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ELECTROSTATIC DISCHARGE (ESD) AWARENESS TRAINING

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1 ELECTROSTATIC DISCHARGE (ESD) AWARENESS TRAINING
Credits Prepared by CAPT JESSE D. S. MORGAN, III Additional Slides by JULIUS BRODBECK Technical Assistance by Steve Gerken and Mike Manders AF ESD Control Center Materials Integrity Branch Materials and Manufacturing Directorate Air Force Research Laboratories AFMC This is Version 3a 9/5/03 Most of the notes pages are filled in.

2 What is ESD? Electrostatic Discharge (ESD) is the discharge of stored static electricity. Some circuits today are sensitive to as little as 25 volts. Typically humans begin to feel a static discharge at 3500 volts. You can damage a circuit without feeling it!

3 ELECTROSTATIC DISCHARGE (ESD)
CONTROL TRAINING Notes Included For those viewing this on their computer, most of the slides have their ‘Notes’ pages filled in which amplify the information provided on the slides. Version 3a 9/5/03

4 Overview Extent of ESD Damage Directives Definitions
Summary of ESD Principles Tribocharging Effects of Humidity Controlling Body Voltage Packaging Marking, Labeling, and signs ESD Worksurfaces Air Ionization Grounding The Role of Capacitance Reference

5 Extent of ESD Damage Photo taken on a Microscope of ESD damage
ESD Damage, 1st of 7 Photo taken on a Microscope of ESD damage Micro Wire

6 A DEMO on a MOSFET A 3N157 MOSFET is lying on a circuit board to
illustrate the relative size of the all metal package. The unit under test (UUT) is a 4 pin 3N157 MOSFET from the 1980’s. If you look closely, you can see the shunt wire around the pins at the base of the metal cap. The MOSFET is lying on a modern circuit board to show how miniature today’s components are compared to this robust FET. Over the decades the size of the components have gotten many times smaller. There is one transistor in the 3N157 and it is protected with a metal lid – not nearly exposed as today’s components seen on the circuit board.

7 An ESD Shock is applied The 3N157 MOSFET is tested on the white tester in the background. The test consisted of adjusting the gate voltage to a level that would cause a 10uA current between the drain and source pins. With ESD precautions it is inserted into a single socket circuit board. The Master Sergeant charged his body to volts and touched the metal lid on the device. The device was retested and it was found that the gate voltage had to be increased by 20% to produce the same 10uA current between the drain and the source. The device is still functional, but it is close to being out-of-spec.

8 Microscopic Postmortem
There is no visible damage at 150 power ! The metal lid was removed from the 3N157 MOSFET showing three of the 4 pins (Source at the bottom, Gate to the right, and Drain at the top). The square box on the right is a close-up of the square in the center of the circle on the left. There is no visible damage at this level of magnification.

9 At 2500 power, damage to a via is seen.
2500 Magnification At 2500 power, damage to a via is seen. The 150x magnification is now on the left, and the photo on the right shows damage to one of the traces (via). This damage is not large enough to extend all the way across the via, so current can still pass through. This type of damage is called latent (present or potential damage, but not evident or active). This damage to the via will cause local heating because the current has a smaller conductor at this point to flow through. The UUT is now a walking wounded. Recall from a couple slides back, the device is still functional, but it is close to being out-of-spec.

10 Extent of ESD Damage Device Type Range of ESD Susceptibility (Volts)
Susceptibility of Various Devices Exposed to ESD Device Type Range of ESD Susceptibility (Volts) MOSFET JFET CMOS Schottky Diodes, TTL Bipolar Transistors SCR ,000 ,000 ,500 ,000 ,000 The chart above shows the general range of potential on a person that can damage various electronic components when the person touches and discharges to the device. Note, that people and materials can easily charge to levels that greatly exceed the damage potential for most device structures. Here-in lies the crux of the ESD problem. From: “Basic ESD Seminar” prepared by Burt Unger for the ESD Association, Rome, NY, P.39 “Basic ESD Seminar” prepared by Burt Unger for the ESD Association, Rome, NY, P.39

11 Estimate of Telephone System ESD Costs
Extent of ESD Damage Telephone Systems Estimate of Telephone System ESD Costs 160 150 160 129 140 120 94 100 Cost in Millions 80 60 Here are the ranges of estimated ESD failure costs for Bell System transmission product from 1978 through The bounds are pretty large because of some uncertainty in some assumptions, but the order of magnitude are believed to be correct. ESD failures were a significant burden. From: “Basic ESD Seminar” prepared by Burt Unger for the ESD Association, Rome, NY, P.17 40 43 43 20 35 25 78 79 Year 80 81 = Range of ESD Damage “Basic ESD Seminar” prepared by Burt Unger for the ESD Association, Rome, NY, P.17

12 Extent of ESD Damage Published ESD Losses
1980 Delco Electronics study on Auto $22M Electronics Product ESD Failures 1983 AT&T HIC Shop ESD Losses % 1984 USAF Missile Guidance Video Board $492,000 ESD Failures (250 Failed) 1984 USAF Depot ESD failures $788,000 1985 Early IBM Printer Module ESD Failures % This shows some interesting published loss and cost data. From: “Basic ESD Seminar” prepared by Burt Unger for the ESD Association, Rome, NY, P.19 “Basic ESD Seminar” prepared by Burt Unger for the ESD Association, Rome, NY, P.19

13 Air Force’s ESD Estimate
Extent of ESD Damage Air Force’s ESD Estimate Estimate of Failures Due to ESD 1988 USAF, A Review of EOS/ESD Field Failures in Military Equipment. Up to 12 % of the Failures could be ESD. Capt Thomas Green 1988 EOS / ESD Symposium Proceedings

14 Damage in Manufacturing
Extent of ESD Damage Damage in Manufacturing EOS/ESD Damage During Manufacturing. Data from 23 designs from High Reliability Facility. Out of 1193 Processing Failures. There were 414 EOS/ESD Failures. At Another Plant 1607 Devices Were Analyzed. The Conclusion in 1993 was. “25.8 % of the product rejected by this. facility was damaged by the cumulative. effects of EOS and ESD, all of which. were avoidable.” “Basic ESD Seminar” prepared by Burt Unger for the ESD Association, Rome, NY, P.20 Some recent data shows that EOS/ESD continues to be a significant cause of IC failure. The data was presented in a paper by Wagner et al, Sandia National Laboratories, at the 1993 EOS/ESD Symposium.

