The Difference between ElectroStatic Charges & Electrostatic Discharges (ESD)

A question that comes up, again and again, is “Are ElectroStatic charges and ElectroStatic discharges different?” so we thought it’d be helpful for everyone to put together a blog post on the subject. So let’s get started:

ElectroStatic charges vs. ElectroStatic discharges

ElectroStatic charges and ElectroStatic discharges are different. All material can tribocharge (generate ElectroStatic charges). This is static electricity which is an electrical charge at rest. When an electrical charge is not at rest but discharges (i.e. ESD), problems can occur. All matter is constructed from atoms which have negatively charged electrons circling the atom’s nucleus which includes positively charged protons. The atom having an equal number of electrons and protons balances out having no charge.

Balanced AtomBalanced Atom with no Charge

Electrostatic charges are most commonly created by contact and separation; when two surfaces contact then separate, some atom electrons move from one surface to the other, causing an imbalance. One surface has a positive charge and one surface has a negative charge.

Charge Generation

The simple separation of two surfaces, as when tape is pulled off a roll, can cause the transfer of electrons between surfaces, generating an ElectroStatic charge.

  • 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

Charge Generation Unwinding a Roll of TapeCharge Generation Unwinding a Roll of Tape

The amount of static electricity generated varies and is affected by materials, friction, area of contact and the relative humidity of the environment. At lower relative humidity, charge generation will increase as the environment is drier. Common plastics generally create the greatest static charges.

Typical Electrostatic Voltages

Many common activities may generate charges on a person’s body that are potentially harmful to electronic components.

  • Walking across carpet: 1,500 to 35,000 volts
  • Walking over untreated vinyl floor: 250 to 12,500 volts
  • Vinyl envelop used for work instructions: 600 to 7,000 volts
  • Worker at bench: 700 to 6,000 volts
  • Picking up a common plastic bag from a bench: 1,200 to 20,000 volts

Generating Charges by walking across a Carpet
Generating Charges by walking across a Carpet

Electrostatic Discharge (ESD)

If two items are at the same electrostatic charge or at equipotential, no discharge will occur. However, if two items are at different levels of ElectroStatic charge, they will want to come into balance. If they are in close enough proximity, there can be a rapid, spontaneous transfer of electrostatic charge. This is called discharge, or ElectroStatic Discharge (ESD).

Examples in daily life:

  • Lightning Steel handle on the door close-up
  • Lightning, creating lots of heat and light
  • The occasional zap felt when reaching for a door knob
  • The occasional zap felt when sliding out of an automobile and touching the door handle

Electrostatic Discharge in Daily Life

In a normal environment like your home, there are innumerable ESD events occurring, most of which you do not see or feel. It takes a discharge of about 2,000 volts for a person to feel the “zap”. It requires a much larger ESD event to arc and be seen. While a discharge may be a nuisance in the home, ESD is the hidden enemy in a high-tech manufacturing environment. Modern electronic circuitry can be literally burned or melted from these miniature lightning bolts. Even less than 100 volts might damage a sensitive Class 0A component! ESD control is necessary to reduce and limit these ESD events. For more information on the damages ESD can cause, check out this post. For tips on how you can fight ESD in your production area, you should read this post.

6 Steps to defining ESD Protective Packaging Requirements for ESD Sensitive Items


If your company has an ESD Control Programme per EN 61340-5-1 in place, you need to define ESD protective packaging for ESD sensitive items (ESDs). But where do you start? Don’t panic – we’re here to help!

What is ESD Protective Packaging?

ESD Protective Packaging comprises all “items and materials that provide intimate protection for ESDS parts during all phases of handling, shipping and storage”. [EN 61340-5-2 User Guide clause 4.8.1 Introduction and purpose]
You don’t need to worry about secondary or exterior packaging unless it’s used for ESD protection purposes.

37150Example of ESD Protective Packaging – Protektive Pak Inplant Handlers

Why do you need ESD Protective Packaging?

The fundamentals of ESD control include grounding all conductors in the EPA. ESD packaging will have special material composition to lower the resistance so that when grounded, electrostatic charges will be removed to ground thus protecting your ESD sensitive devices inside.
An ESD protective packing system’s basic function is to make up the difference between the ESD sensitivity of the product and the level of threat that exists in the distribution environment. For example, if the product has a human body model sensitivity of 100 V and the people that will be handling the package are known to have a maximum of 1 000 V on their bodies, then a package shall be selected that will make up the difference between the product’s ESD sensitivity and the distribution environment.” [EN 61340-5-2 User Guide clause 4.8.3 Selecting/designing the right package]
Packaging is to be determined for all material movements inside and outside of the ESD Protected Area (EPA). Best practice is to define the required packaging or material handling item on the product’s bill of materials. Remember: the ESD packaging is just as important as a component part.
Customer contract packaging can take precedence, but otherwise “the organization shall define ESD protective packaging requirements for ESDS within the plan based on IEC 61340-5-3. Packaging, when required, shall be defined for all material movement within EPAs, between EPAs, between job sites, field service operations and to the customer.” [EN 61340-5-1 clause 5.3.5 Packaging]

Choosing your ESD Protective Packaging

A number of factors need to be taken into consideration when choosing your ESD protective packaging including “the ESD sensitivity of the product as well as the expected distribution environment hazards.” [EN 61340-5-2 User Guide clause 4.8.3 Selecting/designing the right package]

Protektive Pak Circuit Board Shippers with Pink or Black FoamExample of ESD Protective Packaging – Protektive Pak Circuit Board Shippers

The User Guide EN 61340-5-2 recommends the following steps to implement your ESD Protective Packaging:

1. Understand the product sensitivity
You can gather information about the ESD sensitivity of an item by either measuring it in-house, contacting the manufacturer of the product or by analysing published ESD sensitivity data.

2. Determine the distribution environment for the packaged product
Knowing the environment in which the product is shipped and how it will be handled is extremely important. Humidity and temperature are the main factors to consider when it comes to choosing the right type of packaging for your ESD sensitive items. If items are susceptible to moisture, barrier material should be chosen to prevent excessive humidity exposure. On the other hand, condensation may occur inside the packaging if temperatures vary around the dew point of the established interior conditions. In those instances, desiccant should be put inside of the package or the air should be evacuated from the package before shipment.

