ISO 18927:2008
(Main)Imaging materials — Recordable compact disc systems — Method for estimating the life expectancy based on the effects of temperature and relative humidity
Imaging materials — Recordable compact disc systems — Method for estimating the life expectancy based on the effects of temperature and relative humidity
ISO 18927:2008 specifies a test method for estimating the life expectancy of information stored on recordable compact disc systems. Only the effects of temperature and relative humidity on the media are considered. ISO 18927:2008 does not cover the effects of light, air pollution, or time-dependent flow phenomena.
Matériaux pour image — Systèmes de CD enregistrables — Méthode d'estimation de l'espérance de vie basée sur les effets de la température et de l'humidité relative
Upodobitveni materiali - Snemalni kompaktni diski - Metode za določanje pričakovane življenjske dobe na podlagi učinkov zaradi temperature in relativne vlage
Ta mednarodni standard določa preskusno metodo za določanje pričakovane življenjske dobe informacij, shranjenih na snemalnih kompaktnih diskih. Obravnavani so samo učinki temperature in relativne vlage na medije. Ta mednarodni standard ne zajema učinkov svetlobe, zračnega onesnaženja in pojavov časovno odvisnega toka.
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INTERNATIONAL ISO
STANDARD 18927
Second edition
2008-10-15
Imaging materials — Recordable compact
disc systems — Method for estimating
the life expectancy based on the effects
of temperature and relative humidity
Matériaux pour image — Systèmes de CD enregistrables — Méthode
d'estimation de l'espérance de vie basée sur les effets de la
température et de l'humidité relative
Reference number
ISO 18927:2008(E)
©
ISO 2008
---------------------- Page: 1 ----------------------
ISO 18927:2008(E)
PDF disclaimer
This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but
shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In
downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat
accepts no liability in this area.
Adobe is a trademark of Adobe Systems Incorporated.
Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation
parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In
the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.
COPYRIGHT PROTECTED DOCUMENT
© ISO 2008
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or
ISO's member body in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2008 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 18927:2008(E)
Contents Page
Foreword .iv
1 Scope.1
2 Normative references.1
3 Terms and definitions .1
4 Purpose and assumptions.4
4.1 Purpose .4
4.2 Assumptions.4
5 Measurements .4
5.1 Summary .4
5.2 Block error rate (BLER).5
5.3 Test equipment .5
5.4 Test specimen.5
6 Accelerated stress test plan.6
6.1 General .6
6.2 Stress conditions .7
6.3 Accelerated test cell sample population.10
6.4 Time intervals .10
6.5 Test plan.10
6.6 Measurement conditions .11
7 Data evaluation .11
7.1 Lognormal distribution model.11
7.2 Eyring acceleration model.11
7.3 Acceleration factors .12
7.4 Survivor analysis.12
7.5 Aids.13
8 Disclaimer .13
Annex A (informative) Step analysis outline .14
Annex B (informative) Example of test plan and data analysis.15
Bibliography.27
© ISO 2008 – All rights reserved iii
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ISO 18927:2008(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 18927 was prepared by Technical Committee ISO/TC 42, Photography.
This second edition cancels and replaces the first edition (ISO 18927:2002), of which it constitutes a minor
revision.
The following changes have been made to the first edition:
⎯ modification of definition 3.10 (life expectancy);
⎯ modification of 5.2 on block error rate;
⎯ updating of normative and bibliographical references;
⎯ removal of the original Annex A.
iv © ISO 2008 – All rights reserved
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INTERNATIONAL STANDARD ISO 18927:2008(E)
Imaging materials — Recordable compact disc systems —
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 of information stored on
recordable compact disc systems. Only the effects of temperature and relative humidity on the media are
considered.
This International Standard does not cover the effects of light, air pollution, or time-dependent flow
phenomena.
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)
IEC 60908:1999, Audio recording — Compact disc digital audio system
Experimental statistics, U.S. National Bureau of Standards Handbook 91, 1963
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
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.
3.2
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)
1) Equivalent to ECMA 130.
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ISO 18927:2008(E)
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]
3.2.1
maximum block error rate
max BLER
maximum BLER measured anywhere on a disc
3.3
compact disc-recordable
CD-R
recordable optical disc in which information can be recorded to certain areas in compact disc format
NOTE 1 Information can be recorded once and read many times.
