Ionizers

The best way to keep electrostatic sensitive devices (ESDs) from damage is to ground all conductive objects and remove insulators from your ESD Protected Area (EPA). This is not always possible because some insulators are “process-essential” and are necessary to build or assemble the finished product. The only way to control charges on these necessary non-conductive items is the use of ionization systems.

However, 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.

It is therefore essential to regularly clean your ionizers and verify they function correctly. Below we have put together a list of tasks you need to perform with your ionizers on a regular basis.

Maintenance

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 uses will generally require more frequent attention. It is important to set-up a routine schedule for ionizer service. Routine service is typically required to meet quality audit requirements.” (ESD Handbook TR20.20 section 5.3.6.7 Maintenance / Cleaning)

EIA-625, recommends checking ionizers every 6 months, but this may not be suitable for many programs particularly since an out-of-balance may exist for months before it is checked again. ANSI/ESD S20.20 section 6.1.3.1 Compliance Verification Plan Requirement states: “Test equipment shall be selected to make measurements of appropriate properties of the technical requirements that are incorporated into the ESD program plan.

Under normal conditions, an ionizer will attract dirt and dust (especially on the emitter points). To maintain optimum neutralization efficiency and operation, cleaning should be performed on a regular basis.

1. Case

Wipe the case with a soft cloth and deionized water. Fully squeeze the wiping cloth or sponge to remove any excess liquid. If a stronger cleaning solution is required, dab a soft cloth with mixture of isopropyl alcohol and deionized water (70% IPA and 30% DI water).

2. Emitter Points

The emitter points should be cleaned using specific emitter point cleaners or a swab dampened with Isopropyl alcohol. Below are general instructions on how to clean emitter points. However, each unit is slightly different so always refer to the ionizer’s manual.

  1. Turn the unit OFF and unplug the power cord.
  2. Open the top screen by loosening the screw and swinging the grill to one side.
  3. Clean the emitter points using the an emitter point cleaner or a swab dampened with Isopropyl alcohol.
  4. Re-attach the top screen.
  5. Plug in the power cord and turn the unit ON.
  6. Verify the performance of the ionizer by using a charged plate monitor or ionization test kit (see below).

Cleaning of Emitter Points using SCS 9110-NO as an example

With normal handling, the emitter points should not require replacement during the life of the unit.

Verification

Per ESD TR53 section 5.3.6.7.1 “The best practice is to measure the offset voltage and discharge times, clean the unit, including emitter points and air filters if present, offset voltage to zero (if adjustable), and then repeat offset voltage and discharge time testing. If the unit does not meet offset voltage specifications or minimum established discharge time limits, further service is indicated. Manufacturers should provide details on service procedures and typical service intervals.

Most companies will assign a number or otherwise identify each ionizer and setup a Compliance Verification / Maintenance / Calibration schedule. If the ionizers all test good, the data can justify lengthening the calibration period. If ionizers require adjustment, the calibration period should be shortened. Although ESD TR53 does not advise a test frequency, JESDD625-A (Revision of EIA-625) recommends ionizers be tested semi-annually, noting to use “S3.1 except the number of measurement points and locations may be selected based on the application.

Verification should be performed in accordance with the ESD Association ionization standard ANSI/ESD STM3.1.

Below are general instructions on how to verify your ionizer’s offset voltage and discharge time. Always refer to the User Guide accompanying your Charge Plate Monitor or Ionization Test Kit for proper operation and setup.

1. Testing Ionizer Offset Voltage:

The required limit per ANSI/ ESD S20.20 is less than ± 35 volts. Check your ionizer’s operating manual or consult with the ionizer manufacturer to determine what the offset voltage should be for your ionizer.

Charge Plate Monitor (CPM)

  1. Position the ionizer and charge plate monitor as shown below.
  2. Set the CPM to Decay/Offset mode.
  3. Set the CPM to decay and offset voltage mode with a starting charge at either + or – 1 KV and a stopping charge at either + or -100 Volts.
  4. Start the decay/offset test sequence on the CPM. This will take a few seconds.
  5. Record the decay time, and offset voltage as displayed on the CPM.

