Category Archives: Ionisation

Are your Ionisers working correctly?

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 ionisation systems.
However, if an ioniser is out of balance, instead of neutralising 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 ionisers and verify their functionality. Below we have put together a list of tasks that need to be performed with ionisers 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.” (User Guide CLC/TR 61340-5-2 clause 4.7.6.7 Maintenance and cleaning)
EIA-625, recommends checking ionisers 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. EN 61340-5-1 clause 5.2.4 Compliance Verification Plan  states: “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.
Under normal conditions, an ioniser will attract dirt and dust (especially on the emitter points). To maintain optimum neutralisation efficiency and operation, cleaning should be performed on a regular basis.

1. Case
Wipe the case with a soft cloth and deionised 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 deionised 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 ioniser’s manual.

  • Turn the unit OFF and unplug the power cord.
  • Open the top screen by loosening the screw and swinging the grill to one side.
  • Clean the emitter points using an emitter point cleaner or a swab dampened with Isopropyl alcohol.
  • Re-attach the top screen.
  • Plug in the power cord and turn the unit ON.

Verify the performance of the ioniser by using a charged plate monitor or ionisation test kit (see below).

Cleaning of Emitter Points using SCS 9110-NO as an exampleCleaning 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
EN 61340-4-7 provides test methods and procedures for evaluating and selecting air ionisation equipment. It is recommended to measure the offset voltage and discharge times, clean the unit, including emitter points and air filters if present, offset the voltage to zero (if adjustable), and then repeat offset voltage and discharge time testing. Should the unit not meet offset voltage specifications or minimum established discharge time limits, further service is required. Manufacturers should provide details on service procedures and typical service intervals.
Most companies will assign a number or otherwise identify each ioniser and setup a Compliance Verification / Maintenance / Calibration schedule. If the ionisers all test good, the data can justify lengthening the calibration period. If ionisers require adjustment, the calibration period should be shortened.

Verification should be performed in accordance with EN 61340-4-7.
Below are general instructions on how to verify your ioniser’s offset voltage and discharge time. Always refer to the User Guide accompanying your charge plate monitor or ionisation test kit for proper operation and setup.

1. Testing Ioniser Offset Voltage:
The required limit per EN 61340-5-1 is less than ± 35 volts. Check your ioniser’s operating manual or consult with the ioniser manufacturer to determine what the offset voltage should be for your ioniser.

Charge Plate Monitor (CPM)

  • Position the ioniser and charge plate monitor as shown below.
  • Set the CPM to Decay/Offset mode.
  • 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.
  • Start the decay/offset test sequence on the CPM. This will take a few seconds.
  • Record the decay time, and offset voltage as displayed on the CPM.

Positioning your Charge Plate Monitor for Overhead and Benchtop Ionisers

Ionisation Test Kit

  • 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.
  • Hold the meter approximately one foot (30.5 cm) in front of the ioniser.
  • Monitor the display. The value displayed is the offset balance of the ioniser, which is the difference between the number of positive and negative ions being emitted.

Auditing ionisation equipment with the Digital Static Field Meter and Conductive PlateAuditing ionisation equipment with the Digital Static Field Meter and Conductive Plate

2. Testing Ioniser Discharge Time:
The required limit per EN 61340-5-1 is “(1 000 V to 100 V and –1 000 V to –100 V) < 20 s or user defined”. Please refer to the ioniser’s operating manual or consult with the ioniser manufacturer to determine what this discharge time should be.

Charge Plate Monitor (CPM)

  • Set the CPM to Decay/Offset mode.
  • 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.
  • Start the decay/offset test sequence on the CPM. This will take a few seconds.
  • Record the decay time, and offset voltage as displayed on the CPM.

Ionisation Test Kit

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

Some ionisers offer adjustment options (e.g. trim pots) which allow modification of the offset voltage.
However, if your ioniser is out of balance (and cannot be adjusted) or if the discharge time is out of specification, the ioniser will require service/repair by an authorised company.

Conclusion
Ionisation is one of the best methods of removing charges from insulators and as a result plays an important role in controlling ESD.
Remember though: ionisers require periodic cleaning of emitter pins and verifying of the offset voltage and discharge time. Otherwise, instead of neutralising charges, the ioniser will primarily produce positive or negative ions. The ioniser will therefore place an electrostatic charge on items that are not grounded, potentially discharging and causing ESD damage to nearby sensitive items.

How does Ionisation fit into an ESD Control Programme?

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.

Ionisation
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 neutralised.

