Controlling ESD/EOS during the Soldering Process

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 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:

  • 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
1. 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.
    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).
    SCS CTM048 EM Eye – ESD Event Meter

2. 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.SCS CTC331-WW Iron Man® Plus Workstation Monitor

3. 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.
    SCS Static Management Program

Eliminating EOS during the Soldering Process
Once the source of 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
The only way to handle voltage on a PCB board is through ionisation. 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 (or voltage) on a PCB board in a matter of seconds.
For more information on ionisation and how to choose the right type of ioniser 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. Sitting personnel is 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. Utilising 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.

Managing CurrentSoldering 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:

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

Desco Europe offer 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 ionisers.
  • 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.

 

 

References:

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Is air humidification a necessity for ESD Control?

Have you ever walked across the car park on a bright cold winter’s day only to get zapped by your car’s door handle? Yup, we’ve all been there and it’s commonly known that these ‘zaps’ are much more frequent in cold dry weather. It begs the question: if I don’t get zapped when the air is moist, will using air humidifiers in a manufacturing environment prevent ESD damage of sensitive components? Let’s find out!

Humidity
Humidity describes the amount of water vapour in the air. There are 3 main measurements of humidity with the most common one being the relative humidity (RH). It is expressed in percent and describes “how much humidity there is in the air, compared to how much there could be. Meteorologists often use the relative humidity as a measurement to describe the weather at various places.” [Source]
At 0% the air is completely dry; at 100% it is so moist that mist or dew can form. The optimum relative humidity level is somewhere between 40% and 60%:

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

Charge Generation and ElectroStatic Discharge (ESD)
The simple separation of two surfaces generates an ElectroStatic charge. Examples:

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

Generating Charges by walking across a CarpetWalking across a floor generates ElectroStatic charges

The amount of static electricity generated varies and is affected by materials, friction, area of contact and the relative humidity of the environment. A higher charge is generated at low humidity, in a dry environment.
Once an item has generated a charge, it will want to come into balance. If it is in close enough proximity to a second item, there can be a rapid, spontaneous transfer of electrostatic charge. This is called discharge or ElectroStatic Discharge (ESD).

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

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

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

PCB-Damage

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

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

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

Let’s address both of these questions:

  • Let’s be very clear about one thing here: air humidifiers cannot replace ESD Control measures.As explained further above, ESD is caused by two items that are at a different electrostatic equipotential and want to equalise their charges. Adding moisture to the air using humidifiers will not stop this discharge from happening. The only thing you may achieve is a reduction in the number of ESD events. BUT: they will still happen; just walking across a carpet will generate a charge on an operator. If they then touch an ESD sensitive component, discharge will still occur and may damage the component. No humidifier in the world will prevent this.
    The only way to control electrostatic charges on a person or object is through ESD grounding – this will ensure any charges generated dissipate to earth:

    • Operators need to be grounded using wrist straps or a footwear/flooring system.
    • Surfaces need to grounded using appropriate matting and ground cords.

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

EBP-Bar-for-Flyer

Grounding of an operator using a wrist strap

  • Low air humidity can increase the number of ESD events so it may make sense to keep a factory at a higher humidity level. However, there are many other factors that come into play when choosing the ‘right’ humidity for a manufacturing environment. The recommended humidity range is usually determined by the specifications of the devices and components being assembled. Increasing the humidity in an electronics manufacturing facility can help to reduce ESD events but increased humidity can lead to other unwanted quality issues in an electronics manufacturing environment such as corrosion, soldering defects and the popcorn effect on moisture sensitive devices.
    A normal range for humidity in electronics manufacturing is between 30% RH and 70% RH. Some facilities try to maintain a constant moderate RH (~50%), whereas other environments may want lower % RH due to corrosion susceptibility to humidity sensitive parts.
    And remember: you will not eliminate ESD by using humidifiers and keeping humidity levels at a higher humidity level. You need an ESD Control Programme in place to avoid ESD and associated damages.

Conclusion
A lower relative humidity level increases charge generation as the environment is drier. This will result in more ESD events which can potentially damage sensitive components. The only way to protect sensitive components from ESD damage is by having proper ESD control measures in place and connecting operators, objects and surfaces to ground. This will ensure each element is kept at the same electrical potential and any electrostatic discharge is being removed to ground.
Humidification can help reduce the number of ESD events in an electronics manufacturing environment but at the same time there are other factors (e.g. moisture sensitivity of components) that need to be considered, too.

“Product Qualification” is a new Requirement of IEC 61340-5-1

In a previous blog post we discussed the “Walking Test”, a new requirement that was introduced with the latest ESD Standard published in 2016. There was another significant update to the ESD Standard that most people are not aware of: product qualification. Today’s post will explain in detail what this requirement entails and how you can ensure you’re compliant with the current ESD Standard.

