Welcome back to “A Minute with Miranda.” This week we will be covering how to test ESD footwear entering an ESD Protected Area (EPA).
Per the ESD Handbook ESD TR20.20, A system test of the footwear in combination with the existing or proposed flooring materials in the plant should be made to ensure that the criteria for the facility are met. When using a footwear checker it is important to make sure the upper and lower resistance limits of the checker match the user’s requirements. When testing the footwear should test within the range of 1 x 106 to 1 x 108 ohms.
Heel, sole and toe grounders should be worn on both feet to ensure effective use. They should be worn by all personnel and visitors within an ESD controlled area. If worn improperly, the heel, sole and toe grounders become ineffective. ESD footwear should be tested daily before use within an ESD Protected Area (EPA).
Welcome back to “A Minute with Miranda.” This week we will be covering why you need to use ESD footwear within your ESD Protected Area (EPA).
Per the ESD Handbook ESD TR20.20, Personnel may also be grounded through the use of ESD footwear with an ESD Flooring system. This method is useful for situations where personnel are mobile or standing in areas where a wrist strap is not feasible and ESDS items must be handled or transported. ESD protective footwear is designed to reduce body charge levels by providing a conductive path from the body to the ESD flooring material.
Heel, sole and toe grounders should be worn on both feet to ensure effective use. They should be worn by all personnel and visitors within an ESD controlled area. If worn improperly, the heel, sole and toe grounders become ineffective. ESD footwear should be tested daily before use within an ESD Protected Area.
Welcome back to “A Minute with Miranda.” This week we will be discussing how to test the point-to-point resistance (Rtt) and the resistance-to-ground (Rtg) of a Conductive ESD Floor.
ANSI/ESD S20.20 requires initial and periodic verification of an ESD Flooring System. ANSI/ESD STM7.1 outlines the test methods applicable for the Conductive flooring material. For the Point-to-Point resistance (Rtt) test the flooring will be tested with a resistance measurement meter and 2 x 5lbs cylindrical electrodes positioned 36” apart. The value for the test should be less than or equal to 1 x 106 ohms.
The Resistance Point-to-Ground (Rtg) test should be conducted with a resistance measurement meter and 1 x 5lbs cylindrical electrode. One lead from the meter should be connected to the ground point and the other lead will be connected to the electrode. The test value should be less than or equal to 1 x 106 ohms.
View the full range of SCS Surface Resistance Testers here.
Static discharges can be noticed when you touch an object of different electrical potential such as a door knob, and a bolt of electricity flows from your charged body to the door knob. This flow of electricity is actually a result of the stored static charge that is being rapidly transferred to the knob. This discharge that can be felt as well as seen, is commonly referred to as an electrostatic discharge, or “ESD”.
The generated static charges are a potentially costly occurrence for office and factory employers. You will learn in today’s post how they can easily be controlled with different types of floor material.
Static Charge Generation from Flooring
When a person walks across a floor, a triboelectric charge builds up in the body due to the friction between the shoes and floor material. The simple separation of two surfaces (such as a person walking across a floor with soles contracting and separating from the floor) can cause a transfer of electrons resulting in one surface being positively and the other one negatively charged, resulting in static charges.
It is not necessarily the static charge generated in the body that does the damage as much as it is the difference in potential that creates an electrostatic discharge.
The Problem with ESD (Electrostatic Discharge)
The generation of a static charge can pose quite a problem for environments that contain sensitive equipment or components that are vulnerable to static damage, such as electronics manufacturing, repair facilities and medical facilities – including computer rooms and clean rooms.
Controlling the damage and costs caused by ESD is usually the main concern that drives a company to implement a static control program. The costs involved with static damage not only include the immediate cost of the damaged component, but the contributing cost of diagnostic, repair and labor that is needed to replace or fix the component. In many cases the labor involved can far exceed the component cost.
ESD Flooring Materials
There are several options available on the market ranging from coatings (floor finish or paint) to coverings (vinyl or rubber). The choice of material depends on the mechanical and optical properties required as well as the available budget.
In general, floor coverings will last longer (10 years or more) than a floor coating. They are more durable and have a specific resistance to ground that remains constant over time.