NOTE 2 The term “compact disc-write once” (CD-WO) has also been used to describe this type of disc.
3.4
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
3.4.1
lognormal cumulative distribution function
F()t
cumulative distribution function in which the logarithm of the relevant parameter, in this International Standard
the disc lifetime, has a normal distribution and is defined by the following equation:
t ln( x)−µ
2
1l
−()
11
2 σ
l
F()tx= e d
∫
σ x
2π
l
0
where
t is the time;
x is a variable representing disc lifetime;
σ is the log standard deviation;
l
µ is the log mean;
l
ln(x) is the natural logarithm of x
µ
1
NOTE When t = e , the lognormal cumulative distribution function evaluates to 0,5. In other words, the model
predicts that half the samples have failed at that time.
3.5
disc-at-once recording
method of recording a CD-R disc whereby the entire CD is recorded in one pass without turning off the laser
3.6
end-of-life
occurrence of any loss of information
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ISO 18927:2008(E)
3.7
extended-term storage conditions
storage conditions suitable for the preservation of recorded information having permanent value
3.8
glass transition
reversible change in an amorphous polymer from, or to, a viscous or rubber condition to, or from, a hard and
relatively brittle one
3.8.1
glass transition temperature
T
g
approximate mid-point of the temperature range over which glass transition takes place
NOTE 1 T can be determined readily only by observing the temperature at which a significant change takes place in a
g
specific electrical, mechanical, or other physical property.
NOTE 2 T can also be sensitive to the moisture content of the polymer.
g
3.9
information
signal or image recorded using the system
3.10
life expectancy
LE
length of time that information is predicted to be acceptable in a system after dark storage at 23 °C and 50 %
relative humidity (RH)
3.10.1
standardized 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
3.11
retrievability
ability to access information as recorded
3.12
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.
3.13
survivor function
R()t
probability that a random unit drawn from the population survives at least time t, or the fraction of all units in
the population which survive at least time t
NOTE R()tF=−1 (t).
3.14
system
combination of material, hardware, software and documentation necessary for recording and/or retrieving
information
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ISO 18927:2008(E)
3.15
test cell
device that controls the stress to which the specimen is exposed
3.16
track-at-once recording
method of recording a CD-R disc whereby each track is recorded individually with 150 empty sectors
immediately preceding it and two run-out sectors immediately following
3.17
uncorrectable error
error in the playback data that is not correctable by the cross interleave Reed-Solomon code defined in
IEC 60908 as implemented in a system
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 recordable compact disc systems. This methodology provides a technically and
statistically sound procedure for obtaining and evaluating accelerated test data.
The methodology deals only with the effects of temperature and humidity on the retrievability of stored
information. For this reason, this International Standard is primarily directed to those storage applications, e.g.
libraries and archives, in which exposure to other influences potentially detrimental to information life
expectancy, such as chemical agents, intense light sources and improper handling, is controlled and
minimized.
4.2 Assumptions
The validity of the procedure defined by this International Standard relies on three assumptions:
⎯ specimen life distribution is appropriately modelled by the lognormal distribution;
⎯ the kinetics of the dominant failure mechanism is appropriately modelled by an Eyring acceleration model;
⎯ the dominant failure mechanism acting at the usage condition is the same as that at the accelerated
conditions.
Publications by Hamada and Stinson provide data indicating that these assumptions are applicable to
compact disc-recordable (CD-R) systems (see references [5] and [6] in the Bibliography).
5 Measurements
5.1 Summary
A sampling of 80 recorded discs shall be divided into five groups according to a specified plan. Each group of
discs (test cell) shall be subjected to one of five test stresses, combinations of temperature and relative
humidity. Periodically during the stress conditions, all discs from each stress group shall have their block error
rate (BLER) measured. Data collected at each time interval for each individual disc are then used to determine
a lifetime for that disc.
The disc lifetimes at each stress level are fitted to a lognormal distribution to determine a mean lifetime for the
stress. The resulting five mean lifetimes are regressed against temperature and relative humidity according to
an Eyring acceleration model. This model is then used to estimate the distribution of lifetimes at a usage
condition.