15 Repair Cost vs Discovery
Extent of ESD Damage Repair Cost vs Discovery REPAIR COSTS Level where Fault was Discovered Device Board System Field Hewlett Packard Commercial Product $1 $5 $50 $500 Gould Military $1,500 $10,000 Although the factory failure costs are relatively inexpensive, the large failure numbers can frequently add up to the more costly but more less frequent systems or field failures. Here we present data showing the escalation of failure costs through various product stages. From: “Basic ESD Seminar” prepared by Burt Unger for the ESD Association, Rome, NY, P.16 “Basic ESD Seminar” prepared by Burt Unger for the ESD Association, Rome, NY, P.16

16 Directives Air Force Policy Directive 21-1 and 21-3
Directives, 1st of 6 Air Force Policy Directive 21-1 and 21-3 “Compliance with AF T.O.s is mandatory” T.O , General Shop Practice Requirement for the Repair, Maintenance, and Test of Electrical Equipment. ANSI/ESD S20.20, Development of an ESD Control Program is replacing Mil-Std-1686 MIL-HDBK-263B, Electrostatic Discharge Local Operating Instructions AFP Directive 21-1 defines Aerospace Equipment as: “Equipment used and maintained to meet the Air Force mission. It includes aircraft, missiles, space equipment, communications, electronic equipment, avionics, engines, training equipment, support equipment, aerospace ground equipment, sound suppresser systems, test, measurement and diagnostic equipment, and major-end-items of all equipment.” T.O paragraph 1-2 (scope) states that: “The provisions contained herein are applicable to Air Force and contractual personnel engaged in repair, maintenance, or test of Aerospace Electronic Equipment.” It can not be said much plainer than that.

17 Directives Authorize Time & Money
The following Air Force documents authorize AF time and money for ESD Control as indicated Section 7 of T.O )? AF Policy Directive 21-3 AF Policy Directive 21-1 AFI AFI

18 Directives Mandatory Compliance
AIR FORCE POLICY DIRECTIVE 21-3, “Technical Orders” Says… “Compliance with Air Force T.O.s is mandatory” Includes TO AIR FORCE POLICY DIRECTIVE “Managing Aerospace Equipment Maintenance” Defines Aerospace Equipment as “Equipment used and maintained to meet the Air Force mission. It includes aircraft, missiles, space equipment, communications, electronic equipment, avionics, engines, training equipment, support equipment, aerospace ground equipment, sound suppresser systems, test, measurement and diagnostic equipment and major-end-items of all equipment”

19 Directives AFI AIR FORCE INSTRUCTION “Maintenance and Management of Communication Electronics” Para , under responsibilities of the Maintenance Support Representative (MSR) requires: “Compliance with Electrostatic Discharge practices, where applicable. (TO )” TECHNICAL ORDER , “General Shop Practice Requirements for the Repair, Maintenance, and Test of Electrical Equipment” Says… “The provisions contained herein are applicable to Air Force and contractual personnel engaged in repair, maintenance, or test of Aerospace Electronic Equipment”

20 Directives ESD Control in Supply
Supply is to Comply ESD Control in Supply AIR FORCE INSTRUCTION “Preservation and Packaging” Chapter 2 (Packaging Operations), paragraph 2.4: Packaging Line Layout should include: “At least one electrostatic discharge (ESD) protective workstation where trained personnel can package sensitive (ESDS) items. This must include a conductive work surface and personnel grounding devices. TO , Section VII, contains detailed information about ESD protective workstations. Post signs prohibiting entry of unauthorized personnel and static-producing materials in areas designated for packaging ESDS items”

21 Directives Supply & AFI AIR FORCE INSTRUCTION Chapter 3, “Preserving Supply and Equipment Items”, para 3.2, “Electrostatic Discharge Sensitive Items” says: 3.2 “Never handle ESD-sensitive items, regardless of condition, without their protective packaging except at a grounded ESD workstation.” Use care in opening ESD items. ESD bags are usually constructed with enough extra material to allow for at least one additional heat seal, thereby facilitating reuse in the maintenance activity. Identify ESD items by Type Cargo Code 3 on DD Form A, and by special interior and exterior sensitive-electronic-device caution label .

22 Electrical Definitions
Conductors Materials that permit the free movement of electrons. Electrons Small negatively charged particles Electric Current - Movement of free electrons Insulators Materials that impede the free Negative Charge - A surplus of electrons Positive Charge - A deficiency of electrons A Proton A positively charged particle This slide was contributed by: Ms. Kim Wagner, Hill AFG, OO-ALC / TIUBA Ms. Kim Wagner, Hill AFG, OO-ALC / TIUBA

23 Resistance Classification
Definitions Resistance Classification Classification Sheet Resistivity Conductive Static Dissipative Insulative Ohms/Square 105 to 1012 Ohms/Square Greater than 1012 Ohms/Square Ohms 106 to 109 Ohms Not Defined Section 7 of AF T.O Conductive Static Dissipative Insulative EIA 541 (Electronic Industries Association specification 541) classifies materials with respect to sheet resistivity into three categories as shown. The conductive materials are considered too conductive to safely discharge a charged component. A charged device contacting such a material would discharge rapidly and may damage the device. The insulative material retains charge for long times and therefore poses an ESD threat by induction. Materials should be selected to be in the static dissipative range (10 to the fifth to 10 to the twelfth ohms per square) to provide a safe resistive discharge in generally less than one second. Most commercially available materials are characterized for sheet resistivity. However, many of the new specifications are describing material properties in terms of resistance between fixed points, rather than the more confusing sheet resistivity. Ohms / Square is done with special electrodes and converted to a number that is about 10 X more than is obtained by 7.8 a Work Surface Test Procedure.

