- ESD Basics for the Program Manager
- How To’s of In-Plant ESD Survey and Evaluation Measurements
- Make sure you have people with the right knowledge to maintain
your ESD control program at the highest level.
- Learn from top industry professionals.
- ESDA Certification courses are part of the globally recognized Certified Professional
Program Manager Program developed by the ESD Association.
February 26-27, 2014
EOS/ESD Association Inc.
7900 Turin Rd. Bld 3
Rome, NY 13440
Drag chains and grounding mobile equipment, such as carts, can be a challenge in any ESD Control Plan. The required limit for cart work surfaces per ANSI/ESD S20.20 is less than 1 x 109 ohms resistance to ground. In the most recent edition the ESDA November 2013 Threshold E-News Question and Answer section there is a good discussion on what is required to make a drag chain work reliably. Read the details and the rest of the Threshold E-News Here.
Desco’s approach to drag chains is very similar to what the ESDA recommends. If drag chains are used, ideally a 18” long portion should rest on the conductive floor, and frequent compliance verification tests should be performed. To have more confidence in reliably having a path-to-ground, Desco has consistently recommended that drag chains be replaced with a more reliable system if possible:
- Conductive casters – Also recommended by the ESDA in this Q and A
- Using ground wire from the cart attached to a common point ground when stationary
It should be noted that carts are an optional part of any ESD Control Plan. As long as ESD susceptible devices are packaged in ESD shielding containers (shielding bags, boxes, totes, etc) while stored or transported, the cart may not have to be grounded.
For additional information on conductive casters, see ANTI-STATIC CASTERS: The Newest Development in the Ongoing Battle Against ElectroStatic Discharge” by The Darnell Corporation
“The researchers stated: ‘Insulative wheels can accumulate a charge when a cart is moved on an insulative or conductive floor, regardless of the cart being equipped with a grounding chain or not’ if the cart stops at a point where the grounding chain does not make proper contact with the floor.”
“The final conclusion is: For a good ESD protection the carts should be equipped with conductive wheels, preferably all [four] wheels, and the floor must be conductive with short distance between the conductive spots.”
There are three ESD Awareness Symbols defined in ANSI/ESD S8.1:
To view information about each symbol please click the link or image above.
Desco provides downloadable symbol artwork at no charge:
Desco utilizes the proper symbols in manufacturing our packaging products, worksurface and floor mats, and a number of other products where these symbols are recommended or required. We can also offer custom labeling. For more information contact us.
The ESD susceptibility symbol incorporates a reaching hand in a triangle with a slash through it and is used to indicate that an electrical or electronic device or assembly is susceptible to damage from an ESD event. Used to identify ESDS [ESD sensitive items] and that personnel should be grounding when unpackaging or handling that item. It is also referred to as the ESD sensitivity symbol or ESD warning symbol.
The ESD susceptibility symbol should be used on assemblies and devices that have a sensitivity to ESD events. The symbol may be incorporated on a sticker used to close or seal ESD protective packaging to indicate that materials inside the package are ESD susceptible.
The symbol is a reaching hand with defined fingers and fingernail, in a contrasting triangle with a slash in front of the hand.
The choice of color for this symbol is arbitrary. The color red shall not be used because it suggests a hazard to personnel. The preferred color is a yellow hand and slash on a black background.
Note: Three Arrows In A Circle Symbol, per ESD Handbook ESD TR20.20 “Military organizations sometimes use MIL-STD-1285 for hardware marking and that document once required the use of the “three arrows in a circle” symbol. That symbol has been changed for consistency with industry marking to the “hand in triangle” ESD Susceptibility symbol”
ESD Protective Symbol
The ESD protective symbol differs from the ESD susceptibility symbol, by the addition of an arc around the outside of the triangle and the omission of the slash across the hand and the triangle.
The ESD protective symbol should be used to identify items that are specifically designed to provide ESD protection for ESDS items. Examples of these are packaging, ESD protective clothing and personnel grounding equipment. The ESD protective symbol should also be used on items designed to replace static generative materials. Examples of these items are ESD protective work station equipment, trash can liners, and chairs. The item is to be ESD protective or non-static generative by design.
The choice of color for this symbol is arbitrary. The color red shall not be used because it suggests a hazard to personnel. The preferred color is a yellow hand on a black background.
Note: In Europe per Packaging standard EN 61340-5-3 there is a requirement to place a letter under the triangle denoting the product’s primary ESD control function:
F electrostatic field shielding
C electrostatic conductive
D electrostatic dissipative
If the letter is “L” the primary ESD control property is low charging (antistatic); if “EPA” is meant to indicate the product is designed to be used in an ESD protected area.
