esd vs anti

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ESD vs Anti-Static vs Dissipative vs Conductive vs Insulative

byAN DY on JULY 9, 2007

In order to distinguish

the differencesbetween these five terms,

you need to know what each one means.

ESD(as definedin the previous post) is

an acronymforelectrostatic discharge.

Many times it is used incorrectly as a termfor something that is electrostatic

discharge safe.

The terms anti-static, conductive, and dissipativeare all

terms that subdivide ESDinto more detail.Somethinginsulativeis not considered ESD safe.Materials are divided into these terms based on theirindividual surface resistance. Surface resistance is

a measurementof how easily an electric charge can travel

across a medium.Conductive materialsare materials thathave a surface resistance of less than 1 x 10 5ohms/square.Dissipative items have a surface resistance of more than 1 x10 5ohms/square but less than 1 x10 11ohms/square.

Anti-static materials are generallyreferred to as any material

which inhibitstriboelectric charging. This kind of charging is

the buildup of an electric charge by the rubbing or contact withanother material. An insulative material is one that has a

surface resistance of greater than 1 x 10 12ohms/square.For more ESD productsand ESD information, visit theAll-

Spec websiteor theElectrostatic Discharge Associationwebsite.
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When youre looking to buy safety footwear, dont assume things. Ask questions, even if you think you already know

the answers. At the end of the day, there are no short cuts for safety. Whether youre buying footwear just for yourself

or for the entire workforce, you must choose the safest option. And because there are so many options to choose

from - non-conductive, antistatic, conductive - there is no better approach than to do your homework. Ask the

questions and get factual answers on whats best for your specific environment.

GLOBAL FOOTWEAR STANDARDS REFERENCE GUIDEWork Environment HazardsEvery work environment exposes workers to different types of hazards. Each employer is required to perform aworkplace assessment to determine the presence of work hazards and the need for personal protective equipment(PPE). In the case of foot injuries, common potential hazards include falling or rolling objects, electrical shock orpiercing of footwear soles with sharp objects. There are countless situations and hazards that occur in the workplaceeveryday that can cause serious foot injury. The best protection from the work hazards that you can and cannotanticipate is quality PPE. For footwear, Red Wing Shoe Company is committed to providing quality, safety footwearfor every worker every day.

The footwear protection guidelines shown on this page were gathered to provide a general overview and quickcomparison of global footwear safety standards. This guide is not a definitive standard and we encourage you to referto the official safety standard for clarification.

Testing Methods

1. Impact ResistanceThis is a test of a shoe's capacity to protect the toe area of the foot against falling objects. ForImpact testing, a weight is dropped onto the protective toe cap area of the footwear. Each standard identifies theatmospheric conditions of the test, the shape of the striker, the amount of weight and distance from which the weightmust be dropped, the velocity of the drop and the impact energy delivered. The clearance remaining inside the capafter impact is then determined.

2. Compression ResistanceThis is a test of a shoe's capacity to protect the toe area of the foot against heavyrolling objects. For Compression testing, the toe cap area of the footwear is compressed between parallel platens at agiven rate of speed until the required compressive force is reached. The clearance remaining inside the cap after thecompression is then determined.

3. Metatarsal ProtectionThis test measures the level of protection provided to the upper foot (metatarsal bones)and toe areas. Footwear offering metatarsal protection is designed to prevent or reduce injuries when the toe andmetatarsal areas of the foot are exposed to "drop" hazards. Metatarsal protection safety shoes may be constructedwith either internal or external metatarsal guards. For testing, a wax form is fit into the footwear and a weight isdropped onto the protected metatarsal area of the footwear, similar to the impact test. The height of the wax formafter impact is then determined.

4. Puncture ResistancePR footwear reduces the possibility of sharp objects (nails, glass or metal) penetratingthrough the outsole causing injury to the foot. Protection is provided by a steel or puncture resistant materialimbedded in the insole of the footwear. Puncture resistant devices are tested using a sharp steel pin forced into thedevice at a given speed. The force required to puncture the device is measured. The devices are also tested forflexibility and corrosion resistance.

5. Electric Shock ResistanceThis type of footwear is designed to provide a secondary source of protection againstaccidental contact with live electrical circuits, electrically energized conductors, parts or apparatus under dry

conditions, reducing the potential of electric shock. Protection is severely deteriorated in wet environments. To testelectric shock resistant properties, the footwear is placed on a metal mesh platform acting as a large electrode. Thefootwear is filled with small metal spheres and a second electrode is placed within the spheres. A specified highvoltage is applied to the footwear through the metal platform for a given length of time. Resistance is determined bythe current flow (or leakage) through the footwear.