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ISO 18927:2008(E)
5.2 Block error rate (BLER)
End-of-life is the occurrence of any loss of information. Ideally, each specimen is tested until the first loss of
information occurs. Realistically, this is impractical. This International Standard considers max BLER to be a
high-level estimate of the performance of the system. The objective of measuring BLER is to establish a
practical estimation of the system's ability to read recorded data without uncorrectable errors. A change in
max BLER in response to the time at an accelerated 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.
A BLER of 220 is an arbitrary level chosen as a predictor of the onset of uncorrectable errors and thereby
end-of-life. A BLER of 220 corresponds to an upper limit for error correction. As a result, lower BLER discs are
recommended to use for long-term storage.
5.3 Test equipment
5.3.1 General requirements
A compact disc player that conforms to ISO/IEC 10149 and software capable of producing a display of max
BLER.
If it becomes necessary to replace the test equipment, the US National Bureau of Standards Handbook 91
shall be followed for correlating test equipment outputs.
The make, model and version of the test equipment (including software) shall be reported with the test results.
5.3.2 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 an accredited source.
In addition to the calibration disc, one control disc shall be maintained at ambient conditions and its max BLER
measured before and after each data collection interval. A control chart shall be maintained for this control
disc.
The mean and standard deviation of the control disc shall be established by collecting at least five
measurements. Should any individual max BLER reading differ from the mean by more than three times the
standard deviation, the problem shall be corrected and all data collected since the last valid control point shall
be remeasured.
5.4 Test specimen
5.4.1 General requirements
A test specimen is any disc that, after recording, meets ISO/IEC 10149 specifications and contains
representative data extending to within 2 mm of the maximum recording diameter.
5.4.2 Specimen selection
All discs shall be nominally identical with regard to substrate groove structure, layer structure, coating
composition, recording capacity, and age prior to test initiation. It is preferred that the CD-R media be chosen
from different lots and production lines in order to be representative of normal process variations.
All discs shall be maintained in the manufacturer's transportation and storage conditions prior to recording.
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ISO 18927:2008(E)
The nominal disc capacity shall be reported with the test results.
5.4.3 Recording system
Specimen discs may be recorded in any appropriate recording device. Since the extrapolated lifetime is a
function of the system including the CD-R media, all discs shall be recorded identically to the extent possible.
Similar recording devices shall be used, as well as similar software and recording conditions. Discs recorded
on different physical devices shall be distributed as equally as possible across the test cells.
The make and model of the recording device, the linear velocity employed during recording and the software
used in the recording system shall be reported with the test results.
5.4.4 Ambient recording conditions
Ambient conditions during recording shall be within the following limits:
⎯ temperature: 15 °C to 35 °C;
⎯ relative humidity: 45 % to 75 %.
During recording, the recording system shall be isolated from external vibrations.
5.4.5 Recording method
It is strongly recommended that all discs be recorded using the "disc-at-once" method. If discs are recorded
using the "track-at-once" method, all errors occurring at the gap between tracks shall be ignored for the
purpose of this International Standard. Packet writing (in which several write events are allowed within a track)
shall not be employed.
Independent of the writing method, the specimen discs shall be recorded as a single session and finalized.
6 Accelerated stress test plan
6.1 General
Information properly recorded in a CD-R system of good manufacture should have a life of 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 a test plan that will provide the information necessary to
satisfactorily evaluate the particular system.
Many accelerated life test plans follow a rather traditional approach in specimen selection, 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;
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ISO 18927:2008(E)
⎯ 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-R system will have different characteristics, a specific, detailed
optimum plan is impossible to forecast.
This test plan borrows from the optimum plan, the traditional plan and 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-R
media assessments.
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. This is
because, in an ideal case, the relationship between changes in the parameter investigated and changes in
stress are 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 condition 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 conditions that shall be used is shown in Table 1.
Additional specimens and conditions may be used if desired for improved precision.
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 5
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.
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ISO 18927:2008(E)
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 shall not be so high that plastic deformation occurs anywhere within the disc structure.
