ISO 18938:2008

Imaging materials - Optical discs - Care and handling for extended storage

ISO 18938:2008 establishes general principles for the care and handling of digital optical discs during use. It addresses the issues of physical integrity of the medium necessary to preserve access to the recorded data (information). ISO 18938:2008 includes recommendations for handling procedures to maximize the effective life of optical discs. Faulty handling, packing and transporting techniques and methods often cause physical damage to the discs and to the content recorded thereon. Extending the longevity of optical discs requires the identification of appropriate handling methods, as well as well-developed and implemented training programs. For the purposes of ISO 18938:2008, the term “optical disc” includes the families of compact disc (CD), digital versatile disc (DVD), high definition digital versatile disc (HD DVD) and Blu-ray disc (BD), and any hybrids of these families. The term “optical disc” also includes each type of disc within a family, including injection moulded [read-only memory (ROM)], dye-layer [recordable (R)] and phase change [rewriteable (RW), random access memory (RAM)] technologies. While some of the recommendations in ISO 18938:2008 (e.g. those for staff training) apply specifically to large-scale or long term usage, the basics of all recommendations in ISO 18938:2008 are intended to be applied in circumstances where the desired result is long-term usage of the medium whether archival, commercial or personal. ISO 18938:2008 does not cover magneto-optical (MO) discs, laser discs (LD) or glass discs. At the time of writing, International Standards do not exist for HD DVD and Blu-ray discs. Nonetheless, it is believed that the recommendations in ISO 18938:2008 for care and handling can equally apply to them. It is recognized that some of these requirements are not necessarily possible for the individual user to achieve. The following are within the scope of ISO 18938:2008: use and handling environments, including pollutants, temperature and humidity and light exposure; contamination concerns; inspection; cleaning and maintenance, including cleaning methods and frequency; transportation; disasters, including water, fire, construction and post-disaster procedures; staff training.

Matériaux pour l'image — Disques optiques — Précautions et manipulation pour stockage étendu

Upodobitveni materiali - Optične plošče - Nega in ravnanje za dolgo shranjevanje

Ta mednarodni standard vzpostavlja splošna načela za nego in ravnanje z digitalnimi optičnimi ploščami med uporabo. Obravnava vprašanja fizikalne celovitosti medija, ki je potrebna za ohranjanje dostopa do posnetih podatkov (informacij). Ta mednarodni standard vključuje priporočila za postopke ravnanja, s katerimi se čim bolj podaljša efektivna življenjska doba optičnih plošč. Napačne tehnike in metode ravnanja, pakiranja in prevoza pogosto povzročajo fizično škodo na ploščah in vsebini, ki je na njih navedena. Za podaljšanje življenjske dobe optičnih plošč je potrebna identifikacija ustreznih metod ravnanja ter dobro razviti in izvajani programi usposabljanja. Za ta mednarodni standard izraz »optična plošča« vključuje družine kompaktnih diskov (CD), digitalnih prilagodljivih plošč (DVD, digitalnih prilagodljivih plošč z veliko ločljivostjo (HD DVD) in diskov Blu-ray (BD)2) ter hibride teh družin. Izraz »optična plošča« vključuje tudi vse vrste plošč v družini, vključno z brizganimi [plošča z bralnim pomnilnikom (ROM)], barvnoslojnimi [snemalna plošča (R)] in fazno spremenljivimi [zapisljiva plošča (RW), plošča z bralno-pisalnim pomnilnikom (RAM)] tehnologijami. Čeprav nekatera od priporočil v tem mednarodnem standardu (npr. priporočila za usposabljanje osebja) veljajo specifično za obsežno ali dolgotrajno uporabo, osnove vseh priporočil v tem mednarodnem standardu veljajo v okoliščinah, v katerih je želeni rezultat dolgotrajna uporaba medija, ne glede na to, ali gre za arhivsko, komercialno ali osebno rabo. Ta mednarodni standard ne zajema magnetno-optičnih (MO) plošč, laserskih plošč (LD) ali steklenih plošč. V času, ko to pišemo, mednarodni standardi za plošče HD DVD in Blu-ray ne obstajajo. Domneva pa se, da priporočila za nego in ravnanje iz tega mednarodnega standarda lahko veljajo tudi zanje. Priznava se, da nekaterih od teh zahtev posamezen uporabnik morda ne more izpolniti. V okvir tega mednarodnega standarda spada spodaj navedeno: - okolja za uporabo in ravnanje, vključno z izpostavljenostjo onesnaževalom, temperaturi in vlagi ter svetlobi; - pomisleki glede kontaminacije; - nadzor; - čiščenje in vzdrževanje, vključno z metodami in pogostostjo čiščenja; - prevoz; - nesreče, vključno s poplavami, požarom, nesrečami pri izdelavi in postopki po nesreči; - usposabljanje osebja. Kakovost podatkov, zapisanih na ploščo, ni predmet tega mednarodnega standarda. Vendar pa je visoka kakovost rezultatov med snemanjem pomembna za dolgoživost informacij. Priporočljivo je, da se izvaja strog program preskušanja celovitosti podatkov, saj je obvezen del vsakega dolgoročnega shranjevanja digitalnih zapisov. Poleg tega je pri shranjevanju digitalnih informacij v arhiv priporočljivo, da je vzpostavljena strategija več kopij/več lokacij.

General Information

• Status: Withdrawn
• Publication Date: 31-Aug-2008
• Withdrawal Date: 31-Aug-2008
• ICS: 35.220.30 - Optical storage devices
• ICS: 37.040.99 - Other standards related to photography
• Technical Committee: ISO/TC 42 - Photography
• Drafting Committee: ISO/TC 42/WG 5 - Physical properties and image permanence of photographic materials
• Current Stage: 9599 - Withdrawal of International Standard
• Start Date: 05-Sep-2014
• Completion Date: 13-Dec-2025
• Ref Project: SIST ISO 18938:2011 - Imaging materials - Optical discs - Care and handling for extended storage

Relations

• Revised: ISO 18938:2014 - Imaging materials - Optical discs - Care and handling for extended storage
• Effective Date: 17-Nov-2012

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 18938
First edition
2008-09-15
Imaging materials — Optical discs — Care
and handling for extended storage
Matériaux pour l'image — Disques optiques — Précautions et
manipulation pour stockage étendu

Reference number
©
ISO 2008
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ii ISO 2008 – All rights reserved

Contents Page
1 Scope . 1
2 Normative references . 2
3 Terms and definitions . 2
4 Composition of optical discs . 6
4.1 General . 6
4.2 Polycarbonate substrate (plastic) layer . 6
4.3 Data layer . 6
4.4 Reflective layer . 7
4.5 Protective layers . 7
4.6 Adhesive layers . 7
4.7 Additional layers . 8
5 Failure mechanisms . 8
5.1 General . 8
5.2 Physical stress . 8
5.3 Layer sensitivity . 8
5.4 Scratches . 9
5.5 Effects of disc play . 9
6 Handling techniques . 10
6.1 General . 10
6.2 Flexing . 10
6.3 Contamination . 10
6.4 Disc enclosures . 10
7 Identification . 11
7.1 Basic concepts . 11
7.2 Adhesive labels . 11
7.3 Printing on optical discs . 11
7.4 Thermal printing . 11
7.5 Inkjet printable surface . 12
7.6 Silk screening . 12
7.7 Marking . 12
8 Contamination . 12
8.1 Fingerprints, smudges, dirt, dust . 12
8.2 Moisture . 12
8.3 Organic solvents . 12
8.4 Gaseous impurities . 13
8.5 Consumables . 13
9 Use environment . 13
9.1 General . 13
9.2 Temperature and humidity . 13
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ISO 2008 – All rights reserved iii