24 ESD Physics Tribocharging Separation of surfaces Tape Binder Pages
ESD Physics, 1st of 6 Tribocharging Separation of surfaces Tape Binder Pages Rubbing of surfaces together Footwear against the floor Clothing against anything it touches Flow of fluids Fuel, oil and water + Some History: The earliest mention of the knowledge of electrostatics was by the Greeks as early as 600 B.C. They were aware of the charging of amber by rubbing and the attraction of small objects to amber. Electrostatics was not a significant interest for study until the 16th and 17th centuries. In the mid 1700’s Benjamin Franklin reported that lightning was an electrostatic discharge phenomena. he is also credited with defining the two stages of charge as “positive” or “negative”. Black top is insulative with a resistance of 1010 to 1012 ohms. Cement contains calcium hydroxide which is ionic in nature and conducts electricity. Cement has a resistance around 108 ohms which is low enough that charge can drain through it.

25 Ben Franklin Painting Ben Franklin was surely protected by the Angels during his foolish kite stunt, or should we say shunt? This slide was contributed by: Ms. Kim Wagner, Hill AFG, OO-ALC / TIUBA Ms. Kim Wagner, Hill AFG, OO-ALC / TIUBA

26 ESD Physics Both Molecules are Electrically Neutral Both Molecules are
At the Molecular Level Both Molecules are Electrically Neutral Both Molecules are Electrically Charged

27 ESD Physics Charges Opposite Charges Attract + - Like Charges Repel +
Charge, Attract & Repel Opposite Charges Attract Charges + - + Like Charges Repel

28 Electric Field Demonstrations
ESD Physics Electric Field Demonstrations Around insulators Styrofoam Teflon Around human body standing on an insulator With wrist strap Without wrist strap Absent around grounded conductors

29 ESD Physics NONCONDUCTOR CONDUCTOR Before and After grounding
Charge Distribution NONCONDUCTOR CONDUCTOR Before and After grounding Can have Random Charge Distribution (Mixed Shown) Will have Uniform (Positive Shown) Does not Discharge Complete Discharge “Basic ESD Seminar” prepared by Burt Unger for the ESD Association, Rome, NY, P.27 Materials can be classified in general as conductors and non-conductors or insulators. (Let’s not consider the class of materials called semiconductors.) Conductors permit the flow, or conduct electricity, while insulators do not. Therefore, charge on a conductor will distribute over the entire conductor surface, even if generated at a localized area, while the charge on an insulator is fixed at the generating site. Therefore, it frequently happens, that both positive and negative charge can exist as localized charge on the same insulator. This cannot happen on a conductor. Also, the charge on a conductor can only reside on the surface.

30 Retention of Charges After Separation of Surfaces
ESD Physics Retention of Charges Retention of Charges After Separation of Surfaces GROUNDED CONDUCTOR GROUNDED CONDUCTOR no charge no charge GROUNDED CONDUCTOR INSULATOR no charge charged All materials charge when brought to intimate contact and then taken apart. Materials charge to a greater extent with frictional rubbing. One material will charge positively and the other will charge negatively. Two conductors will charge when rubbed, but by virtue of their conductivity, the charge will recombine unless the separation is very rapid. In practical terms, this is very difficult to show, except possibly with metal flakes propelled at a conductor. An insulated conductor will be charged when rubbed with an insulator; but a grounded conductor will not charge when rubbed with an insulator. The insulator will charge but the grounded conductor will dissipate the charge because it is grounded. Two insulators will be charged after rubbing, one charged positively and one negatively. In fact, the materials will charge to the same magnitude, but opposite in sign. INSULATED CONDUCTOR INSULATOR charged charged INSULATOR INSULATOR charged charged “Basic ESD Seminar” prepared by Burt Unger for the ESD Association, Rome, NY, P.28 From: “Basic ESD Seminar” prepared by Burt Unger for the ESD Association, Rome, NY, P.28

31 Tribocharging Triboelectric Series - + Brass, Silver Human Hair
Nickel, Copper Brass, Silver Gold, Platinum Polyester Celluloid Saran Polyurethane Polyethylene Polypropylene PVC Silicon Teflon Glass Human Hair Nylon Wool Lead Aluminum Paper Cotton Steel Wood Sealing Wax Hard Rubber - + A listing of materials, with respect to the polarity and magnitude of charge, is called the Triboelectric Series. It is arranged so that those materials at the top lose electrons and charge positively when rubbed with materials below it on the Series. The bottom material gains electrons and charges negatively. And the farther away the materials are listed, the greater the charge generation for like rubbing characteristics. The series should be considered a guide to polarity and relative magnitude between two materials from what the Series indicates. Sometimes complete reversals of material positions have been observed. “Basic ESD Seminar” prepared by Burt Unger for the ESD Association, Rome, NY, P.32 From: “Basic ESD Seminar” prepared by Burt Unger for the ESD Association, Rome, NY, P.32

32 Tribocharging Amount of Charge Generated Rate of Discharge
Amount & Rate of Charge Amount of Charge Generated - Relative position in triboelectric series - Intimacy of contact - Rate of separation - Coefficient of friction Rate of Discharge - Conductivity of materials - Relative humidity Moisture on surface The magnitude of charge depends on the properties of the two materials in contact, and the characteristics of the frictional event, including environment. In a similar way, the parameters of the discharge depend on the materials and the parameters of the discharge event. “Basic ESD Seminar” prepared by Burt Unger for the ESD Association, Rome, NY, P.37