6. Static DissipationThis footwear is constructed to reduce excess static electricity by conducting the charge fromthe body to the ground. The footwear allows for limited protection against incidental contact with live electrical circuitsand should not to be worn around highly charged electrical equipment. It is recommended that static dissipativefootwear be worn only in clean environments and worn in conjunction with static dissipative flooring.


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Test methods for Static Dissipation vary by standard, using either human subjects or metal spheres inside footwearthat are placed on either a wet or dry base electrode plate. A specified voltage is applied for a prescribed time andthe electrical resistance is measured. Test conditions also vary in specified atmospheric conditions.

7. ConductivityConductive footwear is designed to facilitate/discharge static electricity from your body through your shoes into grounded floors. The floors must be grounded sothat a charge can be dissipated properly, minimize static electricity and reduce the possibility of ignition of volatile

chemicals or explosives. To test for conductivity, the footwear is placed on a base electrode plate. Depending on thestandard, it is tested dry or in water. The footwear is filled with small metal spheres and a second electrode isembedded in the spheres. A specified voltage is applied for a prescribed time and the electrical resistance ismeasured

Comparison of Footwear Safety StandardsStandards compared in this section include Impact, Compression, Metatarsal, Puncture Resistance, Electric Shock,Static Dissipation and Conductive requirements.

Impact Requirement

ASTM

Class 75(I) footwear for men shall demonstrate a minimum interior height clearance of (75 ft-lbf). Applies to both

steel and composite protective caps.

Class 75footwear for women shall demonstrate a minimum interior height clearance and 11.9 mm (0.468 in.)during impact exposure of 101.7 J (75 ft-lbf). Applies to both steel and composite protective caps.

CSA

Grade 1Footwear for men and women must withstand an impact energy of 125 joules (the equivalent of a 50 lb. objectdropped at a height of 22 inches) with no cracking through the thickness of the cap wall.

Samples must be conditioned and tested at both 70 and 0 degrees Fahrenheit. The minimum interior heightclearance varies according to shoe size (ranging from10.7 mm for a womans size 3 to 14.2 mm for a mans size 14).Protective toecaps must show no signs of corrosionwhen exposed to a 5% salt solution for 24 hours.

ENSafety footwear must be tested in accordance with EN ISO 20344:2004. After an impact energy of 200 joules isdelivered, the clearance under the toe cap shall be the following:

Sizes:Min.

French English Clearance< 36 < 3.5 12.5 mm37-38 4-5 13.0 mm39-40 5.5-6.5 13.5 mm41-42 7-8 14.0 mm43-44 8.5-10 14.5 mm45+ 10.5 + 15.0 mm

SINGAPORETested in accordance with SS 513 : Part 2 : 2005

Singapore test methods and requirements are identical to the EN Standard.

Compression Requirement

ASTM

Class 75(C) footwear for men shall demonstrate a minimum interior height clearance of 12.7 mm (0.50 in.) duringexposure to a compressive force of 11,121 newtons (2500 lbf). Applies to both steel and composite protective caps.


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Class 75footwear for women shall demonstrate a minimum interior height clearance of 11.9 mm (0.468 in.) duringexposure to a compressive force of 11,121 newtons (2500 lbf). Applies to both steel and composite protective caps.

CSAThere is no compression standard for CSA.

EN

Safety footwear must be tested in accordance with EN ISO 20344:2004. The clearance under the toe cap at acompression load of 15,000 newtons shall be the following:

Sizes:Min.

French English Clearance< 36 < 3.5 12.5 mm37-38 4-5 13.0 mm39-40 5.5-6.5 13.5 mm41-42 7-8 14.0 mm43-44 8.5-10 14.5 mm45+ 10.5 + 15.0 mm



Metatarsal Requirement

ASTMMetatarsal (Mt) protective footwear must first meet the Class 75 requirements for impact and compression resistantfootwear.

The height of the wax form used to measure metatarsal protection of mens footwear shall be a minimum of 25.4 mm(1.0 inch) after exposure of impact energy of 101.7 J (75 ft-lbf).

For womens metatarsal protection there shall be a minimum of 23.8 mm (0.937 in.) after exposure of impact energyof 101.7 J (75 ft-lbf).

CSAMetatarsal protective footwear must meet the Grade 1 Toe Cap requirement for impact resistant footwear.

The Metatarsal protector must overlap the protective toe cap. Metal metatarsal guards must show no signs ofcorrosion when exposed to a 5% salt solution for 24 hours.

ENSafety footwear must be tested in accordance with EN ISO 20344:2004. The minimum clearance at the moment ofimpact shall be:

Sizes:Min.

