Category Archives: Resources

Internet of Things (IoT) in ESD Control

In today’s connected world, we are surrounded by home monitoring networks, fitness trackers and other smart systems. They all use an IoT platform to keep us up to-date with the current temperature in our house or the number of steps we have taken in a day. Is there a way to use this incredibly smart technology to improve ESD Control? Let’s take a look!

1. Internet of Things (IoT)
The Internet of Things (IoT):

  • Connects “things” in the physical world to the internet using sensors.
  • Collects data for these “things” via sensors.
  • Analyses the collected data and provides a deeper insight into the “things”.

This is a very broad and vague definition but then IoT is used everywhere today – from medical devices to vehicles, homes etc.
The Internet of Things (IoT) is the network of physical devices, vehicles, home appliances, and other items embedded with electronics, software, sensors, actuators, and connectivity which enables these things to connect and exchange data, creating opportunities for more direct integration of the physical world into computer-based systems, resulting in efficiency improvements, economic benefits, and reduced human exertions.” [Source]

The history of IoTThe history of IoT [Source]

The Industrial Internet of Things (IIoT) applies specifically to manufacturing and industrial processes.
It has slightly different requirements compared to consumer IoT products but the principle is the same: smart machines (incorporating various sensors) accurately and consistently capture and analyse real-time data allowing companies to pick-up problems as soon as (or even before) they appear.

2. Industry 4.0
IoT helped push the 3rd industrial revolution (machine automation) one step further. “Cyber Physical Systems (CPS) dominate the manufacturing floor, linking real objects with information processing, and virtual objects via the internet. The goal is to converge Operational Technology (OT) and Information Technology (IT).” [Source]
The 4th industrial revolution is also referred to as “Industry 4.0”. “At the very core Industry 4.0 includes the (partial) transfer of autonomy and autonomous decisions to cyber-physical systems and machines, leveraging information systems”. [Source]

Industry-4.0-shutterstock_524444866_pk_cutIndustry 4.0 as fourth industrial revolution [Source]

So, how can companies use the power of IoT and create accessible, real-time feedback on the status of their ESD Control Protected Area (EPA) and ESD control items?

3. IoT in ESD Control
ESD damages can be extremely costly – especially when it comes to latent defects that are not detected until the damaged component is installed in a customer’s system. Conventional ESD control programmes incorporate periodic verification checks of ESD control products to detect any issues that could result in ESD events and ESD damage. The problem is that ESD control products (and the EPA as a whole) are not constantly monitored.
Take an ioniser for example: if a company uses ionisation to handle process-essential insulators, the ionisers need to be fully reliable at all times. If an ioniser passes one check but is found to be out of balance at the next, the company faces a huge problem: nobody knows WHEN exactly the ioniser failed or if contributed to a charged insulator potentially causing ESD damage.
The Industry 4.0 IoT platform will be a game changer when it comes to creating a reliable and dependable ESD control programme. Sensors collecting vital ESD information like field voltage, Electromagnetic Interference (EMI), temperature, humidity etc. in an EPA will help detect potential threats in real-time allowing supervisors to take action even before an ESD threat occurs. Here is a (by no means exhaustive) list of advantages, IoT can bring to ESD Control:

Collecting Data
The day in an EPA can be busy. Taking the time to capture and record measurements of ionisers, wrist straps, work surfaces, automated processes etc. can be disruptive and is prone to errors. IoT allows data to be collected automatically without any input from users. This helps to increase the accuracy of data and allows operators and supervisors more time focusing on their actual jobs.

SmartLogwithUnitSmartLog Pro®: the SMART Access Control System – more information

Analysing Data
Supervisors have all the essential data in one place right in front of them and are able to make informed decisions; they can provide feedback and give suggestions in case of an ESD emergency. IoT allows to pinpoint areas of concern and prevent ESD events.

24/7 Monitoring
IoT continuously monitors processes and provides a real-time picture of them – no manual checks required. If a potential threat is detected, warnings will show-up immediately. There is no need to worry about potentially damaging sensitive devices because the next scheduled check of ionisers, wrist straps etc. has not been completed yet.

Cutting Costs
The number one reason for adapting an ESD control programme is to reduce costs by:

  • Enhancing quality and productivity,
  • Increasing reliability,
  • Improving customer satisfaction,
  • Lowering repair, rework and field service costs and
  • Reducing material, labour and overhead costs.

IoT pushes all of the above even further

  • Reduced workload for operators: Data is collected remotely without any input from users. Operators are not disrupted in their day-to-day activities.
  • Reduced workload for supervisors: Supervisors don’t have to collect and analyse data from personnel testers, field meters, monitors etc. The system does it for them and will highlight any issues.
  • Further increases in productivity and cost reductions: An ESD Programme can be managed better and with fewer resources.