33 Effects of Humidity Varies with Season Location and and Time
Winter, Low Humidity, High Static Extra caution is necessary The colder it gets, the more electrostatic discharge Summer, High Humidity, Low Static Exception is Lightening Difficult to demonstrate static events Desert Areas and at High Atmospheres These places have low humidity Static is a problem year around

34 Voltages at Various Humidities
Effects of Humidity Voltage & Humidity Voltages at Various Humidities Means of Static Generation Electrostatic Voltages Refer to Table 7-2 in T.O % % % R.H R.H R.H. Person Walking Across Carpet , , ,500 Person Walking Across Vinyl Floor , , ,000 Worker at a Bench (No wrist Strap!) , White Styrofoam packing , , ,000 Common plastic bag picked up from bench , , ,000 The T.O. only shows the 10% data, but this is to show the effect of increasing humidity. Our experience indicate that these voltages may be high. However, studies in electronic assembly plants have shown charging potentials to follow a pattern similar to those in this chart. Electrostatic potentials on people, workplace items, and standard untreated packing materials can reach thousands of volts. Notice that with higher humidity, the charging potentials decrease significantly but are still at damaging levels. From: “Basic ESD Seminar” prepared by Burt Unger for the ESD Association, Rome, NY, P.38 Notice that with higher humidity, the charging potentials decrease significantly but are still at damaging levels. “Basic ESD Seminar” prepared by Burt Unger for the ESD Association, Rome, NY, P.38

35 ESD Control Work Areas T.O. 00-25-234, Section VII Requires:
ESD Control Work Area Survey: The Work Area Survey (performed by the ESD POC) defines the ESD work area and identifies the necessary ESD control items required for that work area. Keep Two Basic Rules in Mind: Handle all ESD Sensitive items at an approved static control workstation. Transport and store all static sensitive components, circuit boards, assemblies and systems in static shielding (Faraday Cage) packages or containers.

36 ESD Control Work Areas T.O. 00-25-234, Section VII Requires:
ESD Control Work Area Certification: The Work Area Certification is an evaluation by the ESD POC to ensure an ESD work area meets the requirements of the Work Area Survey. The appropriate certification document (letter signed by ESD POC) shall be posted at the entrance to the ESD work area or in a readily accessible file.

37 Controlling Body Voltage
Wrist Straps Purpose: An ESD control wrist strap is used to prevent body voltage from damaging ESD sensitive items. Use: Typically, an ESD control wrist strap should be worn anytime you are handling an ESD sensitive item. Testing Requirement: Single conductor wrist straps shall be tested prior to first use each day per person. Dual conductor wrist straps used with continuous monitors are continually checked by the monitor and require no periodic testing.

38 Controlling Body Voltage
Wrist Straps Advantages: Drains body voltage to ground An economical ESD solution Can be used almost anywhere Prevents body voltage buildup Adjustable size and cord length Light weight Ease of use The wrist strap cord has a megohm resistor built into the wire under the little cap the snaps to the cuff. This is a million ohms (1x10 to the 6th power). The work surface also has resistance between 1 and a 1000 megohms. These items have relatively high resistance to slow down electrostatic discharges. Current flow is reduced to a small value by the high resistance in the path to ground. Small current flows are less likely to burn out micron size traces found in electronic chips. The megohm resistor in the wrist strap cord is not meant as a safety device; however, if one were grounded through the wrist strap and touched 120V they would have 0.12 milliamp of current through their body. Table 7-4 of the TO indicates that one would feel the current but it is not enough to cause reflex action.

39 Controlling Body Voltage
Wrist Straps Controlling Body Voltage Wrist Straps Disadvantages: You have to remember to use them. Requires testing ! You don’t know when they are working ! You have to test them periodically Reasons for test failures: They frequently do not make good body contact because: Body hair, Dry skin, Loose fit Worn Cuff, Broken cord, etc.

40 Controlling Body Voltage
Adjustable Cuffs Controlling Body Voltage Wrist Straps T.O requires that all wrist straps have adjustable diameter cuffs. Metal wrist strap cuffs have not been approved.

41 WARNING Controlling Body Voltage
Wrist Strap Warning Controlling Body Voltage WARNING Question: Is it all right to wear a wrist strap when working with powered equipment at an ESD Bench? We power down the device under test (DUT, LRU, UUT etc.) but we still have powered soldering irons, ionizers, oscilloscopes, and other testing and repair equipment on the ESD work bench. However, TO , Section 7, has several warning statements which say "The personnel wrist strap shall not be worn when working on energized parts, assemblies and equipment." Answer: The key word here is ‘on’; working ‘on’ versus working ‘with’. DUTs, LRUs, UUTs etc.. have exposed electrical paths which can be easily contacted. We have no idea how much voltage such an item may contain. Working 'with' is like touching the knobs on your TV set; however, working 'on' is like removing the cover and probing inside the TV with a screw driver or some other instrument. (Don't pull that funny little cap off the picture tube when you get in there!) The same kind of logic applies to the ESD work bench. Test and repair equipment, like your TV, is safe to use with a wrist strap on. You do not come in contact with high voltage electrical paths of the test equipment if you use the equipment in the intended manner. One works 'with' equipment, but they work 'on' items being tested. When the protective cover of the item being tested has been removed, it is possible to contact electrical paths. We realize that at times the item being tested has to be powered up and that is when you remove your wrist strap. The personnel wrist strap shall not be worn when working on energized parts, assemblies and equipment.

