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ABSTRACT
The European Union (EU) directive 2002/95/EC “on the
Restriction of the use of certain Hazardous Substances in elec-
trical and electronic equipment” or RoHS was implemented
in July 2006. However, this was only the first of many RoHS(-
like) regulations that have been passed or are being considered
in many countries. The aim being shared by almost all RoHS
legislation is the elimination of lead in electronic products.
These policies are now generally referred to as the RoHS
Directive and are often referred to as “Lead-Free” legislation.
A printed circuit board, or PCB, is used to mechanically
support and electrically connect electronic components using
conductive pathways laminated onto a non-conductive
substrate. PCBs have conducting layers on their surface typi-
cally made of thin copper foil which if left unprotected, will
oxidize and deteriorate. Research has shown that printed
circuit boards made using lead-free materials can be more
susceptible to corrosion than their tin/lead counterparts and
it was soon discovered that lead-free products with immersion
silver (ImmAg) surface finish will creep corrode in high sulfur
environments. The majority of creep corrosion failures
occurred on hard disk drives (HDD), graphic cards, and moth-
erboards in desktop or workstation systems (only those with
ImmAg PCB finish were affected).
Corrosion-induced failures are frequent in electronics
products used in industrial environments. Now even in envi-
ronments previously considered relatively benign with
regards to electronics corrosion are experiencing serious
problems as a direct result of RoHS compliance. Data centers
in many urban locations have reported failures of servers and
hard disk drives due to sulfur corrosion. Gaseous contami-
nation can result in intermittent equipment glitches,
unplanned shutdowns, or failure of critical systems that often
result in significant business and financial loss.
Desktop and laptop computers, servers, data communi-
cations (datacom) equipment and other information technol-
ogy (IT) equipment are now at risk due to RoHS. There are
indications that this may even trickle down into personal
computers and electronic devices.
Manufacturers have to comply with RoHS if they want to
continue in to do business in the EU, China, etc., and many
have taken the ImmAg route as their path to compliance. This
has taken care of one issue but has presented new challenges
with regards to equipment reliability.
INTRODUCTION
In 1998, the European Union (EU) discovered that alarm-
ingly large amounts of hazardous waste were being dumped
into landfill sites. Trends also indicated that the volumes were
likely to grow 3-5 times faster than average municipal waste.
This highlighted a massive, and growing, source of environ-
mental contamination.
In order to address these issues, the member states of the
EU decided to create the Waste Electrical and Electronics
Equipment (WEEE, 2002/96/EC) directive, whose purpose
was to:
1. Improve manufacturers’ designs to reduce the creation of
waste,
2. Make manufacturers responsible for certain phases of
waste management,
3. Separate collections of electronic waste (from other types
of waste), and
What’s Creeping Around
in Your Data Center?
Chris Muller
Member ASHRAE
Chris Muller is the Technical Director at Purafil, Inc., in Doraville, GA.
OR-10-023
2OR-10-023
4. Create systems to improve treatment, refuse, and recy-
cling of WEEE.
The WEEE directive laid the groundwork for additional
legislation and a proposal called EEE (Environment of Elec-
trical & Electronics Equipment) was also introduced along the
same lines. However, this policy is generally referred to as the
RoHS Directive and is often referred to as “Lead-Free” legis-
lation. This is not a very accurate nickname, because it extends
to other pollutants as well.
The European Union (EU) directive 2002/95/EC “on the
Restriction of the use of certain Hazardous Substances in elec-
trical and electronic equipment” or RoHS was implemented in
July 2006. This directive applies to electrical and electronic
equipment designed for use with a voltage rating not exceed-
ing 1,000 volts for alternating current and 1,500 volts for direct
current. The requirements of this directive are applicable to the
member states of the European Union.
The purpose of the directive is to restrict the use of hazard-
ous substances in electrical and electronic equipment and to
contribute to the protection of human health and the environ-
mentally sound recovery and disposal of waste electrical and
electronic equipment. The EU’s RoHS Directive restricts the
use of six substances in electrical and electronic equipment:
mercury (Hg), lead (Pb), hexavalent chromium (Cr(VI)),
cadmium (Cd), polybrominated biphenyls (PBB) and poly-
brominated diphenyl ethers (PBDE).
In order to comply with the EU RoHS legislation, all of
these substances must either be removed, or must be reduced
to within maximum permitted concentrations, in any products
containing electrical or electronic components that will be
sold within the European Union. Manufacturers have made
significant investments in new processes that will eliminate
these substances – especially lead.
All applicable products in the EU market must now pass
RoHS compliance. In short, RoHS impacts the entire electron-
ics industry and compliance violations are costly – product
quarantine, transport, rework, scrap, lost sales and man-hours,
legal action, etc. Non-compliance also reflects poorly on
brand and image and undercuts ongoing environmental and
“due diligence” activities.
WHERE IS ROHS IN EFFECT?
Companies selling a broad range of electrical goods in the
EU must now conform to WEEE and those same companies
must also conform to RoHS. WEEE and RoHS rules, while
laid down at the European level, are put into law at the national
level. When exporting to Europe, it is essential to comply with
national law in each relevant country. The EU law simply
serves as a template for national laws, which may differ
considerably. European countries currently requiring confor-
mance with the EU RoHS Directive include: Austria,
Belgium, Bulgaria, Croatia, Cyprus, Czech Republic,
Denmark, Estonia, Finland, France, Germany, Greece,
Hungary, Ireland, Italy, Latvia, Lithuania, Luxembourg,
Malta, Netherlands, Norway, Poland, Portugal, Romania,
Slovak Republic, Slovenia, Spain, Sweden, Switzerland,
Turkey, and the United Kingdom.1
China RoHS regulations have also been put into effect and
many consider them to be considerably more restrictive. As
described by a potentially-impacted customer: “Without
exemptions, it is impossible to build a compliant board” (Anon
2008)
RoHS regulations are also either in effect or pending in
many countries – including the United States. Additional
RoHS-like regulations include:
• Argentina has both a WEEE and RoHS bill.
• Japan recently adopted “RoHS” labeling requirements
for certain products.
• Taiwan has a voluntary RoHS program.
• Korea is considering RoHS legislation.
• Australia is conducting a survey.
U.S. State bills:
• California SB20 – has the same requirements as EU
RoHS except that its scope includes only products with
displays larger than 4”.
• California AB2202 – includes all EU RoHS products.
• Minnesota – patterned after EU RoHS, however only for
consumer products.
• Several other states are looking at RoHS legislation (see
Figure 1).
1. Note that Croatia, Norway, and Switzerland are not part of the
EU. They may nevertheless have legislation implementing EU
WEEE and RoHS rules, or similar legislation.
