We occasionally hear from customers who have ESD footwear (Foot Grounders or ESD Shoes) that is failing high on their ESD footwear tester (personnel grounding tester). There is often an assumption that the issue is a faulty tester or out of spec footwear. However, most of the time the problem turns out to be as simple as a “bad match”. This is between the upper resistance setting of the footwear tester and the resistance of the ESD footwear.
The first step in identifying the cause of the problem is to identify the upper limit setting of the tester being used.
Upper Test Limits of ESD Testers
The upper limit settings on SCS footwear testers are:
The upper limit is 1 gigaohm or 1 x 109 ohms however the factory setting 35 megaohm or 3.5 x 107 ohms
SmartLog Pro
The upper limit 1 gigaohm or 1 x 109 ohms however the factory setting 35 megaohm or 3.5 x 107 ohms
Identifying the Resistance of the ESD Footwear
The next step is to identify the resistance of the ESD footwear being used, both by itself and with a person wearing the footwear.
Heel Grounders/Foot Grounders
Foot Grounder Test
Test Method 1 – Resistance of the Foot Grounder
Using a surface resistance tester and its alligator clip, clip the lead to the foot grounder tab
Clip the other lead to the cup material
This test will tell you the overall resistance of the tab, resistor (if there is one), and the cup material
If the foot grounder tab to cup resistance exceeds the upper limit of the footwear tester it’s very likely that you won’t pass on the tester.
Test Method 2 – Resistance of the Foot Grounder and Person Together
Use test method from TR53-01-15, 8.3.2 Meter, which has been summarised below:
Use a surface resistance tester, a handheld electrode and a foot electrode
Have the person hold the handheld electrode connect to one lead
Have the other lead connected to the foot electrode
Place one foot on the foot electrode making sure your other foot is not on an ESD floor or the electrode
This test will tell you the overall resistance of the whole foot grounder and person.
If the result is higher than the upper limit of your footwear tester you will not pass at the tester.
ESD Shoes
When we hear about ESD Footwear failing regularly at the personnel grounding tester, more often than not it is ESD Shoes that are failing rather than foot grounders.
Test Method 1 – Resistance of the ESD Shoes Using Foot Plate Electrode
Place the shoe on a metal plate.
Put the 5 lb weight from the surface resistance meter inside the shoe.
Place the other weight on the metal plate next to the shoe.
Lean on the weight inside the shoe and test.
This will give the resistance of the shoe itself from inside the shoe to the bottom of the shoe.
ESD Shoe test with footplate
ESD Shoe Test with 5 lb Electrodes
Test Method 2 – Resistance of the ESD Shoe Using Two 5 lb Electrodes
Put one of the 5 lb weights from the surface resistance meter inside the shoe.
Put the other weight on the sole of shoe, make like a sandwich
Press the Test
See what the resistance of the shoe is using either of these methods and compare it to the testers upper limit.
Perform the TR53 test below, see what the resistance is of the person and ESD shoe while the shoe is being worn.
The same test from TR53 used for foot grounders above can also be used for ESD Shoes. This will provide you with the total resistance is of the person and ESD shoe.
Conclusion
The tests above will identify a clear discrepancy between footwear resistance and tester settings, but there can also be other factors in play. These factors should be considered when the footwear resistance and the tester settings are close to being the same.
Tester accuracy
Test voltage
Weight of personnel
Sock thickness and material
Humidity
Any questions regarding this post, please get in contact.
The best-equipped service bench in your shop can be a real money-maker when set up properly. It can also be a source of frustration and lost revenue if the threat of ElectroStatic Discharge (ESD) is ignored.
A typical scenario might be where an electronic product is brought in for service, properly diagnosed and repaired, only to find a new symptom requiring additional repair. Unless the technician understands the ESD problem and has developed methods to keep it in check damage from static electricity cannot be ruled out as a potential source of the new problem.
Static electricity is nothing new; it’s all around us and always has been. What has changed is the spread of semiconductors in almost every consumer product we buy. As device complexity increases, often its static sensitivity increases as well. Some semiconductor devices may be damaged by as little as 20-30 volts!
It is important to note that this post is addressing the issue of ESD in terms of control, and not elimination. The potential for an ESD event to occur cannot be completely eliminated outside of a laboratory environment, but we can greatly reduce the risk with proper training and equipment. By implementing a good static control program and developing some simple habits, ESD can be effectively controlled.
The Source of the Problem
Static is all around us. We occasionally will see or feel it by walking on carpet, touching something or someone and feeling the “zap” of a static discharge. The perception level varies but static charge is typically 2000-3000 volts before we can feel it. ESD sensitivity of some parts is under 100 volts – well below the level that we would be able to detect.
Even though carpet may not be used around the service bench, there are many other static “generators” may not be obvious and frequently found around or on a service bench. The innocent-looking Styrofoam coffee cup can be a tremendous source of static. The simple act of pulling several inches of adhesive tape from a roll can generate several thousand volts of static! Many insulative materials will develop a charge by rubbing them or separating them from another material. This phenomenon is known as “tribocharging” and it occurs often where there are insulative materials present.
Sources of Charge Generation: Unwinding a Roll of Tape
People are often a major factor in generation of static charges. Studies have shown that personnel in a manufacturing environment frequently develop 5000 volts or more just by walking across the floor. Again, this is “tribocharging” produced by the separation of their shoes and the flooring as they walk.
A technician seated at a non-ESD workbench could easily have a 400-500 volt charge on his or her body caused not only by friction or tribocharging, but additionally by the constant change in body capacitance that occurs from natural movements. The simple act of lifting both feet off the floor can raise the measured voltage on a person as much as 500-1000 volts.
Setting up a “Static Safe” Program
Perhaps the most important factor in a successful static control program is developing an awareness of the “unseen” problem. One of the best ways to demonstrate the ESD hazard is by using a “static field meter”. The visual impact of locating and measuring static charges of more than 1000 volts will get the attention of skeptical individuals.
ESD education and awareness are essential basic ingredients in any effective static control program. A high level of static awareness must be created and maintained in and around the protected area. Once personnel understand the potential problem, reinforce the understanding by hanging up static control posters in strategic locations. The technician doesn’t need an unaware and/or unprotected person wandering over and touching things on the service bench.
Workstation Grounding
To minimize the threat of an ESD event, we need to bring all components of the system to the same relative potential and maintain that potential. Workstations can be grounded with the following options:
Establish an ESD Common Grounding Point, an electrical junction where all ESD grounds are connected to. Usually, a common ground point is connected to ground, preferably equipment ground.