Introduction
A second edition of IEC 61340-5-1 was published in 2016 cancelling and replacing the first edition issued in 2007. The current document added section 5.2.3 on “product qualification”.
Product qualification “is the process of certifying that a certain product has passed performance tests and quality assurance tests, and meets qualification criteria stipulated in contracts, regulations, or specifications (typically called “certification schemes” in the product certification industry).” [Source]

So, you’re now probably wondering what exactly this change means for you – simple: if you want to be compliant with IEC 61340-5-1, you have to ensure that any ESD control items you are using in your ESD Control Programme meet the Product Qualifications outlined in the Standard.

Tables 2 and 3 of the Standard outline:

  • Test methods and
  • Associated limits

for the product qualification of each ESD control item.

Requirement for 61340-5-1 ComplianceProduct Qualification is a Requirement for 61340-5-1 Compliance

Acceptable proofs of Product Qualification
So, now you know WHAT is required, the next question is HOW to verify if your ESD control items comply with the ESD Standard 61340-5-1. First things first: for any products you have acquired before adopting IEC 61340-5-1:2016, you can use ongoing compliance verification records as proof of product qualification. For more information on compliance verification, we suggest reading this post.

Once you have adopted IEC 61340-5-1:2016, any new products you chose to purchase need to be qualified to ensure they comply with the ESD Standard. There are a number of things you can use:

  1. The manufacturer’s datasheets.
  2. Test reports from independent laboratories or
  3. Your own internal test reports

Whatever option you choose, the datasheet or report of each product needs to fulfil the following requirements:

  • Display the IEC test method and
  • Mentioned test limits needed to comply with the ESD Standard.

If you are using ESD control items that are not listed in tables 2 and 3 of the ESD Standard, you need to qualify those items before starting to use them. The test method and acceptable limits need to be documented in your ESD control programme. If you need help setting up an ESD control plan, have a look at this post.

Summary
The latest ESD Standard 61340-5-1 published in 2016 added section 5.2.3 on “product qualification”. If your company wants to be compliant with IEC 61340-5-1, you have to ensure that any ESD control items you are using in your ESD Protected Area (EPA) meet the requirements of the ESD Standard.

Acceptable proofs of product qualification are:

  1. The manufacturer’s datasheets.
  2. Test reports from independent laboratories or
  3. Your own internal test reports
  4. Ongoing compliance verification records (only for items acquired before adopting the ESD Standard)

Desco Europe has a comprehensive range of technical information online, including product specification to the required Standards. Contact Desco Europe today for assistance with your product qualification plan.

Organising your ESD Workstation using 5S

Although not strictly related to ElectroStatic Discharge (ESD), we all know that a tidy workstation is essential when it comes to ‘getting the job done’. Having a cluttered desk and not being able to find the tools you need makes everything take twice as long. Ever heard of the 5S methodology? In today’s post, we will show how this approach can be applied to an ESD workstation. We’ll also introduce a few ESD products that can help in becoming more efficient and productive when handling ESD sensitive devices.

5S Methodology
5S is the name of a workplace organization method that uses a list of five Japanese words: seiri, seiton, seiso, seiketsu, and shitsuke. Transliterated into Roman Script, they all start with the letter “S”.[1] The list describes how to organize a work space for efficiency and effectiveness by identifying and storing the items used, maintaining the area and items, and sustaining the new order.” [Source]
Generally speaking, 5S incorporates 5 phases:

  1. Sort
  2. Arrange
  3. Clean
  4. Standardise
  5. Sustain

This post is going to focus on the first two steps of 5S.

Sorting an ESD Workstation
Items at an ESD protective workstation should be either dissipative or conductive so that electrostatic charges are removed to ground when in contact with a grounded operator or grounded ESD mat.
The protection of ESDS is accomplished by providing a ground path to bring ESD protective materials and personnel to the same electrical potential. All conductor and dissipative items in the environment, including personnel, shall be bonded or electrically connected to a known ground or common connection point. This connection results in sharing of charge which equalizes the voltage across all items and personnel and eliminates the chances of an ESD event to ESD sensitive devices. Electrostatic protection can be maintained at a potential different from a “zero” voltage ground reference as long as all items in the system are at the same potential.“ [CLC/TR 61340-5-2 Clause 4.4 Grounding/bonding systems]

So, before moving any further operators need to take a good look at their workstation and eliminate any items that are not essential to their workflow.
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.

If the measured electrostatic field or surface potential exceeds the stated limits, ionization or other charge mitigating techniques shall be used.” [IEC 61340-5-1 Clause 5.3.4.2 Insulators]

Arranging an ESD Workstation
Once the essential items required to do the job have been identified, the next step is to arrange them in a way that is suitable to the operator’s workflow. Here are a few tools and items that can be useful:

1. Use Colour and Labels
Having a proper colour and labelling system in place will help arrange a workstation and put items in the right places. This in return will ensure operators can find tools and accessories quickly when required.