French English Clearance< 36 < 3.5 37.0 mm

37-38 4-5 38.0 mm39-40 5.5-6.5 39.0 mm41-42 7-8 40.0 mm43-44 8.5-10 40.5 mm45 + 10.5 + 41.0 mm




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Puncture Resistant Requirement

ASTMPuncture Resistant (PR) footwear must also meet the Class 75 requirements for impact and compression resistantfootwear.

The puncture resistant insole must withstand a puncture force of 270 lbs., will not crack after 1.5 million flexes and

show no signs of corrosion when exposed to a 5% salt solution for 24 hours.

CSAFootwear with protective sole inserts must also meet the Grade 1 requirement for impact resistant footwear. Theprotective insert shall cover the sole including the heel area.

The puncture resistant insole must withstand a puncture force of 1200 newtons, will not crack after 1.5 million flexesand show no signs of corrosion when exposed to a 5% salt solution for 24 hours.

Footwear is labeled with a green triangle.

ENPenetration Resistant Footwear must be tested in accordance with EN ISO 20344:2004. The force required topenetrate the sole unit shall not be less than 1,100 newtons. The metal insole must not crack after 1 million flexesand show no more than 5 areas of corrosion smaller then 2.5 mm2 when exposed to a 1% salt solution for 7 days.

Non-metallic penetration resistant insoles will be tested according to EN 12568:1998.



Electric Shock Resistance Requirement

ASTMElectric Shock Resistant (EH) footwear shall also meet the Class 75 requirements for impact and compressionresistant footwear.

Must withstand the application of 14,000 volts at 60 Hz for 1 minute with no current flow or leakage in excess of 3.0milliamperes under dry conditions.

CSAElectric Shock Resistant (ESR) footwear must also meet the Grade 1 requirement for impact resistant footwear.

ESR footwear must withstand a test potential of 18,000 volts at 60Hz for 1 minute without disruptive discharge toground. Under dry conditions, the leakage current shall not exceed 1 milliamperes.

Footwear is labeled with an orange omega on a white rectangle.

ENElectrical Insulation is determined according to the method described inEN 50321:1999. Footwear must comply with electrical class O or OO.

SINGAPORE

Tested in accordance with SS 513 : Part 2 : 2005


Static Dissipative Requirement

ASTMStatic dissipative (SD) footwear shall also meet the Class 75 requirements for impact and compression resistantfootwear.


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SD footwear shall reduce the accumulation of excess static electricity while maintaining a level of electrical resistancebetween 106 ohms (1 megohm) and 108 ohms (100 megohms).

CSAStatic dissipative footwear may or may not meet Grade 1 impact resistance. It is tested in water and the electricalresistance shall fall within a range of 106 ohms (W) to 108 ohms (W) for a period of 5 seconds.

Footwear is labeled with a green SD on a yellow rectangle.

ENAntistatic Footwear must be tested in accordance with EN ISO 20344:2004 after conditioning in both wet and dryconditions. Electrical resistance shall be above100,000 ohms (105 W ) and less than or equal to 1,000 megohms (109 W).



Conductive Protection Requirement

ASTM

Conductive (CD) footwear must also meet the Class 75 requirements for impact and compression resistant footwear.

Footwear shall dissipate static electricity from the body to reduce the possibility of ignition of volatile compounds.Electrical resistance must range between 0 to 500,000 ohms.

CSAConductive footwear must meet also the Grade 1 requirement for impact resistant footwear and must electricallyground the foot.

The footwear is tested in water and the electrical resistance shall fall within a range of 0 to 500,000 ohms (W) for aperiod of 5 seconds.

Footwear is labeled with a black C on a red rectangle.

ENThe electrical resistance of Conductive footwear must be tested in accordance with EN ISO 20344:2004 afterconditioning in a dry atmosphere and cannot be greater than 100,000 ohms (W).



Other Requirements

ASTMASTM safety footwear must be tested by a third party laboratory. The footwear does not need to be retested unlessthe standard is revised or the platform construction changes.

CSACSA safety footwear and the factories that produce the footwear must be certified by CSA International. CSAperforms regular audits of both the factory and the footwear. One pair for every 500 pair produced must be tested bythe manufacturing facility.

ENEN safety footwear must be tested by an EN certifying body. EN certification encompasses far more than just thesafety aspects of the shoe. All components are individually tested as well as the fit and comfort of the footwear. ENhas severalcategories of safety footwear depending on performance and the footwear is labeled accordingly. The footwear doesnot need to be retested unless the standard is revised or the platform construction changes.


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SINGAPORESingapore safety footwear and the factories that produce the footwear must be tested by an approved certifying body.Singapore certification encompasses far more than just the safety aspects of the shoe. All components areindividually tested as well as the fit and comfort of the footwear. Singapore has several categories of safety footweardepending on performance and the footwear is labeled accordingly. Singapore performs regular audits of the factoryand each batch of footwear is inspected upon entry into Singapore.

