Electrostatic Charge

How to Neutralize a Charge on an Object that Cannot be Grounded

We have learned in a previous post that within an ESD Protected Area (EPA) all surfaces, objects, people and ESD Sensitive Devices (ESDs) are kept at the same electrical potential. We achieve this by using only ‘groundable’ materials.

But what do you do if an item in your EPA is essential to assembly and it cannot be grounded? Don’t sweat, not all hope is lost! Let us explain a couple of options which will allow you to use the non-groundable item in question.

Conductors and Insulators

In ESD Control, we differentiate items as conductors and insulators.

Materials that easily transfer electrons are called conductors. Examples of conductors are metals, carbon and the human body’s sweat layer.

Grounding cable snap with connection to a ground.
A charged conductor can transfer electrons which allows it to be grounded

Insulators are materials that do not easily transfer electrons are non-conductors by definition. Some well-known insulators are common plastics, polystyrene foam, and glass.

Plastic cup with charged electrons
Insulators like this plastic cup will hold the charge and cannot be grounded and “conduct” the charge away.

Both, conductors and insulators, may become charged with static electricity and discharge.

Electrostatic charges can effectively be removed from conductive or dissipative conductors by grounding them. A non-conductive insulator will hold the electron charge and cannot be grounded and “conduct” the charge away.

Conductors and Insulators in an EPA

The first two fundamental principles of ESD Control are:

  1. Ground all conductors (including people).
  2. Remove all insulators.

To ground all conductors per the first ESD Control principal, all surfaces, products and people are electrically bonded to ground. Bonding means linking or connecting, usually through a resistance of between 1 and 10 megohms.

Wrist straps and worksurface mats are some of the most common devices used to remove static charges:

  • Wrist straps drain charges from operators and a properly grounded mat will provide path-to-ground for exposed ESD susceptible devices.
  • Movable items (such as containers and tools) are bonded by standing on a bonded surface or being held by a bonded person.

If the static charge in question is on something that cannot be grounded, i.e. an insulator, then #2 of our ESD Control principles will kick in and insulators must be removed. Per the ESD Standard ANSI/ESD S20.20, “All nonessential insulators such as coffee cups, food wrappers and personal items shall be removed from the EPA.” [ANSI/ESD S20.20 clause 8.3.1 Insulators]

The ESD Standard differentiates between these two options:

  1. If the field measured on the insulator is greater than 2000 volts/inch, keep it at a minimum distance of 12 inches from the ESDs or
  2. If the field measured on the insulator is greater than 125 volts/inch, keep it at a minimum distance of 1 inch from the ESDs.
Moving an insulated keyboard away from ESD sensitive workspace
Aim to keep insulators away from ESDs

“Process-Essential” Insulators

Well, nothing in life is black and white. It would be easy if we were always able to follow the above ESD Control ‘rules’ but there are situations where said insulator is an item used at the workstation, e.g. hand tools. They are “process-essential” insulators – you cannot remove them from the EPA or the job won’t get done.

How do you ‘remove’ these vital insulators without actually ‘removing’ them from your EPA?

Here are four ways to reduce the ESD risk of these insulators:

  1. Keep all insulators a minimum of 1 inch or 12 inches from ESDs at all times per recommendation of the ESD Standard.
    This reduces the chance of insulators coming in contact with ESDs during workstation processes and assembly.
  2. Replace regular insulative items with an ESD protective version.
    There are numerous tools and accessories available that are ESD safe – from document handling to cups & dispensers, soldering tools, brushes and waste bins. They are either conductive or dissipative and replace the standard insulative varieties that are generally used at a workbench.
  3. Periodically apply Topical Antistat on non-ESD surfaces.
    After Topical Antistat has been applied and the surface dries, an antistatic and protective static dissipative coating is left behind. The static dissipative coating will allow charges to drain off when grounded. The antistatic properties will reduce triboelectric voltage to under 200 volts. It therefore gives non-ESD surfaces electrical properties until the hard coat is worn away.
  4. Neutralization with Ionization
    If these three options are not feasible for your application, the insulator is termed “process-essential” and therefore neutralization using an ionizer becomes a necessary part of your ESD control program. This allows for control of charged particles that can cause ESD events which we will cover next.

Neutralization

Most ESD workstations will have some insulators or isolated conductors that cannot be removed or replaced. These should be addressed with ionization.

Examples of some common process essential insulators are a PC board substrate, insulative test fixtures and product plastic housings.

Electronic enclosures are process-essential insulators (shown on ESD workstation)
Electronic enclosures are process-essential insulators

An example of isolated conductors are conductive traces or components loaded on a PC board that is not in contact with the ESD worksurface.

An ionizer creates great numbers of positively and negatively charged ions. Fans help the ions flow over the work area. Ionization can neutralize static charges on an insulator in a matter of seconds, thereby reducing their potential to cause ESD damage.

