measured.

6.2

Determine

the electric strength in volts per mil for each

specimen by dividing the breakdown voltage expressed in

kilovolts by the thickness express in inches.

ES =

6.8 KV

.005

inch

1000 V

inch

1000

mils

= 1360 v/mil

6.3

Determine

the average electric strength by averaging the

individual values for each specimen. Round the average to the

nearest 10 volts/mil.

6.4

any specimen falls below the specification minimum,

calculate the percentage of the requirement:

min =

Lowest

Value

Spec

Value

X 100%

e.g. Value = 670 volts per mil

Specification = 750 volts per mil

min =

670

750

100% = .893 X 100% = .89 X 100% = 89%

7.0

Report

7.1

Report

the average value for electric strength in volts per

mil to the nearest 10 volts per mil.

IPC-TM-650

Number

2.5.6.2

Subject

Electric

Strength of Printed Wiring Material

Date

8/97

Revision

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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.

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