Today’s post concludes our 2-part series on periodic verifcation. If you have missed the first part, you can catch-up on it here. As a reminder, it is recommended to regularely check all ESD Protected Area (EPA) products to ensure they are working correctly. After covering working surface matting and wrist straps in last week’s post, we’ll jump right in to discuss the remaining components in your EPA.
A flooring / footwear system is an alternative for personnel grounding for standing or mobile workers. Foot grounders quickly and effectively drain the static charges which collect on personnel during normal, everyday activities. Foot grounders should be used in conjunction with floor surfaces which have a surface resistance of less than 1010 ohms.
As ESD floors get dirty, their resistance increases. For optimum electrical performance, floor matting must be cleaned regularly using an ESD mat cleaner, such as Reztore™ Surface & Mat Cleaner. Do not use cleaners with silicone as silicone build-up will create an insulative film on the surface.
Dissipative floor finish can be used to reduce floor resistance. Periodic verification will identify how often the floor finish needs to be applied. As the layer(s) of dissipative floor finish wear, the resistance measurements will increase. So, after some amount of data collection, a cost effective maintenance schedule can be established.
Testing floor matting
Floor matting can be checked using a resistance meter. Surface resistance meters are designed to measure resistance point-to-point (Rp-p) or surface to ground (Rg) in accordance with EN 61340-5-1 Electrostatics and its test method IEC 61340-2-3.
ESD Shoes or Foot Grounders play an essential part in the flooring/footwear system.
Before handling ESD sensitive devices, visually inspect your ESD footwear for any damage. Just like wrist straps, footwear should be checked while being worn using a wrist strap/footwear tester.
Checking foot grounders using 99032
Records of each test should be kept. Analysis and corrective action should take place when a footwear tester indicates a failure. Footwear needs to be checked daily.
Re-using shielding bags is acceptable as long as there is no damage to the shielding layer. Shielding bags with holes, tears or excessive wrinkles should be discarded.
Make sure your ESD shielding bags are un-damaged
It is up to the user to determine if a shielding bag is suitable for re-use or not. The testing of every bag before re-use is not practical. Many companies will discard the shielding bag once used and replace it with a new one. Others will use a system of labels to identify when the bag has gone through five handling cycles:
- Non-reusable labels are used that require the label be broken to open the bag.
- The bag is then resealed with a new label.
- When there are five broken labels, the bag is discarded.
The same principle applies to other ESD packaging, e.g. component shippers.
Ionisers are intended to neutralise static charges on insulators thereby reducing their potential to cause ESD damage. However, poorly maintained ionisers with dirty emitter pins and out-of-balance ionisers can put a charge on ungrounded items.
Remember to clean ioniser emitter pins and filters regularly. You can now even purchase ionisers that will alarm when emitter pins need to be cleaned or the ioniser is out of balance.
Checking ionisers using 50598
The EMIT Ionisation Test Kit 50598 allows the Digital Static Field Meter 50597 to be used to measure the offset voltage (balance) and charge decay of ionisation equipment. The Test Kit also includes a Charger used to place a ±1000V charge on the 50567 Conductive Plate, making it possible to measure the discharge times of air ionisation equipment per ANSI/ESD SP3.3 Periodic Verification of Air Ionizers.
Wrist Strap/Footwear and Resistance Testers etc.
So you check your wrist straps and/or footwear and bench and/or floor matting regularly. But have you remembered the testers themselves? What good do all the checks do, if the testers you use are out-of-spec and show you incorrect results?
Yearly calibration is recommended – many manufacturers offer a calibration service or alternatively you can purchase calibration units from them and perform the calibration yourself.
So there you have it – a list of the most commonly used products in your ESD Protected Area (EPA) that you should check on a regular basis.
Questions for you: Do you have a verfication plan in place? If so, how often do you check your ESD protection products?
Today we want to talk about a subject many users forget about when it comes to ESD protection: periodic verification.
Whilst many people understand the basic concepts of ESD and as a result insist on a properly equipped ESD Protected Area (EPA), they then forget all about it. They use the same products day-in, day-out, year after year, without knowing if their products are actually still working properly.
