ESD Sensitive Devices

Conductors and Insulators

Image scsstaticcontrol September 7, 2017 4

Good morning everyone – how is your Thursday going so far?
Over the next couple of posts, we’ll tackle another important aspect of any ESD Control Program: Ionization. But before we dig into the nitty gritty and explain the different types of ionizers, we’ll have to cover a bit of theory and discuss the different types of materials that can be found in an ESD Protected Area: conductors and insulators. But don’t worry – we’ll keep it brief!

Conductors
Materials that easily transfer electrons (or charge) are called conductors and are said to have “free” electrons. Some examples of conductors are metals, carbon and the human body’s sweat layer. Grounding works effectively to remove electrostatic charges from conductors to ground. However, the item grounded must be conductive.

The other term often used in ESD control is dissipative which is 1 x 10⁴ to less than 1 x 10¹¹ ohms and is sufficiently conductive to remove electrostatic charges when grounded.

*When a conductor is charged, the ability to transfer electrons gives it the ability to be grounded.*

Per ESD Handbook ESD TR20.20-2008 section 2.5 Material Electrical Characteristics – Insulative, Conductive and Static Dissipative: ” A conductive material allows electrons to flow easily across its surface. Conductive materials have low electrical resistance. If the charged conductive material makes contact with another conductive material, the electrons will transfer between the materials quite easily. If the second conductor is a wire lead to an earth grounding point, the electrons will flow to or from ground and the excess charge on the conductor will be “neutralized”. Static dissipative material will allow the transfer of charge to ground or to other conductive objects. The transfer of charge from a static dissipative material will generally take longer than from a conductive material of equivalent size.”
“There is no correlation between resistance measurements and the ability of a material to be low charging. Static dissipative material shall have a surface resistance of greater than or equal to 1.0 x 10^4 ohms but less than 1.0 x 10^11 ohms. Conductor less than 1.0 x 10^4, and non-Conductor or Insulator 1 x 10^11 ohms or higher.” [ANSI/ESD S541 section 7.2]

Take-away:

Electrical current flows easily in conductors.
Conductors can be grounded.

Insulators
Materials that do not easily transfer electrons are called insulators and are by definition non-conductors. Some well-known insulators are common plastics and glass. An insulator will hold the charge and cannot be grounded and “conduct” the charge away.

Both conductors and insulators may become charged with static electricity and discharge. Grounding is a very effective ESD control tool; however, only conductors (conductive or dissipative) can be grounded.

*Insulators like this plastic cup will hold the charge and*
*cannot be grounded and “conduct” the charge away.*

Per ESD Handbook ESD TR20.20-2008 section 2.5 Material Electrical Characteristics – Insulative, Conductive and Static Dissipative: “Virtually all materials, including water and dirt particles in the air, can be triboelectrically charged. An insulator is a material that prevents or limits the flow of electrons across or through its volume is called an insulator. A considerable amount of charge can be formed on the surface of an insulator.”

Take-away:

Electrical current does not flow easily in insulators.
Insulators cannot be grounded.

Insulators are non-conductors and therefore cannot be grounded. Insulators can only be controlled by doing the following within an EPA:

Always keep insulators a minimum of 12 inch from ESDS items or
Replace regular insulative items with an ESD protective version or
Periodically apply a coat of topical Antistat.

“All nonessential insulators such as coffee cups, food wrappers and personal items shall be removed from the workstation or any operation where unprotected ESDS items are handled.” [ANSI/ESD S20.20-2007 section 8.3]

“Process essential” Insulators
When none of the above is possible, the insulator is termed “process essential” and therefore neutralization using an ionizer should become a necessary part of the ESD control program.

Examples of some common process essential insulators are:

PC board substrate,
insulative test fixtures and
product plastic housings.

An example of isolated conductors can be conductive traces or components loaded on a PC board that is not in contact with the ESD worksurface.

Reduction of charges on insulators does occur naturally by a process called neutralization. Ions are charged particles that are normally present in the air and as opposite charges attract, charges will be neutralized over time.

A common example is a balloon rubbed against clothing and “stuck” on a wall by static charge. The balloon will eventually drop. After a day or so natural ions of the opposite charge that are in the air will be attracted to the balloon and will eventually neutralize the charge. An ionizer greatly speeds up this process.

*A balloon “stuck” on a wall by static charge.*

Ionizers and Neutralization
An ionizer creates great numbers of positively and negatively charged ions. Fans help the ions flow over the work area. Ionization can neutralize static charges on an insulator in a matter of seconds, thereby reducing their potential to cause ESD damage.

