Personnel Grounding

Many companies implement an ElectroStatic Discharge (ESD) Control Program with the aim of improving their operations. Effective ESD control can be a key to improving:

  • Productivity
  • Quality
  • Customer Satisfaction

Problems arise when an organization invests in ESD protective products and/or equipment and then misuses them. Misuse of ESD protective products and/or equipment wastes invested money and can also be causing more harm than good. Today’s blog post will highlight some of the major issues we have come across and how you can avoid or fix them.

About ESD Control and ESD Protection

Remember that for a successful ESD control program, ESD protection is required throughout the manufacturing process: from goods-in to assembly all the way through to inspection. Anybody who handles electrical or electronic parts, assemblies or equipment that are susceptible to damage by electrostatic discharges should take necessary precautions.

Just like viruses or bacteria that can infect the human body, ESD can be a hidden threat unable to be detected by human eyes. Hidden viral/bacterial threats in hospitals are controlled by extensive contamination control procedures and protective measures such as sterilization. The same principles apply to ESD control: you should never handle, assemble or repair electronic assemblies without taking adequate protective measures against ESD.

Common Mistakes in ESD Control

1. Ionizers are poorly maintained or out-of-balance

If an ionizer is out of balance, instead of neutralizing charges, it will produce primarily positive or negative ions. This results in placing an electrostatic charge on items that are not grounded, potentially discharging and causing ESD damage to nearby sensitive items.

Step3 Remember to clean emitter pins and filters using appropriate tools. Create a regular maintenance schedule which will extend the lifespan of your ionizers tremendously.

Consider using ionizers with “Clean Me” and//or “Balance” alarms. These will alert you when maintenance is required.

Step2.png All ionization devices will require periodic maintenance for proper operation. Maintenance intervals for ionizers vary widely depending on the type of ionization equipment and use environment. Critical clean room use will generally require more frequent attention. It is important to set up a routine schedule for ionizer service.”

[ESD TR20.20 Handbook Ionization clause 15.8 Maintenance / Cleaning]

If you would like to learn more about how ionizers work and what type of ionizer will work best for your application, check out this post for detailed coverage.

2. ESD Garments are Ungrounded

We’ve seen it so many times: operators wearing an ESD coat (without appropriate wrist straps and/or footwear/flooring) thinking they are properly grounded. However, without proper electrical bonds to a grounding system they are not grounded!

Step3 Every ESD garment needs to be electrically bonded to the grounding system of the wearer. Otherwise it just acts as a floating conductor. There are a few options to choose from:

  • Wrist Straps
  • ESD footwear/flooring
  • Hip-to-Cuff grounding
Step2 After verifying that the garment has electrical conductivity through all panels, the garment should be electrically bonded to the grounding system of the wearer so as not to act as a floating conductor.

This can be accomplished by several means:

  1. Ground the garment to the body through a wrist strap-direct connection with an adapter.
  2. Ground the garment through conductive wrist or heel cuffs in direct contact with the skin of a grounded operator.
  3. Ground the garment through a typical separate ground cord, directly attached to an identified groundable point on the garment.
  4. Garments should be worn with the front properly snapped or buttoned to avoid exposure of possible charge on personal clothing worn under the garment.

[ESD TR20.20 Handbook Garments clause 19.4 Proper Use]

ESD clothing loses their ESD properties over time. It is therefore an important part of the ESD Control Program to incorporate periodic checks (see #3 below) of ESD garments.

If you need more information on ESD garments, we recommend having a look at this post.

3. No Compliance Verification Plan / Not Checking ESD Control Products

Companies can invest thousands of dollars in purchasing and installing ESD control products but then waste their investment by never checking their ESD items. This results in ESD equipment that is out of specification. Without the tools in place to check their ESD items, companies may have no idea if they are actually working correctly. Remember: ESD products (like any other product) are subject to wear and tear, and other errors when workstations get moved, ground cords get disconnected…etc. The list goes on.

Step3 When investing in ESD control products, make sure you also establish a Compliance Verification Plan. This ensures that:

  • ESD equipment is checked periodically
  • Necessary test equipment is available
Step2 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.
”[ANSI/ESD clause 7.4 Compliance verification plan]

We provide detailed instructions on how to create a Compliance Verification Plan in this post.

4. Improperly Re-Using Shielding Bags / Using Shielding Bags with Holes or Scratches

ESD Shielding Bags are used to store and transport ESD sensitive items. When used properly, they create a Faraday Cage effect which causes charges to be conducted around the outside surface. Since similar charges repel, charges will rest on the exterior and ESD sensitive items on the inside will be ‘safe’. However, if the shielding layer of an ESD Shielding Bag is damaged, ESD sensitive items on the inside will not be protected anymore.

Step3 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.

Use a system of labels to identify when the bag has gone through five (5) handling cycles. When there are five broken labels, the bag is discarded.

Step2 ESD shielding packaging is to be used particularly when transporting or storing ESD sensitive items outside an ESD Protected Area.

Transportation of ESDS items outside an ESD Protected Area (hereafter referred to as “EPA”) requires enclosure in static protective materials, although the type of material depends on the situation and destination. Inside an EPA, low charging and static dissipative materials may provide adequate protection. Outside an EPA, low charging and static discharge shielding materials are recommended. While these materials are not discussed in

the document, it is important to recognize the differences in their application. For more clarification see ANSI/ESD S541.

[ANSI/ESD Foreword]

This post provides further “dos and don’ts” when using ESD Shielding Bags.

5. Using Household Cleaners on ESD Matting

The use of standard household cleaners on ESD matting can put an ESD Control Program at risk and damage the ESD properties of items. Many household cleaners contain silicone or other insulative contaminants which create that lovely shine you get when wiping surfaces in your home. The problem is that silicone and other chemical contaminates can create an insulative layer which reduces the grounding performance of the mat.

