IPC-TM-650 EN 2022 试验方法.pdf - 第19页

1 Scope Tests performed on presumably identical samples under seemingly identical conditions do not always yield iden- tical results. This is due to errors inherent in every measure- ment or evaluation. During the develo…

interpreting test results, it is essential that all values are

known to be valid. Usually the values are placed in one of the

three following categories and evaluated to ultimately arrive at

a sound decision:

a. Results are declared valid. A decision can be made imme-

diately

b. Results obviously must be discarded. Specimens that

break or otherwise fail because of some obvious flaw, or

that do not behave in the same general manner as the

other specimens, should be discarded. Retests should be

performed on new specimens.

c. Results deviate from the mean value. All test data obtained

from properly performed tests must be included in deter-

mining mean and standard deviation unless there is an

assignable cause not to do so.

The above information is to be used if not found in an indi-

vidual test method.

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IPC-TM-650

TEST METHODS MANUAL

Number

1.7

Subject

Reporting,

Invalid Test Results

Date

01/03

Revision

Originating Task Group

N/A

Material

in this Test Methods Manual was voluntarily established by Technical Committees of 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 IPC.

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Scope

Tests

performed on presumably identical samples

under seemingly identical conditions do not always yield iden-

tical results. This is due to errors inherent in every measure-

ment or evaluation. During the development of a new test

procedure or use of an existing test procedure, this variability

must be understood and precautions taken to ensure that it is

controlled to within necessary limits. Performance of this test

method will help to estimate measurement error and trouble-

shoot causes of measurement variability. Use of this test

method will provide some evidence that a new test procedure

is suitable for use when submitted for review, or an existing

test procedure is capable of measuring the applicable param-

eter.

This method provides a standard procedure for determining

the precision of a test method involving binary data or tests

that result in two outcomes. These include evaluations where

the results are recorded as pass/fail or go/no-go. Examples

include solderability tests and visual inspections. This method

helps to estimate how often the disposition is performed cor-

rectly.

This method is not useful for measurements which result in

variables data, or where more than three repeated measure-

ments or more than ten testers are used. These situations are

covered under other methods (see 6.1).

1.1 Definitions

Accuracy

–

The

difference between an observed measure-

ment and the true (but perhaps unknown) value being mea-

sured.

Precision

–

The

closeness to each other of repeated mea-

surements of the same quantity.

Binary

Data –

Inspections

or tests in which parts are placed

in one of two classes. This includes pass/fail, go/no-go tests

and inspections.

Applicable Documents

The

test procedure under evalu-

ation.

Test Specimens

The

test specimens used will be as

specified in the test procedure under investigation.

The number and types of test materials to be used will

depend on the range of levels in the class of materials to be

tested. If it is known that precision is worse at one end of the

range, evaluation could be limited to that end of the range. In

general, evaluations are generally advisable for all combina-

tions of materials, levels, set-ups, and conditions. If resources

are limited, begin the study with those combinations deemed

to be the most critical, or where measurement error is likely to

be greatest.

The number of samples will also depend on the difficulty

involved in obtaining, processing, and distributing the test

specimens, the difficulty, length of time required for, and

expense of performing the test, and other prior known infor-

mation.

This test method will assume that evaluations can be repeated

on the same samples. For situations where this is not possible

or the sample is consumed during the test, other methods

may be better suited (see 6.1).

Apparatus

The

apparatus used will be as specified by

the test procedure under investigation.

Procedure

5.1 Planning Evaluation

Keep the evaluation as simple as

possible to obtain data that is free of unintended secondary

effects.

Prepare a procedure that is complete and describes the test

parameters as well as recommended techniques for assess-

ing the outcome. Include known best practices and draw

extensively on the experience of test users.

The method used in this procedure allows for up to 10 test

conditions. Solicit participants from among the community of

facilities with the proper equipment, competent operators and

familiarity with the test. In order to obtain representative pre-

cision estimates, do not select only from a small group of

users who are considered exceptionally qualified. Be sure to

specify any special calibration procedures or material prepara-

tion requirements.