Dispensing Bottles
Operators working with solder irons or performing various cleaning tasks at an ESD workstation will likely be using water or some sort of cleaning agent. ESD dispensing bottles can store these liquids. They come in all sorts of sizes and with various pumps or spouts. Using different colours will help identify the many liquids needed at an ESD workstation.

ESD Dispensing BottlesExamples of Dispensing Bottles – more information

Waste Bin Liners
Bin liners come in different sizes and colours and can be useful when it comes to separating waste. They are non-tribocharging and are designed for use in ESD protected areas where electrostatic sensitive devices are present. Even at low humidity they do not become charged with static electricity. They are made from high quality polyethylene and are as strong as conventional refuse sacks.

BinLinersExamples of Waste Bin Liners – more information

Document Holders
Document holders are designed for use within ESD Protected Areas in accordance with EN 61340-5-1. They are static dissipative which means charges are removed to ground when placed on a grounded working surface or handled by a grounded operator. Applying them to ESD safe containers will help finding tools, components and accessories.

Document WalletsExamples of Document Holders – more information

2. Use Boxes and Containers
Everything is tidier when using boxes, right? The workstation looks clean and using document wallets (see above) will instantly tell the operator what is inside of each container or box. Everyone’s a winner!

Letter Trays
Generally conductive, any electrostatic charges on letter trays are removed to ground when the tray is placed on a grounded working surface or contacted by a grounded operator. They are helpful when organising documents (e.g. production orders) at an ESD workstation.

Letter TrayExample of a Letter Tray

Workstation Organisers
Workstation Organisers are ideal for improving the organisation of a workstation and standardising the placement of tools which is a key concept of the 5S methodology. They can be used for various items which are used on the workstation:

– dispensing bottles,
lotions,
flux bottles,
– solder spools,
– cutters,
– tweezers,
– wash bottles and
– various other workbench accessories.

Workstation OrganiserExample of a Worstation Organiser – more information

Ideally, Workstation Organisers should be the exact size required for your work area and have the tool openings cut for the tools you have “sorted” and determined need to be kept at the workstation.

Rack Holders, Containers and Hanging Bins
These types of storage solutions are perfect for PCB boards and components. They are generally made of a conductive material so that when placed on a grounded surface, any charges will dissipate to ground.

PCB ContainersExamples of a PCB Containers – more information

Maintaining an ESD Workstation
The hard part of ‘change’ is sticking with it and not falling back into old habits – this is where the last 3 steps of 5S come into play: clean, standardise and sustain. It’s essential that:

  1. An ESD Workstation is cleaned on a regular basis. Ensure all tools, accessories etc. are in the correct place and ESD precautions are followed.
  2. Procedures and processes are in place so every operator is aware of their responsibilities and how to perform their jobs correctly.
  3. A regular training and audit schedule is created. They are part of any ESD Programme and will not only ensure that ESD sensitive items are handled properly, but that ESD workstations are maintained.

Conclusion
The 5S methodology can be applied to a wide range of industries including an ESD workstation. There are numerous ESD tools and accessories available that can support companies with the implementation of 5S. The results will be increased efficiency, productivity and output.

References:
Huffington Post: 7 Tips to Organize Your Work Space and Stay Productive
Wikipedia: 5S (methodology)

Creating an ESD Workstation

When referring to an “ESD Protected Area” or “EPA”, a lot of people imagine rooms or even whole factory floors with numerous workstations. This very common misconception leads to nervousness and even fear when it comes to implementing an ESD Control Programme. There is a concern regarding the cost and time implications to establish an EPA. However, most often, a simple ESD workstation is completely sufficient to fulfil a company’s needs to protect their ESD sensitive products. Today’s post will provide a step-by-step guide on:

  • how to create an EPA at your workstation,
  • what ESD control products are required and
  • how to correctly set them up.

Introduction
An EPA is an area that has been established to effectively control Electrostatic Discharge (ESD) and its purpose is therefore to avoid all problems resulting from ESD damage, e.g. catastrophic failures or latent defects. It is a defined space within which all surfaces, objects, people and ESD Sensitive Devices (ESDs) are kept at the same electrical potential. This is achieved by simply using only ‘groundable’ materials for covering of surfaces and for the manufacture of containers and tools. All surfaces, products and people are bonded to Ground. Bonding means linking, usually through a resistance of between 1 and 10 megohms. Movable items (such as containers and tools) are bonded by virtue of standing on a bonded surface or being held by a bonded person. Everything that does not readily dissipate charge must be excluded from the EPA.
An EPA can be just one workstation or it could be a room containing a number of different workstations. “The size of an EPA can vary greatly. A protected area may be a permanent workstation within a room or an entire factory floor encompassing thousands of workstations. A protected area may also be a portable worksurface or mat used in a field service situation.” [CLC/TR 61340-5-2:2008 Use guide clause 4.6 Protected areas (EPA)]

Converting your Workstation into an EPA
Creating an EPA at your existing workstation does not need to be complicated or expensive. There are just a few things you will need:

ESD Workstation

1. Working Surface Mat
ESD protective working surfaces aid in the prevention of damage to ESD sensitive items (ESDS) and assemblies from electrostatic discharge.
ESD working surfaces, such as mats, are typically an integral part of the ESD workstation, particularly in areas where hand assembly occurs. The purpose of the ESD working surface is two-fold:

  • To provide a surface with little to no charge on it.
  • To provide a surface that will remove ElectroStatic charges from conductors (including ESDS devices and assemblies) that are placed on the surface.

