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ISA_standard.pdf | Printed Circuit Board | Environmental Monitoring
ISA Standard 71.
04: Changes Required for Protection of Today's Process Control
Chris Muller, Purafil, Inc., Doraville, Georgia, USA
Grant Crosley, Visy Pulp & Paper, Campbellfield VIC Australia
Corrosion-induced failures remain frequent in electronics products used in industrial environments. The
International Society for Automation (ISA) Standard 71.04-1985 provides a classification system using corrosion (or
reactivity) monitoring to determine the corrosive potential of an environment towards electronic equipment.
Changes to electronic equipment mandated by the European Union directive 2002/95/EC “on the Restriction of the
use of certain Hazardous Substances in electrical and electronic equipment” (RoHS) required the elimination of lead
in electronic equipment. Recent research has shown that printed circuit boards made using lead-free materials can be
more susceptible to corrosion than their tin/lead counterparts. Now even environments previously considered
relatively benign concerning electronics corrosion are experiencing serious problems as a direct result of RoHS
With the passage of a number of RoHS regulations and the switch to lead-free finishes on printed circuit boards,
many are now questioning whether this type of environmental monitoring is adequate. Reactivity monitoring now
needs to provide a more complete environmental assessment than the monitoring techniques described in ISA
Standard 71.04. This standard is long overdue for a major revision to address issues described for and since the
implementation of RoHS. This paper will discuss changes that have been proposed for the current vision and what
changes may be anticipated in future revisions.
Ever since the pulp and paper industry began replacing pneumatic and hydraulic controls with computer control
systems, the reliability of these electronic and electrical devices has been challenged by attack from corrosive
gaseous contaminants present in the operating environment. In the context of electronic equipment, corrosion is
defined as the deterioration of a base metal resulting from a reaction with its environment. More specifically,
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 or short-circuits. Pitting and metal loss can also occur.
Corrosion of metals is a chemical reaction caused (primarily) by attack of gaseous contaminants and is accelerated
by heat and moisture. Rapid shifts in either temperature or humidity cause parts of circuits to fall below the
dewpoint temperature, thereby facilitating condensation of contaminants. Relative humidity above 50% accelerates
corrosion by forming conductive solutions on a small scale on electronic components. Microscopic pools of
condensation then absorb contaminant gases to become electrolytes where crystal growth and electroplating occur.
Above 80% RH, electronic corrosive damage will occur regardless of the levels of contamination.
STANDARDS FOR AIR QUALITY ASSESSMENT
To address these concerns and to protect multi-million dollar investments in new control systems, a 10-year study
was performed by Battelle Laboratories underwritten by process control system manufacturers and by many of the
major pulp and paper companies. The goal was to develop the information necessary to establish a correlation
between electronic equipment reliability and environmental corrosion rates. This ultimately led to the publication of
standard S71.04-1985: "Environmental Conditions for Process Measurement and Control Systems: Airborne
Contaminants," by the Instrument Society of America (ISA, now known as the International Society of Automation)
This document was followed in 1987 by the International Electrotechnical Commission (IEC) Standard, IEC 60654-
4 (1987-07) “Operating Conditions for Industrial-Process Measurement and Control Equipment. Part 4: Corrosive
and Erosive Influences” [2]. Japan's standard, JEIDA-29-1990, was revised in 1990 and published as the Japan
the severity level may be classified as G2. only gaseous contaminants will be considered in this paper. Although the standard also includes classifications for liquid and solid contaminants. In addition to the contaminant gases themselves. TABLE I . Å)* The gas concentration levels shown below are provided for reference purposes. the easiest method of measurement has been through the use of CCCs according to the method prescribed in the ISA standard. 3.000 25. This standard defines or characterizes environments in terms of their overall corrosion potential. At this level. Item Numbers 2.” a quantitative measure of this potential can be established. The optimum severity level is G1 .” or CCCs. This analysis technique allows for the classification of the total amount of corrosion. SO3 < 10 < 100 < 300 300 Group A Cl2 <1 <2 < 10 10 Reactive NOX < 50 < 125 < 1250 1250 Species†. These “corrosion classification coupons. corrosion is not a factor in determining equipment reliability. Therefore. As the corrosive potential of an environment increases. See Appendix C. provides a method for determining equipment reliability.