ESD workbench

When referring to an “ESD Protected Area” or “EPA”, a lot of people imagine rooms or even whole factory floors with numerous workstations. This very common misconception leads to nervousness and even fear when it comes to implementing an ESD Control Program. There is a concern regarding the cost and time implications when establishing an EPA. However, most often, a simple ESD workstation is completely sufficient to fulfill a company’s needs to protect their ESD sensitive products. Today’s post will provide a step-by-step guide on:

  • How to create an EPA at an existing workstation,
  • What ESD control products are required
  • How to correctly set up ESD control products

What is an “ESD Protected Area” or “EPA”?

An EPA is an area that has been established to effectively control Electrostatic Discharge (ESD) and its purpose is therefore to avoid all problems resulting from ESD damage, e.g. catastrophic failures or latent defects. It is a defined space within which all surfaces, objects, people and ESD Sensitive Devices (ESDs) are kept at the same electrical potential. This is achieved by simply using only ‘groundable’ materials for covering of surfaces and for the manufacture of containers and tools. All surfaces, products and people are grounded to Ground.

What is Grounding?

Grounding means linking, usually through a resistance of between 1 and 10 megohms. Movable items (such as containers and tools) are grounded by virtue of lying on a grounded surface or being held by a grounded person. Everything that does not readily dissipate a charge must be excluded from the EPA.

How big does an EPA need to be?

An EPA can be just one workstation, or it could be a room containing several different workstations. “The definition of an EPA depends somewhat on the user environment. An EPA may be a permanent workstation within a room or an entire factory floor encompassing thousands of workstations. An EPA may also be portable as used in a field service situation.” [Handbook ESD TR20.20-2016 Clause 9.0 ESD Protected Areas]

What is needed to convert a Workstation into an EPA?

Creating an EPA at an existing workstation does not need to be complicated or expensive. There are just a few things that are required:

Workstation-Setup.png

1. Wrist Strap

Wrist straps are the most common personnel grounding devices and are used to link people to ground. They are required if the operator is sitting. A wrist strap is made up of two components:

  • A wristband that is worn comfortably around the wrist and
  • A coiled cord that connects the band to Ground or a Wrist Strap Grounding System as explained in #4.

2. Wrist Strap Grounding System

These have been designed to be installed underneath bench tops where they are easily accessible to operators and where they are unlikely to be knocked and damaged or hinder the operator. The grounding cord of the Grounding System needs to be connected to a suitable Ground.

3.Worksurface Mat

ESD protective worksurfaces aid in the prevention of damage to ESD sensitive items (ESDS) and assemblies from electrostatic discharge.

ESD worksurfaces, such as mats, are typically an integral part of the ESD workstation, particularly in areas where hand assembly occurs. The purpose of the ESD worksurface 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) that are placed on the surface.

4. Worksurface Mat Grounding Cord

An ESD worksurface needs to be grounded using a ground cord. A ground wire from the surface should connect to 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.

Where sitting personnel will be grounded via a wrist strap, this method is not feasible for operators moving around in an ESD Protected Area. In those situations, a flooring / footwear system is required.

5. Foot Grounders

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.

6. Floor Mat

Floor matting is an essential component in the flooring / footwear system when grounding moving or standing personnel. The path to Ground from operators via heel grounders to Ground is maintained by using dissipative or conductive flooring.

Floor mats don’t just ground personnel; they are also used to ground ESD control items (e.g. mobile carts or workstations).

7. Floor Mat Grounding Cord

Just like worksurface matting, floor matting needs to be connected to Ground. This ensures that any charges on the operator are dissipated through their heel grounders and the floor matting to Ground. A floor mat grounding cord is used to link the floor mat to Ground.

Alternatively, matting can be grounded via a strip of copper foil.