SMT-Line-LayoutStatic Management Program (SMP): the next generation of ESD Process Control – more information

4. Conclusion
IoT will no doubt change ESD control and the way EPAs are monitored. Quantifiable data allows companies to see trends, become more proactive and improve the efficiency of their ESD process control system. IoT will support organisations’ efforts to make more dependable products, improve yields, increase automation and provide a measurable return on investment. Not only will this benefit users and supervisors, but the company as a whole.

 

 

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Resources:
Bill McCabe: Quick History of the Internet of Things..
Margaret Rouce: industrial internet of things (IIoT)
Michelle Lam: ESD Control in the World of IoT
Ian Wright: What Is Industry 4.0, Anyway?
Pascal Kriesche: Humans vs. machines – who will manage the factory of the future?
Industry 4.0: the fourth industrial revolution – guide to Industrie 4.0

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Increase your Return on Investment with a successful ESD Control Programme

It is now well-known that electronic devices and systems can be damaged by exposure to high electric fields as well as by direct electrostatic discharges. Many companies implement an ElectroStatic Discharge (ESD) Control Programme with the aim of improving their operations. Effective ESD control can be a key to improving:

  • Productivity,
  • Quality and
  • Customer satisfaction.

A successful ESD Control Programme can also save you money which we want to focus on in today’s post.

Types of ESD Damage
There are two types of ESD damage:
1) catastrophic failure and
2) latent defects.

While catastrophic failures cause an ESD sensitive item to be damaged permanently, latent defects only partially degrade an ESD sensitive item that is exposed to an ESD event. It may continue to perform its intended function and may not be detected by normal inspection. However, intermittent or permanent failures may occur later. Even if an ESD sensitive component has quite a high withstand voltage and no catastrophic failure has been caused, latent defects may still make your life miserable.

Types of ESD DamageTypes of ESD Damage

A catastrophic failure of an electronic component can be the least costly type of ESD damage as it may be detected and repaired at an early manufacturing stage.
Latent damage caused by ESD is potentially costlier since damage occurs that cannot be felt, seen or detected through normal inspection procedures. Latent defects can be very expensive as the product passes all inspection steps and the product is completed and shipped. Latent defects can severely impact the reputation of a company’s product. Intermittent failures after shipping a product can be frustrating, particularly when the customer returns a product, reporting a problem which the factory again fails to detect. It consequently passes inspection and the product is returned to the customer with the problem unresolved.

Implementing an ESD Control Programme
A prerequisite of ESD control is the accurate and consistent identification of ESD susceptible items. Some companies assume that all electronic components are ESD susceptible. However, others write their ESD control plan based on the device and item susceptibility or withstand voltage of the most sensitive components used in the facility. A general rule is to treat any device or component that is received in ESD packaging as an ESD susceptible item.

The Organization shall prepare an ESD Control Program Plan that addresses each of the requirements of the Program. Those requirements include:

  • training
  • compliance verification
  • grounding / equipotential bonding systems
  • personnel grounding
  • EPA requirements
  • packaging systems
  • marking.” [EN 61340-5-1 clause 5.2.1 ESD control program plan]

Each company has different processes, and so will require a different blend of ESD prevention measures for an optimum ESD control program. It is vital that these measures are selected, based on technical necessity and carefully documented in an ESD control program plan, so that all concerned can be sure of the program requirements.” [EN 61340-5-1 Introduction]

Increasing Return on Investment with an ESD Control Programme
When it comes to reducing quality failures due to ESD, a thorough ESD Control Programme that is followed throughout the receiving, manufacturing, storage and shipping departments, is essential.

Below are two case studies that show what return on investment (ROI) can be achieved from implementing an ESD Control Programme.

1. AT&T
Former ESD Manager Terry O’Malley collected data for their Albuquerque and St. Louis facilities. The graph clearly displays a reduction in return and repair costs of more than 50% after an ESD Control Programme was implemented.

AT&TROI for AT&T (Source)

2.Lucent Technologies
The below overview shows the relationship between the relative cost benefits and compliance to Lucent’s ESD Control Programme. You can expect a typical ROI of 1,000% for a strict ESD Control Pogramme used by Lucent.

Lucent“Cost Benefit and ESD Control Programme Compliance” Relationship for Lucent (Source)

Organisations like AT&T, Motorola, Agilent Technologies and IBM were able to demonstrate the benefits of implementing an ESD Control Programme. In each of these companies, the introduced programme resulted in a substantial return on their original investment. The only way to accurately calculate the return on investment (ROI) from an ESD Control Programme, is to track the return, repair and scrap cost data before and after the introduction.