Figure 1 Darker areas denote active or pending RoHS
legislation (Anon A 2008).
OR-10-023 3
UNINTENDED CONSEQUENCES
An aim shared by almost all RoHS legislation is the elim-
ination of lead in electronic products. Thus the main issue for
the electronics industry became the use of lead in the manu-
facture of components and circuit board assemblies.
A printed circuit board, or PCB, is used to mechanically
support and electrically connect electronic components using
conductive pathways, or traces, laminated onto a non-conductive
substrate. Alternative names are printed wiring board (PWB),
and etched wiring board. A PCB populated with electronic
components is a printed circuit assembly (PCA), also known as
a printed circuit board assembly (PCBA).
All PCBs have conducting layers on their surface typi-
cally made of thin copper foil. If the copper is left unprotected,
it will oxidize and deteriorate. Traditionally, any exposed
copper was plated with lead(-based) solder by the hot air
solder leveling (HASL) process.
HASL has been working well for many years, is the
predominant surface finish used in the industry, and is also the
cheapest PCB available. Now RoHS essentially makes PCBs
using the HASL process obsolete. Failure modes on other
common lead-free PCB finishes such as organic solder preser-
vative (OSP) and electroless-nickel immersion gold (ENIG)
make these technologies undesirable. As a result, alternatives
such as immersion silver (ImmAg) and organically coated
copper (OCC) are currently used as board finishes. Due to
inherent processing difficulties with OCC boards, ImmAg
boards are quickly becoming the standard PCB finish in the
electronics industry (Mazurkiewicz 2006).
Immersion silver would seem to have a bright future
under RoHS (Anon B 2008). It is easy to apply to the boards,
relatively inexpensive, and usually performs well. While
ENIG presently has a larger market share, over the past 12
months more immersion silver process lines have been
installed in PCB facilities than any other finish. However,
some manufacturers have complained about issues with corro-
sion. If severe enough, this could lead to shorts and ultimate
failure of the board.
The International Society for Automation (ISA)2 Stan-
dard ISA-71.04-1985 (ISA 1985) classifies several levels of
environmental severity for electrical and electronic systems:
G1, G2, G3 and GX, providing a measure of the corrosion
potential of an environment. G1 is benign and GX is open-
ended and the most severe.
In a study performed by Rockwell Automation (Anon C
2008) looking at lead-free finishes, four alternate PCB finishes
were subjected to an accelerated mixed flowing gas corrosion
test. Important findings can be summarized as follows:
1. The immersion gold (ENIG) and immersion silver
(ImmAg) surface finishes failed early in the testing.
These coatings are the most susceptible to corrosion fail-
ures and are expected to be much more susceptible than
traditional HASL coatings. The use of these two coatings
may make the PCB the weak link with regard to the sensi-
tivities of the electronic devices to corrosion.
2. None of the coatings can be considered immune from
failure in an ISA Class G3 environment.
3. The gold and silver coatings could not be expected to
survive a mid to high Class G2 environment based on
these test results.
A leading world authority on RoHS, ERA Technology,
has also reported that, “Recent research has shown that printed
circuit boards made using lead-free materials can be more
susceptible to corrosion than their tin/lead counterparts”
(Anon D 2008). Industry is working diligently to address these
concerns but they cannot be addressed overnight.
The Reliability and Failure Analysis group at ERA Tech-
nology has diagnosed failures in electronic devices due to
interaction with low levels of gaseous sulfides – failures that
caused both a financial impact to the manufacturers and safety
issues with their customers. Recent work showed that corro-
sion could occur even with measured hydrogen sulfide levels
as low as 0.2µg/m3 (0.14 ppb). Another reference describes the
formation of a 200 angstrom thick layer of silver sulfide in 100
hours at a concentration of just 100 µg/m3 [72 ppb] (Anon E
2008).
CAUSES OF CORROSION
Corrosion can be defined as “deterioration of a substance
(usually a metal) because of a reaction with its environment”
(ISA 1985). Corrosion of metals is actually a chemical reac-
tion caused primarily by attack of gaseous contaminants and
is accelerated by heat and moisture. Rapid shifts in either
temperature or humidity cause small portions of circuits to fall
below the dew point temperature, thereby facilitating conden-
sation of contaminants. Note that even at low relative humidity
(RH) corrosion may occur, depending on the temperature and
contaminants present (Henriksen et al. 1991). Relative humid-
ity above 50% accelerates corrosion by forming conductive
solutions on a small scale on electronic components. Micro-
scopic pools of condensation then absorb contaminant gases to
become electrolytes where crystal growth and electroplating
occur. These can cause breaks and shorts in the circuits by
either coating a conductive surface with a non-conductive
layer or by connecting conductive surfaces (Figure 2). Above
80% RH causes electronic corrosive damage regardless of the
levels of contamination.
More generally, corrosive gases and water vapor coming
into contact with a base metal result in the buildup of various
chemical reaction products. As the chemical reactions
continue, these corrosion products can form insulating layers
on circuits which can lead to thermal failure, conductive fail-
ure, or short-circuits. Pitting and metal loss can also occur as
a result of corrosive attack on metal. Pitting can be described
2. Known as the Instrumentation Society of America when the stan-
dard was published and later as the Instrumentation, Systems, and
Automation Society.
4OR-10-023
as the formation of pits that penetrate into the metal causing
structural damage and thus hindering edge connectors, etc.
from completing the circuit. Metal loss is self-explanatory and
would cause a conductive failure in the circuit.
Corrosive Gases (ISA 1985)
There are three types of gases that can be considered as
prime candidates in the corrosion of data center electronics:
acidic gases such as hydrogen sulfide, sulfur and nitrogen
oxides, chlorine, and hydrogen fluoride; caustic gases, such as
ammonia; and oxidizing gases, such as ozone. Of these, the
acidic gases are of particular concern. For instance, it takes
only 10 ppb (28.98 µg/m3)of chlorine to inflict the same
amount of damage as 25,000 ppb (17.40 mg/m3)of ammonia.
Each site may have different combinations and concen-
tration levels of corrosive gaseous contaminants. Performance
degradation can occur rapidly or over many years, depending
on the specific conditions at a site. Common sources of corro-
sive gases are shown in Table 1. Descriptions of common
pollutants and a discussion of their contributions to equipment
performance degradation follow.
Active Sulfur Compounds. Active sulfur compounds
refers to hydrogen sulfide (H2S), elemental sulfur (S), and
organic sulfur compounds such as the mercaptans (R-SH).
When present at low ppb levels, they rapidly attack copper,
silver, aluminum, and iron alloys. The presence of moisture
and small amounts of inorganic chlorine compounds and/or
nitrogen oxides greatly accelerate sulfide corrosion. Note,
however, that attack still occurs in low relative humidity envi-
ronments. Active sulfurs rank with inorganic chlorides as the
predominant cause of atmospheric corrosion.