The typical substrate material for CD-R media is polycarbonate (glass transition temperature ∼ 150 °C). The
glass transition temperature of other layers may be lower. Experience with high-temperature testing of CD-R
discs indicates that an upper limit of 80 °C is practical for most applications.
6.2.4 Relative humidity (RH)
Practical experience shows that 85 % RH is the upper limit for control 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. The 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 undergo a transition from the ambient
conditions to stress conditions and back again a number of times during the course of testing. The transition
(or 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 information-recording layer. Gradients in the water concentration through
the thickness of the substrate shall also be limited. These gradients drive expansion gradients which can
cause significant disc curvature.
In order to minimize the effects of moisture-concentration gradients, the ramp profile outlined in Table 2 shall
be used. The objects of the profile are:
⎯ to avoid any situation that may cause moisture condensation within the substrate;
⎯ to minimize the time during which substantial moisture gradients exist in the substrate;
⎯ to produce at the end of the profile a disc that is sufficiently equilibrated to proceed directly to testing
without delay.
The profile accomplishes this by varying the moisture content of the disc only at the stress incubation
temperature, and allowing sufficient time for equilibration during ramp-down based on the diffusion coefficient
of water in polycarbonate.
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ISO 18927:2008(E)
Table 2 — Temperature and relative humidity transition (ramp) profile
Temperature Relative humidity Duration
Process step
T RH h
°C %
a a
Start at T(amb) at RH(amb) —
b c
T, RH ramp to T(inc) to RH(int) 1,5 ± 0,5
b
RH ramp at T(inc) to RH(inc) 1,5 ± 0,5
Incubation at T(inc) at RH(inc) See Table 1
RH ramp at T(inc) to RH(int) 1,5 ± 0,5
Equilibration at T(inc) at RH(int) See Table 1
T, RH ramp to T(amb) to RH(amb) 1,5 ± 0,5
End at T(amb) at RH(amb) —
Transitions should not deviate from a linear change over the chosen duration by more than ± 2 °C and ± 3 % RH. Ramp transitions may
be controlled automatically or manually.
a
T(amb) and RH(amb) are room ambient temperature and relative humidity.
b
T(inc) and RH(inc) are the stress incubation temperature and relative humidity.
c
RH(int) is the intermediate relative humidity that at T(inc) supports the same equilibrium moisture absorption in polycarbonate as
that supported at T(amb) and RH(amb) (see Table 1).
Figure 1 graphically portrays the temperature and relative humidity changes that would occur during one cycle
of incubation at 80 °C and 85 % RH, as specified in Tables 1 and 2.
Figure 1 — Graph of nominal 80 °C/85 % RH transition (ramp) profile
6.2.6 Independent verification of chamber conditions
A system independent of the chamber control system shall be used to monitor temperature and relative
humidity conditions in the test chamber during the stress test.
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ISO 18927:2008(E)
6.2.7 Specimen placement
Disc specimens shall be placed uncovered, either vertically or horizontally, within the test chamber. Discs
shall be aligned so that their surface is parallel to the chamber airflow. A space of at least 2 mm shall be
maintained between discs.
6.2.8 Other influences
During the course of
...
SLOVENSKI STANDARD
SIST ISO 18927:2011
01-julij-2011
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Imaging materials - Recordable compact disc systems - Method for estimating the life
expectancy based on the effects of temperature and relative humidity
Matériaux pour image - Systèmes de CD enregistrables - 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 18927:2008
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 18927:2011 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
---------------------- Page: 1 ----------------------
SIST ISO 18927:2011
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SIST ISO 18927:2011
INTERNATIONAL ISO
STANDARD 18927
Second edition
2008-10-15
Imaging materials — Recordable compact
disc systems — Method for estimating
the life expectancy based on the effects
of temperature and relative humidity
Matériaux pour image — Systèmes de CD enregistrables — Méthode
d'estimation de l'espérance de vie basée sur les effets de la
température et de l'humidité relative
Reference number
ISO 18927:2008(E)
©
ISO 2008
---------------------- Page: 3 ----------------------
SIST ISO 18927:2011
ISO 18927:2008(E)
PDF disclaimer
This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but
shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In
downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat
accepts no liability in this area.
Adobe is a trademark of Adobe Systems Incorporated.
Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation
parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In
the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.
COPYRIGHT PROTECTED DOCUMENT
© ISO 2008
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or
ISO's member body in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2008 – All rights reserved
---------------------- Page: 4 ----------------------
SIST ISO 18927:2011
ISO 18927:2008(E)
Contents Page
Foreword .iv
1 Scope.1
2 Normative references.1
3 Terms and definitions .1
4 Purpose and assumptions.4
4.1 Purpose .4
4.2 Assumptions.4
5 Measurements .4
5.1 Summary .4
5.2 Block error rate (BLER).5
5.3 Test equipment .5
5.4 Test specimen.5
6 Accelerated stress test plan.6
6.1 General .6
6.2 Stress conditions .7
6.3 Accelerated test cell sample population.10
6.4 Time intervals .10
6.5 Test plan.10
6.6 Measurement conditions .11
7 Data evaluation .11
7.1 Lognormal distribution model.11
7.2 Eyring acceleration model.11
7.3 Acceleration factors .12
7.4 Survivor analysis.12
7.5 Aids.13
8 Disclaimer .13
Annex A (informative) Step analysis outline .14
Annex B (informative) Example of test plan and data analysis.15
Bibliography.27
© ISO 2008 – All rights reserved iii
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SIST ISO 18927:2011
ISO 18927:2008(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 18927 was prepared by Technical Committee ISO/TC 42, Photography.
This second edition cancels and replaces the first edition (ISO 18927:2002), of which it constitutes a minor
revision.
The following changes have been made to the first edition:
⎯ modification of definition 3.10 (life expectancy);
⎯ modification of 5.2 on block error rate;
⎯ updating of normative and bibliographical references;
⎯ removal of the original Annex A.
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SIST ISO 18927:2011
INTERNATIONAL STANDARD ISO 18927:2008(E)
Imaging materials — Recordable compact disc systems —
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 of information stored on
recordable compact disc systems. Only the effects of temperature and relative humidity on the media are
considered.
This International Standard does not cover the effects of light, air pollution, or time-dependent flow
phenomena.
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)
IEC 60908:1999, Audio recording — Compact disc digital audio system
Experimental statistics, U.S. National Bureau of Standards Handbook 91, 1963
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
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.
3.2
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)
1) Equivalent to ECMA 130.
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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]
3.2.1
maximum block error rate
max BLER
maximum BLER measured anywhere on a disc
3.3
compact disc-recordable
CD-R
recordable optical disc in which information can be recorded to certain areas in compact disc format
NOTE 1 Information can be recorded once and read many times.
NOTE 2 The term “compact disc-write once” (CD-WO) has also been used to describe this type of disc.
3.4
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
3.4.1
lognormal cumulative distribution function
F()t
cumulative distribution function in which the logarithm of the relevant parameter, in this International Standard
the disc lifetime, has a normal distribution and is defined by the following equation:
t ln( x)−µ
2
1l
−()
11
2 σ
l
F()tx= e d
∫
σ x
2π
l
0
where
t is the time;
x is a variable representing disc lifetime;
σ is the log standard deviation;
l
µ is the log mean;
l
ln(x) is the natural logarithm of x
µ
1
NOTE When t = e , the lognormal cumulative distribution function evaluates to 0,5. In other words, the model
predicts that half the samples have failed at that time.
3.5
disc-at-once recording
method of recording a CD-R disc whereby the entire CD is recorded in one pass without turning off the laser
3.6
end-of-life
occurrence of any loss of information
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3.7
extended-term storage conditions
storage conditions suitable for the preservation of recorded information having permanent value
3.8
glass transition
reversible change in an amorphous polymer from, or to, a viscous or rubber condition to, or from, a hard and
relatively brittle one
3.8.1
glass transition temperature
T
g
approximate mid-point of the temperature range over which glass transition takes place
NOTE 1 T can be determined readily only by observing the temperature at which a significant change takes place in a
g
specific electrical, mechanical, or other physical property.
NOTE 2 T can also be sensitive to the moisture content of the polymer.
g
3.9
information
signal or image recorded using the system
3.10
life expectancy
LE
length of time that information is predicted to be acceptable in a system after dark storage at 23 °C and 50 %
relative humidity (RH)
3.10.1
standardized 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
3.11
retrievability
ability to access information as recorded
3.12
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.