The charged ions created by an ionizer will:

  • neutralize charges on process required insulators,
  • neutralize charges on non- essential insulators,
  • neutralize isolated conductors and
  • minimize triboelectric charging.
SCS Benchtop ionizer on a workstation removing charges from isolated conductors on PCB Board
Insulators and isolated conductors are common in ESDs – Ionizers can help

For more information on ionizers and how to choose the right type of ionizer for your application, read this post.

Summary

The best way to keep electrostatic sensitive devices (ESDs) from damage is to ground all conductive objects and remove insulators. This is not always possible because some insulators are “process-essential” and are necessary to build or assemble the ESDs.

Insulators, by definition, are non-conductors and therefore cannot be grounded, but they can be controlled to minimize potential ESD damage.

Insulators can be controlled by doing the following within an EPA:

  • Keep insulators a minimum distance from ESDS at all times (1 or 12 inch minimum distance depending on field voltage measurements of the insulator per ESD Standard recommendation)
  • Replace regular insulative items with ESD protective versions
  • Periodically apply a coat of Topical Antistat
  • Neutralize charges for “process-essential” insulators with ionization

With these steps added to your ESD control process, all surfaces, objects, people and ESD Sensitive Devices (ESDs) are kept at the same electrical potential in an ESD Protected Area (EPA) to reduce the risk of ESD events and ESD damage.

How to Reduce the Risk of Damaging ESD Sensitive Devices in Critical Applications

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.

Introduction to ESD

Welcome to this little corner of the interwebs! Today marks the beginning of something truly amazing: our very own blog! You’re currently reading through our first blog post and we appreciate you taking time out of your busy life and spending it here.

The intention of this blog is to provide you with resources, information and tools – all focused around ESD! So, if you have any ideas for future blog posts or suggestions on what we could do better, don’t be a stranger and leave a comment! We look forward to hearing from you.

Now, for this first post we thought we’d start right at the beginning: what is ESD? It’s the core of our business but a lot of people don’t understand what it’s all about so let’s clear that up – right here and right now!

ElectroStatic Charge
Everything you see around you is made from atoms – your mouse, keyboard, screen, cup of coffee etc. Every atom is constructed of a nucleus, which includes positively charged protons, and one or more negatively charged electrons bound to the nucleus. As atoms have an equal number of electrons and protons, it balances out having no charge. No problems so far!

Structure of an AtomStructure of an Atom (Source)

Unfortunately, all materials can tribocharge and generate ElectroStatic charges. Most of the time this happens through contact and separation; some everyday life examples are:

  • Opening a plastic bag
  • Combing hair
  • Walking across a floor

Walking across a floor.pngWalking across a floor can generate an ElectoStatic Charge

For most people, static electricity is represented by the noise or crackle heard on a radio that interferes with good reception or the shock experienced when touching a metal object after walking across a carpeted room or sliding across a car seat. Static electricity is also observed as static cling when clothes are stuck together after coming out of a clothes dryer. Most of the time, people observe static electricity when the weather is cold and dry.” “While many people tend to think of static electricity as being at rest or not moving, static electricity causes the most concern when it ceases to be stationary.” [ESD Handbook ESD TR20.20 section 2.1 Basics of Static Electricity, Introduction]

When two materials make contact and are then separated, a transfer of electrons from one surface to the other may take place. The amount of static electricity generated depends upon the materials subjected to contact or separation, friction, the area of contact or separation, and the relative humidity of the environment. At lower relative humidity (as the environment is drier) charge generation will increase significantly. Common plastics generally will create the greatest static charges.
Electrostatic charge is most commonly formed by the contact and separation of two materials. The materials may be similar or dissimilar although dissimilar materials tend to liberate higher levels of static charge. An example is a person walking across the floor. Static electricity is produced when the person’s shoe soles make contact, then separate from the floor surface. Another example is an electronic device sliding into or out of a bag, magazine or tube.” [ESD Handbook ESD TR20.20 section 2.3 Nature of Static Electricity]

ElectroStatic Discharge (ESD)
If two items are at different ElectroStatic charge levels (i.e. one is positively and the other negatively charged) and approach one another, a spark or ElectroStatic Discharge (ESD) can occur. This rapid, spontaneous transfer of an ElectroStatic charge can generate heat and melt circuitry in electronic components.

ESD.png

ElectroStatic Discharge (ESD)

ESD events are happening around us all the time – yet, most of these cannot be seen or felt. For a person to sense ElectroStatic Discharge (ESD) (the dreaded ‘zap’), a discharge of about 2,000V is needed. To actually see ESD (in form of an arc, e.g. lightning) even greater voltages are required.