The Service Bench Surface should be covered with a dissipative material. This can be either an ESD-type high-pressure laminate formed as the benchtop surface, or it may be one of the many types of dissipative mats placed upon the benchtop surface. The mats are available in different colors, with different surface textures, and with various cushioning effects. Whichever type is chosen, look for a material with surface resistivity of 1 x 109 or less, as these materials are sufficiently conductive to discharge objects in less than one second. The ESD laminate or mat must be grounded to the ESD common grounding point to work properly. Frequently, a one Megohm current limiting safety resistor is used in series with the work surface ground. This blog post will provide more information on how to choose and install your ESD working surface.
Types of Worksurface Matting – click here for more information
A Dissipative Floor Mat may also be used, especially if the technician intends to wear foot-grounding devices. The selection of the floor mat should take into consideration several factors. If anything is to roll on the mat, then a soft, cushion-type mat will probably not work well. If the tech does a lot of standing, then the soft, anti-fatigue type will be much appreciated. Again, the mat should be grounded to the common ground point, with or without the safety resistor as desired.
Workstation Tools and Supplies should be selected with ESD in mind. Avoid insulators and plastics where possible on and around the bench. Poly bags and normal adhesive tapes can generate substantial charges, as can plastic cups and glasses. If charge-generating plastics and the like cannot be eliminated, consider using one of the small, low cost air ionizers It can usually be mounted off the bench to conserve work area, and then aimed at the area where most of the work is being done. The ionizer does not eliminate the need for grounding the working surface or the operator, but it does drain static charges from insulators, which do not lend themselves to grounding.
Personnel Grounding
People are great static generators. Simple movements at the bench can easily build up charges as high as 500-1000 volts. Therefore, controlling this charge build-up on the technician is essential. The two best known methods for draining the charge on a person are wrist straps with ground cords and foot or heel grounders. Personnel can be grounded through:
Wrist Straps are probably the most common item used for personnel grounding. They are comprised of a conductive band or strap that fits snugly on the wrist. The wrist strap is frequently made of an elastic material with a conductive inner surface, or it may be a metallic expandable band similar to that found on a watch. For more information on wrist straps, check out this post.
Ground Cords are typically made of a highly flexible wire and often are made retractable for additional freedom of movement. There are two safety features that are usually built into the cord, and the user should not attempt to bypass them. The first, and most important, is a current limiting resistor (typically 1 Megohm) which prevents hazardous current from flowing through the cord in the event the wearer inadvertently contacts line voltage. The line voltage may find another path to ground, but the cord is designed to neither increase or reduce shock hazard for voltages under 250 volts. The second safety feature built into most cords is a breakaway connection to allow the user to exit rapidly in an emergency. This is usually accomplished by using a snap connector at the wrist strap end.
Foot or Heel Grounders are frequently used where the technician needs more freedom of movement than the wrist strap and cord allow. The heel grounder is often made of a conductive rubber or vinyl and is worn over a standard shoe. It usually has a strap that passes under the heel for good contact and a strap of some type that is laid inside the shoe for contact to the wearer. Heel grounders must be used with some type of conductive or dissipative floor surface to be effective and should be worn on both feet to insure continuous contact with the floor. Obviously, lifting both feet from the floor while sitting will cause protection to be lost.Don’t forget to regularly check and verify your personnel grounding items:
The Personnel Grounding Checklist
Summary
An effective static control program doesn’t have to be expensive or complex. The main concept is to minimize generation of static and to drain it away when it does occur, thereby lessening the chance for an ESD event to happen. The ingredients for an effective ESD program are:
Education: to ensure that everyone understands the problem and the proper handling of sensitive devices.
Workstation Grounding: use a dissipative working surface material and dissipative flooring materials as required.
Personnel Grounding: using wrist straps with ground cords and/or foot-grounding devices.
Follow-up to ensure Compliance: all elements of the program should be checked frequently to determine that they are working effectively.
The ESD “threat” is not likely to go away soon, and it is very likely to become an even greater hazard, as electronic devices continue to increase in complexity and decrease in size. By implementing a static control program now, you will be prepared for the more sensitive products that will be coming.
Static discharges can be noticed when you touch an object of different electrical potential such as a door knob, and a bolt of electricity flows from your charged body to the door knob. This flow of electricity is actually a result of the stored static charge that is being rapidly transferred to the knob. This discharge that can be felt as well as seen, is commonly referred to as an electrostatic discharge, or “ESD”.
The generated static charges are a potentially costly occurrence for office and factory employers. You will learn in today’s post how they can easily be controlled with different types of floor material.
Static Charge Generation from Flooring
When a person walks across a floor, a triboelectric charge builds up in the body due to the friction between the shoes and floor material. The simple separation of two surfaces (such as a person walking across a floor with soles contracting and separating from the floor) can cause a transfer of electrons resulting in one surface being positively and the other one negatively charged, resulting in static charges.
Generating Charges by walking across carpet
It is not necessarily the static charge generated in the body that does the damage as much as it is the difference in potential that creates an electrostatic discharge.
The Problem with ESD (Electrostatic Discharge)
The generation of a static charge can pose quite a problem for environments that contain sensitive equipment or components that are vulnerable to static damage, such as electronics manufacturing, repair facilities and medical facilities – including computer rooms and clean rooms.
Controlling the damage and costs caused by ESD is usually the main concern that drives a company to implement a static control program. The costs involved with static damage not only include the immediate cost of the damaged component, but the contributing cost of diagnostic, repair and labor that is needed to replace or fix the component. In many cases the labor involved can far exceed the component cost.
ESD Flooring Materials
There are several options available on the market ranging from coatings (floor finish or paint) to coverings (vinyl or rubber). The choice of material depends on the mechanical and optical properties required as well as the available budget.
In general, floor coverings will last longer (10 years or more) than a floor coating. They are more durable and have a specific resistance to ground that remains constant over time.
Types of Floor Coverings – click here for more information
Coatings are easier to apply and repair and their initial cost is considerably lower. Coatings are usually applied to existing floors and often serve to convert a conventional floor into an ESD floor. However, regular maintenance is required as coatings will lose their ESD properties over time.
ESD Floor Coatings
Topical Antistat:
Conventional carpets can be treated with a Topical Antistat or other treatment. It is required that the treatment be replenished on the carpet as it wears away due to foot traffic.
ESD carpet is available but proper maintenance is very important.
ESD Floor Finish:
Existing hard surfaces (e.g. concrete, sealed or painted wood, linoleum, asphalt) can be treated with ESD Floor Finish to eliminate the need for ESD control flooring. Repeat applications are required periodically to keep ESD properties within specification.
ESD Paint:
Paint is ideal for providing a cost effective static-free environment and is very effective as a
static control floor coating for electronics manufacturing, assembly and storage. It controls dissipation of static electricity and provides path to ground.
ESD Floor Coverings:
Floor coverings will have either “conductive” or “dissipative” electrical properties.