3.13
survivor function
R()t
probability that a random unit drawn from the population survives at least time t, or the fraction of all units in
the population which survive at least time t
NOTE R()tF=−1 (t).
3.14
system
combination of material, hardware, software and documentation necessary for recording and/or retrieving
information
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3.15
test cell
device that controls the stress to which the specimen is exposed
3.16
track-at-once recording
method of recording a CD-R disc whereby each track is recorded individually with 150 empty sectors
immediately preceding it and two run-out sectors immediately following
3.17
uncorrectable error
error in the playback data that is not correctable by the cross interleave Reed-Solomon code defined in
IEC 60908 as implemented in a system
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 recordable compact disc systems. This methodology provides a technically and
statistically sound procedure for obtaining and evaluating accelerated test data.
The methodology deals only with the effects of temperature and humidity on the retrievability of stored
information. For this reason, this International Standard is primarily directed to those storage applications, e.g.
libraries and archives, in which exposure to other influences potentially detrimental to information life
expectancy, such as chemical agents, intense light sources and improper handling, is controlled and
minimized.
4.2 Assumptions
The validity of the procedure defined by this International Standard relies on three assumptions:
⎯ specimen life distribution is appropriately modelled by the lognormal distribution;
⎯ the kinetics of the dominant failure mechanism is appropriately modelled by an Eyring acceleration model;
⎯ the dominant failure mechanism acting at the usage condition is the same as that at the accelerated
conditions.
Publications by Hamada and Stinson provide data indicating that these assumptions are applicable to
compact disc-recordable (CD-R) systems (see references [5] and [6] in the Bibliography).
5 Measurements
5.1 Summary
A sampling of 80 recorded discs shall be divided into five groups according to a specified plan. Each group of
discs (test cell) shall be subjected to one of five test stresses, combinations of temperature and relative
humidity. Periodically during the stress conditions, all discs from each stress group shall have their block error
rate (BLER) measured. Data collected at each time interval for each individual disc are then used to determine
a lifetime for that disc.
The disc lifetimes at each stress level are fitted to a lognormal distribution to determine a mean lifetime for the
stress. The resulting five mean lifetimes are regressed against temperature and relative humidity according to
an Eyring acceleration model. This model is then used to estimate the distribution of lifetimes at a usage
condition.
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5.2 Block error rate (BLER)
End-of-life is the occurrence of any loss of information. Ideally, each specimen is tested until the first loss of
information occurs. Realistically, this is impractical. This International Standard considers max BLER to be a
high-level estimate of the performance of the system. The objective of measuring BLER is to establish a
practical estimation of the system's ability to read recorded data without uncorrectable errors. A change in
max BLER in response to the time at an accelerated 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.
A BLER of 220 is an arbitrary level chosen as a predictor of the onset of uncorrectable errors and thereby
end-of-life. A BLER of 220 corresponds to an upper limit for error correction. As a result, lower BLER discs are
recommended to use for long-term storage.
5.3 Test equipment
5.3.1 General requirements
A compact disc player that conforms to ISO/IEC 10149 and software capable of producing a display of max
BLER.
If it becomes necessary to replace the test equipment, the US National Bureau of Standards Handbook 91
shall be followed for correlating test equipment outputs.
The make, model and version of the test equipment (including software) shall be reported with the test results.
5.3.2 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 an accredited source.
In addition to the calibration disc, one control disc shall be maintained at ambient conditions and its max BLER
measured before and after each data collection interval. A control chart shall be maintained for this control
disc.
The mean and standard deviation of the control disc shall be established by collecting at least five
measurements. Should any individual max BLER reading differ from the mean by more than three times the
standard deviation, the problem shall be corrected and all data collected since the last valid control point shall
be remeasured.
5.4 Test specimen
5.4.1 General requirements
A test specimen is any disc that, after recording, meets ISO/IEC 10149 specifications and contains
representative data extending to within 2 mm of the maximum recording diameter.
