IPC-TM-650 EN 2022 试验方法.pdf - 第301页

5.2 Production Testing (Twist) 5.2.1 Place the sample on the surface plate. While applying sufficient pressure to flatten the test sample, take the diagonal measurement across the sample and record it as D (see Fig- ure …

Equipment/Apparatus

4.1

Precision

surface plate

4.2

Thickness

measurement shims (feeler or pin gauges)

4.3

Leveling

jacks

4.4

Standard

metrology height dial indicator gauge

4.5

Gauge

blocks

4.6

Linear

measuring devices of suitable accuracy

4.7

Micrometer

of suitable accuracy for thickness measure-

ment

Procedure

Unless

otherwise specified, testing shall be

performed at standard laboratory conditions (see IPC-TM-

650, Section 1.3).

5.1

Production Testing (Bow)

5.1.1

Place

the sample on the surface plate. While applying

sufficient pressure to flatten the test sample, measure the

length and width of the sample and record it as length (L) &

width (W) (see Figure 3).

5.1.2

Calculate

the size of the feeler/pin gauge (Go/No-Go)

to be used for maximum bow percentage using the following

formula:

L (B)

100

Rw =

W (B)

100

Where:

Go/No-Go feeler/pin gauge size for sample length

Go/No-Go feeler/pin gauge size for sample width

L = Length measurement as determined above

W = Width measurement as determined above

B = Maximum allowable bow percentage

5.1.3

Place

the sample to be measured on the surface plate

with the convex of the sample facing upwards. For each edge,

apply sufficient pressure on both corners of the same sample

edge to ensure contact with the surface (see Figure 4).

5.1.4

Attempt

to slide the feeler/pin gauge of thickness R

under

the length side(s) of the sample and R

under

the width

side(s) of the sample. If the Go/No-Go feeler/pin gauge will

slide between the sample and the surface plate, the bow in

that direction exceeds the allowable percentage used in the

calculation above. Repeat this procedure until all sides of the

sample have been measured.

5.1.5

a determination of actual percentage of bow is

desired, repeat 5.1.1 through 5.1.4 using a feeler/pin gauge

that will easily fit between the side of the sample and the sur-

face plate. Continue to increase the feeler/pin gauge size until

the largest feeler/pin gauge that will fit between the sample

and the surface plate for both the length (x2) and width (x2) is

obtained. Measure this feeler/pin gauge with the micrometer

and record as R

Calculate

the percentage for bow as follows:

100 B

100

Where:

Percentage bow in the length direction

Percentage bow in the width direction

Measured maximum feeler/pin gauge size across

sample length

Measured maximum feeler/pin gauge size across

sample width

L = Length measurement as determined above

W = Width measurement as determined above

IPC-2422-3

Figure

3 External Measurements

IPC-TM-650

Number

2.4.22

Subject

Bow

and Twist (Percentage)

Date

6/99

Revision

age2of5

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5.2

Production Testing (Twist)

5.2.1

Place

the sample on the surface plate. While applying

sufficient pressure to flatten the test sample, take the diagonal

measurement across the sample and record it as D (see Fig-

ure 3).

5.2.2

Calculate

the size of the feeler/pin gauge (Go/No-Go)

to be used for maximum twist percentage using the following

formula:

R =

2 (D)(T)

100

Where:

= Go/No-Go feeler/pin gauge size

D = Diagonal measurement across the sample as determined

above

T = Maximum allowable twist percentage

Note: This formula includes a factor of two because, by con-

straining one corner of the sample on a surface plate, the ver-

tical deflection of twist is approximately doubled.

5.2.3

Place

the sample to be measured on the surface plate

with any three corners of the sample touching the surface.

Apply sufficient pressure (if necessary) to only one corner of

the sample to ensure three of the four corners are in contact

with the surface plate. It may be necessary to turn the sample

over to accomplish this (see Figure 5).

5.2.4

it is not possible to get three corners of the sample

to touch the surface plate by restraining only one corner, this

production test is not applicable and the referee test

described in 5.3 shall be used.

5.2.5 Attempt

to slide the feeler/pin gauge of thickness R

under the corner not touching the surface plate. If the

Go/No-Go feeler/pin gauge will slide under the corner not

touching the surface plate without lifting any of the other three

corners of the sample from the surface plate, the twist in that

direction exceeds the allowable percentage used in the calcu-

lation above. Repeat this procedure until all corners of the

sample that can be measured using this technique have been

measured.

5.2.6

a determination of actual percentage of twist is

desired, repeat 5.2.1 through 5.2.5 using a feeler/pin gauge

that will easily fit under the corner that is not touching the sur-

face plate. Continue to increase the feeler/pin gauge size until

the largest feeler/pin gauge size that does not lift any of the

three touching corners from the surface plate is obtained.

Measure this feeler/pin gauge with the micrometer and record

as R.

5.2.7

Calculate

the percentage of twist as follows:

Percentage Twist =

2 (D)

100

Where:

R = Go/No-Go feeler/pin gauge size

D = Diagonal measurement across the sample as determined

above

Note: This formula includes a factor of two because, by con-

straining one corner of the sample, the vertical deflection of

twist is approximately doubled.

5.3

Referee Method (Twist)

5.3.1

Place

the sample to be measured on the datum sur-

face with the two lower opposite corners touching the datum

surface or on a raised parallel surface of equal height from the

datum surface (see Figure 6).

IPC-2422-4

Figure

4 Bow Measurement

ouching Datum

Surface

HIGHEST POINT

measured as R or R

Touching Datum

Surface

IPC-TM-650

Number

2.4.22

Subject

Bow

and Twist (Percentage)

Date

6/99

Revision

age3of5

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5.3.2

Support

the other two corners with leveling jacks or

some other appropriate devices, ensuring the two raised cor-

ners are of equal height from the datum surface. This may be

checked by using the dial indicator (see Figure 7).

5.3.3

Using

the dial indicator, measure the highest raised

portion on the board and record the reading as R1 (see Fig-

ure 8).

5.3.4

Without

disturbing the sample, take a reading with the

dial indicator on one of the corners contacting the surface (R2)

and record the reading (see Figure 8).

5.3.5

Take

the diagonal measurement of the sample and

record the reading.

5.3.6

Calculation

Deduct

the measured R2 from the mea-

surement R1. This difference is denoted as twist. Divide the

measured deviation by the recorded length and multiply by

100. The result of this calculation is the percentage of twist.

Percentage Twist =

R1 − R2

100

6 Notes

None

IPC-4442-5

Figure

5 Measurement of Twist

R = Highest

oint of Board

Shim under raised

corner of A.

B, C, and D touching

Datum Surface. Only

one corner may be

physically restrained.

IPC-2422-6

Figure

6 Sample Placement

▼

R2 Lowest

Corners

Raised Parallel

Surfaces

IPC-TM-650

Number

2.4.22

Subject

Bow

and Twist (Percentage)

Date

6/99

Revision

age4of5

电子技术应用　　　　　　　ｗｗｗ．ＣｈｉｎａＡＥＴ．ｃｏｍ