PROTECTION FROM ELECTROSTATIC DISCHARGES IN THE ELECTRONIC ENVIRONMENTS ISO 9001 CERTIFIED edition

Transcription

1 ESD BOOK PROTECTION FROM ELECTROSTATIC DISCHARGES IN THE ELECTRONIC ENVIRONMENTS eco ISO 9001 CERTIFIED 2004 edition

2 PREFACE This publication is intended to help users in understanding and prevent the Electrostatic Discharges Phenomena, it is not a substitute for reference to the ESD or Safety Standards The information given in this ESD BOOK is based on CEI/IEC : 1998 and CEI/IEC /TS:1999 published by the International Electrotechnical Commission, 3, rue de Varambe, Geneva, Switzerland. It is recommended to buy the IEC Technical Report and IEC Technical Specification, or their national versions, as IEC documents, they have world-wide applicability. STANDARDS IEC Protection of electronic devices from electrostatic phenomena - General requirements (1999) IEC Protection of electronic devices from electrostatic phenomena - User Guide (1999) IEC Electrical resistance of floor coverings and installed floors ANSI/ESD S Protection of Electrical and Electronic Parts, Assemblies and Equipment USA 1999 (download free in pdf format, source ) ANSI/ESD S Packaging Materials for ESD Sensitive Items USA (download free in pdf format, source ) page 2

3 Index ESD BOOK PROTECTION FROM ELECTROSTATIC DISCHARGES IN THE ELECTRONIC ENVIRONMENTS CONTENTS References Standards 2 What is ESD? 4 ESD damage 5 Material classification 6 ESD protections 7 Labels 8 Signs 9 Grounding: wrist-straps, foot grounders 10 Grounding: garments, gloves, chairs 11 EPA ESD protected area 12 Typical Workstation 13 Monitoring 14 Monitoring 15 In Field working, tools 16 Safety 17 Handling 18 Carts and Shelving 19 Packaging General 20 Packaging - Bags 21 Flooring Humidity Control - Ionization 24 Ionization 25 Testing 26 Testing 27 Testing 28 Testing 29 Training - Visitors 30 Check list 31 page 3

4 ESD Electro Static Discharge what is it? Electrostatic discharge is defined as the transfer of charge between bodies at different electrical potentials. The electrostatic charge occurs when two different materials rub or slide together or are separated. Examples are : - walking over synthetic floors - rubbing of synthetic garments - shifting of plastic boxes - unrolling of PVC adhesive tape - moving of conveyor belt Static electricity can build up high voltages in modern operating environments - over 10kV is not uncommon, and with related humidity lower than 20%, over 30 kv has been recorded. When two objects with different charges get closer, electrons can suddenly flow from one object to the other ESD can also occur when a high electric field develops between two objects in close proximity. CMOS page 4

5 ESD ESD can results in : higher costs lower quality unhappy customers Many of the common activities may generate charges harmful to components STATIC GENERATION TYPICAL VOLTAGE LEVELS Means of generation 10-25% RH 65-90% RH Walking across carpet Walking across vinyl tile Worker at bench Poly bag picked up from bench Chair with urethane foam 35,000 Volt 12,000 Volt 6,000 Volt 20,000 Volt 18,000 Volt 1,500 Volt 250 Volt 100 Volt 1,200 Volt 1,500 Volt DEVICE TYPE ESD SUSCEPTIBILITY DEVICE TYPE ESD SUSCEPTIBILITY VMOS 30-1,800 Volt CMOS 250-3,000 Volt MOSFET Volt OP-AMP 190-2,500 Volt GaAsFET Volt BI-POLAR TRANSISTORS 380-7,000 Volt EPROM 100 Volt SCHOTTKY DIODES 300-2,500 Volt JFET 140-7,000 Volt SCHOTTKY TTL ,500 Volt Catastrophic in-house failure ESD DAMAGE COST LEVELS Latent failure Limited cost It is the easiest type of ESD damage normally detected during testing Higher cost due to: - customer support - servicing facility - replacement equipment - loss of reputation - loss of customers page 5