*An ionizer creates positively and negatively charged ions.*

Per ESD Handbook ESD TR20.20-2008 Ionization, section 5.3.6.1 Introduction and Purpose / General Information “The primary method of static charge control is direct connection to ground for conductors, static dissipative materials, and personnel. A complete static control program must also deal with isolated conductors that cannot be grounded, insulating materials (e.g. most common plastics), and moving personnel who cannot use wrist or heel straps or ESD control flooring or footwear. Air ionization is not a replacement for grounding methods. It is one component of a complete static control program. Ionizers are when it is not possible to properly ground everything and as backup to other static control methods.”

Note: Ionizers require periodic cleaning of emitter pins and the offset voltage must be kept in balance. Otherwise, instead of neutralizing charges, if it is producing primarily positive or negative ions, the ionizer will place an electrostatic charge on items that are not grounded.

Summary
The 2^nd of the three fundamental ESD Control principles is to neutralize process essential insulators with ionizers:
Per ANSI/ESD S20.20-2007 Foreword “The fundamental ESD control principles are:

All conductors in the environment, including personnel, must be attached to a known ground
Necessary non-conductors in the environment cannot lose their electrostatic charge by attachment to ground. Ionization systems provide neutralization of charges on these necessary non-conductive items (circuit board materials and some device packages are examples of necessary non-conductors).
Transportation of ESDS items outside of an ESD Protected Area requires enclosure in static protective materials… Outside an EPA, low charging and static discharge shielding materials are recommended.“

In addition, if a conductor is not grounded, it is an isolated conductor, and an ionizer is the only means to neutralize ElectroStatic charges on it.

Now that you know what conductors and insulators are, how to treat them in an EPA and when to use ionization, the next step is to learn about the different types of ionizers available. Stay tuned for next time.

Creating a Compliance Verification Plan in 7 Steps

Image scsstaticcontrol July 17, 2017 1

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.

Testing-Wrist-Straps — *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.

SRMeter2_use — *Checking an ESD Worksurface using a Surface Resistance Meter*

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.

EOS and ESD

Image scsstaticcontrol June 15, 2017 1

Electrical Overstress, or EOS, has become a widely-used term over the past few years. However, a lot of people are still unsure as to what exactly it is and how it differs from ElectroStatic Discharge (ESD). Today’s blog post is intended to put an end to the confusion.

What is Electrical Overstress?
One huge problem with Electrical Overstress, or EOS, is the fact that people use the phrase in different ways. Up until now there has been no widely recognized definition. A White Paper on EOS published by the Industry Council on ESD Target Levels in 2016 uses the following definition: “An electrical device suffers an electrical overstress event when a maximum limit for either the voltage across, the current through, or power dissipated in the device is exceeded and causes immediate damage or malfunction, or latent damage resulting in an unpredictable reduction of its lifetime. “

Simplified, EOS is the exposure of a component or PCB board to a current or voltage beyond its maximum ratings. This exposure may or may not result in a catastrophic failure.

ElectoStatic Discharge (ESD) versus Electrical Overstress (EOS)
You can compare an ESD event with a knocked-over glass of water on a floor: you’ll get a small puddle but once all the water has spilt from the cup, it’s gone. There is no more water left and the damage is fairly limited. [Source]

*ESD can be compared to a knocked-over glass of water*

However, an EOS event can be compared to an open tap; there may be just a little drip in comparison but there is an unlimited amount of water available. After a while, the entire floor may be flooded and could cause some serious damage. As you can see, EOS events last several magnitudes longer than most ESD events. [Source]

By many, ESD is seen as just one type of electrical stress. EOS on the other hand, describes a wide number of outcomes resulting from multiple stresses or root causes.

ESD does not require a “victim” or damaged product. There will be an ESD event if two objects are at different charge levels and a rapid, spontaneous transfer of an ElectroStatic charge between them occurs. An electrical stress can only become an overstress (as in EOS) if we’re aware of how much stress the “victim” (i.e. sensitive device) can withstand. One specification used to document these limits is the “Absolute Maximum Rating” (AMR). More on that in a little while. Back to EOS and ESD for now. The below image highlights the relationship and contrast between EOS and ESD:

*Relationship between EOS and ESD* [Source]

Generally speaking, EOS describes extreme signals other than ESD. The following table lists the main differences:

