IPC-TM-650 EN 2022 试验方法.pdf - 第300页

4 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…

Scope

This

test method covers three procedures used to

determine the bow and twist percentage of individual rigid

printed boards, rigid portions of rigid-flex printed boards,

and/or multiple printed panels. Measurements on non-

rectangular samples pose a unique testing problem and may

necessitate careful evaluation of the requirements imposed by

the users of this test method. This test method does not

describe the special considerations necessary when testing

the bow and twist of printed board assemblies (i.e., compo-

nent placement & weight, edge supports & connectors, etc.).

The first two procedures describe production (Go/No-Go)

methods that generally characterize the bow and twist as

being no more than a specific value. The other procedure is a

referee method used to precisely determine the twist.

1.1

Definitions

Bow

and twist are defined in IPC-T-50.

The definitions are repeated in this test method for conve-

nience.

1.1.1

Bow (Sheet, Panel, or Printed Board)

The

devia-

tion from flatness of a board characterized by a roughly cylin-

drical or spherical curvature such that, if the product is rect-

angular, its four corners are in the same plane (see Figure 1).

1.1.2

Twist

The

deformation of a rectangular sheet, panel,

or printed board that occurs parallel to a diagonal across its

surface, such that one of the corners of the sheet is not in the

plane that contains the other three corners (see Figure 2).

2 Applicable Documents

IPC-T-50

Terms

and Definitions for Interconnecting and

Packaging Electronic Circuits

IPC-TM-650

Test

Methods

Test Specimens

The

test specimens shall be in the form

of either printed boards or multiple printed panels (single-

sided, double-sided, multilayer, or rigid-flex boards).

3.1 For

non-rectangular test specimens, the most conve-

nient way to measure bow and twist is approximating a rect-

angle over the test specimen. To accomplish this, an imagi-

nary rectangle that totally encloses the sample must be

superimposed over the test specimen. The dimensions of this

superimposed rectangle should be the smallest that will fully

enclose the specimen. Although this technique will give an

approximation of bow and twist, the actual noted values will

be less than the actual bow and twist of the sample.

IPC-2422-1

Figure

1 Box

BOW

With constraining f

orce applied

to both corners of the same edge.

1 & 2 deflection from surface plane.

IPC-2422-2

Figure

2 Twist

oints A, B, C

Touching Base

With constraining force

applied to one corner only.

2215

Sanders Road

Northbrook, IL 60062-6135

IPC-TM-650

TEST

METHODS MANUAL

Number

2.4.22

Subject

Bow

and Twist (Percentage)

Date

6/99

Revision

Originating Task Group

Rigid Printed Board Test Methods Task Group

(7-11d)

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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ASSOCIA

TION CONNECTING

ELECTRONICS INDUSTRIES

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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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