The Standards For Footwear Protection

ASTMThe American Society for Testing and Materials (ASTM) International, a preeminent source for technicaldocumentation for industries world wide announced that the former ANSI Z41 Standard for Personal ProtectionProtective Footwear waswithdrawn in 2005. It was replaced by two new ASTM standards, titled F 2413-05 Standard Specification forPerformance Requirements for Foot Protection and F 2412-05 Standard Test Methods for Foot Protection. Thesenew standards provide safety and performance standards previously put forward by ANSI since 1967.

ASTM websiteWWW.ASTM.ORG

CAN/CSA-Z195-02 Protective Footwear

A National Standard of Canada approved March 2003

The Canadian Standards Association (CSA) was chartered in 1919 and is a non-profit, voluntary membershipassociation engaged in standards development and certification activities. The standards are used widely by industryand commerce and often adopted by municipal, provincial and federal governments in their regulations.

CSA Standard Z195, Protective Footwear, covers the design and performance requirements for protective footwear,including toe protection, sole puncture protection, electric-shock resistant soles and other requirements relating tometatarsal protection and general stability of the footwear.

CSA websiteWWW.CSA.CA

EN ISO 20345:2004The European Standard was approved by CEN (European Committee for Standardization) on 2 January 2004 andsupersedes EN 345. This European Standard specifies basic and additional (optional) requirements for safetyfootwear. The European Standard exists in three official versions (English, French and German). A version in anyother language made by translation under the responsibility of a CEN member into its own language and notified tothe Central Secretariat has the same status as the official versions. CEN members are the national standards bodiesof Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary,Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia,Slovenia, Spain, Sweden, Switzerland and United Kingdom.

EN website www.iso.org

Singapore Standard SS 513:2005 (ISO 20345:2004)This Singapore Standard was prepared by the Technical Committee on Personal Safety and Ergonomics under thepurview of the General Engineering and Safety Standards Committee. This standard, comprised of Part 1 and Part 2,supersedes SS 105: 1997Safety footwear. Part 1 specifies basic and additional (optional) requirements for safety

footwear and Part 2 specifies methods for testing footwear designed as personal protective equipment.

Part 1 of SS 513 is identical with EN ISO 20345:2004Personal protective equipment- Safety footwear. Part 2 ofSS 513 is identical with EN ISO 20344:2004 Personal protective Equipment- Test Methods for Footwear.

Singapore Standard website www.standards.org.sg

DisclaimerRed Wing Shoe Company, Inc. expressly states that this guide does not represent the actual formal standard it onlyprovides a quick comparison and general descriptions of testing methods and requirements. Refer to the actualpublished standards for specific requirements.
http://www.redwingsafety.com/intl/content/www.astm.orghttp://www.redwingsafety.com/intl/content/www.astm.orghttp://www.redwingsafety.com/intl/content/www.astm.orghttp://www.csa.ca/http://www.csa.ca/http://www.csa.ca/http://www.csa.ca/http://www.redwingsafety.com/intl/content/www.astm.org


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This general standards reference guide does not purport to address all of the safety concerns, if any, associated withits use. It is the responsibility of the user of these standards to establish appropriate safety and health practices anddetermine the applicability of regulatory limitations prior to use.

The standards are subject to revision at any time by the responsible technical committee(s). ASTM standards mustbe reviewed every five years and if not revised, either re-approved or withdrawn.

ReferencesASTM Web Site:WWW.ASTM.ORGCanadian Standards Association (CSA):WWW.CSA.CAEuropean Standard (EN):WWW.ISO.ORGSingapore Standard (SS):WWW.STANDARDS.ORG.SG

American National Standards Institute (ANSI):WWW.ANSI.ORGInternational Organization for Standardization (ISO):WWW.ISO.CHOccupational Safety and Health Administration (OSHA):HTTP://WWW.OSHA.GOV

Basics of Electrostatic Discharge

Part Three

An Overview of ESD Control Procedures and Materials

by

The ESD Association Special to Compliance Engineer ing Magazine

May 5, 1998

In our previous column we introduced you to four principles of static control

and nine key elements of ESDprogram development and implementation. In

this column, we will cover some of the primary specific static control

procedures and materials that become part of your program. First, a quick

review.