2. Working Surface Mat Grounding Cord
Your ESD working surface needs to be grounded using a ground cord. A ground wire from the surface should connect to the common point ground (in our example an Earth Bonding Point Plug) which is connected to ground, preferably equipment ground. Best practice is that ground connections use firm fitting connecting devices such as metallic crimps, snaps and banana plugs to connect to designated ground points. The use of alligator clips is not recommended.

3. Earth Bonding Point Plug
Earth Bonding Point (EBP) plugs are designed to provide a common ground point for grounding using protective earth in an EPA. The plugs fit into the mains supply socket, making a connection with the earth conductor only. In place of the live and neutral pins are moulded insulating plastic pins to allow positive location in the socket.
Connectors on the front of the plug are available for connection via ground cords to the various elements of the EPA. Thus each element is held at a common potential.

4. Wrist Strap
Wrist straps are the most common personnel grounding device and are used to link people to ground. They are required if the operator is sitting. A wrist strap is made up of two components:

  • a wrist band that is worn comfortably around your wrist and
  • a coiled cord that connects the band to Ground (in our example an Earth Bonding Point (EBP) Bar).

5. Earth Bonding Point Bar
Note: instead of connecting your wrist strap to an Earth Bonding Point (EBP) bar, you can also connect it to the EBP plug described in #3. EBP bars fulfil the same function as EBP. However, they have been designed to be installed underneath bench tops where they are easily accessible to operators and where they are unlikely to be knocked and damaged or hinder the operator. The earthing cord of the bar needs to be connected to a suitable earth.

Where sitting personnel will be grounded via a wrist strap, this method is not feasible for operators moving around in an ESD Protected Area. In those situations, a flooring / footwear system is required.

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

7. Floor Mat
Floor matting is an essential component in the flooring / footwear system when grounding moving or standing personnel. The path to ground from operators via heel grounders to ground is maintained by using dissipative or conductive flooring.
Floor mats don’t just ground personnel; they are also used to ground ESD control items (e.g. mobile carts or workstations).

8. Floor Mat Grounding Cord
Just like working surface matting, floor matting needs to be connected to ground. This ensures that any charges on the operator are dissipated through their heel grounders and the floor matting to ground. A floor mat grounding cord is used to link the floor mat to ground (in our example an EBP bar).
Alternatively, matting can be earthed via a strip of copper foil.

Installing an ESD Workstation
Below is a step-by-step guide as to who you can create an ESD workstation at your existing workbench:

1.  Working Surface Mat Lay the working surface mat flat on the workbench with the stud(s) facing upwards.
2.  Working Surface Mat Grounding Cord Connect the working surface mat grounding cord to the working surface mat.
3.  EBP Plug Plug the earth bonding point plug into the appropriate socket at the wall. Note: if you are located outside the UK, there are country-specific bonding points available.
4.  Working Surface Mat Grounding Cord Grounding Connect the other end of the working surface mat grounding cord to the earth bonding point plug
5.  Wristband Place the wristband on the wrist.
6.  Coiled Cord Connect the coiled cord to the wristband.
7.  EBP Bar Attach the earth bonding point bar to the bench. Remember that it needs to be connected to a suitable earth.
8.  Coiled Cord Grounding Connect the other end of the coiled cord to the earth bonding point bar.

If your operators are standing or mobile and grounding via a wrist strap is not feasible, follow these steps:

1. Follow steps #1 to #4 above.
2.  Floor Mat Lay the floor mat flat on the floor with the stud(s) facing upwards.
3.  Floor Mat Grounding Cord Connect the floor mat grounding cord to the floor mat.
4.  EBP Bar Attach the earth bonding point bar to the bench. Remember that it needs to be connected to a suitable earth.
5.  Floor Mat Grounding Cord Connect the other end of the floor mat grounding cord to the earth bonding point bar.
6.  Foot Grounders Place the foot grounders on the feet.

Conclusion
To sum-up, in an EPA you:

  • ground all conductors (including people),
  • remove all insulators (or substituting with ESD protective versions) or
  • neutralise process essential insulators with an ioniser.