3. Determine the type of packaging system that is best suited for the intended application
The first step is to choose low charging or static dissipative materials when in contact with ESD sensitive devices. Many companies also require the packaging to protect the contents from a direct discharge or exposure to electric fields. In addition to these requirements, there are further questions that need to be asked:

  • Returnable or reusable packaging?
  • Disposable or one-time only packaging?
  • Aesthetic requirements for packaging?

4. Select and test packaging materials
Test methods are explained in EN 61340-5-1 and will classify packaging materials as conductive, static dissipative or insulative.

5. Design a packaging system
Once the ESD sensitivity and distribution environment have been evaluated and available materials have been selected, the design of the packaging system can begin. Per the User Guide, the following general rules apply:

  • If the package is primarily used to transport product in an ESD protected environment then a low charging, static dissipative package may suffice.
  • If the product is moving between ESD protected areas (uncontrolled environment) a low charging, discharge shielding package may be required.
  • When the package is shipped into a totally uncontrolled environment a low charging discharge shielding package is recommended.

In addition to these guidelines, there may be additional factors that should be considered, e.g.:

  • Cost/value relationship: The cost of the packaging compared to the total value of the contents is important. Some companies choose less expensive packaging for less valuable parts.
  • Handling: If rigorous handling is expected, cushioned packaging may need to be considered.

6. Test the final packaging design for effectiveness
It is highly recommended to subject packages to the type of hazards that can be expected during shipments. These tests can, for example, involve the following:

  • High voltage discharges to the exterior of the packaging
  • Simulated over the road vibration
  • Drop tests
  • Environmental exposure

Final thoughts on ESD Protective Packaging

Now that you have an understanding of the factors to consider when choosing your ESD Protective Packaging, you’re ready to implement the above guidelines. ESD packaging comes in all sorts of shapes and forms so bear in mind to not just look at bags when deciding what type of packaging to choose. If you want to learn more about the different types of options, we recommend reading this post.
Also, remember that ESD packaging should be marked. This post will help you finding the correct symbol for your application.

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Example of ESD Protective Packaging – ESD Bags

Do you currently use ESD Protective Packaging? Do you use bags or boxes or something else? How did you choose your ESD Protective Packaging?

The importance of Personnel Grounding Testers

We already know that in an ESD Protected Area (EPA) all surfaces, objects, people and ESD Sensitive Devices (ESDs) are kept at the same potential which is achieved by using ‘groundable’ materials that are then linked to ground. We have also learnt that the most common personnel grounding device to ground people to ground are wrist straps. People who are moving around should instead wear ESD footwear. So how do you know if your wrist straps and ESD footwear are working properly? Excellent question! And one we’ll answer with today’s post so let’s jump right in!

1. Purpose of Personnel Grounding Testers

Wrist Straps and ESD footwear should be part of your Verification Plan. Each component in an EPA plays a vital part in the fight against electrostatic discharge (ESD). If just one component is not performing correctly, you could damage your ESD sensitive devices potentially costing your company thousands of pounds. The problem with wrist straps and ESD footwear is that you can’t always see the damage. Just by looking at the items you would not know if they still provide sufficient protection. That’s where personnel testers provide feedback. They verify the functionality of an operator’s wrist strap and/or footwear and can determine if a person’s wrist strap and/or footwear function correctly.

Personnel Grounding ChecklistYour Personnel Grounding Checklist

Your Personnel Grounding Checklist:

  1. Both wrist straps and footwear need to be tested at least daily before handling ESD sensitive devices and should be worn while checking.
  2. Verify your personnel grounding system using a wrist strap and/or footwear tester.
  3. Remember that a record of each test should be kept for quality control purposes.
  4. ONLY handle ESD sensitive components if your wrist strap and/or footwear pass(es) the test.

2. Types of Personnel Grounding Testers

Broadly speaking, personnel grounding testers can be purchased in two configurations:

  • Wrist strap tester and
  • Wrist strap and footwear tester.

As wrist straps are the most commonly used personnel grounding device to ground operators, you will find a lot of testers on the market that check wrist straps only.
As the name suggests, combined wrist strap and footwear testers will verify your wrist straps AND footwear.

In addition to WHAT they test, you will also be faced with a wide range of devices differing in HOW they test. Below you will find a (by no means complete) list of options:

    • Continuous and split footplate: You will find testers with a continuous footplate which require each foot to be tested separately one after the other. Dual-footplate or independent footwear testers feature a split footplate which allows the unit to verify both feet independently at the same time. This can be a huge time-saver if you have a number of operators in your company who are required to check their personnel grounding devices.
    • Portable, wall-mountable and fitted testers: Portable battery-powered (predominantly) wrist strap testers are perfect for small labs or for supervisors to spot-check workers and ensure compliance. Wall-mountable units are generally supplied with a wall plate which attaches to a wall; the tester is then mounted on to the wall plate. Some personal grounding devices are accompanied by a stand (and built-in footplate) which allow for a more freely positioning of the unit within a room.
    • Relay terminal: A few testers on the market are fitted with a relay terminal that can be integrated with electronic door locks, turnstiles, lights, buzzers, etc. This can be of advantage if companies only want to allow personnel in an EPA that have passed their wrist strap and/or footwear test.
    • Data acquisition: A growing number of personnel grounding devices allow for test activity data to be logged in a database. The units link to a computer which records operator identification, test results, resistance measurements, time and more. Paperless data can enhance operator accountability, immediately identifying problems while reducing manual logging and auditing costs.


Example of a Data Acquisition Tester – more information

3. Operation of Personnel Grounding Testers

Wrist strap testing:
If you are not using a continuous or a constant monitor, a wrist strap should be tested while being worn at least daily. This quick check can determine that no break in the path-to-ground has occurred. Wrist straps should be worn while they are tested. This provides the best way to test all three components: the wrist band, the ground cord (including the resistor) and the interface with the operator’s skin.

Wrist straps should be tested periodically. The frequency of testing, however, is driven by the amount of usage, wear and ESD risk exposure that can occur between tests. For example, what is the quantity of product handled between test periods? Typical test programs recommend that wrist straps that are used daily should be tested daily. However, if the products that are being produced are of such value that a guarantee of a continuous, reliable ground is needed then continuous monitoring should be considered or even required.” (CLC TR 61340-5-2 User guide Wrist Strap clause 4.7.2.4.4 Test frequency)
The operator shall wear the wrist strap in the normal position and plug the free end of the cord into the test apparatus. The hand contact plate shall be pressed to verify that the wrist strap system resistance is within acceptable parameters. The test apparatus can be an integrated, commercially available tester or other Instrumentation that is capable of measuring resistance from 5,0 x 104 ohms to at least 1,0 x 108 ohms. The tester open-circuit voltage is typically between 9 V d.c. and 100 V d.c.” (EN 61340-5-1 Annex A Test method A.1 Measurement method for wrist strap testing).