6 Materials For ESD purposes, many materials are classified by their resistance or resistivity characteristics. SURFACE RESISTANCE W Conductive materials SHIELDING materials Static-dissipative materials Insulative materials Surface resistance measurements are not always appropriate to establish the effectiveness of the materials, where resistance is higher than 1x10 10 W, or where the material is of non-homogeneous woven it is mandatory to measure the decay time of the generated charge ELECTROSTATIC SHIELDING MATERIALS providing a Faraday cage protection, limit the passage of current and attenuate the energy resulting from an electrostatic discharge. Most static shielding materials include a conductive (less than 1x10 3 W) metal or carbon element that suppresses the field, attenuates, or reflects field energy. CONDUCTIVE MATERIALS characterised by a low electrical resistance (less than 1x10 5 W), allow the charge to quickly distribute itself throughout the material. If the conductive material is connected to ground, all charge will flow away. Some examples of conductors are metals, carbon and the human body's sweat layer. STATIC-DISSIPATIVE MATERIALS 5 are defined as those having a surface resistance greater than 1 x 10 W but less 12 than 1 x 10 W. Charges will flow to ground slower than with conductive materials, reducing its destroying potential. INSULATIVE MATERIALS 12 are defined as those having a surface resistance of at least 1 x 10 W. Insulative materials have a high electrical resistance and are difficult to ground. Static charges remain in place on these materials for a very long time. This property make insulators a hazard that must be controlled as part of an ESD program. Some examples of insulators are common plastics, glass and air. page 6

7 Controls ESD DAMAGE CAN OCCUR AT ANY TIME: GOODS INPUT ACCEPTANCE PRODUCTION ASSEMBLY TESTING STORING PACKING SHIPPING MAINTENANCE BASIC ESD CONTROLS GROUNDING SHIELDING NEUTRALIZATION (ionizers) Four gold rules 1 - Assume that all active components are sensitive to ESD 2-1 Handle electronic components only in the ESD protected area (EPA) and only when you are properly grounded. 3 - Store and transport the ESD-sensitive items in ESD protective containers. 4 -Check regularly the ESD protection system, internal and external (suppliers) Take in evidence the principle 'No Charge/No discharge', the elimination of charge build-up is obtained by using conductive and dissipative materials that have less tendency to generate static charges. All equipment must be free of moving parts that may generate charges, e.g., rubber rollers, plastic stoppers, etc. Things which the devices may come in contact with or get transported on must also be antistatic or conductive. The use of ionizers to neutralize newly generated charges will also prevent charge build-up. The minimization of movements in the work area, as well the use of ESD-safe equipment, will help in minimizing static charges generated by personnel. page 7

8 Labels BASIC SYMBOL The basic symbol consists of a yellow hand within a black triangle. It is intended to identify devices and assemblies which are ESD sensitive. min. 4mm PROTECTION SYMBOL Used to designate all ESD protective products such as bags, boxes, garments. A letter is added under the symbol to indicate the primary function: * * C D S L conductive dissipative shielding low charging EPA LABEL Used to designate EPA equipments such as tables, trolleys, chairs. EPA ATTENTION OBSERVE PRECAUTIONS FOR HANDLING ELECTROSTATIC DISCHARGE SENSITIVE DEVICES EARTH min. 4mm ESD CAUTIONARY SYMBOL BONDING POINT EARTH BONDING POINT (EBP) page 8

9 Signs EPA WARNING SIGN The signs are designed to attract attention and deliver a clear message to personnel and visitors before they enter the EPA. Where high voltages greater than 250VAC or 500VDC are present, use proper warning signs. ATTENTION ESD PROTECTED AREA OBSERVE PRECAUTIONS FOR HANDLING ELECTROSTATIC DISCHARGE SENSITIVE DEVICES EPA WHICH CONTAIN HIGH VOLTAGE HIGH ATTENTION VOLTAGE ESD PROTECTED AREA OBSERVE PRECAUTIONS FOR HANDLING ELECTROSTATIC DISCHARGE SENSITIVE DEVICES EPA EXIT SIGN ATTENTION YOU ARE LEAVING THE EPA page 9