Step3 Don’t spend all this extra money on ESD matting and then coat it with an insulative layer by using household cleaners. There are many specially formulated ESD surface and mat cleaners available on the market. Only clean your ESD working surfaces using those cleaners.
Step2 “Periodic cleaning, following the manufacturer’s recommendations, is required to maintain proper electrical function of all work surfaces. Ensure that the cleaning products used to not leave an electrically insulative residue which is common with some household cleaners that contain silicone.”

[ESD TR20.20 Handbook Worksurfaces clause 10.5 Maintenance]

Conclusion

There are many more issues we see when setting foot into EPAs and the above list is by no means complete. These are the most common issues we’ve found when assessing EPAs.

It is important to train all personnel using ESD products and/or equipment to follow proper ESD control programs, and maintenance procedures to avoid common ESD control mistakes. Basic ESD control principles should be followed for an ESD control program to be successful:

  • Ground conductors.
  • Remove, convert or neutralize insulators with ionizers.
  • Shield ESD sensitive items when stored or transported outside the EPA.

What mistakes do you commonly see when walking through an EPA? Let us know what you commonly see in the comments and your solutions for fixing them!

For more information on how to get your ESD control program off the ground and create an EPA, check this post.

When talking about ESD Classifications a little while ago, we identified a “class 0” item as withstanding discharges of less than 250 volts.

The introduction of ANSI/ESD S20.20 states: “This standard covers the requirements necessary to design, establish, implement and maintain an Electrostatic Discharge (ESD) Control Program for activities that manufacture, process, assemble, install, package, label, service, test, inspect or otherwise handle electrical or electronic parts, assemblies and equipment susceptible to damage by electrostatic discharges greater than or equal to 100 volts Human Body Model (HBM) and 200 volts Charged Device Model (CDM).

So how do you handle items that are susceptible to voltages of less than 100V? That’s what we’re going to answer in today’s blog post.

 

Introduction

Years ago, it was common for devices to be vulnerable to voltages greater than 100 V. As the need for smaller and faster devices increased, so did their sensitivity to ElectroStatic Discharges as circuit-protection schemes were removed to stay ahead of the market. These new extremely sensitive components are now susceptible to discharges nearing 0 V. This causes problems for companies handling these devices: while their ESD program may be in compliance with the ESD Standard, extremely sensitive devices require tighter ESD Control to protect them from ESD failures.

 

What is a “Class 0” device?

Before moving any further, we need to qualify the term “class 0”. As stated above, the HBM Model refers to any item with a failure voltage of less than 250 V as a “class 0” component. However, in recent times, the term has been used more and more to describe ultra-sensitive devices with failure voltages of less than 100 V. Whilst the following tips and tricks work on any “class 0” item, they are specifically designed to protect extremely sensitive items that withstand discharges of less than 100 V.

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Ultra-sensitive devices are extremely common

Before Updating Your ESD Program

“Class 0” refers to a wide range of items and there are a few things you should remember before making any changes to your existing ESD program:

  1. Verify what ESD Model your company/engineers/customers etc. are referring to. As we have learnt in the past, there are different ESD models (HBM, CDM, MM) as well as individual classifications for each model. A lot of people get confused when it comes to citing ESD classifications. There is only one “class 0” which refers to the human body model (HBM) but it’s always best to check.
  2. Check the specific withstand voltage an individual part is susceptible to. “Class 0” refers to all items that withstand discharges of less than 250 V. However, there is a big difference between a failure voltage of 240 V or 50 V. You need to have detailed ESD sensitivity information available before being able to make decisions on how to improve your existing ESD control program. This step is part of creating a compliance verification plan.
  3. A part’s ESD classification is only of importance until it is ‘merged’ into an assembly. So, the ESD classification of a device only refers to the stand-alone component. Once it goes into another construction, the classification of the whole assembly is likely to change.

 

Tips for handling “Class 0” Items

Below are 6 tips that will help your company to upgrade your ESD control program so you can effectively and efficiently handle ultra-sensitive items without risking ESD damage.

One thing to note: The best approach to stay ahead of the game is taking proactive actions. It is critical to figure out how to protect your components from ESD damage before you receive them. If actions are taken after components are received, the components are susceptible to receiving ESD damage.

 

1. Improve Grounding

Inside an EPA, all conductors (including people) are grounded. Now you’re probably thinking: “But I’ve already grounded my operators and worksurfaces. What else is there left to do?”. Firstly, well done for properly grounding the ‘objects’ in your EPA. The next step is to adjust and improve your current program to allow for even better protection. Here are some suggestions:

Personnel:

  • Decrease the wrist strap and ESD footwear upper limit. The ESD Association has test data showing charge on a person is less as the path-to-ground resistance is less.
  • Use continuous monitors and ESD smocks
  • Introduce/increase the use of ESD flooring
  • Use sole or full coverage foot grounders (rather than heel grounders)
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Full coverage foot grounders are recommended when handling ultra-sensitive devices

Worksurfaces:

  • Reduce the required limit for Point-to-Point resistance of 1 x 109 per the ESD Standard to 106 to 108 ohms (see #5). The reason for this reduction is simple: 1 x 109 is too high as it still produces thousands of volts of in electrostatic charges. However, the resistance cannot be too small either as this can lead to a sudden ‘hard discharge’ potentially damaging ESD sensitive components.

Other:

  • Improve grounding of carts, shelves and equipment to Ground
  • Minimize isolated conductors like devices on PCBs

 

2. Minimize Charge Generation

The best form of control is to minimize charge generation. First, you should always use shielding packing products like bags or containers (especially when outside an EPA) as these protect from generating charges in the first place. For more information on choosing the correct type of ESD Packaging, we recommend reading this post.

The next step is to eliminate charges once they are generated – this can be achieved through grounding and ionization. We’ll cover ionization in #3 and #4. We’ve already talked about improved grounding in #1. However, for ultra-sensitive components, we also recommend the following:

  • Personnel: Use low-charging floor finish
  • Surfaces: Use low-charging topical antistatic treatments

Both types of ESD products create a low tribocharging coating which allows charges to drain off when grounded. The antistatic properties will reduce triboelectric voltage to under 200 volts.