Positioning your Charge Plate Monitor for Overhead and Benchtop Ionizers

Ionization Test Kit

  1. Zero the charge plate by touching it with a grounded object. This can either be the finger of a grounded person or some other item which is connected to electrical ground. In either case, zeroing the charge plate should make the display on the field meter read zero.
  2. Hold the meter approximately one foot (30.5 cm) in front of the ionizer.
  3. Monitor the display. The value displayed is the offset balance of the ionizer, which is the difference between the number of positive and negative ions being emitted.
Testing Ionizer Offset Voltage using the SCS 718A Air Ionizer Test Kit

2. Testing Ionizer Discharge Time:

The required limit per ANSI/ESD S20.20 is “user defined”. Please refer to the ionizer’s operating manual or consult with the ionizer manufacturer to determine what this discharge time should be.

Charge Plate Monitor (CPM)

  1. Set the CPM to Decay/Offset mode.
  2. Set the CPM to decay and offset voltage mode with a starting charge at either + or – 1 KV and a stopping charge at either + or -100 Volts.
  3. Start the decay/offset test sequence on the CPM. This will take a few seconds.
  4. Record the decay time, and offset voltage as displayed on the CPM.

Ionization Test Kit

  1. After charging the plate of the ionization test kit, hold the field meter approximately one foot (30.5 cm) away from the ionizer.
  2. Monitor the display of the meter to see how quickly the 1.1 kV charge is dissipated to 0.1 kV.
  3. The speed at which this occurs (the discharge time) indicates how well the ionizer is operating.
  4. Repeat this procedure for both a positively and a negatively charged plate.

Some ionizers offer adjustment options (e.g. trim pots) which allow modification of the offset voltage.

However, if your ionizer is out of balance (and cannot be adjusted) or if the discharge time is out of specification, the ionizer will require service/repair by an authorized company.

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: ionizers require periodic cleaning of emitter pins and verifying of the offset voltage and discharge time. Otherwise, instead of neutralizing charges, the ionizer will primarily produce positive or negative ions. The ionizer will therefore place an electrostatic charge on items that are not grounded, potentially discharging and causing ESD damage to nearby sensitive items.

Setting up an ESD-safe workstation is often more challenging than it first appears. There are many methods of controlling ElectroStatic Discharge (ESD), and typically, it requires a combination of these to curb all static problems. Unfortunately, there is no single method that will fill all requirements.

Wrist straps and work surface mats are probably the most familiar to everyone, draining charges from operators as well as from the product being worked on. But what if the static charge in question is on an insulator? Electronic products, by nature, will normally consist of conductors and insulators. Insulators at the workstation can be found on the product itself, tools being used, tapes for masking, even circuit boards. A static charge on an insulator cannot be drained by grounding, as you could with a conductive material.

Ionization

To effectively remove charges from insulators, we need to make the surrounding air more conductive. We have all seen a balloon cling to a wall because of a static charge, and we know that, after a period of time, it will drop. That is because the air is somewhat conductive and the charge eventually drains off. The problem with this concept is that it takes too long. The more conductive the air is, the faster the charge will be neutralized.


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

The method most frequently used to increase the conductivity of the air is ionization.

Ionizers are useful in preventing electrostatic charge generation, ElectroStatic Discharge, ElectroStatic Attraction, as well as preventing equipment latch-up. Per ANSI/ESD S20.20 section 6.2.3.1. Protected Areas Requirement states: “Ionization or other charge mitigating techniques shall be used at the workstation to neutralize electrostatic fields on all process essential insulators if the electrostatic field is considered a threat.”

How do Ionizers work?

Most ESD workstations will have some insulators (e.g. product plastic housing) or isolated conductors (e.g. PCB board components not in contact with ESD worksurface) that cannot be removed or replaced. These should be controlled using ionization.