10 Earth Bonding Point 1M 1M 1M Grounding people are the primary source of electrostatic charges The elimination of charge build-up is obtained by using conductive and dissipative materials that have less tendency to generate static charges. Grounding systems shall be used to ensure that components, personnel and any other conductors are at the same electrical potential. For proper and safe grounding the ESD ground must be tied directly to and at the same potential as the building or green/yellow ground. PERSONNEL GROUNDING DEVICES The wrist strap is the most used device to ground personnel, it will safely and effectively drain static charges from the body. Someone offers ESD Wrist straps without cord (cordless), we can assure that are ineffective. EBP (earth bonding point) Earth In some locations, such as stores and around equipment, conductive shoes or foot grounders are used. Foot grounders should be worn on both feet to ensure constant contact to ground floor or floor mat. Foot grounders will not function properly if used on surfaces which are insulative or improperly grounded. Earth page 10

11 Grounding Garments The main purpose for wearing conductive smocks is to suppress static fields on employee clothing. The conductive fibers woven into the material provide a Faraday cage that prevents dangerous fields from extending to and damaging sensitive products. There shall be electrical conductivity between all parts of the garment. Gloves ESD sensitive device can experience a damaging discharge if touched by a person, even if that person is properly grounded. Increasing the electrical path's contact resistance is one way to control the speed of the discharge. A good way to accomplish this is by wearing static dissipative cots and gloves. Chairs The resistance to ground from any part of the seat which may have contact with personnel, 10 must be less than 1x10 W. At least two castors or feet must provide a path to ground. page 11

12 EPA EPA Area An EPA (ESD Protected Area) is a defined space where no items or activity are able to cause damage to a sensitive device. In the simplest case - a field work station - it may consist of a dissipative mat, a wrist strap and common grounding facility for both. MAXIMUM ALLOWED ELECTROSTATIC FIELD: 100V/cm Groundable castors 2 Groundable surface 3 Wrist-strap tester 4 Footwear tester 5 Footwear foot plate 6 Wrist cord and wrist band 7 Ground cord 8 Ground 9 Earth bonding point (EBP) 10 Groundable point of trolley 11 Toe and heel strap (footwear) 12 Ionizer 13 Static-dissipative working surface 14 Seat with groundable feet and pads 15 Static-dissipative floor 16 Low charging garments 17 Shelvings with grounded surfaces 18 EPA sign page 12

13 Earth Bonding Point 1M 1M 1M Workstation TYPICAL WORKSTATION It is important that each bench, or work surface, is covered with the proper ESD material and properly connected to earth using a system of cords and Earth Bonding Points (EBPs) ATTENTION ESD PROTECTED AREA OBSERVE PRECAUTIONS FOR HANDLING ELECTROSTATIC DISCHARGE SENSITIVE DEVICES Wriststrarp with coiled cord, 1MW built-in EBP Dissipative footwear Dissipative flooring connected to the EBP (Earth Bonding Point) Earth When using this type of grounding method be sure that the total resistance "hand to earth" is lower than 7 3.5x10 W. Ground all soldering iron tips. Rg max 1x10 7 W Remove all extraneous materials from the workstation (food, beverages, combs, bags, clothing etc) Test the wrist strap/operator daily or install constant monitors. Inspect the ESD grounding connections, the mats, the EBP, weekly. Clean the surfaces with purpose-made antistatic cleaner, do not use commercial products, the cleaners may leave a residue insulative layer. page 13

14 FAIL LOW PASS HIGH FAIL LO BAT WRISTLAB PERSONNEL CIRCUIT TESTER TOUCHPLATE FOOTWEAR FOOTWEAR CORD TEST CORD TEST ATTACH END ATTACH CORD Monitoring Check your ESD equipment regularly ESD protection systems as wrist straps, foot grounders, work surfaces and floors need to be checked on a regular basis. This is an important requirement of the ESD standard IEC Personnel testing The personnel grounding tester is a wrist strap and/or footwear tester to check personnel grounding systems before entering an EPA. WRISTLAB TEST STATION HOW TO TEST YOUR WRIST STRAP 1) Indossare il bracciale. Assicurarsi che sia aderente. 3) Collegare il cordone nell'ingresso "ATTACH CORD". 4) Premere con le dita "TOUCHPLATE". 5)ATTENZIONE a non alterare la misura toccando con l'altra mano il tester o il bracciale. 6) La luce verde ed il buzzer indicano che il bracciale e l'operatore sono conformi. 7) la luce rossa o gialla segnalano non-conformità. 8) L'indicatore "LO-BAT" segnala batteria esaurita. mod check wrist straps and footwear twice a day For standing operations ESD flooring used with approved footwear, may be an alternative to the wrist strap system, in this case the standard is more restrictive and one of the following conditions must be met: - the resistance of the person to the ground must be less than 3.5x the maximum body voltage generation must be less than 100 volts. It is easier to check the first condition, we suggest to use a Megaohmmeter with one lead attached to the ground and one electrode held by the person wearing ESD footwear standing on the factory's protective floor. check the "footwear/flooring system" twice a year Garments Rs<1x10 12 Charge decay 2s Glove and finger coats as worn 7.5x10 5 Rg 1x10 12 page 14