9.3 Water avoidance . 14
9.4 Air quality . 14
9.5 Light exposure . 14
9.6 Acclimatization . 14
9.7 Vibrations . 15
10 Transportation and shipping . 15
10.1 Enclosures . 15
10.2 Cartons . 15
10.3 Exposure . 16
10.4 Security . 16
10.5 External fields . 16
10.6 Biological irradiation . 16
11 Inspection . 16
11.1 General requirements . 16
11.2 Error rate monitoring . 17
12 Cleaning and maintenance . 17
12.1 General . 17
12.2 Solvents and cleaning compounds . 17
12.3 Cleaning methods . 17
13 Disasters . 18
13.1 General . 18
13.2 Water . 18
13.3 Fire . 18
13.4 Dry debris . 18
13.5 Impact from disasters . 19
13.6 Repair . 19
14 Disaster response . 19
14.1 General . 19
14.2 Wet discs . 19
14.3 Dry discs . 19
15 Staff training . 19
15.1 General . 19
15.2 Purpose . 20
15.3 Training paths . 20
15.4 Schedule for training . 20
15.5 Update of training . 20
15.6 Content of training . 20
16 Minimum handling requirements checklist . 21
16.1 General . 21
16.2 Do list . 21
16.3 Not-to-do list . 21
Annex A (informative) Disc structure . 22
Bibliography . 24
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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 18938 was prepared by Technical Committee ISO/TC 42, Photography.
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ISO 2008 – All rights reserved v