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

The method most frequently used to increase the conductivity of the air is ionisation.
Ionisers are useful in preventing electrostatic charge generation, ElectroStatic Discharge, ElectroStatic Attraction, as well as preventing equipment latch-up. EN 61340-5-1 clause 5.3.4.2 Insulators states: “If the measured electrostatic field or surface potential exceeds the stated limits, ionization or other charge mitigating techniques shall be used.

How do Ionisers 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 ionisation.

Ionisers 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 neutralised by attracting opposite polarity charges from the air.
Ionisation can neutralise static charges on an insulator in a matter of seconds, thereby reducing their potential to cause ESD damage.

Electronic enclosures are process-essential insulatorsElectronic enclosures are process-essential insulators.

The charged ions created by an ioniser will:

  • neutralise charges on process required insulators,
  • neutralise charges on non-essential insulators,
  • neutralise isolated conductors and
  • minimise triboelectric charging.

How does Ionisation fit into an ESD Control Programme?
Ionisation is just one component of your ESD Control Programme. Before utilising ionisation, 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.” (User Guide CLC/TR 61340-5-2 clause 4.7.6 Ionization)

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

The SCS Ioniser 9110-NO in use.The SCS Ioniser 9110-NO in use.

It is recommended to use ionisers with feedback mechanisms, so you’re notified if the offset voltage is out of balance.
Ionisers 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 neutralising charges the out of balance ioniser 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 ionisation systems. Applications include:

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

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

How to neutralise a charge on an object that cannot be grounded

We have learnt 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 you absolutely need an item in your EPA and it cannot be grounded? Don’t sweat, not all hope is lost! There are a couple of options which will allow you to use the item in question. Let us explain…

Conductors and Insulators
In ESD Control, we differentiate conductors and insulators.
Materials that easily transfer electrons are called conductors. Some examples of conductors are metals, carbon and the human body’s sweat layer.

ConductorA charged conductor can transfer electrons which allows it to be grounded

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.

InsulatorInsulators 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 conductors by grounding them. However, the item grounded must be conductive or dissipative. An insulator on the other hand, will hold the 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 achieve #1, all surfaces, products and people are bonded to Ground. Bonding means linking, usually through a resistance of between 1 and 10 megohms. Wrist straps and work surface 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 virtue of standing on a bonded surface or being held by a bonded person.

However, what 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. Per the ESD Standard, “All non-essential insulators and items (plastics and paper), such as coffee cups, food wrappers and personal items shall be removed from the workstation or any operation where unprotected ESDS are handled.
The ESD threat associated with process essential insulators or electrostatic field sources shall be evaluated to ensure that:

  • the electrostatic field at the position where the ESDS are handled shall not exceed 5 000 V/m;

or

  • if the electrostatic potential measured at the surface of the process required insulator exceeds 2 000 V, the item shall be kept a minimum of 30 cm from the ESDS; and
  • if the electrostatic potential measured at the surface of the process required insulator exceeds 125 V, the item shall be kept a minimum of 2,5 cm from the ESDS.”

[IEC 61340-5-1:2016 clause 5.3.4.2 Insulators]

Always keep insulators a minimum of 31cm from ESDS itemsAlways keep insulators a minimum of 31cm from ESDS items

“Process-essential” Insulators
Well, we all know that nothing in life is black and white. It would be easy to just follow the above ‘rules’ and Bob’s your uncle – but unfortunately that’s not always possible. There are situations where said insulator is an item used at the workstation such as a hand tools. They are essential – you cannot just throw them out of the EPA. If you do, the job won’t get done.
So, the question is – how do you ‘remove’ these vital insulators without actually ‘removing’ them from your EPA? There are 2 options you should try first:

1. 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 and brushes and waste bins. They are either conductive or dissipative and replace the standard insulative varieties that are generally used at a workbench. For more information on using ESD safe tools and accessories, check this post.

2. Periodically apply a coat of Topical Antistat
The Reztore® Topical Antistat (or similar solution) is for use on non-ESD surfaces. After it 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.

If these two options are not feasible for your application, the insulator is termed “process-essential” and therefore neutralisation using an ioniser should become a necessary part of your ESD control programme.

Neutralisation
Most ESD workstations will have some insulators or isolated conductors that cannot be removed or replaced. These should be addressed with ionisation.
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
Electronic enclosures are process-essential insulators

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.