	ESD Event	EOS Event
Cause	Rapid discharge of accumulated charge	Voltage and/or currents associated with operation of equipment or with power generating equipment
Duration	Once accumulated charge is consumed, ESD event can no longer manifest itself	Lasts as long as originating signals; no inherent limitation
Characteristics	Have specific waveform which includes rapid rising edge and asymptotic read edge	Can have any physically possible waveform as sources of EOS are often unpredictable
Occurrence	Non-periodic and non-repeatable (accumulation of charge cannot be guaranteed)	Mostly (but not always) periodic and repeatable

Differences between EOS and ESD [Source]

The importance of Electrical Overstress (EOS)
Many failures in the electronics industry can be contributed to EOS. Yes, ESD has received a lot of attention over the past years. However, ESD represents only a small percentage of total EOS damages.

*Typical causes of device failures* [Source]

As explained further above, EOS and ESD are NOT the same thing. This is extremely important because:

EOS damages are much more common compared to failures caused by ESD.
A comprehensive ESD Control Program will provide protection against ESD but not EOS.

Now that you have learned what EOS is, how it’s different from ESD and that ESD protection is not effective for EOS damage, the obvious question will be “How can I protect my sensitive devices from EOS failures?”. That’s where we go back to our “Absolute Maximum Rating” (AMR) mentioned earlier.

Absolute Maximum Rating (AMR) and Electrical Overstress (EOS)
We’ve established earlier that EOS is caused by exceeding specific limits of a device, the so called Absolute Maximum Rating or AMR.
AMR represents “the point beyond which a device may be damaged by a particular stress” [Source].

*the yellow line represents the number of components suffering catastrophic damage

Region A is the safe operating area in which devices are to operate as anticipated.
Region B does not guarantee for the device to function as it should. No physical damage is expected in this area; however, if a device is operated in this region for extended periods of time, it may cause reliability problems.
The upper limit of region B represents the AMR. Issues will arise if a device is operated beyond this point.
Region C is the first area of electrical overstress causing latent failures.
Region D is the second area of electrical overstress causing immediate damages.

Protecting your sensitive devices from Electrical Overstress (EOS)
As already stated, ESD Protection measures are useless when it comes to protecting your sensitive devices from EOS. “Rather, improvement and mitigation of EOS failure causes will only advance through better communication between the supplier and the customer. This includes proper understanding of AMR, realistic specifications for it, finding the root cause of EOS damage incidents, and identifying the field and system application issues.” [Source]

References:

Industry Council on ESD Targets: White Paper 4: Understanding Electrical Overstress – EOS
In Compliance: Rethinking Electrical Overstress
EEWeb: Electric Overstress (EOS) and Its Effects on Today’s Manufacturing
Dangelmayer Associates/ESD Association: Electrical Overstress – Many Sources; Any Solutions?

3 Steps to Fight ESD

Image scsstaticcontrol June 2, 2017 3

Happy Friday to everyone! Are you ready for another round of ESD updates? We’ve got a real gem for you today so let’s jump right in.
We’ve so far learned what ESD is and why ESD Protected Areas are so important. In today’s post, we want to arm you with 3 simple tactics to protect your ESD sensitive items. It’s easier than you think!

ESD Protection is a Requirement!
As electronic technology advances, electronic circuitry gets progressively smaller. As the size of components is reduced, so is the microscopic spacing of insulators and circuits within them, increasing their sensitivity to ESD. Industry experts estimate that average electronics product losses due to static discharge range from 8 to 33%. Others estimate the actual cost of ESD damage to the electronics industry as running into the billions of dollars annually. It is therefore critical to be aware of the most sensitive items being handled in your factory as the need for proper ESD protection increases every day.
Per ESD Handbook ESD TR20.20-2008 section 2.2: “Electronic items continued to become smaller, faster and their susceptibility to static damage increased…all electronic devices required some form of electrostatic control to assure continued operation and product reliability.”

Below you will find 3 simple tips to get ahead of the game.

1. Establish your ESD Protected Area
As a reminder, an ESD Protected Area (EPA) is a defined space within which all surfaces, objects, people and ESD Sensitive Devices (ESDs) are kept at the same potential. That means:

All surfaces, products and people are linked to ground.
Moveable items, such as containers and tools, are bonded by standing on a grounded surface or being held by a grounded operator.
Everything that does not readily dissipate a charge must be excluded from the EPA.

In our last post we talked in detail about how to set-up an ESD Protected Area so if you’re unsure where to start, catch-up with the post here.