42 Current, Physiologic Effects
Controlling Body Voltage Current, Physiologic Effects Effect of Electrical Current on Humans Current Values (Milliamperes) Effect AC 25 TO 400 HZ DC 0-1 1-4 4-21 21-40 Over 100 0-4 4-15 15-80 80-160 Over 300 Perception Surprise Reflex Action Muscular inhibition Respiratory block Usually fatal The wrist strap cord has a megohm resistor built into the wire under the little cap the snaps to the strap. This is a million ohms (1x10 to the 6th power). The work surface also has resistance between 1 and a 1000 megohms. These items have relatively high resistance to slow down electrostatic discharges. Current flow is reduced to a small value by the high resistance in the path to ground. Small current flows will not burn out micron size traces found in electronic chips. The megohm resistor in the wrist strap cord is not meant as a safety device; however, if one were grounded through the wrist strap and touched 120V they would have 0.12 milliamperes (mA) of current through their body. Table 7-4 of the TO indicates that one may feel the current but it is not enough to cause a surprise reaction mA is equivalent to a 9 volt battery through a 75K ohm resistor. I = V/R = 120V/1x106 = 1.2 x = x 10-3 (Ref. MIL-STD-454) Also in Table 7-4 of TO

43 Don’t use an Ohmmeter to test wrist straps.
Wrist Strap Testing Controlling Body Voltage Wrist Strap Testers, Electrical Aspects Table 7-3 ITEM Passing Range Output Ohms Volts x105 to 1x Skin resistance is not linear like that of a typical resistor . It can easily be 20 to 30 megohms on some individuals on a low humidity day when measured at 0.1 to 0.5 volts. However, the same person can be measured at 10 volts and show a resistance below 1x105 ohms. The next slide describes this in greater detail. Most DMMs use a low voltage to measure Ohms. This is fine since they are typically used on linear resistors which have the same resistance over a wide voltage range. Don’t use an Ohmmeter to test wrist straps.

44 Non-Linear Resistance
Controlling Body Voltage Skin Resistance is Non-Linear VERY MOISTURE DEPENDENT. LOTIONS SOMETIMES REQUIRED A wrist strap test is not much good unless the wrist strap is on the person who will be using it. This is because the greatest variable is a person’s skin resistance from day to day or hour to hour. There is also a difference in skin resistance from person to person. The test has to be done while the subject is wearing the strap to get valid results. In addition, the test voltage has to be high enough to get beyond the steeply non-linear region shown on the chart above. A DMM puts out less than a volt when measuring ohms; therefore, a good cuff will test as defective.

45 Controlling Body Voltage
Continuous Monitors Controlling Body Voltage Wrist Strap Continuous Monitors Resistance Measurement Type: The system resistance is continuously monitored during use. Resistance Range: 0.8 to 10 Meg ohms The Voltage constant monitoring system has been tested at the Air Force ESD Control Technology Center. The results of testing have confirmed that the system meets current Air Force requirements for constant monitoring systems. The Voltage system will be added to Technical Order authorizing its use by Air Force organizations. Procurement of the system by Air Force organizations will require the following configuration settings: Wrist Strap Monitor Alarm Points: +/-10 volts Ground Monitor Alarm Point: 2 ohm Wrist Strap “Test” Alarm Point: 1x107 ohms Be sure to specify the above settings on your purchase order. Voltage Sensing Type: Body Voltage is monitored continuously. Acceptable Voltage Range: 0 to +/-10V

46 Controlling Body Voltage
Dual Wire Cords Controlling Body Voltage Wrist Strap Continuous Monitors Both types require dual wire cords and special wrist strap cuffs.

47 Controlling Body Voltage
Footwear Testing Controlling Body Voltage Footwear Testing Refer to ESD STM Demonstrate Footwear Test with: Integrated wrist strap / footwear tester Portable Flooring Megger Demonstrate the Footwear Test Combat Boots ESD Shoes Stocking Feet

48 Footwear/Floor System
Controlling Body Voltage Lab Data on Max Body Voltage Without Wrist Strap Actual Lab Data On Nylon Carpet At 10 % RH With Combat Boots V With ESD Shoes V On ESD Carpet With Combat Boots V With ESD Shoes V Good ESD control requires a complete system approach! People develop a charge when walking on tiled floors, waxed floors, or carpeted floors with standard footwear. The magnitude of charge also is a function of the friction developed during the contact, the environment and the material cleanliness. Leather soles generally charge the least; soft rubber or crepe soles the most. Combat boots are insulated to protect the soldier from electrical shock from fallen electrical lines which may occur during battle. The soles of these boots are usually made of neoprene which has a tendency to tribocharge easily. The insulation which is a benefit on the battle field, is a detriment in the electronic repair facility. This is because the insulation prevents charges from leaving the body and the body becomes highly charged. The demo will compare body voltages on various surfaces with combat boots versus ESD shoes. The amount of tribocharging will also be compared. The results show the superiority of a complete system approach to ESD control.

49 Packaging SUMMARY OF ESD CONTROL. Workstation.
Packaging, 1st of 8 SUMMARY OF ESD CONTROL. STRATEGIES. RULE 1. Handle all ESD Sensitive items at an ESD. Workstation. RULE 2. Transport and store all ESDS items ( both. reparable and serviceable) in static. shielding and non-charge generating. packages or containers. TO Chapter 7, 7-5.b

50 Packaging ESD Packaging Objectives Provides Shielding
Immune to Tribocharging Allow charge transfer from package exterior to an ESD protective worksurface

51 Packaging Types 1, 2, & 3 Mil-Prf-81705D for ESD Protective, Heat-Sealable, Barrier Materials A Navy Spec 3 Sep 98 Three Types: Type I Not transparent, Water-vapor proof, ESD protective, EMI and ESD shielding. Heavy duty. Type II Transparent, Waterproof, ESD protective and dissipative. Pink Poly fits here. Type III Transparent, Waterproof, ESD protective and static shielding

52 Packaging EMI/Static Shield Bag (Type I) Required for long
Type 1, details EMI/Static Shield Bag (Type I) Top of the Line, heavy duty outer wrap. Required for long term storage. Protects from water vapor & Electromagnetic Fields. ESD Protective.

