ESD Protective Area (EPA)

Have you ever walked across a car park on a bright cold winter’s day only to get zapped by your car’s door handle? It’s commonly known that these ‘zaps’ are much more common in cold dry weather. It begs the question: if there are less ‘zap, will using air humidifiers in a manufacturing environment prevent ESD damage of sensitive components? Let’s find out!

 

Humidity

Humidity describes the amount of water vapor in the air. There are 3 main measurements of humidity with the most common one being the relative humidity (RH). It is expressed in percent and describes “how much humidity there is in the air, compared to how much there could be. Meteorologists often use the relative humidity as a measurement to describe the weather at various places.” [Source]

At 0% the air is completely dry; at 100% it is so moist that mist or dew can form. The optimum relative humidity level is somewhere between 40% and 60%:

  • A lower relative humidity increases charge generation as the environment is drier.
  • If the humidity level is too high, condensation can form on surfaces.

 

Charge Generation and ElectroStatic Discharge (ESD)

The simple separation of two surfaces generates an ElectroStatic charge. Examples:

  • Unwinding a roll of tape
  • Gas or liquid moving through a hose or pipe
  • A person walking across a floor with heels and soles contacting and separating from the floor

 

Walking across a floor generates ElectroStatic charges.
Walking across a floor generates ElectroStatic charges.

 

The amount of static electricity generated varies and is affected by materials, friction, area of contact and the relative humidity of the environment. A higher charge is generated at low humidity or in a dry environment.

Once an item has generated a charge, it will want to come into balance. If it is in close enough proximity to a second item, there can be a rapid, spontaneous transfer of electrostatic charge. This is called discharge or ElectroStatic Discharge (ESD).

Going back to our earlier example of getting a zap from your car’s door handle:

  1. Charge generation: you walk across the car park with your soles contacting and separating from the floor. A charge is built-up on you.
  2. ElectroStatic Discharge (ESD): you touch the door handle. Charges move from your body to your car until both are balanced out.

 

Impact of relative humidity on ESD

Many people will notice a difference in the ability to generate static electricity when the air gets dryer (relative humidity decreases). Relative humidity (RH) directly affects the ability of a surface to store an electrostatic charge. “With a humidity level of 40% RH, surface resistance is lowered on floors, carpets, table mats and other areas. … the moisture in the air forms a thin protective “film” on surfaces that serves as a natural conductor to dissipate electric charges. When humidity drops below 40% RH, this protection disappears, and normal employee activities lead to objects being charged with static electricity.” [Source]

ESD Damage on an integrated circuit. No Magnification, 400x magnification, 5,000x magnification.

In an electronics manufacturing environment lower humidity may result in lower output from production due to an increase in ESD events during manufacturing processes.

 

Air Humidification and ESD

Air humidifiers are used to add moisture to the air and are commonly used in drier environments to keep humidity at a constant (optimum) level. Given that a lower humidity level increases the risk of ESD events, the obvious questions are:

  1. Can air humidifiers replace normal ESD Control measures?
  2. Are air humidifiers required for complete ESD protection?

Let’s address both questions:

  • Let’s be very clear about one thing here: air humidifiers cannot replace ESD Control measures.

As explained further above, ESD is caused by two items that are at a different electrostatic equipotential and want to equalize their charges. Adding moisture to the air using humidifiers will not stop this discharge from happening. The only thing you may achieve is a reduction in the number of ESD events. BUT: they will still happen; just walking across a carpet will generate a charge on an operator. If they then touch an ESD sensitive component, discharge will still occur and may damage the component. No humidifier will prevent this.

The only way to control electrostatic charges on a person or object is through ESD grounding – this will ensure any charges generated dissipate to earth:

For more information on how to create a ESD workstation and how to correctly ground all elements, have a look at this post.

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Grounding of an operator using a wrist strap
  • Low air humidity can increase the number of ESD events so it may make sense to keep a factory at a higher humidity level. However, there are many other factors that come into play when choosing the ‘right’ humidity for a manufacturing environment. The recommended humidity range is usually determined by the specifications of the devices and components being assembled. Increasing the humidity in an electronics manufacturing facility can help to reduce ESD events but increased humidity can lead to other unwanted quality issues in an electronics manufacturing environment such as corrosion, soldering defects and the popcorn effect on moisture sensitive devices.