With a few simple steps, you can convert your existing workstation into an ESD workstation. You will need:

  • Working Surface Mat
  • Working Surface Mat Grounding Cord
  • Earth Bonding Point Plug
  • Wrist Strap
  • Earth Bonding Point Bar

Optional:

  • Foot Grounders
  • Floor Mat
  • Floor Mat Grounding Cord

 

How to measure the effectiveness of your ESD Control Programme

Introduction
It is now well established that electronic devices and systems can be damaged by exposure to high electric fields as well as by direct electrostatic discharges. While good circuit layout and on-board protection may reduce the risk of damage by such events, the only safe action at present is to ensure that devices are not exposed to levels of static electricity above the critical threshold.
This can only be achieved by introducing a static control programme which usually involves setting up an ESD Protected Area (EPA) in which personnel are correctly grounded and all materials e. g. flooring, bench tops etc. meet the of the ESD Standard. However, setting up an EPA does not of itself guarantee a low static environment. Production procedures may change, new materials may be introduced, the performance of older materials may degrade and so on.
To ensure the effectiveness of any static control programme it is important that regular measurements are carried out:

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

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

1. Determining the sensitivity of ESDs
The bottom line is: you need to know what you’re dealing with before you can create an action plan. Only once you know the sensitivity of the items you are handling, can you work towards ensuring you’re not exceeding those levels.
Part of every ESD control plan is to identify items in your company that are sensitive to ESD. At the same time, you need to recognize the level of their sensitivity. As explained by the ESD Association, how susceptible to ESD a product is depends on the item’s ability to either:

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

For further information, check out this post.

2. Measurements to prove the effectiveness of an ESD Control Programme
Measuring electrostatic quantities poses rather special problems because electrostatic systems are generally characterised by high resistances and small amounts of electrical charge; the latter being true despite the dramatic effects often associated with static. Consequently, conventional electronic instrumentation cannot normally be used.

Electrical Field
Wherever electrostatic charges accumulate, they can be detected by the presence of an associated electric field. The magnitude of this field is determined by many factors, e. g. the magnitude and distribution of the charge, the geometry and location of grounded surfaces and also the medium in which the charge is located.
The current general view of experts is that the main source of ESD risk may occur where ESDS can reach high induced voltage due to external fields from the clothing, and subsequently experience a field induced CDM type discharge.” [CLC TR 61340-5-2 User guide Garments clause 4.7.7.1 Introductory remarks]

50597_Use2Using a Digital Static Field Meter to test static fields

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

A field meter can be used to:

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

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

CTM048-21_Use2Using the SCS EM Eye ESD Event Meter to detect ESD Events

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

3. Checking materials in your EPA
When talking about material properties, the measurement you will most frequently come across is “Surface Resistance”. It expresses the ability of a material to conduct electricity. It is therefore related to current and voltage. In fact, the surface resistance of a material is the ratio of the voltage and current that’s flowing between two pre-defined electrodes.
It is important to remember that the surface resistance of a material is dependent on the electrodes used (shape as well as distance). If your company implements an ESD control programme compliant to the ESD Standard EN 61340-5-1, it is therefore vital to carry out surface resistance measurements as described in the Standard itself. For more information on the definition of resistance measurements used in ESD control, check out this post.
A company’s compliance verification plan should include periodic checks of surfaces measuring:

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

222643UseMeasuring Surface Resistance of worksurface matting using a Digital Surface Resistance Meter Kit

Surface resistance testers can be used to perform these tests in accordance with EN 61340-5-1 and its test method IEC 61340-2-3; if these measurements are within acceptable ranges, the surface and its connections are good. For more information on checking your ESD control products, catch-up with this and this post. This 2-part series goes into depth as to what products you should be checking in your EPA and how they should be checked.

Conclusion
Measurements should form an integral part of any ESD control programme. High quality instruments are available commercially for measuring all the parameters necessary for quantifying the extent of a static problem. We hope the list above has provided an introduction to the techniques most commonly used.

Managing your ESD Control Programme

It’s Thursday and time for a new blog post! Although, today’s post is a little different…

A few years ago, a great article was published on the Circuits Assembly website. The article was written by the ESD Association and is titled Managing Your ESD Program.
The article discusses the challenges manufactures face in designing and maintaining an ESD control programme for their operations. The article goes on to breakdown managing an ESD programme in the following areas:

  • Identify and establish ESD teams
  • Identify your losses
  • Identify ESD sensitive items
  • Evaluate your facility and processes
  • Establish and implement procedures
  • Train personnel
  • Evaluate, adjust and provide feedback

We wanted to share the article with you because it contains loads of information that we think you will find useful!

Here is a link to the article – happy reading!

5 (additional) common mistakes in ESD Control & how to avoid them

A little while ago we published a post listing some of the most common issues we see when visiting EPAs and how to fix them. We had a lot of positive feedback from this post so thought we’d create a follow-up post with another 5 mistakes that are creeping up on a regular basis.

