SIST ISO 18921:2011

SLOVENSKI STANDARD
SIST ISO 18921:2011
01-julij-2011
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Imaging materials - Compact discs (CD-ROM) - Method for estimating the life
expectancy based on the effects of temperature and relative humidity
Matériaux pour l'image - Disques compacts (CD-ROM) - Méthode d'estimation de
l'espérance de vie basée sur les effets de la température et de l'humidité relative
Ta slovenski standard je istoveten z: ISO 18921:2008
ICS:
35.220.30 2SWLþQHVKUDQMHYDOQH Optical storage devices
QDSUDYH
37.040.99 Drugi standardi v zvezi s Other standards related to
fotografijo photography
SIST ISO 18921:2011 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST ISO 18921:2011

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SIST ISO 18921:2011

INTERNATIONAL ISO
STANDARD 18921
Second edition
2008-10-15


Imaging materials — Compact discs
(CD-ROM) — Method for estimating
the life expectancy based on the effects
of temperature and relative humidity
Matériaux pour l'image — Disques compacts (CD-ROM) — Méthode
d'estimation de l'espérance de vie basée sur les effets de la
température et de l'humidité relative





Reference number
ISO 18921:2008(E)
©
ISO 2008

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SIST ISO 18921:2011
ISO 18921:2008(E)
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ii © ISO 2008 – All rights reserved

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SIST ISO 18921:2011
ISO 18921:2008(E)
Contents Page
Foreword .iv
1 Scope.1
2 Normative references.1
3 Terms and definitions .1
4 Purpose and assumptions.3
4.1 Purpose .3
4.2 Assumptions.3
5 Measurements .3
5.1 Block error rate (BLER).3
5.2 Test equipment .3
5.3 Test specimen.4
6 Accelerated stress test plan.4
6.1 General .4
6.2 Stress conditions .5
6.3 Accelerated test cell specimen population.7
6.4 Time intervals .8
6.5 Test plan.8
6.6 Measurement conditions .8
7 Data evaluation .8
7.1 Eyring acceleration model.8
7.2 Failure distribution model .9
7.3 Acceleration factors .9
7.4 Survivor analysis.10
8 Disclaimer .10
Annex A (informative) Step analysis outline .11
Annex B (informative) Example of test plan and data analysis.12
Bibliography.19

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SIST ISO 18921:2011
ISO 18921:2008(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 18921 was prepared by Technical Committee ISO/TC 42, Photography.
This second edition cancels and replaces the first edition (ISO 18921:2002), of which it constitutes a minor
revision.
The following changes have been made to the first edition:
⎯ modification of definition 3.8 (life expectancy);
⎯ modification of 5.1 on block error rate;
⎯ correction of Equations (1) and (2) in 7.1;
⎯ updating of normative and bibliographical references;
⎯ removal of the original Annex A.

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SIST ISO 18921:2011
INTERNATIONAL STANDARD ISO 18921:2008(E)

Imaging materials — Compact discs (CD-ROM) — Method
for estimating the life expectancy based on the effects
of temperature and relative humidity
1 Scope
This International Standard specifies a test method for estimating the life expectancy (LE) of information
stored on compact disc (CD-ROM) media, including CD audio, but excluding recordable media. Only the
effects of temperature and relative humidity on the media are considered.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
1)
ISO/IEC 10149 , Information technology — Data interchange on read-only 120 mm optical data disks
(CD-ROM)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
cumulative distribution function
F(t)
probability that a random unit drawn from the population fails by time t, or the fraction of all units in the
population which fails by time t
3.2
survivor function
R(t)
probability that a unit drawn from the population will survive at least time t, or the fraction of units in the
population that will survive at least time t
NOTE R()tF=−1 (t) .
3.3
baseline
condition representing the disc at time of manufacture
NOTE This is customarily the initial parameter measurement taken prior to any application of stress. The designation
is usually t = 0 for a stress time equal to zero hours.