‡ HF <1 <2 < 10 10 Group B§ NH3 < 500 < 10. and severity levels within each classification. Copper reactivity was measured as the total corrosion film thickness (in angstroms) normalized to a 30-day exposure. * Measured in angstroms after one month’s exposure. Reactivity monitoring involves placing specially prepared metal strips into the environment. They are believed to approximate the Copper Reactivity Levels stated above. Relative humidity of less than 50 percent is specified by the standard. This data is used to determine the severity level of the environment which refers to the potential damage that corrosive gases could cause to electronics and electrical equipment and. as well as the thicknesses individual corrosion films attributed to different classes of corrosive gases. ISA Standard 71. according to the type of contaminant. presents the manufacturers and users of electronic devices and computer control systems a classification system to gauge the corrosive potential of an environment. providing the relative humidity is less than 50%. Four levels of corrosion severity have been established by Standard 71. The goal of all three standards was the same – correlate equipment reliability to levels of airborne corrosive contaminants. as it is known now.04-1985. § The synergistic effects of Group B contaminants are not known at this time. G3 or GX (the most severe). † mm3/m3 (cubic millimeters per cubic meter) parts per billion average for test period for the gases in Groups A and B. would be exposed for a period of time and then analyzed to determine the thickness of the corrosion films that had formed.Electronic Industry Development Association’s (JEIDA) "Standard for Operating Conditions of Industrial Computer Control System” [3]. By the use of “reactivity monitoring.04-1985 Standard 71.000 O3 <2 < 25 < 100 100 The synergistic effects of various combinations of corrosive gases make the determination of severity levels complex. High or variable relative humidity and elevated temperatures may cause the acceleration of corrosion by gaseous contaminants. The effects of humidity and temperature are also quantified in this standard. It establishes environmental classifications. . therefore. Gas Concentrations (in ppb) Contaminant Gas Concentration H2S <3 < 10 < 50 50 SO2. temperature and humidity also have a major impact on the corrosion rates.000 < 25. For a given gas concentration.04 (see TABLE I).Mild. 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.ISA Classification of reactive environments Severity Level G1 G2 G3 GX Mild Moderate Harsh Severe Copper Reactivity Level < 300 < 1000 < 2000 2000 (in angstroms. ‡ The Group A contaminants often occur together and the reactivity levels include the synergistic effects of these contaminants.
Some of the more important work is summarized below. it was discovered that one of the main limitations in using copper alone for environmental monitoring and assessment is that the presence or absence of environmental chlorine. but must be periodically reviewed and updated to incorporate changes as necessary to remain relevant as a tool for predicting equipment reliability. too. and analysis of copper reactivity samples.04. Each coupon can be examined for the type of film present and its relative contribution to the total corrosion. • The standard was shown not to be internally consistent with respect to the four main Group A contaminants.04 is actually the sum of individual corrosion films.g. sulfide. standards are subject to review at least once every five to seven years. .04 Through the regular ISA review process. to be of real value. which would enhance the standards application. the method most commonly used since the standard was published is reactivity monitoring. the complex nature of gas interactions can produce some unknown films – even in a controlled laboratory environment. This standard had been developed with the goal of uniformity of equipment reliability in the field of industrial process measurement and control instrumentation. Corrosion Coupon Research [5. These reviews are intended to address any comments and criticism as well as any advances in technology. have been used for almost since the standard was published to provide what is known to be a more accurate assessment of the corrosion potential of a local environment. CORROSION RESEARCH APPLICABLE TO STANDARD 71. much research has been performed in the area of environmental classification via corrosion monitoring.04 [4] and in research performed since its publication. this document cannot be static. For this reason.” at its own unique electrochemical potential. • While H2S and NO2 were not particularly corrosive by themselves. Data was subsequently examined in terms of the individual corrosion films. Silver. Some of the main findings from this corrosion coupon research are listed below. • Copper corrosion was dominated by active sulfur contamination (e. When standard S701. Initial testing only examined the total amount of corrosion formed on the coupons which was consistent with the reactivity monitoring described in the standard..7] Corrosion reported per Standard S701. • There was poor correlation with field-observed results. this combination produced more than four times the expected silver corrosion.04 initially came up for review in 1990. chloride. These unknown films. H2S) when present. cannot be accurately determined. in addition to copper coupons. • The standard should be reviewed for inclusion of actual single gas corrosion levels for all severity levels and their use in setting the reactivity levels. However. Corrosion potentials have been determined for the various corrosion products which form of copper and silver. From the research performed in support of developing Standard 71. on the other hand. or “stripped away. • Single gas corrosion levels did not agree with the corresponding copper reactivity levels put forth in the standard. a particularly damaging contaminant to metals. were used in the data described below. • Using the copper reactivity levels put forth in the standard. Depending upon the type of coupon used and the gases present. silver coupons.The standard actually describes two methods of environmental characterization – direct concentration monitoring and reactivity monitoring. Although electrochemical potentials have been determined for individual corrosion products when analyzed by electrolytic/cathodic reduction. exposure. each individual film is dissolved. one could significantly overstate the corrosive potential of an environment when using gas concentrations as the sole determinant. In the twenty-five years since publication of S71. oxide. However.6. and/or other films may be produced. When using electrolytic/cathodic reduction as an analysis technique. new research was available and applicable for inclusion into the standard. is extremely sensitive to chlorine. The standard provides instructions for the preparation.