Introduction
You may remember how we talked in the previous post about companies wasting a lot of money by misusing their ESD products? No? Catch-up here.
The bottom line is: the job doesn’t end with purchasing ESD control items. Operators need to be trained on how to use their ESD products and ESD products need to be checked on a regular basis. If this doesn’t happen, you might as well throw the money you invested in your ESD Control Programme out the window…
Remember: ElectroStatic Discharge (ESD) is silent, quick and potentially lethal to electronic parts. When electronic parts are not properly handled during manufacturing, assembly, storage or shipping, damage from ESD can reach into the millions of dollars each year.

5 (additional) common Mistakes in ESD Control

1. Using insulators at the workstation
Non-essential insulators at an ESD protective workstation might include regular packaging, document holders, binders and tape. In addition, workers like to personalise their work areas so they might have high charging plastics in the form of radios, picture frames, purses, drinking cups etc. on the bench.
None of these are essential to get your job done and all of them pose a risk to your sensitive components.

 Check Insulators can be controlled by doing the following within an EPA:
• 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.
 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]

If you want to learn more about controlling insulators, have a look at this post.

2. Using open shielding bags or containers
So, you may have heard of a Faraday Cage but do you know what role it plays in ESD Protection? We see a lot of companies that have a state-of-the-art EPA but when it comes to shipping sensitive components, everything falls apart. They may use component shippers but without a lid or they use shielding bags that are stapled together. None of these practises will do your sensitive components any good.

 Check In ESD Protection, the Faraday Cage effect causes charges to be conducted around the outside surface of the conductor. Since similar charges repel, charges will rest on the exterior and ESD sensitive items on the inside will be ‘safe’. However, to complete the enclosure, make sure to place lids on boxes/containers and seal shielding bags using a label or tape.
This is the only way to ensure ESD sensitive devises placed inside the shielding bag are protected.
 Standard Transportation of sensitive products outside of an EPA shall require packaging that provides both:
– dissipative or conductive materials for intimate contact;
– a structure that provides electrostatic discharge shielding.”
[EN 61340-5-3 Clause 5.3 Outside an EPA]

3. Ungrounded ESD Work Surface
ESD mats and laminate work surfaces cost a lot more than their regular insulative counterparts. The ESD dissipative characteristics are added so when charged conductors (conductive or dissipative) items are placed on the surface, a controlled discharge occurs and electrostatic charges are removed go ground. However, this only occurs if the ESD work surface is actually connected to ground.

 Check Best industry practice is that ESD ground connections should be firm fitting connecting devices such as metallic crimps, snaps and banana plugs that shall be connected to designated ground points. The use of alligator clips is not recommended. The companies’ Compliance Verification Plan should include periodic checks of worksurfaces measuring Resistance-to-Ground from the work surface centre or the most worn area to ground.
Many companies also use a daily checklist, which requires the operator to verify that ground cords are firmly connected.
 Standard Periodic testing of work surfaces is necessary to ensure that they continue to meet specifications. Resistance to ground measurements are typically used to verify that the path to ground is intact. In cases where the resistance go ground measurements exceeds the established resistance limits, the following steps can be taken to identify the cause of the high resistance readings:

  • Verify visually that the work surface is connected to the ground reference.
  • Clean the work surface. Sometimes a dirty surface can cause the resistance to exceed acceptable limits. Once the surface has been cleaned (note: clean the bottom of the resistance measuring electrode as well) repeat the resistance to ground measurement. If the second measurement is within specification this might lead to a further investigation concerning the cleaning practices used by the organization.
  • Disconnect the grounding wire and measure the resistance from the top surface of the work surface to the work surface groundable point. This measurement shall show whether or not the work surface is functioning as designed and it will verify that there is a good connection between the groudable point and the work surface.
  • Using an ohmmeter, measure the resistance of the wire used to ground the work surface. The measurement is made from the point where the wire is connected to the work surface’s groundable point to the ground reference.

The frequency of periodic testing is normally specified in corporate operating procedures. However, a common guide would be to conduct these measurements at least quarterly.
[CLC TR 61340-5-2 User guide Work surface clause 4.7.1.4.3 Periodic tests]

The most important functional consideration for work surfaces is the resistance from the top of the surface to the groundable point. This establishes the resistance of the primary path to ground for items placed on the surface. IEC 61340-5-1 has set a resistance to ground range for work surfaces of less than 1,0 x 109.
[CLC TR 61340-5-2 User guide Work surface clause 4.7.1.2.5 Electrical considerations]

For more information how to ground and look after your ESD work surface, have a look at this post.

4. Dissipative ESD Floor is measuring high
Electrostatic dissipative materials have a resistance to ground of greater than 1 x 105 ohm but less than 1 x 1012 ohm. EN 61340-5-1 requires the Resistance-to-Ground of ESD flooring to be less than 1 x 109 ohms. So, if you install new dissipative flooring and it measures 1 x 106 ohms, you’re all good. The problem with flooring is that when it gets dirty (and trust us, it will get dirty!), the resistance increases which potentially results in out-of-spec flooring.