 

3. Remove Insulators

When talking about conductors and insulators, we explained that insulators cannot be grounded and can damage nearby sensitive devices with a sudden uncontrolled discharge. It is therefore critical to eliminate ALL insulators that are not required in your EPA: plastic cups, non-ESD brushes, tapes etc. How? Here are a couple of options:

  • Replace regular production supplies and fixtures with dissipative, low charging versions, e.g. ESD dissipative brushes, ESD dispensers, ESD tape, ESD Chairs etc.
  • Shield charges on clothing by using ESD smocks.
Workstation.png
Use ESD safe accessories whenever possible

If an insulator is absolutely necessary for production and cannot be removed from the EPA, you could consider a topical treatment which will reduce triboelectric charges.

Is this not an option, then move on to tip #4.

 

4. Use Ionization

First, ionization is not a cure-all. We’ve learnt that ionizers neutralize charges on an insulator.

However, that does not mean that you can just have any insulator in your EPA because the ionizer will “just fix it”. No, in this instance, prevention is generally a better option than the cure. So, your priority should ALWAYS be to remove non-process essential insulators from your EPA – see tip #3. If this is not possible – then ionization becomes essential.

Ionization:

  • Ionizers can be critical to reduce induction charging caused by process necessary insulators
  • Ionizers can be critical in eliminating charges on isolated conductors like devices on PCBs
  • Offset voltage (balance) and discharge times are critical considerations depending on the actual application
  • Ionization can reduce ElectroStatic Attraction (ESA) and charged particles clinging and contaminating products.

It is recommended to use ionizers with feedback mechanisms, so you’re notified if the offset voltage is out of balance.

 

5. Increase ESD Training and Awareness

ESD Training is a requirement of every ESD Program. When handling ultra-sensitive devices, it is even more important to remind everyone what pre-cautions are necessary to avoid damage. Regular ‘refreshers’ are a must and it is recommended to verify the effectiveness of the training program, e.g. through tests. So, who, when and what should be taught?

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ESD Training is a vital part of every successful ESD Control Program
  • ESD training needs to be provided to everyone who handles ESD sensitive devices – that includes managers, supervisors, subcontractors, visitors, cleaners and even temporary personnel.
  • Training must be given at the beginning of employment (BEFORE getting anywhere near a sensitive products) and in regular intervals thereafter.
  • Training should be conducted on proper compliance verification procedures and on the proper use of equipment used for verification.

 

6. Create an enhanced Compliance Verification Plan

We talked in a previous post about compliance verification, what it is and how to create a plan that complies with the ESD standard. So, if you already followed our steps and have a plan in place, here are a few tips to improve your compliance verification plan:

  • Use a computer data collection system for wrist straps and foot grounders testing
  • Increase the test frequency of personnel grounding devices from once per day to every time the operator enters the EPA
  • Use continuous monitors where operators are grounded via wrist straps. Consider computer based monitor data collection system, e.g. SMP. This should include continuous monitoring of the mat Ground.
  • Use Ground continuous monitors, e.g. Ground Master. At a large facility, the most frequent reoccurring violation is the ESD mat ground cord either becoming disconnected from the mat or grounding point. As Ground continuous monitors will only test the fact that the mat is grounded, it is still imperative that the Resistance to Ground of the mat is regularly tested. Remember that the use of improper mat cleaners can raise the mat surface resistance above the upper recommended level of <109
  • Test ionizers more frequently or consider self-monitoring ionizers. Computer based data collection systems are a good alternative, too.
  • Increase the use of a static field meter and nano coulomb testing to verify that automated processes (like auto insertion, tape and reel, etc.) are not generating charges above acceptable limits.

 

Conclusion

“Class 0” items require additional measures of ESD protection due to their sensitivity to ESD damage. The best way to protect these ultra-sensitive components is to increase ESD protective redundancies and periodic verifications to all ESD Control technical elements.

To decrease the probability of ESD damage while handling ultra-sensitive items, additional precautions are required. This includes additional and/or more stringent technical requirements for ESD control products, increasing redundancies, and more frequent periodic verifications or audits.

Additionally, ESD control process systems should be evaluated as to their performance as a system. It is important to understand how the technical elements in use perform relative to the sensitivity of the devices being handled. Thus, tailoring the process to handle the more sensitive parts. For example: If the footwear/flooring allows a person’s body voltage to reach 80 volts and a 50 withstand voltage item gets introduced into the process, you must either allow only handling via wrist straps or would have to find a way to modify the footwear/flooring performance to get peak voltages below the 50 volt threshold.

Remember: The ESD Standard gives recommendations that will always be behind current/future developments. As soon as a Standard is published, technology will have progressed. In order to protect your devices and company reputation for reliable devices – it is recommended your company take responsibility to implement methods/procedures that exceed the recommendations of the ESD Standard to fit your sensitive component requirements.

 

References:

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 link 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 in today’s post so let’s jump right in!

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, ESD sensitive devices can be damaged, potentially costing your company thousands of dollars.

Wrist straps and ESD footwear can fail and damage cannot always be detected by visual inspection. Just by looking at the items you would not know if they still provide sufficient protection. Personnel grounding testers should be used to provide feedback to verify the functionality of an operator’s wrist strap and/or footwear.

Your Personnel Grounding Checklist - Wear, Verify, Log, Handle
Your Personnel Grounding Checklist

Your Personnel Grounding Checklist:

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

Types of Personnel Grounding Testers

Personnel grounding testers can be purchased in two configurations:

  • Wrist strap tester
  • 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. Combined wrist strap and footwear testers will verify your wrist straps AND footwear.

In addition to WHAT the testers verify, you will also be faced with a wide range of devices differing in HOW they test. Below you will see 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 an efficient 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 suitable 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 (electrically operated switch) 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.