Introduction
1)
In addition to storage conditions, the proper care and handling of optical discs is also vital to prolonged disc
life. This is becoming increasingly important as optical discs are widely used for the recording and storage of
information. This International Standard gives guidelines for their recommended care and handling and will be
beneficial for all digital optical discs, regardless of their inherent stability.
Probably no form of data storage has been accepted and adopted as rapidly as the optical disc. It has become
the medium of choice for numerous applications with ever increasing use for the recording and storage of
information. Information is recorded in digital format that not only provides high storage density, but also allows
duplication without information loss, ease of data manipulation and facilitates transmission. It is of tremendous
benefit for audio usage since it permits uninterrupted playback for long periods of time. Information in a disc
format can be accessed very quickly, unlike that in a roll format such as magnetic tape, which requires longer
search time.
While the advantages are many, as with other media, there are nevertheless concerns about the life expectancy
of recorded information on optical discs. This depends upon three independent components, namely the
permanence of the disc itself, the disc drive and the software. Obsolescence of the disc drive and software, lack
of playback device or inoperability of the playback device are all serious uncertainties. Another important issue
is the quality of the initial data recorded onto the disc, which needs to be as high as possible. In addition, the
very popularity of recordable optical discs has led to their wide availability, and wide variability in the quality of
discs for long term preservation of information. Many discs may not be of sufficient quality for long term use.
The finite life of optical discs is well recognized and one approach to addressing this issue is by periodically
transferring or reformatting the information. In addition, the ability to play back a disc in the future depends on
the existence of functional playback equipment. As newer formats and equipment become popular, equipment
manufacturers will probably discontinue production and support of the older, superseded equipment. Eventually,
usable equipment to play obsolete optical disc formats will become difficult to find. Before this occurs, it is
advisable that a migration plan be in place. However, these issues are outside the scope of this International
Standard, which is only concerned with the stability of the optical disc itself. A primary objective of those
involved with the preservation of information on this media is to ensure that the disc is not the weak link among
the necessary components. To support this objective, it is advisable that steps be taken to maximize the optical
disc's potential to be more stable than either the hardware or the software.
As with paper records, photographic film and magnetic tape, optical discs are subject to both damage and
decay. They have a finite life. Predictions of the life expectancy of optical discs have involved extrapolations of
property retention after high temperature and humidity incubations back to practical conditions. These
extrapolations follow mathematical treatments that were developed for simpler chemical reactions, and
therefore the results need to be interpreted with some caution. Predictions cover a very wide range, from
25 years to over 250 years, which vary with the manufacturer and the disc type. Their effective life can be
increased or decreased significantly depending upon the conditions under which they are stored. Storage
recommendations for optical discs are given in ISO 18925. Following these recommendations promotes the
physical integrity of the media and increases their effective life.
1) It is recognized that both “optical discs” and “optical disks” are acceptable spellings. In this International Standard, the
former spelling is used.
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INTERNATIONAL STANDARD ISO 18938:2008(E)
Imaging materials — Optical discs — Care and handling for
extended storage
1Scope
This International Standard establishes general principles for the care and handling of digital optical discs
during use. It addresses the issues of physical integrity of the medium necessary to preserve access to the
recorded data (information). This International Standard includes recommendations for handling procedures to
maximize the effective life of optical discs. Faulty handling, packing and transporting techniques and methods
often cause physical damage to the discs and to the content recorded thereon. Extending the longevity of
optical discs requires the identification of appropriate handling methods, as well as well-developed and
implemented training programs.
For the purposes of this International Standard, the term “optical disc” includes the families of compact disc
2)
(CD), digital versatile disc (DVD), high definition digital versatile disc (HD DVD) and Blu-ray disc (BD) , and any
hybrids of these families. The term “optical disc” also includes each type of disc within a family, including
injection moulded [read-only memory (ROM)], dye-layer [recordable (R)] and phase change [rewriteable (RW),
random access memory (RAM)] technologies.
While some of the recommendations in this International Standard (e.g. those for staff training) apply
specifically to large-scale or long term usage, the basics of all recommendations in this International Standard
are intended to be applied in circumstances where the desired result is long-term usage of the medium whether
archival, commercial or personal.
This International Standard does not cover magneto-optical (MO) discs, laser discs (LD) or glass discs. At the
time of writing, International Standards do not exist for HD DVD and Blu-ray discs. Nonetheless, it is believed
that the recommendations in this International Standard for care and handling can equally apply to them. It is
recognized that some of these requirements are not necessarily possible for the individual user to achieve.
The following are within the scope of this International Standard:
— use and handling environments, including pollutants, temperature and humidity and light exposure;
— contamination concerns;
— inspection;
— cleaning and maintenance, including cleaning methods and frequency;
— transportation;
— disasters, including water, fire, construction and post-disaster procedures;
— staff training.
The quality of the data written on the disc is outside the scope of this International Standard. However, a high
quality result of the recording phase is important to the longevity of information. It is advisable that a rigorous
program of data integrity testing be implemented, as this forms an obligatory part of all digital long-term storage.
In addition, when keeping digital information for archival purposes, it is advisable that a multiple copy/multiple
location strategy be in place.
2) Blu-ray disc and HD DVD are examples of suitable products available commercially. This information is given for the
convenience of users of this International Standard and does not constitute an endorsement by ISO of these products.
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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.
ISO 14644-1, Cleanrooms and associated controlled environments — Part 1: Classification of air cleanliness
ISO 18925, Imaging materials — Optical disc media — Storage practices
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
3)
Amaray case
case designed for DVD discs slightly larger than a jewel case
3.2
acclimatization
staging
process of conditioning material from one set of temperature-moisture conditions to another
3.3
balance
precision vertical position of the disc as it spins
3.4
blister
localized delamination that looks like a bubble
3.5
Blu-ray disc
BD
optical disc in which one or more information layers are located between two layers and the data can be read by
an optical beam with a wave length of 405 nm
3.5.1
read only memory BD-ROM
optical disc to which information is transferred during manufacture to moulded areas in the Blu-ray disc format
and can be read multiple times by an optical beam
3.5.2
recordable BD-R
recordable optical disc in which information can be recorded once to areas in the Blu-ray disc format and read
many times
3.5.3
rewriteable BD-RE
recordable optical disc in which information can be recorded to areas in the Blu-ray disc format and can be
erased, rerecorded and read many times
3) Amaray case is an example of a suitable product available commercially. This information is given for the convenience of
users of this International Standard and does not constitute an endorsement by ISO of this product.
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3.6
carton
box outer container that can hold one or more individual units and can be a fabrication of paper, card stock or
plastic
3.7
compact disc
CD
optical disc in which the information layer is located near one surface of a substrate and the data can be read by
an optical beam
NOTE Described in IEC 60908.
3.7.1
read only memory CD-ROM
optical disc to which information is transferred during manufacture to moulded areas in the compact disc format
and can be read multiple times by an optical beam
NOTE Described in ISO/IEC 10149.
3.7.2
recordable CD-R
recordable optical disc in which information can be recorded once to areas in the compact disc format and read
many times
3.7.3
rewritable CD-RW
recordable optical disc in which information can be recorded to areas in the compact disc format and can be
erased, rerecorded and read many times
3.8
conditioning
exposure of a material to air at a given relative humidity and temperature until equilibrium is reached
3.9
container
box, can or carton used for storage and shipping of recording materials
EXAMPLE The box into which a reel, cassette, cartridge or shell is placed.
3.10
delamination
separation of a laminate into its constituent layers
3.11
digital versatile disc
DVD
optical disc in which one or more information layers are located between two substrates and the data can be
read by an optical beam with a wave length of between 635 nm and 650 nm
NOTE Formerly called digital video disc.
3.11.1
read only memory DVD-ROM
optical disc in which information is transferred during manufacture to certain areas in the DVD format and can
be read multiple times by an optical beam
NOTE Described in ISO/IEC 16448 and ISO/IEC 16449.
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3.11.2
recordable DVD-R, +R
recordable optical disc in which information can be recorded once to areas in the DVD disc format and read
many times
NOTE Described in ISO/IEC 23912, ISO/IEC 17344 and ISO/IEC 25434.
3.11.3
rewriteable DVD-RAM, DVD-RW, +RW
DVD optical discs that can be written, read and overwritten many times using phase change technology
NOTE 1 See Annex A.
NOTE 2 Described in ISO/IEC 17592, ISO/IEC 17341 and ISO/IEC 26925.
3.12
enclosure
case, cartridge, folder, envelope, sleeve or clam shell that is intended for physical protection against mechanical
damage
3.13
extended-term storage conditions
storage conditions suitable for the preservation of recorded information having permanent value
3.14
high definition digital versatile disc
HD DVD
optical disc in which one or more information layers are located between two substrates and the data can be
read by an optical beam with a wave length of 405 nm
NOTE Sometimes called high density digital versatile disc.
3.14.1
read only memory HD DVD-ROM
optical disc in which information is transferred during manufacture to certain areas in the HD DVD format and
can be read multiple times by an optical beam
3.14.2
recordable HD DVD-R
recordable optical disc in which information can be recorded once to areas in the HD DVD disc format and read
many times
3.14.3
rewriteable HD DVD-RW
DVD optical discs that can be written, read and overwritten many times using phase change technology
3.15
information
data recorded using the system
3.16
insulated record container
storage box designed to provide an environmental buffer against temperature and humidity fluctuations
3.17
jewel case
plastic enclosure featuring a hinged lid and one or more trays, each containing a hub clamp to secure and
protect the disc surface
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3.18
macroenvironment
atmospheric conditions in a large area in which records are kept
NOTE Atmospheric conditions are temperature, relative humidity and pollutants.
3.19
medium
material on which information is recorded
3.20
microenvironment
atmospheric conditions inside a storage enclosure in which records are kept
NOTE Atmospheric conditions are temperature, relative humidity and pollutants.
3.21
optical disc
disc that will accept and retain information from light modulation changes in a recording or reflective layer that
can be read with an optical beam
3.22
optical disc cartridge
ODC
optical disc enclosure required for the operation of the disc
3.23
recording layer
layer of an optical disc on which data is written either during manufacture or in use
3.24
relative humidity
RH
ratio, defined as a percentage, of the existing partial vapour pressure of water to the vapour pressure at
saturation
NOTE It is usually, but not always, equal to the percentage of the amount of moisture in the air to that at saturation.
3.25
replicated disc
disc made by an injection moulding process where the land and pits that make up the data are physically
pressed into the polycarbonate
3.26
retrievability
ability to access information as recorded
3.27
slimline case
slimmer version of the jewel case
3.28
snapper case
alternative to the Amaray case with a cardboard cover
3.29
storage environment
conditions for storing materials
NOTE The conditions are temperature, relative humidity, cleanliness of facilities and atmospheric pollutants.
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3.30
storage housing
physical structure supporting materials and their enclosures
NOTE It can consist of drawers, racks, shelves or cabinets.
3.31
substrate
transparent layer of an optical disc which provides mechanical support of the recording layer
3.32
system
combination of media, hardware, software and documentation necessary for recording and/or retrieving
information
3.33
WORM disc
optical disc in which the data in specified areas can be written only once and read multiple times by an optical
beam
4 Composition of optical discs
4.1 General
Optical discs are composed of a series of layers made of different materials assembled like a sandwich.
Typically, these layers include the polycarbonate substrate (plastic) layer(s), the data layer(s), the metal
layers(s) or reflective layer, the metal protective layers, the adhesive layer and an optional extra layer for
labelling or added protection. These layers are listed in Annex A.
4.2 Polycarbonate substrate (plastic) layer
The polycarbonate substrate makes up most of the disc. The polycarbonate is typically clear, but may be
coloured for appearance or to prevent copyright infringement. The disc drive laser beam travels through this
substrate. This substrate provides the disc depth necessary to maintain laser focus. It also gives the disc
enough strength to remain flat.
A CD is one continuous 1,2 mm thick polycarbonate layer. Both DVDs and HD DVDs are made up of two
0,6 mm thick polycarbonate layers bonded together. BDs are made up of one 1,1 mm and one 0,1 mm
polycarbonate layer bonded together. CDs are read from one side only. DVDs, HD DVDs and BDs are read from
one or both sides.
4.3 Data layer
As its name implies, the data layer of optical discs is the layer that contains the encoded data. The encoded
data appear as marks or pits that either transmit or alter light from the laser beam back to the laser photosensor
by way of the metal reflective layer. Write-once (–R, +R) discs use organic dye material or phase change
materials, whereas rewritable (–RW, +RW, –RAM, –RE) discs use phase change materials as the layer(s) for
holding record data written by a disc drive. ROM discs do not use a separate layer, but the data has been
pressed in the form of pits from injection moulding on the inner surface of the polycarbonate substrate during
the disc manufacturing process.
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4.4 Reflective layer
The metal layer in optical discs reflects the laser beam back to the laser photodiode in the optical pickup unit
(OPU). Three main types of reflective metals typically are used for this layer:
a) aluminium or aluminium alloy,
b) gold, and
c) silver or silver alloy.
In “double-layer” DVDs, silicon is sometimes used as one of the semi-reflective layers. Some discs use a copper
alloy for the purposes of appearance.
Aluminium is used in ROM, RW and RAM discs. Silver, silver alloy or gold are used in R discs, since aluminium
is too active to use with dye. Aluminium is also prone to corrosion when exposed to moisture or other pollutants
that penetrate into the disc. Oxidation of the aluminium diminishes its reflectivity, eventually making the disc
unreadable by the laser. This is sometimes referred to as disc “rot”.
Silver can lose reflectivity due to corrosion on exposure to pollutants such as sulphur dioxide. Silver alloys are
designed to inhibit corrosion.
In double-layer DVDs, the outer reflective layer (silicon, gold, silver or silver alloy) is only semi-reflective, i.e. it
reflects back some of the laser beam and allows some of it to pass through to the fully reflective layer and then
reflects back.
To summarize, the relative properties of the three main types of reflective metals are as follows:
— Cost: aluminium < silver < silver alloy < gold;
— Stability: aluminium < silver or silver alloy < gold.
4.5 Protective layers
A very thin lacquer layer is applied to the label side of CDs to protect the metal from exposure to the
environment. Without this protective layer, the aluminium will oxidize within several days. The layer also gives
some limited protection from writing on or labelling the disc. Some solvents used in markers (e.g. xylene,
toluene) can also affect lacquer coatings and expose or react with the metal. Once the metal is damaged, the
laser cannot read data in the damaged areas. DVDs have no such protective lacquer coating, due to the
reflective layer location in the middle of the disc.
Sometimes a manufacturer will add an additional layer designed specifically to provide more resistance to
fingerprints and scratches on the label side of CDs.
Protective layers also are available to place on the laser reading side of the disc. These are specifically
designed for protection against scratches and other surface damage.
4.6 Adhesive layers
The discs of all DVD formats are formed by bonding two 0,6 mm discs together. Disc durability and reliability
require excellent bonding. The bonding methods include hot-melt bonding and ultraviolet (UV) bonding. The
bonding layer needs to be optically transparent for some double-layer DVDs.
The DVD bonding process mainly uses the following three methods:
— the spinning method, using a radical UV resin;
— the screen printing method, using a cationic UV resin;
— the sheet method, using a double-sided adhesive sheet.
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It is essential that the adhesive layer be uniform within close tolerances, that it does not introduce tilt out of the
range of the DVD specification, that no defects such as bubbles occur and that it is optically transparent in dual
layer DVDs.
4.7 Additional layers
An optional layer may also be added to optical discs to provide a writable, printable or coloured surface. Such
surfaces include thermal-printable, inkjet-printable and silkscreen-printable surfaces. These layers are applied
over the lacquer layer on CDs, or over the polycarbonate substrate on other single-sided discs.
5 Failure mechanisms
5.1 General
Optical disc performance depends on the performance of the disc drive and the characteristics of the disc itself.
This clause only discusses failure mechanisms due to the disc.
5.2 Physical stress
Optical discs are typically handled directly by users. They are subject to a variety of physical stresses, including
mechanical impact and thermal shock. Mechanical impact can result in scratching, fracturing, breakage,
warpage or delamination. Thermal shock is a rapid temperature change that can cause differential expansion or
contraction resulting in warpage or delamination. Warping can be a temporary condition that returns to normal,
but severe warping or repetitive warping can cause delamination and permanent damage.
5.3 Layer sensitivity
5.3.1 General
Proper care and handling of optical discs requires knowledge of the sensitivities of the various layers which
make up optical discs. Various types of defects can be encountered because of the complex structure of these
materials. Optical discs are laminates of very dissimilar layers and each layer can cause malfunctions. It is
essential that the disc does not undergo any delamination. The primary layers and their susceptibilities to failure
or damage sensitivities are as described in 5.3.2 to 5.3.6 below.
5.3.2 Polycarbonate substrate
The complete transmission of the laser beam to its focus point and back to the reading sensor shall go through
the polycarbonate substrate. Eccentricity, manufacturing flaws, off-centring, lack of flatness or balance creates
tracking and/or reading problems. This may be caused by physical stress, exposure to high or rapidly changing
temperatures, humidity or manufacturing errors. Surface or penetrated containments can hinder or obstruct the
laser beam.
5.3.3 Data layer
In ROM (replicated) discs, the data is moulded into the substrate and the data layer is not a separate layer as in
R, RW and RAM discs. The recording layer in R, RW and RAM discs can be damaged by light, heat or moisture.
The recorded signal therefore can be degraded by unwanted exposure to these factors or by chemical
degradation due to aging. Physical damage that is deep enough to reach the data layer will also damage the
data.
©
8 ISO 2008 – All rights reserved