An ioniser creates great numbers of positively and negatively charged ions. Fans help the ions flow over the work area. Ionisation can neutralise static charges on an insulator in a matter of seconds, thereby reducing their potential to cause ESD damage.
The charged ions created by an ioniser will:

  • neutralise charges on process required insulators,
  • neutralise charges on non- essential insulators,
  • neutralise isolated conductors and
  • minimise triboelectric charging.

Ioniser ExampleInsulators and isolated conductors are common in ESD Sensitive (ESDS) Devices – Ionisers can help

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

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

  • Keep insulators a minimum of 31cm from ESDS items at all times or
  • Replace regular insulative items with an ESD protective version or
  • Periodically apply a coat of Topical Antistat

When none of the above is possible, the insulator is termed “process-essential” and therefore neutralisation using an ioniser should become a necessary part of your ESD control programme.

The impact of relative humidity on ESD

A video making the rounds on Social Media this week highlights a very common problem in ESD Protection: dry air.
The report shows energy minister Simon Bridges walking around his office spraying the floor with water, applying tape to door handles and using an antistatic mat at his desk. The reason? Simple: a new carpet which was installed at the Beehive and the “little tickles” ministers are getting as a result.

SImon Bridges spraying the floor in his office with water
Simon Bridges spraying the floor in his office with water (Source)

Jim Robb who is in charge of maintaining the parliament building provides the following explanation: “We’re in the middle of winter, we’ve got cold polar air, there’s no moisture in it and it’s a very common problem, I’ve been dealing with this for thirty years.”

While the ministers at the Beehive seem to have figured out solutions to avoid the “zap”, we want to show you how you can solve the issue of dry air in your EPA.

Impact of relative humidity on ESD

Just like the ministers in the above report, many people will notice a difference in the ability to generate static electricity when the air gets dryer (the % RH decreases).
Relative humidity (RH) directly affects the ability of a surface to store an electrostatic charge. As RH increases, the time a surface will hold a charge will decrease and the dissipation rate will increase. 

An example: walking across a carpet can yield a charge of 35kV at 10% RH (very dry air) but will drop significantly to 7.5kV at 55% RH. In an electronics manufacturing environment lower humidity may result in lower output from production due to an increase in ESD events during manufacturing processes.

A normal range for humidity in an electronics manufacturing environment is be 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.
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 sn electronics manufacturing environment such as corrosion, soldering defects and the popcorn effect on moisture sensitive devices.

The popcorn effect
The popcorn effect (Source)

Dealing with dry air in an EPA

While not a replacement for grounding, shielding or ESD working surfaces, ionisation can mitigate ESD events in areas where dry air is normal. For more information on ionisation and the different types of ionisers, we recommend reading these two posts:

In summary, worksurface ionisers (Bench Top and Overhead Ionisers) produce positively and negatively charged ions that are moved to the controlled area with fan driven airflow. Point-of-use air ionisers use compressed gas to combat electrostatic attraction neutralising charges on particles causing contamination or visual defects on products.

Using a point-of-use air ioniserUsing a point-of-use air ioniser

The ESD Standard on Relative Humidity

The ESDA’s TR20.20-2008 discusses RH in a few different places. Some significant statements are listed below.

ESD Handbook ESD TR20.20-2008 section 2.3 Nature of Static Electricity:
The moisture level in the air, or relative humidity in the environment, are important considerations in the liberation and accumulation of static electricity. It is well known that static electricity in the form of static cling and static shocks are more prevalent when the air is dry. Heating interior air in the winter months dries out the already dry air in the higher latitudes. Static charge accumulation is easier on dry materials since moisture on surfaces tends to allow charges to slowly dissipate or recombine.
However, it is impractical to use humidity control alone to provide static control since static charges are developed even at relative humidity levels of 90% and greater. For most situations, 30 to 70% RH is considered the appropriate range. Special areas, such as wafer fabrication, may require lower humidity control for processes that are affected by moisture (e.g., photoresist application). Soldering is known to be affected by high relative humidity conditions (>70%). For areas that have low ambient humidity, ionization is an important consideration to aid in reducing charge accumulation levels and provide neutralization of charges after they are developed but before they can cause difficulties.