1) Equivalent to ECMA 130.
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SIST ISO 18921:2011
ISO 18921:2008(E)
3.4
block error rate
BLER
ratio of erroneous blocks to total blocks measured at the input of the first (C1) decoder (before any error
correction is applied)
NOTE The more commonly reported value for BLER is the number of erroneous blocks per second measured at the
input of the C1-decoder during playback at the standard (1X) data rate.
[IEC 60908:1999]
3.5
CD-ROM
compact disc-read only medium
3.6
end-of-life
occurrence of any loss of information
3.7
information
signal or image recorded using the system
3.8
life expectancy
LE
length of time that information is predicted to be retrieved in a system at 23 °C and 50 % relative humidity
(RH)
3.8.1
standard life expectancy
SLE
minimum life span, predicted with 95 % confidence, of 95 % of the product stored at a temperature not
exceeding 25 °C and a relative humidity (RH) not exceeding 50 % RH
3.9
retrievability
ability to access information as recorded
3.10
stress
experimental variable to which the specimen is exposed for the duration of the test interval
NOTE In this International Standard, the stress variables are confined to temperature and relative humidity.
3.11
system
combination of recording medium, hardware, software and documentation necessary to retrieve information
3.12
test cell
device that controls the stress to which the specimen is exposed
3.13
test pattern
distribution of the characters l and 0 within a block and the block-to-block variation
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SIST ISO 18921:2011
ISO 18921:2008(E)
4 Purpose and assumptions
4.1 Purpose
The purpose of this International Standard is to establish a methodology for estimating the life expectancy of
information stored on CD-ROMs. This methodology provides a technically and statistically sound procedure
for obtaining and evaluating accelerated test data.
4.2 Assumptions
The validity of the procedure defined by this International Standard relies on three assumptions:
⎯ the dominant failure mechanism acting at the usage condition is the same as at the accelerated
conditions;
⎯ the dominant failure mechanism is appropriately modelled by an Eyring acceleration model;
⎯ life expectancy is appropriately modelled by the two parameter Weibull distribution (see [1] in the
Bibliography). The shape parameter of the Weibull distribution is assumed to be independent of the stress
level.
5 Measurements
5.1 Block error rate (BLER)
The objective of measuring the block error rate (BLER) is to establish a practical estimation of the system's
ability to read the pre-recorded bits using a standard drive. This International Standard considers BLER to be
a high level estimate of the performance of the system. A change in BLER in response to the time at an
elevated temperature and humidity is the principal quality parameter.
–2
IEC 60908 states that the BLER averaged over any 10 s shall be less than 3 × 10 . At the standard (1X) data
rate, the total number of blocks per second entering the C1-decoder is 7 350. Thus, an equivalent limit on
BLER is 220 blocks per second.
For the purposes of this International Standard, recorded data are considered to have reached end-of-life
when the BLER, measured as erroneous blocks per second, exceeds 220 anywhere on the disc, i.e. when the
maximum BLER exceeds 220. It is recognized that the correlation between actual loss of information and
maximum BLER is very system dependent. A BLER of 220 is an arbitrary level chosen as a predictor of the
onset of uncorrectable errors and thereby end-of-life.
5.2 Test equipment
5.2.1 Compact disc test system
Any compact disc test system (tester) that is in accordance with ISO/IEC 10149 may be used. The make,
model and version of the test equipment (including software) shall be reported with the test results.
5.2.2 Calibration and repeatability
Calibration according to the tester manufacturer's procedure shall be performed prior to any measurement
data being collected. A calibration disc shall be available from the tester manufacturer.
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SIST ISO 18921:2011
ISO 18921:2008(E)
In addition to the calibration disc, one control disc shall be maintained at ambient conditions and its maximum
BLER measured before and after each data collection interval. A control chart shall be maintained for this
control disc with ± 3 σ action limits. The mean and standard deviation of the control disc shall be established
by collecting at least five measurements. Should any individual maximum BLER reading exceed the action
limit, the problem shall be corrected and all data collected since the last valid control point shall be
remeasured.
If it becomes necessary to replace the tester, a method shall be followed for correlating tester outputs (see [2]
in the Bibliography).
5.3 Test specimen
A test specimen is any disc that meets ISO/IEC 10149 specifications and contains representative data
extending to within 2 mm of the maximum recording diameter.
6 Accelerated stress test plan
6.1 General
A CD-ROM of good manufacture should last several years or even decades. Consequently, it is necessary to
conduct accelerated ageing studies in order to develop a life expectancy estimate. The key is conducting and
evaluating a test plan that will provide the information necessary to satisfactorily evaluate the particular
product.
Many accelerated life test plans follow a rather traditional approach in sampling, experimentation and data
evaluation. These “traditional plans” share the following characteristics:
a) the total number of specimens is evenly divided amongst all the accelerated stresses;
b) each stress is evaluated at the same time increments;
c) the Arrhenius relationship is used as the acceleration model;
d) the least squares method is used for all regressions;
e) the calculated life expectancy is for the mean or median life rather than for the first few failure percentiles.
On the other hand, “optimum test plans” have been proposed which differ in significant aspects from
traditional plans. These plans have the following characteristics:
⎯ two and only two acceleration levels for each stress;
⎯ a large number of specimens distributed mostly in the lowest stress levels;
⎯ the need to know the failure distribution, a priori, in order to develop the plan.
The maximum effectiveness of a plan can either be estimated before the test starts or determined after the
results have been obtained. As each CD-ROM system has different characteristics, a specific, detailed
optimum plan is impossible to forecast.
This test plan borrows from the optimum plan, the traditional plan, previous experience with the systems, test
equipment and accelerated test stresses to put together a “compromise test plan”. Modifications of this plan
will be required to design the best plan for other applications. The methodology shall be applicable to all
CD-ROM media assessments.
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SIST ISO 18921:2011
ISO 18921:2008(E)
6.2 Stress conditions
6.2.1 Levels
As mentioned in 6.1, an optimum test plan utilizes only two stress levels for each parameter evaluated, since
in an ideal case the relationship between changes in the parameter investigated and changes in stress is
known. The compromise test plan documented in this International Standard does not make such an
assumption; therefore, three different stress levels per parameter shall be used so that the linearity of the
parameter function versus the stress level may be demonstrated.
The test plan shall have the majority of test specimens placed at the lowest stress condition. This minimizes
the estimation error at this condition and results in the best estimate of the degradation rate at a level close to
the usage condition. The greater number of specimens at the lower stress also tends to equalize the number
of failures observed by test completion.
6.2.2 Conditions
For implementing the test plan documented in this International Standard, five stress conditions shall be used.
The minimum distribution of specimens among the stress points that shall be used is shown in Table 1. For
improved precision, additional specimens and conditions may be used if desired.
Table 1 — Summary of stress conditions
Intermediate
Minimum
Test stress
Incubation Minimum total
RH
equilibrium
Test cell Number of
duration time
duration
a a b
number specimens
T(inc) RH(inc) RH(int)
°C % h h % h
1 80 85 10 500 2 000 31 6
2 80 70 10 500 2 000 31 8
3 80 55 15 500 2 000 31 4
4 70 85 15 750 3 000 33 8
5 60 85 30 1 000 4 000 36 11
a
T(inc) and RH(inc) are the stress incubation temperature and relative humidity.
b
RH(int) is the intermediate relative humidity that at T(inc) supports the same equilibrium moisture absorption in polycarbonate as
that supported at room ambient temperature and relative humidity.