53 Packaging Pink Poly Bags (Type II). Does not provide.
Type 2, details Pink Poly Bags (Type II). Pink Polyethylene reduces tribocharging. Does not provide. good ESD protection. Is used to protect. from physical damage. Shown: Zip Lock Bubble. Wrap. Pink Poly is often called Anti-Static which means that it will not produce static electricity. When Pink Poly is rubbed against something, the Pink Poly does not become greatly charged either positive or negative. Anti-Static does not mean the material will protect from static. Most Pink Poly has a high resistance in the neighborhood of 1 x1011 ohms at 1000 volts. It does not readily conduct electricity; however, it should dissipate a charge in less than 2 seconds.. Since it is nonconductive, it can not shield components from electric fields. Polypropylene punctures at 2 to 3 pounds. It is not a water vapor barrier.

54 Packaging Static Shielding Bag (Type III) Reduces need to open bags
Type 3, Details Static Shielding Bag (Type III) Transparent, Local use, Shielding bag Reduces need to open bags Water proof (not vapor proof) Protects from Electrostatic fields (not magnetic fields) Dissipates a Charge

55 Packaging Avoid Unnecessary Charge Generators Styrofoam materials
Materials to Avoid Avoid Unnecessary Charge Generators Styrofoam materials Clear Polyethylene and Polypropylene films and bags

56 Packaging Demonstrate the Properties of the three types of bags:
Packaging, Demos Demonstrate the Properties of the three types of bags: Transparency Tribocharging ESD Shielding EMI Shielding Puncture Resistance Vapor and water Resistance This is not a Faraday Cage !

57 Packaging When does ESD susceptibility stop?
When ESD sensitive items are properly packaged in ESD control packaging materials. When the level of assembly or packaging is such that a complete electrostatic shield (Faraday Cage) exists around the item. Faraday Cage Examples: ESD Shielding Bag/Pouch, Conductive Tote Box (with lid), Conductive Case/Enclosure

58 Cabinets, Shelves, & Work Surfaces
Cabinets, Shelves, & Work Surfaces Requirements: Ground cabinets, shelves, and work surfaces used during handling or storage of ESD sensitive items. All ESD control work surfaces, storage cabinets, and shelves shall be tested annually. Non ESD designed shelves and storage cabinets may require fitted ESD work surface material to meet this requirement. Cabinets and shelves used exclusively for storage of non ESD Sensitive items (or ESD Sensitive items protected by a complete Faraday Cage) do not require a ground connection or periodic testing.

59 ESD Connector Caps Connector Caps, NASM5501/31 & 32 Formerly Mil-C-5501/31A & 32A They complete the Faraday Cage They protect against discharge to the pins. They keep moisture and dust out. They need to be conductive to work. Pink Poly will not work None of the colored ones will protect electronics They can be tested with a DMM There is a supply problem Some are not labeled correctly. WAIVER AND CORRECTIVE ACTION NOTICE Subject: ESD Protective Cap Usage, Technical Order (TO) , Section VII, Electrostatic Discharge Control Background: Protective connector caps are required per the subject TO to ensure Faraday Cage protection of ESD Sensitive devices contained within various enclosures (i.e. black boxes, LRUs, etc.). All caps are part of protective packaging provisions outlined in the TO and must (1) Provide electrostatic shielding and (2) Be resistant to triboelectric or frictional charging. Two specific problems and corrective actions associated with the usage of these caps are addressed in this notice. Problem 1: All caps currently being ordered must meet requirements outlined in MIL-C-5501/31A and 32A. Several organizations have reported that the caps being received do not meet these provisions. Corrective Action (Waiver): This document allows for the usage of caps obtained using the part numbers and national stock numbers (NSN) within Table 7-3 of the TO even though they may not meet all requirements of MIL-C The Air Force ESD Control Technology Center will continue to work with the Defense Industrial Supply Center (DISC), and cap manufacturers to resolve these problems. Problem 2: Caps already in stock at Air Force facilities may or may not provide BOTH shielding and non-charge generating properties required for ESD protection. Corrective Actions: Current cap supplies must be checked to remove deficient caps. A variety of cap types currently exist throughout the Air Force. Removal procedures for the existing types are as follows: a. Colored Plastic Caps. These caps may be red, green, pink, yellow or any color other than black. It is highly unlikely any of these caps provide any ESD protection. All caps of this type currently used to cap ESDS items must be discarded. b. Black Caps. Most of these caps contain carbon or a conductive additive that provides shielding properties. Caps containing carbon (or conductive additive) are also resistive to tribocharging. There are some black caps however that are plastic without any conductive properties. For this reason, all black caps must be tested with an ohmmeter to determine their suitability for use. Use an ohmmeter with leads containing alligator clips and clip each lead to opposite sides of the cap. Since most ohmmeters are generally capable of readings up to 50 megohms, any observable reading is acceptable. If no reading is observed, discard the cap. Marking : Organizations wishing to mark those caps tested and found to be acceptable may do so by using the MIL-STD-129, ESDS symbol (triangle and reaching hand). Labels containing the symbol (See below) may be used for this purpose.

60 Marking, Labeling, & Signs
Marking & Signs, 1st of 4 Equipment Label TO , Fig 7-8 Attach on a readily visible exterior surface, if space is available and does not hinder operation of the item.

61 Marking, Labeling, & Signs
Unit Pack Label The Unit Pack Label TO , Fig 7-11 Attach to both sides of outermost bag. ATTENTION HANDLE ONLY AT STATIC SAFE WORK STATIONS STATIC SENSITIVE DEVICES

62 Shipping Container Label
Marking, Labeling, & Signs Shipping Container Label Shipping Container Label TO , Fig 7-12 Attach to Fast-Pack, Intermediate Pack, Exterior Pack, or Shipping Container which contain the unit packs. The preferred color scheme is shown.