Sulfur Oxides. Oxidized forms of sulfur (SO2, SO3) are
generated as combustion products of fossil fuels and from auto
emissions. Low parts per billion levels of sulfur oxides can
cause reactive metals to be less reactive and thus retard corro-
sion. At higher levels, however, they will attack certain types
of metals. The reaction with metals normally occurs when
these gases dissolve in water to form sulfurous and sulfuric
acid (H2SO3 and H2SO4).
Nitrogen Oxides (NOX). Some common sources of reac-
tive gas compounds (NO, NO2, N2O4) are formed as combus-
tion products of fossil fuels and have a critical role in the
formation of ozone in the atmosphere. They are also believed
to have a catalytic effect on corrosion of base metals by chlo-
rides and sulfides. In the presence of moisture, some of these
gases form nitric acid (HNO3) that, in turn, attacks most
common metals.
Inorganic Chlorine Compounds. This group includes
chlorine (Cl2), chlorine dioxide (ClO2), hydrogen chloride
(HCl), etc., and reactivity will depend upon the specific gas
composition. In the presence of moisture, these gases generate
chloride ions that, in turn, attack most copper, tin, silver, and
iron alloys. These reactions are significant even when the
gases are present at low ppb levels. At higher concentrations,
many materials are oxidized by exposure to chlorinated gases.
Particular care must be given to equipment that is exposed to
atmospheres which contain chlorinated contaminants.
Sources of chloride ions, such as bleaching operations, seawa-
ter, cooling tower vapors, and cleaning compounds, etc.,
should be considered when classifying industrial environ-
ments. They are seldom absent in major installations.
Hydrogen Fluoride (HF). This compound is a member
of the halogen family and reacts like inorganic chloride
compounds.
Ammonia and Derivatives. Reduced forms of nitrogen
(ammonia, NH3), amines, ammonium ions (NH4+) occur
mainly in fertilizer plants, agricultural applications, and
chemical plants. Copper and copper alloys are particularly
susceptible to corrosion in ammonia environments.
Photochemical Species. The atmosphere contains a wide
variety of unstable, reactive species that are formed by the
reaction of sunlight with moisture and other atmospheric
constituents. Some have lifetimes measured in fractions of a
second as they participate in rapid chain reactions. In addition
to ozone (O3), a list of examples would include the hydroxyl
radical as well as radicals of hydrocarbons, oxygenated hydro-
carbons, nitrogen oxides, sulfur oxides, and water. Because of
the transient nature of most of these species, their primary
effect is on outdoor installations and enclosures. In general,
metals are only slightly susceptible to photochemical effects.
However, ozone can function as a catalyst in sulfide and chlo-
ride corrosion of metals.
Strong Oxidants. This includes ozone plus certain chlo-
rinated gases (chlorine, chlorine dioxide). Ozone is an unsta-
ble form of oxygen that is formed from diatomic oxygen by
electrical discharge or by solar radiation in the atmosphere.
These gases are powerful oxidizing agents. Photochemical
Figure 2 Short-circuit on PCB caused by corrosion.
OR-10-023 5
oxidation - the combined effect of oxidants and ultraviolet
light (sunlight) - is particularly potent.
Hydrogen sulfide (H2S), sulfur dioxide (SO2), and active
chlorine compounds (Cl2, HCl, ClO2), have all been shown to
cause significant corrosion in electrical and electronic equip-
ment at concentrations of just a few parts per billion in air.
Even at levels that are not noticed by or harmful to humans,
these gases can be deadly to electronic equipment. Most of the
odor threshold levels are much higher than the levels at which
corrosive damage will occur.
THE NATURE OF CORROSION
When discussing electronic equipment, the corrosion of
copper, silver, or composite materials gives the same result: a
disruption of electrical current flow. The severity of the envi-
ronment (i.e. the types and levels of gases, humidity, and
temperature) will determine the speed at which corrosion
forms and how soon corrosion-related effects may appear.
Sign of Corrosion
For the purposes of this paper, corrosion can be thought of
as two distinct types: the first being the more conventional
Table 1. Sources of Reactive Environmental Contaminants (ISA 1985)
Constituent Symbol Category Common Sources
Acetic acid CH3COOH Gas Semiconductor manufacturing, wood and wood products, photo developing
Active organic nitrogen N2Gas Automobile emissions, animal waste, vegetable combustion, sewage, wood
pulping
Ammonia NH3Gas Microbes, sewage, fertilizer manufacture, geothermal steam, refrigeration
equipment, cleaning products, reproduction (blueprint) machines
Arsine AsH3Gas Semiconductor manufacturing
Carbon CSolid Incomplete combustion (aerosol constituent), foundry
Carbon monoxide CO Gas Combustion, automobile emissions, microbes, trees, wood pulping
Chloride ions Cl Liquid Aerosol content, oceanic processes, ore processing
Chlorine, Chlorine dioxide Cl2, ClO2Gas Chlorine manufacture, aluminum manufacture, paper mills, refuse decompo-
sition, cleaning products
Ethylene C2H4Gas Fruit, vegetable, cut flower storage & transportation
Formaldehyde HCHO Gas Wood products, floor & wall coverings, adhesives, sealants, photo develop-
ing, tobacco smoke
Halogen compounds HBr, HI Gas Automotive emissions
Hydrocarbons (alcohols,
aldehydes, ketones, organic
acids)
HC, THC Gas Automotive emissions, fossil fuel processing, tobacco smoke, water treat-
ment, microbes. Many other sources, both natural and industrial, paper mills
Hydrogen chloride HCl Gas Automobile emissions, combustion, oceanic processes, polymer combustion
Hydrogen fluoride HF Gas Fertilizer manufacture, aluminum manufacture, ceramics manufacture, steel
manufacture, electronic device manufacture, fossil fuel
Hydrogen sulfide H2SGas
Geothermal emissions, microbiological activities, fossil fuel processing,
wood pulping, sewage treatment, combustion of fossil fuel, auto emissions,
ore smelting, sulfuric acid manufacture
Inorganic dust Solid Crystal rock, rock and ore processing, combustion, blowing sand and many
industrial sources
Mercaptans S8, R-SH Gas Foundries, sulfur manufacture
Oxides of nitrogen NOxGas Automobile emissions, fossil fuel combustion, microbes, chemical industry
Ozone O3Gas Atmospheric photochemical processes mainly involving nitrogen oxides and
oxygenated hydrocarbons, automotive emissions, electrostatic filters
Sulfur dioxide SO2, SO3Gas Combustion of fossil fuel, auto emissions, ore smelting, sulfuric acid manu-
facture, tobacco smoke
6OR-10-023
corrosive attack where the acid gases react with the metals
themselves to form non-conductive salts and second type
being “whisker growth”.