Wrist Strap TesterExample of a Wrist Strap Tester – more information

If the wrist strap tester outputs a FAIL test result, stop working and test the wrist band and cord individually to find out which item is damaged.  Replace the bad component and repeat the test.  Obtain a PASS test result before beginning work. For more information on troubleshooting failed wrist straps, check this post.

Footwear testing:
If using a flooring / footwear system as an alternative for standing or mobile workers, ESD footwear should be tested independently at least daily while being worn. Proper testing of foot grounders involves the verification of the individual foot grounder, the contact strip and the interface between the contact strip and the operator’s perspiration layer.
The operator shall stand with one foot on the conductive footwear electrode. The hand contact plate shall be pressed to verify that the person footwear system resistance is within acceptable parameters. The test shall be repeated for the other foot. The test apparatus can be an integrated, commercially available tester or other instrumentation that is capable of measuring resistance from 5,0 x 104 ohms to at least 1,0 x 108 ohms. The tester open-circuit voltage is typically between 9 V d.c.and 100 V d.c.” (EN 61340-5-1 Annex A Test method A.2 Measurement procedure for footwear testing).

 
Example of a Wrist Strap and Footwear Tester – more information

If the footwear tester outputs a FAIL test result, stop working, and test the foot grounder and contact strip individually to find out which item is damaged.  Replace the foot grounder.  Obtain a PASS test result before beginning work.

How to reduce the risk of damaging ESD sensitive devices in critical applications

Do your employees handle ESD sensitive high-end components that would be extremely expensive to replace if they failed? If so, you want to make sure that the risk of ESD damage is as low as possible. Today’s blog post will look at an option of protecting your critical applications: dual-wire wrist straps.

Introduction

In an ESD Protected Area (EPA) all surfaces, objects, people and ESD sensitive devices (ESDs) are kept at the same potential. This is achieved by simply using only ‘groundable’ materials that are then linked to ground.

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 coil cord that connects the band to an Earth Bonding Point (EBP).

Wrist Strap
Components of a Wrist Strap

Advantages of Dual-Wire Wrist Straps

Dual-wire wrist straps have two conductors (compared to single-wire monitors which have only one conductor inside the insulation of the coil cord). They offer a reduced risk of damaging ESD sensitive devices because even if one conductor is severed, the operator still has a reliable path-to-ground with the other conductor. For that reason, they are generally used in critical applications. Dual-wire wrist straps:

  • eliminate intermittent failures and
  • extend the lifespan of wrist straps.

MagSnap 360 Dual-Wire Metal Wrist StrapExample of a Dual-Wire Wrist Strap – more information

Using Dual-Wire Continuous Monitors

For maximum benefits dual-wire wrist straps should be used together with dual-wire continuous monitors. So instead of connecting your coil cord to an Earth Bonding Point, you would connect it to your Continuous Monitor. The operator will be grounded and at the same time monitored. Continuous Monitors provide operators with instant feedback on the status and functionality of their wrist strap and/or workstation. They detect split-second failures when the wrist strap is still in the “intermittent” stage. This is prior to a permanent “open” which could result in damage to ESD sensitive components.
Since people are one of the greatest sources of static electricity and ESD, proper grounding is paramount. One of the most common ways to ground people is with a wrist strap. Ensuring that wrist straps are functional and are connected to people and ground is a continuous task.” “While effective at the time of testing, wrist strap checker use is periodic. The failure of a wrist strap between checks may expose products to damage from electrostatic charge. If the wrist strap system is checked at the beginning of a shift and subsequently fails, then an entire shift’s work could be suspect.” “Wrist strap checkers are usually placed in a central location for all to use.  Wrist straps are stressed and flexed to their limits at a workstation.  While a wrist strap is being checked, it is not stressed, as it would be under working conditions.  Opens in the wire at the coiled cord’s strain relief are sometimes only detected under stress.“ [ESD TR 12-01 Technical Report Survey of Constant (Continuous) Monitors for Wrist Straps]

Example of a Dual-Wire Continuous MonitorExample of a Dual-Wire Continuous Monitor – more information

Dual Polarity Technology provides true continuous monitoring of wrist strap functionality and operator safety according to accepted industry standards. Dual-wire systems are used to create redundancy. In critical applications you build-in redundancy in order to have a backup if your primary fails. That’s the concept. With dual-wire wrist straps the redundancy is there as a protection rather than an alternative. If you are monitoring your dual-wire wrist strap and one wire fails, then the unit will alarm. You will still be grounded by the other wire, so there will be a significantly reduced risk of damaging ESD sensitive components if you happen to be handling them when the wrist strap fails. The wrist strap would still need to be replaced immediately.
Resistance (or dual-wire) constant monitors are “… used with a two wire (dual) wrist strap. When a person is wearing a wrist strap, the monitor observes the resistance of the loop, consisting of a wire, a person, a wristband, and a second wire.  If any part of the loop should open (become disconnected or have out of limit resistance), the circuit will go into the alarm state.” “While the continuity of the loop is monitored, the connection of the wrist strap to ground is not monitored.” “There are two types of signals used by resistance based constant monitors; steady state DC and pulsed DC.  Pulsed DC signals were developed because of concerns about skin irritation.  However, pulse DC units introduce periods of off time (seconds) when the system is not being monitored.“ [ESD TR 12-01 Technical Report Survey of Constant (Continuous) Monitors for Wrist Straps]

Conclusion

And there you have it: if you do have a critical application, make sure you use dual-wire wrist straps together with dual-wire continuous monitors.

How to create a Compliance Verification Plan

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

ESD protected area (EPA) products should be tested:

  1. Prior to installation to qualify product for listing in user’s ESD control plan.
  2. During the initial installation.
  3. For periodic checks of installed products as part of IEC 61340-5-1 Edition 2 2016 clause 5.2.3 Compliance verification plan.