63 Marking, Labeling, & Signs
ESD Work Area Sign ESD Work Area Sign TO , Fig 7-16 Placed at or near the entrance to ESD Work Area. ATTENTION STATIC SAFEGUARDED WORK AREA

64 ESD Worksurfaces TYPES OF ESD WORKSURFACES RIGID CUSHIONED FOLDABLE
ESD Worksurfaces, 1st of 4 TYPES OF ESD WORKSURFACES RIGID None approved at this time They have smooth hard surfaces, but do not dissipate charge at low humidity. CUSHIONED These are most commonly used. Available in standard 2 x 4’ size (Table 7-3 item 16) The 40’ Roll, Item 19 in Table 7-3, does about 10 work benches FOLDABLE These are portable and have CPG & W/S

65 ESD Worksurfaces Permanent ESD Workstation Surface.
Permanent Type Permanent ESD Workstation Surface. Glued to the wood subsurface. Prevents sliding and buckling of the surface. Durable hard rubber increases service life. Surface hardness is between Rigid and Cushioned. Passes AF’s static dissipation, and resistance. tests. Refer to items in Table 7-3

66 ESD Worksurfaces What to do with a non ESD Workstation?
Add a 2 x 4’ ESD control work surface. Sits on top of existing surface. Reduces cost of replacing entire workstation Reference Table 7-3, item 13 in T.O

67 ESD Worksurfaces CLEANING WORKSURFACES.
Cleaning them CLEANING WORKSURFACES. Best to use 70 / 30 IPA / water. Do not use any silicones ! Do not use oils or waxes ! Demonstrate Testing the Work Surface. Test Annually or sooner if desired. The Work Surface Test Procedure is in 7-8 a. A Megohmmeter and a 5 LB electrode is used. Test points from the surface to the CPG.

68 ESD Worksurfaces Scrim Layer Functions
Provides a uniform top to top resistance It is part of the grounding system Test the electrical contact from Snap to Scrim Use a DMM or Megger across the Snaps Cardboard Layer #2 for strength and thickness Insulative, Protective, Transparent Paper Layer Humectants, Metal particles, Salts, Ionic Materials The Colored Decorative Paper Layer The Conductive Scrim layer, usually carbon doped paper Cardboard Layer #1 for strength and thickness

69 Air Ionizers, what they do
AIR IONIZATION Air Ionizers, what they do IONIZED AIR REMOVES CHARGES FROM JOB ESSENTIAL NON CONDUCTORS PACKAGING MATERIALS LAMINATED SCHEMATICS & DRAWINGS AND FROM ISOLATED CONDUCTORS NEED TO MAINTAIN A BALANCE OF POSITIVE & NEGATIVE IONS The ionizer produces ions by high voltage corona from 4 needle points positioned equidistant around and behind the fan. Opposite pairs of points generate positive and negative ions. The ion cloud is mixed by the action of the fan blades and propelled across the work bench by the wind. Ionizers are also used for neutralizing charges on non-conductors and isolated conductors as well. The ions flood the workplace and are attracted to surfaces that are charged with the opposite polarity. The ions in the air neutralize the charged surfaces. Portable, area, and room, ionization systems are commercially available. A needle point can become distorted and fowled after many hours of use and lose efficiency. If one point does not work as well as the others, then the balance of positive and negative ions may no longer be equal. This could result in putting a negative or a positive voltage on nonconductors, just what you are trying to avoid. Therefore, ionizers have to be tested quarterly (Table 7-5) according to the method in 7-8 f “Test Procedures for Bench Top Electrical Ionizers”. Ionization systems are also useful in neutralizing charges. Both positive and negative ions can be generated from electrically powered sharp points. The ions flood the workplace, are attracted to surfaces that are charged with the opposite polarity, and neutralize the surface. Portable, area, and room, ionization systems are commercially available.

70 AIR IONIZATION Demonstrate Value of Ionization: Ionizers require
When to use Ionizers Use When: The Work Area Survey requires it. Demonstrate Value of Ionization: Ionizers require periodic testing. Refer to 7-7.d.6.a

71 Grounding Grounding, 1st of 5 View of Open Outlet Box Showing Equipment Grounding Conductors. Equipment Grounding Conductors Third Wire “Ground” Power for receptacles and lights on adjacent benches, 4 and 5, come in from the black power cords. Three green grounding wires enter the right side of the wall outlet. They come from the common point ground connector, one on each bench, and the third is ground for a nearby storage cabinet. The wiring inside the wall outlet shows that the green grounding wires are tied to the third-wire ground that comes in through the conduit from the Circuit Breaker box. Refer to Figures 7-13 and 7-14 in section 7.

72 Wiring Verification Test
Grounding Wiring Verification Test photo This tester is showing correct receptacle wiring when both side leds light. Six separate defects can be identified with the combination of 3 leds. The led covers are Yellow Red and White although the leds themselves glow yellow. Utility Wiring Verification Test is done first. Par. 7-5.e(3)(b) of T.O

73 Grounding Utility Ground Wiring Verification Check, Par. 7-5.e(3)(c)
Utility Ground Check Utility Ground Wiring Verification Check, Par. 7-5.e(3)(c) Item 66 of Table 7-3 Pictured here is the PGT-601A Ground Circuit Tester (item 66 in table 7-3). This is multipurpose test device. With three leds across the top, it can do the basic receptacle test shown previously. The meter at the bottom can read average line voltage and % voltage drop. This is used to detect a false ground. A false ground is when the third wire is tied to the neutral wire somewhere to simulate a mechanical ground. This device can also determine if the conduit is being used as the ground conductor. The two vertical leds near the top right are used to indicate if there is an AC voltage between the ground and the neutral wires. The red led lights if there is greater than 4 VAC present. The unit also test GFI (Ground Fault Interrupt) trip points, which should be in the range of 4 to 6 milliamps. Ground Impedance Testing: If the work bench has a GFI circuit, then this meter cannot use a receptacle on a bench to test for low resistance to ground without tripping the GFI. In that situation, unplug the bench at the wall receptacle, as shown here, and test the quality of the ground at that location. Refer to the user manual for details on the procedure for this test.