ESD Common Point Ground
This symbol is established to indicate an ESD common point ground, which is defined by ANSI/ESD-S6.1 as “a grounded device where two or more conductors are bonded.”
The ESD common point ground symbol should be used to indicate the location of an acceptable common point ground as defined by ANSI/ESD-S6.1.
This symbol consists of a bold outer circle inside of which are the words, ESD COMMON POINT GROUND, in bold type. Inside that are two thick contrasting circles and one thick circle that may fill the center or extend to the center where a snap, plug or other fastener may be connected.
The choice of color for this symbol is arbitrary but black or white on green is suggested. The color red shall not be used because it suggests a hazard to personnel.
Note: in Europe they used for the same purpose the Earth Bonding Point symbol:
See published article Now Is The Time for ESD Control Programs to be Improved It includes:
HUMAN BODY MODEL
- Part of the challenge may be for the first time needing to handle electronics having a HBM Class 0A withstand voltage. Per the ANSI/ESD S20.20 Foreword: “This standard covers electrical or electronic parts, assemblies and equipment susceptible to damage by electrostatic discharges greater than or equal to 100 volts Human Body Model (HBM).
- When handling devices susceptible to less than 100 volts HBM, more stringent ESD Control Program Technical Requirements may be required, including adjustment of program Technical Element Recommended Ranges.
ANSI/ESDA/JEDEC JS-001-2011 Table 3. HBM ESD Component Classification Levels
Classification Voltage Range (V)
- 0A < 125
- 0B 125 to < 250
- 1A 250 to < 500
- 1B 500 to < 1000
- 1C 1000 to < 2000
- 2 2000 to < 4000
- 3A 4000 to < 8000
- 3B ≥ 8000
JESD22-C101C Field-Induced Charged-Device Model Test Method for Electrostatic-Discharge-Withstand Thresholds of Microelectronic Components Table 3
Devices shall be classified as follows:
- CLASS I < 200 volts
- CLASS II 200 to < 500 volts
- CLASS III 500 to 1000 volts
- CLASS IV > 1000 volts
The article lists possible steps one can take to improve their ESD control program; it is an update of what we have online at Class Zero and ESD Control.
There are companies that do ESD simulation and can destructively test a component, sub-assembly, or product to determine the ESD sensitivity or “withstand voltage.” For example, ETS or Electro-Tech Systems at www.electrotechsystems.com/ in Glenside, Pennsylvania should be able to perform withstand voltage testing. However, we understand taht most of our customers rely upon classification or withstand voltage documentation from component suppliers and then have a program to protect the very most ESD sensitive item.
Desco offers a number of standard sized Statshield® Moisture Barrier Bags. We always recommend evaluating our product to ensure it meets your requirements. We will gladly provide samples for your evaluation; just fill out a request here.
|3M Series||Statshield® Moisture Barrier Bags Series||Drawing/Specs|
|3M 2000||3.5 mil||#13806|
|3M 2700||6.5 mil||#13760
|3M 3000||4.0 mil Foil||#13950|
|3M 3400||4.0 mil Foil||#13950|
|3M 3700||4.0 mil Foil||#13950|
To see the details and specs for 3M bags – Click Here
Standard items normally ship within 3 working days of an order being received. If you have Read the rest of this entry
An excerpt from Terry Welsher’s InCompliance article titled -
The “Real” Cost of ESD Damage about using “split lot” experiments to determine the effectiveness of ESD control when manufacturing electronics.
“At the time of the first EOS/ESD symposium in 1979 there were few mature ESD programs, but many companies were trying to establish them. Some of these companies were also developing their case for management through actual split-lot experiments.
Western Electric Denver Works (1981) – In this study the initial deployment of a basic ESD program was observed with careful collection of yield loss data for five key operations. Documented yield improvement up to 10.73% was observed, and with the assistance of the plant financial organization, the return-on-investment was estimated to be in the range of 900-2300%, depending on assumptions. This study was also significant in that it demonstrated that an effective program could be implemented in a very dry environment such as Denver, Colorado’s without humidity control.
Western Electric North Andover Works (1983) – This work included three separate definitive experiments on the effectiveness of ESD programs. Again, since ESD controls of any kind had not yet been implemented, simple split -lot experiments could be conducted. In these experiments as many as 1275 units were processed in single experiment with and without controls. Clearly, it would be difficult to justify taking these risks today. Ratios of the number of failures in the unprotected and protected lots ranged from 1.9:1 to 5.5:1. The return on investment (for implementation of wrist straps and some ESD-protective transport materials) was as high as 950%. The quality assurance organization also studied the quality of outgoing product. The controls instituted in the factory resulted in a 3:1 reduction of defect rates.