LabCoatsTestingChecking an ESD Lab Coat using a Surface Resistance Tester

A compliance verification plan shall be established to ensure the organization’s fulfilment of the requirements of the plan. Process monitoring (measurements) shall be conducted in accordance with a compliance verification plan that identifies the technical requirements to be verified, the measurement limits and the frequency at which those verifications shall occur. The compliance verification plan shall document the test methods used for process monitoring and measurements. If the organization uses different test methods to replace those of this standard, the organization shall be able to show that the results achieved correlate with the referenced standards. Where test methods are devised for testing items not covered in this standard, these shall be adequately documented including corresponding test limits. Compliance verification records shall be established and maintained to provide evidence of conformity to the technical requirements.
The test equipment selected shall be capable of making the measurements defined in the compliance verification plan.
” [IEC 61340-5-1:2016 clause 5.2.4 Compliance verification plan]

Components of a Verification Plan

As outlined in the User Guide 61340-5-2:2008, each company’s verification plan needs to include:

1. A list of items that are used in the EPA and need to be checked on a regular basis

This would include ESD working surfaces, personnel grounding devices like wrist straps or foot grounders, ionisers etc. It is recommended to create a checklist comprising all ESD control products: this will ensure EPAs are checked consistently at every audit.

2. A schedule specifying what intervals and how each item is checked

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

222566use
It is recommended that Wrist Straps are checked before each shift

The user guide offers a solution: “Some organizations may want to increase the time between verifications of an ESD control item after it has been in use for a period of time. This is typically done by monitoring the failures of the ESD control item. Once the organization has evidence that there is an acceptable period of time where no failures were found, the time between verifications can be increased. The new verification interval is then monitored. If an unacceptable level of failures is identified, then the verification frequency should revert back to the previous level.” [User Guide 61340-5-2:2008 clause 4.3.3 Verification frequency]
The industry typically uses 2 types of verification to achieve maximum success: visual and measurement verification. As the name suggests, visual verification is used to ensure ESD working surfaces and operators are grounded, ESD flooring is in good shape or wrist straps are checked before handling ESD sensitive items.

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

3. The suitable limits for every item used to control ESD damage

IEC 61340-5-1:2016 contains recommendations of acceptable limits for every ESD control item. Following these references reduces the likelihood of 100V (HBM) sensitive devices being damaged by an ESD event.

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

4. The test methods used to ensure each ESD product meets the set limits

Tables 1 to 3 of IEC 61340-5-1:2016 list the different test methods a company has to follow. If a company uses other test methods or have developed their own test methods, the ESD control programme plan needs to include a statement explaining why referenced standards are not used. The company also needs to show their chosen test methods are suitable and reliable.

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

5. The equipment used to take measurements specified in the test methods

Every company needs to acquire proper test equipment that complies with the individual test methods specified in Tables 1 to 3 of IEC 61340-5-1:2016. Personnel performing measurements need to be trained on how equipment is used.

222643UseChecking ESD Working Surface using a Surface Resistance Tester

6. A list of employees who will be performing the audits

Part of the verification plan is the choice of internal auditors. A few suggestions for the selection process:

  • Each induvial is required to know the ESD Standard IEC 61340-5-1 AND the company’s individual ESD programme.
  • It is essential that the selected team member recognises the role of the ESD control programme in the company’s overall quality management system.
  • It is recommended that each nominated worker has been trained on performing audits.
  • The designated employee should be familiar with the manufacturing process they are inspecting.

7. How to deal with non-compliance situations

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

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

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

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

Here is an example of a Verification Plan using ESD flooring for demonstration purposes. A few notes:

  • Our sample company has 2 different areas where ESD floor matting is used: the packaging area and the main EPA.
  • Flooring is not used for grounding personnel handling ESD sensitive items
  • Our sample company has established that the limits outlined in the standard are suitable for their internal requirements.

Bear in mind that ALL your ESD control items need to be included in your verification plan. So if your company uses wrist straps, smocks, chairs, gloves etc. then ALL of them have to be listed as part your ESD control programme.

4 Benefits of Continuous Monitoring

We have previously learnt that wrist straps are considered the first line of ESD Control. They are used to link people to ground which ensures that that the operator is kept at the same potential as surfaces, objects and ESD sensitive devices. We’ve also discovered that wrist straps need to be visually inspected and checked (while worn) on a daily basis – BEFORE handling any ESD sensitive item. This will alert the operator if their wrist strap has developed a fault and as a result does not ground them any longer.
An alternative to periodic testing is the use of continuous monitors. Per ESD Handbook TR 20.20 paragraph 5.3.2.4.4 Test Frequency, “Because wrist straps have a finite life, it is important to develop a test frequency that will guarantee integrity of the system. Typical test programs recommend that wrist straps that are used daily should be tested daily. However, if the products that are being produced are of such value that knowledge of a continuous, reliable ground is needed, then continuous monitoring should be considered or even required.

In today’s post we will highlight 4 benefits of continuous monitoring which may help you decide to move away from daily wrist strap checks.
But first a little reminder of what continuous monitors actually are: Continuous monitors come in different styles and sizes but are intended to be kept on your workstation. Some units just ‘sit’ on your bench; others are attached to your working surface matting; some can even be attached underneath the workbench so they don’t take away valuable workspace. Operators connect their wrist strap to the unit to allow for real-time continuous monitoring. If the wrist strap fails, the unit will alarm. Many continuous monitors also feature a parking stud providing a means for the operator to disconnect when leaving their workstation.

There are two different types of continuous monitors available:

  • Single-wire continuous monitors allow the use of any standard, single-wire wrist strap and coil cord. The monitor / wrist strap system life-cycle costs are significantly lower than dual-wire systems. While they would not be suitable for the most critical applications, single-wire continuous monitors are an economical way to monitor both the operator’s wrist strap and/or workstation surface.
  • Dual-wire constant monitors provide true continuous monitoring of wrist strap functionality and operator safety according to accepted industry standards. Dual-wire continuous monitors provide redundancy because even if one dual-wire wrist strap conductor is severed, the operator still has a reliable path-to-ground with the other conductor.

1. Instant Feedback

Imagine this scenario: you come to work in the morning, you test your wrist strap, it passes and you start work on your ESD sensitive devices. 3 hours later, when you come back from your tea break, you test your wrist strap again and it fails. What to do? You don’t know if the wrist strap only just failed or if it failed right after your first test in the morning. How do you know if the devices you worked on all morning have been damaged? You don’t – after all, latent defects are not visible and failures may only occur at a later time. Using continuous monitoring while working on those ESD sensitive devices will alert the operator as soon as their wrist strap fails. The faulty wrist strap can be replaced with a new model from stock and everyone is happy – no ESD sensitive devices damaged and no unhappy customers.

