ESD susceptible items

Effective ESD Control in a Service or Repair Center

Image scsstaticcontrol September 21, 2018 0

The best-equipped service bench in your shop can be a real money-maker when set up properly. It can also be a source of frustration and lost revenue if the threat of ElectroStatic Discharge (ESD) is ignored.

A typical scenario might be where an electronic product is brought in for service, properly diagnosed and repaired, only to find a new symptom requiring additional repair. Unless the technician understands the ESD problem and has developed methods to keep it in check damage from static electricity cannot be ruled out as a potential source of the new problem.

Static electricity is nothing new; it’s all around us and always has been. What has changed is the spread of semiconductors in almost every consumer product we buy. As device complexity increases, often its static sensitivity increases as well. Some semiconductor devices may be damaged by as little as 20-30 volts!

It is important to note that this post is addressing the issue of ESD in terms of control, and not elimination. The potential for an ESD event to occur cannot be completely eliminated outside of a laboratory environment, but we can greatly reduce the risk with proper training and equipment. By implementing a good static control program and developing some simple habits, ESD can be effectively controlled.

The Source of the Problem

Static is all around us. We occasionally will see or feel it by walking on carpet, touching something or someone and feeling the “zap” of a static discharge. The perception level varies but static charge is typically 2000-3000 volts before we can feel it. ESD sensitivity of some parts is under 100 volts – well below the level that we would be able to detect.

Even though carpet may not be used around the service bench, there are many other static “generators” may not be obvious and frequently found around or on a service bench. The innocent-looking Styrofoam coffee cup can be a tremendous source of static. The simple act of pulling several inches of adhesive tape from a roll can generate several thousand volts of static! Many insulative materials will develop a charge by rubbing them or separating them from another material. This phenomenon is known as “tribocharging” and it occurs often where there are insulative materials present.

*Sources of Charge Generation: Unwinding a Roll of Tape*

People are often a major factor in generation of static charges. Studies have shown that personnel in a manufacturing environment frequently develop 5000 volts or more just by walking across the floor. Again, 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 as much as 500-1000 volts.

Setting up a “Static Safe” Program

Perhaps the most important factor in a successful static control program is developing an awareness of the “unseen” problem. One of the best ways to demonstrate the ESD hazard is by using a “static field meter”. The visual impact of locating and measuring static charges of more than 1000 volts will get the attention of skeptical individuals.

*Static Field Meter – find more information here*

Education of Personnel

ESD education and awareness are essential basic ingredients in any effective static control program. A high level of static awareness must be created and maintained in and around the protected area. Once personnel understand the potential problem, reinforce the understanding by hanging up static control posters in strategic locations. The technician doesn’t need an unaware and/or unprotected person wandering over and touching things on the service bench.

Workstation Grounding

To minimize the threat of an ESD event, we need to bring all components of the system to the same relative potential and maintain that potential. Workstations can be grounded with the following options:

Establish an ESD Common Grounding Point, an electrical junction where all ESD grounds are connected to. Usually, a common ground point is connected to ground, preferably equipment ground.
The Service Bench Surface should be covered with a dissipative material. This can be either an ESD-type high-pressure laminate formed as the benchtop surface, or it may be one of the many types of dissipative mats placed upon the benchtop surface. The mats are available in different colors, with different surface textures, and with various cushioning effects. Whichever type is chosen, look for a material with surface resistivity of 1 x 10⁹ or less, as these materials are sufficiently conductive to discharge objects in less than one second. The ESD laminate or mat must be grounded to the ESD common grounding point to work properly. Frequently, a one Megohm current limiting safety resistor is used in series with the work surface ground. This blog post will provide more information on how to choose and install your ESD working surface.

