Methods for Anti Static Mats Archives

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When you work with sensitive electronic products, you know that static electricity is one of the problems affecting company safety and profitability. Electrostatic discharge (ESD) is an ongoing issue, even for organizations that don’t directly handle electronic products, such as hospitals. Regardless of the industry or company type, the first line of defense against the effects of static electricity is to establish and implement approved ESD grounding requirements.

Getting a Handle on ESD Grounding Requirements

To determine your specific ESD grounding requirements, you must first identify the areas where grounding is needed. These areas can include:

• Manufacturing floors
• Work benches
• Packing and shipping centers
• Clean rooms
• Research and development labs

ESD grounding requirements are, in essence, a codified form of static controlas set out in the American National Standards Institute S20.20. By creating an official written policy that outlines how employees should ground themselves and their equipment, you can expect to experience an increase in safety that minimizes the risk of damage to both personnel and products. Static control is the act of defining the amount of control needed, and subsequently creating a plan to allow for static dissipation. Naturally, this plan for static dissipation is largely concerned with how your organization handles ESD grounding.

Determining Your ESD Grounding Requirements

Your company’s ESD grounding requirements will generally depend on the size of your workspace, as well as the type of work that your company performs.

Smaller work environments, such as computer repair shops, will need to adhere to just the basic ESD grounding requirements. In practice, this involves providing a two-step grounding solution for employees and work equipment.

1. The first step is to connect all equipment and personnel to a common ground point. This could be a grounding wrist strap, a dissipative work mat, or anything else that allows a static charge to dissipate.
2. The second step involves connecting the common ground point to the grounding conductor.

For larger facilities, such as Hospitals, more stringent ESD groundingrequirements need to be followed due to the extremely sensitive nature of their work. The nature of modernized hospitals means they have a strong chance of containing flammable or explosive gasses, making static electrical events more dangerous than ever. Strict protective measures are especially important to enforce in these types of situations.

Operations with large working environments will often require the establishment of ESD protected areas (EPA). EPAs are sections of the workspace that are partitioned off from the rest of the facility and specially marked to notify employees and visitors of the potential for electrostatic events.

ESD Grounding Requirements Are All About Protection

As one might expect, the ultimate purpose of ESD grounding requirements is the ongoing safety of personnel working in the EPA, as well as the facility at large. Safety begins with the use of duly-enforced ESD grounding requirements within an EPA.

These grounding requirements help protect employees because they work to reduce the threat of harmful discharge. Although static shocks themselves may not be very painful, they can cause serious injuries and health complications when allowed to escalate. In extreme circumstances, static shocks can even cause fires and severe electrical shocks, in addition to interfering with personal electronic medical equipment, such as hearing aids and pacemakers.

Time to Get Equipped

To reach full compliance with your company’s ESD grounding requirements, you will almost certainly have to use grounding wrist straps, antistatic work mats, and earth bonding plugs. These are standard industry equipment used for controlling and dissipating static electricity.

If your facility includes the presence of a clean room, there will be a greater need for specialized equipment and cleaning chemicals in order to meet ESD grounding requirements. Clean rooms often require the use of full-body anti-static safety suits, ionized blowers, and antistatic work tools.

Review the ESD threats within your work environment, determine the level of ESD grounding requirements needed, and then create a plan to maximize safety.

Most ESD Protected Areas (EPAs) will contain a bench or a series of benches. It is important that each bench, or worksurface, is covered with the correct ElectroStatic Discharge (ESD) protective material. They also have to be properly connected to earth using a system of cords and common point grounds. Today’s post will explain in more detail how these ESD protective worksurface work and what you need to look out for.

Introduction

The purpose of an ESD protective worksurface is to aid in the prevention of damage to ESD sensitive items (ESDS) and assemblies from electrostatic discharge.
ESD worksurfaces, such as mats, are typically an integral part of the ESD workstation, particularly in areas where hand assembly occurs. An ESD protective worksurface provides protection in two ways:

1. Providing a low charging (antistatic) worksurface area that will limit static electricity to be generated below potentially damaging levels.
2. Removing the electrostatic charge from conductive objects placed on the worksurface.

Types of ESD protective worksurfaces

When deciding to invest in ESD protective worksurfaces, you have the choice of ESD matting (laid-out on a standard non-ESD bench) or ESD benches. Performance-wise there is no difference.

Generally speaking, ESD matting offers a lower initial investment and is easier to replace. On the other hand, some people prefer the robust and consistent approach of ESD benches.