Zero Volt Monitor SoloThe EMIT Zero Volt Monitor (50579) in Use

Continuous monitors provide operators with instant feedback on the status and functionality of their wrist strap. The instant an operator’s wrist strap or cord fails, the monitor will issue audible and visual (LEDs) alarms alerting the user and supervisor of the problem. Full time continuous monitoring is superior to periodic or pulsed testing, and can save a significant amount of money in testing costs and rejected product. Periodic testing only detects wrist strap failures after ESD susceptible products have been manufactured. The costs of dealing with the resulting catastrophic failures or latent defects can be considerable. “A properly grounded wrist strap will keep a person’s body voltage to approximately + 10 V. The main advantage to a constant [or continuous] monitor is the immediate indication that the employee receives if the wrist strap falls open. With an unmonitored system, the employee will not be aware of a wrist strap failure until the start of the next shift. This has reliability benefits for an ESD program as it might help reduce or eliminate ESD damage.” [CLC/TR 61340-5-2:2008 User guide Annex B.1.3 Constant monitors].

2. Monitor Operator AND Workstation

An option available with most continuous or constant monitors is the ability to monitor working surface ground connections. “Some continuous monitors can monitor worksurface ground connections. A test signal is passed through the worksurface and ground connections. Discontinuity or over limit resistance changes cause the monitor to alarm. Worksurface monitors test the electrical connection between the monitor, the worksurface, and the ground point. The monitor however, will not detect insulative contamination on the worksurface.” [ESD TR 12-01 Technical Report Survey of Constant (Continuous) Monitors for Wrist Straps]
When the monitor is connected to an ESD Mat working surface, the amount of current that flows is a function of the total resistance between the monitor and through the working surface to ground. When the resistance of the working surface is below a pre-set threshold*, the monitor will indicate good. Conversely, if the resistance level is high when compared to the monitor’s reference*, the unit will alarm. This is an integrating resistance measuring circuit, therefore it is relatively insensitive to externally induced electromagnetic fields.

Installing the Multi-Mount Monitor to Ground the WorksurfaceInstalling the Vermason Multi-Mount Monitor (222608) to ground the worksurface

For units that also monitor the connection of a worksurface to protective earth, it is also possible to reduce or eliminate the checking of the worksurface as part of the periodic audit of the process.” [CLC/TR 61340-5-2:2008 User guide Annex B.1.3 Constant monitors].

*The resistance threshold limits can vary between brands and models (and can sometimes also be adjusted by the user) so make sure you do your homework before committing to a particular unit and check the limit meets your individual requirements.

3. Detect Initial Flex Fatigue

Unlike wrist strap testers, continuous monitors detect split-second failures when the wrist strap is still in the “intermittent” stage. This is prior to a permanent “open” which could result in damage to ESD sensitive components.

Using ESD shielding bagsThe Jewel Mini Workstation Monitor (222603) in Use

Wrist strap checkers are usually placed in a central location for all to use. Wrist straps are stressed and flexed to their limits at a workstation. While a wrist strap is being checked, it is not stressed, as it would be under working conditions. Opens in the wire at the coiled cord’s strain relief are sometimes only detected under stress.” [ESD TR 12-01 Technical Report Survey of Constant (Continuous) Monitors for Wrist Straps]

4. Eliminate Need for Periodic Testing

Many customers are eliminating periodic touch testing of wrist straps and are utilising continuous monitoring to better ensure that their products were manufactured in an ESD protected environment. Continuous monitors eliminate the need for users to test wrist straps and log the results; by their function, these monitors satisfy the EN 61340-5-1 test logging requirements. “There are also other process benefits from using constant monitors such as the elimination of the need to maintain daily test logs and a reduction in the time for employees to make the daily test.” [CLC/TR 61340-5-2:2008 User guide Annex B.1.3 Constant monitors].

No more Paper LogsNo more Paper Logs!

So when using constant monitoring, operators:

  • Don’t have to waste time queuing at a wrist strap test station before each shift.
  • Don’t have to remember to complete their daily test logs.

It’s also harder to ‘cheat’ with continuous monitors. We’re not saying, your employees would do naughty things like that but we’ve seen it all before: operators ‘pretending’ to perform a wrist strap check, operators failing a wrist strap test and still recording a pass etc. There are always options to bypass a system, but it’s definitely harder when continuous monitors are used.

So should you now run-out and equip all your users with continuous monitors? As with most things in life, the answer is not that simple: it depends! 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.

6 steps to choosing and installing an ESD working surface

The purpose of an ESD protective working surface is to aid in the prevention of damage to ESD sensitive items (ESDS) and assemblies from electrostatic discharge. An ESD protective working surface provides protection in the following two ways:

  1. Providing a low charging (antistatic) working surface area that will limit static electricity to be generated below potentially damaging levels.
  2. Removing the electrostatic charge from conductive objects placed on the working surface.

1. Types of ESD working surfaces

ESD protective working surfaces are categorised into two general categories: conductive and dissipative.

A conductive working surface is defined by most documents as a material that has a surface resistance of less than 1 x 104 ohms. Conductive materials are the quickest to ground a charge but they can also cause damage by discharging too rapidly. Conductive materials are usually used as floor mats or flooring products.

A dissipative working surface is defined as being materials having a surface resistance of at least 1 x 104, but less than 1 x 109 ohms. Dissipative materials will dissipate a charge slower and are recommended for handling electronic components. Dissipative materials are usually the preferred choice for bench top working surfaces.

Most people in the industry consider working surfaces to be the second most important part of an ESD Control Programme, with personnel grounding being most important.

2. Grounding Methods for working surfaces
Method 1: Grounding via ground cords

  1. Vermason recommends using an earth bonding point cord when grounding via ground cords. Most earth bonding point cords will ground an ESD protective working surface and provide banana jacks for two wrist strap grounds.
    Grounding via Grounding Cords

    Earth Bonding Point for each workstation

  2. An earth bonding point should be installed at each workstation and should be connected directly to a verified electrical system ground or to a verified grounding bus which is connected to the protective earth ground. Only one groundable point should be installed on a working surface.
  3. Wrist straps should never be grounded through a working surface, as the added resistance of the working surface material will prevent the wrist strap from operating properly.

Proper Grounding of Wrist StrapsProper Grounding of Wrist Straps

Method 2: Grounding via a grounded conductive surface

  1. This alternate form of grounding should only be employed when using a homogeneous dissipative material with a volume resistance of less than 1 x 108
  2. The dissipative working surface may be placed on a properly grounded laminate, metal or other conductive surface. The working surface will electrically couple to the grounded surface and may not require a separate ground cord.
  3. When using this type of grounding method be sure to test that the working surface Rg is less than 1 x 109 ohms, tested per IEC 61340-2-3. Also consider increasing Compliance Verification test frequency.