A normal range for humidity in electronics manufacturing is between 30% RH and 70% RH. Some facilities try to maintain a constant moderate RH (~50%), whereas other environments may want lower % RH due to corrosion susceptibility to humidity sensitive parts.
And remember: you will not eliminate ESD by using humidifiers and keeping humidity levels at a higher level. You need an ESD Control Program in place to avoid ESD and associated damages.

 

Conclusion

Air humidification can help reduce the number of ESD events in an electronics manufacturing environment but at the same time there are other factors (e.g. moisture sensitivity of components) that need to be considered.

A lower relative humidity level increases charge generation as the environment is drier. This will result in more ESD events which can potentially damage sensitive components. The only way to protect sensitive components from ESD damage is by having proper ESD control measures in place and connecting operators, objects and surfaces to ground. This will ensure each element is kept at the same electrical potential and any electrostatic discharge is being removed to ground.

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

 

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:

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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]

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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).
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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!

 

 

The best-equipped service bench in your shop can be a real money-maker when set up properly. It can also be a source of frustration and lost revenue if the threat of ElectroStatic Discharge (ESD) is ignored.

A typical scenario might be where an electronic product is brought in for service, properly diagnosed and repaired, only to find a new symptom requiring additional repair. Unless the technician understands the ESD problem and has developed methods to keep it in check damage from static electricity cannot be ruled out as a potential source of the new problem.

Static electricity is nothing new; it’s all around us and always has been. What has changed is the spread of semiconductors in almost every consumer product we buy. As device complexity increases, often its static sensitivity increases as well. Some semiconductor devices may be damaged by as little as 20-30 volts!

It is important to note that this post is addressing the issue of ESD in terms of control, and not elimination. The potential for an ESD event to occur cannot be completely eliminated outside of a laboratory environment, but we can greatly reduce the risk with proper training and equipment. By implementing a good static control program and developing some simple habits, ESD can be effectively controlled.

The Source of the Problem

Static is all around us. We occasionally will see or feel it by walking on carpet, touching something or someone and feeling the “zap” of a static discharge. The perception level varies but static charge is typically 2000-3000 volts before we can feel it. ESD sensitivity of some parts is under 100 volts – well below the level that we would be able to detect.

Even though carpet may not be used around the service bench, there are many other static “generators” may not be obvious and frequently found around or on a service bench. The innocent-looking Styrofoam coffee cup can be a tremendous source of static. The simple act of pulling several inches of adhesive tape from a roll can generate several thousand volts of static! Many insulative materials will develop a charge by rubbing them or separating them from another material. This phenomenon is known as “tribocharging” and it occurs often where there are insulative materials present.

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Sources of Charge Generation: Unwinding a Roll of Tape

People are often a major factor in generation of static charges. Studies have shown that personnel in a manufacturing environment frequently develop 5000 volts or more just by walking across the floor. Again, this is “tribocharging” produced by the separation of their shoes and the flooring as they walk.

A technician seated at a non-ESD workbench could easily have a 400-500 volt charge on his or her body caused not only by friction or tribocharging, but additionally by the constant change in body capacitance that occurs from natural movements. The simple act of lifting both feet off the floor can raise the measured voltage on a person as much as 500-1000 volts.

Setting up a “Static Safe” Program

Perhaps the most important factor in a successful static control program is developing an awareness of the “unseen” problem. One of the best ways to demonstrate the ESD hazard is by using a “static field meter”. The visual impact of locating and measuring static charges of more than 1000 volts will get the attention of skeptical individuals.

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Static Field Meter – find more information here

Education of Personnel

ESD education and awareness are essential basic ingredients in any effective static control program. A high level of static awareness must be created and maintained in and around the protected area. Once personnel understand the potential problem, reinforce the understanding by hanging up static control posters in strategic locations. The technician doesn’t need an unaware and/or unprotected person wandering over and touching things on the service bench.