Lockheed Missiles and Space Company (1983) – In this study failure data before and after program implementation was collected and explicit cost avoidance estimates were made. A detailed itemization of implementation and maintenance costs was weighed against extrapolated expected failure costs and an annual savings of almost $2 million/year was demonstrated.”
Also, we have HBM Human Body Model, CDM Charged Device Model, MM Machine Model; he mentions CBE Charged Board Events and CDE Cable Discharge Events, noting “Recent data and experience reported by several companies and laboratories now suggest that many failures previously classified as EOS may instead be the result of ESD failures due to Charged Board Events (CBE). The reason for this is that boards may store considerably more charge than is stored in the standard CDM tests. The resulting failure signature shows more physical damage (Figure 2) than a stand-alone device failure would and thus FA experts unfamiliar with this phenomenon often make the wrong diagnosis. In addition, similar observations have been made regarding the misdiagnosis of Cable Discharge Events (CDE) as EOS. Some companies have estimated that about 50% of failures originally designated as EOS were actually CBE or CDE.”
If using ESD flooring for a flooring / footwear personnel grounding system (or a possibility in the future), we recommend conductive flooring.
A “Conductive ESD Floor” is defined by ANSI/ESD S7.1 (the flooring standard) as a floor that measures <1.0 x 106 ohm Rtg.
The ANSI/ESD S20.20 standard states that an ESD floor must measure <1.0 x 109, This same standard also states if the Footwear / Flooring grounding system (Operator to footwear to floor to ground) is <3.5 x 107 ohm Rtg, no additional testing is required. If the system measures >3.5 x 107, but less that 1.0 x 109 ohm Rtg, then Charge Generation tests with operator voltage of <100 volts must be preformed.
Since floors get dirty, which can raise floor resistance, it is good to start off with a floor that is Conductive <1.0 x 106 ohm Rtg.
The figure to the left is from ESD TR 20.20, the Handbook for ANSI/ESD S20.20. At 3.5 x 107, ohm (35 megohm), by straight resistance (testing done wrist strap grounding), an operator’s voltage will always be <100 volts. This also shows that the lower the resistance to ground, the lower the body voltage.
Therefore, in selecting ESD Flooring products, you would want that them to be <1.0 x 106 ohm Rtg, unless there were special circumstances, like cleanroom concerns, that do not allow you to achieve the lower resistance level of “conductive”.
Desco manufactures a number of conductive flooring products:
Customer Feed-back: Desco Premium Full Coverage Foot Grounder is a better value, providing triple the life.
The customer was easily convinced that the path-to-ground of a full coverage style foot grounder outperformed a standard heel grounder due to the contact points on both the heel and sole of the full coverage style. What surprised the customer was when they tested for lifespan of the product. The customer found that the full coverage design lasts 2-3 times longer than a standard heel grounder. The test results determined that the reason for the longer lifespan was that the initial point of contact with the floor, during a normal walking motion was at the back of the heel; exactly where a normal heel grounder fits on a shoe. The heel portion of the full coverage foot grounder is moved slightly towards the toe of foot. So the majority of the wear and tear caused by walking is placed on the operator’s shoe rather than the full coverage foot grounder. The results of the customer’s tests were that the Desco Full Coverage Foot Grounders were a better value due to the longer useful life and provided a superior flooring/footwear personnel grounding as compared to standard heel grounders.
To request a sample of a Desco Full Coverage Foot Grounder, use the below chart to determine your size, click on the item number and then click on the button on the items webpage.
|4 to 8||Small||17290|
|8 to 12||6 to 10||Medium||17291|
|10 to 14||Large||17292|
Or take advantage of Desco’s current deal on Full Coverage Foot Grounders through September 4, 2013.
This year’s EOS/ESD Symposium Information will be at the Rio All Suite Hotel in Las Vegas, NV on September 4-13, 2013.
For a complimentary pass to the exhibits area please Contact us.
6:00 pm to 9:00 pm on Monday, September 9.
9:30 a.m. – 5:00 p.m. on Tuesday, September 10
8:30 a.m. – 1:30 p.m. on Wednesday, September 11
Hope to see you there.