Ionizers create great numbers of positively and negatively charged ions. Fans help the ions flow over the work area. If there is a static charge present on an item in the work area, it will be reduced and neutralized by attracting opposite polarity charges from the air.

Ionization can neutralize static charges on an insulator in a matter of seconds, thereby reducing their potential to cause ESD damage.


Electronic enclosures are process-essential insulators

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.

How does Ionization fit into an ESD Control Program?

Ionization is just one component of your ESD Control Program. Before utilizing ionization, you should follow the fundamental principles of ESD Control:

  • Ground all conductors (including people) using conventional grounding methods (e.g. wrist straps or footwear/flooring system).
  • Remove all insulators, e.g. coffee cups, food wrappers etc.

“Air ionization is not a replacement for grounding methods. It is one component of a complete static control program. Ionizers are used when it is not possible to properly ground everything and as backup to other static control methods. In clean rooms, air ionization may be one of the few methods of static control available.” (ESD Handbook ESD TR20.20 Ionization, section 5.3.6.1 Introduction and Purpose / General Information)

  • Ionizers can be critical to reduce induction charging caused by process necessary insulators
  • Ionizers can be critical in eliminating charges on isolated conductors like devices on PCBs
  • Ionization can reduce ElectroStatic Attraction (ESA) and charged particles clinging and contaminating products.

The SCS Ionizer 9110-NO in Use

It is recommended to use ionizers with feedback mechanisms, so you’re notified if the offset voltage is out of balance.

Ionizers should be pieces of equipment that have serial numbers and are included in the company’s maintenance and calibration schedules. This is particularly critical to ensure that the offset voltage or balance is within acceptable limits. Otherwise, instead of neutralizing charges the out of balance ionizer will charge insulators and isolated conductors. The user, depending on the value and function of their products, must determine the appropriate frequency of maintenance and calibration.

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 finished product. The only way to control charges on these necessary non-conductive items is the use of ionization systems. Applications include:

  • eliminating charges on process essential insulators,
  • neutralizing workstations where ESDS are handled,
  • removing charged particulates to create a static free work area.

For more information and to select the right ionizer for your application, check out our Ionizer Selection Guide.

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.

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

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

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

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

 

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

Take-away:

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

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

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

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

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

Take-away:

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

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

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

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

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

Examples of some common process essential insulators are:

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

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

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

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

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

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

An ionizer creates positively and negatively charged ions.

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

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

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

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

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

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

 

Last time we explained how to easily create a compliance verification plan and why it’s important to have one in place. Today’s post will elaborate on the subject of periodic verification and highlight common products in your EPA that should be regularly verified and more importantly how they should be checked.

Why periodic verification
Compliance verification is a requirement of ANSI/ESD S20.20:
The Organization shall prepare an ESD Control Program Plan that addresses each of the requirements of the Program. Those requirements include:
– Training
– Product Qualification
– Compliance Verification
– Grounding / Equipotential Bonding Systems
– Personnel Grounding
– ESD Protected Area (EPA) Requirements
– Packaging Systems
– Marking” [ANSI/ESD S20.20 clause 7.1 ESD Control Program Plan]

Installed ESD Control products must be checked regularly to ensure they meet the required limits per the ESD Standard. “Compliance verification records shall be established and maintained to provide evidence of conformity to the technical requirements. The test equipment selected shall be capable of making the measurements defined in the Compliance Verification Plan.” [ANSI/ESD S20.20 clause 7.3 Compliance Verification Plan]

Below, you will find a list of the most common ESD Control Products in your EPA and how to test them:

Worksurface Matting
The purpose of ESD workbench matting is to ensure that when charged conductors (conductive or dissipative) are placed upon the surface, a controlled discharge occurs and electrostatic charges are removed to ground. However, this only occurs if the ESD worksurface is connected to ground. If the matting is out-of-spec, not grounded at all, or the stud on the mat has become loose or if the ground cord has become disconnected, charges cannot be removed.
Many companies use a daily checklist, which includes the operator having to verify that ground cords are firmly connected.
Remember to regularly clean your workbench matting to maintain proper electrical function. Do not use cleaners with silicone as silicone build-up will create an insulative film on the surface.
The company’s compliance verification plan should include periodic checks of worksurfaces measuring:

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

Testing a worksurface using SRMETER2

A surface resistance tester can be used to perform these tests in accordance with ANSI/ESD S20.20 and its test method ESD TR53; if these measurements are within acceptable ranges, the worksurface matting and its connections are good.