coupled with the time it takes to obtain results from reactivity monitoring using coupons. too. and temperature and relative humidity monitoring. examination of some large corrosion coupon databases has produced some interesting observations and conclusions. There have been only a few studies with side- by-side reactivity monitoring. Conversely. single film formation was confined predominantly to G1 and G2 coupons. without silver sulfide (Ag2S) confirms a sulfur-free environment. This was an oxide film as opposed to a sulfide film. Except for SO2. some copper coupons exhibited no Cu2S and were concluded to have been exposed in an SO2-only environment. The addition of gold coupons provides even further definition of the subject environment. • Total copper corrosion.04 has been. only one third of the corresponding copper coupons exhibited an unknown copper film. • Of those silver coupons which showed no silver chloride. By reporting only copper corrosion. each single contaminant produced a single film and were the only instances where a single film was observed on silver. Any remedial actions recommended as a result of this monitoring would be more concise. For the copper coupons almost all of these exhibited only Cu2O. These coupons were concluded to have been exposed to a SO2-only environment.04. resulted in the development of real-time corrosion monitors using piezoelectric quartz crystal . which did show silver chloride showed no corresponding unknown copper films. on silver. This. produced only a copper oxide (Cu2O) film. is dominated by H2S. SO2. One of the main criticisms with reactivity monitoring has been that some were trying to read too much into what is actually only circumstantial evidence that corrosive gases are present in the subject environment. one can and often does make incorrect assessments about the environment in question. many have acknowledged the shortcomings of the standard by using combination copper/silver corrosion classification coupons. Examination of the corresponding silver data showed about a quarter of these exhibited only Ag2S corrosion. This further illustrates how one could mistakenly state the presence or absence of chlorine in the environment. Some have tried to extrapolate contaminant gases and concentrations from the electrolytic reduction analysis alone. and particularly copper sulfide film (Cu2S) formation. gas concentration monitoring. and consequently. This film was observed only when H2S was present in the test environment. about one third of all silver coupons. even with the breakdown of the individual films. and continues to be. However. By using copper and silver coupons for this monitoring. Real-time Corrosion Monitoring These inconsistencies and shortcomings. All testing which included this contaminant produced a silver chloride (AgCl) corrosion film. However. • For both copper and silver coupons. • The assumption that an unknown copper film could be attributed solely to the presence of chlorine was proved false. can be clarified by including silver coupons. This has been shown to be inconclusive at best. Examination of silver corrosion results clearly showed only Cl2 was present. A few coupons similarly exhibited no Cu2O and were concluded to have been exposed in H2S-only environment. • Examination of individual corrosion film data for copper and silver coupons further supported the assertion that one cannot accurately determine the corrosive potential of an environment when following the methodology in standard S701. it has been shown that the subject environment can be more accurately characterized as to the severity class(es) and type(s) of contaminants present. • A single copper film was produced for only one contaminant – SO2. The copper-only reactivity monitoring prescribed cannot conclusively determine the presence or absence of Cl2 or SO2. Therefore. Cu2O. • Within this group. by itself. one must be able to accurately determine whether or not this contaminant is present or not. New data for silver and gold (-plated) coupons established the need to review the standard for the applicability and reliability of copper-only environmental reactivity monitoring. Corrosion Coupon Field Results This and other research allowed for examination of field-exposed corrosion coupons. the absence of Cu2S does not indicate a sulfur-free environment. The most obvious example of this is where some continue to attribute an unknown copper film to the presence of Cl2. With the standard giving Cl2 the lowest tolerable concentration for a G1 environment. a single silver film can be associated with a specific contaminant and SO2 can be speciated when copper and silver films are compared. However. less expensive. a useful tool for characterizing the corrosive potential of an environment. Standard 71.