Remember that it’s just as important to mark your ESD Protected Area as it is to have it set-up correctly in the first place. If your EPA is not clearly identified, operators will not realize that special pre-cautions are required when entering. You really don’t want an unprotected person wandering over and touching things on the ESD workbench. All your hard work, time and money could be wasted. Make sure you use signs and tape to distinguish your EPA from the rest of your workshop.

Employee working at an ESD Protected Workstation — *An employee working at an ESD Protected Workstation*

Some take-away points for you:

The ESD Protected Area (EPA) should have signage to clearly identify where it is.
All conductors including personnel must be grounded. Operators must either wear wrist straps or footwear in combination with an ESD floor. ESD working surfaces (e.g. mats) are to be grounded.
Wristbands are to be worn snug; the grounding tab of foot grounders must be placed under the foot in the shoe; ESD smocks need to cover all clothing on the torso.
Wrist straps and footwear are to be tested daily. For wrist straps a continuous monitor can be used instead.
Remove all non-essential insulators or neutralize essential insulators with ionizers.
Use packaging with shielding properties to store or transport ESDS outside the EPA.
Only handle unpackaged ESDs in an EPA when grounded.
Periodic checks of installed products (e.g. ESD working surfaces, ESD flooring etc.) are required.
Only trained or escorted people are to be allowed in the EPA.

2. Determine your ESD sensitive items
It is critical to be aware of the most sensitive item being handled in your factory. As with any type of control, there are several levels of protection. The method for choosing the necessary degree of ESD protection starts with defining your static sensitivity for electronic components. The ESD Association defines different classes of sensitivity for the HBM (Human Body Model) and CDM (Charged Device Model).

*ESDS Component Sensitivity Classification*

How can you determine the class of sensitivity of the devices within your facility? Look at your product flow through your facility, start at receiving and walk the components or products through until they are at dispatch ready to ship. Chances are, you have several different product flows through your facility. Each flow or loop will have specific components that enter or travel the loop. Make a list of all the sensitive components in each loop and determine the static voltage sensitivity or rating from each of the manufacturers. The lowest voltage sensitivity will dictate the sensitivity class of each loop. The philosophy here is “the chain is only as strong as the weakest link”. Each loop should have the required ESD protection for the most sensitive components that will travel this loop. This will define what class of protection is needed for each loop. You can have different class loops as long as the loops are closed, not allowing other components in. The objective here is to define a static control program to safeguard your most sensitive component.

Per ESD Handbook ESD TR20.20-2008 section 4.1.1 Determining Part ESD Sensitivity “The first step in developing an ESD Control Program plan is to determine the part, assembly or equipment sensitivity level under which the plan is to be developed. The organization can use one of several methods to determine the ESD sensitivity of the products that are to be handled. Some of the various methods are: 1) Assumption that all ESD products have a HBM sensitivity of 100 volts; 2) Actual testing of products using accepted test methods.”
Any ESD sensitive item should be identified with the ESD sensitivity symbol, either on itself or its container. The ESD Sensitivity Symbol (also called Susceptibility or Warning Symbol) identifies items that can be damaged by ESD and should ONLY be unpackaged and handled while grounded at an ESD protected workstation.

3. Train, train train!
No, we’re not talking about railway cars here. What we are referring to is teaching your employees. “Initial and recurrent ESD awareness and prevention training shall be provided to all personnel who handle or otherwise come into contact with any ESDS [ESD sensitive] items. Initial training shall be provided before personnel handle ESDS items. The type and frequency of ESD training for personnel shall be defined in the Training Plan. The Training Plan shall include a requirement for maintaining employee training records and shall document where the records are stored. Training methods and the use of specific techniques are at the Organization’s discretion. The training plan shall include the methods used by the Organization to verify trainee comprehension and training adequacy.” [ANSI/ESD S20.20-2007 section 7.2]

*Training is an essential part of an ESD Control Program*

Perhaps the most important factor in a successful static control program is developing an awareness of the “unseen” problem. People are often a major factor in the 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.
Educating your personnel is therefore an essential basic ingredient 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, it might help to reinforce this understanding by hanging up a few static control posters in strategic locations. The technician doesn’t need an unprotected person wandering over and touching things on the service bench.

The importance of an ESD Protected Area (EPA)

Image scsstaticcontrol May 18, 2017 3

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-EPA-Area — *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:
1. To provide a surface with little to no charge on it.
2. 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 (R_G) 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:
1. Connect the ESD working surface mat to the common point ground using the grounding cord.
2. 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.