Creep Corrosion. Any place where a non-precious metal
meets the atmosphere, corrosion may occur. Some metals
undergo self-limiting, or passive corrosion. Once an oxide or
sulfide layer forms, it will not grow any further. The layer of
corrosion products effectively insulates the underlying base
metal from the environment, and further corrosion is
prevented.
In active corrosion, the corrosion layer is not self-limiting.
The base metal will continually corrode, and the corrosion
product will tend to spread out from its point of origin. Any pre-
plated or clad contact (coated before stamping) will have bare
edges. These edges are free to corrode, and the corrosion prod-
uct can grow from the edges and slowly spread across the
surface as shown in Figure 3. This is known as “creep corro-
sion” (Anon F 2008).
Creep corrosion is a mass-transport process during which
solid corrosion products migrate over a surface. Eventually,
the corrosion product will interfere with the electrical connec-
tion by creating unacceptably high levels of contact resistance.
Pollutants such as chlorine, hydrogen sulfide, and sulfur diox-
ide are known to promote creep corrosion. For components
with noble metal pre-plated leadframes, creep corrosion is a
potential reliability risk for long-term field applications (Zhao
and Pecht 2005).
Pore Corrosion. In an ideal world, surface platings
would be uniformly thick, continuous, and stress-free. In the
real world, there will always be some imperfections in the plat-
ing. In many cases, platings will have pores, through which the
base metal will be exposed. The degree of porosity depends on
the plating thickness, application method, base metal rough-
ness, and base metal cleanliness. As plating thickness
increases, there is less likelihood of a pore extending all the
way to the base metal. In a very thin plating layer (on the order
of those used for gold), the likelihood is high that many pores
will extend all the way through this layer. Platings over base
metals with rough surfaces show more porosity than those
over smooth surfaces. Dirt or oxide on the surface of the base
metal can also lead to the appearance of pores.
If the base metal is exposed to a corrosive environment
through these pores, pore corrosion can occur. Base metal
corrosion can occur entirely in the pores, where it may be
hidden from view, or the corrosion product may creep across
the surface (Anon F 2008). An example of this is shown in
Figure 4. Pore corrosion is promoted by the many of the same
gases that promote creep corrosion.
Via Corrosion. When a multi-layer circuit board is
created, vertical interconnects must be added. These intercon-
nects are called vias and can be defined as a plated-through
hole used to connect two or more conductor layers of a multi-
layer board, in which there is no intention to insert a compo-
nent lead or other reinforcing material.
There are areas on circuit boards that can contain exposed
copper, such as the inside of via barrels. The purpose of
surface finish (or coating) is to protect the copper beneath. If
the coating is complete, corrosion would not take place as
Figure 3 Example of creep corrosion on connectors.
Figure 4 Example of pore corrosion on connectors.
OR-10-023 7
rapidly. An experimental investigation of the via holes on a
typical silver immersion board shows that the silver coating
does not typically extend all the way through the via barrel
(Mazurkiewicz 2006).
In situations where the via hole is not completely coated,
copper metal is vulnerable to atmospheric attack (Figure 5).
This situation which involves a more noble metal coating a
metal that is prone to oxidation in the presence of an electro-
lyte (atmospheric water) is highly prone to galvanic corrosion.
Indeed, this appears to be the case when one reviews the
dozens of incidents and hundreds of failures in which PCB
technology is used in an environment high in reduced sulfur
gasses. The majority of the failures show the heaviest corro-
sion mainly inside the via holes.
Whisker Growth. This type of corrosion typically refers
to electrically conductive, crystalline structures of tin that some-
times grow from surfaces where tin (especially electroplated
tin) is used as a final finish. Tin whiskers have been observed to
grow to lengths of several millimeters (mm) and in rare
instances to lengths up to 10 mm (0.4 in). Numerous electronic
system failures have been attributed to short circuits caused by
tin whiskers that bridge closely-spaced circuit elements main-
tained at different electrical potentials (Anon G 2008).
“Whisker growth” can be described as corrosion in which
microscopic metal crystals grow out of the surface of the
conductive metal. It is caused by the presence of sulfide mole-
cules, e.g., silver sulfide on a silver surface, which can migrate
freely over the metallic surface and collect at dendrite bound-
aries where nucleation takes place and sulfide crystals grow
out of the surface of the metal. These whiskers can be of size
long enough to connect portions on a board, chip, etc. and
cause short-circuits (Figure 6). By some accounts, whisker
growth accounts for approximately 10% of documented fail-
ures (Brusse et al. 2007).
Other specific areas on PCB that are particularly sensitive
to corrosion attack are briefly described below.
Edge Connectors. These contacts are typically gold-
plated over a nickel-plated copper substrate that is intended to
ensure that the electrical contact between the board and the
connector is maintained with the highest integrity over a long
period of time. Since the gold layer is typically only between
4 and 8 µm thick, and at these plating thicknesses fairly porous,
the passage of corrosive gases can occur through the gold layer
and attack the underlying layers of nickel and/or copper.
The salts formed by corrosion reactions are of a higher
volume than the pure metal and can either “flake off” the gold
plating or be forced back up through the pores onto the surface
of the gold plating. In both cases the contact arm no longer
rests on the conductive metal but rests on a high resistance
coating.
Earlier generations of electronic equipment with operat-
ing voltages as high as 24-48 volts DC, equipment failures
only occurred after many years of operation since these volt-
ages were high enough to break down the thin high-resistance
layers caused by salt formation. Modern electronics are,
however, much more sensitive to this type of corrosion since
operating voltages are lower and cannot break down these
corrosion films.
Figure 6 Tin whiskers causing bridging across circuits.
Figure 5 Example of via corrosion.
8OR-10-023
Pin Connectors. The problems experienced on pin
connectors and IC plug-in sockets show the same problems as
edge connectors. However, edge connectors appear to be more
susceptible to corrosive attack and failures occur earlier than
on pin connectors and IC sockets.
Wire-wrap Connections. Wire-wrap connection pins are
particularly sensitive to corrosive attack because the wire forms a
“smear” contact between the pin and the wire with up to four
different metallic alloys being exposed to the atmosphere. Corro-
sive attack can thus occur concurrently with electrolytic action
which greatly increases the corrosive influence.
Electrical Systems. Previous generations of electronic
equipment contained only heavy current systems in which the
build-up of corrosion by-products could cause overheating
that result in a reduction in equipment life. Today, however,
central offices, internet data centers, and remote locations
using the most advanced microelectronics operate with much
lower voltages and are much more sensitive to corrosive attack
as described above. As such, the air quality in these rooms will
have a great effect on the life of the equipment.