 

Installing an ESD Workstation

To install the ESD workstation, it is necessary to ground the worksurface and operator with the following steps:

1. Working-Surface-Mat.png Lay the worksurface mat flat on the workbench with the stud(s) facing upwards.
2. Working-Surface-Mat-Grounding-Cord.png Connect the worksurface mat grounding cord to the worksurface mat.
3. Wrist-Strap-Ground.png Connect the other end of the worksurface mat grounding cord to Ground.
4. Wristband.png Place the wristband on the wrist.
5. Coiled-Cord.png Connect the coiled cord to the wristband.
6. Grounding-System.png Attach the Wrist Strap Grounding System to the bench. Remember that it needs to be connected to a suitable Ground.
7. Wrist-Strap-Grounding-System.png Connect the other end of the coiled cord to the Wrist Strap Grounding System and verify personnel is properly grounded.

If your operators are standing or mobile and grounding via a wrist strap is not feasible, ground the worksurface, and the ESD flooring:

1. Working-Surface-Mat-Grounding-Cord.png Ground the worksurface mat by following steps #1 to #4 above
2. Floor-Mat.png Lay the floor mat flat on the floor with the stud(s) facing upwards.
3. Floor-Mat-Grounding-Cord.png Connect the floor mat grounding cord to the floor mat.
4. Wrist-Strap-Ground.png Connect the other end of the floor mat grounding cord to Ground.
5. Foot-Grounders.png Place the foot grounders on the feet and verify personnel is properly grounded.

 

Conclusion

An EPA can be created at an existing workstation in a facility. To establish an EPA it is important to:

  • Ground all conductors (including people),
  • Remove all insulators (or substituting with ESD protective versions) or
  • Neutralize process essential insulators with an ionizer.

With a few simple steps, you can convert your existing workstation into an ESD workstation. You will need:

  • Worksurface Mat
  • Worksurface Mat Grounding Cord
  • Wrist Strap
  • Wrist Strap Grounding System

Optional:

  • Foot Grounders
  • Floor Mat
  • Floor Mat Grounding Cord

We hope this article has introduced the basics of an ESD Protected Area (EPA), and the steps needed to create an ESD Workstation.

For more information on how to get your ESD control program off the ground, 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!

Most ESD Protected Areas (EPAs) will contain a bench or a series of benches. It is important that each bench, or worksurface, is covered with the correct ElectroStatic Discharge (ESD) protective material. They also have to be properly connected to earth using a system of cords and common point grounds. Today’s post will explain in more detail how these ESD protective worksurface work and what you need to look out for.

Introduction

The purpose of an ESD protective worksurface is to aid in the prevention of damage to ESD sensitive items (ESDS) and assemblies from electrostatic discharge.
ESD worksurfaces, such as mats, are typically an integral part of the ESD workstation, particularly in areas where hand assembly occurs. An ESD protective worksurface provides protection in two ways:

  1. Providing a low charging (antistatic) worksurface area that will limit static electricity to be generated below potentially damaging levels.
  2. Removing the electrostatic charge from conductive objects placed on the worksurface.

 

Types of ESD protective worksurfaces

When deciding to invest in ESD protective worksurfaces, you have the choice of ESD matting (laid-out on a standard non-ESD bench) or ESD benches. Performance-wise there is no difference.

Generally speaking, ESD matting offers a lower initial investment and is easier to replace. On the other hand, some people prefer the robust and consistent approach of ESD benches.

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Types of ESD protective worksurface matting – more information

An ESD protective worksurface is usually dissipative. Although conductive materials are the quickest to ground a charge, they can also cause damage by discharging too rapidly. Dissipative worksurfaces have a surface resistance of at least 1 x 104, but less than 1 x 109 ohms. Dissipative materials will dissipate a charge slower and are recommended for handling electronic components. Dissipative materials are usually the preferred choice for bench top worksurfaces.