15 Monitoring Continuous Monitors can be used to constantly monitor ESD protective items such as wrist straps, work surfaces and floors, all the systems provide visual and audible alarms. Continuous monitoring reduces but not replace the periodic checks. CONTINUOUS MONITORING METHODS Capacitive affected by noise and capacitive variations associated with personnel and environmental conditions. Dual-wire / Current loop accurate but expensive system requires special wrist straps Wave distortion detection good system not affected by interference check the continuous monitor functions semi-annually EPA testing check workstations, floor mats, ESD ground connections, ionizers monthly check ESD control instruments annually Resistance to ground should be: Worksurface: 7.5 x 10 5 Rg 1 x 10 9 W W 9 Floors: Rg 1 x 10 W 10 Seating: Rg 1 x 10 W 12 Tools: Rg 1 x 10 W Ionizers Ionizers neutralize electrostatic charges with fans that blow large quantities of positive and negative ions. Ionizers out of balance (different quantities of negative and positive ions), can place a significant charge on items instead of neutralizing the charges. check ionizers monthly (see Test method on page 29) page 15

16 Earth Bonding Point 1MW 1M W 1MW In Field IN FIELD WORKS Field work is perhaps the most risky situation of handling ESD sensitive devices, it is also often the most neglected aspect of ESD damage prevention. The situation is risky as there are usually many potential ESD sources in the environment. Spare parts should be transported inside static shielding bags or containers. Where modules have to be worked on in an exposed state, staticdissipative matting should be bonded to the product's electrostatic bonding point, and to the ground to act as a work surface. Typical "field service kit" Wriststrap with 1MW resistor with coiled cord Lay ESD sensitive devices only on the mat Grounding cord with 1MW resistor built-in Static dissipative mat Tools Tools should not have insulating handles. Decay of charge to less than 10% of initial value (1000V) within 2 sec. is required. Soldering irons tips must be grounded to earth, and must be used only at low voltages (6 to 24V) pag.16

17 Safety Before we get to the key issues of ESD control, it is important to note that personnel safety is paramount. In no way should an ESD control program replace or supersede any requirements for personnel safety. In the factory, grounding personnel around the AC power line is a possible hazard. Personal grounding should not be used when working around voltages greater than 250 VAC. Although personal grounding items must include a 1MW resistor to limit current to less than 0.25 ma, ground fault circuit interrupters should be used. Where high voltages greater than 250VAC or 500VDC are present, use proper warning signs.(see page 9) TYPICAL EPA AREA CONFIGURATION WRISTSTRAP 1MW WORKING BENCH FLOORING 3x1MW Safety management is responsible for selecting equipment that complies with applicable laws and regulatory codes. EARTH BONDING POINT GROUNDING CONNECTION <1x10 6 W page 17

18 D 04 Handling TRANSPORTATION AND STORAGE Store and transport ESD-sensitive items properly When transporting and storing ESD sensitive devices, use trays, racks, tote boxes and bags made of conductive, dissipative or shielding materials. To transport loose leaded devices, conductive foam is often employed. This prevents a potential difference of more than a few volts appearing across the pins. Dissipative tubes are used for bulk supply of dual-in-line packages. Dissipative or conductive open part bins, tote boxes, PCB holders, trays, are used for subassemblies and printed circuit boards. Bags Packaging used within an EPA shall be: - all with low charge generation properties - made in dissipative or conductive material for intimate contact (see page 21 for bag specifications) LABESTAT - A3 3-LAYERS DISSIPATIVE FILM PE-LD page 18