Workstation Grounding

To minimize the threat of an ESD event, we need to bring all components of the system to the same relative potential and maintain that potential. Workstations can be grounded with the following options:

  1. Establish an ESD Common Grounding Point, an electrical junction where all ESD grounds are connected to. Usually, a common ground point is connected to ground, preferably equipment ground.
  2. The Service Bench Surface should be covered with a dissipative material. This can be either an ESD-type high-pressure laminate formed as the benchtop surface, or it may be one of the many types of dissipative mats placed upon the benchtop surface. The mats are available in different colors, with different surface textures, and with various cushioning effects. Whichever type is chosen, look for a material with surface resistivity of 1 x 109 or less, as these materials are sufficiently conductive to discharge objects in less than one second. The ESD laminate or mat must be grounded to the ESD common grounding point to work properly. Frequently, a one Megohm current limiting safety resistor is used in series with the work surface ground. This blog post will provide more information on how to choose and install your ESD working surface.
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Types of Worksurface Matting – click here for more information
  1. A Dissipative Floor Mat may also be used, especially if the technician intends to wear foot-grounding devices. The selection of the floor mat should take into consideration several factors. If anything is to roll on the mat, then a soft, cushion-type mat will probably not work well. If the tech does a lot of standing, then the soft, anti-fatigue type will be much appreciated. Again, the mat should be grounded to the common ground point, with or without the safety resistor as desired.
  2. Workstation Tools and Supplies should be selected with ESD in mind. Avoid insulators and plastics where possible on and around the bench. Poly bags and normal adhesive tapes can generate substantial charges, as can plastic cups and glasses. If charge-generating plastics and the like cannot be eliminated, consider using one of the small, low cost air ionizers It can usually be mounted off the bench to conserve work area, and then aimed at the area where most of the work is being done. The ionizer does not eliminate the need for grounding the working surface or the operator, but it does drain static charges from insulators, which do not lend themselves to grounding.

Personnel Grounding

People are great static generators. Simple movements at the bench can easily build up charges as high as 500-1000 volts. Therefore, controlling this charge build-up on the technician is essential. The two best known methods for draining the charge on a person are wrist straps with ground cords and foot or heel grounders. Personnel can be grounded through:

  1. Wrist Straps are probably the most common item used for personnel grounding. They are comprised of a conductive band or strap that fits snugly on the wrist. The wrist strap is frequently made of an elastic material with a conductive inner surface, or it may be a metallic expandable band similar to that found on a watch. For more information on wrist straps, check out this post.
  2. Ground Cords are typically made of a highly flexible wire and often are made retractable for additional freedom of movement. There are two safety features that are usually built into the cord, and the user should not attempt to bypass them. The first, and most important, is a current limiting resistor (typically 1 Megohm) which prevents hazardous current from flowing through the cord in the event the wearer inadvertently contacts line voltage. The line voltage may find another path to ground, but the cord is designed to neither increase or reduce shock hazard for voltages under 250 volts. The second safety feature built into most cords is a breakaway connection to allow the user to exit rapidly in an emergency. This is usually accomplished by using a snap connector at the wrist strap end.
    Wrist-Strap.png
  3. Foot or Heel Grounders are frequently used where the technician needs more freedom of movement than the wrist strap and cord allow. The heel grounder is often made of a conductive rubber or vinyl and is worn over a standard shoe. It usually has a strap that passes under the heel for good contact and a strap of some type that is laid inside the shoe for contact to the wearer. Heel grounders must be used with some type of conductive or dissipative floor surface to be effective and should be worn on both feet to insure continuous contact with the floor. Obviously, lifting both feet from the floor while sitting will cause protection to be lost.Don’t forget to regularly check and verify your personnel grounding items:
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The Personnel Grounding Checklist

 

Summary

An effective static control program doesn’t have to be expensive or complex. The main concept is to minimize generation of static and to drain it away when it does occur, thereby lessening the chance for an ESD event to happen. The ingredients for an effective ESD program are:

  1. Education: to ensure that everyone understands the problem and the proper handling of sensitive devices.
  2. Workstation Grounding: use a dissipative working surface material and dissipative flooring materials as required.
  3. Personnel Grounding: using wrist straps with ground cords and/or foot-grounding devices.
  4. Follow-up to ensure Compliance: all elements of the program should be checked frequently to determine that they are working effectively.

The ESD “threat” is not likely to go away soon, and it is very likely to become an even greater hazard, as electronic devices continue to increase in complexity and decrease in size. By implementing a static control program now, you will be prepared for the more sensitive products that will be coming.

Static discharges can be noticed when you touch an object of different electrical potential such as a door knob, and a bolt of electricity flows from your charged body to the door knob. This flow of electricity is actually a result of the stored static charge that is being rapidly transferred to the knob. This discharge that can be felt as well as seen, is commonly referred to as an electrostatic discharge, or “ESD”.