MEASURING CORROSION
There are many methods available to measure ambient air
quality and two methods have been used extensively for environ-
mental characterization with regards to corrosion. One is a direct
measure of selected gaseous air pollutants. The other, which can
be termed “reactivity monitoring,” provides a quantitative
measure of the overall corrosion potential of an environment.
Pollution analysis may provide short-term estimates for
specific sites. High values will confirm that a severe environ-
ment exists. The reverse, however, is not necessarily true.
Many environments may contain a complex mixture of
contaminants that interact to greatly accelerate (or retard) the
corrosive action of individual gas species.
As a direct measure of overall corrosion potential, reac-
tivity monitoring involves the placement of specially prepared
metal coupons in the operating environments.3 Analyses may
consist of measurements of film thickness, film chemistry, or
weight loss. However, ISA Standard 71.04-1985 references
measurement of film thickness by cathodic (electrolytic, colu-
meteric) reduction as a preferred method to perform reactivity
monitoring. By using this method, the air with contaminant
gases can be rated as to its effect on the electronic equipment.
Quantifying the Corrosive Potential
of an Environment
Environmental Reactivity Coupons. Since the ISA
Standard was published hundreds of thousands these “envi-
ronmental reactivity coupons,” or ERCs, have been used to
provide a measure of the corrosive potential of an environment
(Figure 7). ERCs may be used to indicate the presence of SO2,
NO2, Cl2, O3, and many other corrosive materials which can
cause damage to PCBs and many types of electronic equip-
ment.
ERCs originally used only copper reactivity to establish
environmental classifications. However, copper is not suffi-
ciently sensitive to many of those pollutants ubiquitous to
most urban environments - the same environments in which
most data centers are located. Further, copper coupons cannot
detect the presence of chlorine, a particularly dangerous
contaminant to metals. Finally, with the passage of RoHS
legislation, and the switch to Imm-Ag and other lead-free
finishes, many control systems manufacturers and end-users
are now questioning whether this type of environmental moni-
toring is adequate or not.
Due to all of this, the use of silver reactivity monitoring,
in addition to copper reactivity monitoring, has seen an
increase in use in these environments. Although silver is not an
equipment reliability determinant in the ISA standard, it has
been long been included because of independent studies citing
silver being able to detect changes in the levels of gaseous
contaminants in the ambient environment as small as 1 ppb
and differentiate between different classes of contaminants as
well as being a better indicator of environmental chlorine than
copper (Rice et al 1981, Muller 1999).
The use of these two types of coupons presented, on occa-
sion, results that were quite surprising. Some environments that
were non-corrosive to copper, and thus considered harmless to
3. Copper has been the primary coupon material because data exist
which correlates copper film formation with reactive (corrosive)
environments and it has proven to be particularly useful for envi-
ronmental characterization.
Figure 7 Copper/silver ERC.
OR-10-023 9
equipment (by the ISA standard), were extremely corrosive to
silver. While this alone does not necessarily indicate an envi-
ronment requiring direct control of contaminants, it does point
out the potential for corrosion-related effects. Many in the
process industries (e.g., pulp and paper, petrochemical) feel
that using copper-only reactivity monitoring results can seri-
ously understate the potential for equipment failure in these
environments (Muller 1990).
The primary reasons for using both copper and silver
reactivity monitoring to gauge data center air quality are:
1. Corrosion on silver is not humidity-dependent. In a
temperature and humidity-controlled data center, any
corrosion that forms on silver can be attributed solely to
the presence of chemical contaminants. Copper corrosion
is humidity dependent and can therefore be attenuated in
these environments.
2. Silver can be used to positively indicate the presence of
inorganic chlorine which is an extremely reactive
contaminant. Environmental chlorine cannot be defini-
tively determined from copper ERC analysis.
3. Silver is much more sensitive to low levels of contami-
nants. This is due to a passivating oxide layer that can
form on copper. Silver is not reactive with oxygen and,
again, any corrosion that forms is due to the presence of
reactive contaminant gases.
The corrosion reported from reactivity monitoring with
ERCs is actually the sum of individual corrosion films. For
copper coupons, sulfide and oxide films are most commonly
produced and are reported as copper sulfide (Cu2S) and copper
oxide (Cu2O), respectively. For silver coupons, sulfide, chlo-
ride, and oxide films may be produced and are reported as
silver sulfide (Ag2S), silver chloride (AgCl), and silver oxide
(Ag2O), respectively. Each coupon is analyzed as to the type
and amount of film present and its relative contribution to the
total corrosion produced.
Environmental Reactivity Monitors. One consideration
faced in designing an air quality monitoring program is the
choice of passive vs. active sampling. The immediate feedback
of an active monitor is a most desirable aspect and is what often
precludes the use of passive monitors. The main limitation in
the use of ERCs is their inability to provide a continuous envi-
ronmental classification. To address this, reactivity monitoring
has been taken a step farther through the development of a real-
time monitoring device employing metal-plated quartz crystal
microbalances (QCMs, Figure 8). These microprocessor-
controlled devices are able to measure the total environmental
corrosion attributable to gaseous pollutants. ERMs employing
QCMs can detect and record changes <1 ppb for many
common contaminants. This ability is regarded as one of the
main requirements for any real-time monitoring protocol to be
used in data center environments (England et al. 1991, Weiller
1994).
To date, there are two commercially available ERMs that
employ copper and silver-plated QCMs that provide real-time
information on the amount of corrosion forming due to the
presence of gaseous contaminants. These devices measure
film thickness similar to the ERCs and report cumulative and
incremental corrosion rates in angstroms, correlating to the
reporting requirements of ISA 71.04-1985.
One device measures corrosion on a continuous basis and
allows for preventive action to be taken before serious damage
has occurred. Appropriate reactivity and alarm levels for a
particular application can be adjusted. It can be operated inde-
pendently as a battery-operated data logger unit or operated as
a data transmitter wired directly into a facility monitoring
system (FMS). Environmental classification databases can be
established and maintained to provide historical data.
The second device is similar in that it employs QCMs to
monitor the environment in real-time. However, it does not
store data but transmits it directly to an FMS or computer
directly via a 4-20 mA output signal.
Classification of Reactive Environments (ISA 1985)
The classification of reactive environments per ISA Stan-
dard 71.04 is based on the thickness of the reaction film(s)
formed on the copper coupon when determined by cathodic
reduction. The total film thickness is measured in angstroms
(Å) normalized to a one month exposure and correlated to
severity levels that predict effects of corrosion on electronic
equipment reliability. This classification scheme also
provided approximations of the concentrations of gases in the
environment being analyzed. The classification of reactive
Figure 8 QCM.