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 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)
  • the interface (contact) with the operator’s skin
The SCS Combo Wrist Strap/ Footwear Tester
The SCS Combo Tester can be used to test wrist straps – more information

To ensure that the resistance to ground of personnel is within specification it is important to measure the entire system (i.e., wrist strap, person, and ground connection). The wrist strap system test method is described in ANIS/ESD S1.1. In general, the test method measures the resistance of the ground cord, wristband or cuff, and the interface of the band or cuff of the wearer.” [Handbook ESD TR20.20 Clause 8.2 Wrist Strap System]

The wrist strap system should be tested daily to ensure proper electrical resistance. Nominally, the upper resistance reading should be < 35 megohms or a user-defined resistance. Daily test records can provide evidence of conformity. Daily testing may be omitted if continuous monitors are used.” [ANSI/ESD S1.1 Clause A3. Frequency of System Testing]

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 you are 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
  • the interface between the contact strip and the operator’s perspiration layer

a) Place the foot grounders on the user’s shoes per the manufacturer’s instructions.
b) Place the left foot on the floor plate and touch the body contact area on the tester with one hand. Activate the tester per the manufacturer’s instructions.
c) Remove the left foot from the floor plate.
d) Repeat steps b and c with the right foot.
[ANSI/ESD SP9.2 Clause 6.2.2 Procedure (Integrated Tester)]

The SCS Dual Combination Tester is used to test wrist straps and footwear
The SCS Dual Combination Tester is used to test wrist straps and footwear – 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.

Conclusion

Wrist straps and footwear need to be tested at least daily before handling any ESD sensitive devices. Personnel grounding devices need to be worn for verification using a wrist strap and/or footwear tester.

A record of each test has to be kept for quality control purposes.

Only handle ESD sensitive components if your wrist strap and/or footwear pass(es) the test.

 

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

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

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

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

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

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

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

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

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

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

Sources of EOS during the Soldering Process

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

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

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

Detecting EOS during the Soldering Process

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

Diagnostic Tools

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

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

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

EOS Continuous Monitors

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

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

Data Acquisition

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

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    The SCS 770063 EM Aware Monitor

Eliminating EOS during the Soldering Process

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

1. Managing Voltage on a PCB board

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

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

2. Managing Voltage on an Operator

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

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

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

This post provides more details on continuous monitors.

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

3. Managing Current

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

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

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

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

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

Conclusion

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

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

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

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

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

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

References:

Do your employees handle ESD-sensitive high-end components that are expensive to replace if they failed? If so, reducing the possibility of ESD damage is an important part of an ESD control program. Today’s blog post will look at one 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 electric potential. This is achieved by using only ‘groundable’ materials that are then linked to ground.

This is in line with the requirements of ANSI/ESD S20.20: “The Organization shall prepare an ESD Control Program Plan that addresses each of the requirements of the Program. Those requirements include:
– Training
– Product Qualification
– Compliance Verification
– Grounding / Equipotential Bonding Systems
– Personnel Grounding
– ESD Protected Area (EPA) Requirements
– Packaging Systems
– Marking

[ANSI/ESD S20.20 clause 7.1 ESD Control Program Plan]

Wrist Straps

Wrist straps are the most common personnel grounding device and are used to link people to ground. They are required if the operator is sitting.

A wrist strap is made up of two components:

  • A wrist band that is worn comfortably around your wrist and
  • A coiled cord that connects the band to a Common Grounding Point.

wristbandComponents of a Wrist Strap 

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 coiled cord). They offer a reduced risk of damaging ESD sensitive devices because if one conductor is severed or damaged, the operator still has a reliable path-to-ground with the second conductor. For that reason, they dual-wire wrist straps are generally used in critical applications.

Advantages of using Dual-Wire Wrist Straps:

  • Elimination of intermittent failures
  • Extension of wrist strap lifespan
  • Compatible with high performance continuous monitors

 2231
The MagSnap 360™ Dual-Wire Wrist Strap and Coil Cord –
more information

Dual-Wire Continuous Monitors

For maximum benefit, dual-wire wrist straps should be used together with dual-wire continuous monitors. Instead of connecting a coil cord directly to a common grounding point, the operator connects to a continuous monitor. The operator is grounded through the continuous monitor and the operator-to-ground connection is monitored.

The monitors provide operators with instant feedback on the status and functionality of their wrist strap and/or workstation. 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 “intermittent” stage is characterized by sporadic failures as the cord is not completely severed. Once the cord is fully split, the “open” stage is reached.

WS-Aware-UseThe WS Aware Dual-Wire Workstation Monitor – more information


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]

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

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 redundancy is built-in to have a backup if the primary source fails. 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 still needs to be replaced immediately.

And there you have it: dual-wire wrist straps together with dual-wire continuous monitors offer better protection than intermittent monitoring or testing if you have a critical application.

Check-out the SCS Wrist Strap Selection Guide and Workstation Monitor Selection Guide to find the correct products for your application.

We get a lot of inquiries regarding wrist straps: what they do, why there are different types, how they are used, etc. So, the purpose of today’s blog post is to answer all those questions for you. If there is something we did not cover in the blog post make sure you ask us in the comments!
Let’s get started!

Introduction
The ESD Standard S20.20 requires “an ESD Control Program Plan that addresses each of the requirements of the Program. Those requirements include:

  • Training
  • Product Qualification
  • Compliance Verification
  • Grounding/Equipotential Bonding Systems
  • Personnel Grounding
  • ESD Protected Area (EPA) Requirements
  • Packaging Systems
  • Marking”
    [ANSI/ESD S20.20 clause 7.1 ESD Control Program Plan]

The most common personnel grounding device is a wrist strap which is used to connect people to ground.
A wrist strap in general is a conductive wristband which provides an electrical connection to skin of an operator and, in turn, is connected to a known ground point at a workbench or a tool. While a wrist strap does not prevent generation of charges, its purpose is to dissipate these charges to ground as quickly as possible. Wrist straps are required if the operator is sitting. They are not necessary if an operator is wearing two foot grounders on a conductive grounded floor and doesn’t lift both heels/toes at the same time. As some people lift both feet off the ground while seated, wrist straps are essential for sitting personnel.
A wrist strap is made up of two components:

  • a wristband that is worn comfortably around your wrist and
  • a coil cord that connects the band to ground.

