The major advantage* of ESD shoes is that they do not require a tab to connect to the operator. Conductive additives are blended into the sole (inside to outside) of the ESD shoes and connects (through the sweat layer) to the operator’s feet. However, there are a number of other considerations to when selecting ESD footwear:
Does the footwear meet the ESD Association (ESDA) standards?
Many manufactures of ESD shoes often reference ASTM standards for their ESD spec, but state nothing about ESDA standards. The ESDA standards are written specifically for electronics manufacturing and handling. The walking test defined in the ANSI/ESD STM97.2-2006 is one of the most important methods for qualifying ESD footwear for used in ESD Protected Areas.
Not all ESD footwear is created equal.
There are different styles of both ESD shoes and ESD footwear. In most cases the specs of each style will vary. While one style of ESD footwear may retain its ESD properties for 6 months or longer, another will start failing within 90 days. The performance of all styles of ESD footwear should be verified on an on-going basis (twice daily testing is the norm) and records should be kept for quality control purposes.
Involve operators in the selection process.
The intentions of a ESD Control Plan are always to improve the quality control process of a facility. However, getting employees to participate and support the program is not always that simple. When selecting an ESD footwear is a good idea to consider the opinion on the operators. They may not find the style of ESD shoe being considered to be comfortable or they may become frustrated that the ESD foot grounder that has been selected does not stayed secured properly. In some facilities, many operators are temporary or on a flexible schedule that would not justify certain types of ESD footwear and it is never recommended that operators share footwear due to hygiene issues.
Consider the cost/value of the footwear program.
In most cases a ESD footwear-flooring system is an ongoing program that will need to be continuously managed. With ESD footwear there are is two major value components of an ESD footwear product- ESD properties and the durability of the footwear. ESD footwear must maintain a consistent Point to Groundable Point Resistance of < 1 x 109 (ANSI/ESD STM97.1) and Walking Voltage Generation of <100 volts (ANSI/ESD STM97.2) throughout the useful life of the product. The concern with the ESD footwear’s durability is that a breakdown can contribute to foot, leg, back pain or other discomfort in the operator. Initial qualification of footwear for both the ESD properties and physical structure is an important factor in the ESD footwear selection process.
Desco offers samples of foot grounders for product qualification and sizing purposes.
*In some cases protective footwear (shoes, boots, etc) is required to prevent foot injuries due to falling or rolling objects, or from objects piercing the sole. Safety of the operator takes priority over ESD control at all times. If protective footwear with reliable ESD properties is not available or foot grounders cannot be worn with the protective footwear in the ESD Protected Area, other personnel grounding devices such as wrist straps should be used.
Most people notice a difference in the ability to generate static electricity when the air gets dryer (the % RH decreases). As an example, walking across a carpet can yield a charge of 35kV at 10% RH [very dry air], but will drop significantly to 7.5kV at 55% RH. In an electronics manufacturing environment lower humidity may result in lower yields from production due to an increase in ESD events during manufacturing processes.
A normal range for humidity in an electronics manufacturing environment is be between 30%RH and 70%RH. Some facilities try to maintain a constant moderate RH (~50%), whereas other environments may want lower %RH due to corrosion susceptibility to humidity sensitive parts. The recommended humidity range is usually determined by the specs of the devices and components being assembled. Increasing the humidity in a an electronics manufacturing facility can help to reduce ESD events, increased humidity can lead to other unwanted quality issues in electronics manufacturing environment such as corrosion, soldering defects and the popcorn effect on moisture sensitive devices.
While not a replacement for grounding, shielding, or ESD worksurfaces, ionization can mitigate ESD events in areas where dry air is normal*. Worksurface ionizers (Benchtop and Overhead Ionizers ) produce positively and negatively charged ions that are moved to the controlled area with fan driven airflow. Point-of-use air ionizers use compressed gas to combat electrostatic attraction neutralizing charges on particles causing contamination or visual defects on products. Laminar Flow Ionization Bars are used with Laminar Flow Hoods, controlled chambers and other contained applications. Room Ionization reduces electrostatic discharge (ESD) and electrostatic attraction (ESA) in cleanroom environments.
The ESDA’s TR20.20-2008 discusses RH in a few different places. Some significant statements are listed below.