*Types of Worksurface Matting – click here for more information*

A Dissipative Floor Mat may also be used, especially if the technician intends to wear foot-grounding devices. The selection of the floor mat should take into consideration several factors. If anything is to roll on the mat, then a soft, cushion-type mat will probably not work well. If the tech does a lot of standing, then the soft, anti-fatigue type will be much appreciated. Again, the mat should be grounded to the common ground point, with or without the safety resistor as desired.
Workstation Tools and Supplies should be selected with ESD in mind. Avoid insulators and plastics where possible on and around the bench. Poly bags and normal adhesive tapes can generate substantial charges, as can plastic cups and glasses. If charge-generating plastics and the like cannot be eliminated, consider using one of the small, low cost air ionizers It can usually be mounted off the bench to conserve work area, and then aimed at the area where most of the work is being done. The ionizer does not eliminate the need for grounding the working surface or the operator, but it does drain static charges from insulators, which do not lend themselves to grounding.

Personnel Grounding

People are great static generators. Simple movements at the bench can easily build up charges as high as 500-1000 volts. Therefore, controlling this charge build-up on the technician is essential. The two best known methods for draining the charge on a person are wrist straps with ground cords and foot or heel grounders. Personnel can be grounded through:

Wrist Straps are probably the most common item used for personnel grounding. They are comprised of a conductive band or strap that fits snugly on the wrist. The wrist strap is frequently made of an elastic material with a conductive inner surface, or it may be a metallic expandable band similar to that found on a watch. For more information on wrist straps, check out this post.
Ground Cords are typically made of a highly flexible wire and often are made retractable for additional freedom of movement. There are two safety features that are usually built into the cord, and the user should not attempt to bypass them. The first, and most important, is a current limiting resistor (typically 1 Megohm) which prevents hazardous current from flowing through the cord in the event the wearer inadvertently contacts line voltage. The line voltage may find another path to ground, but the cord is designed to neither increase or reduce shock hazard for voltages under 250 volts. The second safety feature built into most cords is a breakaway connection to allow the user to exit rapidly in an emergency. This is usually accomplished by using a snap connector at the wrist strap end.
Foot or Heel Grounders are frequently used where the technician needs more freedom of movement than the wrist strap and cord allow. The heel grounder is often made of a conductive rubber or vinyl and is worn over a standard shoe. It usually has a strap that passes under the heel for good contact and a strap of some type that is laid inside the shoe for contact to the wearer. Heel grounders must be used with some type of conductive or dissipative floor surface to be effective and should be worn on both feet to insure continuous contact with the floor. Obviously, lifting both feet from the floor while sitting will cause protection to be lost.Don’t forget to regularly check and verify your personnel grounding items:

Summary

An effective static control program doesn’t have to be expensive or complex. The main concept is to minimize generation of static and to drain it away when it does occur, thereby lessening the chance for an ESD event to happen. The ingredients for an effective ESD program are:

Education: to ensure that everyone understands the problem and the proper handling of sensitive devices.
Workstation Grounding: use a dissipative working surface material and dissipative flooring materials as required.
Personnel Grounding: using wrist straps with ground cords and/or foot-grounding devices.
Follow-up to ensure Compliance: all elements of the program should be checked frequently to determine that they are working effectively.

The ESD “threat” is not likely to go away soon, and it is very likely to become an even greater hazard, as electronic devices continue to increase in complexity and decrease in size. By implementing a static control program now, you will be prepared for the more sensitive products that will be coming.

5 Common Mistakes in ESD Control & How to Avoid Them

Image scsstaticcontrol July 26, 2018 1

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.

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.

“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!

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

“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:

Ground the garment to the body through a wrist strap-direct connection with an adapter.
Ground the garment through conductive wrist or heel cuffs in direct contact with the skin of a grounded operator.
Ground the garment through a typical separate ground cord, directly attached to an identified groundable point on the garment.
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.

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

“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.

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.

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.

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.

“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.

ESD Symbols You Need To Know

Image scsstaticcontrol June 28, 2018 0

If you’ve been handling ElectroStatic Discharge (ESD) sensitive devices for a while, you’ve probably come across the various ESD symbols already. But do you know the difference(s) and when to use them?

If you are new to ESD protection or have just taken over responsibility for an existing ESD program, this is where to start!