Conductive materials have a resistance to ground (RG) of greater than 1 x 103 ohms but less than 1 x 105
Dissipative materials have a resistance to ground (RG) of greater than 1 x 105 ohms but less than 1 x 1012
It is recommended to use conductive flooring material; S20.20 requires ESD flooring to be less than 1 x 109 ohms (RG). The same standard requires a person/footwear/flooring to be less than 3.5 x 107 ohms (resistance in series of operator plus footwear plus floor). Remember that floors get dirty which can raise floor resistance. Therefore, it is good to start off with a floor that is conductive (less than 1 x 106 ohms). So even if the resistance increases, you’re within the required limits of the ESD Standard.
ESD Carpet:
ESD control carpets are made with static dissipative yarn and only require that the yarn be kept clean and free of insulative dirt, dust and spray cleaners.
ESD Matting:
Types of matting range from vinyl to rubber and anti-fatigue matting.
Vinyl (e.g. SCS 8200 Series) is generally cheaper and provides high resistance to many chemicals. Rubber (e.g. SCS CONDFM Series) on the other hand is more durable and can withstand extreme hot and cold temperatures. Anti-fatigue matting (AFM Series) is designed to provide comfort for personnel that must stand or walk for long periods.
Considerations when Using Flooring Materials
1. Grounding
ANSI/ESD S20.20 requires that all conductors in an ESD protected area, including personnel, must be grounded. This includes ESD flooring. The ESD ground must be tied directly to and at the same potential as the building or “green wire” equipment ground. The SCS floor mat ground cord FGC151M is just one option for grounding floor matting.
2. Periodic Verification
All ESD control items (including ESD flooring) have to be tested:
Prior to installation to qualify product for listing in user’s ESD control plan.
During initial installation.
For periodic checks of installed products as part of ANSI/ESD S20.20 clause 7.4 Compliance verification plan.
Measuring Surface Resistance of ESD Floor Matting – click here for more information
A surface resistance meter (e.g. SCS SRMETER2) can be used to verify compliance of the ESD floor with the ESD standard.
3. Person/Footwear/Flooring System
ESD flooring does not ensure protection from ESD damage unless operators walking across the ESD floor wear ESD footwear, either ESD shoes or ESD foot grounders.
ESD foot grounders are designed to reliably contact grounded ESD flooring and provide a continuous path-to-ground by removing electrostatic charges from personnel. They are easy to install and can be used on standard shoes by placing the grounding tab in the shoe under the foot.
Foot grounders must be worn on both feet to maintain the integrity of the body-to-ground connection Wearing a foot grounder on each foot ensures contact with ground via the ESD floor even when one foot is lifted off the floor. This will more reliably remove static charges generated by human movement.
Static charges can easily be controlled with different types of floor material which vary in their properties, cost and durability. The best static control systems are not only the ones that protect sensitive components and equipment but are: A) at hand and readily available, B) easily maintained. Floor coverings are long lasting and maintain their ESD properties over time, while existing floors can be economically converted for use in an ESD control program using various types of coatings.
Remember that all ESD control items such as flooring, personnel grounding and specialty equipment should be grounded and tested periodically to verify all components are within specification.
Not sure which ESD flooring is right for you? Request a free ESD/EOS Assessment at your facility by one of our knowledgeable local representatives to evaluate your ESD program and answer any ESD questions!
Many companies implement an ElectroStatic Discharge (ESD) Control Program with the aim of improving their operations. Effective ESD control can be a key to improving:
Productivity
Quality
Customer Satisfaction
Problems arise when an organization invests in ESD protective products and/or equipment and then misuses them. Misuse of ESD protective products and/or equipment wastes invested money and can also be causing more harm than good. Today’s blog post will highlight some of the major issues we have come across and how you can avoid or fix them.
About ESD Control and ESD Protection
Remember that for a successful ESD control program, ESD protection is required throughout the manufacturing process: from goods-in to assembly all the way through to inspection. Anybody who handles electrical or electronic parts, assemblies or equipment that are susceptible to damage by electrostatic discharges should take necessary precautions.
Just like viruses or bacteria that can infect the human body, ESD can be a hidden threat unable to be detected by human eyes. Hidden viral/bacterial threats in hospitals are controlled by extensive contamination control procedures and protective measures such as sterilization. The same principles apply to ESD control: you should never handle, assemble or repair electronic assemblies without taking adequate protective measures against ESD.
Common Mistakes in ESD Control
1. Ionizers are poorly maintained or out-of-balance
If an ionizer is out of balance, instead of neutralizing charges, it will produce primarily positive or negative ions. This results in placing an electrostatic charge on items that are not grounded, potentially discharging and causing ESD damage to nearby sensitive items.
Remember to clean emitter pins and filters using appropriate tools. Create a regular maintenance schedule which will extend the lifespan of your ionizers tremendously.
Consider using ionizers with “Clean Me” and//or “Balance” alarms. These will alert you when maintenance is required.
“All ionization devices will require periodic maintenance for proper operation. Maintenance intervals for ionizers vary widely depending on the type of ionization equipment and use environment. Critical clean room use will generally require more frequent attention. It is important to set up a routine schedule for ionizer service.”
If you would like to learn more about how ionizers work and what type of ionizer will work best for your application, check out this post for detailed coverage.
2. ESD Garments are Ungrounded
We’ve seen it so many times: operators wearing an ESD coat (without appropriate wrist straps and/or footwear/flooring) thinking they are properly grounded. However, without proper electrical bonds to a grounding system they are not grounded!
Every ESD garment needs to be electrically bonded to the grounding system of the wearer. Otherwise it just acts as a floating conductor. There are a few options to choose from:
Wrist Straps
ESD footwear/flooring
Hip-to-Cuff grounding
“After verifying that the garment has electrical conductivity through all panels, the garment should be electrically bonded to the grounding system of the wearer so as not to act as a floating conductor.
This can be accomplished by several means:
Ground the garment to the body through a wrist strap-direct connection with an adapter.
Ground the garment through conductive wrist or heel cuffs in direct contact with the skin of a grounded operator.
Ground the garment through a typical separate ground cord, directly attached to an identified groundable point on the garment.
Garments should be worn with the front properly snapped or buttoned to avoid exposure of possible charge on personal clothing worn under the garment.”
ESD clothing loses their ESD properties over time. It is therefore an important part of the ESD Control Program to incorporate periodic checks (see #3 below) of ESD garments.
If you need more information on ESD garments, we recommend having a look at this post.
3. No Compliance Verification Plan / Not Checking ESD Control Products
Companies can invest thousands of dollars in purchasing and installing ESD control products but then waste their investment by never checking their ESD items. This results in ESD equipment that is out of specification. Without the tools in place to check their ESD items, companies may have no idea if they are actually working correctly. Remember: ESD products (like any other product) are subject to wear and tear, and other errors when workstations get moved, ground cords get disconnected…etc. The list goes on.