While ESD in your home can be annoying, it’s generally harmless. However, in the electronics industry ESD is the hidden enemy. Damages caused by invisible and undetectable ESD 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. In the electronics industry, it’s ESD Protection; we will get into more detail on that in a later post.

Many of the common activities you perform daily may generate charges on your body that are potentially harmful to electronic components. Some of these activities include:

  • Walking across a carpet: 1,500V to 35,000V
  • Walking over untreated vinyl floor: 250V to 12,000V
  • Worker at a bench: 700V to 6,000V
  • Picking up a common plastic bag from a bench: 1,200V to 20,000V

Many of the CMOS technology components can be damaged by discharges of less than 1,000 volts. Some of the very sophisticated components can be damaged by charges as low as 10 volts.

Types of ESD Device Damage
So, we’ve established what ESD is and learned that ESD can damage electronics components. But what exactly does this damage look like? We’re so glad you asked!

The industry differentiates between catastrophic failures and latent defects. Per ESD Handbook ESD TR20.20 section 2.7 Device Damage – Types and Causes “Electrostatic damage to electronic devices can occur at any point, from the manufacture of the device to field service of systems. Damage results from handling the devices in uncontrolled surroundings or when poor ESD control practices are used. Generally damage can manifest itself as a catastrophic failure, parametric change or undetected parametric change (latent defect).

Catastrophic failures occur when a component is damaged to the point where it is DEAD NOW and will never again function. In these cases, the ESD event may have caused a metal melt, junction breakdown or oxide failure. This is the easiest type of ESD damage to find since it can be detected during inspection and testing.
When an electronic device is exposed to an ESD event it may no longer function. The ESD event may have caused a metal melt, junction breakdown, or oxide failure. The device’s circuitry is permanently damaged, resulting in a catastrophic failure.” [ESD Handbook ESD TR20.20 section 2.7.1 Catastrophic Failures]

Catastrophic Failures

Catastrophic failures will lead to completely failed or dead components.

Latent defects occur when ESD weakens or wounds the component to the point where it will still function properly during testing, but over time the wounded component may cause poor system performance. Later, after final inspection, perhaps in the hands of your customer, a latent defect may become a catastrophic failure.
A device that is exposed to an ESD event may be partially degraded, yet continue to perform its intended function. However, the operating life of the device may be reduced dramatically. A product or system incorporating devices with latent defects may experience a premature failure after the user places them in service. Such failures are usually costly to repair and in some applications may create personnel hazards.” It is easy with the proper equipment to confirm that a device has experienced catastrophic failure or that a part is degraded or fails test parameters. Basic performance tests will substantiate device damage. However, latent defects are virtually impossible to prove or detect using current technology, especially after the device is assembled into a finished product. Some studies claim that the number of devices shipped to users with latent defects exceeds the number that fail catastrophically due to ESD in manufacturing.” [ESD Handbook ESD TR20.20 section 2.7.2 Latent Defects]

Latent Defects

Latent defects lead to degraded or wounded components

Costly Effects of ESD
Catastrophic failures are straight forward: they can be detected and repaired at an early manufacturing stage. This is the least costly type of ESD damage.

Latent defects on the other hand are not only hard to find, but they can also severely affect the reputation of your company’s product. Latent defects can cause upset or intermittent failures and can be very frustrating: customers return a product with a problem which the factory fail to detect so it ends up at the customer’s again with the problem unresolved.

ESD Damage on an Integrated Circuit

The cost for repairing latent defects increases as detection of the failure moves through the system. One study indicated the repair cost to be:

  • $10 Device
  • $10 Device in board: $100
  • $10 Device in board and in system: $1,000
  • $10 Device and system fails: $10,000

Industry experts estimate that product losses in the electronics industry due to static discharge range from 8 to 33%. Others believe the actual cost of ESD damage amount to billions of dollars annually.

Conclusion
ESD is the hidden enemy in the electronics industry:

  • It cannot be felt
  • It cannot be seen
  • It cannot necessarily be detected through normal inspection procedures.

Therefore, it is absolutely crucial to be aware of the most sensitive items in your factory. Technology advances all the time: electronic circuitry gets progressively smaller which leads to a reduction of microscopic spacing of insulators and circuits within components. “Electronic items continued to become smaller, faster and their susceptibility to static damage increased…all electronic devices required some form of electrostatic control to assure continued operation and product reliability.” [ESD Handbook ESD TR20.20 section 2.2]. While this is great news for the consumer with better, faster and stronger computers, tablets, phones etc., it’s bad news for the manufacturers. The evolution of technology leads to devices being even more sensitive to ESD. As a result, the need for appropriate ESD Protection is now more important than ever.

Over the next few weeks, we will provide you with all the tips, tools and techniques to create an effective ESD Control Program so that your sensitive components are protected against damages from ESD.