ESD Systems’ ESD Technical Newsletter
Issue 5, November 1998: Volume 1
Sender : ESD SYSTEMS, 19 Brigham Street #9, Marlboro, MA 01752-3170
Phone : 508-485-7390
To be removed from this mailing list, simply reply with "UNSUBSCRIBE ESD_Newsletters" in the subject.
This is a free monthly newsletter, which specializes on issues in static control in the workplace.
Need your own copy? Want to subscribe to this free Newsletter? All you or your colleague(s) need to do is simply fill out the subscription form athttp://www.esdsystems.com/?PageNo=NEWSSUBSCRIBE
This Newsletter is never sent unsolicited. To unsubscribe from this mailing, send an e-mail to ESD_Newletters@esdsystems.com and put " UNSUBSCRIBE ESD_Newsletters" in the subject.
Let us know what you think. Tell us what you would like to see in future issues. Want to contribute articles or other related information to our Newsletter? Send your comments email@example.com
IN THIS ISSUE:
GASES DO NOT CHARGE!
It is well known that early on, the aerospace industry learned that the surface of an aircraft would charge up considerably when flying within our troposphere. Re-fueling required an operator to attach a grounded cable first to the aircraft before bringing a fuel hose near the craft. In later designs, the wings deployed corona discharge points on the trailing edges of the wings to help neutralize the charging.
What was happening to cause the aircraft to charge? Simply put, the surface of aircraft had undergone triboelectric charging due to the collision with impurities and other large (non-gases) particles that are also present in the air. These large, actually huge particles compared to oxygen, nitrogen and argon atoms, collide with the fuselage and wing surfaces and can both depart and extract a surface charge.
Niels Jonassen (Mr. Static) had early on (1954) been part of an extremely sensitive experiment to help investigate a fatal explosion involving an anaesthetic machine at a local hospital. This experiment utilized a Wolf electrometer, and demonstrated that the flow of oxygen, cyclopropane and mixtures thereof did not show any signs of charging. The cause of the explosion was later found to be due to the tribocharging and consequent ESD of the metal pin and rubber bag that comprised part of the anaesthetic machine.
NEPCON WEST 1999, ANAHEIM, CA
NEPCON West '99is the World's leading source for electronics manufacturing solutions.
With nearly 1,000 global companies exhibiting in over 300,000 net square feet of space, display the newest and best technological advances in electronic manufacturing. Attendees of over 31,000 industry professionals including engineers and managers involved with designing, manufacturing, testing and servicing of electronic products attend NEPCON. Attendees also include corporate managers and general managers responsible for development/management at OEMs and contract manufacturers. Industry buyers from more than 50 countries now attend NEPCON West.
As the World's leading source for electronics manufacturing solutions, NEPCON continues to meet the growing needs of the electronics manufacturing industry. From design through assembly, the solutions-oriented conference and special events provides practical information and address the questions every member of the electronics manufacturing team wants answered.
We encourage you to stop by the ESD Systems exhibit to learn more about our wide-variety of Electrostatic Discharge (ESD) Control products. This is a great opportunity to meet some of our ESD Systems’ team. We look forward to seeing you there.
For More Information:Contact NEPCON at Reed Exhibition Companies, 383 Main Avenue, Norwalk, CT 06852-6059. Via Telephone: (800) 467-5656 or surf to http://nepcon.reedexpo.com/west/index.html
ESD Q&A CORNER
The following questions and answers are selected from our FAQ WEB Page:http://www.esdsystems.com/?PageNo=QANDAINDEX concerning ESD & Standards.
Q1:I am trying to find companies that can meet MIL-W-80 spec. It is a 1966 MIL Spec related to static dissipative acrylics or acrylic coatings. Please advise as I am having a difficult time. - Anonymous, Inglewood, CA
A1: We do sell an acrylic-based zinc-free ESD floor finish as part of our Statproof® family. The MIL-W-80 refers to solid materials in sheet or strip form and wouldn't apply to our floor finish system. The Statproof® floor finish does meet several industry recognized standards (ANSI/ESD-S7.1 for surface resistance, AATCC TM-134-1979 for charge generation, and FTMS 101C, M-4046 for charge decay) and is UL listed (#SA6524) for slip resistance. The Tech Brief is available on-line at http://www.esdsystems.com/pdf/ps-2026.pdf
Q2: My company is the manufacture of PCs. One of our reliability test is ESD. Our standard is IEC-810-4 L3, Air:8kV, contact:6kV. But we want to sell to buyers in California, USA. Can you tell me about how many kV of ESD there [is used for testing in the States]? - Anonymous, Hsin-Chu, Taiwan
A2:There are 3 tests that should be used when testing for ESD susceptibility:
Which includes a summary of the voltage stress limits. Note, there are varying waveform requirements based on different impedance loads. These standards are available from ESD Systems in Marlboro, Massachusetts and from the ESD Association in Rome, New York.
