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Unraveling The Dynamics of ESD Safety

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Danielle Woodruff, Marketing Manager, Controlled Environment

When it comes to Electrostatic Discharge (ESD) Safety, it’s all about control – static control. The ESD Association® sets many of the global standards that are considered guiding principles for static control and ESD Safety. Devising the control of electrostatic discharge within a set environment is challenging and there are key static control concepts that are essential to the design of successful ESD control programs.

THE PRINCIPLES OF STATIC CONTROL

Effective ESD Safety means going on the offensive because no matter what we do, a built-up static charge will always try to find a way to discharge. That leaves two options: (1) trying to prevent or slow the build-up of static or (2) manipulating an environment so static can discharge safely. These are the steps that ESD professionals take to further develop these concepts into comprehensive ESD Control programs:

1. Identify the areas where ESD Susceptible (ESDS) items are to be handled
2. Determine and define the level of control needed within that environment and label them as Electrostatic Protected Areas (EPA)
3. Reduce the generation of static charge by balancing the electrostatic potential of processes and materials, as well as creating grounding paths
4. Dissipate and neutralize electric charge through the use of static control materials
5. Use proper grounding and ESD Safe materials to protect products from discharge

THE ROLE OF ANSI / ESD S20.20

Over the years, the large variation in the types of ESD Controlled Environments has resulted in the development of standards, guidelines and manufacturing best practices that cover the requirements necessary to design, implement and maintain an organization’s ESD Control Program. ANSI/ESD S20.20 is a comprehensive standard that outlines tests and requirements that tailor the development of an ESD program for the protection of electrical and electronic parts, assemblies and equipment. More specifically, the standard sets out technical requirements, limits and test methods associated with grounding and bonding systems, personnel grounding and EPA ESD control items.

ESD CONTROL: ALWAYS A CHALLENGE

If we think about it, it is inherently challenging to reduce static generation within a Controlled Environment when one of the leading generators of static electricity is the workers (technicians) themselves. Every time they walk or move, they can generate static electricity. And, when they pick up an object or create contact or separation between two material surfaces, they may potentially be discharging thousands of volts of static charge from their body. So, how can an ESD safe environment be properly managed when one of the biggest hazards is the people themselves?

THE IMPORTANCE OF PERSONAL ESD PROTECTION

Mitigating the risk that humans pose in an ESD environment is evaluated holistically in terms of the working environment. Everything from air quality, relative humidity, walls and flooring – as well as equipment and furniture are considered. Workers are expected to wear ESD safe personal protective gear which may include garments, gloves, footwear and grounding straps with static control properties to ensure the parameters set by the ESD control program are maintained. By using the correct materials to balance static potential and creating grounding paths to prevent the buildup of electric charge, the product is protected.

STATIC CONTROL GARMENTS

Static control garments are essential in most EPAs, particularly in dry or cleanroom environments. A commonly asked question is “If a technician is wearing a wrist strap, why do they also need an ESD static control garment?”

The primary purpose of static control garments is to protect ESD items from the static discharge caused by the buildup on worker clothing.

While wrist straps provide a reliable path to ground, the static buildup on clothes will not be removed through the wrist strap. This is because regular clothing fabrics are typically non-conductive (insulative) meaning they do not easily transfer electrons. Certain synthetic fabrics may actually be the cause of a significant amount of static buildup. Upon contact with a sensitive electronic part, technicians risk having thousands of volts discharge.

Static control garments provide a solution by primarily acting as a conductive control shield that surrounds the user’s clothing, blocking electrostatic influences. Static control garments are made of a dissipative material that incorporates conductive elements, such as carbon, into material fibers that are then interwoven in a mesh throughout the garment’s design. Continuous panel-to-panel conductivity is tested to ensure the garment can effectively block isolated static buildup.

So now the question is – does a worker need to wear a wrist strap if they are wearing a static control garment? The answer depends on the design of the garment and the ESD program’s required level of resistivity. ESD static control garments have conductive elements built into the fabric and therefore need to be grounded or they can run the risk of becoming a charged conductor. There are a few ways that static control garments release charge to ground.

• Garment Ground Snaps and Cords: Technicians use a grounding cord that can attach to grounding snaps on the garment, usually located on the waist, hip or wrist areas.
• Garment Skin Contact: The conductive material of the garment equalizes and dissipates charge through the direct skin contact of a grounded operator. (Note that if a technician is relying on skin contact to dissipate any static buildup, they need to either be wearing short sleeves or push their sleeves up to ensure that continuous contact is made with the garment.)

There are three main categories of ESD garments. They are tested for product qualification under ANSI/ESD STM2.1 and compliance verification under ESD TR53. Both methods are part of the ANSI / ESD S20.20 program and test the resistance of each garment to ensure it is classified under the correct limits.

ESD SAFE HAND PROTECTION

Gloves and finger cots with static control properties are made of (or treated with) materials that are inherently anti-static or static dissipative or blended with conductive materials. The ANSI / ESD SP15.1 is the standard of reference for In-Use Resistance Testing of Gloves and Finger Cots. It covers multiple resistivity tests, including:

• ANSI/ESD STM11.11: Surface Resistance Measurement of Static Dissipative Planar Materials
• ANSI/ESD STM 11.12: Volume Resistance Measurement of Static Dissipative Planar Materials
• ANSI/ESD STM 11.13: Two-Point Resistance Measurement of Dissipative and Insulative Materials
• Constant Area and Force Electrode (CAFE): Specifically designed for resistance measurements at the thumb and fingertips

The values of each of these tests are important to electrical engineers developing an ESD program, however the CAFE resistivity test is often cited on spec sheets to help compare the static dissipative characteristics of different gloves. Depending on the type of glove and environment that it must operate in, other glove standards may be applied such as testing for chemical, heat and cut resistance – as well as cleanroom level.

DEFINING RANGES OF SURFACE RESISTANCE

Often, people will characterize ESD performance as ranging from anti-static to static dissipative and conductive. The reality is that ranges are dynamic and dependent on the materials and industry. This being said, producers of ESD safe protective gear such as gloves, clothing and accessories will still outline surface resistivity ranges because it helps more easily identify products that meet the needs of specific ESD Control Programs. Below is the illustrated range PIP® has suggested for our lines of ESD safe gloves and finger cots:

 

CHOOSING THE RIGHT PROTECTION FORA PROFESSIONALLY MANAGED ESD PROGRAM

It is important to remember that ESD protective products are to be considered as a part of a comprehensive ESD Control program developed and managed by an ESD program manager or coordinator. They will develop a program that specifies building, equipment and personal protective products that meet the performance criteria outlined in their program.

PIP® offers a full range of ESD gloves, finger cots and garments. Explore PIP’s range of ESD Safe products to discover the best options to meet a customer’s professionally managed ESD Control Program.

• Precision ESD Knit Gloves for electronics manufacturing and assembly
• ESD Safety for Cleanroom that exceeds standards for the lowest levels of extractables and particulates
• ESD Safe Finger Cots for precision ESD and cleanroom applications
• Special ESD Protection for chemical and thermal applications
• ESD Safe Garments for electronics, industrial and aerospace manufacturing

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