Introduction

The ESD Standard ANSI/ESD S20.20 requires that “ESDS items, system or packaging marking shall be in accordance with customer contracts, purchase orders, drawing or other documentation.” [ANSI/ESD S20.20 clause 8.5 Marking]. If ESD sensitive items are not covered in any of these documents, each company has to decide whether marking is required. If it is deemed necessary, the ESD Control Program Plan needs to define the details.

ESD Susceptibility Symbol

The ESD Susceptibility Symbol is the most commonly known symbol which consists of a yellow hand in the act of reaching, deleted by a bar; all within a black triangle. It is intended to identify devices and assemblies that are susceptible to ESD.

When to use the ESD Susceptibility Symbol:

The ESD Susceptibility Symbol is correctly used as follows:

on individual components and related documents to state: ‘this device is static sensitive; do not touch without appropriate precautions’
on assemblies and related documents to state: ‘includes static sensitive components; take appropriate precautions’
as part of a sign identifying an area where sensitive devices are handled; to warn all who approach it that precautions are required

Color of the ESD Susceptibility Symbol

The color is optional except “the color red shall not be used because it suggests a hazard to personnel.” [ANSI/ESD S8.1 clause 4.2.1 color].

Normally, the hand and slash symbol is used on a black triangle on a yellow or orange background.

ESD Protective Symbol

Just like the ESD Susceptibility Symbol, the ESD Protective Symbol has a reaching hand in a triangle. However, note the arc and missing slash through the triangle! Because of these differences it has a very different meaning.

This symbol should be on ESD protective products identifying a specialty product that has at least one ESD control property.

The ESD Protective Symbol is also called the ESD Packaging Symbol.

If a letter is under the triangle, it should identify the most important ESD control property:

L = Low Charging
D = Static Dissipative
C = Conductive EPA (for use in the ESD Protected Area)

When to use the ESD Protective Symbol

The ESD Protective Symbol may be used to identify items that possess at least one ESD control property:

Low Charging (formerly referred to as astatic or antistatic)
Resistance (Conductive or Static Dissipative) able to remove electrostatic charges when grounded
Discharge Shielding

Color of the ESD Protective Symbol

The color is optional except “the color red shall not be used because it suggests a hazard to personnel.” [ANSI/ESD S8.1 clause 5.2.1 color].

Normally, a hand symbol is used on a black triangle on a yellow background.

ESD Common Ground Point and Earth Bonding Point Symbols

These two symbols identify where all ESD elements at an ESD workstation should be connected. There is a newer and older symbol; they are very different but basically have the same meaning:

The Earth Bonding Point Symbol has the earth ground symbol and concentric circles around the ground snap, plug or jack. This is the older symbol.
The ESD Common Ground Point Symbol has concentric circles with thick circle around the ground snap, plug or jack. This is the newer symbol.

Both symbols should include text identification.

ESD Common Ground Point (newer symbol) and Earth Bonding Point (older symbol)

Color of the ESD Common Ground Point and Earth Bonding Point Symbols

The color is optional except “the color red shall not be used because it suggests a hazard to personnel.” [ANSI/ESD S8.1 clause 5.2.1 color].

Conclusion

The ESD Standard S20.20 recommends that every organisation handling ESD sensitive items marks their products using the above 3 symbols for every. Correct use of markings will “indicate that an item or material is ESD susceptible and those that indicate that an item is designed to afford some degree of ESD protection.” [ANSI/ESD S8.1 clause 1.1 Purpose]

Symbol artwork for all of the above symbols can be downloaded at no charge from the ESD Association.

Controlling ESD/EOS During the Soldering Process

Image scsstaticcontrol April 12, 2018 0

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.

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).

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.

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.

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.

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:

Industry Council on ESD Targets: White Paper 4: Understanding Electrical Overstress – EOS
In Compliance: Rethinking Electrical Overstress
EEWeb: Electric Overstress (EOS) and Its Effects on Today’s Manufacturing
EEWeb: EOS Exposure of Components in Soldering Process
Dangelmayer Associates/ESD Association: Electrical Overstress – Many Sources; Any Solutions?

11 Steps to an ESD Control Program

Image scsstaticcontrol June 29, 2017 0

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]

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
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.
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.
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

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 foot grounders on an ESD floor as a personnel grounding method

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