When investing in ESD control products, make sure you also establish a Compliance Verification Plan. This ensures that:
ESD equipment is checked periodically
Necessary test equipment is available
“A compliance verification plan shall be established to ensure the organization’s fulfilment of the requirements of the plan. Process monitoring (measurements) shall be conducted in accordance with a compliance verification plan that identifies the technical requirements to be verified, the measurement limits and the frequency at which those verifications shall occur. The compliance verification plan shall document the test methods used for process monitoring and measurements. If the organization uses different test methods to replace those of this standard, the organization shall be able to show that the results achieved correlate with the referenced standards. Where test methods are devised for testing items not covered in this standard, these shall be adequately documented including corresponding test limits. Compliance verification records shall be established and maintained to provide evidence of conformity to the technical requirements.
The test equipment selected shall be capable of making the measurements defined in the compliance verification plan.”[ANSI/ESD clause 7.4 Compliance verification plan]
We provide detailed instructions on how to create a Compliance Verification Plan in this post.
4. Improperly Re-Using Shielding Bags / Using Shielding Bags with Holes or Scratches
ESD Shielding Bags are used to store and transport ESD sensitive items. When used properly, they create a Faraday Cage effect which causes charges to be conducted around the outside surface. Since similar charges repel, charges will rest on the exterior and ESD sensitive items on the inside will be ‘safe’. However, if the shielding layer of an ESD Shielding Bag is damaged, ESD sensitive items on the inside will not be protected anymore.
Re-using shielding bags is acceptable as long as there is no damage to the shielding layer. Shielding bags with holes, tears or excessive wrinkles should be discarded.
Use a system of labels to identify when the bag has gone through five (5) handling cycles. When there are five broken labels, the bag is discarded.
ESD shielding packaging is to be used particularly when transporting or storing ESD sensitive items outside an ESD Protected Area.
“Transportation of ESDS items outside an ESD Protected Area (hereafter referred to as “EPA”) requires enclosure in static protective materials, although the type of material depends on the situation and destination. Inside an EPA, low charging and static dissipative materials may provide adequate protection. Outside an EPA, low charging and static discharge shielding materials are recommended. While these materials are not discussed in
the document, it is important to recognize the differences in their application. For more clarification see ANSI/ESD S541. “
[ANSI/ESD Foreword]
This post provides further “dos and don’ts” when using ESD Shielding Bags.
5. Using Household Cleaners on ESD Matting
The use of standard household cleaners on ESD matting can put an ESD Control Program at risk and damage the ESD properties of items. Many household cleaners contain silicone or other insulative contaminants which create that lovely shine you get when wiping surfaces in your home. The problem is that silicone and other chemical contaminates can create an insulative layer which reduces the grounding performance of the mat.
Don’t spend all this extra money on ESD matting and then coat it with an insulative layer by using household cleaners. There are many specially formulated ESD surface and mat cleaners available on the market. Only clean your ESD working surfaces using those cleaners.
“Periodic cleaning, following the manufacturer’s recommendations, is required to maintain proper electrical function of all work surfaces. Ensure that the cleaning products used to not leave an electrically insulative residue which is common with some household cleaners that contain silicone.”
There are many more issues we see when setting foot into EPAs and the above list is by no means complete. These are the most common issues we’ve found when assessing EPAs.
It is important to train all personnel using ESD products and/or equipment to follow proper ESD control programs, and maintenance procedures to avoid common ESD control mistakes. Basic ESD control principles should be followed for an ESD control program to be successful:
Ground conductors.
Remove, convert or neutralize insulators with ionizers.
Shield ESD sensitive items when stored or transported outside the EPA.
What mistakes do you commonly see when walking through an EPA? Let us know what you commonly see in the comments and your solutions for fixing them!
For more information on how to get your ESD control program off the ground and create an EPA, check this post.
When talking about ESD Classifications a little while ago, we identified a “class 0” item as withstanding discharges of less than 250 volts.
The introduction of ANSI/ESD S20.20 states: “This standard covers the requirements necessary to design, establish, implement and maintain an Electrostatic Discharge (ESD) Control Program for activities that manufacture, process, assemble, install, package, label, service, test, inspect or otherwise handle electrical or electronic parts, assemblies and equipment susceptible to damage by electrostatic discharges greater than or equal to 100 volts Human Body Model (HBM) and 200 volts Charged Device Model (CDM).”
So how do you handle items that are susceptible to voltages of less than 100V? That’s what we’re going to answer in today’s blog post.
Introduction
Years ago, it was common for devices to be vulnerable to voltages greater than 100 V. As the need for smaller and faster devices increased, so did their sensitivity to ElectroStatic Discharges as circuit-protection schemes were removed to stay ahead of the market. These new extremely sensitive components are now susceptible to discharges nearing 0 V. This causes problems for companies handling these devices: while their ESD program may be in compliance with the ESD Standard, extremely sensitive devices require tighter ESD Control to protect them from ESD failures.
What is a “Class 0” device?
Before moving any further, we need to qualify the term “class 0”. As stated above, the HBM Model refers to any item with a failure voltage of less than 250 V as a “class 0” component. However, in recent times, the term has been used more and more to describe ultra-sensitive devices with failure voltages of less than 100 V. Whilst the following tips and tricks work on any “class 0” item, they are specifically designed to protect extremely sensitive items that withstand discharges of less than 100 V.
Ultra-sensitive devices are extremely common
Before Updating Your ESD Program
“Class 0” refers to a wide range of items and there are a few things you should remember before making any changes to your existing ESD program:
Verify what ESD Model your company/engineers/customers etc. are referring to. As we have learnt in the past, there are different ESD models (HBM, CDM, MM) as well as individual classifications for each model. A lot of people get confused when it comes to citing ESD classifications. There is only one “class 0” which refers to the human body model (HBM) but it’s always best to check.
Check the specific withstand voltage an individual part is susceptible to. “Class 0” refers to all items that withstand discharges of less than 250 V. However, there is a big difference between a failure voltage of 240 V or 50 V. You need to have detailed ESD sensitivity information available before being able to make decisions on how to improve your existing ESD control program. This step is part of creating a compliance verification plan.
A part’s ESD classification is only of importance until it is ‘merged’ into an assembly. So, the ESD classification of a device only refers to the stand-alone component. Once it goes into another construction, the classification of the whole assembly is likely to change.
Tips for handling “Class 0” Items
Below are 6 tips that will help your company to upgrade your ESD control program so you can effectively and efficiently handle ultra-sensitive items without risking ESD damage.
One thing to note: The best approach to stay ahead of the game is taking proactive actions. It is critical to figure out how to protect your components from ESD damage before you receive them. If actions are taken after components are received, the components are susceptible to receiving ESD damage.