So today we want to look at the most common products in your EPA that you should be checking on a regular basis. And because there are quite a few product groups to discuss, we have split this post in 2 parts – we don’t want to scare you away with a never-ending blog post…
Why periodic verification?
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 damage your ESD sensitive devices potentially costing your company money. The problem with many ESD protection products (think wrist straps!) is that you can’t always see the damage. Just by looking at a coiled cord that has no visibly damage to the insulation you would not know if the conductor on the inside is damaged. That’s where periodic verification comes into play.
ESD protected area (EPA) products should be tested:
- Prior to installation to qualify product for listing in user’s ESD control plan.
- During initial installation.
- For periodic checks of installed products as part of IEC 61340-5-1 Edition 1 2007-08 clause 5.2.3 Compliance verification plan.
It’s #3 we will be focusing on in this 2-part series.
The purpose of ESD bench matting is to ensure that when charged conductors (conductive or dissipative) are placed upon the surface, a controlled discharge occurs and electrostatic charges are removed to ground. However, this only occurs if the ESD work surface is actually connected to ground. If the matting is out-of-spec, not grounded at all, the stud on the mat has become loose or the ground cord has become disconnected, charges cannot be removed.
Many companies use a daily checklist, which includes the operator having to verify that ground cords are firmly connected.
Remember to regularly clean your bench matting to maintain proper electrical function (e.g. Reztore Surface and Mat Cleaner). Do not use cleaners with silicone as silicone build-up will create an insulative film on the surface.
The company’s compliance verification plan should also include periodic checks of work surfaces measuring:
- Resistance Point-to-Point (Rp-p) and
- Resistance-to-ground (Rg).
Testing a working surface using 99026
Surface resistance testers can be used to perform these tests in accordance with EN 61340-5-1 Electrostatics and its test method IEC 61340-2-3; if these measurements are within acceptable ranges, the worksurface matting and its connections are good.
As discharges from people handling ESD sensitive devices cause significant ESD damage, the wrist strap is considered the first line of ESD control.
Before handling ESD sensitive items, you should visually inspect the wrist strap to see if there are any breakages etc. The wrist strap should then be tested while worn using a wrist strap tester. This ensures all three components are checked: the wrist band, the ground cord (including resistor) and the interface with the wearer’s skin. Records of each test should be kept. Wiggling the resistor strain relief portion of the coil cord during the test will help identify failures sooner. Analysis and corrective action should take place when a wrist strap tester indicates a failure.
Checking wrist straps using 99031
It is recommended that wrist straps are checked at least daily. An even better solution to daily wrist strap checks is the use of continuous monitors. They will alarm if the person or work surface is not properly grounded.
A note on worksurface matting and wrist straps: if you are using earth bonding points, earth bonding bars etc. to ground the operator and/or bench matting, remember to inspect and test those regularly as well (every 6 months for example).
Keep your eyes peeled for our follow-up post.
We get asked about ionisers all the time:
- What are they used for?
- How do they work?
- What type to choose?
With today’s post we want to answer one of the more common questions: what type of ioniser to select for your application. So let’s jump right in…
What is an Ioniser?
An ioniser creates great numbers of positively and negatively charged ions. Fans help the ions flow over the work area. Ionisation can neutralise static charges on an insulator in a matter of seconds, thereby reducing their potential to cause ESD damage.
Types of Ionisers
Electrical ionisers generate air ions by a process known as corona discharge. A high voltage is applied to one or more sharp points and quantities of air ions are created. Fans or blowers may be incorporated in the ioniser to assist the movement of the ions and enhance performance.
- AC Ionisers
AC Ionisers use a transformer to multiply the AC power line voltage. AC stands for Alternating Current, which means that the power cycles from positive to negative sixty times per second. The AC ioniser therefore produces both positive and negative ions from the same points or emitters. The drawback with this approach is that many ions recombine because the cycle frequency is too fast. For this reason, most AC ionisers rely on fans or blowers to be effective.
- Pulsed DC Ionisers
Pulsed DC ionisers utilise separate power supplies to generate positive and negative voltages and usually each power supply has it’s own dedicated emitters. The power supply alternates between positive and negative, but usually at a lower frequency than AC units. In this way, ion recombination is reduced and performance is increased. Airflow may then be reduced for operator comfort without sacrificing much performance. With pulsed DC, it is important to cycle at least two or three times per second to prevent harmful voltage swings on the object being protected.