ESD Handbook ESD TR20.20-2008 section 2.3 Nature of Static Electricity:
“The moisture level in the air, or relative humidity in the environment, are important considerations in the liberation and accumulation of static electricity. It is well known that static electricity in the form of static cling and static shocks are more prevalent when the air is dry. Heating interior air in the winter months dries out the already dry air in the higher latitudes. Static charge accumulation is easier on dry materials since moisture on surfaces tends to allow charges to slowly dissipate or recombine.
However, it is impractical to use humidity control alone to provide static control since static charges are developed even at relative humidity levels of 90% and greater. For most situations, 30 to 70% RH is considered the appropriate range. Special areas, such as wafer fabrication, may require lower humidity control for processes that are affected by moisture (e.g., photoresist application). Soldering is known to be affected by high relative humidity conditions (>70%). For areas that have low ambient humidity, ionization is an important consideration to aid in reducing charge accumulation levels and provide neutralization of charges after they are developed but before they can cause difficulties.”
ESD Handbook ESD TR20.20-2008 section 5.3.16 Humidity:
“Humidity is beneficial in all ESD control program plans. Contact and separation of dry materials generates greater electrostatic charges than moist materials because moisture provides conductivity that helps to dissipate charge. For this reason, ESD effects are most noticeable in the winter since heating systems reduce building environment moisture. Geographic location (desert vs. coastland) is also a major contributor to ambient conditions inside buildings. Any circumstance that results in a low relative humidity will permit a greater accumulation of electrostatic charges. Relative humidity above 30% in ESD protective areas is desirable as long as other adverse conditions are not created as a result of humidity levels. Generally speaking an upper limit of 70% is desirable to prevent corrosive effects on the metal portions of electronic devices and assemblies.
Besides the increasing propensity to generate electrostatic charges on dry materials in general, performance of many ESD protective materials degrade. In fact, when exposed to low humidity conditions, some ESD protective materials become totally ineffective or become sources of electrostatic charges. Therefore, evaluation of ESD control materials should include performance testing in controlled environments at the lowest expected operating relative humidity level. Manufacturers of ESD protective materials should be able to provide performance data in regards to relative humidity. Likewise, materials should be tested in moderate humidity conditions as well to ensure they do not become “too conductive” and present a potential safety hazard to personnel working with substantial voltages. See the Personnel Safety section of this handbook for further guidance in this area.
Humidity control in factories or physically large areas or buildings can be difficult and expensive. In smaller rooms or areas, it may be possible to use portable humidifiers to raise the immediate area humidity. However, in large facilities and factories the environmental systems many need to include steam generation and monitoring equipment to control humidity. This type of equipment is expensive to install and purchase especially in pre-existing facilities. To reduce the total cost impact, companies should consider the need for humidification equipment when planning new facility construction.”
A complete static control program must also deal with isolated conductors that cannot be grounded and insulating materials (e.g., most common plastics). If an insulator cannot be removed from the ESD Protected Area, substituted with an ESD protective version, or controlled with a topical antistat, ionization must be used. These insulators are often referred to as process necessary insulators. Common process necessary insulators used for manufacturing electronics include flex cables, product enclosures, test fixtures, and the PCB substrate substrate itself*.
Neutralization of charges on insulators does occur naturally as positive and negative charged ions are in the atmosphere. As opposite charged ions are attracted to the charge on the insulator, the charges will be neutralized over time (same charged ions will be repelled). However, the process is much too slow for ESD susceptible components.
Examples of some common process necessary insulators are PC board substrate, insulative test fixtures, and product plastic housings. Examples of isolated conductors can be conductive traces or components loaded on a PC board that are not in contact with ESD worksurface.
The primary functions of ionizers are to:
- Discharge / Neutralize process necessary insulators that can charge ESDS devices / assemblies via induction, thus creating potential CDM damage, and/or
- Discharge / Neutralize ESDS devices / assemblies that are not grounded, thus are an isolated conductor, thus creating potential CDM damage, and/or
- Discharge / Neutralize insulators where particulate contamination can cause visual defects (for example – dust on plastic or glass lenses, attracted to / held in place by Electrostatic Attraction [ESA])
*Note. The PCB substrate is a process necessary insulator and can become charged during automated handling processes and the ESD susceptible components on the PCB may be isolated or floating conductors as well.
Desco offers a variety of ionizers:
Contact Desco for more information about when you need to ionize or how to choose the right ionizer for your application.
Lenovo Service posted a video on their youtube site called “Understanding Electrostatic Discharge (ESD) for Technicians.” We encourage you to take a look.