1. Improve Grounding
Inside an EPA, all conductors (including people) are grounded. Now you’re probably thinking: “But I’ve already grounded my operators and worksurfaces. What else is there left to do?”. Firstly, well done for properly grounding the ‘objects’ in your EPA. The next step is to adjust and improve your current program to allow for even better protection. Here are some suggestions:
Personnel:
Decrease the wrist strap and ESD footwear upper limit. The ESD Association has test data showing charge on a person is less as the path-to-ground resistance is less.
Full coverage foot grounders are recommended when handling ultra-sensitive devices
Worksurfaces:
Reduce the required limit for Point-to-Point resistance of 1 x 109 per the ESD Standard to 106 to 108 ohms (see #5). The reason for this reduction is simple: 1 x 109 is too high as it still produces thousands of volts of in electrostatic charges. However, the resistance cannot be too small either as this can lead to a sudden ‘hard discharge’ potentially damaging ESD sensitive components.
Other:
Improve grounding of carts, shelves and equipment to Ground
Minimize isolated conductors like devices on PCBs
2. Minimize Charge Generation
The best form of control is to minimize charge generation. First, you should always use shielding packing products like bags or containers (especially when outside an EPA) as these protect from generating charges in the first place. For more information on choosing the correct type of ESD Packaging, we recommend reading this post.
The next step is to eliminate charges once they are generated – this can be achieved through grounding and ionization. We’ll cover ionization in #3 and #4. We’ve already talked about improved grounding in #1. However, for ultra-sensitive components, we also recommend the following:
Personnel: Use low-charging floor finish
Surfaces: Use low-charging topical antistatic treatments
Both types of ESD products create a low tribocharging coating which allows charges to drain off when grounded. The antistatic properties will reduce triboelectric voltage to under 200 volts.
3. Remove Insulators
When talking about conductors and insulators, we explained that insulators cannot be grounded and can damage nearby sensitive devices with a sudden uncontrolled discharge. It is therefore critical to eliminate ALL insulators that are not required in your EPA: plastic cups, non-ESD brushes, tapes etc. How? Here are a couple of options:
Replace regular production supplies and fixtures with dissipative, low charging versions, e.g. ESD dissipative brushes, ESD dispensers, ESD tape, ESD Chairs etc.
If an insulator is absolutely necessary for production and cannot be removed from the EPA, you could consider a topical treatment which will reduce triboelectric charges.
Is this not an option, then move on to tip #4.
4. Use Ionization
First, ionization is not a cure-all. We’ve learnt that ionizers neutralize charges on an insulator.
However, that does not mean that you can just have any insulator in your EPA because the ionizer will “just fix it”. No, in this instance, prevention is generally a better option than the cure. So, your priority should ALWAYS be to remove non-process essential insulators from your EPA – see tip #3. If this is not possible – then ionization becomes essential.
Ionization:
Ionizers can be critical to reduce induction charging caused by process necessary insulators
Ionizers can be critical in eliminating charges on isolated conductors like devices on PCBs
Offset voltage (balance) and discharge times are critical considerations depending on the actual application
Ionization can reduce ElectroStatic Attraction (ESA) and charged particles clinging and contaminating products.
It is recommended to use ionizers with feedback mechanisms, so you’re notified if the offset voltage is out of balance.
5. Increase ESD Training and Awareness
ESD Training is a requirement of every ESD Program. When handling ultra-sensitive devices, it is even more important to remind everyone what pre-cautions are necessary to avoid damage. Regular ‘refreshers’ are a must and it is recommended to verify the effectiveness of the training program, e.g. through tests. So, who, when and what should be taught?
ESD Training is a vital part of every successful ESD Control Program
ESD training needs to be provided to everyone who handles ESD sensitive devices – that includes managers, supervisors, subcontractors, visitors, cleaners and even temporary personnel.
Training must be given at the beginning of employment (BEFORE getting anywhere near a sensitive products) and in regular intervals thereafter.
Training should be conducted on proper compliance verification procedures and on the proper use of equipment used for verification.
6. Create an enhanced Compliance Verification Plan
We talked in a previous post about compliance verification, what it is and how to create a plan that complies with the ESD standard. So, if you already followed our steps and have a plan in place, here are a few tips to improve your compliance verification plan:
Use a computer data collection system for wrist straps and foot grounders testing
Increase the test frequency of personnel grounding devices from once per day to every time the operator enters the EPA
Use continuous monitors where operators are grounded via wrist straps. Consider computer based monitor data collection system, e.g. SMP. This should include continuous monitoring of the mat Ground.
Use Ground continuous monitors, e.g. Ground Master. At a large facility, the most frequent reoccurring violation is the ESD mat ground cord either becoming disconnected from the mat or grounding point. As Ground continuous monitors will only test the fact that the mat is grounded, it is still imperative that the Resistance to Ground of the mat is regularly tested. Remember that the use of improper mat cleaners can raise the mat surface resistance above the upper recommended level of <109
Test ionizers more frequently or consider self-monitoring ionizers. Computer based data collection systems are a good alternative, too.
Increase the use of a static field meter and nano coulomb testing to verify that automated processes (like auto insertion, tape and reel, etc.) are not generating charges above acceptable limits.
Conclusion
“Class 0” items require additional measures of ESD protection due to their sensitivity to ESD damage. The best way to protect these ultra-sensitive components is to increase ESD protective redundancies and periodic verifications to all ESD Control technical elements.
To decrease the probability of ESD damage while handling ultra-sensitive items, additional precautions are required. This includes additional and/or more stringent technical requirements for ESD control products, increasing redundancies, and more frequent periodic verifications or audits.
Additionally, ESD control process systems should be evaluated as to their performance as a system. It is important to understand how the technical elements in use perform relative to the sensitivity of the devices being handled. Thus, tailoring the process to handle the more sensitive parts. For example: If the footwear/flooring allows a person’s body voltage to reach 80 volts and a 50 withstand voltage item gets introduced into the process, you must either allow only handling via wrist straps or would have to find a way to modify the footwear/flooring performance to get peak voltages below the 50 volt threshold.
Remember: The ESD Standard gives recommendations that will always be behind current/future developments. As soon as a Standard is published, technology will have progressed. In order to protect your devices and company reputation for reliable devices – it is recommended your company take responsibility to implement methods/procedures that exceed the recommendations of the ESD Standard to fit your sensitive component requirements.
We already know that in an ESD Protected Area (EPA) all surfaces, objects, people and ESD Sensitive Devices (ESDs) are kept at the same potential which is achieved by using ‘groundable’ materials that are then linked to ground. We have also learnt that the most common personnel grounding device to link people to ground are wrist straps. People who are moving around should instead wear ESD footwear.
So how do you know if your wrist straps and ESD footwear are working properly? Excellent question! And one we’ll answer in today’s post so let’s jump right in!
Purpose of Personnel Grounding Testers
Wrist straps and ESD footwear should be part of your Verification Plan. Each component in an EPA plays a vital part in the fight against electrostatic discharge (ESD). If just one component is not performing correctly, ESD sensitive devices can be damaged, potentially costing your company thousands of dollars.