The generated static charges are a potentially costly occurrence for office and factory employers. You will learn in today’s post how they can easily be controlled with different types of floor material.

 

Static Charge Generation from Flooring

When a person walks across a floor, a triboelectric charge builds up in the body due to the friction between the shoes and floor material. The simple separation of two surfaces (such as a person walking across a floor with soles contracting and separating from the floor) can cause a transfer of electrons resulting in one surface being positively and the other one negatively charged, resulting in static charges.

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Generating Charges by walking across carpet

It is not necessarily the static charge generated in the body that does the damage as much as it is the difference in potential that creates an electrostatic discharge.

 

The Problem with ESD (Electrostatic Discharge)

The generation of a static charge can pose quite a problem for environments that contain sensitive equipment or components that are vulnerable to static damage, such as electronics manufacturing, repair facilities and medical facilities – including computer rooms and clean rooms.

Controlling the damage and costs caused by ESD is usually the main concern that drives a company to implement a static control program. The costs involved with static damage not only include the immediate cost of the damaged component, but the contributing cost of diagnostic, repair and labor that is needed to replace or fix the component. In many cases the labor involved can far exceed the component cost.

 

ESD Flooring Materials

There are several options available on the market ranging from coatings (floor finish or paint) to coverings (vinyl or rubber). The choice of material depends on the mechanical and optical properties required as well as the available budget.

In general, floor coverings will last longer (10 years or more) than a floor coating. They are more durable and have a specific resistance to ground that remains constant over time.

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Types of Floor Coverings – click here for more information

Coatings are easier to apply and repair and their initial cost is considerably lower. Coatings are usually applied to existing floors and often serve to convert a conventional floor into an ESD floor. However, regular maintenance is required as coatings will lose their ESD properties over time.

 

ESD Floor Coatings

  • Topical Antistat:
    Conventional carpets can be treated with a Topical Antistat or other treatment. It is required that the treatment be replenished on the carpet as it wears away due to foot traffic.
    ESD carpet is available but proper maintenance is very important.
  • ESD Floor Finish:
    Existing hard surfaces (e.g. concrete, sealed or painted wood, linoleum, asphalt) can be treated with ESD Floor Finish to eliminate the need for ESD control flooring. Repeat applications are required periodically to keep ESD properties within specification.
  • ESD Paint:
    Paint is ideal for providing a cost effective static-free environment and is very effective as a

static control floor coating for electronics manufacturing, assembly and storage. It controls dissipation of static electricity and provides path to ground.

ESD Floor Coverings:

Floor coverings will have either “conductive” or “dissipative” electrical properties.

  • Conductive materials have a resistance to ground (RG) of greater than 1 x 103 ohms but less than 1 x 105
  • Dissipative materials have a resistance to ground (RG) of greater than 1 x 105 ohms but less than 1 x 1012

It is recommended to use conductive flooring material; S20.20 requires ESD flooring to be less than 1 x 109 ohms (RG). The same standard requires a person/footwear/flooring to be less than 3.5 x 107 ohms (resistance in series of operator plus footwear plus floor). Remember that floors get dirty which can raise floor resistance. Therefore, it is good to start off with a floor that is conductive (less than 1 x 106 ohms). So even if the resistance increases, you’re within the required limits of the ESD Standard.

  • ESD Carpet:
    ESD control carpets are made with static dissipative yarn and only require that the yarn be kept clean and free of insulative dirt, dust and spray cleaners.
  • ESD Matting:
    Types of matting range from vinyl to rubber and anti-fatigue matting.
    Vinyl (e.g. SCS 8200 Series) is generally cheaper and provides high resistance to many chemicals. Rubber (e.g. SCS CONDFM Series) on the other hand is more durable and can withstand extreme hot and cold temperatures. Anti-fatigue matting (AFM Series) is designed to provide comfort for personnel that must stand or walk for long periods.

 

Considerations when Using Flooring Materials

1. Grounding

ANSI/ESD S20.20 requires that all conductors in an ESD protected area, including personnel, must be grounded. This includes ESD flooring. The ESD ground must be tied directly to and at the same potential as the building or “green wire” equipment ground. The SCS floor mat ground cord FGC151M is just one option for grounding floor matting.