5.3.4 Reflective layer
This layer serves to reflect the modulated optical beam to the receiver. Any change in reflectivity caused by
dents, abrasion or corrosion due to moisture or other contaminant penetration is very detrimental. Any change
in flatness will change the laser beam angular reflection.
5.3.5 Protective (lacquer) layer
This layer exists on the label side and edge of CDs to protect the metal layer. Any removal, abrasion or chemical
reaction can destroy the reflective layer and the information it contains.
5.3.6 Adhesive layer
In addition to maintaining the integrity of each layer, it is essential that the disc does not undergo any
delamination. This may occur because of an inherent weakness of the disc, exposure to rapid changes and
extremes in temperature and humidity, mechanical stresses, edge damage or the effect of external agents such
as solvents and adhesives.
5.4 Scratches
5.4.1 Scratches on the laser-reading side of optical discs
Scratches that are deep, wide or bunched together are most likely to affect adversely the readability of the disc.
These scratches can cause the laser to misread enough data to make error correction remedies ineffectual.
If scratches are deep enough to damage the data or reflective layer(s) on the reading side of a disc, the data
cannot be read or repaired. Tangential and circular scratches can be more damaging than radial scratches
because it is more difficult for error correction software to repair sequential errors.
5.4.2 Scratches on the non laser-reading side of optical discs
A scratch on the non laser-reading side of a CD can easily damage the reflective and data layers directly
beneath the surface and therefore cause direct and severe damage. A surface scratch on the non-laser reading
side of a DVD, HD DVD or BD only scratches the polycarbonate and does not impair laser reading/writing.
5.5 Effects of disc play
5.5.1 General
Optical discs do not wear from friction as vinyl records or magnetic tapes do. There is no mechanical contact
between the disc and the optical pickup unit (OPU) of the player or the drive, which uses more than one
photodiode to achieve correct mutual positioning between them. There is, however, the potential for wear on the
hub from repeated insertion and removal of the disc from reading devices. Such wear may cause imbalance in
the spinning disc and exacerbate manufacturing flaws.
5.5.2 ROM Discs
The laser light will have no effect on the data or reflective layer in ROM discs. It is possible for the disc to be read
so many times that the cumulative effect of the laser light can eventually affect the polycarbonate. There is,
however, no record of such discs having been played a sufficient number of times to incur damage from laser
light. Accordingly, it is felt that any effects of laser light on ROM discs are negligible. The disc would likely fail
much earlier from some other condition than from the effects of laser light.
©
ISO 2008 – All rights reserved 9