19 Handling Movement of carts and other wheeled equipment through the facility can generate static charges that can transfer to products being transported. ESD safe carts are made from dissipative or conductive materials and are equipped with dissipative or conductive wheels. If wheels are insulating the structure can be grounded to the floor through a metallic chain. If the floor of the EPA is not grounding, then the trolley should be grounded from its grounding point to an earth bonding point, when stationary for loading or unloading. RACK, CART AND SHELVING Every surface on which ESDS are placed must be connected to ground, and have a point-to-point resistance between 1x10 4 W 10 and 1x10 W, and resistance-to-ground 5 9 between 7.5x10 W and 1x10 W. Surface to ground resistance values may be achieved by including discrete resistors in the ground path, or by the resistance of the material which is directly grounded. Conductive wheels When surfaces (example: crome plated steel) have a point to point resistance lower than 1x10 4 W, for housing ESD sensitive devices, use proper static dissipative boxes or mats. page 19

20 The aim of ESD protective packaging is to prevent a direct electrostatic discharge to the ESDS item contained within and allow for dissipation of charge from the exterior surface. Packaging material will also often provide mechanical protection and protection against contamination by dust or humidity. Packaging IEC defines three levels of packaging: Intimate proximity secondary in contact with the ESDS does not make contact with the ESDS, but may enclose one or more ESDS mainly used to give physical protection, is kept away from ESDS and is not allowed in the EPA INSIDE THE EPA OUTSIDE THE EPA Intimate Proximity Intimate Proximity ESDS Either low charging Low charging As for inside Electrostatic and conductive and electrostatic EPA shielding or low charging shielding or and static-dissipative low charging and conductive or (for powered ESDS only static-dissipative low charging and static-dissipative above 1x10 W shall be used) Non ESDS Dissipative or low charging No requirements Note: Where surface resistance >1x W is used, the material shall be procured with a T 1000 < 2 sec caution in purchasing: some packaging materials may be humidity dependent and may have limited shelf life, some other may contaminate or shed particles that cause production-related problems. ( example: a too brittle hard foam) page 20

21 antistatic (low charge) Packaging Use: Cost: Appearance: BAGS within the EPA for packing non-esd sensitive items low clear or tinted (pink, blue, green) Material: conductive shielding Characteristics Shelf-life: Use: Cost: Appearance: Material: Characteristics Shelf-life: Use: Cost: Appearance: Polyethylene mono or multilayer Rs x10 to 1x10 W T 1000 < 2 sec at 50% rh, 22 C generally 1 year good degree of protection for many ESD sensitive items. Don't use with powered devices. medium black polyethylene with carbon added 3 5 Rs 1x10 to 1x10 W more than 5 years for intimate packaging of all ESD sensitive items. high metallized semi-transparent Material: generally a vacuum deposited aluminium between layers of polyester and polyethylene film Characteristics shielding bags meet the two main requirements: low charging and electrostatic discharge shielding barrier. Shelf-life: more than 2 years moisture barrier Corrosion and thus moisture protection is becoming increasingly important, Dry Packaging is usually required for electronic devices that have to be placed into long term storage. To provide a complete protection of devices, one desiccant pack and one Humidity Monitor Card are inserted into the bag prior the vacuum sealing. page 21

22 Flooring Static protective permanent flooring, in conjunction with conductive footwear or heel grounding straps, drains static charge away to ground through the floor. It is a solid foundation for a comprehensive static control system. In addition to dissipating charges, the static-dissipative flooring reduces triboelectric charge generation in walking and minimise charge accumulation on chairs, carts, lift trucks and other objects that move across the floor. However, these items require dissipative or conductive castors or wheels to make electrical contact with the floor. Use dissipative shoes or footgrounders on ESD protective flooring Lower conductive layer Dissipative floor Concrete subfloor Rs 1x10 10 W Rg 1x10 9 W Recommendations 7 - choose a floor covering with Rg lower than 3,5x10 W, this enable the grounding of personnel via the flooring-footwear system (see page 14) in alternative with the wriststrap system. - choose a floor covering suitable for your traffic level (frequency, weight, type of castors ) - take in consideration the sound absorption, anti-fatigue and anti slip properties - ask to the supplier a guarantee that the earth leakage resistance will be maintained, throughout the useful life of the floor material. page 22