Wristband and coil cord of a wrist strapWristband and coil cord of a wrist strap

The key to the wrist strap is the intimate contact of the conductive band to the skin and of course the coil cord connecting to ground. It doesn’t matter if the contact point to your body is on your wrist, finger, forearm, ankle, etc., as long as it is in direct contact with your skin. The skin is electrically continuous over your whole body. The wrist is just a convenient place to couple the band to.

Styles of Wrist Straps
Operators can choose between elastic and metal wristbands:

  • Elastic wristbands are the most popular wristband as they are comfortable to wear and easy to adjust. Compared to metal wristbands they are also less expensive.
  • Some people prefer metal wristbands as they are generally longer lasting and easier to clean.

The key to personnel grounding is to have an adequate path to ground so that there is never a potential difference with respect to ground on the human body for longer than 150 milliseconds (ms) body movement time. Such rapid grounding is accomplished well by elastic or metal wrist straps. So, in terms of their effectiveness to protect against ESD, there is no difference between elastic and metal wristbands.

Both elastic and metal wristbands are (to a certain degree) adjustable. Metal wristbands offer less adjustment, so you will find those are generally available in different sizes depending on the circumference of your wrist. However, you are still able to adjust metal wristbands if you need a tighter/looser fit.
To adjust your wristband, follow the below steps:
1. Elastic wristbands:

  • Open the clasp by pulling upward on the “tail” of material that extends out from the clasp.
  • Tighten or loosen the elastic material through the clasp until the wristband fits snug but comfortably.
  • We recommend that you close the clasp and wear the band with the excess tail extended for a day to be sure the adjustment is snug, comfortable, and has the proper electrical contact with the skin before cutting.
  • Test the wrist strap system to be sure of proper electrical resistance and skin contact.
  • When you are ready to cut off excess material, mark with a pencil where excess material is to be trimmed.
  • Remove band from wrist. Open clasp. Cut off strip excess material about 1/4″ short of pencil mark so that the end of material is concealed by cap. This will eliminate the possibility of frayed ends.
  • Close clasp and use as a fixed elastic wristband.

Adjusting an elastic wristbandAdjusting an elastic wristband

2. Metal wristbands:

  • Insert the link end of the wristband into the slotted opening on the cap. Insert it at a downward angle to allow the links to slide inside the channel in the backplate.
  • Change the size of the band by sliding the links in or out of the stainless steel backplate. For extra small size, you can cut off excess links with cutters.
  • Lock the links into place by pulling down on the band, seating the band securely over the lip on the edge of the backplate.
  • Test the wrist strap system to be sure of proper electrical resistance and skin contact.

Adjusting a metal wristbandAdjusting a metal wristband

1 megohm Safety Resistors
The purpose of the 1 megohm resistor found in series with wrist straps is solely to provide safety to the human body by limiting the amount of current that could be conducted through the body. The 1 megohm resistor is designed to limit the current to 250 microamps at 250 Volts rms AC. This is just below the perception level (and a bit before the nervous system goes awry) of most people. Physical perception of current traveling in/on the body varies depending on size, weight, water content, skin conditions, etc. Remember that the termination of the coil cord with the 1 megohm resistor must always be connected to the operator.
Such safety resistors are built into the wrist straps themselves and also in such wrist strap monitors as WS Aware, Iron Man® Plus and Ground Man Plus manufactured by SCS. 

Typical Problems with Wrist Straps
Some of the typical problems with proper grounding of an operator using a wrist strap are:

  • worn out wrist strap which no longer has good electrical properties
  • stretched out wrist strap which doesn’t make good electrical contact with the skin
  • loosely-worn wrist strap which doesn’t make good electrical contact with the skin either
  • dry skin of an operator increasing electric resistance of a contact beyond specification
  • improper placement of a wrist strap, such as over the cuff of the garment

Also, another issue we often see is that wrist strap users connect their wrist cord to a stud on their ESD protective mat. This process is not recommended as it can increase the total system resistance to ground to over the 35 megohm limit required by ANSI/ESD S20.20 table 2.

Testing of Wrist Straps
Wrist straps need to be checked regularly to ensure they are faultless and ground the operator properly. Wrist straps should be worn while they are tested. This provides the best way to test all three components: the wristband, the ground cord (including the resistor) and the interface with the operator’s skin.
Wrist straps need to be checked before each use. Periodic testing is not required if continuous monitors are used. They provide instant feedback should the wrist strap fail while handling ESD sensitive devices.

Verifying a wrist strap using a wrist strap/footwear testerVerifying a wrist strap using a wrist strap/footwear tester

If the wrist strap tester outputs a FAIL test result, stop working. Test the wristband and cord individually to find out which item is damaged. There are some methods to troubleshoot your wrist straps. First make sure your tester is properly adjusted and calibrated.

If the operator and wrist strap system fails low:

  • Make sure that the person is not directly connected to ground via another path, i.e., touching a grounded metal structure.
  • The most common cause of a fail low is a shorted resistor in the wrist strap coil cord. Replace the coiled cord with a new one and repeat the test.

If the operator and wrist strap system fails high:

  • Make sure the coiled cord has a secure connection both the banana jack/socket to tester and the stud snap to wrist strap buckle.
  • Ensure there is continuity in the coiled cord (you can test with an ohmmeter).
  • Remove the wrist strap and hold the bottom part of the band tightly between the operator’s thumb and index finger and test. If the test fails high, the band may be soiled and needs cleaning or the buckle to band connection may be suspect. Either replace the band or clean and then retest.
  • If the above test is okay, then the skin of the operator’s wrist may be too dry. Apply ESD lotion to the wrist to re-moisturize the skin thereby increasing its conductivity. Retest. Operators with dryer skin should wear metal banded wrist straps to minimize the contact resistance. If their skin is very dry, application of an ESD lotion may be required as part of their donning process.