6.2.3 Temperature (T)
The temperature levels chosen for this test plan are based on the following:
⎯ there shall be no change of phase within the test system over the test temperature range; this restricts the
temperature to greater than 0 °C and less than 100 °C;
⎯ the temperature level shall not be so high that plastic deformation occurs.
The typical substrate material for CD-ROMs is polycarbonate (glass transition temperature ~ 150 °C). The
glass transition temperature of other layers may be lower. Experience with high temperature testing of
CD-ROMs indicates that an upper limit of 80 °C is practical for most applications.
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SIST ISO 18921:2011
ISO 18921:2008(E)
6.2.4 Relative humidity (RH)
Practical experience shows that 85 % RH is the upper limit within most accelerated test cells. This is due to
the tendency for condensation to occur on cool sections of the chamber, e.g. observation windows, cable
ports, wiper handles, etc. Droplets may become dislodged and entrained in the circulating air within the
chamber. If these droplets fall on the test specimen, false error signals could be produced.
6.2.5 Rate of stress change
The process described in this International Standard requires that discs be ramped from the test conditions to
stress conditions and back again a number of times during the course of testing. The ramp duration and
conditions shall be chosen to allow sufficient equilibration of absorbed substrate moisture.
Large departures from equilibrium conditions may result in the formation of liquid water droplets inside the
substrate or at its interface with the reflecting layer. Gradients in the water concentration through the thickness
of
...