Wrist Straps
As discharges from people handling ESD sensitive devices cause significant ESD damage, the wrist strap is considered the first line of ESD control.
Before handling ESD sensitive items, you should visually inspect the wrist strap to see if there are any breakages etc. The wrist strap should then be tested while worn using a wrist strap tester. This ensures all three components are checked: the wrist band, the ground cord (including resistor) and the contact with the operator’s skin. Records of each test should be kept. Wiggling the resistor strain relief portion of the coil cord during the test will help identify failures sooner. Analysis and corrective action should take place when a wrist strap tester indicates a failure.

Checking wrist straps using 746

It is recommended that wrist straps are checked at least daily. An even better solution to daily wrist strap checks is the use of continuous monitors. They will alarm if the person or worksurface is not properly grounded.

A note on worksurface matting and wrist straps: if you are using common ground points to ground the operator and/or work surface matting, remember to measure resistance to ground regularly as well (every 6 months for example).

Floor Matting
A flooring / footwear system is an alternative for personnel grounding for standing or mobile workers. Foot grounders quickly and effectively drain the static charges which collect on personnel during normal, everyday activities. Foot grounders should be used in conjunction with floor surfaces which have a surface resistance of less than 1010 ohms.
As ESD floors get dirty, their resistance increases. For optimum electrical performance, floor matting must be cleaned regularly using an ESD mat cleaner. Do not use cleaners with silicone as silicone build-up will create an insulative film on the surface.
Dissipative floor finish can be used to reduce floor resistance. Periodic verification will identify how often the floor finish needs to be applied. As the layer(s) of dissipative floor finish wear, the resistance measurements will increase. So, after some amount of data collection, a cost-effective maintenance schedule can be established.
Floor matting can be checked using a resistance meter. A surface resistance meter is designed to measure resistance point-to-point (Rp-p) or surface to ground (Rg) in accordance with ANSI/ESD S20.20 and its test method ESD TR53.

Footwear
ESD Shoes or foot grounders play an essential part in the flooring/footwear system.
Before handling ESD sensitive devices, visually inspect your ESD footwear for any damage. Just like wrist straps, footwear should be checked while being worn using a wrist strap/footwear tester.

Checking foot grounders using 770750

Records of each test should be kept. Analysis and corrective action should take place when a footwear tester indicates a failure. Footwear needs to be checked daily.

ESD Packaging
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.

An operator packing an ESD sensitive item into a Shielding Bag
Make sure your ESD shielding bags are un-damaged

It is up to the user to determine if a shielding bag is suitable for re-use or not. The testing of every bag before re-use is not practical. Many companies will discard the shielding bag once used and replace it with a new one. Others will use a system of labels to identify when the bag has gone through five handling cycles:

  • Non-reusable labels are used that require the label be broken to open the bag.
  • The bag is then resealed with a new label.
  • When there are five broken labels, the bag is discarded.

The same principle applies to other ESD packaging, e.g. component shippers.

Ionizers
Ionizers are intended to neutralize static charges on insulators thereby reducing their potential to cause ESD damage. However, poorly maintained ionizers with dirty emitter pins and out-of-balance ionisers can put a charge on ungrounded items.
Remember to clean ionizer emitter pins and filters regularly. You can now even purchase ionizers that will alarm when emitter pins need to be cleaned or the ionizer is out of balance.