23 Flooring With reference to the installation systems, static control flooring can be classified into three groups: Permanently installed floors Vinyl tiles usually earthed via a strip of copper foil and bonded with conductive acrylic adhesive. Aesthetically attractive Poor heat and chemical resistance Rubber tiles usually earthed via a strip of copper foil and bonded with conductive acrylic adhesive. Excellent heat and chemical resistance Carpet Aesthetically attractive, mostly used in offices Difficult to reach a good static dissipation Resinous flooring (Epoxy, vinyl ester, polyurethane coating) Variable thickness for different traffic condition Chemical resistant. Easy to clean. Topcoats may get scratched or abraded Periodically applied topical coatings on existing floor surfaces Lower material cost, easy to apply Difficult to reach a good static dissipation Worn away easily and frequent recoating is required Mats placed over existing floors Vinyl mats Possibility to move the mat Poor heat and chemical resistance Limited coverage area Rubber mats Possibility to move the mat Excellent heat and chemical resistance Limited coverage area Grid mats (polypropylene, polyethylene) Possibility to move the mat Good operator comfort, insulation from cold floor Limited coverage area page 23

24 Humidity The most significant environmental factor in ESD Control is the relative humidity (Rh) When humidity in the working environment decreases, the human body and other insulators can easily charge with static electricity due to friction. The air itself, being dry, becomes a part of the electrostatic build-up mechanism, every time an air flow (wind, air conditioning, blower) come over an insulated surface. Relative Humidity shall be maintained over 30%. Below that value it is recommended the use of ionization. Environmental Monitoring Each EPA area shall be equipped with a Humidity/Temperature meter to record these data.these informations are useful to establish the distribution through the time of ESD related failures (needed to the Failure Process Analysis ). Ionization Where grounding of some equipment or parts of it through the traditional earthing techniques is impractical and where it is impossible to exclude all charging materials from the working area, the use of suitable ionizers is highly Air Ionization systems work by flooding the atmosphere with positive and negative ions. When the ionized air comes in contact with a charged surface, the surface attracts ions of the opposite polarity. As a result the static electricity that has built up on products and equipment is neutralised. Ions do remove small particles or smoke and pollens from the air, and subjective research suggest that people working in ionized area are happier. IONIZER PROTECTION Nuclear AC DC Local (little area) Complete (whole room) High maintenance required Low discharge time when using high volume blowers Very Low discharge time bench Ionizers Ionizing bars Ionizing guns Manual Environmental Control Automatic Environmental Control 3 Maximum Ozone generation accepted by law: 0.2mg per m (0.1ppm) DC Ionizers with balanced ions emission are the best solution for local protection. page 24

25 Ionization some types of ionizers BENCH TOP IONIZING BLOWER OVERHEAD IONIZING BLOWER AIR FORCE BLOW-OFF GUN very useful to blow off charged dust particles from electronic card, and other equipment or materials. The most common test to evaluate air ionizer performance is the static decay time measurement (see pag. 29) page 25

26 Testing RESISTANCE MEASUREMENTS Resistance measurement is the most common tests to verify the efficiency of working surfaces POINT TO POINT RESISTANCE Is the resistance measured between two points on the surface using a Megaohmmeter with two electrodes. Always record: T ( C) Rh (%) values, as the resistance measurements may change with these two parameters. RESISTANCE TO GROUND should be measured using a Megohmeter with one electrode placed on the surface and the other terminal connected to the groundable point. The resistance should measure between x10 and 1x10 W. For many materials, the measured resistance depends on the applied voltage; according to IEC the test voltage applied by the Megohmeter is given in the following table Rx (W) Open circuit test voltage (V) Rx 1x10 5 1x10 5 < Rx 1x Cylindrical probes with 63mm diameter and 2.3kg weight, meets IEC and ANSI/ESD standards. page 26