You need to obtain a PASS test result before beginning work.

Now that we’ve covered the basics of wrist straps, we will dive into the different types of wrist straps – but that will have to wait until next time as this post is already very long. Stay tuned!

People pose the biggest threat to ESD sensitive components. However, when properly trained, operators can become the key weapon in the fight against ESD. Every person coming into contact with ESD sensitive items should be able to prevent ESD related problems before they occur or provide immediate action when they do occur. Today’s blog post will explain in detail the role operators play in ESD Protection and how your company can support them in the fight against ESD.

Introduction
As an employee, the invisible threat of ESD should be of great concern to you. ESD damage can significantly reduce your company’s profitability. This may affect your company’s ability to compete in the marketplace, your profit sharing and even your employment. Everyone likes to take pride in their work, but without proper ESD controls, your best efforts may be destroyed by ElectroStatic discharges that you can neither feel nor see.

motherboard doctors
People are often a major factor in the generation of static charges

Perhaps the most important factor in a successful static control program is developing an awareness of the “unseen” problem. People are often a major factor in the generation of static charges. Studies have shown that personnel in a manufacturing environment frequently develop 5000 volts or more by just walking across the floor. This is “tribocharging” produced by the separation of their shoes and the flooring as they walk.
A technician seated at a non-ESD workbench could easily have a 400-500 volt charge on his or her body caused not only by friction or tribocharging but additionally by the constant change in body capacitance that occurs from natural movements. The simple act of lifting both feet off the floor can raise the measured voltage on a person by as much as 500-1000 volts.
Educating your personnel is therefore an essential basic ingredient in any effective static control program. A high level of static awareness must be created and maintained in and around the ESD protected area. Once personnel understand the potential problem, it might help to reinforce this understanding by hanging up a few static control posters in strategic locations. No technician needs an unprotected person wandering over and touching things on the service bench.

The invisible enemy
The biggest issue with ElectroStatic discharges is that you can neither see nor feel the threat. Daily life has other examples of hidden enemies where careful procedures must be followed to regularly obtain positive results. One example is sterilization which combats germs and contamination in hospitals.
Damage caused by invisible and undetectable events can be understood by comparing ESD damage to medical contamination of the human body by viruses or bacteria. Although invisible, they can cause severe damage. In hospitals, the defense against this invisible threat is extensive contamination control procedures including sterilization.

A medical team performing an operation
Would you consider having surgery in a contaminated operating room?

We are aware of the benefits of sterilization in medicine. We must develop the same attitude towards ESD control and “sterilize” against its contamination. Just as you would never consider having surgery in a contaminated operating room, you should never handle, assemble or repair electronic assemblies without taking adequate measures against ESD. For the hospital to sterilize most of the instruments is not acceptable; actually, it may waste money. Every single instrument needs to be sterilized. Likewise, it is not acceptable to protect the ESD sensitive items most of the time. Effective ESD control must occur at each and every step where ESDS items are manufactured, processed, assembled, installed, packaged, labelled, serviced, tested, inspected, transported or otherwise handled.
Everyone handling sensitive components should:

  • recognize ESD threat
  • know what equipment to use, and how to use it
  • know the correct ESD procedures, and work to them
  • know how to check equipment
  • know which packaging to use
  • take corrective actions when required.” [Source]

It is obvious that ESD training of personnel is a prerequisite for a functioning ESD control program.

Training
ESD training needs to be provided to everyone who handles ESD sensitive devices – that includes managers, supervisors, subcontractors, cleaners and even temporary personnel. Training must be given at the beginning of employment (BEFORE getting anywhere near an ESDS) and in regular intervals thereafter.
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 ESDS items. 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 the methods used by the Organization to verify trainee comprehension and training adequacy.” [ANSI/ESD S20.20-2007 section 7.2]

Training
Training is an essential part of an ESD Control Program

ESD training should include:

  • an introduction to ESD – what it is, what it’s caused by and how to control it
  • how to handle sensitive devices and what precautions to take when coming into contact with them
  • how to identify and mark ESD sensitive items
  • an overview of the ESD Standard.

For operators working in assembly, repair or field service, job specific training will be required, too.
If visitors are entering an EPA, they must possess basic ESD awareness and understand how to use their wrist straps and footwear.

Operator’s safety comes first
One final word of warning: while ESD control is important, it is of secondary importance to employee safety. ElectroStatic charges or static electricity can be everywhere; however, conductors can be effectively grounded and charges removed to ground. A fundamental rule in ESD control is to ground all conductors, including people. BUT: Personnel should not be grounded in situations where they could come into contact with voltage over 250 volts AC.

Last time we explained how to easily create a compliance verification plan and why it’s important to have one in place. Today’s post will elaborate on the subject of periodic verification and highlight common products in your EPA that should be regularly verified and more importantly how they should be checked.

Why periodic verification
Compliance verification is a requirement of ANSI/ESD S20.20:
The Organization shall prepare an ESD Control Program Plan that addresses each of the requirements of the Program. Those requirements include:
– Training
– Product Qualification
– Compliance Verification
– Grounding / Equipotential Bonding Systems
– Personnel Grounding
– ESD Protected Area (EPA) Requirements
– Packaging Systems
– Marking” [ANSI/ESD S20.20 clause 7.1 ESD Control Program Plan]

Installed ESD Control products must be checked regularly to ensure they meet the required limits per the ESD Standard. “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.” [ANSI/ESD S20.20 clause 7.3 Compliance Verification Plan]

Below, you will find a list of the most common ESD Control Products in your EPA and how to test them:

Worksurface Matting
The purpose of ESD workbench 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 worksurface is connected to ground. If the matting is out-of-spec, not grounded at all, or the stud on the mat has become loose or if 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 workbench matting to maintain proper electrical function. 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 include periodic checks of worksurfaces measuring:

  • Resistance Point-to-Point (Rp-p) and
  • Resistance-to-ground (Rg)
Testing a worksurface using SRMETER2

A surface resistance tester can be used to perform these tests in accordance with ANSI/ESD S20.20 and its test method ESD TR53; if these measurements are within acceptable ranges, the worksurface matting and its connections are good.