Charge plate monitor and static decay measurements using 963E ionized air blower

Static neutralization (the ability to reduce or eliminate a charge on a surface) is an important quality for ionizers. Static decay time is defined as the time interval needed to reduce a defined voltage potential on an object to a defined lower potential by means of applied ionized air. Another important aspect for ionizers is the ability to produce a balanced stream of positive and negative ions. A charged plate monitor or equivalent can be used to accurately measure both of these parameters.
For more detailed information on measuring the performance of ionizers refer to the ESD standard ANSI/EOS/ESD-S3.1 for Protection of Electrostatic Discharge Susceptible Items-Ionization.

Wrist Strap/Footwear and Resistance Testers etc.
So, you check your wrist straps and/or footwear and workbench and/or floor matting regularly. But have you remembered the testers themselves? What good do all the checks do, if the testers you use are out-of-spec and show you incorrect results?
Yearly calibration is recommended – many manufacturers offer a calibration service or alternatively you can purchase calibration units from them and perform the calibration yourself.

There you have it – a list of the most commonly used products in your ESD Protected Area (EPA) that you should check on a regular basis.
Questions for you: Do you have a verification plan in place? If so, how often do you check your ESD protection products?

Every component in an ESD protected area (EPA) plays an important role in the fight against electrostatic discharge (ESD). Just one element not performing correctly could harm your ESD sensitive devices and potentially cost your company a lot of money. The problem with many ESD protection products is that you can’t always see the damage – think wrist straps! By just looking at a coiled cord, you can’t confirm it’s working correctly; even without any visible damage to the insulation, the conductor on the inside could be broken. This is where periodic verification comes into play.

Introduction
When implementing an ESD control program plan, ANSI/ESD S20.20 asks for several requirements to be addressed, one of which is “Compliance Verification”:
The Organization shall prepare an ESD Control Program Plan that addresses each of the requirements of the Program. Those requirements include:

  • Training
  • Product Qualification
  • Compliance Verification
  • Grounding / Equipotential Bonding Systems
  • Personnel Grounding
  • ESD Protected Area (EPA) Requirements
  • Packaging Systems
  • Marking” [ANSI/ESD S20.20 clause 7.1 ESD Control Program Plan]

ESD protected area (EPA) products should be tested:

  • Prior to installation to qualify product for listing in user’s ESD control program.
  • During the initial installation.
  • For periodic checks of installed products as part of TR20.20.

A Compliance Verification Plan shall be established to ensure the Organization’s fulfillment of the technical requirements of the ESD Control Program Plan. Process monitoring (measurements) shall be conducted in accordance with a Compliance Verification Plan that identifies the technical requirements to be verified, the measurement limits and the frequency at which those verifications shall occur. The Compliance Verification Plan shall document the test methods and equipment used for process monitoring and measurements. If the test methods used by the organization differ from any of the standards referenced in this document, then there must be a tailoring statement that is documented as part of the ESD Control Program Plan. Compliance verification records shall be established and maintained to provide evidence of conformity to the technical requirements. The test equipment selected shall be capable of making the measurements defined in the Compliance Verification Plan.” [ANSI/ESD S20.20 clause 7.3 Compliance Verification Plan]

Components of a Verification Plan
Each company’s verification plan needs to contain:

1. A list of items that are used in the EPA and need to be checked on a regular basis
All ESD working surfaces, personnel grounding devices like wrist straps or foot grounders, ionizers etc. need to be included on the list. In summary: every item that is used for ESD Control purposes. It is recommended to create a checklist comprising all ESD control products as this will ensure EPAs are checked consistently at every audit.

2. A schedule specifying what intervals and how each item is checked
The test frequency will depend on several things, e.g.

  • how long the item will last,
  • how often it is used or
  • how important it is to the overall ESD control program.