Q3: I'm interested in the foot grounders but I'm not aware of what the ESD floor requirements or specs are. Do you have any info (in layman's terms please) on what would have to be done to test the floor for ESD compliance and/or what would have to be done for it to meet compliance? - Anonymous, Ashburn, VA
A3:An ESD floor should be greater than 1x105 Ohms and less than 1x109 Ohms according to EIA-625 standard. The ESD Association has a draft standard, ESD DSTM54.1-1997 that incorporates both the floor material and footwear in combination when measuring resistance. This is actually a testing method and doesn't specify or recommend a working resistance range. To actually test the floor the standard, ANSI/ESD-S7.1-1994, has a specific test method that uses two five pound probes and driving voltages of 10 and 100 Volts. Our meter, item # 41273, was designed to be used with this test method.
PRODUCT UPDATES (NEW!)
Topics: ESD Standards and Program Design (gleaned from paper http://www.esdsystems.com/whtpaper/standards.htm)
I STANDARDS from the Ground Up
ESD and Standards
There are about 60 of the more commonly used standards for ESD control listed in Tables I and II. These standards and specifications originate from many different organizations and serve different purposes, as are outlined below.
If your company supplies various electronic components or is a board house, your customers may require you to follow certain prescribed standards to which they adhere. If you are establishing a new ESD control program then the Electrostatic Discharge Association’s Standards listed in Tables I through IV will aid you to establishing the proper criteria.
The Electrostatic Discharge Association (ESDA) standards are the most comprehensive and up-to-date industry accepted standards for the control of ESD. Their current standards are listed in Table I by application.
Six years ago, the ESD Association became an American National Standards Institute (ANSI) accredited standards development organization, and this attainment is reflected in some of the ESDA standards carrying the ANSI accreditation.
The first place to look for guidance in developing your ESD Control program would be from within the ESDA standards. As of February 1998, the ESDA has refined their definitions of standards by specifying the following categories.
Furthermore, as a new standard evolves, it becomes ready for industry review and is classified as a Draft Standard and can be represented by the designation Draft Standard (DS), Draft Standard Practice (DSP), Draft Standard Test Method (DSTM), and Draft Technical Report (DTR). And lastly, an Advisory (ADV), which may be replaced by the Technical Report (TR), can be educational in nature and consists of general information and guidelines deemed helpful to the industry in understanding the use of standards and related technology.
The ESD Association has recently accepted the task of refining MIL-STD-1686 Electrostatic Discharge Control Program for Protection of Electrical and Electronic Parts, Assemblies and Equipment as a commercial document and now has a draft standard ESD DS20.20-1998.
II Defining Your Program
The starting point of a sound program is to classify the sensitivity to ESD damage of the devices you need to protect. Classification of these devices should include all simulation models (HBM, MM, and CDM refer to the ESD STM5 series in Table I) that will properly characterize the devices' sensitivity when handled at various locations within the facility.
If you do not classify the devices then you can assume the worst case for all 3 models, (Classes 0, M0, C0 - refer to the ESD STM5 series standards in Table I), making the program design critical and expensive.
III Program Design
Once the ESD device sensitivities for the various areas in the facility have been determined then this information can be mapped over the complete facility and will act as a guide to designing the ESD control program.
Now, the location/sensitivity map of the facility needs to be expanded upon by determining what standards you will use to evaluate the success and monitor the program’s progress. This map should also consider the transportation systems and traffic flow of the sensitive devices between various working areas. Additional design criteria to ensure device protection that needs to be broadened are listed as follows.
IV Selecting General Product Criteria for each Area
Which standard(s) should you reference when building your ESD Control program from scratch, updating or evaluating your current program? When you look to build an ESD-safe workstation, you need to know what industry-wide acceptability criteria to comply with.
Table IV will help aid the design and development of an ESD control program for each area using either the ESD ADV-2.0-1994 or the MIL-STD-1686. The former is more recent at this time. Table III lists various ESD Control products and the associated ESDA Standards that can be used to qualify them.
As an example, an ESD Sensitive (ESDS) workstation that is designed for worst case criteria may have the following ESD Control products: an ESD floor; grounded floor mats with use of ESD footwear (such as foot grounders); grounded and monitored table mats covering all exposed surfaces; a common point ground with monitored wrist strap connections; and air ionizers covering all areas on the work surface to which the devices would be exposed. In addition, all exposed insulators and metal surfaces would be replaced with grounded dissipative materials; all non-essential items, especially insulators, would be removed the ESDS area; and most importantly, the ESDS workstation would have ESD Control Trained operator(s) at the helm.