74 Grounding Resistance Check from Bench’s Groundable point to third wire
Bench Ground Check Resistance Check from Bench’s Groundable point to third wire ground. Par. 7-5.e(3)(d) Verifying the integrity of the common point ground connections to the groundable point. The resistance should be less than one ohm providing that there is not a megohm resistor in the workstation’s ground cord.

75 Grounding USE AN OHMMETER TO CHECK CONTINUITY FROM THE CPG TO:
Common Point Ground USE AN OHMMETER TO CHECK CONTINUITY FROM THE CPG TO: WRIST STRAP PLUG-INS, BENCH DRAWERS, BENCH MATS, SHELF MATS This is an expanded Figure 7-4 showing how each ESD control device is grounded to a single Common Point Ground Fixture which is itself grounded to the equipment (mechanical) ground.

76 The Role of Capacitance
A KEY PLAYER IN ESD

77 Capacitance Equations
The Role of Capacitance Capacitance Equations CAPACITANCE EQUATIONS Q = CV C = Q / V V = Q / C Q - charge in coulombs C - Capacitance in farads V - potential in volts The relationship between charge, capacitance and voltage is given here. In this expression, the capacitance relates to a device, circuit pack, or an assembly’s capacity to hold charge. Obviously, the larger the conductive area, the greater the charge carrying capacity. The capacitance also varies with respect to the distance to ground. If a device is charged and then moved away from ground, its capacitance will decrease and the voltage will have to increase to satisfy this expression. Nanocoulomb (nc) = 10-9 C Picofarad (pF) = F

78 Parallel Plate Example
The Role of Capacitance Parallel Plate Example Parallel Plate Capacitance A d A C = --- 0K d C = Farads A = meters2 d = meters 0 = 8.85 x f/m K = dielectric constant Capacitance becomes larger as the distance becomes less. Let Q (coulombs) remain constant. The Voltage goes down as the capacitance goes up. A capacitor stores electrical charge. In its simplest form, a capacitor consists of two plate electrodes separated by a dielectric. The capacitance, measured in farads, varies directly with the electrode area and dielectric constant, and inversely with the dielectric thickness. V = Q / C

79 The Role of Capacitance
Your Capacitance A PRACTICAL EXAMPLE OF CAPACITANCE AT WORK If you have insulative shoes, your soles become the dielectric in a capacitor between you and the grounded floor. With a charge on your body lift your leg high. What happens in terms of the equations ? What happens to the voltage on your body ? The Area becomes smaller; therefore the capacitance becomes smaller. Nothing happened to the total Coulombs on your body. But since Capacitance is inversely proportional to Voltage, the Voltage goes up.

80 Reference Measuring Charge, Coulombs Faraday Cup Electrometer
Reference, 1st of 4 Measuring Charge, Coulombs Electrometer Faraday Cup The measure of charge is the COULOMB. A more familiar term, the Ampere is equal to one coulomb flowing in one second. Charge can be measured with a Faraday cup and a coulomb meter or electrometer. A Faraday cup is a metal cup within an outer, grounded metal enclosure. A coaxial cable attaches the inner cup to the electrometer. The magnitude and polarity of the net charge on any item placed in the inner cup will be displayed on the meter. The construction of the Faraday cup is shown here. The inner cup is isolated from the outer cup with an insulating standoff. The inner cup is below the lip of the outer cup to permit the assembly to be covered with a metal lid which contacts the outer cup. The inner cup is connected to the center conductor of the coaxial cable. The other end of the coaxial cable is attached to the instrument. The magnitude and polarity of charge on any item placed in the inner cup is measured with respect to the grounded outer cup by the electrometer. A conductor placed in the cup will share its charge with the cup, when it touches the cup, and the charge and polarity will be indicated on the meter. The charge on an insulator will also be registered on the electrometer. However, since the charge on an insulator will remain on the insulator and not be conducted off, the meter will reflect the decrease in charge when the insulator is removed from the cup. One can therefore distinguish between the charge on conductors and insulators, or the mobile or immobile charge on a composite, by measuring with the device in the cup and after removing it from the cup. The mobile charge is what is measured after the device is removed. The immobile charge is the difference between the two measurements.

81 Reference Energy Equations E = 1/2 C V 2 E = 1/2 Q V E = 1/2 Q 2 / C
E = energy in Joules C = Capacitance in Farads V = Volts DC

82 Reference Numerical Prefixes
In practice, many measurements are either much larger or much smaller than a simple unit of measure would indicate. Therefore, we provide these Latin and Greek prefixes that indicate order of magnitude changes. One coulomb is a very large charge. In our work, we normally are concerned with billionth of coulombs (10 to the minus ninth power C), which we call a nanocoulomb, nC. Examples: 1 nanocoulomb = 1 x coulombs 10 picofarad = 10 x farads

83 Reference Useful Derived Units

84 Rome Site ESD Contacts See Next slide
ANY Questions??? Rome Site ESD Contacts See Next slide

85 ESD Contacts Rome Site 1Lt Christopher Lowe x2276
RIB Ron Ziminski x4450 RIE Bob Macior x2480 RIF 1Lt Christopher Lowe x2276 RIG Steve Tyler x3618 RIK Charlene Booth x2203 RIO Linda Dittmar x2684 RIS Julie Brichacek x4995 RIT John Rooks x2618 RY Bill Lipe x4878


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