5.5.3 R discs
Although R discs may have a limited number of read times, it is possible for the discs to be read more than
106 times. As with ROM discs, there is no recorded evidence of the ill effects of laser light. Accordingly, it is felt
that any harmful effects of the laser light on R discs are negligible.
5.5.4 RW discs
In RW discs, unlike the other types, the recording layer can “wear-out”. However, these discs should be
rewritable many hundreds of times. While the maximum number of possible read times after writing is unknown,
it may decline after each successive writing.
5.5.5 RAM discs
In RAM discs, as in RW discs, the recording layer can “wear-out”. However, these discs should be rewritable
several thousands of times. While the maximum number of possible read times after writing is unknown, it may
decline after each successive writing.
6 Handling techniques
6.1 General
Proper handling techniques will help maximize the life of discs. Discs shall be handled by the edges.
6.2 Flexing
Flexing (bending) the disc by any means, such as removing it from a jewel case without releasing the hub
clamp, may harm the disc by causing stresses. The disc should be stored in its case.
6.3 Contamination
Anything on an optical disc surface that impedes the ability of the laser to focus on the data layer can result in
missing data as the disc is being read. Fingerprints, smudges, scratches, dirt, dust, solvents, moisture and any
other foreign material can interfere with the ability of the laser to read or record data on the disc.
6.4 Disc enclosures
Optical discs shall be kept in chemically inert storage containers that are designed to hold one or more discs.
Those designed to keep surfaces of the disc from contact with the inside of the case, thereby minimizing
possible damage from surface contact, are recommended. Jewel cases and Amaray cases are examples that
provide optimum storage. Polypropylene or other more stable cases are recommended.
For long-term disc storage, it is recommended to remove the label insert or booklet from inside the case and
attach it to the outside. Paper can produce higher moisture content in the case, and may release harmful
pollutants or in certain conditions adhere to the disc. These potentially harmful affects depend on relative
humidity conditions and the insert material properties, as well as their proximity to the disc.
Potentially harmful enclosures, including cardboard, paper or highly plasticized materials, shall be replaced with
a standard jewel case.
Plastic sleeves made of polypropylene or polyester will
...

SLOVENSKI STANDARD
01-julij-2011
8SRGRELWYHQLPDWHULDOL2SWLþQHSORãþH1HJDLQUDYQDQMH]DGROJRVKUDQMHYDQMH
Imaging materials - Optical discs - Care and handling for extended storage
Matériaux pour l'image - Disques optiques - Précautions et manipulation pour stockage
étendu
Ta slovenski standard je istoveten z: ISO 18938:2008
ICS:
35.220.30 2SWLþQHVKUDQMHYDOQH Optical storage devices
QDSUDYH
37.040.99 Drugi standardi v zvezi s Other standards related to
fotografijo photography
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

INTERNATIONAL ISO
STANDARD 18938
First edition
2008-09-15
Imaging materials — Optical discs — Care
and handling for extended storage
Matériaux pour l'image — Disques optiques — Précautions et
manipulation pour stockage étendu

Reference number
©
ISO 2008
PDF disclaimer
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©
ii ISO 2008 – All rights reserved

Contents Page
1 Scope . 1
2 Normative references . 2
3 Terms and definitions . 2
4 Composition of optical discs . 6
4.1 General . 6
4.2 Polycarbonate substrate (plastic) layer . 6
4.3 Data layer . 6
4.4 Reflective layer . 7
4.5 Protective layers . 7
4.6 Adhesive layers . 7
4.7 Additional layers . 8
5 Failure mechanisms . 8
5.1 General . 8
5.2 Physical stress . 8
5.3 Layer sensitivity . 8
5.4 Scratches . 9
5.5 Effects of disc play . 9
6 Handling techniques . 10
6.1 General . 10
6.2 Flexing . 10
6.3 Contamination . 10
6.4 Disc enclosures . 10
7 Identification . 11
7.1 Basic concepts . 11
7.2 Adhesive labels . 11
7.3 Printing on optical discs . 11
7.4 Thermal printing . 11
7.5 Inkjet printable surface . 12
7.6 Silk screening . 12
7.7 Marking . 12
8 Contamination . 12
8.1 Fingerprints, smudges, dirt, dust . 12
8.2 Moisture . 12
8.3 Organic solvents . 12
8.4 Gaseous impurities . 13
8.5 Consumables . 13
9 Use environment . 13
9.1 General . 13
9.2 Temperature and humidity . 13
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ISO 2008 – All rights reserved iii

9.3 Water avoidance . 14
9.4 Air quality . 14
9.5 Light exposure . 14
9.6 Acclimatization . 14
9.7 Vibrations . 15
10 Transportation and shipping . 15
10.1 Enclosures . 15
10.2 Cartons . 15
10.3 Exposure . 16
10.4 Security . 16
10.5 External fields . 16
10.6 Biological irradiation . 16
11 Inspection . 16
11.1 General requirements . 16
11.2 Error rate monitoring . 17
12 Cleaning and maintenance . 17
12.1 General . 17
12.2 Solvents and cleaning compounds . 17
12.3 Cleaning methods . 17
13 Disasters . 18
13.1 General . 18
13.2 Water . 18
13.3 Fire . 18
13.4 Dry debris . 18
13.5 Impact from disasters . 19
13.6 Repair . 19
14 Disaster response . 19
14.1 General . 19
14.2 Wet discs . 19
14.3 Dry discs . 19
15 Staff training . 19
15.1 General . 19
15.2 Purpose . 20
15.3 Training paths . 20
15.4 Schedule for training . 20
15.5 Update of training . 20
15.6 Content of training . 20
16 Minimum handling requirements checklist . 21
16.1 General . 21
16.2 Do list . 21
16.3 Not-to-do list . 21
Annex A (informative) Disc structure . 22
Bibliography . 24
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iv ISO 2008 – All rights reserved

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 18938 was prepared by Technical Committee ISO/TC 42, Photography.
©
ISO 2008 – All rights reserved v