Starting from the ground up, your floor would be the first place to start. One of the most important characteristics of an ESD floor is its ability to conduct charges to ground. The second most important aspect is its anti-static property. One of the main mechanisms of charge generation is triboelectric generation or tribocharging. Some examples of tribocharging are people walking along a floor and carts carrying sensitive devices rolling across a floor. Depending on where the materials in contact with the floor are in the triboseries, voltages of over 30,000 Volts can be attained. If a floor has the property of being anti-static, tribocharging becomes a much smaller concern. The standards documents to help choose a floor are ANSI/ESD S7.1-1994, AATCC Step Test - Method 134-1979, ANSI/EIA-625-1994, MIL-STD-1686, MIL-HDBK-263B, and the AT&T Electrostatic discharge Control Handbook.
Typically protection on an ESDS device should start at receiving, continue to inventory storage, and then travel through its production flow usually from one workstation to the next before ending up in shipping. All throughout its handling, the device should be handled by grounded personnel. The easiest way to ground people who travel from one station to the next, delivering or picking up sensitive materials, is through mobile grounding. Wearing foot grounders (one on each foot) in conjunction with a conductive floor is one way to ensure that the operator is grounded and protected from delivering or receiving an ESD event. There are several ESDA standards to help in the testing and verification of foot grounders and shoes: ESD DSTM54.1-1997, ESD DSTM54.2-1997, and ESD S9.1-1995.
The surfaces where ESDS devices are handled should be both conductive (in the dissipative range) and properly grounded to the equipment-grounding conductor to be an effective ESD control element. There are several materials to choose from such as rubber mats, vinyl mats, both single and multi-layered and FRP and Micastat® for rigid or permanent bench surfaces. Conductive metal work surfaces should be discontinued or covered with a dissipative material because it is highly susceptible to causing an ESD event from a metal-metal contact. It is very important to control your discharge time by minimizing the energy transfer by employing resistive materials to ground . The ESDA standards to help characterize a work surface are ESD STM4.2-1998 and ESD ADV53.1-1995.
The human being can be the most dynamic part of a working environment and consequently should be considered one of the most important objects to ground. Wrist straps, a conductive wristband with a connecting ground cord, is the most popular and effective way to ground a person. Wrist straps should always be properly employed when working with ESDS devices. The ESDS standard EOS/ESD S1-1987 can aid in qualifying your wrist straps before implementation.
Materials that must stay with the ESDS work area but are neither conductive nor groundable should be treated with air ionization. Ionizers come in several types; the most popular is the corona discharge air ionizer. Corona discharge air ionizers can have emitters that are powered by AC, DC or pulsing DC high voltage. Air ionizers can be qualified by applying the ESDA standards ANSI-EOS/ESD, S3.1-1991ADV3.2-1995, and ESD SP3.3-1998.
ESDS devices should always be stored in an enclosed antistatic shielding bag or conductive closed tote or bin when not being handled. This includes inventory storage, transportation, and WIP. Further precautions during transportation include using dissipative carts with conductive wheels or drag chains in conjunction with a conductive floor when transporting ESDS devices in their shielded containers. The standards to help characterize and qualify packaging materials are ANSI/ESD S11.31-1994 for shielding bags, ANSI/EOS/ESD S8.1-1993 for proper use of package markings, ANSI/EIA-541-88 and ANSI/EIA-583-91 for packaging materials.
Determining the product sensitivities within the facility and then mapping this information helps in choosing the right materials to keep each work area under control. Using the ESDA or other related Standards will help your ESD Control program comply with industry-accepted requirements and procedures that govern the materials, products, systems or processes. Acceptability, repeatability, and dependability can be expected from an ESD Control program that employs a good design using the appropriate standards along with proper training and monitoring.
This is a free monthly newsletter, which specializes on issues in static control in the workplace.
Need your own copy? Want to subscribe to this Newsletter? All you or your colleague(s) need to do is simply fill out the subscription form athttp://www.esdsystems.com/forms/esdmail.asp
This Newsletter is never sent unsolicited. To unsubscribe from this mailing, simply reply to this e-mail and include in the subject field the following:UNSUBSCRIBE ESD_Newsletters
Let us know what you think. Tell us what you would like to see in future issues. Want to contribute articles or other related information to our Newsletter? Send your comments to firstname.lastname@example.org