- Steady-state DC Ionisers
Steady-state DC ionisers also employ separate power supplies and emitters, but instead of alternating positive and negative, both supplies are on all the time as the name implies. As would be expected, there is some degree of recombination, however, the ion density is still greater because of continuous operation of both supplies. The offset or balance voltage at the output will normally be more consistent than pulse units.
There are also nuclear types of ionisers which are non-electric. They are more frequently used in flammable or explosive environments for applications other than electronics.
- Room Ionisation
This type of configuration will typically have multiple emitters just below ceiling height and will rely on some amount of air movement for moving the ions down to bench level. It used to be considered as the most effective way to protect large areas against ESD hazards. However, these days localised workstation ionisation is recommended:
- Product sensitivity has become much greater and long decay times of room ionisation cannot be tolerated.
- With room ionisation often only a fraction of the ionised area may be ESD sensitive. Localised ionisers bring protection to the areas where it’s needed and performance is often 10 times faster than the ceiling height system.
- Localised ionisation moves with the workstation (or to a new workstation) making it much more flexible with changing production line layouts.
Advantages Disadvantages + Effective for large areas – Long decay times – Cannot easily be moved once set-up
- Workstation Ionisers
These come in many shapes and sizes. Probably the best known type is the bench top ioniser which is about the size of an iPad mini and about 10cm deep. They’ve been around for many years and are to this day still in high demand. Over the years, smaller and lighter units were developed. As workstation space is incredibly valuable, many users prefer the smaller units. Some bench top ionisers can even be suspended above the bench using a flexible mounting arm.
Whatever style is chosen, care should be taken to assure that items normally on the bench would not obstruct the flow of ionised air.
A Bench Top Ioniser mounted using an adjustable arm – find more informaiton here
A real benefit of bench top ionisers is the fact that they can easily be moved between workstations. So if you only have a small EPA with a few users and shared workload, you can save money by moving one ioniser between different benches.
Advantages Disadvantages + Compact – Potential obstruction of air flow + Lightweight + Portable
- Overhead Ionisers
Overhead ionisation was established to solve the problem of items on a bench blocking the flow of ionised air. Overhead ionisers have a unique hanging capability and are suspended about 45cm to 60cm above the bench – either by hanging from chains or by using mounting brackets attached to a shelf or bench.
Example of an Overhead Ioniser – find more information here
Using this method of ionisation makes it very unlikely for items to block the flow of ionised air to the item being protected. In addition, the downward airflow is more consistent over the entire bench. To ensure that adequate air is delivered an overhead ioniser with 2 to 4 fans should be used. Overhead Ionisation are ideal for areas where bench space is limited.
Advantages Disadvantages + Large & consistent air flow coverage – Heavy + Don’t take up valuable workspace + Items unlikely to block air flow
- Forced Air Ionisers
Most companies address ElectroStatic Attraction, visual imperfections and contamination issues by dislodging charged dust and debris with compressed air ionisers. They use compressed air or nitrogen to neutralise static charges in localised areas – they are a quick “point-and-shoot” option. They are either hand-held or may be mounted in a fixed location.
Example of an Forced Air Ioniser – find more information here
The main advantage of this type is that the user has the benefit of a strong air blast (20 to 100 P.S.I.) to help dislodge contamination, while the ionisation in the air stream eliminates the static attraction of the particles at the same time. Hand-held air nozzle types will usually have a trigger or push-button to activate the air and ion flow, while the stationary-mounted type is frequently remote controlled with a foot pedal, photo sensor or some other switch closure.
Advantages Disadvantages + “Point-and-shoot” operation – Use valuable workstation space + Strong air blast
What type of ioniser you choose depends on a lot of different factors. There is no right or wrong – just different options.
A few things you should consider before making any decisions:
- Type of operation
Depending on the work your operators are doing, one type/configuration of ioniser may have more benefits then another. For example, if your workspace is limited, an overhead ioniser might be the answer. On the other hand if there is an issue with debris & dust in your operation, then a compressed air ioniser would be better suited.