Wrist Straps
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 contact with the operator’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 746

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 worksurface is not properly grounded.

A note on worksurface matting and wrist straps: if you are using common ground points to ground the operator and/or work surface matting, remember to measure resistance to ground regularly as well (every 6 months for example).

Floor Matting
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. 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.
Floor matting can be checked using a resistance meter. A surface resistance meter is designed to measure resistance point-to-point (Rp-p) or surface to ground (Rg) in accordance with ANSI/ESD S20.20 and its test method ESD TR53.

Footwear
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 770750

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.

ESD Packaging
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.

An operator packing an ESD sensitive item into a Shielding Bag
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.

Ionizers
Ionizers are intended to neutralize static charges on insulators thereby reducing their potential to cause ESD damage. However, poorly maintained ionizers with dirty emitter pins and out-of-balance ionisers can put a charge on ungrounded items.
Remember to clean ionizer emitter pins and filters regularly. You can now even purchase ionizers that will alarm when emitter pins need to be cleaned or the ionizer is out of balance.

Charge plate monitor and static decay measurements using 963E ionized air blower

Static neutralization (the ability to reduce or eliminate a charge on a surface) is an important quality for ionizers. Static decay time is defined as the time interval needed to reduce a defined voltage potential on an object to a defined lower potential by means of applied ionized air. Another important aspect for ionizers is the ability to produce a balanced stream of positive and negative ions. A charged plate monitor or equivalent can be used to accurately measure both of these parameters.
For more detailed information on measuring the performance of ionizers refer to the ESD standard ANSI/EOS/ESD-S3.1 for Protection of Electrostatic Discharge Susceptible Items-Ionization.

Wrist Strap/Footwear and Resistance Testers etc.
So, you check your wrist straps and/or footwear and workbench 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.

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 verification plan in place? If so, how often do you check your ESD protection products?

Every component in an ESD protected area (EPA) plays an important role in the fight against electrostatic discharge (ESD). Just one element not performing correctly could harm your ESD sensitive devices and potentially cost 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.

Introduction
When implementing an ESD control program plan, ANSI/ESD S20.20 asks for several requirements to be addressed, one of which is “Compliance Verification”:
The Organization shall prepare an ESD Control Program Plan that addresses each of the requirements of the Program. Those requirements include:

  • Training
  • Product Qualification
  • Compliance Verification
  • Grounding / Equipotential Bonding Systems
  • Personnel Grounding
  • ESD Protected Area (EPA) Requirements
  • Packaging Systems
  • Marking” [ANSI/ESD S20.20 clause 7.1 ESD Control Program Plan]

ESD protected area (EPA) products should be tested:

  • Prior to installation to qualify product for listing in user’s ESD control program.
  • During the initial installation.
  • For periodic checks of installed products as part of TR20.20.

A Compliance Verification Plan shall be established to ensure the Organization’s fulfillment of the technical requirements of the ESD Control Program 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 and equipment used for process monitoring and measurements. If the test methods used by the organization differ from any of the standards referenced in this document, then there must be a tailoring statement that is documented as part of the ESD Control Program Plan. 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.” [ANSI/ESD S20.20 clause 7.3 Compliance Verification Plan]

Components of a Verification Plan
Each company’s verification plan needs to contain:

1. A list of items that are used in the EPA and need to be checked on a regular basis
All ESD working surfaces, personnel grounding devices like wrist straps or foot grounders, ionizers etc. need to be included on the list. In summary: every item that is used for ESD Control purposes. It is recommended to create a checklist comprising all ESD control products as 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 several things, e.g.

  • how long the item will last,
  • how often it is used or
  • how important it is to the overall ESD control program.

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 ionizer is used in a critical clean room, the test frequency may need to be increased.

Testing-Wrist-Straps
It is recommended that Wrist Straps are checked before each shift
Testing and monitoring of smock and ground cord assembly

Test frequency limits are not listed in this document, as each user will need to develop their own set of test frequencies based on the critical nature of those ESD sensitive items handled and the risk of failure for the ESD protective equipment and materials.

Examples of how test frequencies are considered:

  • Daily wrist strap checks are sufficient in some applications while in other operations constant wrist strap monitoring may be used for added operator grounding reliability.
  • Packaging checks may depend on the composition of the packaging and its use. Some packaging may have static control properties that deteriorate more quickly with time and use, and some packaging may be humidity dependent and may have limited shelf life.
  • Some materials, such as ESD floor finishes, may require more frequent monitoring because of their lack of permanency. Other materials, such as ESD vinyl floor covering, may require less monitoring. The testing of a floor should also be considered after maintenance on the floor has been performed.” [ESD TR53-01-15 Annex A – Test 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
ANSI/ESD S20.20 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 ANSI/ESD S20.20 list the different test methods a company must follow.

If a company uses other test methods or have developed their own test methods, the ESD control program 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 ANSI/ESD S20.20. Personnel performing measurements need to be trained on how equipment is used. ESD TR53-01-15 lists test procedures and equipment that can be used to verify ESD Control items.

SRMeter2_use
Checking an ESD Worksurface using a Surface Resistance Meter

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 individual is required to know the ESD Standard ANSI/ESD S20.20 AND the company’s individual ESD program.
  • It is essential that the selected team member recognizes the role of ESD control 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 verification process. It is the responsibility of the ESD coordinator to categorize 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 program and if improvements can be seen over time.