10 OR-10-023
environments is shown in Table 2 and described and illustrated
below (Figure 9).
Severity Level G1—Mild. An environment sufficiently
well-controlled such that corrosion is not a factor in determin-
ing equipment reliability.
Severity Level G2—Moderate. An environment in
which the effects of corrosion are measurable and may be a
factor in determining equipment reliability.
Severity Level G3—Harsh. An environment in which
there is a high probability that corrosive attack will occur.
These harsh levels should prompt further evaluation resulting
in environmental controls or specially designed and packaged
equipment.
Severity Level GX—Severe. An environment in which
only specially designed and packaged equipment would be
expected to survive. Specifications for equipment in this class
are a matter of negotiation between user and supplier.
This classification scheme allows for the evaluation of a
subject environment with respect to its corrosion potential and
ultimately the reliability of electronic equipment being used in
the environment. From this a decision can be made as to
whether or not action is needed to improve the environment for
the protection of the electronic equipment.
SO WHAT DOES ALL THIS MEAN?
Corrosion-induced failures are frequent in electronics prod-
ucts used in industrial environments. A typical failure mecha-
nism of electronic systems in these environments is the reaction
of atmospheric sulfur with exposed metals – particularly copper
Figure 9 QCMs and ERCs showing ISA classes G1-GX.
Table 2. ISA Classification of Reactive Environments*
Severity Level G1
Mild
G2
Moderate
G3
Harsh
GX
Severe
Copper Reactivity Level
(in angstroms)§<300 <1000 <2000 ≥2000
*The gas concentration levels shown below are provided for reference purposes. They are believed to approximate the Copper Reactivity Levels stated above, providing the relative
humidity is less than 50%. For a given gas concentration, the Severity Level (and Copper Reactivity Level) can be expected to be increased by one level for each 10% increase in
relative humidity above 50% or for a relative humidity rate of change greater than 6% per hour.
Gas Concentrations (in ppb)
Contaminant Gas Concentration
Reactive Species**,†† Group A H2S
SO2, SO3
Cl2
NOX
<3
<10
<1
<50
<10
<100
<2
<125
<50
<300
<10
<1250
50
300
10
1250
Group B HF
NH3
O3
<1
<500
<2
<2
<10,000
<25
<10
<25,000
<100
10
25,000
100
§Measured in angstroms after one month’s exposure.
**The Group A contaminants often occur together and the reactivity levels include the synergistic effects of these contaminants.
††The synergistic effects of Group B contaminants are not known at this time.
OR-10-023 11
and silver. These metals are found in PCB traces, integrated
circuit (IC) leads and device terminations. Copper sulfide or
silver corrosion products can grow and creep across surfaces
such as IC packages and PCB substrates.
Historically, the use of silver in electronic assemblies has
been a reliability risk unless the silver is protected from the
environment. Creep corrosion (electromigration) can occur
quite readily in humid environments especially in the presence
of small amounts of atmospheric sulfur and chlorides which
are common in many industrial and other environments.
Manufacturers of industrial computer equipment specify
the control of corrosive gases in their site planning guides and/
or their terms and conditions to maintain warranties and
service contracts. Now even environments previously consid-
ered benign with regards to electronics corrosion are experi-
encing serious problems as a direct result of RoHS
compliance. Data centers in many urban locations have
reported failures of servers and hard disk drives due to sulfur
corrosion. There are hints that this may even trickle down into
personal computers and electronic devices.
Many millions of lead-free desktop and notebook
systems, and related peripherals, were put into service by Dell
Computers starting in 2005, a year prior to the effective date
of the RoHS legislation and a large amount of resources were
invested in optimizing and qualifying lead-free assemblies.
Field data showed the overall quality of Dell’s lead-free prod-
ucts to be as good, and in some cases, better than the previous
generation of tin-lead products (Schueller 2007).
However, one failure mechanism caused by the lead-free
transition was not foreseen by Dell or the industry. It was soon
discovered that lead-free products with ImmAg surface finish
will creep corrode in high sulfur environments (ISA Class G2
or higher). The majority of creep corrosion failures occurred
on hard disk drives (HDD), graphic cards, and motherboards
in desktop or workstation systems (only those with ImmAg
PCB finish were affected).
Echoing the study by Rockwell, Hewlett Packard
(Mazurkiewicz 2006) documented several case studies where
creep corrosion of ImmAg finish caused failures of computer
systems in high sulfur environments. It was stated that sulfur-
based corrosion failures increased dramatically upon intro-
duction of ImmAg surface finish on computer products (due to
ROHS requirements). Alcatel-Lucent also has experience
with this issue in a paper detailing their work with mixed flow-
ing gas testing of various lead-free surface finishes and their
resistance to creep corrosion (Reid et al. 2007).
Analysis revealed the corrosion products to be copper
sulfide (Cu2S) and silver sulfide (Ag2S). Other studies have
shown that high amounts of Cu2S typically indicate the pres-
ence of active sulfur compounds such as elemental sulfur, H2S,
or organic sulfur compounds. Ag2S can also be formed by
these contaminants but can also be formed by exposure to SO2
contamination – a primary urban contaminant.
The most common failures are with the most common
components, with the highest incidence of failures being
found in capacitors, plastic encapsulated microcircuits
(PEMs) and printed circuit boards (PCBs). A University of
Maryland study of field failures from 70 companies revealed
30% of ALL failures were capacitors – mainly MLCCs [multi-
layer chip capacitors] (Anon H 2008).
CORROSION OF DATACOM EQUIPMENT
The reason for the dramatic increase in corrosion failures
due to the use of ImmAg involves the propensity of silver and
copper to react with sulfur. This is further complicated by the
fact that there are areas on ImmAg circuit boards that contain
both exposed silver and copper in contact, such as the inside
of via barrels. The purpose of the silver coating is to protect the
copper beneath. If the coating was complete, corrosion would
not take place as rapidly (Mazurkiewicz 2006).
ERCs and ERMs have been used to evaluate the severity
levels of data center environments all over the world. It has
been found that many areas have levels of corrosive contami-
nants high enough to be harmful to electronic equipment
performance to the point of failure. Examples of reactivity
monitoring data collected from data centers with documented
cases of corrosion-related equipment failure (PCBs, servers,
hard disk drives, etc.) is shown in Table 3 (Purafil 2008).