Basic Principles of Static Control

We suggested that static control programs become more effective and less

complex if we focus on just four basic principles of static control as follows:

Design In Immunityby designingproducts and assemblies to be as immune

as reasonable from the effects of ESD.
http://www.redwingsafety.com/intl/content/www.astm.orghttp://www.redwingsafety.com/intl/content/www.astm.orghttp://www.redwingsafety.com/intl/content/www.astm.orghttp://www.csa.ca/http://www.csa.ca/http://www.csa.ca/http://www.iso.org/http://www.iso.org/http://www.iso.org/http://www.standards.org.sg/http://www.standards.org.sg/http://www.standards.org.sg/http://www.redwingsafety.com/intl/content/www.ansi.orghttp://www.redwingsafety.com/intl/content/www.ansi.orghttp://www.redwingsafety.com/intl/content/www.ansi.orghttp://www.redwingsafety.com/intl/content/www.iso.chhttp://www.redwingsafety.com/intl/content/www.iso.chhttp://www.redwingsafety.com/intl/content/www.iso.chhttp://www.osha.gov/http://www.osha.gov/http://www.osha.gov/http://www.osha.gov/http://www.redwingsafety.com/intl/content/www.iso.chhttp://www.redwingsafety.com/intl/content/www.ansi.orghttp://www.standards.org.sg/http://www.iso.org/http://www.csa.ca/http://www.redwingsafety.com/intl/content/www.astm.org


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Eliminate and Reduce Generationby reducingand eliminatingstatic

generatingprocesses, keeping processes and materials at the same

electrostatic potential, and by providing appropriate ground paths to reducecharge generation and accumulation.

Dissipate and Neutralizeby grounding, ionization, and the use ofconductive and dissipative staticcontrol materials.

Protect Products from ESDwith proper grounding or shunting and the use

of static controlpackagingand materials handlingproducts.

In most facilities, our static control efforts center around the last three

principles. In this column we will concentrate on the primary materials and

procedures that eliminate and reduce generation, dissipate and neutralizecharges, or protect sensitive products from ESD.

Identifying the Problem Areas

You may also recall from our previous article that we suggested that there

were at least nine critical elements to successfully developing andimplementing an effective ESD control program. Selecting appropriate static

control materials and developing and implementing effective procedures

begins with two of these critical elements:

Identifying and classifying ESD sensitive items used in your facility.

Evaluating your facility and processes to determine the areas that need to be

protected.

One of the first questions answeredwith this information is "Which areas of

our facility need ESD protection?" Often you will find that there are more

areas that require protection than you originally thought, usually wherever

ESDS devices are handled. Typical areas requiring ESD protection are

shown in Table 1.


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Personnel and Moving Equipment

In many facilities, people are one of theprimegenerators of static electricity.

The simple act of walking around or repairing a board can generate several

thousand volts on the human body. If not properly controlled, this static

charge can easily discharge into a static sensitive device-a human body

model (HBM) discharge.


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Even in highly automated assemblyand test processes, people still handle

static sensitive devicesin the warehouse, in repair, in the lab, in transport.

For this reason, static control programs place considerable emphasis oncontrolling personnel generated electrostatic discharge. Similarly, the

movement of carts and other wheeled equipment through the facility also can

generate static charges that can transfer to the products being transported on

this equipment.

Wrist Straps

Typically, the primary means of controlling static charge onpersonnelis

with a wrist strap. When properly worn and connected to ground, a wriststrap keeps the person wearing it near ground potential. Because the person

and other grounded objects in the work areaare at or near the same potential,there can be no hazardous discharge between them. In addition, static charges

are safely dissipated from the person to ground and do not accumulate.

Wrist strapshave two major components, the cuff that goes around the

person's wrist and the ground cord that connects the cuff to the commonpoint ground. Most wrist straps have a current limiting resistor molded into

the ground cord head on the end that connects to the cuff. The resistor most

commonly used is a one megohm, 1/4 watt with a working voltage rating of

250 volts.

Wrist straps should be tested on a regular basis. Daily testing or continuousmonitoring is recommended.

Floors, Floor Mats, Floor Finishes

A second method of controlling electrostatic charge on personnel is with theuse of ESD protective floors in conjunction with ESD control footwear or

footstraps. The combination of floor materials and footwear provides


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a groundpath for the dissipation of electrostatic charge, thus reducing the

charge accumulation on personnel and other objects to safe levels. In

addition to dissipating charge, some floor materials (and floor finishes) also

reduce triboelectric charging. The use of floor materials is especially

appropriate in those areas where increased personnel mobility is necessary.

In addition, floor materials can minimize charge accumulation on chairs,carts, walking stackers, lift trucks and other objects that move across the

floor. However, those items require dissipative or conductive casters orwheels to make electrical contact with the floor.

Shoes, Grounders, Casters

Used in combination with ESD protective floor materials, static control

shoes, grounders, casters and wheels provide the necessary electrical contactbetween the person or object and the floor material. Insulative footwear,

casters, or wheels prevent static charges from flowing from the body to thefloor to ground.