 

Grounding of ESD protective worksurfaces

ESD protective worksurfaces need to be grounded. A ground wire from the surface should connect to the common point ground which is connected to ground, preferably equipment ground. For electronics manufacturing a worksurface resistance to ground (Rg) of 1 x 104 to less than 1 x 109 ohms is recommended. 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.

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Grounding an ESD Protective Worksurface – click here for more grounding products

Using a current limiting resistor in the ground cord is the user’s choice. However, the resistor is not for ESD control purposes. The ESD Association standard for grounding is ANSI/ESD S6.1 which recommends a hard ground (no resistor) but allows the use of a current limiting resistor in the mat’s ground cord. “The grounding conductors (wires) from wrist straps, working surfaces, flooring or floor mats, tools, fixtures, storage units, carts, chairs, garments and other ESD technical elements may or may not contain added resistance. Where added resistance is not present, a direct connection from the ESD technical element to the common point ground or common connection point is acceptable and recommended.

Note: Manufacturers may add resistance to the grounding conductors for purposes other than ESD (e.g. current limiting). Added resistance is acceptable for the purposes of controlling ESD provided electrostatic accumulation does not exceed specific EPA requirements. The typical added resistance in grounding conductors is 1 megohm, although other values may be specified.” [ANSI/ESD S6.1 section 5.3.3 ESD Technical Element Conductors]

 

Using ESD protective worksurfaces

Operators need to ensure that the ESD workstation is organized to perform work and that all unnecessary insulators and personal items are removed. Regular plastics, polystyrene foam drink cups and packaging materials etc. are typically high charging and have no place at an ESD protective workstation.

When working at an ESD workstation, users have to be grounded, too. A wrist strap is arguably the best way to provide a safe ground connection to the operator. While it does not prevent the generation of charges, its purpose is to dissipate these charges to ground as quickly as possible.

When working on high-end sensitive components, the use of Continuous Monitors is recommended. Operators connect their wrist strap to the unit to allow for real-time continuous monitoring. If the wrist strap fails, the unit will alarm.

724use.jpg
Using a Continuous Monitor at an ESD Workstation – more information

An option available with most Continuous Monitors is the ability to monitor worksurface ground connections. “Some continuous monitors can monitor worksurface ground connections. A test signal is passed through the worksurface and ground connections. Discontinuity or over limit resistance changes cause the monitor to alarm. Worksurface monitors test the electrical connection between the monitor, the worksurface, and the ground point. The monitor however, will not detect insulative contamination on the worksurface.” [ESD TR 12-01 Technical Report Survey of Constant (Continuous) Monitors for Wrist Straps]

When the monitor is connected to an ESD worksurface mat, the amount of current that flows is a function of the total resistance between the monitor and through the working surface to ground. When the resistance of the worksurface is below a pre-set threshold, the monitor will indicate good. Conversely, if the resistance level is high when compared to the monitor’s reference, the unit will alarm. This is an integrating resistance measuring circuit, therefore it is relatively insensitive to externally induced electromagnetic fields.

 

Maintaining your ESD protective worksurface

An ESD worksurface 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.

Operators need to be on guard every day and check visually that ground wires are attached correctly. The company’s compliance verification plan should also include periodic checks of worksurfaces measuring:

  • Resistance Point-to-Point (Rp-p) and
  • Resistance-to-ground (Rg).

Surface resistance testers can be used to perform these tests in accordance with S20.20 and its test method ESD TR53. If these measurements are within acceptable ranges, the worksurface and its connections are good.

770007_UseMatt

Verifying Surface Resistance using the SCS 701 Analog Surface Resistance Megohmmeter

Conclusion

Most people in the industry consider worksurfaces to be the second most important part of an ESD Control Program, with personnel grounding being the most important.

It is therefore important to install, use and maintain ESD protective worksurfaces correctly. Following all steps outlined above will ensure your ESD sensitive components are protected.

Not sure which ESD worksurface is right for you? Request a free ESD/EOS Assessment for 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.

Step3 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.

Step2.png 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.”