ESD Handbook ESD TR20.20-2008 section 5.3.16 Humidity:
Humidity is beneficial in all ESD control program plans. Contact and separation of dry materials generates greater electrostatic charges than moist materials because moisture provides conductivity that helps to dissipate charge. For this reason, ESD effects are most noticeable in the winter since heating systems reduce building environment moisture. Geographic location (desert vs. coastland) is also a major contributor to ambient conditions inside buildings. Any circumstance that results in a low relative humidity will permit a greater accumulation of electrostatic charges. Relative humidity above 30% in ESD protective areas is desirable as long as other adverse conditions are not created as a result of humidity levels. Generally speaking an upper limit of 70% is desirable to prevent corrosive effects on the metal portions of electronic devices and assemblies.
Besides the increasing propensity to generate electrostatic charges on dry materials in general, performance of many ESD protective materials degrade. In fact, when exposed to low humidity conditions, some ESD protective materials become totally ineffective or become sources of electrostatic charges. Therefore, evaluation of ESD control materials should include performance testing in controlled environments at the lowest expected operating relative humidity level. Manufacturers of ESD protective materials should be able to provide performance data in regards to relative humidity. Likewise, materials should be tested in moderate humidity conditions as well to ensure they do not become “too conductive” and present a potential safety hazard to personnel working with substantial voltages. See the Personnel Safety section of this handbook for further guidance in this area.
Humidity control in factories or physically large areas or buildings can be difficult and expensive. In smaller rooms or areas, it may be possible to use portable humidifiers to raise the immediate area humidity. However, in large facilities and factories the environmental systems many need to include steam generation and monitoring equipment to control humidity. This type of equipment is expensive to install and purchase especially in pre-existing facilities. To reduce the total cost impact, companies should consider the need for humidification equipment when planning new facility construction.

ESD TR20.20-2008 can be purchased directly from the ESD Association.

Checking your ESD Control Products – Part 2

Today’s post concludes our 2-part series on periodic verifcation. If you have missed the first part, you can catch-up on it here. As a reminder, it is recommended to regularely check all ESD Protected Area (EPA) products to ensure they are working correctly. After covering working surface matting and wrist straps in last week’s post, we’ll jump right in to discuss the remaining components in your EPA.

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, such as Reztore™ Surface & 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.

Testing floor mattingTesting floor matting

Floor matting can be checked using a resistance meter. Surface resistance meters are designed to measure resistance point-to-point (Rp-p) or surface to ground (Rg) in accordance with EN 61340-5-1 Electrostatics and its test method IEC 61340-2-3.

Footwear
ESD Shoes or Foot Grounders play an essential part in the flooring/footwear system. For more information on how to ground moving personnel effectively, check this post.
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 groundersChecking foot grounders using 222567

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.

Using ESD shielding bagsMake 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.

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

Checking ionisersChecking ionisers using 50598

The EMIT Ionisation Test Kit 50598 allows the Digital Static Field Meter 50597 to be used to measure the offset voltage (balance) and charge decay of ionisation equipment. The Test Kit also includes a Charger used to place a ±1000V charge on the 50567 Conductive Plate, making it possible to measure the discharge times of air ionisation equipment per ANSI/ESD SP3.3 Periodic Verification of Air Ionizers.

Wrist Strap/Footwear and Resistance Testers etc.
So you check your wrist straps and/or footwear and bench 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.

 

So 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 verfication plan in place? If so, how often do you check your ESD protection products?

What type of Ioniser to choose

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Last week we learned the difference between conductors & insulators. We went on to explain what ionisers are and when you need them in your EPA. As promised, today we’ll be looking at the different types of ionisers available.

What is an Ioniser?

But first a quick recap of what an ioniser is: An ioniser creates great numbers of positively and negatively charged ions. Fans help the ions flow over the work area. Ionisation can neutralise static charges on an insulator in a matter of seconds, thereby reducing their potential to cause ESD damage.

Types of Ionisers

Electrical ionisers 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 ioniser to assist the movement of the ions and enhance performance.

  1. AC Ionisers
    AC Ionisers 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 ioniser 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 ionisers rely on fans or blowers to be effective.
  2. Pulsed DC Ionisers
    Pulsed DC ionisers utilise separate power supplies to generate positive and negative voltages and usually each power supply has it’s 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 Ionisers
    Steady-state DC ionisers 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 ionisers which are non-electric. They are more frequently used in flammable or explosive environments for applications other than electronics.

Ioniser Configurations

    1. Room Ionisation
      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 localised workstation ionisation is recommended:

      • Product sensitivity has become much greater and long decay times of room ionisation cannot be tolerated.
      • With room ionisation often only a fraction of the ionised area may be ESD sensitive. Localised ionisers bring protection to the areas where it’s needed and performance is often 10 times faster than the ceiling height system.
      • Localised ionisation 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 Ionisers
      These come in many shapes and sizes. Probably the best known type is the bench top ioniser which is about the size of an iPad mini and about 10cm 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 bench top ionisers 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 ionised air.
      50604

      A Bench Top Ioniser mounted using an adjustable arm

      A real benefit of bench top ionisers 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 ioniser between different benches.