2. Periodic Verification

All ESD control items (including ESD flooring) have to be tested:

  • Prior to installation to qualify product for listing in user’s ESD control plan.
  • During initial installation.
  • For periodic checks of installed products as part of ANSI/ESD S20.20 clause 7.4 Compliance verification plan.
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Measuring Surface Resistance of ESD Floor Matting – click here for more information

A surface resistance meter (e.g. SCS SRMETER2) can be used to verify compliance of the ESD floor with the ESD standard.

3. Person/Footwear/Flooring System

ESD flooring does not ensure protection from ESD damage unless operators walking across the ESD floor wear ESD footwear, either ESD shoes or ESD foot grounders.

ESD foot grounders are designed to reliably contact grounded ESD flooring and provide a continuous path-to-ground by removing electrostatic charges from personnel. They are easy to install and can be used on standard shoes by placing the grounding tab in the shoe under the foot.
Foot grounders must be worn on both feet to maintain the integrity of the body-to-ground connection Wearing a foot grounder on each foot ensures contact with ground via the ESD floor even when one foot is lifted off the floor. This will more reliably remove static charges generated by human movement.

SCS offers a number of different foot grounder types for your requirements.

 

Conclusion

Static charges can easily be controlled with different types of floor material which vary in their properties, cost and durability. The best static control systems are not only the ones that protect sensitive components and equipment but are: A) at hand and readily available, B) easily maintained. Floor coverings are long lasting and maintain their ESD properties over time, while existing floors can be economically converted for use in an ESD control program using various types of coatings.

Remember that all ESD control items such as flooring, personnel grounding and specialty equipment should be grounded and tested periodically to verify all components are within specification.

Not sure which ESD flooring is right for you? Request a free ESD/EOS Assessment at your facility by one of our knowledgeable local representatives to evaluate your ESD program and answer any ESD questions!

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.

scs-esd-workstation-mats.jpg
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.

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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.

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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!

 

When the tip of a soldering iron comes into direct electrical contact with the pins of a sensitive component, there is a danger of voltage and/or current signal transfer between:

  • the grounded iron tip and the grounded PC board,
  • the ungrounded iron tip and the grounded PC board,
  • the grounded iron tip and the ungrounded PC board.

This can cause Electrical Overstress (EOS) and Electrostatic Discharge (ESD).

What is Electrical Overstress (EOS) and why is it important to detect?

EOS is the exposure of a component or PCB board to a current and/or voltage outside its operational range. This absolute maximum rating (AMR) differs from one device to the next and needs to be provided by the manufacturer of each component used during the soldering process. EOS can cause damage, malfunction or accelerated aging in sensitive devices.

ESD can be generated if a component and a board have different potentials and the voltage transfers from one to the other. When such an event happens, the component goes through EOS. ESD can influence EOS, but EOS can also be influenced by other signals.

Many people are familiar with Electrostatic Discharge (ESD) which is caused by the spontaneous discharge between two materials that are at different levels of ElectroStatic potential. Once electrostatic potential between the two materials is balanced, the ESD event will stop.

An EOS event on the other hand is created by voltage and/or current spikes when operating equipment; it can therefore last “as long as the originating signal exists”. [Source] The potentially never-ending stimulus of EOS is what makes it such a big concern in the electronics industry. Even though the voltage levels are generally much lower compared to an ESD event, applying this smaller voltage combined with a larger peak current over a long period of time will cause significant damage.

The high temperatures during an EOS event (created by the high current) can lead to visible EOS damage.

For more information on EOS and the differences to ESD, check-out this post.

Sources of EOS during the Soldering Process

When soldering components, it’s the tip of the soldering iron that comes into contact with the potentially sensitive device. Therefore, many people assume the soldering tip is the cause of ESD/EOS. However, the soldering iron and its tip are just some of the components used at a workbench. Other components on the bench like tweezers, wiring, test equipment, etc. can also be sources of ESD/EOS as they come into contact with the component or board.

There are many sources of EOS during the soldering process, which can include:

  • Loss of Ground
    The tip of an ungrounded soldering iron can accumulate a voltage of up to ½ of the iron’s supply voltage. It can be caused within the soldering iron itself or in power outlets.
  • Noise on Ground
    If a noise signal exists on ground, the tip of the solder iron will carry noise, too. These high-frequency signals, or electromagnetic interference (EMI), are disturbances that affect an electrical circuit, due to either electromagnetic induction or electromagnetic radiation emitted from an external source.
  • Noise on Power Lines
    Noise not only generates via ground but in power lines, too. Transformers and power supplies that convert voltages to 24V are the main culprit. They regularly carry high-frequency spikes which end up on the tip of the soldering iron.
  • Power Tools
    Although not technically related to the soldering process itself, it’s worth mentioning that the tips of power tools (e.g. electric screwdrivers) may not be properly grounded during rotation. This can result in high voltage on the tip itself.
  • Missing/Inadequate ESD Protection
    ESD can be a cause of EOS damage. Therefore, it is essential to have proper ESD Protection in place. A voltage on the operator or the PCB board can otherwise lead to an ESD Event and expose the components on the PCB to EOS.