Even if your company is unable to track detailed data, it is still worth investing in an ESD Control Programme. “A properly implemented ESD program can have an ROI exceeding five to one within six months.” (Source)

Conclusion
As electronic technology advances, electronic circuitry gets progressively smaller. As the size of components is reduced, so is the microscopic spacing of insulators and circuits within them, increasing their sensitivity to ESD. Therefore, the need for proper ESD protection increases every day – not just to protect sensitive devices but also to allow companies to survive, be profitable and grow.
Independent consultants and corporate studies have found that ESD losses can be as high as 10% of annual revenues with an estimated average negative impact of 6.5% of revenues. Based on 1997-2001 production data, the international electronics industry is losing in excess of $84 billion every year. Other than increasing sales, ESD control is the single most profitable opportunity for our industry in today’s economic conditions.” (Source)

A proper ESD control programme will increase profitability of a company by:

  • Enhancing quality and productivity,
  • Increasing reliability,
  • Improving customer satisfaction,
  • Lowering repair, rework and field service costs and
  • Reducing material, labour and overhead costs

 

 

 

 

References:
Michael T. Brandt: What does ESD really cost?
Ryne C. Allen: ESD Control and ROI

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:

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.

Why Wave Distortion Technology is superior

We talked in the past about the benefits of continuous monitors and also introduced the different types (single-wire vs. dual-wire) to you. The focus of today’s post is the technology behind continuous monitors – how they work and how they compare to each other. So, let’s jump right in.

Introduction to Continuous Monitors
While wrist straps are the first and best line of defence against ElectroStatic Discharge (ESD), they must be tested to ensure that they are installed and working properly. On-demand or “touch” testers have become the most common testing method; they complete a circuit when the wrist strap wearer touches a contact plate.
One drawback with on-demand type testers is that they require a dedicated action by the wearer of the wrist strap to make the test. Also, knowing that the wrist strap has failed after the fact may possibly have exposed a highly sensitive or valuable assembly to risk. Continuous monitors eliminate the possibility of a component being exposed to ESD during the time that the wrist strap was not working properly.
If your company manufactures products containing ESD sensitive items, you need to ask yourself “how important is the reliability of our products”? Sooner or later a wrist strap is going to fail. If your products are of such high value that you need to be 100% sure your operators are grounded at all times, then you should consider a continuous monitoring system.

Technologies used for Continuous Monitors
There are three types of wrist strap monitoring on the market today:
1. Basic Capacitance / Impedance Monitoring,
2. Resistance Monitoring and
3. Wave Distortion Capacitance / Impedance Monitoring.

So, let’s look at all 3 types in a bit more detail:

1. Basic Capacitance / Impedance Monitoring
This single-wire technology makes use of the fact that a person can be thought of as one plate of a capacitor with the other plate being ground. The ground and the person are both conductors and they are separated (sometimes) by an insulator (shoes, mats, carpet, etc.) thus forming a capacitor. The combined resistance of the wrist strap and person forms a resistor so that the total circuit is a simple RC circuit.
A tiny AC current applied to this circuit will cause a displacement current in the capacitance to flow to ground providing a simple way to make sure the person (capacitor) resistor (wrist strap) and coil cord are all hooked up. Any break in this circuit results in a higher impedance that can be used to trigger an alarm.

AC capacitance monitors have a few drawbacks:

  1. They do not provide a reliable way to know if the total resistance of the circuit is too low, i.e., if the current limiting safety resistor is shorted.
  2. Simple AC capacitance monitors can be tricked into thinking the person is wearing the wrist strap when they are not. For example, laying a wrist strap and cord on a grounded mat will increase the shunt capacitance, which allows the monitor to show a good circuit even with the person out of the circuit. Forming the cord into a tight bundle or stretching it can also provide false readings.
  3. Since the capacitance and therefore the impedance of the circuit will also vary with such things as the persons size, clothing, shoe soles, conductance of the floor, chair, table mat, the person’s positions (standing or sitting), etc., these monitors often have to be “tuned” to a specific installation and operator.

2. Resistance Monitoring
Dual-wire resistance monitors were developed to overcome some of the problems with the AC capacitance types. Here again the concept is simple. By providing a second path to ground (without relying on the capacitor above) we can apply a tiny DC current. It is then simple to measure the DC resistance of the circuit and alarm if that resistance goes too high (open circuit) or too low (the safety resistor is shorted). Thus, a two-wire monitor provides the same reliability as a touch tester and a simple, easy to understand measurement. The shortcomings with the AC capacitance monitor are eliminated.

Two-wire monitors require two wires to work. This means that the wearer must wear a dual wire two-conductor wrist strap / coil cord which are more expensive than standard single wire wrist straps.
There have been some reports that a constant DC voltage applied to the wristband causes skin irritations.