      Advantages  Disadvantages
      + Compact – Potential obstruction of air flow
      + Lightweight
      + Portable
    3. Overhead Ionisers
      Overhead ionisation was established to solve the problem of items on a bench blocking the flow of ionised air. Overhead ionisers have a unique hanging capability and are suspended about 45cm to 60cm above the bench – either by hanging from chains or by using mounting brackets attached to a shelf or bench.
      50672

      Example of an Overhead Ioniser

      Using this method of ionisation makes it very unlikely for items to block the flow of ionised 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 ioniser with 2 to 4 fans should be used. Overhead Ionisation are 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 Ionisers
      Most companies address ElectroStatic Attraction, visual imperfections and contamination issues by dislodging charged dust and debris with compressed air ionisers. They use compressed air or nitrogen to neutralise static charges in localised areas – they are a quick “point-and-shoot” option. They are either hand-held or may be mounted in a fixed location.
      50644

      Example of an Forced Air Ioniser

      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 ionisation 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

What type of ioniser 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 ioniser may have more benefits then another. For example, if your workspace is limited, an overhead ioniser might be the answer. On the other hand if there is an issue with debris & dust in your operation, then a compressed air ioniser would be better suited.
    • Features required
      Does your ioniser need to be made of stainless steel? Does it need to use zero-volt technology? 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 ioniser. 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 Ioniser Selection Chart!
Alternatively, why not request a Survey? It’s a great way to have an extra set of eyes look at your ESD control plan!

Conclusion

Ionisation 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 ioniser is a secondary form of defence and does not eliminate the need for standard ESD control devices such as wrist straps, heel grounders and work surface mats. It is only one element in an effective ESD programme.

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

 

Conductors & Insulators

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We’ve previously published a post that explains when you need ionisation. However, following this post, we got a number of questions that prompted us to dive a bit deeper into the whole subject of ionisers. Basically with this post we’re starting right at the beginning so stay tuned…
Before talking about ionisers in more detail, we need to have a little chat about the types of materials that can be found in an EPA – conductors and insulators:

Conductors

• Electrical current flows easily
• Can be grounded

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.

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

Insulators

• Electrical current does not flow easily
• Cannot be grounded

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.

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

Insulators, by definition, are non-conductors and therefore cannot be grounded. Insulators can be controlled by doing the following within an EPA:
• Keep insulators a minimum of 31cm from ESDS items at all times or
• Replace regular insulative items with an ESD protective version or
• Periodically apply a coat of topical antistat

“Process essential” Insulators

When none of the above is possible, the insulator is termed “process essential” and therefore neutralisation using an ioniser should become a necessary part of the ESD control programme.

Examples of some common process essential insulators are a 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 neutralisation. Ions are charged particles that are normally present in the air and as opposite charges attract, charges will be neutralised 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 neutralise the charge. An ioniser greatly speeds up this process.

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

What is an ioniser?

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

IoniserAn ioniser creates positively and negatively charged ions.

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

Summary

This citation from the ESD handbook provides an excellent summary:
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 and footwear. 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)

Now that you know what conductors and insulators are, how to treat them in an EPA and when to use ionisation, the next step is to learn about the different types of ionisers available. However, as this post is already quite long, we will save that part for next week so stay tuned…. Click here to read the follow-up post.

When do you need Ionisation?

Materials that do not easily transfer electrons are called insulators or non-conductors. An insulator will hold the charge and cannot be grounded; therefore the charge cannot dissipate in a controlled way. This could lead to static damage of nearby sensitive components as there can be a rapid, spontaneous transfer of electrostatic charge.

Insulators can be controlled by doing the following:
– Keep insulators a minimum of 30cm from ESDS items at all times, or
– Replace regular insulative items with an ESD protective version, or
– Periodically apply a coat of topical antistat.

When none of the above is possible, the insulator is termed “process essential” and therefore neutralisation using an ioniser should become a necessary part of the ESD control programme.

Ionisers can neutralise static charges on an insulator in a matter of seconds.

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

Vermason offers a wide product range of ionisers: bench-top, overhead and compressed air/gas point of use. Vermason products incorporate superior technology providing fast charge decay times, and such features as auto balancing offset voltage feedback controls and “clean me” alarms.

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