Introduction
1)
In addition to storage conditions, the proper care and handling of optical discs is also vital to prolonged disc
life. This is becoming increasingly important as optical discs are widely used for the recording and storage of
information. This International Standard gives guidelines for their recommended care and handling and will be
beneficial for all digital optical discs, regardless of their inherent stability.
Probably no form of data storage has been accepted and adopted as rapidly as the optical disc. It has become
the medium of choice for numerous applications with ever increasing use for the recording and storage of
information. Information is recorded in digital format that not only provides high storage density, but also allows
duplication without information loss, ease of data manipulation and facilitates transmission. It is of tremendous
benefit for audio usage since it permits uninterrupted playback for long periods of time. Information in a disc
format can be accessed very quickly, unlike that in a roll format such as magnetic tape, which requires longer
search time.
While the advantages are many, as with other media, there are nevertheless concerns about the life expectancy
of recorded information on optical discs. This depends upon three independent components, namely the
permanence of the disc itself, the disc drive and the software. Obsolescence of the disc drive and software, lack
of playback device or inoperability of the playback device are all serious uncertainties. Another important issue
is the quality of the initial data recorded onto the disc, which needs to be as high as possible. In addition, the
very popularity of recordable optical discs has led to their wide availability, and wide variability in the quality of
discs for long term preservation of information. Many discs may not be of sufficient quality for long term use.
The finite life of optical discs is well recognized and one approach to addressing this issue is by periodically
transferring or reformatting the information. In addition, the ability to play back a disc in the future depends on
the existence of functional playback equipment. As newer formats and equipment become popular, equipment
manufacturers will probably discontinue production and support of the older, superseded equipment. Eventually,
usable equipment to play obsolete optical disc formats will become difficult to find. Before this occurs, it is
advisable that a migration plan be in place. However, these issues are outside the scope of this International
Standard, which is only concerned with the stability of the optical disc itself. A primary objective of those
involved with the preservation of information on this media is to ensure that the disc is not the weak link among
the necessary components. To support this objective, it is advisable that steps be taken to maximize the optical
disc's potential to be more stable than either the hardware or the software.
As with paper records, photographic film and magnetic tape, optical discs are subject to both damage and
decay. They have a finite life. Predictions of the life expectancy of optical discs have involved extrapolations of
property retention after high temperature and humidity incubations back to practical conditions. These
extrapolations follow mathematical treatments that were developed for simpler chemical reactions, and
therefore the results need to be interpreted with some caution. Predictions cover a very wide range, from
25 years to over 250 years, which vary with the manufacturer and the disc type. Their effective life can be
increased or decreased significantly depending upon the conditions under which they are stored. Storage
recommendations for optical discs are given in ISO 18925. Following these recommendations promotes the
physical integrity of the media and increases their effective life.
1) It is recognized that both “optical discs” and “optical disks” are acceptable spellings. In this International Standard, the
former spelling is used.
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INTERNATIONAL STANDARD ISO 18938:2008(E)
Imaging materials — Optical discs — Care and handling for
extended storage
1Scope
This International Standard establishes general principles for the care and handling of digital optical discs
during use. It addresses the issues of physical integrity of the medium necessary to preserve access to the
recorded data (information). This International Standard includes recommendations for handling procedures to
maximize the effective life of optical discs. Faulty handling, packing and transporting techniques and methods
often cause physical damage to the discs and to the content recorded thereon. Extending the longevity of
optical discs requires the identification of appropriate handling methods, as well as well-developed and
implemented training programs.
For the purposes of this International Standard, the term “optical disc” includes the families of compact disc
2)
(CD), digital versatile disc (DVD), high definition digital versatile disc (HD DVD) and Blu-ray disc (BD) , and any
hybrids of these families. The term “optical disc” also includes each type of disc within a family, including
injection moulded [read-only memory (ROM)], dye-layer [recordable (R)] and phase change [rewriteable (RW),
random access memory (RAM)] technologies.
While some of the recommendations in this International Standard (e.g. those for staff training) apply
specifically to large-scale or long term usage, the basics of all recommendations in this International Standard
are intended to be applied in circumstances where the desired result is long-term usage of the medium whether
archival, commercial or personal.
This International Standard does not cover magneto-optical (MO) discs, laser discs (LD) or glass discs. At the
time of writing, International Standards do not exist for HD DVD and Blu-ray discs. Nonetheless, it is believed
that the recommendations in this International Standard for care and handling can equally apply to them. It is
recognized that some of these requirements are not necessarily possible for the individual user to achieve.
The following are within the scope of this International Standard:
— use and handling environments, including pollutants, temperature and humidity and light exposure;
— contamination concerns;
— inspection;
— cleaning and maintenance, including cleaning methods and frequency;
— transportation;
— disasters, including water, fire, construction and post-disaster procedures;
— staff training.
The quality of the data written on the disc is outside the scope of this International Standard. However, a high
quality result of the recording phase is important to the longevity of information. It is advisable that a rigorous
program of data integrity testing be implemented, as this forms an obligatory part of all digital long-term storage.
In addition, when keeping digital information for archival purposes, it is advisable that a multiple copy/multiple
location strategy be in place.
2) Blu-ray disc and HD DVD are examples of suitable products available commercially. This information is given for the
convenience of users of this International Standard and does not constitute an endorsement by ISO of these products.
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ISO 2008 – All rights reserved 1

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.
ISO 14644-1, Cleanrooms and associated controlled environments — Part 1: Classification of air cleanliness
ISO 18925, Imaging materials — Optical disc media — Storage practices
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
3)
amaray case
case designed for DVD discs slightly larger than a jewel case
3.2
acclimatization
staging
process of conditioning material from one set of temperature-moisture conditions to another
3.3
balance
precision vertical position of the disc as it spins
3.4
blister
localized delamination that looks like a bubble
3.5
blu-ray disc
BD
optical disc in which one or more information layers are located between two layers and the data can be read by
an optical beam with a wave length of 405 nm
3.5.1
read only memory bd-rom
optical disc to which information is transferred during manufacture to moulded areas in the Blu-ray disc format
and can be read multiple times by an optical beam
3.5.2
recordable BD-R
recordable optical disc in which information can be recorded once to areas in the Blu-ray disc format and read
many times
3.5.3
rewriteable bd-re
recordable optical disc in which information can be recorded to areas in the Blu-ray disc format and can be
erased, rerecorded and read many times
3) Amaray case is an example of a suitable product available commercially. This information is given for the convenience of
users of this International Standard and does not constitute an endorsement by ISO of this product.
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3.6
carton
box outer container that can hold one or more individual units and can be a fabrication of paper, card stock or
plastic
3.7
compact disc
CD
optical disc in which the information layer is located near one surface of a substrate and the data can be read by
an optical beam
NOTE Described in IEC 60908.
3.7.1
read only memory CD-ROM
optical disc to which information is transferred during manufacture to moulded areas in the compact disc format
and can be read multiple times by an optical beam
NOTE Described in ISO/IEC 10149.
3.7.2
recordable CD-R
recordable optical disc in which information can be recorded once to areas in the compact disc format and read
many times
3.7.3
rewritable CD-RW
recordable optical disc in which information can be recorded to areas in the compact disc format and can be
erased, rerecorded and read many times
3.8
conditioning
exposure of a material to air at a given relative humidity and temperature until equilibrium is reached
3.9
container
box, can or carton used for storage and shipping of recording materials
EXAMPLE The box into which a reel, cassette, cartridge or shell is placed.
3.10
delamination
separation of a laminate into its constituent layers
3.11
digital versatile disc
DVD
optical disc in which one or more information layers are located between two substrates and the data can be
read by an optical beam with a wave length of between 635 nm and 650 nm
NOTE Formerly called digital video disc.
3.11.1
read only memory DVD-ROM
optical disc in which information is transferred during manufacture to certain areas in the DVD format and can
be read multiple times by an optical beam
NOTE Described in ISO/IEC 16448 and ISO/IEC 16449.
©
ISO 2008 – All rights reserved 3