5.4.2 Specimen selection
All discs shall be nominally identical with regard to substrate groove structure, layer structure, coating
composition, recording capacity, and age prior to test initiation. It is preferred that the CD-R media be chosen
from different lots and production lines in order to be representative of normal process variations.
All discs shall be maintained in the manufacturer's transportation and storage conditions prior to recording.
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The nominal disc capacity shall be reported with the test results.
5.4.3 Recording system
Specimen discs may be recorded in any appropriate recording device. Since the extrapolated lifetime is a
function of the system including the CD-R media, all discs shall be recorded identically to the extent possible.
Similar recording devices shall be used, as well as similar software and recording conditions. Discs recorded
on different physical devices shall be distributed as equally as possible across the test cells.
The make and model of the recording device, the linear velocity employed during recording and the software
used in the recording system shall be reported with the test results.
5.4.4 Ambient recording conditions
Ambient conditions during recording shall be within the following limits:
⎯ temperature: 15 °C to 35 °C;
⎯ relative humidity: 45 % to 75 %.
During recording, the recording system shall be isolated from external vibrations.
5.4.5 Recording method
It is strongly recommended that all discs be recorded using the "disc-at-once" method. If discs are recorded
using the "track-at-once" method, all errors occurring at the gap between tracks shall be ignored for the
purpose of this International Standard. Packet writing (in which several write events are allowed within a track)
shall not be employed.
Independent of the writing method, the specimen discs shall be recorded as a single session and finalized.
6 Accelerated stress test plan
6.1 General
Information properly recorded in a CD-R system of good manufacture should have a life of 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 a test plan that will provide the information necessary to
satisfactorily evaluate the particular system.
Many accelerated life test plans follow a rather traditional approach in specimen selection, 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;
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⎯ 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-R system will have different characteristics, a specific, detailed
optimum plan is impossible to forecast.
This test plan borrows from the optimum plan, the traditional plan and 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-R
media assessments.
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. This is
because, in an ideal case, the relationship between changes in the parameter investigated and changes in
stress are 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 condition 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 conditions that shall be used is shown in Table 1.
Additional specimens and conditions may be used if desired for improved precision.
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 5
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.
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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 shall not be so high that plastic deformation occurs anywhere within the disc structure.
The typical substrate material for CD-R media is polycarbonate (glass transition temperature ∼ 150 °C). The
glass transition temperature of other layers may be lower. Experience with high-temperature testing of CD-R
discs indicates that an upper limit of 80 °C is practical for most applications.
6.2.4 Relative humidity (RH)
Practical experience shows that 85 % RH is the upper limit for control 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. The 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 undergo a transition from the ambient
conditions to stress conditions and back again a number of times during the course of testing. The transition
(or 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 information-recording layer. Gradients in the water concentration through
the thickness of the substrate shall also be limited. These gradients drive expansion gradients which can
cause significant disc curvature.
In order to minimize the effects of moisture-concentration gradients, the ramp profile outlined in Table 2 shall
be used. The objects of the profile are:
⎯ to avoid any situation that may cause moisture condensation within the substrate;
⎯ to minimize the time during which substantial moisture gradients exist in the substrate;
⎯ to produce at the end of the profile a disc that is sufficiently equilibrated to proceed directly to testing
without delay.
The profile accomplishes this by varying the moisture content of the disc only at the stress incubation
temperature, and allowing sufficient time for equilibration during ramp-down based on the diffusion coefficient
of water in polycarbonate.
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Table 2 — Temperature and relative humidity transition (ramp) profile
Temperature Relative humidity Duration
Process step
T RH h
°C %
a a
Start at T(amb) at RH(amb) —
b c
T, RH ramp to T(inc) to RH(int) 1,5 ± 0,5
b
RH ramp at T(inc) to RH(inc) 1,5 ± 0,5
Incubation at T(inc) at RH(inc) See Table 1
RH ramp at T(inc) to RH(int) 1,5 ± 0,5
Equilibration at T(inc) at RH(int) See Table 1
T, RH ramp to T(amb) to RH(amb) 1,5 ± 0,5
End at T(amb) at RH(amb) —
Transitions should not deviate from a linear change over the chosen duration by more than ± 2 °C and ± 3 % RH. Ramp transitions
...
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