or other reactive metals and circuit is made incorporating an oscillator with the QCM so that the frequency at which the crystal is vibrating can be measured. or must be reduced to within maximum permitted concentrations. however.microbalances (QCM) as sensors [8]. In order to comply with the EU legislation. A QCM is plated with copper. also known as a printed circuit board assembly. or traces. in any products containing electrical or electronic components that will be sold within the EU. in practice. Thus the main issue for the electronics industry became the use of lead in the manufacture of components and circuit board assemblies. These changes had nothing to do with product improvement. More recently. RoHS AND ELECTRONIC EQUIPMENT RELIABIILTY The European Union (EU) directive 2002/95/EC “on the Restriction of the use of certain Hazardous Substances in electrical and electronic equipment” or RoHS was implemented in July 2006 (EU 2003). rather. However.10]. In February 2006. The use of QCMs as corrosion monitors has been described in several studies [9. the resonance frequency of the crystal changes. All PCBs have conducting layers on their surface typically made of thin copper foil. While there is some commonality between the RoHS requirements in the EU and those in China. hexavalent chromium (Cr(VI)). The hot air solder leveling (HASL) process worked well for many years. If the copper is left unprotected. there are also significant differences that must be recognized and dealt with. Data from both laboratory and field-exposed copper and silver coupons produced close and reproducible correlation between the passive CCCs and the real-time QCMs because both methods involve the measurement of weight-gain caused by the buildup of corrosion films. These changes can be correlated to the amount of corrosion which has built up over time. Manufacturers have made significant investments in new processes that will eliminate these substances – especially lead. A PCB populated with electronic components is a printed circuit assembly (PCA). and more reliable. Unintended Consequences A printed circuit board. laminated onto a non-conductive substrate. The EU's RoHS Directive restricts the use of six substances in electrical and electronic equipment: mercury (Hg). and was also the cheapest PCB available. silver. was the predominant surface finish used in the industry. As corrosion films are formed. Traditionally. or PCB. these devices have been modified due to changes mandated by new environmental laws passed in Europe. the maximum measurable film thickness still needs to be determined. and etched wiring board. Corrosion-Indicating Bridge (CIB). it will corrode and deteriorate.” The purpose of this law is similar to that of the EU’s RoHS Directive and the Chinese law is simply called “China RoHS” in the industry. and was the first of many RoHS (-like) regulations that have been passed [11]. they were required due to restrictions on the use of various substances in electronic products. even very slight changes in temperature may produce resistance changes far greater than those due to corrosion alone. is used to mechanically support and electrically connect electronic components using conductive pathways. These real-time corrosion monitors – especially those using QCMs – have been improved since their introduction in the 1980s due to technology advances and the ability to make these devices smaller. Another method of monitoring corrosion is to measure the increase in resistance of a metal film. However. more sensitive. One of the purposes of these regulations has been to restrict the use of hazardous substances in electrical and electronic equipment. Now RoHS essentially makes PCBs using the HASL process . This type of measurement is limited by the sensitivity of the instrumentation. China promulgated a law entitled “Administration on the Control of Pollution Caused by Electronic Information Products. Alternative names are printed wiring board (PWB). polybrominated biphenyls (PBB) and polybrominated diphenyl ethers (PBDE). in both instances these RoHS regulations require the elimination of lead in electronic products and manufacturers have to comply with RoHS if they want to continue in to do business in the EU and China. cadmium (Cd). accompanying a reduction in cross-sectional area by film growth. all of these substances must either be removed. lead (Pb). This technique appears valid. any exposed copper was plated with lead (-based) solder.
As a result. more ImmAg process lines have been installed in PCB facilities than any other finish. ImmAg boards have become the standard PCB finish in the electronics industry [12]. graphic cards. Pulp and Paper Mill CCC Data [11] Location Area/Room Cu2S Cu2O CuUnk Copper Total ISA Class AgCl Ag2S AgUnk Silver Total AHU Room 0 180 0 180 G1 0 3142 0 3142 Austria DCS Room 182 78 0 260 G1 0 3491 0 3491 Electrical Room 115 46 0 161 G1 0 1582 0 1582 Control Room 192 101 0 293 G1 0 1042 0 1042 Brazil Operations Room 205 88 0 293 G1 0 1234 0 1234 MCC 0 125 0 125 G1 0 948 0 948 DCS Room 182 104 0 286 G1 0 1022 0 1022 China Wet End Control 182 78 0 260 G1 0 1118 0 1118 Computer Room 124 44 0 168 G1 0 5467 0 5467 DCS Cabinet 0 118 0 118 G1 0 1636 0 1636 Finland MCC 0 106 0 106 G1 0 2634 0 2634 Control Room 0 150 0 150 G1 0 2796 0 2796 Mechanical Room 0 68 0 68 G1 0 2182 0 2182 Holland Server Room 0 78 0 78 G1 0 1964 0 1964 Splicer Room 0 105 0 105 G1 0 1145 0 1145 Control Room 0 173 0 173 G1 0 1497 0 1497 Japan IPC Room 0 231 0 231 G1 0 2145 0 2145 DCS Room 215 62 0 277 G1 0 1038 0 1038 DCS Panel 187 61 0 248 G1 0 1848 0 1848 Korea MCC Room 204 56 0 260 G1 0 1810 0 1810 PLC Panel 102 50 0 160 G1 0 1155 0 1155 Electrical Room 172 34 0 206 G1 35 1315 0 1340 USA Wet End Drives 196 81 0 277 G1 0 1565 