Coatings are easier to apply and repair and their initial cost is considerably lower. Coatings are usually applied to existing floors and often serve to convert a conventional floor into an ESD floor. However, regular maintenance is required as coatings will lose their ESD properties over time.
ESD Floor Coatings
Conventional carpets can be treated with a Topical Antistat or other treatment. It is required that the treatment be replenished on the carpet as it wears away due to foot traffic.
ESD carpet is available but proper maintenance is very important.
ESD Floor Finish:
Existing hard surfaces (e.g. concrete, sealed or painted wood, linoleum, asphalt) can be treated with ESD Floor Finish to eliminate the need for ESD control flooring. Repeat applications are required periodically to keep ESD properties within specification.
Paint is ideal for providing a cost effective static-free environment and is very effective as a
static control floor coating for electronics manufacturing, assembly and storage. It controls dissipation of static electricity and provides path to ground.
ESD Floor Coverings:
Floor coverings will have either “conductive” or “dissipative” electrical properties.
Conductive materials have a resistance to ground (RG) of greater than 1 x 103 ohms but less than 1 x 105
Dissipative materials have a resistance to ground (RG) of greater than 1 x 105 ohms but less than 1 x 1012
It is recommended to use conductive flooring material; S20.20 requires ESD flooring to be less than 1 x 109 ohms (RG). The same standard requires a person/footwear/flooring to be less than 3.5 x 107 ohms (resistance in series of operator plus footwear plus floor). Remember that floors get dirty which can raise floor resistance. Therefore, it is good to start off with a floor that is conductive (less than 1 x 106 ohms). So even if the resistance increases, you’re within the required limits of the ESD Standard.
ESD control carpets are made with static dissipative yarn and only require that the yarn be kept clean and free of insulative dirt, dust and spray cleaners.
Types of matting range from vinyl to rubber and anti-fatigue matting.
Vinyl (e.g. SCS 8200 Series) is generally cheaper and provides high resistance to many chemicals. Rubber (e.g. SCS CONDFM Series) on the other hand is more durable and can withstand extreme hot and cold temperatures. Anti-fatigue matting (AFM Series) is designed to provide comfort for personnel that must stand or walk for long periods.
Considerations when Using Flooring Materials
ANSI/ESD S20.20 requires that all conductors in an ESD protected area, including personnel, must be grounded. This includes ESD flooring. The ESD ground must be tied directly to and at the same potential as the building or “green wire” equipment ground. The SCS floor mat ground cord FGC151M is just one option for grounding floor matting.
2. Periodic Verification
All ESD control items (including ESD flooring) have to be tested:
Prior to installation to qualify product for listing in user’s ESD control plan.
During initial installation.
For periodic checks of installed products as part of ANSI/ESD S20.20 clause 7.4 Compliance verification plan.
A surface resistance meter (e.g. SCS SRMETER2) can be used to verify compliance of the ESD floor with the ESD standard.
3. Person/Footwear/Flooring System
ESD flooring does not ensure protection from ESD damage unless operators walking across the ESD floor wear ESD footwear, either ESD shoes or ESD foot grounders.
ESD foot grounders are designed to reliably contact grounded ESD flooring and provide a continuous path-to-ground by removing electrostatic charges from personnel. They are easy to install and can be used on standard shoes by placing the grounding tab in the shoe under the foot.
Foot grounders must be worn on both feet to maintain the integrity of the body-to-ground connection Wearing a foot grounder on each foot ensures contact with ground via the ESD floor even when one foot is lifted off the floor. This will more reliably remove static charges generated by human movement.
Static charges can easily be controlled with different types of floor material which vary in their properties, cost and durability. The best static control systems are not only the ones that protect sensitive components and equipment but are: A) at hand and readily available, B) easily maintained. Floor coverings are long lasting and maintain their ESD properties over time, while existing floors can be economically converted for use in an ESD control program using various types of coatings.
Remember that all ESD control items such as flooring, personnel grounding and specialty equipment should be grounded and tested periodically to verify all components are within specification.
Not sure which ESD flooring is right for you? Request a free ESD/EOS Assessment at your facility by one of our knowledgeable local representatives to evaluate your ESD program and answer any ESD questions!