27 10V RESISTANCE 1K METER 100V 500V 100K 1M W W W 10G 100G 500G W W W RESISTANCE METER 100V 10V 100K 1K W W 100G 10G W 500V 1M W 500G W 10V RESISTANCE 1K METER 100V 100K W W 10G 100G W W 500V 1M W 500G W MEASURE MEASURE MEASURE GIGALAB PROG Vtest OFF ENTER GIGALAB PROG Vtest OFF ENTER GIGALAB PROG Vtest OFF ENTER Testing MATERIAL UNDER TEST CONCENTRIC RING PROBE SURFACE RESISTIVITY Defines the electrical resistance of the surface of the material, it is expressed in W/square and theoretically is 10 times greater than the point to point resistance. Measurements can be made using a square probe with two parallel electrodes or a concentric ring probe, in compliance with IEC Always record: T ( C) Rh (%) values, as the resistance measurements may change with these two parameters. VOLUME RESISTANCE MATERIAL UNDER TEST COUNTER-ELECTRODE Is defined as the ratio of dc voltage to current passing between two electrodes (of a specified configuration) that contact opposite sides of the material of the object under test. Volume resistance is measured in W. It is normal to test mats or sheets with a cylindrical probe and a flat counter-electrode PERSON TO GROUND RESISTANCE Measuring Resistance through a Person to Ground according IEC for the measurement of a resistance through the combination of a person /shoes / flooring system. FLOOR page 27

28 Testing some hand-held electrostatic instruments useful to locate static charge problems Electrostatic FIELDMETER The accurate measurement of electrostatic fields requires the operator to be familiar with this type of equipment. Most hand-held meters require the measure to be taken at a fixed distance from the object (typical distance is one inch). Equipment manufacturers typically specify that the object being measured needs to have certain minimum dimensions. Objects smaller than the minimum dimensions may not provide an accurate reading. 1 inch (25.4mm) ground the case Electrostatic VOLTMETER There exist noncontacting instruments that can provide accurate measurements at a wide probe-to-surface spacing range and can inspect small charged areas on the surface under test. The higher spot resolution capability is useful to locate charges on non homogeneous materials. 5-25mm ground the case choose instruments that make accurate measurements in ionized environments too. page 28

29 Testing IONIZATION TEST KIT VERIFICATION OF AIR IONIZERS An ionization test kit can very quickly verify the proper functioning of an ionizer. The ionization test kit should be grounded and placed in the ionized airflow to measure the decay time and the balance of air ionization equipment, the charger is used to charge an isolated plate applied on the field-meter. charged electrode placed in the ionizer air stream ionizer ground the case digital field meter charger ( ± 1000Vdc ) CHARGED PLATE MONITOR Charged plate monitor tests the efficiency of ionizer's ion production by measuring how long it takes air ions produced to discharge a floating ion collecting plate that has been precharged to either a positive or negative charge level. plate voltage (adjustable) decay time charge plate placed in the ionized air stream plate dimensions : 150x150mm meet IEC and ANSI/ESD standards page 29

30 Training STANDARDS: purchase, read and get familiar with the IEC Standards ESD TEAM: establish and organise an ESD Team responsible for the ESD control program. TRAINING: train the operators to the use and check of personal protection, handling, etc. Sub/contractors and visitors shall be made aware of local ESD procedures. VIDEO: some video training on ESD event, cause and effect, examples, demonstration, will get everyone aware of this important problematic. SIGNALING: clear signs to identify the Electrostatic Protected Area or any ESD hazard, shall be widely and properly used to alert operators, or to draw their attention over protection. DISCIPLINE: Manager and technicians shall always respect the standards and quality procedure so as to give a good example to the operators. Visitors Visitors entering the EPA shall behave properly to prevent any ESD damage or danger. In case of a conductive floor they shall wear ESD heel and toe grounder, which also exist in the economic disposable version. It is recommended to wear an antistatic overall, and also a connected wrist-strap in case of PCB or component manipulation. page 30

31 Checklist Simple Audit Check List for ESD Control Program. It is essential to implement corrective action if deficiencies are discovered. - Are personnel wearing grounded wrist straps at the ESD protective workstations? - Are personnel checking regularly their wrist strap's continuity or using a continuous ground monitor? - Is the ESD equipment at the workstation properly grounded? - Where ESD protective flooring is used, are dissipative footwear worn? - Where ESD protective floors and footwear are used, do personnel check continuity to ground upon entering the area? - When required, are ESD protective garments correctly worn? - Is the workstation clear of all not-essential personal items? - Are all ESD sensitive devices stored and transported in static- shielding container? YES NO - Are all ESD sensitive devices correctly labelled? - Are visitors crossing the EPA using proper ESD protection? - Do you report any ESD hazards that you notice to your ESD responsible? page 31

32 eco Licefa ION SYSTEMS TRESTON