Grounding via a Grounded Conductive Surface
Alternate Grounding Method via a Grounded Conductive Surface

3. Groundable Point Installation

Before installing a groundable point on your work surface you must first determine whether you will need a male stud or female socket, the type of snap hardware and the desired location.

There are generally 3 types of groundable points available for working surface mats: screw-on snap kits, push & clinch snaps (with prongs) or stud & posts sets (requiring installation using a punch and an anvil).

Snap Kits and ToolsSnap Kits and Tools

Screw-on Snaps:

  1. Determine the position of the grounding snap (one only per mat). Punch a hole through the material with a small Phillips screwdriver or awl.
  2. Insert the screw through the bottom on the snap fastener, the washer and the material. Affix the assembly with the conical nut supplied with the kit and tighten down the screws.

Installing Screw-on Mat Grounding SnapInstalling a screw-on Mat Grounding Snap

Push & clinch snaps:

This snap is designed for use with any type of soft mat material: dissipative, conductive or multi-layered. It is recommended for use with three-layered material, because it provides better contact with the internal conductive layer. It is recommended that before inserting this snap, the mat be punctured with a sharp tool where the snap will be placed.

Centre the prongs on the snap assembly. Apply pressure to the snap until the prongs come through the back of the mat, then clinch over prongs making flat to the mat’s bottom side to secure snap as shown in the below picture.

Installing Push & Clinch Mat Grounding SnapInstalling Push & Clinch Mat Grounding Snap

Stud & post sets:

This type of groundable point must be riveted through bench and floor mats to connect ground cords. A punch and anvil are simple but effective tools to achieve a neat finish with firm materials no more than 4mm thick.

  1. Punch a 5mm diameter hole at the desired location of the mat.
  2. Insert the post from underneath and apply the stud over the protruding post on the top side.
  3. Fit the anvil under the post and place the punch inside the stud and hammer the post (or use an arbor press) until it rolls and a tight assembly is achieved.

Using a Punch and Anvil to install Stud & Post Sets

Using a Punch and Anvil to install Stud & Post Sets

4. Selection of Common Point & Floor Mat Grounding Systems

  1. Determine the type of common point grounding system you will use: barrier strip, bus bar, grounding block or common point ground cord. Vermason recommends the use of common point ground cords and earth bonding bars.
  2. If you determine that you will use ground cords, you must now determine the type of ground cord you will use for your workstation grounds. It is the user’s preference to use a ground cord with or without a current limiting 1 megohm resistor to ground working surfaces or floor mats. Selection of the ground cord is determined by user needs and specifications; the resistor is not for ESD control.Examples of Grounding Cords

    Examples of Grounding Cords

  3. Earth bonding point bars allow the grounding of multiple operators at one common ground point. They also mount easily under the front edge of a workstation benchtop.

Earth Bonding Point InstallationEarth Bonding Point Installation

5. Mat Installation

  1. For best results, allow the mats to lay flat for about four hours at room temperature before installing. This will give the material time to flatten out from being rolled for shipment.
  2. Test all workstation grounds for proper resistance to ground.
  3. Lay the mat in position and snap the ground cord to it. Bring the other end of the ground cord to the common ground point (or earth bonding bar) and attach it using the ring terminal (or other termination device). The electrical systems junction box and connecting conduit should also connect to earth protective ground. Tie the ground wire to the bench to keep it out of the way and neat. You may cut and strip the ground wire to a shorter length and attach it with an extra ring terminal if required.
    Note: DO NOT DAISY CHAIN. Because of the high resistances inherent to many types of protective surfaces, daisy chaining of these materials can cause the overall resistance to exceed the required limit of EN 61340-5-1.
    Do not daisy-chain

    ESD working surface should never be grounded in series, i.e. daisy chained

  4. If your kit includes a floor mat, you should duplicate step 2 and attach the floor mat ground to the same ground point as the working surface ground.
  5. Measure the resistance from the ground snap on the mat to the common ground point. It should read 1 megohm ±20 percent if you are using a ground cord with a resistor, and less than 10 ohms if you are using a ground cord without a resistor.
  6. If you have a surface resistance or resistance to ground tester available, you may wish to test the resistance to ground from the mat surface. Note: depending upon the accuracy of the instrument you are using, you may get a wide range of results in resistance to ground tests. In order to get the electrical readings specified per EN 61340-2-3, two 2.2kg electrodes are to be used. This will require a megohmmeter with 100 volt open test circuit voltage and two 2.2kg electrodes.
  7. If you are using a mat kit that includes the wrist strap, install the wrist strap directly to the common point mat ground cord. Again, test the resistance from the backplate of the wrist strap to the common ground point. It should read 1 megohm ± 20 percent.
    Adding a Wrist Strap

    Adding a Wrist Strap

  8. Your completed installation of an ESD workstation should comply with one of the electrical diagrams illustrated below.

Proper wiring diagrams

Proper wiring diagrams for conductive and dissipative ESD workstations

6. Maintenance and Cleaning

For optimum performance, periodic cleaning is required following the manufacturer’s recommendations.

BE SURE YOU TEST ALL GROUNDS AND THE WRIST STRAP FREQUENTLY

ESD foot grounders or ESD shoes – what’s best?

We get a lot of customers asking us if they should use ESD foot grounders or ESD shoes in their EPA. And our answer is always the same: it depends! There really is no right or wrong when it comes to choosing but there are obviously a few things you need to consider before investing in one or the other.

Safety First!

In some cases, protective footwear (shoes, boots, etc.) is required to prevent foot injuries due to falling or rolling objects or from objects piercing the sole. Safety of the operator takes priority over ESD control at all times. If protective footwear with reliable ESD properties is not available or ESD foot grounders cannot be worn with the protective footwear in the ESD Protected Area, other personnel grounding devices such as wrist straps should be used. For more information on using wrist straps, check out this post.

Introduction to ESD Foot Grounders

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.

Example of ESD Foot GrounderExample of ESD Foot Grounder – more info

Guidelines for ESD foot grounders:

  1. 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).
  2. 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.
  3. A current limiting one or two megohm resistor in series with the contact strip is recommended but not required.
  4. ESD foot grounders should be tested independently at least daily while being worn.