Clothing

Clothing is a consideration in some ESD protective areas, especially in clean

rooms and very dry environments. Clothing materials can generate

electrostatic charges when they contact and separate from other objectsand

the clothing itself. These charges may discharge into sensitive components or

create electrostatic fields that may induce charges on the human body.

Although a person may be grounded, that does not mean that insulativeclothing fabrics can dissipate a charge to that person's skin and then toground. Clothing usually is electrically insulated or isolated from the body.

Static control garments are intended to minimize the effects of electrostatic

fields or charges that may be present on a person's clothing.

Figure 1--Typical ESD Work Station


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Work Stations and Work Surfaces

Worksurfaces and work stations are important parts of an ESD protectiveprogram. Many ESDS devices and assembliesare handled, assembled or

repaired at work stations.An ESD protective workstation refers to the work area of a single individual

that is constructed and equipped with materials and equipmentto limit

damage to ESD sensitive items. It may be a stand-alone station in a

stockroom, warehouse, or assembly area, or in a field location such as a

computer bay in commercial aircraft. A workstation also may be located in a

controlled area such as a clean room.

The work station provides a means for connecting all worksurfaces, fixtures,handling equipment, and grounding devices to a common point ground. In

addition, there may be provision for connecting additional personalgrounding devices, equipment, and accessories such as constant ground

monitors and ionizers. The key ESD control elements comprising mostworkstations are a static dissipative work surface, a means of grounding

personnel (usually a wrist strap), a common grounding connection, and

appropriate signage and labeling. A typical work station is shown in Figure3.

Static protective worksurfaces with a resistance to ground of 106 to 109

provide a surface that is at the same electrical potential as other ESD

protective items in the workstation. They also provide an electrical path toground for the controlled dissipation of any static potentials on materials that

contact the surface. The work surface also helps define a specific work areain which ESD sensitive devices may be safely handled. The worksurface isconnected to the common point ground.

Production Equipment and Production Aids

Although personnel generated static is typically the primary ESD culprit in

many environments, automated manufacturing and testequipment can also

pose an ESD problem. For example, a device may become charged from

sliding down the feeder. If the device then contacts the insertion head oranother conductive surface, a rapid discharge occurs from the device to the

metal object--a Charged Device Model (CDM) event.

In addition, various production aids may also pose an ESD problem.Production aids are those materials, tools and fixtures that help to produce

finished products but do not become part of the finished product. Some

examples are hand tools, soldering irons, tapes, solvents, and so forth.

Grounding is the primary means of controlling static charge on many


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production aids and equipment. The metal chassis or conductive enclosure of

equipment that uses utility power is required by the National Electrical Code

to be connected to the equipment ground (the green wire) in order to carryfault currents. This ground connection also will function for ESD purposes.

All electrical tools and equipment used to process ESD sensitive hardware

require the 3 prong grounded type AC plug. Hand tools that are notelectrically powered, i.e., pliers, wire cutters, and tweezers, are usually

grounded through the ESD worksurface and the (grounded) person using the

conductive tools. Holding fixtures should be made of conductive or staticdissipative materials when possible. If a conductive fixture is not sitting on a

ESD worksurface or handled by a grounded person, a separate ground wire

may be required. For those items that are composed of insulative materials,

the use of ionization or application of topical antistats may be required tocontrol generation and accumulation of static charges.

Packaging and Materials Handling

Direct protection of ESDS devices from electrostatic discharge is provided

by packaging materials such as bags, corrugated, and rigid or semi-rigidpackages. The primary use of these items is to protect the product when it

leaves the facility, usually when shipped to a customer. In addition, materials

handling products such as tote boxes and other containers primarily provide

protection during inter or intra facility transport.

The main ESD function of these packaging and materials handling productsis to limit the possible impact of ESD from triboelectric charge generation,

direct discharge, and electrostatic fields. The initial consideration is to have

low charging materials (antistatic) in contact with ESD sensitive items. Forexample, the antistatic property would control triboelectric charge resultingfrom sliding a board or component into the package or container. A second

requirement is that the material provide protection from direct electrostatic

discharge as well as shield from electrostatic fields.Many materials are available that provide all three benefits: antistatic,

discharge protection, and electric field suppression. The inside of these

packaging material has an antistatic layer, but also has an outer layer with asurface resistance generally in the dissipative range.