- Features required
Does your ioniser need to be made of stainless steel? Does it need to use zero-volt technology? Do activities need to be monitored and recorded with some sort of software? Make a list of what is an absolute must and where you can compromise – see next point.
- Available budget
Even though this one is the last one in this list, it by no means is the least important factor. Quite contrary, it’s generally one of the main considerations when investing in an ioniser. However, it kind of goes hand in hand with the previous 2 points. So you may have to make compromises, e.g. on the features, depending on what monies are available…
Ionisation is one of the best methods of removing charges from insulators and as a result plays an important role in controlling ESD. Remember though: an ioniser is a secondary form of defence and does not eliminate the need for standard ESD control devices such as wrist straps, heel grounders and work surface mats. It is only one element in an effective ESD programme.
Also, ionisers require periodic cleaning of emitter pins and the offset voltage must be kept in balance. Otherwise, instead of neutralising charges, if it is producing primarily positive or negative ions, the ioniser will place an electrostatic charge on items that are not grounded.
Protektive Pak® Material is made from static dissipative impregnated corrugated material with a buried shielding layer – it provides static shielding to protect ESD sensitive items from ElectroStatic charges, and ElectroStatic Discharges [ESD].
Introduction to Protektive Pak® Material
So now you’re probably wondering what’s different about this type of material – loads of companies out there offer similar products, right? That’s true – BUT what makes Protektive Pak® Material so unique is that its ESD properties are manufactured into the liners of the material itself. Many other materials have a coating or paint applied that gives them their ESD properties. This in itself is not a problem. However, it becomes an issue if the outer layer of your ESD container is damaged.
Protektive Pak® Inplant Handler – for more information click here
Have you ever removed tape from your ESD container or accidently pierced the surface with a sharp object? If you have, chances are you’ve found the black coat give way to a lighter brown material. That’s your ESD properties gone potentially damaging your ESD sensitive devices inside the ESD container. This will not happen with Protektive Pak® Material – even if the outer layer is damaged, your ESD sensitive items are still protected. Not convinced? Check-out this video.
Protektive Pak® Circuit Board Shippers – for more information click here
Advantages of Protektive Pak® Material:
Independent ESD tests have proven that Protektive Pak® Impregnated Corrugated Material is superior! Click here to see the full test report. The bottom line is:
- Protektive Pak® impregnated corrugated material has a buried shielding layer.
- Protektive Pak® impregnated corrugated material equals or exceeds the discharge shielding capabilities of a coated box.
- Protektive Pak® impregnated corrugated material has discharge shielding capabilities equal to a metal-out shielding bag.
- Protektive Pak® impregnated corrugated material meets the ANSI/ESD S541 recommendation, avoiding rapid discharge when contacting ESD sensitive items – coated boxes DO NOT.
Comparing Impregnated Corrugated Protektive Pak® and Coated Materials
Now that we have talked about the advantages of Protektive Pak® Material – how exactly does it compare to the more common coated materials out there on the market? The below table provides a summary:
|Impregnated vs. Coated Material|
Manufactured by one paper mill with computerized control, resulting in consistent high quality.
|Manufactured without computer controls and applied at various geographical locations, resulting in quality variations.|
Carbon is added during the paper making process. The paper is a 6-layer process. The top surface layer is static dissipative, measuring 107 to 109 ohms. The conductive layer is in the 5th layer from the surface measuring <104 ohms.
|Material is coated or printed with carbon loaded black ink which is then coated with a clear sealer to help coating stay on. Shielding layer is very close to surface and high carbon content can bleed through. Result is very poor and inconsistent static dissipative effectiveness.|
|3||LOWER SULPHUR CONTENT
Manufactured from 100% recycled paper with consistently low sulphur content.
|Manufactured from either recycled or virgin paper or a combination of both. sulphur content may be low or high which can cause corrosion to leads and circuits.|
1,000 Times Thicker: Abrasion tests have shown no loss in particles at 100 cycles, only 1% loss for 200 cycles and 60% loss for 500 cycles.
|Tests have shown a 50% loss in particles in only 10 cycles and a 100% loss in 100 cycles.|
|5||SLOWS RAPID DISCHARGE
Burying the conductive layer under a dissipative surface reduces the potential for a rapid discharge when contacted by a charged device.
|A very conductive surface that may pose a charged device model (CDM) ESD danger to components stored in open bin boxes, in-plant handlers, shippers, totes, nesting trays, etc.|
|6||BETTER SHIELDING EFFECTIVENESS
Shielding effectiveness is equal to or greater than coated conductive materials.
|Some coated products shield poorly due to inconsistent application procedures by some manufacturers.|
More durable structure, 1,000 times thicker, which consistently shields your product from ESD, is also safer and better for the environment.
|Simple structure which can lack consistency of ESD shielding, durability and safety.|
All microscopic photos are approximately the same scale. A PDF version of the above table is available here.
