Workstation Ionization

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

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

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

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

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

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

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

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

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

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

Sources of EOS during the Soldering Process

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

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

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

Detecting EOS during the Soldering Process

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

Diagnostic Tools

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

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

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

EOS Continuous Monitors

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

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

Data Acquisition

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

    770063.jpg
    The SCS 770063 EM Aware Monitor

Eliminating EOS during the Soldering Process

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

1. Managing Voltage on a PCB board

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

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

2. Managing Voltage on an Operator

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

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

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

This post provides more details on continuous monitors.

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

3. Managing Current

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

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

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

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

Noise-Filter
Soldering Iron with Power Line EMI Filter [Source]

Conclusion

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

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

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

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

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

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

References:

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

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

Conductors and Insulators

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

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

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

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

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

Both, conductors and insulators, may become charged with static electricity and discharge.

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

Conductors and Insulators in an EPA

The first two fundamental principles of ESD Control are:

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

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

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

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

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

The ESD Standard differentiates between these two options:

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

“Process-Essential” Insulators

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

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

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

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

Neutralization

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

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

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

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

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

The charged ions created by an ionizer will:

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

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

Summary

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

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

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

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

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

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

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

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

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

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

Ionizer Configurations

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

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

    Example of a Benchtop Ionizer – click here for more information

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

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

    Example of an Overhead Ionizer – click here for more information

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

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

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

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

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

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

A few things you should consider before making any decisions:

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

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

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

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