 Check A regular maintenance schedule needs to be followed and floor resistance measurements needs to be taken as outlined in the companies’ Compliance Verification Plan. A 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.
 Standard For standing operations, personnel can be grounded via a wrist strap system or by a footwear-flooring system. When a footwear-flooring system is used, personnel shall wear ESD footwear on both feet and the two following conditions shall be met:

  • the total resistance of the system (from the person, through the footwear and
    flooring to ground) shall be less than 1,0 × 109 ;
  • the maximum body voltage generation shall be less than 100 V.

[IEC 61340-5-1 Clause 5.3.3 Personnel grounding]

5. Poorly fitting Wrist Straps
As discharges from people handling sensitive items cause significant ESD damage, the wrist strap is considered the first line of ESD control. However, there are number of issues we see repeatedly when it comes to wrist straps:

  • Operators feel restricted by the wrist strap and stop wearing it altogether.
  • Operators leave their workstation and forget to re-connect their wrist strap when returning to their workstation.
  • Operators don’t pay attention when fitting their wrist straps resulting in an incorrect fit.
  • Operators use ripped wristbands or patched-up coiled cords.

Remember: if your wrist strap is worn incorrectly (or not at all), charges on your body will not dissipate to ground resulting in dangerous ESD exposure to sensitive ESD components.

 Check The wrist strap should be effectively tested while worn on the person and records should be kept. Wiggling the resistor strain relief portion of the coiled cord during the test will help identify failures sooner. Analysis and corrective action should take place when a wrist strap tester indicates a failure.

An even better solution is the use of continuous monitors that will alarm if the person is not properly grounded. Some monitors will beep if a discharge occurs or when a certain voltage level of electrostatic charge is on the person.

 Standard “Because wrist straps do not last forever, they should be tested periodically. A good testing program not only tests the wrist strap itself, but also indicates the quality of the skin contact when performing a system test. Wrist strap bands that are soiled, incorrectly sized or improperly worn will show resistance higher than acceptable.”
[CLC TR 61340-5-2 User guide Wrist strap clause 4.7.2.4 Wrist strap testing]Proper testing of the wrist strap includes the resistance of the groundable point on the end of the cord, the cord itself, the current-limiting resistor, the cord-to-band snap connector, the resistance of the interface of the cuff, the cuff/wrist interface and the resistance of the person between the wrist and the hand that contacts the test electrode. The maximum acceptable resistance for wrist strap grounding is less than 3,5 x107 .
[CLC TR 61340-5-2 User guide Wrist strap clause 4.7.2.4.2 Additional user wrist strap testing]

If you want to learn more about wrist straps, how to use and test them, we recommend having a look at this post.

Do you have anything to add? Let us know in the comments.

How do Foot Grounders work?

A question we repeatedly get from customers is in regards to foot grounders. Wrist straps are generally straight forward and people understand what they do and how they work. But when it comes to foot grounders, there is still a lot of confusion out there – something we want to address in today’s post. So, let’s get started.

Purpose of Foot Grounders
A flooring / footwear system is an alternative for grounding standing or mobile workers. Where sitting personnel will be grounded via a wrist strap, this method is not feasible for operators moving around in an ESD Protected Area.
ESD foot grounders are designed to reliably contact grounded ESD flooring and provide a continuous path-to-ground by removing electrostatic charges from personnel. They are easy to install and can be used on standard shoes by placing the grounding tab in the shoe under the foot.

Structure of Foot Grounders
Foot grounders discharge static from a person to ground by connecting the person to a grounded walking surface. A conductive ribbon placed inside the wearer’s shoe or sock makes electrical contact with the skin through perspiration. The ribbon is joined to a resistor which limits current should accidental exposure to electricity occur. The other end of the resistor is joined to a conductive sole. This sole contacts a grounded ESD floor mat or ESD flooring system.

Structure of a Foot GrounderStructure of a Foot Grounder

Foot grounders must be worn on both feet to maintain the integrity of the body-to-ground connection Wearing a foot grounder on each foot ensures contact with ground via the ESD floor even when one foot is lifted off the floor. This will more reliably remove static charges generated by human movement and more reliably protect ESDS.
EN 61340-5-1 recommends a minimum of 1 Megohm resistance to ground (Rg) in order to limit inadvertent electrical current exposure to a maximum of 0.00025 amperes.

For standing operations, personnel can be grounded via a wrist strap system or by a footwear-flooring system. When a footwear-flooring system is used, personnel shall wear ESD footwear on both feet and the two following conditions shall be met:
• the total resistance of the system (from the person, through the footwear and flooring to ground) shall be less than
1,0 × 109 Ω;
• the maximum body voltage generation shall be less than 100 V.
[IEC 61340-5-1 Clause 5.3.3 Personnel grounding]

Installation of Foot Grounders
1. Foot Grounders with Hook-and-Loop Straps
These heel grounders are designed for use on standard shoes and can be easily adjusted to fit the individual wearer.