An ESD protective worksurface is usually dissipative. Although conductive materials are the quickest to ground a charge, they can also cause damage by discharging too rapidly. Dissipative worksurfaces have a surface resistance of at least 1 x 10⁴, but less than 1 x 10⁹ ohms. Dissipative materials will dissipate a charge slower and are recommended for handling electronic components. Dissipative materials are usually the preferred choice for bench top worksurfaces.

Grounding of ESD protective worksurfaces

ESD protective worksurfaces need to be grounded. A ground wire from the surface should connect to the common point ground which is connected to ground, preferably equipment ground. For electronics manufacturing a worksurface resistance to ground (Rg) of 1 x 10⁴ to less than 1 x 10⁹ ohms is recommended. Best practice is that ground connections use firm fitting connecting devices such as metallic crimps, snaps and banana plugs to connect to designated ground points. The use of alligator clips is not recommended.

Using a current limiting resistor in the ground cord is the user’s choice. However, the resistor is not for ESD control purposes. The ESD Association standard for grounding is ANSI/ESD S6.1 which recommends a hard ground (no resistor) but allows the use of a current limiting resistor in the mat’s ground cord. “The grounding conductors (wires) from wrist straps, working surfaces, flooring or floor mats, tools, fixtures, storage units, carts, chairs, garments and other ESD technical elements may or may not contain added resistance. Where added resistance is not present, a direct connection from the ESD technical element to the common point ground or common connection point is acceptable and recommended.

Note: Manufacturers may add resistance to the grounding conductors for purposes other than ESD (e.g. current limiting). Added resistance is acceptable for the purposes of controlling ESD provided electrostatic accumulation does not exceed specific EPA requirements. The typical added resistance in grounding conductors is 1 megohm, although other values may be specified.” [ANSI/ESD S6.1 section 5.3.3 ESD Technical Element Conductors]

Using ESD protective worksurfaces

Operators need to ensure that the ESD workstation is organized to perform work and that all unnecessary insulators and personal items are removed. Regular plastics, polystyrene foam drink cups and packaging materials etc. are typically high charging and have no place at an ESD protective workstation.

When working at an ESD workstation, users have to be grounded, too. A wrist strap is arguably the best way to provide a safe ground connection to the operator. While it does not prevent the generation of charges, its purpose is to dissipate these charges to ground as quickly as possible.

When working on high-end sensitive components, the use of Continuous Monitors is recommended. Operators connect their wrist strap to the unit to allow for real-time continuous monitoring. If the wrist strap fails, the unit will alarm.

An option available with most Continuous Monitors is the ability to monitor worksurface ground connections. “Some continuous monitors can monitor worksurface ground connections. A test signal is passed through the worksurface and ground connections. Discontinuity or over limit resistance changes cause the monitor to alarm. Worksurface monitors test the electrical connection between the monitor, the worksurface, and the ground point. The monitor however, will not detect insulative contamination on the worksurface.” [ESD TR 12-01 Technical Report Survey of Constant (Continuous) Monitors for Wrist Straps]

When the monitor is connected to an ESD worksurface mat, the amount of current that flows is a function of the total resistance between the monitor and through the working surface to ground. When the resistance of the worksurface is below a pre-set threshold, the monitor will indicate good. Conversely, if the resistance level is high when compared to the monitor’s reference, the unit will alarm. This is an integrating resistance measuring circuit, therefore it is relatively insensitive to externally induced electromagnetic fields.

Maintaining your ESD protective worksurface

An ESD worksurface must be maintained and should be cleaned with an ESD cleaner. Regular cleaners typically contain silicone and should never be used on an ESD working surface.

Operators need to be on guard every day and check visually that ground wires are attached correctly. The company’s compliance verification plan should also include periodic checks of worksurfaces measuring:

• Resistance Point-to-Point (Rp-p) and
• Resistance-to-ground (Rg).

Surface resistance testers can be used to perform these tests in accordance with S20.20 and its test method ESD TR53. If these measurements are within acceptable ranges, the worksurface and its connections are good.

Verifying Surface Resistance using the SCS 701 Analog Surface Resistance Megohmmeter

Conclusion

Most people in the industry consider worksurfaces to be the second most important part of an ESD Control Program, with personnel grounding being the most important.

It is therefore important to install, use and maintain ESD protective worksurfaces correctly. Following all steps outlined above will ensure your ESD sensitive components are protected.

Not sure which ESD worksurface is right for you? Request a free ESD/EOS Assessment for your facility by one of our knowledgeable local representatives to evaluate your ESD Program and answer any ESD questions!