The video is very informative and does a good job of covering the basics of ESD control when working with ESD susceptible devices or components. The basic practices of controlling ESD when handling ESD susceptible items are pretty straight forward.
- Establish and control access to an ESD Protected Area. It can be one bench or a whole facility (or a field service kit that a Lenovo Service person might use)
- Ground all conductors including operators.
- Use a dissipative grounded surface for ESD susceptible products to be placed on if needed.
- Remove all non-process essential insulators from the ESD Protected Area. Use ionization to control charges on process essential insulators.
- If an ESD susceptible item needs to be removed from the ESD Protected Area, place it in a shielding bag or storage container that forms a faraday cage.
- Electrical current flows easily
- Can be grounded
Materials that easily transfer electrons (or charge) are called conductors and are said to have “free” electrons. Some examples of conductors are metals, carbon, and the human body’s sweat layer.
Grounding works effectively to remove ElectroStatic charges from conductors to ground. The other term often used in ESD control is dissipative, which is 1 x 104 to less than 1 x 1011ohms and is sufficiently conductive to remove ESD charges when grounded.
- Electrical current does not flow
- Cannot be grounded
Material that does not transfer electrons are called insulators, by definition non-conductors. Some well known insulators are common plastics and glass. An insulator will hold the charge and cannot be grounded and “conduct” the charge away.
The options for insulators in and ESD Protected Area are:
- Remove the insulative item from the ESD Protected Area
- Substitute the item with an ESD protective version (such as tape, document holders, material handling containers, plastic bottles, etc.)
- Periodically treat insulative surface with a topical antistat
- Neutralize electrostatic charges using ionization
Learn more about the Basics of ESD with the 06821 ESD Awareness Guide.
The ESDA established the TR53 Technician Certification Program, which is based on the ESDA’s technical report, ESD-TR53 Compliance Verification of ESD Protective Equipment and Materials. This important document supports and maintains static control programs designed around ANSI/ESD S20.20 Standard for the Development of an Electrostatic Discharge Control Program for Protection of Electrical and Electronic Parts, Assemblies and Equipment, and the European technically equivalent standard IEC 61340-5-1.
March 16-18, 2016 Professional Certification ESD Technician (German language Course) (ESDA Certified TR53 Technician Course) Hotel Vier Jahreszeiten 82319 Starnberg, Germany. Registration form pdf
April 5-7, 2016 Level 1: ANSI/ESD S20.20 Plant Auditor (ESDA Certified TR53 Technician Course) Double Tree by Hilton Hotel Chicago Wood Dale 1200 N. Mittel Blvd Wood Dale, IL USA 60191 Register Online
May 25-27, 2016 Level 1: ANSI/ESD S20.20 Plant Auditor (ESDA Certified TR53 Technician Course) Singapore Register Online
May 30-June 1, 2016 Level 1: ANSI/ESD S20.20 Plant Auditor (ESDA Certified TR53 Technician Course) Taiwan Register Online
June 21-23, 2016 Professional Certification ESD Technician (ESDA Certified TR53 Technician Course) Holiday Inn Express Dresden City Centre 01067 Dresden. Registration form pdf
Click HERE for more information.
The ideal ESD Control Plan is one that improves productivity, quality, and reliability, in addition to being flexible enough to accommodate changes and improvements in the manufacturing process. ESD Control Plans must evolve to keep pace with costs, device sensitivities, and the way devices are manufactured in the future. The management of an on-going ESD Control Plan can be broken down into 3 steps: 1. Measure, 2. Control, and 3, Verify.
Step 1. Measure the source the of ESD events.
- Measure the resistance of an operator to ground.
- Measure the charge generation (walking test) of an operator.
- Measure the static field on a housing of an assembled product.
Step 2. Control ESD by implementing products to eliminate the source of ESD events.
- Control charges generated by an operator by implementing a personnel grounding (wrist strap/foot grounders) program.
- Control charges generated by operators when walking in the ESD Protected Area by installing a flooring/footwear system.
- Control charges on insulators with point of use ionization at the work area.
Step3. Verify that the ESD control measures implemented are functional and effective.
- Verify that operators are using their wrist strap correctly with continuous monitoring.
- Verify that people entering the ESD Protected Area are wearing properly functioning ESD footwear with access control style wrist strap/footwear testers.
- Verify the charge decay time, balance, and coverage area of an ionizer with static field meter.
Feel free to contact Desco for tips how you can effectively measure, control, and verify ESD in your work area.