The analysis method used in this procedure allows for up to

10 repeated evaluations per sample. Carefully evaluate the

materials to determine the appropriate classification or dispo-

sition before the study. Choose material representing a likely

range of conditions normally encountered during routine tests

or inspections. Randomize the samples prior to dividing into

2215

Sanders Road

Northbrook, IL 60062-6135

IPC-TM-650

TEST METHODS MANUAL

Number

1.8

Subject

Measurement

Precision Estimation for Binary Data

Date

01/03

Revision

Originating Task Group

Measurement Precision Task Group (7-11a)

Material

in this Test Methods Manual was voluntarily established by Technical Committees of 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 IPC.

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ASSOCIATION CONNECTING

ELECTRONICS INDUSTRIES

test groups. Prepare more than the material required to

ensure an adequate amount is available for the study in case

of lost or damaged specimens, errors, test set-up, etc.

Carefully package and label the material. Assign serial num-

bers, if possible. Identify the version of the test procedure.

Specify care and handling procedures. Provide a data sheet,

and describe any documentation required. Require a test log,

and insist that observations of any unusual events be

recorded.

5.2

Conducting the Evaluation

Ensure

the samples are

inspected on receipt. Send replacement material if damaged

or tests are performed improperly.

Inspect the data sheets when returned. Review the test logs

for unusual events. Review the results. Question unusual dis-

positions or comments. Incorrect dispositions and typos must

be fixed prior to analysis.

5.3

Analyzing the Data

Analysis may be performed on the

data sheet or on the Excel spreadsheet (see 6.2).

The basic techniques involve beginning with a set of parts or

materials for which the classification has been previously

determined. Several inspectors or testers then examine and

classify the parts and the results are compared with the

known standard classification.

The effectiveness of the test is the number of correct determi-

nations divided by the total number of classification opportu-

nities (number of parts times the number of inspectors).

E =

Number

of correct dispositions

Number

of parts x Number of testers

(1)

The

probability of a false reject and the probability of a false

accept can be defined as follows:

P(FR)=

Number of dispositions where good parts were rejected

Number

of good parts x Number of testers

(2)

P(FA)=

Number

of dispositions where bad parts were accepted

Number of bad parts x Number of testers

(3)

5.4

Preparing Analysis Conclusions

Goals

for measure-

ment precision should be established before the study begins.

The goals should be established using knowledge of the

anticipated levels of product variability (or process capability),

specifications, customer needs and the possible impact of

dispositioning test samples improperly. As a rule of thumb, the

guidelines shown in Table 1 have been extensively applied.

If the test effectiveness is inadequate, then steps should be

taken to diagnose and improve the causes of the deficiency.

The probabilities of false acceptance and false rejection

should help in this diagnosis. Marginal tests should also be

improved.

An acceptable test effectiveness rating (E) indicates that the

test method dispositions the products with reasonable cor-

rectness.

The results of this evaluation should be compared to the test

efficiency goals for this inspection. The rules of thumb noted

above have been found to be useful. These goals could be

amended, depending on the criticality of the inspection, and

the impact of incorrect disposition.

6 Notes

6.1 Methods for Analyzing Repeatability and Reproduc-

ibility

This

test method covers situations where the mea-

surements result in binary data, such as go and no-go, or

pass and fail tests. The precision of the test is determined by

calculating the consistency and correctness of the sample

dispositions.

Measurements that result in variables data can be analyzed

using IPC Test Method IPC-TM-1.9.

In some cases, the measurement cannot be repeated more

than once on the same sample. This is common where the

sample is consumed during the test, such as chemical analy-

sis, or changed during testing, such as solderability evalua-

tions. In these cases, the analysis using a modified average

and range method is possible. This method is under develop-

ment.

6.2

References

ISO 5725-1 Accuracy (trueness and precision) of measure-

ment methods and results (parts 1 to 6), 1998(E), Interna-

tional Organization for Standardization, Geneva, Switzer-

land (www.iso.org).

b. Measurement Systems Analysis, 2nd edition, June 1998,

Automotive Industry Action Group (AIAG), 26200 Lahser

Road, Southfield, MI 48034 (www.aiag.org).

able 1 Recommended evaluation criteria

Metric

Acceptable Marginal Inadequate

>0.9 0.8 to 0.9 <0.8

P(FR) <0.05 0.05 to 0.10 >0.10

P(FA) <0.02 0.02 to 0.05 >0.05

IPC-TM-650

Number

1.8

Subject

Measurement

Precision Estimation for Binary Data

Date

01/03

Revision

age2of6