Detecting EOS during the Soldering Process

EOS/ESD events can be detected, measured, and monitored during the soldering process using a variety of diagnostic tools.

Diagnostic Tools

  • SCS CTM051 Ground Pro Meter
    The SCS CTM051 Ground Pro Meter is a comprehensive instrument that measures ground impedance, AC and DC voltage on the ground as well as the presence of high-frequency noise or electromagnetic interference (EMI) voltage on the ground. It will alert if the soldering iron tip has lost its ground or has EMI voltage induced into the tip from an internal source on the soldering iron or from an EMI noisy ground or power lines.

    CTM051
    The SCS CTM051 Ground Pro Meter
  • SCS CTM048 EM Eye – ESD Event Meter
    The SCS CTM048 EM Eye – ESD Event Meter paired with the SCS CTC028 EM Field Sensor is a diagnostic tool for the detection and analysis of ESD events and electromagnetic fields and can identify sources of harmful ESD Events and electromagnetic interference (EMI).

    CTM048-21
    The SCS CTM048 EM Eye – ESD Event Meter paired with the SCS CTC028 EM Field Sensor

EOS Continuous Monitors

  • SCS CTC331-WW Iron Man® Plus Workstation Monitor
    The SCS CTC331-WW Iron Man® Plus Workstation Monitor is a single workstation continuous monitor which continuously monitors the path-to-ground integrity of an operator and conductive/dissipative worksurface and meets ANSI/ESD S20.20.The Iron Man® Plus Workstation Monitor is an essential tool when it comes to EOS detection. The unit is capable of detecting EOS on boards and alarms if an overvoltage (±5V or less) from a tool such as a soldering iron or electric screwdriver is applied to a circuit board under assembly.

    CTC331-WW
    The SCS CTC331-WW Iron Man® Plus Workstation Monitor

Data Acquisition

  • SCS Static Management Program
    SCS Static Management Program (SMP) continuously monitors the ESD parameters throughout all stages of manufacturing. It captures data from SCS workstation monitors, ground integrity monitors for equipment, ESD event and static voltage continuous monitors and provides real-time data of manufacturing processes.The SCS 770063 EM Aware Monitor, which is part of SMP, can help during the soldering process by monitoring ESD events and change of static voltage that may result in EOS. The EM Aware alarms (visual and audibly) locally and sends data to the database of the SMP system if any of the ESD parameters are detected to be higher than user-defined limits.

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    The SCS 770063 EM Aware Monitor

Eliminating EOS during the Soldering Process

Once the source of ESD/EOS is known, there are many things that can be done to prevent it in the first place: 

1. Managing Voltage on a PCB board

PCB boards contain isolated conductors and non-conductive (insulative) components. The only way to handle voltage on a PCB board is neutralizing potential static charges through ionization. An ionizer creates great numbers of positively and negatively charged ions. Fans help the generated ions flow over the work area to neutralize static charges (or voltage) on a PCB board in a matter of seconds.

For more information on ionization and how to choose the right type of ionizer for your application, please read these posts.

2. Managing Voltage on an Operator

Static voltage on an operator can be eliminated through proper grounding using a workstation monitor, e.g. WS Aware or Iron Man Plus Monitor, and proper grounding hardware. Sitting personnel are required to wear wrist straps. A wrist strap consists of a conductive wristband which provides an electrical connection to skin of an operator, and a coil cord, which is connected to a known ground point at a workbench, a tool or a continuous monitor. While a wrist strap does not prevent generation of voltages, its purpose is to dissipate these voltages to ground as quickly as possible.

Sitting personnel can also use continuous monitors – not only is the operator grounded through the continuous monitor, but they also provides a number of additional advantages:

  • Immediate feedback should a wrist strap fail
  • Monitoring of operators and work stations
  • Detection of split-second failures
  • Elimination of periodic testing

This post provides more details on continuous monitors.