As electronic technology advances, electronic circuitry gets progressively smaller. As the size of components is reduced, so is the microscopic spacing of insulators and circuits within them, increasing their sensitivity to ESD. Industry experts estimate that average electronics product losses due to static discharge range from 8 to 33%. Others estimate the actual cost of ESD damage to the electronics industry as running into the billions of dollars annually. It is therefore critical to be aware of the most sensitive items being handled in your factory as the need for proper ESD protection increases every day.
Here are some tips on how to get ahead of the game:
1. Establish and identify an ESD Protected Area (EPA)
An ESD Protected Area (EPA) is a defined space within which all surfaces, objects, people and ESD Sensitive Devices (ESDs) are kept at the same potential:
- All surfaces, products and people are linked to ground.
- Movable items, such as containers and tools, are bonded by virtue of standing on a grounded surface or being held by a grounded operator.
- Everything that does not readily dissipate a charge must be excluded from the EPA.
A good to place to start your fight against ESD is our example of an EPA as it lists all products required in a proper EPA.
A few things to remember:
- The ESD protected area should have signage to clearly identify where it is.
- Only trained or escorted people are to be allowed in the EPA.
- All conductors including Personnel must be grounded. Operators must either wear wrist straps or footwear in combination with an ESD floor. ESD worksurfaces (e.g. mats) are to be grounded.
- Wrist straps and footwear are to be tested daily. For wrist straps, a continuous monitor can be used instead.
- Periodic checks of installed products (e.g. ESD worksurfaces, ESD flooring etc.) are required.
- Remove all non-essential insulators or neutralize essential insulators with ionizers.
- Only handle unpackaged ESDs in an EPA when grounded.
- Wristbands are to be worn snug; the grounding tab of foot grounders must be placed under the foot in the shoe; ESD smocks need to cover all clothing on the torso.
- Use packaging with shielding properties to store or transport ESDS outside the EPA.
2. Identify ESD sensitive items (ESDs)
It is critical to be aware of the most sensitive item being handled in your factory. From goods-in through to dispatch packaging shielding properties should be used to protect ESDs during transport and storage. Any ESD sensitive item should be identified with the ESD sensitivity symbol, either on itself or its container. The ESD Sensitivity Symbol (also called Susceptibility or Warning Symbol) identifies items that can be damaged by ESD and should ONLY be unpackaged and handled while grounded at an ESD protected workstation.
3. Provide ESD control training
This is probably the most important point of all. You can have the best EPA in the world but if your staff don’t know about ESD and the problems it creates, it will be money wasted. People handling ESDs are still a major source of ElectroStatic charges and discharges. Operators need training and need to be vigilant that ESD control procedures are followed. In order for an ESD control programme to be effective, operators must be aware of:
- the threat of ESD,
- understand & adhere to the rules of controlling static electricity
- and know how to properly use ESD control items.
Any questions? Feel free to Contact Desco for more tips on controlling ESD.
The EOS/ESD Association is offering tutorials. Don’t miss out on this opportunity to enhance your knowledge of ESD. Both tutorials are requirements of the ESDA Program Manager Certification curriculum. Register early and save!
May 11 – 12, 2016 ($1,710)
The ESD Program Development and Assessment (ANSI/ESD 20.20 Seminar) – Learn How to implement and maintain an effective ESD control program plan.
May 13, 2016 ($510)
Electrostatic Calculations for the Program Manager and the ESD Engineer – Learn the proper understanding of the differences among the calculations for peak current, power, energy, and threshold voltage for a simple device.
Click HERE to learn more.
As pointed out by the ESD Association, “Certification provides confirmation that a person meets certain criteria of knowledge and problem-solving ability. Certification can be beneficial on multiple levels. For the certifying organization, it provides standard practices that create discipline within the industry, it provides awareness and advances in technology, and it can provide increased cooperation between organizations. For the employer, it can result in increased safety, higher product yield, and increased customer and employee confidence that produces dedication and improved teamwork. For the certified professional, it provides credibility in the industry; it demonstrates knowledge, experience and competency. It typically creates increased opportunities for career advancement and increased earnings. It is clearly one form of professional development, and can improve job performance through the increased confidence that comes with “knowing what you know.”
Are you interested in ESD training and certification?
Learn more about ESD Certification and the different certificates available by visiting the ESD Association Certification page: https://www.esda.org/certification/
Additional information on ESD training and certification is available here: http://www.halperinassoc.com/services/esdtraining/esdspecialistprogram/schedule.asp