3. Wave Distortion Capacitance / Impedance Monitoring
Wave Distortion Technology continuous monitors feature:

  • low test voltage,
  • a low monitor range for 1 megohm of resistance in the operator’s wrist strap and
  • instantaneous detection of an intermittent or failure of the path-to-ground of the operator or work surface that other monitors / technologies miss.

Continuous monitors using wave distortion technology apply a continuous test voltage (1.2 volts peak- “Wave Distortion” or vector impedance works by applying a continuous test voltage of 1.2 volts peak-to-peak at 1 to 2 microamperes (0.000002 amperes) to the wrist strap that is connected to the continuous or constant monitor. The test voltage creates a sine wave that the monitor circuit compares to established patterns. By monitoring the “distortions”, or shape of the sine wave, Wave Distortion Technology determines if the monitored circuit is complete – the operator is in the circuit and the total equivalent DC resistance is within specifications. Wave Distortion Technology produces a very fast alarm time (<50 milliseconds) and minimal false alarms.

Comparing Continuous Monitor Technologies
We’ll compare the three different technologies using the following parameters:
1. Safety Resistor Monitoring
2. Test Voltage
3. Banana Jack & 10mm Socket Monitoring
4. Response Time
5. In-Use Verification

1. Safety Resistor Monitoring
The purpose of the 1 megohm resistor found in series with wrist straps is solely to provide safety to the human body by limiting the amount of current that could be conducted through the body. The 1 megohm resistor is designed to limit the current to 250 microamps at 250 Volts rms AC. This is just below the perception level (and a bit before the nervous system goes awry) of most people. “Wrist straps have a current limiting resistor moulded into the ground cord head on the end that connects to the band. The resistor most commonly used is a 1 x 106W, 1/4 watt with a working voltage rating of 250 V.” [IEC TR 61340-5-2 User Guide, Clause 4.7.2.5 Current limiting]

Neutral Basic Capacitance / Impedance Monitoring
Happy Resistance Monitoring
Happy Wave Distortion Capacitance / Impedance Monitoring

2. Test Voltage
We’ve mentioned further above that some people have reported skin irritations when using resistance monitors which apply a constant DC voltage to the wristband. The problem is that the test voltages of resistance monitors is quite high (up to 16V). You have a similar issue with basic capacitance/impedance monitors (3.5V). Another thing to remember is that higher test voltages increase the risk of damage when handling ESD susceptible devices. Luckily for you, wave distortion monitors only use a test voltage of 1.2 – way below the other two technologies.

Neutral Basic Capacitance / Impedance Monitoring
Happy Resistance Monitoring
Happy Wave Distortion Capacitance / Impedance Monitoring

3. Banana Jack & 10mm Socket Monitoring
Coiled cords with banana jack and 10mm sockets are commonly used in the electronics industry. Unfortunately, these cannot be used with dual-wire resistance monitors. As mentioned further above, special dual-conductor wrist straps need to be purchased.

Happy Basic Capacitance / Impedance Monitoring
Sad Resistance Monitoring
Happy Wave Distortion Capacitance / Impedance Monitoring

4. Response Time
Detecting intermittent or complete failures in the path-to-ground of the operator or working surface is the job of a continuous monitor – but, it’s also important to look at how long it takes the monitor to report the issue. What’s the point of using a continuous monitor, if it takes the monitor 5 minutes to tell you there is an issue? All the sensitive devices you handled in the last 5 minutes may have been damaged. An instantaneous detection/alarm is therefore crucial. The slower the response time, the higher the potential impact on sensitive items. Response times for basic capacitance/impedance and resistance monitors is ~1s and ≤ 2s respectively. Wave distortion monitors on the other hand have a response time of <50ms.

Neutral Basic Capacitance / Impedance Monitoring
Neutral Resistance Monitoring
Happy Wave Distortion Capacitance / Impedance Monitoring

5. In-Use Verification
So, imagine this scenario: you received a new constant monitor, you found a nice new home for it, you install it and use it. 12 months down the line, it’s time to verify/calibrate the monitor. You have to remove the monitor from its cosy place, complete the calibration and put it back. What a pain, right? The good news is: the test limits of wave distortion monitors can be verified without removing them from the workstation. Sound like a dream, right?

Sad Basic Capacitance / Impedance Monitoring
Neutral Resistance Monitoring
Happy Wave Distortion Capacitance / Impedance Monitoring

We’ve created the below table for you to easier compare the different technologies:

Comparison of Continuous Monitors Technologies

As you can see, the latest Wave Distortion Technology provides the most reliable and stable confirmation of an operator’s continuous path-to-ground to ensure ESD sensitive product is protected at all times.
Shop our range of Wave Distortion Monitors here.

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