3.11.2
recordable DVD-R, +R
recordable optical disc in which information can be recorded once to areas in the DVD disc format and read
many times
NOTE Described in ISO/IEC 23912, ISO/IEC 17344 and ISO/IEC 25434.
3.11.3
rewriteable DVD-RAM, DVD-RW, +RW
DVD optical discs that can be written, read and overwritten many times using phase change technology
NOTE 1 See Annex A.
NOTE 2 Described in ISO/IEC 17592, ISO/IEC 17341 and ISO/IEC 26925.
3.12
enclosure
case, cartridge, folder, envelope, sleeve or clam shell that is intended for physical protection against mechanical
damage
3.13
extended-term storage conditions
storage conditions suitable for the preservation of recorded information having permanent value
3.14
high definition digital versatile disc
HD DVD
optical disc in which one or more information layers are located between two substrates and the data can be
read by an optical beam with a wave length of 405 nm
NOTE Sometimes called high density digital versatile disc.
3.14.1
read only memory HD DVD-ROM
optical disc in which information is transferred during manufacture to certain areas in the HD DVD format and
can be read multiple times by an optical beam
3.14.2
recordable HD DVD-R
recordable optical disc in which information can be recorded once to areas in the HD DVD disc format and read
many times
3.14.3
rewriteable HD DVD-RW
DVD optical discs that can be written, read and overwritten many times using phase change technology
3.15
information
data recorded using the system
3.16
insulated record container
storage box designed to provide an environmental buffer against temperature and humidity fluctuations
3.17
jewel case
plastic enclosure featuring a hinged lid and one or more trays, each containing a hub clamp to secure and
protect the disc surface
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3.18
macroenvironment
atmospheric conditions in a large area in which records are kept
NOTE Atmospheric conditions are temperature, relative humidity and pollutants.
3.19
medium
material on which information is recorded
3.20
microenvironment
atmospheric conditions inside a storage enclosure in which records are kept
NOTE Atmospheric conditions are temperature, relative humidity and pollutants.
3.21
optical disc
disc that will accept and retain information from light modulation changes in a recording or reflective layer that
can be read with an optical beam
3.22
optical disc cartridge
ODC
optical disc enclosure required for the operation of the disc
3.23
recording layer
layer of an optical disc on which data is written either during manufacture or in use
3.24
relative humidity
RH
ratio, defined as a percentage, of the existing partial vapour pressure of water to the vapour pressure at
saturation
NOTE It is usually, but not always, equal to the percentage of the amount of moisture in the air to that at saturation.
3.25
replicated disc
disc made by an injection moulding process where the land and pits that make up the data are physically
pressed into the polycarbonate
3.26
retrievability
ability to access information as recorded
3.27
slimline case
slimmer version of the jewel case
3.28
snapper case
alternative to the Amaray case with a cardboard cover
3.29
storage environment
conditions for storing materials
NOTE The conditions are temperature, relative humidity, cleanliness of facilities and atmospheric pollutants.
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ISO 2008 – All rights reserved 5

3.30
storage housing
physical structure supporting materials and their enclosures
NOTE It can consist of drawers, racks, shelves or cabinets.
3.31
substrate
transparent layer of an optical disc which provides mechanical support of the recording layer
3.32
system
combination of media, hardware, software and documentation necessary for recording and/or retrieving
information
3.33
worm disc
optical disc in which the data in specified areas can be written only once and read multiple times by an optical
beam
4 Composition of optical discs
4.1 General
Optical discs are composed of a series of layers made of different materials assembled like a sandwich.
Typically, these layers include the polycarbonate substrate (plastic) layer(s), the data layer(s), the metal
layers(s) or reflective layer, the metal protective layers, the adhesive layer and an optional extra layer for
labelling or added protection. These layers are listed in Annex A.
4.2 Polycarbonate substrate (plastic) layer
The polycarbonate substrate makes up most of the disc. The polycarbonate is typically clear, but may be
coloured for appearance or to prevent copyright infringement. The disc drive laser beam travels through this
substrate. This substrate provides the disc depth necessary to maintain laser focus. It also gives the disc
enough strength to remain flat.
A CD is one continuous 1,2 mm thick polycarbonate layer. Both DVDs and HD DVDs are made up of two
0,6 mm thick polycarbonate layers bonded together. BDs are made up of one 1,1 mm and one 0,1 mm
polycarbonate layer bonded together. CDs are read from one side only. DVDs, HD DVDs and BDs are read from
one or both sides.
4.3 Data layer
As its name implies, the data layer of optical discs is the layer that contains the encoded data. The encoded
data appear as marks or pits that either transmit or alter light from the laser beam back to the laser photosensor
by way of the metal reflective layer. Write-once (–R, +R) discs use organic dye material or phase change
materials, whereas rewritable (–RW, +RW, –RAM, –RE) discs use phase change materials as the layer(s) for
holding record data written by a disc drive. ROM discs do not use a separate layer, but the data has been
pressed in the form of pits from injection moulding on the inner surface of the polycarbonate substrate during
the disc manufacturing process.
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4.4 Reflective layer
The metal layer in optical discs reflects the laser beam back to the laser photodiode in the optical pickup unit
(OPU). Three main types of reflective metals typically are used for this layer:
a) aluminium or aluminium alloy,
b) gold, and
c) silver or silver alloy.
In “double-layer” DVDs, silicon is sometimes used as one of the semi-reflective layers. Some discs use a copper
alloy for the purposes of appearance.
Aluminium is used in ROM, RW and RAM discs. Silver, silver alloy or gold are used in R discs, since aluminium
is too active to use with dye. Aluminium is also prone to corrosion when exposed to moisture or other pollutants
that penetrate into the disc. Oxidation of the aluminium diminishes its reflectivity, eventually making the disc
unreadable by the laser. This is sometimes referred to as disc “rot”.
Silver can lose reflectivity due to corrosion on exposure to pollutants such as sulphur dioxide. Silver alloys are
designed to inhibit corrosion.
In double-layer DVDs, the outer reflective layer (silicon, gold, silver or silver alloy) is only semi-reflective, i.e. it
reflects back some of the laser beam and allows some of it to pass through to the fully reflective layer and then
reflects back.
To summarize, the relative properties of the three main types of reflective metals are as follows:
— Cost: aluminium < silver < silver alloy < gold;
— Stability: aluminium < silver or silver alloy < gold.
4.5 Protective layers
A very thin lacquer layer is applied to the label side of CDs to protect the metal from exposure to the
environment. Without this protective layer, the aluminium will oxidize within several days. The layer also gives
some limited protection from writing on or labelling the disc. Some solvents used in markers (e.g. xylene,
toluene) can also affect lacquer coatings and expose or react with the metal. Once the metal is damaged, the
laser cannot read data in the damaged areas. DVDs have no such protective lacquer coating, due to the
reflective layer location in the middle of the disc.
Sometimes a manufacturer will add an additional layer designed specifically to provide more resistance to
fingerprints and scratches on the label side of CDs.
Protective layers also are available to place on the laser reading side of the disc. These are specifically
designed for protection against scratches and other surface damage.
4.6 Adhesive layers
The discs of all DVD formats are formed by bonding two 0,6 mm discs together. Disc durability and reliability
require excellent bonding. The bonding methods include hot-melt bonding and ultraviolet (UV) bonding. The
bonding layer needs to be optically transparent for some double-layer DVDs.
The DVD bonding process mainly uses the following three methods:
— the spinning method, using a radical UV resin;
— the screen printing method, using a cationic UV resin;
— the sheet method, using a double-sided adhesive sheet.
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ISO 2008 – All rights reserved 7