When interpreting the analysis results for the individual
corrosion films, the detection of a silver sulfide (Ag2S) film
without a corresponding copper sulfide (Cu2S) film usually
indicates the presence of oxidized forms of sulfur such as SO2
and SO3. When both films are detected - as is the case here -
it more often than not indicates the presence of active sulfur
compounds such as elemental sulfur, H2S, and organic sulfur
compounds (e.g., mercaptans) as well. When both films are
present and the amount of Cu2S is greater than 50% of the total
corrosion, this is further evidence of the presence of active
sulfur compounds in the subject environment.
Silver chloride (AgCl) indicates the presence of (an) inor-
ganic chlorine compound(s), e.g., Cl2, ClO2, HCl.
The highlighted values in Table 3 under the Cu2S and
AgCl columns indicate an increased risk for corrosive attack
regardless of the ISA Severity Level indicated. The shaded
rows are locations where computer equipment would not be
expected to survive without some type of additional environ-
mental control, i.e., air cleaning to remove corrosive gases.
WHERE DO WE GO FROM HERE?
The requirement for corrosion control in industrial envi-
ronments remains constant. However, more companies are
now taking a much closer look at developing or updating spec-
ifications due to the changes made by controls manufacturers
to comply with the RoHS restrictions on the use of lead. This
includes specifying an ISA Class G1 environment for control
rooms, etc., where in the past a Class G2 environment was
considered acceptable. Specifications are also now showing
up requiring the measurement and quantification of silver
corrosion rates and related corrosion products.
12 OR-10-023
With a majority of control systems, manufacturers opting
to use the ImmAg process for their PCBs and other electrical
components, and the fact that silver is much more sensitive to
lower levels of corrosive gases, we have already seen
increased concerns over equipment reliability. As one Auto-
mation Engineer for an Australian pulp and paper manufac-
turer described it, “The ISA Standard is becoming irrelevant
because it does not take into account silver corrosion. All of
the new equipment I have purchased over the last year contains
silver and the failure rate for some components is now being
measured in weeks instead of years.”
Another contributing factor to concerns over the use of
silver in industrial applications is that even with tightening the
environmental control requirements for temperature and
humidity and the positive effect this has on copper corrosion,
silver can still exhibit high rates of corrosion in well-
controlled environments. Examination of one environmental
reactivity coupon (ERC) database has shown that in locations
reported as ISA Class G1 for copper corrosion, the corre-
sponding silver corrosion rate can be up to 10x higher. Further-
more, every ERC analyzed shows evidence of sulfur
contamination (as silver sulfide, Ag2S). On average, the
amount of silver corrosion measured is double that of the
copper corrosion reported.
Corrosion control in industrial environments is acknowl-
edged as a requirement to assure electrical and electronic
Table 3. Reactivity Monitoring Results for Data Centers
Type Location Copper Corrosion Silver Corrosion
Cu2SCu2OCu-Unk Total ISA Level AgCl Ag2SAg-Unk Total
Bank Inside DC 0 75 0 75 G1 0636 0 636
FSC Server Room 122 70 0 192 G1 0 524 0 524
TCC Inside DC 162 105 0 267 G1 0982 0 982
Bank Inside DC 193 94 0 287 G1 0785 0 785
Bank DC supply air 0288 0 288 G1 23 227 0 250
Bank Under raised floor 258 89 0 347 G2 01,047 01,047
Bank Data storage 265 91 0 356 G2 03,200 03,200
HQ Inside DC 299 80 0 379 G2 01,603 01,603
Bank Inside DC 334 75 0 409 G2 01,833 01,833
FSC Inside DC 209 240 0 449 G2 0 106 0 106
FSC Outside air 355 137 0 492 G2 135 353 0 488
Bank DC supply air 426 85 0 511 G2 0861 0 861
Bank Inside DC 415 179 0 594 G2 01,122 01,122
TCC Server room 474 143 0 617 G2 0852 0 852
Bank Under raised floor 587 180 0 767 G2 45 1,742 01,787
FSC Hub room 1,702 320 02,022 GX 0916 0 916
HQ Outside air 620 1,549 02,169 GX 0 465 0 465
FSC Hub room 1,595 686 02,281 GX 01,309 01,309
IC Outside air 1,749 268 478 2,495 GX 835 96 96 1,027
Bank Outside air 0258 2,315 2,573 GX 87 552 0 639
FSC Hub room 3,297 778 04,075 GX 01,440 01,440
HQ Outside air 6,855 6,794 013,649 GX 05,044 2,421 7,465
HQ Outside air 10,357 7,434 017,792 GX 01,651 2,631 4,282
TCC Inside DC 20,000 0 0 20,000 GX 0655 0 655
ISP Server room 20,000 0 0 20,000 GX 0810 0 810
Bank Outside air 20,000 0 0 20,000 GX 387 374 715 1,476
Bank Outside air 20,000 0 0 20,000 GX 02,855 02,855
FSC Hub room 20,000 0 0 20,000 GX 03,404 03,404
FSC Hub room 20,000 0 0 20,000 GX 03,535 03,535
FSC Hub room 20,000 0 0 20,000 GX 03,927 03,927
ISP Hub room 20,000 0 0 20,000 GX 04,114 04,114
Key: FSC = financial services company, HQ = company headquarters, IC = investment company, ISP = internet service provider, TCC = telephone call center
Note: Gray-shaded areas indicate locations where the total copper and/or silver corrosion rates exceed those recommended for data centers. Bold text indicates the presence of active
sulfur contamination (as Ag2S) and/or inorganic chlorine compounds (as AgCl), either of which indicate a higher corrosion potential.
OR-10-023 13
equipment reliability. However, up to now corrosion control in
non-industrial applications has only been a concern in isolated
instances. Desktop and laptop computers, servers, data
communications (datacom) equipment and other equipment
used in information technology (IT) applications were not
particularly sensitive to the types and concentrations of
contaminants present in urban environments. However, even
these types of computer equipment are now at risk due to
RoHS.
Datacom equipment center owners and operators have
traditionally focused most of their attention on the physical
structure and performance of the data center infrastructure
(e.g. power, cooling, raised access floor equipment). Most IT
hardware is designed to operate in a controlled environment.
There are few moving parts (air handling equipments, drive
motors, etc.) and electronics are not expected to simply “wear
out.”
High reliability is demanded for today’s IT equipment
and projections to first failure are more than 11 years of power
on operation, which is far longer than in the real world, espe-
cially when considering that the equipment becomes obsolete
in half that time. However, that high reliability is only if the
product is maintained in the optimum environment. Any site
climate deviations or deviations in electrical power, static
electricity or air quality will have a negative impact on the
equipment and failure rates.
Even though today’s complex and sensitive IT equipment
requires a higher level of environmental control for gaseous
contamination than would have been considered before RoHS
took effect, this has been one aspect of data center environ-
mental control that was mostly overlooked. Datacom equip-
ment center contamination if left unchecked can influence the
reliability and the continuous operation of mission critical IT
equipment within a facility. Gaseous contamination can result
in intermittent equipment glitches, unplanned shutdowns, or
failure of critical systems that often result in significant busi-
ness and financial loss. Harsh environments are also not
always obvious or restricted to industrial settings.