0 1565 Control Room 175 86 0 261 G1 0 5073 0 5073 Data centers in many urban locations have reported failures of servers and hard disk drives due to sulfur corrosion. alternatives such as immersion silver (ImmAg) and organically coated copper (OCC) are currently used as board finishes. ImmAg is easy to apply to the boards. The common factor for all these locations was that the corresponding silver reactivity rates averaged twice that of the copper rate with several locations showing silver corrosion 10-20 times higher. some manufacturers have complained about issues with corrosion which can lead to shorts and ultimate failure of the board. Due to inherent processing difficulties with OCC boards. Creep corrosion failures in high sulfur environments (ISA Class G2) have been reported on hard disk drives. However. and motherboards in many types of systems. Failure modes on other common lead-free PCB finishes such as organic solder preservative (OSP) and electroless-nickel immersion gold (ENIG) make these technologies undesirable.obsolete. Desktop and laptop computers. data communications (datacom) equipment and other information . and usually performs well. Corrosion-induced failures are frequent in electronics products used in industrial environments. Table II. Now electronics in environments previously considered benign with regards to corrosion are experiencing serious problems as a direct result of RoHS. DIMMs. Table II shows CCC data from a number of pulp and paper mills around the world that met the current definition of an ISA Class G1 environment but still experienced corrosion-related failures of RoHS- compliant electronics. relatively inexpensive.04 Research has shown that printed circuit boards made using lead-free materials can be more susceptible to corrosion than their tin/lead counterparts [13]. Two common chemical failure modes are copper creep corrosion on circuit boards and the corrosion of silver metallization in miniature surface-mounted components. since RoHS has been in effect. While ENIG presently has a larger market share. RoHS AND ISA STANDARD 71. servers.
The increasing number of hardware failures in data centers high in sulfur-bearing gases.04 are highlighted below. The use of new PCB surface finishes – especially ImmAg – and this new susceptibility of electronic equipment to environments previously considered benign has fostered a renewed interest in updating and improving ISA Standard 71.9 has recommended that both copper and silver corrosion rates be used with the higher of the two used to determine severity levels. Data is currently being by a number of organizations to validate the silver reactivity rate. Technology Spaces. and inorganic chlorides are of primary interest. Title Current: Environmental Conditions for Process Measurement and Control Systems: Airborne Contaminants Proposed: Environmental Conditions for Electronic Equipment: Airborne Contaminants Purpose Current: The purpose of this standard is to classify airborne contaminants that may affect process measurement and control instruments. This is even being seen in personal computers and electronic devices. Although most data centers are protected against temperature and humidity variations.technology (IT) equipment are now at risk due to RoHS. particulates and acidic gases can be drawn in through the building's air handling system(s) causing corrosion of electronics – especially in equipment produced since the passage of RoHS regulations. heat and power generation.9: Mission Critical Facilities. four alternate PCB finishes were subjected to an accelerated mixed flowing gas corrosion test.04 to protect RoHS-compliant products for use in both industrial and non-industrial settings. it is felt by many that as mentioned in the studies cited above. Important findings can be summarized as follows: • Immersion gold (ENIG) and immersion silver (ImmAg) surface finishes failed early in the testing. • The gold and silver coatings could not be expected to survive a mid to high Class G2 environment based on these test results. active sulfur compounds. and industrial activity. copper alone cannot provide as complete a picture of the corrosion risk as when using copper and silver. emissions from other forms of transportation. This and other proposed changes to Standard 71. highlighted by the number of recent publications on the subject. ASHRAE Technical Committee 9. In one study that looked at lead-free finishes [14]. . The classification system provides users and manufacturers of instruments with a means of specifying the type and concentration of airborne contaminants to which a specified instrument may be exposed. The word “modified” is used because Standard 71.04 The primary consideration in updating the standard is incorporating silver as a quantifiable metric for corrosion risk assessment. These coatings are the most susceptible to corrosion failures and may make the PCB the weak link with regards to the sensitivities of the electronic devices to corrosion. • None of the coatings can be considered immune from failure in an ISA Class G3 environment. Acidic (corrosive) gases and submicron particulates in urban environments come from motor vehicle exhaust. led to the publication of a white paper on particulate and gaseous contamination [15] by ASHRAE Technical Committee 9. sulfur oxides. PROPOSED CHANGES TO STANDARD 71. A copper reactivity rate of less than 300 Å/month and 2. In electronic component corrosion. A silver reactivity rate of less than 300 Å/month. and Electronic Equipment (ASHRAE 2009) recommending that gaseous contamination should be within the modified severity level G1 which meets: 1.04 uses copper corrosion alone to determine severity levels and with the use of silver and/or silver alloys as a replacement for lead.