As an example: wrist straps are chosen by most companies to ground their operators; they are the first line of defence against ESD damage. They are in constant use and are subjected to relentless bending and stretching. Therefore, they are generally checked at the beginning of each shift to ensure they are still working correctly and ESD sensitive items are protected. Ionisers on the other hand are recommended to be checked every 6 months: whilst they are in constant use, they are designed to be; the only actual ‘interaction’ with the user is turning the unit on/off. If, however, the ionizer is used in a critical clean room, the test frequency may need to be increased.

Testing-Wrist-Straps
It is recommended that Wrist Straps are checked before each shift

Testing and monitoring of smock and ground cord assembly

Test frequency limits are not listed in this document, as each user will need to develop their own set of test frequencies based on the critical nature of those ESD sensitive items handled and the risk of failure for the ESD protective equipment and materials.

Examples of how test frequencies are considered:

  • Daily wrist strap checks are sufficient in some applications while in other operations constant wrist strap monitoring may be used for added operator grounding reliability.
  • Packaging checks may depend on the composition of the packaging and its use. Some packaging may have static control properties that deteriorate more quickly with time and use, and some packaging may be humidity dependent and may have limited shelf life.
  • Some materials, such as ESD floor finishes, may require more frequent monitoring because of their lack of permanency. Other materials, such as ESD vinyl floor covering, may require less monitoring. The testing of a floor should also be considered after maintenance on the floor has been performed.” [ESD TR53-01-15 Annex A – Test Frequency]

The industry typically uses 2 types of verification to achieve maximum success: visual and measurement verification. As the name suggests, visual verification is used to ensure ESD working surfaces and operators are grounded, ESD flooring is in good shape or wrist straps are checked before handling ESD sensitive items.

Actual measurements are taken by trained personnel using specially designed equipment to verify proper performance of an ESD control item.

3. The suitable limits for every item used to control ESD damage
ANSI/ESD S20.20 contains recommendations of acceptable limits for every ESD control item. Following these references reduces the likelihood of 100V (HBM) sensitive devices being damaged by an ESD event.

Please bear in mind that there may be situations where the limits need to be adjusted to meet the company’s requirements.

4. The test methods used to ensure each ESD product meets the set limits
Tables 1 to 3 of ANSI/ESD S20.20 list the different test methods a company must follow.

If a company uses other test methods or have developed their own test methods, the ESD control program plan needs to include a statement explaining why referenced standards are not used. The company also needs to show their chosen test methods are suitable and reliable.

It is recommended that written procedures are created for the different test methods. It is the company’s responsibility to ensure anybody performing the tests understands the procedures and follows them accordingly.

5. The equipment used to take measurements specified in the test methods
Every company needs to acquire proper test equipment that complies with the individual test methods specified in Tables 1 to 3 of ANSI/ESD S20.20. Personnel performing measurements need to be trained on how equipment is used. ESD TR53-01-15 lists test procedures and equipment that can be used to verify ESD Control items.

SRMeter2_use
Checking an ESD Worksurface using a Surface Resistance Meter

6. A list of employees who will be performing the audits
Part of the verification plan is the choice of internal auditors. A few suggestions for the selection process:

  • Each individual is required to know the ESD Standard ANSI/ESD S20.20 AND the company’s individual ESD program.
  • It is essential that the selected team member recognizes the role of ESD control in the company’s overall quality management system.
  • It is recommended that each nominated worker has been trained on performing audits.
  • The designated employee should be familiar with the manufacturing process they are inspecting.

7. How to deal with non-compliance situations
Once an audit has been completed, it is important to keep everyone in the loop and report the findings to the management team. This is particularly vital if “out-of-compliance” issues were uncovered during the verification process. It is the responsibility of the ESD coordinator to categorize how severe each non-conformance is; key problems should be dealt with first and management should be notified immediately of significant non-compliance matters.

Results of audits (especially non-compliance findings) are generally presented using charts. Each chart should classify:

  • The total findings of the audit
  • The type of each finding
  • The area that was audited

It is important to note that each company should set targets for a given area and include a trend report. This data can assist in determining if employees follow the outlined ESD control program and if improvements can be seen over time.