Contaminant gases containing sulfur, such as SO2 and
H2S, are the most common gases in data centers causing hard-
ware corrosion. One example of component failure was due to
sulfur gases entering a component package and attacking the
silver resulting in the formation of Ag2S. The mechanical
pressure created by the Ag2S formation inside the package
damaged its mechanical integrity and caused the device to fail.
This and other failure mechanisms are becoming common
occurrences within data centers using RoHS-compliant equip-
ment and components produced using the ImmAg process,
and to a lesser degree, the ENIG process.
To maintain a high level of equipment dependability and
availability, it should be understood that a data center is a
dynamic environment where many maintenance operations,
infrastructure upgrades, and equipment change activities
occur on a regular basis. Airborne contaminants harmful to
sensitive electronic devices can be introduced into the operat-
ing environment in many ways (e.g., chlorine can be emitted
from PVC insulation use on wires and cables if temperatures
get too high.) However, the outdoor ambient air that is used for
both cooling and pressurization is often the primary source of
corrosive contaminants and should be cleaned before its intro-
duction into the data center environment. And now with the
rediscovery of “free cooling” using air-side economizer tech-
nology, more outside air will be brought into the data center
and along with it higher levels of contamination than previ-
ously encountered. Loosening control limits for humidity will
also contribute an increased potential for corrosion-related
problems.
With the changes to IT equipment due to the RoHS direc-
tives, data center designers, managers, and operators should
include an environmental contamination monitoring and
control section as part of an overall site planning, risk manage-
ment, mitigation, and improvement plan.
Included in this plan should be considerations for the
assessment of the outdoor air and data center environment
with regards to corrosion potential. Even though ISA 71.04 is
considered a standard for industrial applications, it still has
relevance in datacom applications and can be used to provide
site-specific data on the types and levels of gaseous contami-
nation. ERCs can be used as a survey tool to establish baseline
data necessary to determine if and what type of environmental
controls are needed.
The second part of the plan should be the development
and specification of a specific contamination control strategy.
Corrosion in an indoor environment is most often caused by a
short list of contaminants or combinations of a few contami-
nants. The compounds present in an individual data center are
highly dependant on the location and the controls put in place
to mitigate them. Most often this would involve the selection
and application of the appropriate chemical filtration systems
to clean both the outdoor ventilation air as well as the air inside
the data center.
The final part of the plan would be to establish a real-time
environmental monitoring program based on the severity
levels established in the ISA Standard. Real-time environmen-
tal reactivity monitors (ERMs) can provide accurate and
timely data on the performance of the chemical filtration
system as well as the air quality within the data center itself.
The absence of gaseous contamination controls can be the
result of a lack of knowledge and education. Often the rela-
tionship between corrosion levels and hardware failures in
data centers is overlooked or unknown. However, due to the
efforts of companies like Rockwell, Dell, IBM, HP and others,
this knowledge gap is shrinking and successful corrosion
monitoring and control programs can be developed and imple-
mented – assuring reliable operation of data center equipment.
SUMMARY AND CONCLUSION
Most computer systems and associated components, such
as telecommunications and storage systems used in data
centers are protected against the potential threats posed by fire,
14 OR-10-023
power, shock, humidity, temperature and particulate contam-
ination. Unfortunately, the potential damage to this equipment
caused by the corrosive effects of gaseous contaminants due to
RoHS compliance has still not been fully recognized or
addressed.
Manufacturers have to comply with RoHS if they want to
continue to do business in the EU, China, etc., and many have
taken the ImmAg route as their path to compliance. This has
taken care of one issue but has presented new challenges with
regards to equipment reliability.
The first stages of corrosion may show up as untraceable
alarms, as corrosion products grow and provide random circuit
paths that clear themselves as soon as current flows through
them. However, some information may have already been lost.
In the worst cases, substantial resistance to current flow is
developed, variations in voltages occur, and the entire circuit
may become useless due to changes in component value.
These circuit failures, whether in a server, hard disk drive,
switch, or other electrical component, increase equipment
capital cost and warranty and maintenance costs. Something
as simple as a corroded chip may destroy the promise of real-
time connectivity, resulting in consumer dissatisfaction and
lost profit.
Recognizing the severity of the problem, most of the
world's leading manufacturers of computer systems have
placed in their site planning manuals references to the ISA or
similar standards for acceptable levels of airborne contami-
nants. This is because they provide achievable and effective
guidelines to protect electronics and electrical equipment
from the damaging effects of corrosive gases.
The use of reactivity monitoring using both copper and
silver corrosion data is being used to provide a more complete
environmental assessment than the copper-only monitoring
described in ISA Standard 71.04-1985. This is based on stud-
ies that have shown that while copper coupons may be good
indicators of corrosive gases in an environment, they are not
sufficiently sensitive in all cases to many of the contaminants
encountered in many environments (Muller 1991, Muller et al
1991). The standard is currently undergoing a long past-due
update to incorporate the use of silver corrosion data into
quantifiable severity levels relating to equipment reliability. It
is also planned to add the use of real-time reactivity monitors
as an acceptable approach for environmental classification
using reactivity monitoring. Most likely this will be a refer-
ence to mass-gain monitoring techniques (e.g., quartz crystal
microbalances).
When both copper and silver monitoring is used and the
copper reactivity is equal to an ISA G1 classification, the
corresponding silver corrosion rate can be expected to be
approximately double that of the copper coupon for indoor
environments (Purafil 2000). Therefore, total silver corrosion
less than 600Å with no evidence of chlorine contamination
(as AgCl), would be considered an acceptable complement to
a class G1 copper environment with no evidence of sulfur
contamination (as Cu2S). Total silver corrosion above 600Å
with or without evidence of chlorine often indicates an envi-
ronment where the effects of corrosion are measurable and
there is an increased probability of corrosive attack.
The issue and potential for corrosion-related problems in
data centers has been presented. Data from many different
sites shows that corrosive atmospheres exist in locations that
most would consider otherwise benign if not for the changes
in electronics mandated by RoHS legislation. These problems
can be addressed by continuous monitoring of the data center
environment and removal of corrosive contaminants where
indicated. Ultimately, the successful implementation of a
corrosion protection program requires:
• Knowledge and understanding that corrosion of elec-
tronic equipment is a serious problem.
• Commitment to a monitoring program to describe the
potential for electronic equipment failure.
• Commitment to an integrated contamination control
system.
• Commitment to take corrective action whenever necessary.
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