[ESD TR20.20 Handbook Ionization clause 15.8 Maintenance / Cleaning]

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!

Step3 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
Step2 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:

  1. Ground the garment to the body through a wrist strap-direct connection with an adapter.
  2. Ground the garment through conductive wrist or heel cuffs in direct contact with the skin of a grounded operator.
  3. Ground the garment through a typical separate ground cord, directly attached to an identified groundable point on the garment.
  4. 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 TR20.20 Handbook Garments clause 19.4 Proper Use]

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.

Step3 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
Step2 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.

Step3 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.

Step2 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.

Step3 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.
Step2 “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.”

[ESD TR20.20 Handbook Worksurfaces clause 10.5 Maintenance]

Conclusion

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.

In a previous post we learnt how to select the correct ESD bag for your application, we want to focus on the next step: how to correctly use your ESD bag. We’ll use shielding bags as an example as they are the most commonly used ESD bags. However, the below can be applied to all types of ESD bags.

There are a few “dos and do-nots” you should keep in mind to ensure you get the most from your ESD bags. Nothing is worse than investing in all the right equipment and then using it incorrectly rendering all your efforts void. So, on that note, we have comprised a list of 5 tips for you on how to most efficiently use your shielding bags.

5 Tips On Efficient Use of Shielding Bags With ESD Sensitive Items:

1. Enclose Your ESD Sensitive Item with a Shielding Bag

Shielding bags should be large enough to enclose the entire product within. The shielding bag should be closed with a label or tape. Alternatively, you can use a zipper-style shielding bag. Following this advice ensures a continuous Faraday Cage is created which provides electrostatic shielding. This is the only way to ensure ESD sensitive devices placed inside the shielding bag are protected. If you are unfamiliar with the term “Faraday Cage”, scroll to the bottom of this page – we’ve included a more detailed explanation at the end of the post.

 

Enclose_Shielding_Bags
Enclose your ESD sensitive item

 

Please do not staple your shielding bag. The staple punctures the shielding layers and will provide a conductive path from the outside of the shielding bag to the inside. Charges outside the shielding bag could potentially charge or discharge to ESD sensitive components inside the shielding bag.

If you’re unsure as to what the correct size is for your application, catch-up on this post which will provide all the required information.

2. Remove Charges from Shielding Bags

When receiving an ESD sensitive device enclosed in a shielding bag, make sure you place the closed shielding bag on an ESD worksurface before removing the product. This will eliminate any charge that might have accumulated on the surface of the shielding bag.

 

Remove_Static_Charges.jpg
Remove charges

 

 3. Do Not Overuse Shielding Bags

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.

 

Dont_overuse_shielding_bags
Don’t overuse shielding bags


 4. Shielding Bags Are Not A Working Surface

Do not use a shielding bag as an ESD worksurface. Although a shielding bag is safe to use around ESD susceptible products, it is not intended to be a worksurface for product. When working on ESD sensitive devices, do so using ESD worksurfaces that are grounded correctly.

Shielding_Bags_are_no_ESD-Worksurface.jpg
Don’t use shielding bags as your ESD worksurface

 5. A Shielding Bag Is Not A “Potholder” Or “Glove”

Do not use a shielding bag as an “ESD potholder” or “ESD glove”. This type of use offers no ESD protection to the product.

If you need to handle ESD sensitive devices, make sure you are properly grounded using wrist straps or heel grounders.

Shielding_Bags_are_no-Gloves
Shielding bags are no “ESD glove” or “ESD potholder”

Some of you may have read through this post and have stumbled across the term “Faraday Cage” as you have not come across it before. We’ve also mentioned it before when talking about storing and transporting ESD sensitive items. However, we’ve never actually explained what a Faraday Cage is – so let’s rectify that!

What Is A “Faraday Cage” Or “Faraday Shield”?