Advantages of ESD Foot Grounders

ESD foot grounders are often preferred over shoes because one size fits many foot sizes, thereby reducing stock holdings and simplifying operations.
ESD foot grounders also usually pass the mandatory resistance test as soon as worn, whereas some ESD shoes require a ‘warm-up period’ in order for the operator’s RG to drop below 35 megohms.
They are easily replaceable, quick to put on and less bulky than ESD shoes. They can also be easily taken off when leaving an EPA.

Disadvantages of ESD Foot Grounders

A common complaint with ESD foot grounders is that they don’t last very long. However, there are a few simple tricks to avoid a quick ‘burn-out’:

  • The useful life of an ESD foot grounder will depend a lot on the floor and its surface roughness: the rougher the floor the greater the wear. We recommend ESD foot grounders only to be used indoors where floors are usually smoother (and where the ESD foot grounder is less likely to become wet, thereby short circuiting the resistor).
  • The manner in which the wearer walks can also affect the life span of the grounder.

In summary, with reasonable care and if used only indoors, ESD heel and toe grounders can last several weeks.

Introduction to ESD Shoes

Conductive additives are blended into the sole (inside to outside) of ESD shoes and connect to the operator’s feet. ESD shoes provide an electrically conductive path from the wearer to the floor – from the operator’s socks (through the sweat layer), to the insole and then to the other outer sole.

Examples of ESD ShoesExamples of ESD Shoes

There are a number of considerations when selecting ESD shoes:

  1. Does the ESD shoe meet the ESD Association (ESDA) standards?
    Many manufactures of ESD shoes often reference ASTM standards for their ESD specification but state nothing about ESDA standards. The ESDA standards are written specifically for electronics manufacturing and handling. The walking test defined in the ANSI/ESD STM97.2-2006 is one of the most important methods for qualifying ESD shoes for use in ESD Protected Areas.
  2. Not all ESD shoes is created equal.
    There are different styles of ESD shoes. In most cases the specifications of each style will vary. While one style of ESD shoes may retain its ESD properties for 6 months or longer, another will start failing within 90 days. The performance of all styles of ESD shoes should be verified at least daily on an on-going basis and records should be kept for quality control purposes.

Advantages of ESD Shoes

The major advantage of ESD shoes is that they do not require a tab to connect to the operator. There won’t be any issues with the tab not staying inside the shoe – as soon as ESD shoes are put on, the operator is grounded.
ESD shoes are unlikely to be put on incorrectly and have a lower chance of breaking compared to ESD foot grounders. They are generally more reliable and durable.

Disadvantages of ESD Shoes

A big drawback with ESD shoes is obviously the larger initial investment cost. Especially, if you have a large number of operators working in your EPA, it will be costlier to equip everyone with ESD shoes.

Final Thoughts

Now you know all the ins-and-outs of ESD foot grounders and ESD shoes, you’re probably more confused than ever. ESD Foot Grounders in UseSo what should you go for? Well, as we said right at the beginning of this post: it depends! It depends, e.g.

  • On your budget: are you prepared to initially invest a larger amount of money or would you prefer to spread the costs evenly over time? Also consider the cost over a longer period of time (i.e. 2 or 5 years). Whilst ESD shoes are more expensive initially, ESD foot grounders have to be replaced regularly which adds up, as well.
  • On your operators: When selecting your ESD grounding device, it is a good idea to consider the opinion of the operators. They may not find the style of ESD shoe being considered to be comfortable or they may become frustrated that the ESD foot grounder that has been selected does not stay secured properly. In some facilities, many operators are temporary or on a flexible schedule that would not justify certain types of ESD footwear and it is never recommended that operators share footwear due to hygiene issues.

So have a hard look at the numbers and an honest conversation with your employees and then take it from there!

 

Everything you need to know about ESD protective working surfaces

So we’ve talked about various components in an EPA before (e.g. wrist straps, bags, tape and so on). But there is one important part we have not covered yet: ESD protective working surfaces. So let’s change that right now!

Definition of an ESD protective working surface

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.

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

Types of ESD protective working surface

When deciding to invest in ESD protective working surface, you have the choice of ESD matting (laid-out on a standard non-ESD bench) or ESD benches. Performance-wise there is no difference so what option you go for depends solely on your personal preference.

Working-Surface-Matting
Examples of ESD protective working surface matting – for more details click here

Generally speaking, ESD matting offers a lower initial investment and is easier to replace. On the other hand, some people prefer the robust and consistent approach of ESD benches.

Grounding your ESD protective working surface

Whatever your choice, your ESD protective working surface needs to be grounded.
A ground wire from the surface should connect to the common point ground which is connected to ground, preferably equipment ground. For electronics manufacturing a working surface resistance to ground (Rg) of 1 x 104 to less than 1 x 109 ohms is recommended. 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.

ESD Protective Working SurfaceExample of an ESD Protective Working Surface – click here for more grounding products

Using a current limiting resistor in the ground cord is the user’s choice. However, the resistor is not for ESD control purposes. The ESD Association standard for grounding is ANSI/ESD S6.1 which recommends a hard ground (no resistor) but allows the use of a current limiting resistor in the mat’s ground cord. “The grounding conductors (wires) from wrist straps, working surfaces, flooring or floor mats, tools, fixtures, storage units, carts, chairs, garments and other ESD technical elements may or may not contain added resistance. Where added resistance is not present, a direct connection from the ESD technical element to the common point ground or common connection point is acceptable and recommended.
Note: Manufacturers may add resistance to the grounding conductors for purposes other than ESD (e.g. current limiting). Added resistance is acceptable for the purposes of controlling ESD provided electrostatic accumulation does not exceed specific EPA requirements. The typical added resistance in grounding conductors is 1 megohm, although other values may be specified.” [ANSI/ESD S6.1 section 5.3.3 ESD Technical Element Conductors]

Working at an ESD protective working surface

Operators should ensure that the working surface is organised to perform work and that all unnecessary insulators and personal items are removed. Regular plastics, polystyrene foam drink cups and packaging materials etc. are typically high charging and have no place at an ESD protective workstation.

Working Surface Matting and OperatorAn operator installing an ESD protective working surface mat

Insulators can be a considerable threat to your products. Remember that an insulator cannot be grounded so it will retain its charge for a long time. Removing all non-essential insulators from the ESD protective workstation is an important rule. If not, your company’s investment in the grounded ESD working surface may be wasted.
The biggest threat is Field Induced Discharges, which can occur even at a properly grounded ESD working surface. If an ESDS is grounded in the presence of an ElectroStatic charge, instead of the ESDS having charges removed from it, the ESDS may become charged with a voltage induced on it. Then, when placed on the grounded ESD work surface, a discharge occurs. If the ESDS is removed from the presence of the ElectroStatic charge and grounded again, a second discharge may occur.“ (Ref. ESD Handbook, ESD TR20.20, section 2.7.5).