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. 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 188.8.131.52.4 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.
The 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 Charleswater Multi-Mount Monitor (99129) 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.
The Jewel Mini Workstation Monitor (99135) 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 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.
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:
• 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.
An 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]
Example 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.
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.
Example 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.
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”.
The 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.
In the last post we talked about why insulators in your ESD Protected Area (EPA) can cause problems and started creating a list of the most commonly used insulative items that you should replace with ESD safe alternatives. Missed the post? Catch-up here.
So let’s continue with our list:
If you work with solder irons or perform various cleaning tasks at your ESD workstation, you will likely be using water or some sort of cleaning agent. Where do you store those liquids? Plastic cups? If so, that’s a BIG no-no and if you’re truly committed to your ESD Control Programme, you should be switching to ESD protective bottles immediately. ESD dispensing bottles come in all sorts of sizes, colours and with different pumps or spouts. Whatever type you need for your application, you will generally be able to find an ESD alternative.
Examples of ESD safe dispensing bottles – more information
ESD dispensing bottles are dissipative and high-quality types will have no migratory additives which reduces the chance for contamination from the bottle.
Summing-up the most important points in regards to using brushes in your ESD protected area (EPA):
- Use dissipative or conductive brushes in an EPA.
- All portions of the brush (handle and bristles) need to be conductive/dissipative.
- Operators need to be grounded during use.
- Choose dissipative bristles if your product/assembly may be holding a charge and Charged Device Model (CDM) failures are a concern.
Examples of dissipative and conductive brushes – more information
Probes are ideal for opening plastic cases such as MP3 players, cell phones, laptops, etc. and for popping out batteries. They are also used for holding, probing, and manipulating wires and components during assembly and soldering. ESD safe versions are made of nylon, wood or stainless steel.
Examples of ESD safe probes – more information
The hygroscopic (readily accepts moisture) properties of Nylon will make this tool suitable for use around ESD sensitive components after a few minutes of handling the tool with bare hands. If used with gloves in a clean environment the tools must be dipped in a topical antistatic solution before use in sensitive areas. Topical treatment should be repeated at six month intervals. Without exposure to moisture or antistatic treatment, Nylon is in the insulative resistance range and charges will not be removed to ground.
Wood is considered a safe material for use in ESD sensitive areas. It is hygroscopic and has a low propensity for triboelectric charge generation under most conditions.
Any charge on a stainless steel probe can be grounded when it is placed on an ESD protected work surface.
Waste bins and bin liners
ESD safe waste bins are generally conductive and are useful in ESD Protected Areas where waste accumulates and cannot be conveniently removed except in bulk. By placing them on a grounded floor, electrostatic charges are removed to ground. They do not require separate grounding when placed on a grounded surface.
Examples of waste bins and bind liners – more information
If you’re currently using standard bin liners, replace those with non-tribocharging ESD versions. Even at low humidity they do not become charged with static electricity and are designed for use in ESD protected areas where electrostatic sensitive devices are present.
And there you have it – a list of of tools and accessories that you should be replacing with ESD protective alternatives. Can you think of any others? Let us know in the comments!
So you finally have your ESD Protected Area (EPA) in place – you’ve invested in ESD working surface & floor matting, provided wrist straps & foot grounders for your workers and you control access to your EPA. But still: you are experiencing a large number of failures when inspecting your components after the production stage. The reason may be simpler than you think. Read on to find out more.
Conductors and Insulators
Materials that easily transfer electrons (or charge) are called conductors and are said to have “free” electrons. Grounding works effectively to remove electrostatic charges from conductors to ground.