laser and inkjet printers. Examples of data center equipment include: servers. Scope Current: §2. Caution should be used when a combination of factors approach or surpass class "X. Section 6. and 3) similar data does not currently exist for silver reactivity levels. Table 3 – Classification of reactive environments – Terminology Keep only the Severity Levels and Copper and Silver Reactivity Levels in the normative part of the standard and move the part of Table 3 referencing specific gases and concentrations to an informative appendix. keyboards.1 – This standard covers airborne contaminants and biological influences that affect industrial process measurement and control equipment. 2) it has been generally agreed that a more reliable way to measure the potential for or the effects of corrosion is to monitor corrosion directly via reactivity monitoring. in each of two corrosion reactivity groups. Another appendix section is proposed to provide further insight as to possible effects relative humidity may have on the corrosion kinetics experienced. Proposed: §2. Specifications for other environmental conditions. as well as office electronic. switches. data storage hardware. terminals. desktop computers. Caution should be used under this circumstance or when a combination of factors approach or surpass class “X”. Specific examples of electronic office equipment include: laptop computers." Obtaining the guidance of a chemical specialist is suggested when this condition occurs. routers. • It has been suggested that comparing the reaction rates between these metals can infer influences of relative humidity and that this information be included as part of an informational appendix. This document is one of a series of standards on environmental conditions for electronic equipment.1 – This standard covers airborne contaminants and biological influences that affect industrial process measurement and control equipment. Obtaining the guidance of a chemical or biological specialist is suggested when this type of condition occurs. and faxes. and network equipment. networking and data center equipment. including nuclear radiation and hazardous atmospheres.This document is one of a series of standards on environmental conditions for process measurement and control systems. Proposed: The purpose of this standard is to classify airborne contaminants that may affect electronic hardware such as process measurement and control equipment. switches. copiers. §2. workstations. • One recommendation is that the four severity levels described in Table 3 be expanded to five levels. and climate control such as HVAC equipment. Some examples of networking equipment include telecommunications hardware. §2. electronic office equipment.6 – CAUTION – It is possible that airborne contaminants not listed in this document could cause equipment damage. This is for several primary reasons: 1) the stated gas concentrations and corresponding copper reactivity levels generally do not agree. are beyond the scope of this standard. displays. and routers. power distribution equipment. displays.6 – CAUTION – Airborne or biological contaminants not listed in this document could cause equipment damage.1 .Reactivity Recommended changes to this include the inclusion of silver reactivity monitoring as a metric along with copper. The silver coupons will be used primarily for their ability to discern chlorine in the subject environment. data storage hardware. data centers. The classification system provides users and manufacturers of electronic hardware with a means of specifying the type and concentration of airborne contaminants to which a specified piece of electronic hardware may be exposed. These two groups would be used to indicate whether or not chlorine had detected through silver film analysis. . servers.
G2. Because no data exist correlating all possible contaminant of contaminant concentration combinations or the effects of temperature and relative humidity.5 and <1.5 Low humidity attenuation (LHA) Section 6. One proposed addition to an appendix is shown in the second of two tables below. Attempt to do so would result in immediate catastrophic failure. This new level would be defined as an environment in which the operation of process and control equipment is not practical. If these new groups are accepted. A proposal has been offered which correlates the ratio of the silver sulfide/cult of copper sulfide components to humidity effects. It is known that the presence or absence of free moisture may accelerate or attenuate the corrosion reaction. and Harsh.5 No humidity effects (NHE) ≥1. The former G1. or MTBF. Table III – Humidity Effects Corresponding to Silver Sulfide/Copper Sulfide Ratios Ag2S/Cu2S Ratio Effect ≤0.1 – Relative Humidity This section will be reworded for clarity and correctness. and the chloride containing group (GC). this table would be included as an aid in understanding the complexities involved in direct gas concentration monitoring. • A final appendix section is proposed. or no humidity effects. one additional severity level may be considered. Table IV – Reduction of MTBF ISA Severity Class Percent Reduction G1 None G2 <25 G3 <50 G4 <75 GX ≥75 . These effects are described as low humidity attenuation. • The concentration levels of individual gases currently in Table 3 that contribute to these reactivity rates will be moved to a new table in an informative appendix.3 – Explanation of Contaminant Severity Levels Two additional corrosion reactivity groups have been proposed. New Appendix – Reduction of Mean Time Between Failure by Severity Level Mean time between failure. These two reactivity groups would be designated as the primary sulfide group (GS). no silver chloride formed. respectively. The current GX – Severe level would be redesignated as G4 – Severe and the new fifth level would be GX – Extreme. It will also include a reference to the appropriate sections of the appendix pertaining to relative humidity. which are differentiated by the absence or presence of reactive chlorides in the reduced silver films. which will offer some idea of the reduction in mean time between failures (MTBF) when equipment is continuously exposed to contaminants at various severity levels. Moderate.2. high humidity acceleration. Section 6. This new table is described more fully in the following sections. This is represented in Table III below. Section 7 – Biological influences Remove this section and all references to “living” contaminants altogether. is a measure of the time interval expected between faults from a representative sampling of like components or systems. were silver chloride is present. and G3 levels would remain the same as Mild.5 High humidity acceleration (HHA) >0.