Wrist straps and ESD footwear can fail and damage cannot always be detected by visual inspection. Just by looking at the items you would not know if they still provide sufficient protection. Personnel grounding testers should be used to provide feedback to verify the functionality of an operator’s wrist strap and/or footwear.
Your Personnel Grounding Checklist
Your Personnel Grounding Checklist:
Wear your personnel grounding equipment such a wrist strap and/or footwear
Verify your personnel grounding system using a wrist strap and/or footwear tester. Wrist straps and footwear, need to be tested at least daily before handling ESD sensitive devices and should be worn while checking.
Log a record of each test. Records should be kept for quality control purposes.
Handle ESD sensitive components ONLY if your wrist strap and/or footwear pass(es) the test.
Types of Personnel Grounding Testers
Personnel grounding testers can be purchased in two configurations:
Wrist strap tester
Wrist strap and footwear tester
As wrist straps are the most commonly used personnel grounding device to ground operators, you will find a lot of testers on the market that check wrist straps only. Combined wrist strap and footwear testers will verify your wrist straps AND footwear.
In addition to WHAT the testers verify, you will also be faced with a wide range of devices differing in HOW they test. Below you will see a (by no means complete) list of options:
Continuous and split footplate: You will find testers with a continuous footplate which require each foot to be tested separately one after the other. Dual-footplate or independent footwear testers feature a split footplate which allows the unit to verify both feet independently at the same time. This can be an efficient time-saver if you have a number of operators in your company who are required to check their personnel grounding devices.
Portable, wall-mountable and fitted testers: Portable battery-powered (predominantly) wrist strap testers are suitable for small labs or for supervisors to spot-check workers and ensure compliance. Wall-mountable units are generally supplied with a wall plate which attaches to a wall; the tester is then mounted on to the wall plate. Some personal grounding devices are accompanied by a stand (and built-in footplate) which allow for a more freely positioning of the unit within a room.
Relay terminal: A few testers on the market are fitted with a relay terminal (electrically operated switch) that can be integrated with electronic door locks, turnstiles, lights, buzzers, etc. This can be of advantage if companies only want to allow personnel in an EPA that have passed their wrist strap and/or footwear test.
Data acquisition: A growing number of personnel grounding devices allow for test activity data to be logged in a database. The units link to a computer which records operator identification, test results, resistance measurements, time and more. Paperless data can enhance operator accountability, immediately identifying problems while reducing manual logging and auditing costs.
Operation of Personnel Grounding Testers
Wrist strap testing:
If you are not using a continuous or a constant monitor, a wrist strap should be tested at least daily. This quick check can determine that no break in the path-to-ground has occurred. Wrist straps should be worn while they are tested. This provides the best way to test all three components:
the wrist band
the ground cord (including the resistor)
the interface (contact) with the operator’s skin
The SCS Combo Tester can be used to test wrist straps – more information
“To ensure that the resistance to ground of personnel is within specification it is important to measure the entire system (i.e., wrist strap, person, and ground connection). The wrist strap system test method is described in ANIS/ESD S1.1. In general, the test method measures the resistance of the ground cord, wristband or cuff, and the interface of the band or cuff of the wearer.” [Handbook ESD TR20.20 Clause 8.2 Wrist Strap System]
“The wrist strap system should be tested daily to ensure proper electrical resistance. Nominally, the upper resistance reading should be < 35 megohms or a user-defined resistance. Daily test records can provide evidence of conformity. Daily testing may be omitted if continuous monitors are used.” [ANSI/ESD S1.1 Clause A3. Frequency of System Testing]
If the wrist strap tester outputs a FAIL test result, stop working and test the wrist band and cord individually to find out which item is damaged. Replace the bad component and repeat the test. Obtain a PASS test result before beginning work. For more information on troubleshooting failed wrist straps, check this post.
Footwear testing:
If you are using a flooring / footwear system as an alternative for standing or mobile workers, ESD footwear should be tested independently at least daily while being worn. Proper testing of foot grounders involves the verification of:
the individual foot grounder
the contact strip
the interface between the contact strip and the operator’s perspiration layer
“a) Place the foot grounders on the user’s shoes per the manufacturer’s instructions. b) Place the left foot on the floor plate and touch the body contact area on the tester with one hand. Activate the tester per the manufacturer’s instructions. c) Remove the left foot from the floor plate. d) Repeat steps b and c with the right foot.”
[ANSI/ESD SP9.2 Clause 6.2.2 Procedure (Integrated Tester)]
The SCS Dual Combination Tester is used to test wrist straps and footwear –more information
If the footwear tester outputs a FAIL test result, stop working, and test the foot grounder and contact strip individually to find out which item is damaged. Replace the foot grounder. Obtain a PASS test result before beginning work.
Conclusion
Wrist straps and footwear need to be tested at least daily before handling any ESD sensitive devices. Personnel grounding devices need to be worn for verification using a wrist strap and/or footwear tester.
A record of each test has to be kept for quality control purposes.
Only handle ESD sensitive components if your wrist strap and/or footwear pass(es) the test.
Every component in an ESD protected area (EPA) plays an important role in the fight against electrostatic discharge (ESD). Just one element not performing correctly could harm your ESD sensitive devices and potentially cost your company a lot of money. The problem with many ESD protection products is that you can’t always see the damage – think wrist straps! By just looking at a coiled cord, you can’t confirm it’s working correctly; even without any visible damage to the insulation, the conductor on the inside could be broken. This is where periodic verification comes into play.
Introduction When implementing an ESD control program plan, ANSI/ESD S20.20 asks for several requirements to be addressed, one of which is “Compliance Verification”:
“The Organization shall prepare an ESD Control Program Plan that addresses each of the requirements of the Program. Those requirements include:
Training
Product Qualification
Compliance Verification
Grounding / Equipotential Bonding Systems
Personnel Grounding
ESD Protected Area (EPA) Requirements
Packaging Systems
Marking” [ANSI/ESD S20.20 clause 7.1 ESD Control Program Plan]
ESD protected area (EPA) products should be tested:
Prior to installation to qualify product for listing in user’s ESD control program.
During the initial installation.
For periodic checks of installed products as part of TR20.20.