For official registration, a full schedule of meetings, hotel information, and other events at this year’s symposium click HERE
Desco has been a part of the ESD Symposium for all 35 years of its existence. Desco employees have volunteered their time to be a part of the ESD Association’s standards meetings, working groups, and other functions at the annual symposium. Desco will also have a booth (#116) in the exhibits area again this year. We will have many products available for demo throughout the show area including the following new products:
- Newly Updated EMIT SmartLog V5™ Hardware and TEAM5 Software
- New EMIT SIM Software
- New Bubble Cushion Bags
- New Smock Colors – Grey and Pink
- Newly Designed Digital Surface Resistance Meter
- New Menda ESD Shop Travelers
- New Protektive Pak Items
The Rio All-Suite Hotel & Casino is at 3700 West Flamingo Road, Las Vegas, NV 89103. Phone: 702-777-7777. The ESD Association advises using the group rate:
Book reservations by August 12, 2013 in order to guaranteed the group rate!
THE OFFICAL GROUP RATE AND ROOM BLOCK IS AVAILABLE ONLY THROUGH THE RIO DIRECTLY USING THE INFORMATION BELOW
Official Hotel Reservations:
Choose from two room rate options:
Option 1-Without Internet – Group Rate @ $109+tax
Option 2-Internet Included in Guestroom (1 connection) – Group Rate $123+tax CALL-IN: Reservation Center at 888-746-6955 and ask for Electrostatic Discharge Association, group code -SREDA13-$109 with no internet -or- SREDA3F-$123 with internet.
The “standard” resistance value for a wrist strap is to be 1 megohm (+/-20%). Touch-Testers test for this, so should your single-wire constant monitor. One of the ways that manufacturers of low cost continuous monitors cut corners is to not monitor for a current-limiting resistor in the wrist strap system. While there is no industry standard for continuous or constant monitors (although there is useful information in ESD TR 12-01 Survey of Constant (Continuous) Monitors for Wrist Straps), the ESD Association says the following about current limiting resistors in the operator’s ground cord.
“Wrist straps incorporating a resistance of non-standard value (other than 1.0 megohm +/-20%) shall be identified by having a prominent feature, red in color, on the wrist strap.” [ANSI/ESD S1.1 section 5.9 identification of NonStandard Resistance Value]
“A resistance of sufficient resistance to limit current to less than 0.0005 amps (0.5mA), at the highest voltage that may be encountered, should be incorporated into the wrist strap. Nominally, 800,000 ohms (800 kilohms) are sufficient for voltages of up to 240 volts alternating current (AC). The value of 1 megohms is specified because it is a standard value discrete resistor. Special situations may dictate the use of values above or below the 1 megohm value. Wrist straps with nominal resistances other than megohm should be marked in accordance with paragraph 5.9. Discrete current-limiting resistors should be located near the connection between the ground cord and the cuff.” [ANSI/ESD S1.1 Annex B1 Construction Guidelines Current-Limiting Resistance]
Compared to a normal “hard ground” with very low resistance in the path-to-ground, the vast majority of wrist straps used for ESD control use a ground or coil cord with resistance also called a “soft ground.” The typical 1 megohm of in-line resistance is designed to limit any potential current the operator may come in contact with if exposed to 110 VAC and up to 250 VAC maximum. Underwriters Laboratories recommends that the electrical current that the operator be exposed to be limited to 0.25 milliamp at 250 volts, the 1 megohm resistor does this.
If you choose to use continuous monitoring for operator grounding, your continuous monitor should verify this “soft ground” in order to verify that the operators’ wrist straps have a functioning 1 megohm resistor in them as well as a path-to-ground.
To confirm that a continuous monitor verifies a lower limit follow this simple test procedure:
- Use a ground cord with a no resistor in it, and connect the snap to a wristband.
- Make sure the wearer of the wrist strap is isolated from ground other than the wrist strap.
- Then plug the banana end of the cord into the monitor.
If the continuous monitor alarms (Red) with the ground cord without a resistor the continuous monitor is verifying for a lower limit.
If the continuous monitor does not alarm (Green) with the ground cord without a resistor the monitor is not verifying for lower limit. These types of monitors do not verify that there is a resistor in the cord and may allow the operator to be “hard grounded” without a current limiting resistor.
Click HERE to request a sample of a coil cord made with no resistor.
To verify that ground cord has no resistance between the snap and banana, conduct this test:
- Use or a multimeter (set above 1 megohm range and test for continuity)
- If no resistor = <~5 ohms, however if includes 1 megohm resistor = ~ 0.8 to 1.2 megohm