IPC-TM-650 EN 2022 试验方法.pdf - 第675页

After 96 hours total, repeat the measurement series. Regard- less of the outcome of the measurements, the test terminates after this measurement series. 5.6 Data Analysis The average insulation resistance (IR avg ) is ca…

4.2

resistance meter capable of reading high resistance

(10

ohms)

with a test voltage of 100 ± 2 volts DC or an

ammeter capable of reading 10

-10

amperes

in combination

with 100 volts DC power supply. Standard resistors should be

used for routine calibration.

Test

5.1 Sample Sizes

•

Eight test patterns are produced for test with no applied

solder mask (Figure 1).

• Eight test patterns are produced for test with solder mask

applied, imaged, and cleaned (Figure 2).

• Eight test patterns are produced for test with solder mask

applied and the final finish in place (e.g., HASL).

5.2

Specimen Identification

Use

a noncontaminating

method for identifying the test specimen (e.g., vibrating

scribe). During this process, handle the specimens by the

edges only or using noncontaminating gloves.

5.3

Wire Attach

Cover

the test patterns with noncontami-

nating barrier, such as aluminum foil or plastic film, to prevent

flux spattering during the wire attach process. Use water

white rosin to solder PTFE-insulated wires to the connection

points of the specimens. Do not attempt to remove the flux

residues. Alternatively, connections may be made by

mechanical pressure connections (e.g., alligator clips).

NOTE: Because of the very high resistance levels typically

used as pass-fail criteria for this method, a connector-based

or other fixtured setup is not recommended, due to leakage

currents, unless these systems can be shown to have no sig-

nal degradation compared to hardwiring.

5.4

Placing in Chamber

Place

the specimens in the envi-

ronmental chamber in a vertical position such that the airflow

is parallel to the direction of the board in the chamber. Allow

at least 2.5 cm [0.98 in] between each test sample. Dress all

wiring away from the test patterns. Route the wires to the

outside of the chamber. Set the chamber temperature to

35°C [95°F] and 85% minimum relative humidity, with a ramp

time of not less than one hour. There is no electrical potential

applied to any test pattern during the first 24 hours of test

exposure.

5.5

Resistance Measurements

After

24 hours of test

exposure with no applied electrical potential, measure the

insulation resistance of each pattern using an applied voltage

of 100 ± 2 volts DC and an electrification time of 60 seconds.

NOTE: It is recommended that the temperature and humidity

levels be verified to be within the recommended limits prior to

beginning the resistance measurements.

Each comb pattern represents four test measurements. Mea-

surements are made between (see Figure 1):

• Pad 1 to Pad 2

• Pad 3 to Pad 2

• Pad 3 to Pad 4

• Pad 5 to Pad 4

Pads 2 and 4 are at one potential and Pads 1, 3, and 5 are at

the opposite potential (see Note 6.3).

All measurements are to be taken with the specimens at the

test conditions and inside the chamber (in-situ).

Determine the means of the dataset as outlined in 5.6.

If, after 24 hours, the results conform to the specification,

record the values and terminate the test.

If, after 24 hours, the results do not conform to the specifica-

tion, then the test may be extended to 96 hours of exposure

to the test conditions with no applied electrical potential.

Figure

3 IPC-B-50

IPC-TM-650

Number

2.6.3.5

Subject

Bare

Board Cleanliness by Surface Insulation Resistance

Date

01/04

Revision

age2of4

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After

96 hours total, repeat the measurement series. Regard-

less of the outcome of the measurements, the test terminates

after this measurement series.

5.6

Data Analysis

The

average insulation resistance (IR

avg

)

calculated as follows:

avg

= 10

[

log

(IR)

]

Where:

= Number of Test Points (32 nominal for each set of eight

patterns)

individual insulation resistance measurements

See 6.4 for an example

No individual insulation resistance value may be more than a

factor of 10 below the specified minimum value.

Where an assignable cause of low insulation resistance, which

is properly attributable to the laminate itself, or to the process

used to produce the PWB, can be found, then such a value

can be excluded from calculating the average value, provided

that at least 30 test points are included in the average. Such

assignable causes include the following:

• Contamination on the insulating surface of the board, such

as lint, solder splines or water droplets from the chamber.

• Incompletely etched patterns that decrease the insulating

space between the conductors by more than the amount

allowed in the appropriate design requirements drawing.

• Scratched, cracked, or obviously damaged insulation

between conductors.

Notes

6.1

condensation occurs on the test specimens in the

environmental chamber while the samples are under voltage,

dendritic growth will occur. This can be caused by a lack of

sufficient control of the humidification of the oven. Water spot-

ting may also be observed in some ovens where the airflow in

the chamber is from back to front. In this case, water conden-

sation on the cooler oven window can be blown around the

oven as microdroplets which deposit on test specimens and

cause dendritic growth if the spots bridge the distance

between two electrified conductors. Both of these conditions

must be eliminated for proper testing.

6.2

Tight

control of the test humidity is critical for this test

method. A difference of 5% relative humidity can result in a

0.5 - 1.0 decade difference in the measured resistance. The

uniformity of the environment is also important. A fully loaded

chamber, where airflow is severely impeded, may have a

30-40% RH range within the chamber workspace.

6.3

The

polarity of the applied voltage is not important as

long as the application is consistent (e.g., Pads 1, 3, 5 are

positive and 2, 4 are at opposite potential, vs. Pads 2 and 4

positive, and Pads 1, 3, 5 at opposite potential).

6.4

Example of Numerical Calculations

Eight

5-point test patterns (4 measurements each)

LogOhms = base-10 logarithm of measured resistance

Average of LogOhms = 11.62

AVE

Antilog (11.62) = 4.19E+11 ohms

AVE

Geometric Mean

IPC-TM-650

Number

2.6.3.5

Subject

Bare

Board Cleanliness by Surface Insulation Resistance

Date

01/04

Revision

age3of4

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NOTE: 3.98E+11

= 3.98 x 10

NOTE: In

many spreadsheet software packages (.e.g,

Excel®), a Geometric Mean function will yield the same results

as IR

AVE

No.

Pattern Resistance (Ohms) LogOhms

1-2 3.98E+11 11.60

2 3-2 1.58E+11 11.20

3 3-4 6.31E+11 11.80

4 5-4 7.94E+11 11.90

5 1-2 1.00E+12 12.00

6 3-2 1.00E+12 12.00

7 3-4 3.98E+11 11.60

8 5-4 1.58E+12 12.20

9 1-2 1.26E+12 12.10

10 3-2 1.26E+12 12.10

11 3-4 1.00E+12 12.00

12 5-4 3.98E+11 11.60

13 1-2 5.01E+11 11.70

14 3-2 2.00E+11 11.30

15 3-4 1.26E+11 11.10

16 5-4 1.26E+11 11.10

17 1-2 2.51E+11 11.40

18 3-2 1.58E+11 11.20

19 3-4 2.51E+11 11.40

20 5-4 3.98E+11 11.60

21 1-2 1.26E+12 12.10

22 3-2 5.01E+11 11.70

23 3-4 2.00E+11 11.30

24 5-4 2.00E+11 11.30

25 1-2 7.94E+11 11.90

26 3-2 1.00E+12 12.00

27 3-4 3.98E+11 11.60

28 5-4 7.94E+11 11.90

29 1-2 1.26E+11 11.10

30 3-2 6.31E+11 11.80

31 3-4 2.00E+11 11.30

32 5-4 1.00E+11 11.00

IPC-TM-650

Number

2.6.3.5

Subject

Bare

Board Cleanliness by Surface Insulation Resistance

Date

01/04

Revision

age4of4

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