“A Compliance Verification Plan shall be established to ensure the Organization’s fulfillment of the technical requirements of the ESD Control Program Plan. Process monitoring (measurements) shall be conducted in accordance with a Compliance Verification Plan that identifies the technical requirements to be verified, the measurement limits and the frequency at which those verifications shall occur. The Compliance Verification Plan shall document the test methods and equipment used for process monitoring and measurements. If the test methods used by the organization differ from any of the standards referenced in this document, then there must be a tailoring statement that is documented as part of the ESD Control Program Plan. Compliance verification records shall be established and maintained to provide evidence of conformity to the technical requirements. The test equipment selected shall be capable of making the measurements defined in the Compliance Verification Plan.” [ANSI/ESD S20.20 clause 7.3 Compliance Verification Plan]
Components of a Verification Plan Each company’s verification plan needs to contain:
1. A list of items that are used in the EPA and need to be checked on a regular basis All ESD working surfaces, personnel grounding devices like wrist straps or foot grounders, ionizers etc. need to be included on the list. In summary: every item that is used for ESD Control purposes. It is recommended to create a checklist comprising all ESD control products as this will ensure EPAs are checked consistently at every audit.
2. A schedule specifying what intervals and how each item is checked The test frequency will depend on several things, e.g.
how long the item will last,
how often it is used or
how important it is to the overall ESD control program.
As an example: wrist straps are chosen by most companies to ground their operators; they are the first line of defence against ESD damage. They are in constant use and are subjected to relentless bending and stretching. Therefore, they are generally checked at the beginning of each shift to ensure they are still working correctly and ESD sensitive items are protected. Ionisers on the other hand are recommended to be checked every 6 months: whilst they are in constant use, they are designed to be; the only actual ‘interaction’ with the user is turning the unit on/off. If, however, the ionizer is used in a critical clean room, the test frequency may need to be increased.
It is recommended that Wrist Straps are checked before each shift
Testing and monitoring of smock and ground cord assembly
“Test frequency limits are not listed in this document, as each user will need to develop their own set of test frequencies based on the critical nature of those ESD sensitive items handled and the risk of failure for the ESD protective equipment and materials.
Examples of how test frequencies are considered:
Daily wrist strap checks are sufficient in some applications while in other operations constant wrist strap monitoring may be used for added operator grounding reliability.
Packaging checks may depend on the composition of the packaging and its use. Some packaging may have static control properties that deteriorate more quickly with time and use, and some packaging may be humidity dependent and may have limited shelf life.
Some materials, such as ESD floor finishes, may require more frequent monitoring because of their lack of permanency. Other materials, such as ESD vinyl floor covering, may require less monitoring. The testing of a floor should also be considered after maintenance on the floor has been performed.” [ESD TR53-01-15 Annex A – Test Frequency]
The industry typically uses 2 types of verification to achieve maximum success: visual and measurement verification. As the name suggests, visual verification is used to ensure ESD working surfaces and operators are grounded, ESD flooring is in good shape or wrist straps are checked before handling ESD sensitive items.
Actual measurements are taken by trained personnel using specially designed equipment to verify proper performance of an ESD control item.
3. The suitable limits for every item used to control ESD damage ANSI/ESD S20.20 contains recommendations of acceptable limits for every ESD control item. Following these references reduces the likelihood of 100V (HBM) sensitive devices being damaged by an ESD event.
Please bear in mind that there may be situations where the limits need to be adjusted to meet the company’s requirements.
4. The test methods used to ensure each ESD product meets the set limits Tables 1 to 3 of ANSI/ESD S20.20 list the different test methods a company must follow.
If a company uses other test methods or have developed their own test methods, the ESD control program plan needs to include a statement explaining why referenced standards are not used. The company also needs to show their chosen test methods are suitable and reliable.
It is recommended that written procedures are created for the different test methods. It is the company’s responsibility to ensure anybody performing the tests understands the procedures and follows them accordingly.
5. The equipment used to take measurements specified in the test methods Every company needs to acquire proper test equipment that complies with the individual test methods specified in Tables 1 to 3 of ANSI/ESD S20.20. Personnel performing measurements need to be trained on how equipment is used. ESD TR53-01-15 lists test procedures and equipment that can be used to verify ESD Control items.
6. A list of employees who will be performing the audits Part of the verification plan is the choice of internal auditors. A few suggestions for the selection process:
Each individual is required to know the ESD Standard ANSI/ESD S20.20 AND the company’s individual ESD program.
It is essential that the selected team member recognizes the role of ESD control in the company’s overall quality management system.
It is recommended that each nominated worker has been trained on performing audits.
The designated employee should be familiar with the manufacturing process they are inspecting.
7. How to deal with non-compliance situations Once an audit has been completed, it is important to keep everyone in the loop and report the findings to the management team. This is particularly vital if “out-of-compliance” issues were uncovered during the verification process. It is the responsibility of the ESD coordinator to categorize how severe each non-conformance is; key problems should be dealt with first and management should be notified immediately of significant non-compliance matters.
Results of audits (especially non-compliance findings) are generally presented using charts. Each chart should classify:
The total findings of the audit
The type of each finding
The area that was audited
It is important to note that each company should set targets for a given area and include a trend report. This data can assist in determining if employees follow the outlined ESD control program and if improvements can be seen over time.
In our last post, we talked about ESD: what it is, what types of ESD damage there are and what costly effects ESD can have. Missed our very first post? Catch-up here.
All caught up? Right, moving on. Today you will learn how to avoid ESD damage and protect your ESD sensitive items. So, let’s jump right in.
The fundamental ESD Control Principles We’ve established that ESD is the hidden enemy in the electronics industry. Therefore, the BIG question is: how exactly do you control ElectroStatic Discharge (ESD) in your workplace? Easy – just follow these ESD fundamentals:
Ground all conductors including people
Remove all unnecessary non-conductors (also known as insulators)
Place ESD sensitive devices inside of shielding packaging when transported outside of an ESD Protected Area (EPA)
Per ESD Handbook ESD TR20.20-2008 section 2.4 “It should be understood that any object, item, material or person could be a source of static electricity in the work environment. Removal of unnecessary nonconductors, replacing nonconductive materials with dissipative or conductive materials and grounding all conductors are the principle methods of controlling static electricity in the workplace, regardless of the activity.”
These are the essential principles of ESD Control. If you implement all three points above, you will be in control of ESD and your sensitive items will be protected. Well, that wasn’t hard, was it? Don’t be terrified – we’ll go through everything in detail. We’ll cover #2 and #3 in future points – today’s focus is #1.
Definition of an ESD Protected Area (EPA) An ESD Protected Area (EPA) is a designated zone – all surfaces, objects, people and ESD Sensitive Devices (ESDs) within are kept at the same electrical potential. This is achieved by simply using ‘groundable’ materials for covering of surfaces and for the manufacture of containers and tools. This applies to all items with an electrical resistance of less than 109 ohms.
An EPA could be just one workstation or it could be a room containing several different workstations. It can be portable as used in a field service situation or permanent.