Moving or standing personnel are grounded via a flooring/footwear system. ESD Footwear (e.g. foot grounders) are designed to reliably contact grounded ESD flooring and provide a continuous path-to-ground by removing electrostatic voltages from personnel.

3. Managing Current

One solution is the “re-routing of ground connection and separation of “noisy” ground from a clean one” as “connecting soldering iron and the workbench to the “quiet” ground often result in lower level of transient signals.“. [Source]

This will greatly reduce the high-frequency noise that could cause EOS damage.

If the noise on power lines and ground cannot be reduced manually, then the use of noise filters becomes necessary to reduce the risk of EOS exposure during the soldering process. Utilizing these filters suppresses the noise on power lines and will allow the solder iron to use “clean” power only.

In his papers, Vladimir Kraz, explains the set-up of a soldering station using a noise filter in more detail.

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Soldering Iron with Power Line EMI Filter [Source]

Conclusion

During the soldering process, current and voltage spikes between the solder tip and PCB can cause ESD/EOS. Sources are varied and can include:

  • Loss of Ground
  • Noise on Ground
  • Noise on Power Lines
  • Power Tools
  • Missing/Inadequate ESD Protection

ESD/EOS can be identified and controlled using diagnostic tools. SCS offers a number of tools that can detect current, voltage and EMI – all potentially leading to ESD and EOS.

Once the source of ESD/EOS is known, the next step is eliminating the source:

  • Managing voltage on a PCB board using ionizers.
  • Managing voltage on an operator using workstation monitors or foot grounders.
  • Managing current using noise filters.
  • Managing voltage on materials at the work bench.
  • Managing ESD generation during specific processes.
  • Managing grounding.

 For more information regarding this topic, please see below for additional references.

References:

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.

Last time we learned the difference between conductors & insulators. We went on to explain what ionizers are and when you need them in your EPA. Haven’t had a chance to read that post yet? Catch-up here!
All up to speed now? Right, let’s move on: as promised, today we’ll be looking at the different types of ionizers available.

What is an Ionizer?
But first a quick recap of what an ionizer is: An ionizer produces positively and negatively charged ions that are moved to the controlled area with fan driven airflow. Ionization can neutralize static charges on an insulator in a matter of seconds, thereby reducing their potential to cause ESD damage.

Types of Ionizers
Electrical ionizers generate air ions by a process known as corona discharge. A high voltage is applied to one or more sharp points and quantities of air ions are created. Fans or blowers may be incorporated in the ionizer to assist the movement of the ions and enhance performance.

  1. AC Ionizers
    AC ionizers use a transformer to multiply the AC power line voltage. AC stands for “Alternating Current” which means that the power cycles from positive to negative sixty times per second. The AC ionizer therefore produces both positive and negative ions from the same points or emitters. The drawback with this approach is that many ions recombine because the cycle frequency is too fast. For this reason, most AC ionizers rely on fans or blowers to be effective.
  2. Pulsed DC Ionizers
    Pulsed DC ionizers utilize separate power supplies to generate positive and negative voltages and usually each power supply has its own dedicated emitters. The power supply alternates between positive and negative, but usually at a lower frequency than AC units. In this way, ion recombination is reduced and performance is increased. Airflow may then be reduced for operator comfort without sacrificing much performance. With pulsed DC, it is important to cycle at least two or three times per second to prevent harmful voltage swings on the object being protected.
  3. Steady-state DC Ionizers
    Steady-state DC ionizers also employ separate power supplies and emitters, but instead of alternating positive and negative, both supplies are on all the time as the name implies. As would be expected, there is some degree of recombination, however, the ion density is still greater because of continuous operation of both supplies. The offset or balance voltage at the output will normally be more consistent than pulse units.

There are also nuclear types of ionizers which are non-electric. They are more frequently used in flammable or explosive environments for applications other than electronics.