It is essential that the adhesive layer be uniform within close tolerances, that it does not introduce tilt out of the
range of the DVD specification, that no defects such as bubbles occur and that it is optically transparent in dual
layer DVDs.
4.7 Additional layers
An optional layer may also be added to optical discs to provide a writable, printable or coloured surface. Such
surfaces include thermal-printable, inkjet-printable and silkscreen-printable surfaces. These layers are applied
over the lacquer layer on CDs, or over the polycarbonate substrate on other single-sided discs.
5 Failure mechanisms
5.1 General
Optical disc performance depends on the performance of the disc drive and the characteristics of the disc itself.
This clause only discusses failure mechanisms due to the disc.
5.2 Physical stress
Optical discs are typically handled directly by users. They are subject to a variety of physical stresses, including
mechanical impact and thermal shock. Mechanical impact can result in scratching, fracturing, breakage,
warpage or delamination. Thermal shock is a rapid temperature change that can cause differential expansion or
contraction resulting in warpage or delamination. Warping can be a temporary condition that returns to normal,
but severe warping or repetitive warping can cause delamination and permanent damage.
5.3 Layer sensitivity
5.3.1 General
Proper care and handling of optical discs requires knowledge of the sensitivities of the various layers which
make up optical discs. Various types of defects can be encountered because of the complex structure of these
materials. Optical discs are laminates of very dissimilar layers and each layer can cause malfunctions. It is
essential that the disc does not undergo any delamination. The primary layers and their susceptibilities to failure
or damage sensitivities are as described in 5.3.2 to 5.3.6 below.
5.3.2 Polycarbonate substrate
The complete transmission of the laser beam to its focus point and back to the reading sensor shall go through
the polycarbonate substrate. Eccentricity, manufacturing flaws, off-centring, lack of flatness or balance creates
tracking and/or reading problems. This may be caused by physical stress, exposure to high or rapidly changing
temperatures, humidity or manufacturing errors. Surface or penetrated containments can hinder or obstruct the
laser beam.
5.3.3 Data layer
In ROM (replicated) discs, the data is moulded into the substrate and the data layer is not a separate layer as in
R, RW and RAM discs. The recording layer in R, RW and RAM discs can be damaged by light, heat or moisture.
The recorded signal therefore can be degraded by unwanted exposure to these factors or by chemical
degradation due to aging. Physical damage that is deep enough to reach the data layer will also damage the
data.
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5.3.4 Reflective layer
This layer serves to reflect the modulated optical beam to the receiver. Any change in reflectivity caused by
dents, abrasion or corrosion due to moisture or other contaminant penetration is very detrimental. Any change
in flatness will change the laser beam angular reflection.
5.3.5 Protective (lacquer) layer
This layer exists on the label side and edge of CDs to protect the metal layer. Any removal, abrasion or chemical
reaction can destroy the reflective layer and the information it contains.
5.3.6 Adhesive layer
In addition to maintaining the integrity of each layer, it is essential that the disc does not undergo any
delamination. This may occur because of an inherent weakness of the disc, exposure to rapid changes and
extremes in temperature and humidity, mechanical stresses, edge damage or the effect of external agents such
as solvents and adhesives.
5.4 Scratches
5.4.1 Scratches on the laser-reading side of optical discs
Scratches that are deep, wide or bunched together are most likely to affect adversely the readability of the disc.
These scratches can cause the laser to misread enough data to make error correction remedies ineffectual.
If scratches are deep enough to damage the data or reflective layer(s) on the reading side of a disc, the data
cannot be read or repaired. Tangential and circular scratches can be more damaging than radial scratches
because it is more difficult for error correction software to repair sequential errors.
5.4.2 Scratches on the non laser-reading side of optical discs
A scratch on the non laser-reading side of a CD can easily damage the reflective and data layers directly
beneath the surface and therefore cause direct and severe damage. A surface scratch on the non-laser reading
side of a DVD, HD DVD or BD only scratches the polycarbonate and does not impair laser reading/writing.
5.5 Effects of disc play
5.5.1 General
Optical discs do not wear from friction as vinyl records or magnetic tapes do. There is no mechanical contact
between the disc and the optical pickup unit (OPU) of the player or the drive, which uses more than one
photodiode to achieve correct mutual positioning between them. There is, however, the potential for wear on the
hub from repeated insertion and removal of the disc from reading devices. Such wear may cause imbalance in
the spinning disc and exacerbate manufacturing flaws.
5.5.2 ROM Discs
The laser light will have no effect on the data or reflective layer in ROM discs. It is possible for the disc to be read
so many times that the cumulative effect of the laser light can eventually affect the polycarbonate. There is,
however, no record of such discs having been played a sufficient number of times to incur damage from laser
light. Accordingly, it is felt that any effects of laser light on ROM discs are negligible. The disc would likely fail
much earlier from some other condition than from the effects of laser light.
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5.5.3 R discs
Although R discs may have a limited number of read times, it is possible for the discs to be read more than
106 times. As with ROM discs, there is no recorded evidence of the ill effects of laser light. Accordingly, it is felt
that any harmful effects of the laser light on R discs are negligible.
5.5.4 RW discs
In RW discs, unlike the other types, the recording layer can “wear-out”. However, these discs should be
rewritable many hundreds of times. While the maximum number of possible read times after writing is unknown,
it may decline after each successive writing.
5.5.5 RAM discs
In RAM discs, as in RW discs, the recording layer can “wear-out”. However, these discs should be rewritable
several thousands of times. While the maximum number of possible read times after writing is unknown, it may
decline after each successive writing.
6 Handling techniques
6.1 General
Proper handling techniques will help maximize the life of discs. Discs shall be handled by the edges.
6.2 Flexing
Flexing (bending) the disc by any means, such as removing it from a jewel case without releasing the hub
clamp, may harm the disc by causing stresses. The disc should be stored in its case.
6.3 Contamination
Anything on an optical disc surface that impedes the ability of the laser to focus on the data layer can result in
missing data as the disc is being read. Fingerprints, smudges, scratches, dirt, dust, solvents, moisture and any
oth
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