Example of an ESD Protected Area
The user guide CLC/TR 61340-5-2:2008 defines an EPA as follows:
“An ESD protected area (EPA) is an area that is equipped with the ESD control items required to minimize the chance of damaging ESD sensitive devices. In the broad sense, a protected area is capable of controlling static electricity on all items that enter that work area. Personnel and other conductive or dissipative items shall be electrically bonded together and connected to ground (or a common connection point when a ground is not available) to equalize electrical potential among the items. The size of an EPA can vary greatly. A protected area may be a permanent workstation within a room or an entire factory floor encompassing thousands of workstations. A protected area may also be a portable worksurface or mat used in a field service situation.” [CLC/TR 61340-5-2:2008 Use guide clause 4.6 Protected areas (EPA)]
You’re probably wondering now, how exactly you can get all surfaces, objects and operators to the same electrical potential. Fear not – we’ve got you covered!
Personnel Grounding
As previously stated, a fundamental principle of ESD control is to ground conductors including people at ESD protected workstations.Wrist straps are the first line of defense against ESD, the most common personnel grounding device used, and are required to be used if the operator is sitting. The wristband should be worn snug to the skin with its coil cord connected to a common point ground which is connected to ground, preferably equipment ground.
Wearing a wrist strap and connecting it to a common point ground
If you are not using a continuous or a constant monitor, a wrist strap should be tested while being worn at least daily. This quick check can determine that no break in the path-to-ground has occurred. Part of the path-to-ground is the perspiration layer on the person; an operator with dry skin may inhibit the removal of static charges and may cause a test failure.
“The wrist strap system should be tested daily to ensure proper electrical value. Nominally, the upper resistance reading should be ” [ANSI/ESD S1.1 Annex A, 3 Frequency of Functional Testing]
A Flooring / Footwear system is an alternative for personnel grounding for standing or mobile workers. Foot grounders or other types of ESD footwear are worn while standing or walking on an ESD floor. ESD footwear is to be worn on both feet and should be tested independently at least daily while being worn. Unless the tester has a split footplate, each foot should be tested independently, typically with the other foot raised in the air.
“Compliance verification should be performed prior to each use (daily, shift change, etc.). The accumulation of insulative materials may increase the foot grounder system resistance. If foot grounders are worn outside the ESD protected area testing for functionality before reentry to the ESD protected area should be considered.” [ESD SP9.2 APPENDIX B – Foot Grounder Usage Guidance]
Both ESD footwear and ESD floor are required. Wearing ESD footwear on a regular, insulative floor is a waste of time and money.
Wearing foot grounders on an ESD floor
Part of the path-to-ground is the perspiration in the person’s shoes. The conductive tab or ribbon of foot grounders should be placed inside the shoe under the foot with the excess length tucked into the shoe. Thanks to the perspiration in the shoe, direct contact with the skin is normally not necessary.
If an operator leaves the EPA and walks outside wearing ESD footwear, care should be taken not to get the ESD footwear soiled. Dirt is typically insulative, and the best practice is to re-test the ESD footwear while being worn each time when re-entering the EPA.
Working Surfaces
ESD working surfaces, such as mats, are typically an integral part of the ESD workstation, particularly in areas where hand assembly occurs. The purpose of the ESD working surface is two-fold:
To provide a surface with little to no charge on it.
To provide a surface that will remove ElectroStatic charges from conductors including ESDS devices and assemblies) that are placed on the surface.
ESD mats need to be grounded. A ground wire from the mat should connect to the common point ground which is connected to ground, preferably equipment ground. For electronics manufacturing a working surface resistance to ground (RG) of 1 x 106 to less than 1 x 109 ohms is recommended.
“The single most important concept in the field of static control is grounding. Attaching all electrically conductive and dissipative items in the workplace to ground allows built-up electrostatic charges to equalize with ground potential. A grounded conductor cannot hold a static charge.” [Grounding ANSI/ESD S6.1 Foreword]
Per ANSI/ESD S20.20 section 6.2.1.2 Grounding / Bonding Systems Guidance, “In most cases, the third wire (green) AC equipment ground is the preferred choice for ground.”
Best practice is that ground connections use firm fitting connecting devices such as metallic crimps, snaps and banana plugs to connect to designated ground points. The use of alligator clips is not recommended.
The working surface must be maintained and should be cleaned with an ESD cleaner. Regular cleaners typically contain silicone, and should never be used on an ESD working surface. ESD Handbook ESD TR20.20-2008 section 5.3.1.14 Maintenance “Periodic cleaning, following the manufacturerís recommendations, is required to maintain proper electrical function of all worksurfaces. Ensure that cleaners that are used do not leave an electrically insulative residue common with some household cleaners that contain silicone.“
Other moveable objects
Moveable items (such as containers and tools) are grounded when placed on a grounded surface or being held by a grounded operator. Everything that does not readily dissipate charge must be excluded from the EPA (refer to #2 of our ESD Control Principles above). Regular plastics, polystyrene foam drink cups and packaging materials, etc. are typically high charging and have no place at an ESD protective workstation.Intention of an ESD Protected Area (EPA)We’ve learnt in our previous blog post that ElectroStatic discharge (ESD) can damage components and products that contain electronics. A lot of the time, this damage is not detected during quality inspection and can cause significant problems further down the line.An ESD Protected Area (EPA) is an area that has specifically been created to control ESD; its purpose is therefore to avoid ALL problems resulting from ESD damage. Workers need to understand AND follow the basics of ESD control to limit the generation of electrostatic charges as well as limit and slow discharges in the EPA.Recognizing an ESD Protected Area (EPA) An ESD Protected Area must be clearly identified using signs and/or aisle tape. This ensures operators and visitors are alerted when entering (or leaving) an ESD Protected Area which require special precautions (grounding via wrist straps and/or foot grounders etc.). It also indicates that they are entering (or exiting) areas where exposed ESDS items can be handled safely.Remember to be consistent throughout your shop floor, i.e. use the same signs. This will avoid confusion for your operators.
Example of an EPA caution sign
“While signs are one way of indicating the boundaries of an EPA, it is not the only way. Any alternate method that alert the personnel that an EPA begins is acceptable to ANSI/ESD S20.20. Some of the alternate ways to mark the boundaries of an EPA are:
tape on the floor
different color floor tiles
different color carpet
any other way to establish boundary conditions
Anyway to distinguish the boundaries of an EPA would be acceptable as long as the personnel are aware of the indications and take the proper precautions while inside the EPA.” [ESD TR20.20-2016 section 9.1.2 EPA Boundary Indicators]
Building an ESD Protected Area (EPA) A basic form of an ESD Protected Area is a workstation consisting of the following components:
An ESD working surface mat
A grounding cord
A wristband
A coiled cord
A common point ground
To set-up an EPA:
Connect the ESD working surface mat to the common point ground using the grounding cord.
Link the operator to the common point ground using the wristband and coiled cord.
Congratulations – you’ve just created an ESD Protected Area!
By following the above steps, each component (the ESD mat and the operator) is kept at the same electrical potential (ground). Any ElectroStatic charge (ESD) is removed to ground via the common point ground.
