October 2018

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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!

Introduction

Electronic devices and systems can be damaged by exposure to high electric fields as well as by direct electrostatic discharges. A good circuit layout and on-board protection may reduce the risk of damage by such events, but the only safe action at present is to ensure that devices are not exposed to levels of static electricity above the critical threshold.

This can only be achieved by introducing a static control program which usually involves setting up an ESD Protected Area (EPA) in which personnel are correctly grounded and all meet the ESD Standard. However, setting up an EPA does not of itself guarantee a low static environment. Production procedures may change, new materials may be introduced, the performance of older materials may degrade and so on.

Measuring Effectiveness of an ESD Control Program

To ensure the effectiveness of any static control program it is important that regular measurements are carried out:

  1. to determine the sensitivity to ESD of devices being produced or handled.
  2. to confirm that static levels are lower than the critical level, and that new or modified work practices have not introduced high static levels.
  3. to ensure that both new and existing materials in the EPA meet the necessary requirements.

Only after an ‘operational baseline’ has been established by regular auditing will it become possible to identify the origin of unexpected problems arising from the presence of static.

1. Determining the sensitivity of ESD sensitive Devices

It is important to understand the sensitivity of ESD sensitive devices before an action plan can be created. Once you know the sensitivity of the items you are handling, can you work towards ensuring you’re not exceeding those levels.

Part of every ESD control plan is to identify items in your company that are sensitive to ESD. At the same time, you need to recognize the level of their sensitivity. As explained by the ESD Association, how susceptible to ESD a product is depends on the item’s ability to either:

  • dissipate the discharge energy or
  • withstand the levels of current.

2. Measurements to prove the effectiveness of an ESD Control Program

Measuring electrostatic quantities poses special problems because electrostatic systems are generally characterized by high resistances and small amounts of electrical charge. Consequently, conventional electronic instrumentation cannot normally be used.

Measuring Electrical Field

Wherever electrostatic charges accumulate, they can be detected by the presence of an associated electric field. The magnitude of this field is determined by many factors, e. g. the magnitude and distribution of the charge, the geometry and location of grounded surfaces and the medium in which the charge is located.

The current general view of experts is that the main source of ESD risk may occur where ESDS can reach high induced voltage due to external fields from the clothing, and subsequently experience a field induced CDM type discharge.” [CLC TR 61340-5-2 User guide Garments clause 4.7.7.1 Introductory remarks]

718_Use2.jpg
Using the 718 Static Sensor to test static fields

A static field meter is often used for ESD testing of static fields. It indicates surface voltage and polarity on objects and is therefore an effective problem-solving tool used to identify items that are able to be charged.

A field meter can be used to:

  • verify that automated processes (like auto insertion, tape and reel, etc.) are not generating charges above acceptable limits.
  • measure charges generated by causing contact and separation with other materials.
  • demonstrate shielding by measuring a charged object and then covering the charged item with an ESD lab coat or shielding bag. Being shielded the measured charge should be greatly reduced.

 

Measuring ESD Events

ESD events can damage ESD sensitive items and can cause tool lock-ups, erratic behavior and parametric errors. An ESD Event Detector like the EM Eye ESD Event Meter will help detect most ESD events. It detects the magnitude of events and using filters built into the unit, it can provide approximate values for some ESD events for models (CDM, MM, HBM) using proprietary algorithms.

Using the EM Eye ESD Event Meter to detect ESD Events

Solving ESD problems requires data. A tool counting ESD events will help carry out a before-and-after analysis and will prove the effectiveness of implementing ESD control measures.

 

3. Checking Materials in your EPA

When talking about material properties, the measurement you will most frequently come across is “Surface Resistance”. It expresses the ability of a material to conduct electricity and is related to current and voltage. The surface resistance of a material is the ratio of the voltage and current that’s flowing between two pre-defined electrodes.
It is important to remember that the surface resistance of a material is dependent on the electrodes used (shape as well as distance). If your company implements an ESD control program compliant to the ESD Standard ANSI/ESD S20.20, it is therefore vital to carry out surface resistance measurements as described in the Standard itself. For more information on the definition of resistance measurements used in ESD control, check out this post.

A company’s compliance verification plan should include periodic checks of surfaces measuring:

  • Resistance Point-to-Point (Rp-p) and
  • Resistance-to-ground (Rg).
SRMeter2_use.jpg
Measuring Surface Resistance of worksurface matting using the
SRMETER2 Surface Resistance Meter

Surface resistance testers can be used to perform these tests in accordance with ANSI/ESD S20.20 and its test method ANSI/ESD S4.1; if these measurements are within acceptable ranges, the surface and its connections are good. For more information on checking your ESD control products, catch-up with this. It goes into depth as to what products you should be checking in your EPA and how they should be checked.

 

Conclusion

Measurements form an integral part of any ESD control program. Measuring devices help identify the sensitivity of ESD devices that ESD programs are based on, and also are used to verify the effectiveness of ESD control programs set in place. High quality instruments are available commercially for measuring all the parameters necessary for quantifying the extent of a static problem.

We hope the list above has introduced the techniques most commonly used. 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!