If you followed our tips to fight ESD, you will have already identified all ESD sensitive items in your factory. You’re now at a point where you realize 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. But 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
  • Product Qualification
  • Compliance Verification
  • Grounding / Equipotential Bonding Systems
  • Personnel Grounding
  • ESD Protected Area (EPA) Requirements
  • Packaging Systems
  • Marking

 The ESD Control Program Plan is the principal document for implementing and verifying the Program. The goal is a fully implemented and integrated Program that conforms to internal quality system requirements. The ESD Control Program Plan shall apply to all applicable facets of the Organization’s work.” [ANSI/ESD S20.20-2014 clause 7.1 ESD Control Program Plan]

The selection of specific ESD control procedures or materials is at the discretion of the ESD Control Program Plan preparer and should be based on risk assessment and the established ESD sensitivities of parts, assemblies, and equipment.” [ANSI/ESD S20.20-2014 Annex B]

  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. Per ANSI/ESD S20.20-2014 section 6.1 “The Program shall document the lowest level(s) of device ESD sensitivity that can be handled.” A general rule is to treat any device or component that is received in ESD protective 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 ANSI/ESD S20.20-2014 can be obtained from the ESD Association. It covers the “Development of an Electrostatic Discharge Control Program for Protection of Electrical and Electronic Parts, Assemblies and Equipment (Excluding Electrically Initiated Explosive Devices)” and “provides administrative and technical requirements for establishing, implementing and maintaining an ESD Control Program.”Also, consider purchasing the ESDA’s ESD Handbook ESD TR20.20-2016 for guidance on the implementation of the standard.
  3. Select a grounding or equipotential bonding system
    Grounding / Equipotential Bonding Systems shall be used to ensure that ESDS items, personnel and any other conductors that come into contact with ESDS items are at the same electrical potential.” [ANSI/ESD S20.20-2014 section 8.1 Grounding / Equipotential Bonding Systems]
    The elimination of differences in electrostatic charge or potential can be achieved in three different ways:
    – Equipment Grounding Conductor
    – Auxiliary Ground
    – Equipotential Bonding

    • Equipment grounding conductor:
      the first and preferred ESD ground is the electrical system’s ground or equipment ground. In this case, the ESD control elements and grounded personnel are connected to the three-wire electrical system equipment ground;
    • Grounding using auxiliary ground:
      the second acceptable ESD ground is achieved through the use of an auxiliary ground. This conductor can be a ground rod or stake that is used for grounding the ESD control elements in use at a facility. In order to eliminate differences in potential between protective earth and the auxiliary ground system it is required that the two systems be electrically bonded together with a resistance less than 25 ohms;
    • Equipotential bonding:
      in the event that a ground facility is not available, ESD protection can be achieved by connecting all of the ESD control elements together at a common connection point.
  4. Determine the grounding method for operators (Personnel Grounding)
    The two options for grounding an operator are:

    • a wrist strap or
    • footwear / flooring system

    Wrist straps must be worn if the operator is seated. We will talk about wrist straps in more detail at a later point. For now, remember to connect the coil cord part of the wrist strap to a Common Point Ground so that any charges the operator may generate can be removed to Ground.

    An operator using a wrist strap as a grounding method
    An operator using a wrist strap as a grounding method

    A footwear / flooring system is an alternative for standing or mobile workers. ESD footwear needs to be worn on both feet and only works as a grounding device if it is used in conjunction with an ESD floor. Just like with wrist straps, a future blog post will clarify the ins and outs of ESD footwear.

    An operator using a foot grounders on an ESD floor as a personnel grounding method
    An operator using foot grounders on an ESD floor as a personnel grounding method

    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. Implement access control devices, signs and floor marking tape to identify and control access to the ESD Protected Area.
  6. Select ESD control items or elements to be used in the EPA based on your manufacturing process
    Elements that should be considered include: worksurfaces, flooring, seating, ionization, 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. We will discuss ESD Packaging in more detail in a future blog post. All packaging, if used, should be defined for all steps of product manufacture whether inside or outside the EPA.

    An operator packing an ESD sensitive item into a Shielding Bag
    An operator packing an ESD sensitive item into a Shielding Bag
  8. Use proper markings for ESD susceptible items, system or packaging
    From ANSI/ESD S20.20-2014 section 8.5: “ESDS items, system or packaging marking shall be in accordance with customer contracts, purchase orders, drawing or other documentation. When the contract, purchase order, drawing or other documentation does not define ESDS items, system or packaging marking, the Organization, in developing the ESD Control Program Plan, shall consider the need for marking. If it is determined that marking is required, it shall be documented as part of the ESD Control Program Plan.
  9. Implement a Compliance Verification Plan
    From ANSI/ESD S20.20-2014 section 7.4: “A Compliance Verification Plan shall be established to ensure the Organization’s fulfillment of the technical requirements of the ESD Control Program Plan.”. Our next post will explain in detail how to create and implement a Compliance Verification Plan so stay tuned…
    However, developing and implementing an ESD Control Program is only the first step. The second step is to continually review, verify, analyse, evaluate and improve your ESD program:“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 occur. The Compliance Verification Plan shall document the test methods and equipment used for making the measurements. If the test methods used by the Organization differ from any of the standards referenced in this document, then there must be a tailoring statement that is documented as part of the ESD Control Program Plan. 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.” [ANSI/ESD S20.20-2014 section 7.4 Compliance Verification Plan]
    Regular program compliance verification and auditing is a key part of a successful ESD Control Program.
  10. Develop a Training Plan
    From ANSI/ESD S20.20-2014 section 7.2: “Initial and recurrent ESD awareness and prevention training shall be provided to all personnel who handle or otherwise come into contact with any ESDS items.
  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 Program. 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 ESD control items permitted to be used in the ESD Control Program.
    • Compliance Verification Plan: includes periodic checking of ESD control items and calibration of test equipment per manufacturer and industry recommendations.
    • Training Plan: an ESD Program is only as good as the use of the products by personnel. When personnel understand the concepts of ESD control, the importance to the company of the ESD Control Program, and the proper use of ESD products, they will implement a better ESD Control Program improving quality, productivity and reliability.