Ionizer Configurations

  1. Room Ionization
    This type of configuration will typically have multiple emitters just below ceiling height and will rely on some amount of air movement for moving the ions down to bench level. It used to be considered as the most effective way to protect large areas against ESD hazards. However, these days localized workstation ionization is recommended:

    • Product sensitivity has become much greater and long decay times of room ionization cannot be tolerated.
    • With room ionization, often only a fraction of the ionized area may be ESD sensitive. Localized ionizers bring protection to the areas where it’s needed and performance is often 10 times faster than the ceiling height system.
    • Localized ionization moves with the workstation (or to a new workstation) making it much more flexible with changing production line layouts.
      Advantages Disadvantages
      + Effective for large areas – Long decay times
      – Cannot easily be moved once set-up
  2. Workstation Ionizers
    These come in many shapes and sizes. Probably the best-known type is the benchtop ionizer which is about the size of an iPad mini and about 4 inch deep. They’ve been around for many years and are to this day still in high demand. Over the years, smaller and lighter units were developed. As workstation space is incredibly valuable, many users prefer the smaller units. Some benchtop ionizers can even be suspended above the bench using a flexible mounting arm. Whatever style is chosen, care should be taken to assure that items normally on the bench would not obstruct the flow of ionized air.

    Example of a Benchtop Ionizer – click here for more information

    A real benefit of benchtop ionizers is the fact that they can easily be moved between workstations. So, if you only have a small EPA with a few users and shared workload, you can save money by moving one ionizer between different benches.

    Advantages Disadvantages
    + Compact – Potential obstruction of air flow
    + Lightweight
    + Portable
  3. Overhead Ionizers
    Overhead ionization was established to solve the problem of items on a workbench blocking the flow of ionized air. Overhead Ionizers have a unique hanging capability and are suspended about 17 to 24 inch above the bench – either by hanging from chains or by using mounting brackets attached to a shelf or bench.

    Example of an Overhead Ionizer – click here for more information

    Using this method of ionization makes it very unlikely for items to block the flow of ionized air to the item being protected. In addition, the downward airflow is more consistent over the entire bench. To ensure that adequate air is delivered an overhead ionizer with 2 to 4 fans should be used. Overhead ionization is ideal for areas where bench space is limited.

    Advantages Disadvantages
    + Large & consistent air flow coverage – Heavy
    + Don’t take up valuable workspace
    + Items unlikely to block air flow
  4. Forced Air Ionizers
    Most companies address ElectroStatic Attraction, visual imperfections and contamination issues by dislodging charged dust and debris with compressed air ionizers. They use compressed air or nitrogen to neutralise static charges in localized areas – they are a quick “point-and-shoot” option. They are either hand-held or may be mounted in a fixed location.

    Example of a Forced Air Ionizer – click here for more information

    The main advantage of this type is that the user has the benefit of a strong air blast (20 to 100 P.S.I.) to help dislodge contamination, while the ionization in the air stream eliminates the static attraction of the particles at the same time. Hand-held air nozzle types will usually have a trigger or push-button to activate the air and ion flow, while the stationary-mounted type is frequently remote controlled with a foot pedal, photo sensor or some other switch closure.

    Advantages Disadvantages
    + “Point-and-shoot” operation – Use valuable workstation space
    + Strong air blast

Summary
SCS Ionizers meet ANSI/ESD S20.20 tested per ANSI/ESD STM3.1 and ESD TR53. What type of ionizer you choose depends on a lot of different factors. There is no right or wrong – just different options.

A few things you should consider before making any decisions:

  • Type of operation
    Depending on the work your operators are doing, one type/configuration of ionizer may have more benefits then another. For example, if your workspace is limited, an overhead ionizer might be the answer. On the other hand, if there is an issue with debris & dust in your operation, then a compressed air ionizer would be better suited.
  • Features required
    Does your ionizer need to be made of stainless steel? Does it need to use zero-volt technology? Do you need a cost-effective ionizer with built-in emitter point cleaners? Do activities need to be monitored and recorded with some sort of software? Make a list of what is an absolute must and where you can compromise – see next point.
  • Available budget
    Even though this one is the last one in this list, it by no means is the least important factor. Quite contrary, it’s generally one of the main considerations when investing in an ionizer. However, it kind of goes hand in hand with the previous 2 points. So, you may have to make compromises, e.g. on the features, depending on what monies are available…

Need help choosing? Check out our Ionizer Selection Chart!
Alternatively, why not request an EOS/ESD Assessment? It’s a great way to have an extra set of eyes look at your ESD control plan!

Conclusion
Ionization is one of the best methods of removing charges from insulators and as a result plays an important role in controlling ESD. Remember though: an ionizer is a secondary form of defense and does not eliminate the need for standard ESD control devices such as wrist straps, heel grounders and worksurface mats. It is only one element in an effective ESD program.

Also, 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.