A material's antistatic properties are not necessarily predicted by its

resistance or resistivity. However, resistance or resistivity measurements help

define the material's ability to provide electrostatic shielding or chargedissipation. Electrostatic shielding attenuates electrostatic fields on the

surface of a package in order to prevent a difference in electrical potential

from existing inside the package. Electrostatic shielding is provided by

materials that have a surface resistance equal to or less than 1.0 x 103 whentested according to EOS/ESD-S11.11 or a volume resistivity of equal to or

less than 1.0 x 103 ohm-cm when tested according to the methods of EIA

541.


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containing the ESDS item were connected to an auxiliary ground, a

difference in electrical potential could exist between the iron and the ESDS

item. This difference in potential could cause damage to the item.Any auxiliary grounds (water pipe, building frame, ground stake) present and

used at the workstation must be bonded to the equipment ground to minimize

differences in potential between the two grounds.

Ionization

As we have seen, the primary method of static charge control is direct

connection to ground for conductors, static dissipative materials, and

personnel. However, a complete static control program must also deal withisolated conductors that cannot be grounded, insulating materials (e.g., most

common plastics). Topical antistats often are be used to dissipate static

charges from these items under some circumstances

More frequently, however, air ionization can neutralize the static charge oninsulated and isolated objects by charging the molecules of the gases of the

surrounding air. Whatever static charge is present on objects in the work

environment will be neutralized by attracting opposite polarity charges fromthe air. Because it uses only the air that is already present in the work

environment, air ionization may be employed even in clean rooms where

chemical sprays and some static dissipative materials are not usable.Air ionization is not a replacement for grounding methods. It is one

component of a complete static control program. Ionizers are used when it is

not possible to properly ground everything and as backup to other static

control methods. In clean rooms, air ionization may be one of the few

methods of static control available.

Clean Room Requirements

While the basic methods of static control discussed here are applicable inmost environments, there are characteristics of the semiconductor

manufacturing process that require special considerations.

Many objects integral to the semiconductor manufacturing process (quartz,

glass, plastic, and ceramic) are inherently charge generating. Because thesematerials are insulators, this charge cannot be removed easily by grounding.

Many static control materials contain carbon particles or surfactant additivesthat sometimes restrict their use in clean rooms. The need for personnel

mobility and the use of clean room garments often make the use of wriststraps difficult. In these circumstances, ionization and flooring/footwear

systems become key weapons against static charge.

Identification


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A final element in our static control program is the use of appropriate

symbols to identify static sensitive devices and assemblies, as well asproducts intended to control ESD. The traditional symbols traditionally used

to identify ESDS parts or ESD control materials have been replaced with

newer, more appropriate symbols. ESD Association Standard ANSI ESDS8.1-1993 - ESD Awareness Symbolsprovides two symbols for ESD

identification.

Figure 3--ESD Susceptibility Symbol

The ESD Susceptibility Symbol (Figure 3), consists of a triangle, a reachinghand, and a slash through the reaching hand. The triangle means caution

and the slash through the reaching hand means Dont touch. Because of its

broad usage, the hand in the triangle has become associated with ESD and

the symbol literally translates to "ESD sensitive stuff, don't touch."The ESD Susceptibility Symbol is applied directly to integrated circuits,

boards, and assemblies that are static sensitive. It indicates that handling or

use of this item may result in damage from ESD if proper precautions are nottaken. If desired, the sensitivity level of the item may be added to the label.

Figure 4-- ESD Protective Symbol


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The ESD Protective Symbol (Figure 4), consists of the reaching hand in thetriangle. An arc around the triangle replaces the slash. This "umbrella" means

protection. The symbol indicates ESD protective material. It is applied to

mats, chairs, wrist straps, garments, packaging, and other items that provideESD protection. It also may be used on equipment such as hand tools,

conveyor belts, or automated handlers that is especially designed or modified

to provide ESD control.Neither symbol is applied on ESD test equipment, footwear checkers, wrist

strap testers, resistance or resistivity meters or similar items that are used for

ESD purposes, but which do not provide actual protection.

Summary

Effective static control programs require a variety of procedures and

materials. In this column, we have provided a brief overview of the mostcommonly used elements of a program. Additional in-depth discussion of

individual materials and procedures can be found in publications such as the

ESD Handbook published by the ESD Association.Your program is up and running. How do you determine whether it is

effective? How do you make sure your employees follow it? In our next

column, we will cover the topics of Auditing and Training.