  • Place the foot grounder on the shoe so that the lining is making contact with the shoe.
  • Insert the contact strip inside of the shoe and under the foot. Make sure that a solid contact is made between the sock and body. Cut contact strip to desired length.
  • Fasten hook and loop straps together, securing foot grounder firmly on shoe.
  • Test each foot grounder to confirm proper installation.

Installation of Foot Grounders with Hook-and-Loop StrapsInstallation of Foot Grounders with Hook-and-Loop Straps – more information

2. Foot Grounders with elastic Straps and Clip Fasteners
These heel grounders are equipped with a clip fasteners, a quick release fastening system.

  • Insert the contact strip inside of the shoe and under the foot. Make sure that a solid contact is made between the sock and body. Cut contact strip to desired length.
  • Fit the heel cup snugly to shoe and connect the Snap-Loc fastener together. Adjust elastic strap for comfortable fit. Tuck excess elastic strap behind itself.
  • Test each heel grounder to confirm proper installation.

Installation of Foot Grounders with elastic Straps and Clip FastenersInstallation of Foot Grounders with elastic Straps and Clip Fasteners – more information

3. D-Ring Toe Grounders
Toe grounders with the elastic D-ring fastening system are designed for use on heeled shoes.

  • Insert the grounding tab inside of the shoe and under the foot. Make sure that a solid contact is made between the sock and body. Cut grounding tab to desired length.
  • Place rubber toe material under toe area of shoe sole. Pull hook-and-loop strap over top of shoe and cinch down until snug. Install so that the lined surface is making contact with the shoe.
  • Pull elastic strap around the back of the heel. Adjust D-ring plastic loop for a comfortable fit.
  • Test each toe grounder to confirm proper installation

D-RingInstallation of D-Ring Toe Grounders – more information

4. Disposable Foot Grounders
Disposable foot grounders are designed for applications where the use of permanent foot grounders is not economical or practical. They are constructed so that it may be used once and then discarded.

  • Remove shoe. Wipe any excess dirt from underside of heel. Remove release paper from heel grounder.
  • Apply the adhesive end to underside of heel of the shoe. Wrap the tape snugly around the outside of the shoe.
  • Insert the non-adhesive end of the heel grounder inside the shoe so that the black dot is well over the middle of the heel area facing upwards.
  • Put the shoe on.
  • Test each foot grounder to confirm proper installation.

NOTE: This product is not recommended for use on equipment with operating voltage

DisposableHeelGroundersInstallation of Disposable Foot Grounders – more information

Testing of Foot Grounders
Proper testing of your foot grounders involve testing the individual foot grounder, the contact strip and the interface between the contact strip and the wearer’s perspiration layer.
There are a number of personnel grounding testers on the market designed to properly test foot grounders. For more detailed information on how personnel grounding testers work and how to operate them, have a look at this post.
If you obtain a fail reading from the tester you should stop working and test the foot ground and contact strip individually to find out which item has failed. Replace the foot grounder or replace the bad component if possible. Retest the system before beginning work.

Personnel Grounding ChecklistEnsure your Foot Grounders are working before handling ESDs

Cleaning of Foot Grounders
Foot grounders are to ground static charges, while dirt generally provides an insulative layer adversely effecting reliability. For proper operation, the foot grounder and its conductive strip must be kept clean.
The rubber portion of the foot grounder should be cleaned using an ESD cleaner, e.g Desco Europe’s Reztore™ Antistatic Surface & Mat Cleaner. Ensure that your ESD cleaner is silicone free. This is critical as silicone is an insulator. An alternative would be to clean using isopropyl alcohol. ESD cleaners should not be used to clean the nylon polyester grounding tab. Foot Grounders can be safely hand or machine washed on gentle cycle. Mild detergents, such as Woolite® or a liquid dish washing product and warm water are recommended. However, care must be taken to ensure that these detergents are silicone free.

 Conclusion

  • It is recommended that ESD foot grounders are worn on both feet in order to ensure that a continuous path to ground is maintained at all times (even when lifting one foot).
  • Contact strips should be tucked inside the shoe with as much contact area as possible to the bottom of the stockinged foot. ESD foot grounders rely upon the perspiration layer inside of the shoe to make contact through the stocking.
  • Foot grounders must be used with an ESD protected floor (such as correctly grounded ESD floor finish, carpet tiles or floor mats) to provide a continuous electrical path from the user directly to the ESD ground. 
  • A current limiting of one or two megohm resistor in series with the contact strip is recommended but not required.
  • ESD foot grounders should be tested independently at least daily while being worn.

 

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.

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