A Faraday Cage or Faraday shield is an enclosure formed by conducting material or by a mesh of conductive material. Such an enclosure blocks external static and non-static electric fields. Faraday Cages are named after the English scientist Michael Faraday, who invented them in 1836.

What Is An Example of Faraday Cage Effect?

An impressive demonstration of the Faraday Cage effect is that of an aircraft being struck by lightning. This happens frequently but does not harm the plane or passengers. The metal body of the aircraft protects the interior. For the same reason, a car may be a safe place during a thunderstorm.

 

Lightning.jpg
Lightning striking an airplane

 

How Is A Faraday Cage Effect Used In ESD Protection?

In ESD Protection, the Faraday Cage effect causes charges to be conducted around the outside surface of the conductor. Since similar charges repel, charges will rest on the exterior and ESD sensitive items on the inside will be ‘safe’.

Examples of ESD control products that provide a Faraday Cage or shielding include Metal-In and Metal-Out Shielding bags.

When Is ESD Shielding Packaging Used?

ESD shielding packaging is to be used particularly when transporting or storing ESD sensitive items outside an ESD Protected Area.

ESD Packaging Standards For Outside An EPA

Per Packaging Standard ANSI/ESD S541 clause 6.2 Outside an EPA “Transportation of sensitive products outside of an EPA shall require packaging that provides:

  • Low charge generation.
  • Dissipative or conductive materials for intimate contact.
  • A structure that provides electrostatic discharge shielding.

Additional ESD Definitions

Other helpful ESD related definitions from the ESD Association Glossary ESD ADV1.0 include:

Faraday Cage“A conductive enclosure that attenuates a stationary electrostatic field.
Electrostatic discharge (ESD) shield: “A barrier or enclosure that limits the passage of current and attenuates an electromagnetic field resulting from an electrostatic discharge.
Electrostatic shield: “A barrier or enclosure that limits the penetration of an electrostatic field.

So, hopefully we’ve clarified a few things today when it comes to the “shielding” property by explaining the phenomenon of the “Faraday Cage”. Don’t forget to implement our tips when it comes to using your ESD bags!

 

We have learned in a previous post that within an ESD Protected Area (EPA) all surfaces, objects, people and ESD Sensitive Devices (ESDs) are kept at the same electrical potential. We achieve this by using only ‘groundable’ materials.

But what do you do if an item in your EPA is essential to assembly and it cannot be grounded? Don’t sweat, not all hope is lost! Let us explain a couple of options which will allow you to use the non-groundable item in question.

Conductors and Insulators

In ESD Control, we differentiate items as conductors and insulators.

Materials that easily transfer electrons are called conductors. Examples of conductors are metals, carbon and the human body’s sweat layer.

Grounding cable snap with connection to a ground.
A charged conductor can transfer electrons which allows it to be grounded

Insulators are materials that do not easily transfer electrons are non-conductors by definition. Some well-known insulators are common plastics, polystyrene foam, and glass.

Plastic cup with charged electrons
Insulators like this plastic cup 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.

Electrostatic charges can effectively be removed from conductive or dissipative conductors by grounding them. A non-conductive insulator will hold the electron charge and cannot be grounded and “conduct” the charge away.

Conductors and Insulators in an EPA

The first two fundamental principles of ESD Control are:

  1. Ground all conductors (including people).
  2. Remove all insulators.

To ground all conductors per the first ESD Control principal, all surfaces, products and people are electrically bonded to ground. Bonding means linking or connecting, usually through a resistance of between 1 and 10 megohms.

Wrist straps and worksurface mats are some of the most common devices used to remove static charges:

  • Wrist straps drain charges from operators and a properly grounded mat will provide path-to-ground for exposed ESD susceptible devices.
  • Movable items (such as containers and tools) are bonded by standing on a bonded surface or being held by a bonded person.