Materials that do not easily transfer electrons are called insulators or non-conductors. An insulator will hold the charge and cannot be grounded; therefore, the charge cannot dissipate in a controlled way. This could lead to static damage of nearby sensitive components as there can be a rapid, spontaneous transfer of electrostatic charge.
So how do you control static electricity in the workplace? Easy – just follow these principles:
- Remove all unnecessary insulators (non-conductors),
- Replace all non-conductive materials with dissipative or conductive materials and
- Ground all conductors.
So what insulators in your EPA can be replaced with dissipative or conductive materials? Here is a list of the most commonly used insulative items and their replacement options:
Paper is everywhere in the workplace and an ESD Protected Area is no exception. The problem with regular paper is that it is insulative but tends to be low charging because it is hygroscopic (readily absorbs moisture). The primary concern with paper is placing ESD sensitive items on the paper interfering with the path-to-ground of the grounded ESD mat. Best practice is to use dissipative paper or have regular insulative paper in dissipative document holders or wallets.
Dissipative self-stick notes – more information
EN 61340-5-1 states: “Paperwork inside the EPA shall either be kept in containers conforming to the requirements of table 2 or shall not generate a field in excess of that specified in paragraph 5.3.5 (ESDS should not be exposed to electrostatic fields in excess of 10 kV/m).”
There are a number of products available on the market that can assist with handling documents/paper in ESD Protected Areas:
- ESD safe document holders and wallets
Document wallets and holders are designed for use within ESD Protected Areas in accordance with EN 61340-5-1. They are static dissipative which means charges are removed to ground when placed on a grounded working surface or handled by a grounded operator.
Examples of ESD safe document wallets and holders – more information
- ESD safe ring binders and clipboards
Ring Binders and clipboards are designed to replace high charging insulative regular binders for use within ESD protected areas. They come in different widths with different ring sizes and various rings. Just like document holders/wallets they are static dissipative so charges are removed to ground when placed on a grounded working surface or handled by a grounded operator.
Examples of ESD safe ring binders and clipboards – more information
- ESD safe letter trays
Generally conductive, any electrostatic charges on letter trays are removed to ground when the tray is placed on a grounded working surface or touched by a grounded operator. They do not require separate grounding when laid on a grounded surface.
Example of ESD safe letter tray
We all love our cup of tea or coffee in the morning and most of us have water bottles on stand-by throughout the day. But do you know how much charge a foam or plastic cup generates? Well, let’s just say it’s enough to damage your precious sensitive components! The answer: ESD safe drinking cups and water bottles. There aren’t too many options out there so make sure you do your research before purchasing.
ESD safe water bottles are generally dissipative so charges are removed when placed on a grounded surface or handled by a grounded operator.
Menda drinking cup – more information
One option for a drinking cup (for hot drinks) is the MENDA insulated drinking cup. It is low charging and the stainless steel portion is grounded when picked up by a grounded operator or when placed on a grounded ESD working surface.
Stay tuned for our follow-up post.
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:
- Prior to installation to qualify product for listing in user’s ESD control plan.
- During the initial installation.
- For periodic checks of installed products as part of IEC 61340-5-1 Edition 2 2016 clause 5.2.3 Compliance verification plan.
“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.
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.
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.
Creating a Compliance Verification Plan using ESD flooring as an example
The below table outlines a sample verification plan using ESD flooring for demonstration purposes.
|1||ESD Control Item||ESD Floors in Packaging area and main EPA|
If anything unusual is observed, inform ESD coordinator to take action.
|Measurement||6-monthly: follow instructions outlined in #3 to #7|
|3||Acceptable Limits||Resistance-to-Ground Rg < 1 x 109 ohms
[IEC 61340-5-1:2016 paragraph 184.108.40.206 ESD control items]
|4||Test Method||Test Procedure (simplified test procedure in accordance with concepts outlined in IEC 61340-4-1):
Sally Sample (back-up)
|7||Reporting||A. Use ESD Floor Test Record for 6-monthly measurement
audits and record measurements in appropriate column.
B. If audit passes, move on to D.
C. If audit fails:
D. Email summary of the audit results to the management team
The spreadsheet will automatically update all other
E. Note any failings in the body of the email and name person
F. The ESD coordinator will save a copy of the email on the
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.