QCM-based corrosion monitoring will be proposed for inclusion into the next revision of the standard. Whereas reactivity monitoring with CCCs may require exposure times of between 30 and 90 days before analysis and reporting. it is expected that review of this data will reveal as of yet undiscovered trends with her between the different severity classes and coupon types. The prevailing use of silver maintains the same corrosion rates and severity levels as for copper coupons with the overall severity being determined by the higher of the two. etc.000 pairs of coupons. All written reviews will be addressed by the committee and any changes (additions or deletions) agreed upon by all parties. Once this has been accomplished. At the very least.04 is being prepared and will be discussed in the S71 Committee.STATUS OF 71. Once approved. criticisms. ** By paired coupons and is meant a copper and silver coupon exposed simultaneously in a subject environment for an equal period of time. CONCLUSIONS Whereas silver reactivity monitoring has been accepted as necessary for a number of years. When this form of reactivity monitoring is incorporated into the Standard and gains even wider acceptance. Specific corrosion films cannot be determined without destructive testing of the QCM sensors. This database will be set up with data from paired copper and silver coupons** exposed in both industrial and non-industrial environments with an indication of whether the equipment in the spaces monitored are RoHS-compliant. . Over 4. the standard will be submitted to the ISA for publication. FUTURE ACTIVITY FOR STANDARD 71. these devices currently have some shortcomings when compared to coupon monitoring. and will be included in the next revision of ISA Standard 71. Because the mechanisms of copper and silver corrosion are different.04 Corrosion Classification Database A corrosion classification database will be established and maintained by the ISA. concerns. Many comments. Gold Pore Corrosion Monitoring Some are using gold-plated corrosion classification coupons in addition to copper and silver coupons. The dominant monitor type on the market employs copper and silver- plated quartz crystal microbalances (QCM) and have supporting data published that correlates weight gain on the crystal caused by the build-up of corrosion products to changes in crystal frequency. statistical analysis may lead to reformulation of these levels. One of the main uses of this database is to establish and refine silver reactivity levels.04 REVISION A final draft of the proposed revisions to Standard 71. This type of corrosion monitoring has been examined by a number of organizations but little progress had been made in the development of a “visual” gold coupon standards and work has apparently stalled. it will be submitted to the ISA Standards and Practices Board for consideration for public review. Real-Time Corrosion Monitoring. are anticipated due to the wide acceptance of the standard in the processing control industry and a keen interest exhibited in the preparation of the draft revision. reactivity monitoring with metal coupons appears to be headed for ancillary role as opposed to its current everyday status. which in turn is correlated to corrosion film thicknesses. Although the real-time monitors will allow instant access to corrosion data. Good reproducibility of results has been demonstrated with this real-time monitor and side-by-side comparisons of this methodology with both copper and silver coupon reactivity monitoring have shown a high degree of correlation. Solicitations are being made for contribution to this database which by some accounts can consist of data from more than 70. electronic corrosion monitors capable of producing useful data almost immediately have been developed and are being used in good success.000 of these pairs also have a corresponding gold coupon in anticipation that gold coupons may one day be used along with copper and silver. The main trade-off is that corrosion is reported only in terms of total corrosion. it is real-time corrosion monitoring that has been deemed as vital by many in the process control industries.04.