If the static charge in question is on something that cannot be grounded, i.e. an insulator, then #2 of our ESD Control principles will kick in and insulators must be removed. Per the ESD Standard ANSI/ESD S20.20, “All nonessential insulators such as coffee cups, food wrappers and personal items shall be removed from the EPA.” [ANSI/ESD S20.20 clause 8.3.1 Insulators]

The ESD Standard differentiates between these two options:

  1. If the field measured on the insulator is greater than 2000 volts/inch, keep it at a minimum distance of 12 inches from the ESDs or
  2. If the field measured on the insulator is greater than 125 volts/inch, keep it at a minimum distance of 1 inch from the ESDs.
Moving an insulated keyboard away from ESD sensitive workspace
Aim to keep insulators away from ESDs

“Process-Essential” Insulators

Well, nothing in life is black and white. It would be easy if we were always able to follow the above ESD Control ‘rules’ but there are situations where said insulator is an item used at the workstation, e.g. hand tools. They are “process-essential” insulators – you cannot remove them from the EPA or the job won’t get done.

How do you ‘remove’ these vital insulators without actually ‘removing’ them from your EPA?

Here are four ways to reduce the ESD risk of these insulators:

  1. Keep all insulators a minimum of 1 inch or 12 inches from ESDs at all times per recommendation of the ESD Standard.
    This reduces the chance of insulators coming in contact with ESDs during workstation processes and assembly.
  2. Replace regular insulative items with an ESD protective version.
    There are numerous tools and accessories available that are ESD safe – from document handling to cups & dispensers, soldering tools, brushes and waste bins. They are either conductive or dissipative and replace the standard insulative varieties that are generally used at a workbench.
  3. Periodically apply Topical Antistat on non-ESD surfaces.
    After Topical Antistat has been applied and the surface dries, an antistatic and protective static dissipative coating is left behind. The static dissipative coating will allow charges to drain off when grounded. The antistatic properties will reduce triboelectric voltage to under 200 volts. It therefore gives non-ESD surfaces electrical properties until the hard coat is worn away.
  4. Neutralization with Ionization
    If these three options are not feasible for your application, the insulator is termed “process-essential” and therefore neutralization using an ionizer becomes a necessary part of your ESD control program. This allows for control of charged particles that can cause ESD events which we will cover next.

Neutralization

Most ESD workstations will have some insulators or isolated conductors that cannot be removed or replaced. These should be addressed with ionization.

Examples of some common process essential insulators are a PC board substrate, insulative test fixtures and product plastic housings.

Electronic enclosures are process-essential insulators (shown on ESD workstation)
Electronic enclosures are process-essential insulators

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

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.

The charged ions created by an ionizer will:

  • neutralize charges on process required insulators,
  • neutralize charges on non- essential insulators,
  • neutralize isolated conductors and
  • minimize triboelectric charging.
SCS Benchtop ionizer on a workstation removing charges from isolated conductors on PCB Board
Insulators and isolated conductors are common in ESDs – Ionizers can help

For more information on ionizers and how to choose the right type of ionizer for your application, read this post.

Summary

The best way to keep electrostatic sensitive devices (ESDs) from damage is to ground all conductive objects and remove insulators. This is not always possible because some insulators are “process-essential” and are necessary to build or assemble the ESDs.

Insulators, by definition, are non-conductors and therefore cannot be grounded, but they can be controlled to minimize potential ESD damage.

Insulators can be controlled by doing the following within an EPA:

  • Keep insulators a minimum distance from ESDS at all times (1 or 12 inch minimum distance depending on field voltage measurements of the insulator per ESD Standard recommendation)
  • Replace regular insulative items with ESD protective versions
  • Periodically apply a coat of Topical Antistat
  • Neutralize charges for “process-essential” insulators with ionization

With these steps added to your ESD control process, all surfaces, objects, people and ESD Sensitive Devices (ESDs) are kept at the same electrical potential in an ESD Protected Area (EPA) to reduce the risk of ESD events and ESD damage.

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
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
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.