For Additional Information

EOS/ESD S1.0-Wrist Straps

ANSI EOS/ESD S3.-Ionization

ESD STM 4.1 (Revised) ESD Protective Work Surfaces-Resistive

Characterization

ANSI EOS/ESD S6.1-Grounding -- Recommended Practice

ANSI ESD S7.-Floor Materials -- Resistive Characterization of Materials

ANSI ESD S8.-ESD Awareness Symbols

ESD S9.1-Resistive Characterization of Footwear

ANSI ESD S11.1-Surface Resistance Measurement of Static DissipativePlanar Materials

ANSI ESD S11.31-Evaluating the Performance of Electrostatic DischargeShielding Bags

ESD-DS1.1, Evaluation, Acceptance, and Functional Testing of Wrist

Straps.ESD STM2.1-Garments

ESD SP 3.3-Periodic Verification of Air Ionizers


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ESD ADV53.1- ESD Protective Workstations

ESD ADV2.0--ESD Handbook

EIA-541, Packaging of Electronic Products for Shipment

About the ESD Association

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Static Floor Systems

ring- we install electrical conductive/dissipative flooring solutions in areas where static

eration is undesirable and/or potentially dangerous, with such environments including:

nics & semi-conductor production

aceutical, biotechnology and medicalenvironments

otive and aeronautical component manufacturing

chemical industries- storage and processing areas

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"We carry out ant i -stat ic f loor ing p rojects acros s the ent i re

UK -contact us todayto get a free surv ey and quo tat ion fo r

you r pro ject ..."

nformation - Anti-Static Floor Installations In Industrial Buil

cle helps you to understand why anti-static (or static control) flooring solutions are absolutely critical to incorporate

ess areas and how the presently available solutions (such asthe anti-static flooring solutions installed by ATBthe risks associated with unwanted electrostatic discharge in factory/production areas.

ered in this article include:

uses of electrostatic discharge (ESD) in the workplace

al environments where static dischargepresents a serious safety risk

ti-static control flooring systems work

tions available for anti-static industrial flooring

considerations for anti-static flooring systems

es of static build-up/discharge

harge is commonly created by the friction of two materials, so that an imbalance oflectostatic field) is created on a material surface. An electrostatic discharge (ESD) is

transfer (spark) of electrostatic charge between objects at different electrostatic potentials

ct contact or induced by the electrostatic field.

dy is perhaps the most common ESD source, although a person will not feel thesescharges until the body is charged to approximately 3,000 - 4,000 volts - a tiny fraction of

sufficient to cause major damageto sensitive electronic components. One method for

ove static electricity from a persons body (and thus reduce the risk of electrostatico provide a floor surface that allows charge from shoe soles/heels to dissipate to the

nd".

static discharge be dangerous?

vironments wherever chemicals are used, there can be a potential risk of explosive vapour/ air mixtures forming-

provide sufficient energy to ignite such a mixture. In addition, the presence or attraction / adhesion of dust may als
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24/25

ctricity problems. Typical industrial areas which carry such risk include:

cal processing areas in factories

onductor and electronic assemblyareas

aceutical/biotechnology clean rooms, hospitals and similar medical environmentsrocessing areas (particularly those processing powdered foodstuffs)ter & server rooms

ustrial areas will have requirements for an antistatic flooring system.

ept of anti-static flooring coatings

r production environments use a concrete-based flooring surface - typically the watere pores of the concrete would be sufficiently conductive to dissipate any electrostaticsurface. However, the concrete floors of many factories require an epoxy or polyurethane

eatment in order to make the surface sufficiently hard wearing, hygienic, chemical or

sistant to be suitable for the particular processes/activities taking place on-site.

tings introduce a natural insulation to the concrete floor surfaceof the factory - this

he selection of a static controlled grade of resin flooring for the commercial/industrialentioned above.

ns for anti-static resin flooring systems

nherently conductive flooring resin bases - therefore static controlled flooring coatings are generally derived from n

which incorporate a small proportion of conductive additives (carbon powder or metal fibres).

main grades of anti-static floor - "static conductive" and "static dissipative" - the difference is the measured electricors are in the range 103to 106Ohms - dissipative floors are in the range 107to 109Ohms. A static conductive floor ce than a static dissipative floor (carrying static charge to ground much more efficiently) and is usually specified in

risk of explosion or contain extremely sensitive electronic equipment.

ronments dealing with high test voltages, a dissipative floor should be installed so that the static charges can be gground, protecting personnel from electrical shock while at the same time protecting sensitive electronic equipmen

of anti-static floors

rthing of any anti-static flooring system is critical - it may not be possible to lay the flooringon top of a ground concrete layer and guarantee proper electrical earthing. Therefore

g strips can be used to guarantee electrical continuity between the flooring and thending point. This is normally achieved by the use of adhesive copper tape, laid below the of conductive flooring layer and connected to earthing points - care should be taken tosections of the floor are linked together i.e. concrete expansion joints bridged with copperelectrical conductivity.


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o install an anti-static flooring system in your building?

ested in using an anti-static flooring system in your factory or production area?con tact us todayto get aotation for your project!
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