Maintaining your ESD protective working surface

The ESD working surface must be maintained and should be cleaned with an ESD cleaner. Regular cleaners typically contain silicone and should never be used on an ESD working surface.

Reztore ESD Surface & Mat Cleaner
Example of an ESD cleaner – click here for more information

The ESD control plan should require testing of the resistance to ground periodically. For more information on testing your ESD working surface, check this post. However, the operator should be on guard every day and check visually that the ground wire is attached.

How to set-up an ESD Control Plan

So you’ve identified ESD sensitive items in your factory and you realise that you need to implement ESD Control measures. But where do you start? There is so much information out there and it can be completely overwhelming. Don’t panic – today’s blog post will provide you with a step-by-step guide on how to set-up a suitable ESD Control Plan.

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 Edition 1.0 2007-08 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 Edition 1.0 2007-08 Introduction]

1. Define what you are trying to protect

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.

Using continuous monitorsAn operator handling an ESD susceptible item

2. Become familiar with the industry standards for ESD control

A copy of EN 61340-5-1:2007 can be purchased from British Standards: “BS EN 61340-5-1:2007 applies to activities that: manufacture, process, assemble, install, package, label, service, test, inspect, transport or otherwise handle electrical or electronic parts, assemblies and equipment susceptible to damage by electrostatic discharges greater than or equal to 100 V human body model (HBM). BS EN 61340-5-1 provides the requirements for an ESD control program. The user should refer to IEC 61340-5-2 for guidance on the implementation of this standard.

3. Select a grounding / equipotential bonding system

The elimination of differences in potential “can be achieved in three different ways:

  • grounding using protective earth:
    the first and preferred ESD ground is protective earth if available. In this case, the ESD control elements and grounded personnel are connected to protective earth;
  • grounding using functional ground:
    the second acceptable ESD ground is achieved through the use of a functional ground. This conductor can be a ground rod or stake that is used for grounding the ESD control items in use at a facility. In order to eliminate differences in potential between protective earth and the functional ground system it is highly recommended that the two systems be electrically bonded together;
  • equipotential bonding:
    in the event that a ground facility is not available, ESD protection can be achieved by connecting all of the ESD control items together at a common connection point.
    ” [EN 61340-5-1 Edition 1.0 2007-08 clause 5.3.1 Grounding/equipotential bonding systems]

ESD Protective Working SurfaceExample of a grounding/equipotential bonding system

4. Determine the grounding method for operators (Personnel Grounding)

The two options for grounding an operator are:

  • a wrist strap or
  • foot grounders/footwear.

Wrist straps must be worn if the operator is seated.
A flooring / footwear system is an alternative for standing or mobile workers.

In some cases, both (wrist strap and foot grounders) will be used.

5. Establish and identify your ESD Protected Area (EPA)

ESD Control Plans must evolve to keep pace with costs, device sensitivities and the way devices are manufactured. Define the departments and areas to be considered part of the ESD Protected Area. Consider if customers and/or subcontractors should be included. Implement access control devices, signs and floor marking tape to identify and control access to the ESD Protected Area.

EPARoomExample of an ESD Protected Area including signs and floor marking tape

6. Select ESD control items to be used in the EPA based on your manufacturing process

Elements that should be considered include: working surfaces, flooring, seating, ionisation, shelving, mobile equipment (carts) and garments. Check-out this post for more information.

7. Develop a Packaging (Materials Handling & Storage) Plan

When moving ESD susceptible devices outside an ESD protected area, it is necessary for the product to be packaged in an enclosed ESD Shielding Packaging.

8. Use proper markings for ESD susceptible items, system or packaging

From EN 61340-5-1 Edition 1.0 2007-08 clause 5.2.1: “The Organization shall prepare an ESD Control Program Plan that addresses each of the requirements of the Program. Those requirements include: …marking”.
If you are handling ESD sensitive devices, there are 3 symbols you need to know.

ESD SymbolsThe ESD Susceptibility (left) and ESD Protective Symbol (right)

9. Implement a Compliance Verification Plan

Developing and implementing an ESD control programme is only the first step. The second step is to continually review, verify, analyse, evaluate and improve your ESD programme.

Process monitoring (measurements) shall be conducted in accordance with a compliance verification plan that identifies the technical requirements to be verified, the measurement limits and the frequency at which those verifications must occur. The compliance verification plan must document the test methods used for process monitoring and measurements… Compliance verification records shall be established and maintained to provide evidence of conformity to the technical requirements.  The test equipment selected shall be capable of making the measurements defined in the compliance verification plan.” [EN 61340-5-1 Edition 1 2007-08 clause 5.2.3 Compliance verification plan]

Regular programme compliance verification and auditing is a key part of a successful ESD control programme.

10. Develop a Training Plan

The training plan shall define all personnel that are required to have ESD awareness and prevention training. At a minimum, initial and recurrent ESD awareness and prevention training shall be provided to all personnel who handle or otherwise come into contact with any ESDS [ESD sensitive] items. Initial training shall be provided before personnel handle ESD sensitive devices. The type and frequency of ESD training for personnel shall be defined in the training plan. The training plan shall include a requirement for maintaining employee training records and shall document where the records are stored. Training methods and the use of specific techniques are at the organization’s discretion. The training plan shall include methods used by the organization to ensure trainee comprehension and training adequacy.” [EN 61340-5-1 Edition 1.0 2007-08 clause 5.2.2 Training Plan]

11. Make the ESD Control Plan part of your internal quality system requirements

A written ESD Control Plan provides the “rules and regulations”, the technical requirements for your ESD Control Programme. This should be a controlled document, approved by upper management initially and over time when revisions are made. The written plan should include following:

  • Qualified Products List (QPL): a list of EPA ESD control items is used in the ESD control Plan
  • Compliance Verification Plan: includes periodic checking of EPA ESD control items and calibration of test equipment per manufacturer and industry recommendations.
  • Training Plan: an ESD Programme is only as good as the use of the products by personnel. When personnel understand the concepts of ESD, the importance to the company of the ESD control programme and the proper use of ESD products, they will implement a better ESD control programme improving quality, productivity and reliability.
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