1990. By reporting only copper corrosion. England. Muller. CA. 1999. It is possible that all of the corrosion occurred on a single day due to a chemical leak. 64. copper-only reactivity monitoring will not or cannot conclusively determine the presence or absence of environmental chlorine or sulfur oxides.O. 1994.. without revision.” Pulp & Paper. 165-169. Anaheim.A. [10] C. Studies of Natural and Laboratory Environmental Reactions on Materials and Components. National Coalition on Indoor Air Quality. October 1991. the findings described above. Manchester. England. C.eu/LexUriServ/LexUriServ.04 is in need of major revisions to incorporate the use of silver reactivity monitoring as a metric and to take advantage of technology advances in real-time corrosion monitoring.europa. International Society for Automation. [4] W. for more than 30 years.O. both incremental and cumulative is useful in predicting long-term equipment reliability. Short and long-term corrosion rate information.” PITA Annual Technical Conference.” Proceedings of Advancements in Instrumentation and Control. and W. [8] England.H. The development of real-time corrosion monitors measuring both cumulative and incremental corrosion has eliminated these limitations associated with corrosion classification coupons. Muller. Specifically. Instrument Society of America. North Carolina. Part 4: Corrosive and Erosive Influences.. [6] C.G. 1991.” Proceedings of Healthy Buildings '94.O. September 14-16. McShane. Geneva.” International Electrotechnical Commission. “Standard for Operating Conditions of Industrial Computer Control System. [5] Muller. 0019 – 0023. A. Battelle Columbus Laboratories.04. “Multiple Contaminant Gas Effects on Electronic Equipment Corrosion: Further Studies. [7] C. Instrument Society of America. “Electronic Monitoring of Indoor Atmospheric Pollutants.J. Through the regular ISA standard review processes. significant changes have been proposed for standard S701. 2. Affolder. Vol.. From the examination of the available corrosion film data for copper and silver components.J. England. Muller. the ability to measure the short-term variations lasting several hours or days is desirable. it is apparent that one cannot accurately determine the corrosive potential of an environment when following the current methodology of Standard 701. Vol. See http://eur- lex. spill. and ongoing research. 1987. Reports to Environmental Studies Group. [11] European Union (EU) directive 2002/95/EC “on the Restriction of the use of certain Hazardous Substances in electrical and electronic equipment.” Japan Electronic Industry Development Association.” Proceedings of Advances in Instrumentation and Control. Corrosion Journal 47(22):146-151.. “Applications of a Real-Time Electronic Contact Corrosion Monitor. 1978-1987. et al.do?uri=OJ:L:2003:037:0019:0023:EN:PDF (accessed March 2011). [3] Standard: JEIDA-29-1990.G. Anaheim. 46: pp 929-955. C. Switzerland. W. 13/02/2003 P. “Combination Corrosion Coupon Testing Needed for Today’s Control Equipment. [9] Weiller. one can and often does make an incorrect assessment of the environment in question.O. ISA Standard 71. February.SUMMARY The passage of various “lead-free” regulations has resulted in a significant up-tick of corrosion-related failures of new compliant electronic equipment. even with a breakdown of the individual films.G.” Official Journal L 037. Multiple Contaminant Gas Effects on Electronic Equipment Corrosion. W. Research Triangle Park. This is true for industrial application but even more so in non-industrial applications which would have been considered benign had it not been for RoHS Although having been accepted and in wide use. pp 241-243.04.04-1985 – Environmental Conditions for Process Measurement and Control Systems: Airborne Contaminants. No. 1991. Therefore. Abbott. and W. they do not allow for the measurement of any variations that may have occurred during the exposure period. REFERENCES [1] ISA (1985) Standard ISA-71. 1990. [2] Standard: IEC 60654-4 (1987-07) “Operating Conditions for Industrial-Process Measurement and Control Equipment. or some other upset condition common in the process industries. Tokyo. While CCCs are good for the measurement of average corrosion rates. . “Developments in Measurement and Control of Corrosive Gases to Avoid Electrical Equipment Failure. pp.
cfm?PROC_ID=1765. Inc. In: Proceedings of the 32nd International Symposium for Testing and Failure Analysis. Texas. 2008..smta. Austin. Particulate and Gaseous Contamination Guidelines for Data Centers.[12] Mazurkiewicz. October 4-8. F.org/knowledge/proceedings_abstract. California. P. San Diego. G. and Muller. C. [15] ASHRAE 2009. 12-16 November. pp 469-473. [14] Anonymity.” Proceedings of AIMS Harsh Environments Symposium. (2006) Accelerated Corrosion of Printed Circuit Boards due to High Levels of Reduced Sulfur Gasses in Industrial Environments. Created Others - Reliability Reports from the Field. K. “RoHS Solved One Problem.. Atlanta: American Society of Heating. SMTA International Electronics Exhibition 2009. Lembach. Hua. Refrigerating. and Air-Conditioning Engineers. 2009. . [13] Crosley. http://www.
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