ESD flooring is sometimes overlooked as the primary source of protection in electronic product manufacturing. But consider this: It is the first line of defense against triboelectric charges. It covers a large surface area. And it helps to prevent charges from being generated on static-sensitive devices.
No floor is best for all situations. The choice depends on technical issues as well as personal preferences. For instance, you wouldn’t want a highly conductive floor with a resistance level of 25 k in an electronics manufacturing area.
To determine the suitability of tile, carpet, topical treatments or epoxy, first you need to evaluate the features, benefits and cost of each, said Lenard Cohen, Engineering Manager for Plastic Systems. For example, topical antistatic sprays are suitable for low-traffic flooring, and they are relatively inexpensive. But they must be reapplied frequently, so you would not want them for high-traffic floor applications.
Today, there is ESD-safe flooring to meet your requirements, but some are better than others because of the conditions in which they are expected to perform. Vinyl, epoxy and carpet are appropriate for most manufacturing areas.
Carpet is preferred in office areas where it can typically reduce noise levels by 10 dB, reported Steve Fowler, President of ESD Flooring Systems. Carpeting also provides passive air filtering, trapping dust particles and rapidly decaying static charges from personnel. However, carpeting isn’t always desirable, especially in clean rooms or areas that use chemicals or solvents.
The typical conductive fiber in carpeting is carbon-suffused nylon. It helps maintain the electrical properties of the carpet, providing permanent resistance levels from 2.5 x 104 to 1010 . If you combine ESD-protective footwear with conductive carpeting, you generate less than 20 V–not enough to damage the most sensitive devices.
Epoxy and urethane are seamless static-control floorings used in high-traffic manufacturing areas as well as laboratories and office environments. The surface makes it particularly appropriate for clean-room applications, said Michael Campion, Product Manager for Stonhard.
The static-control properties of these materials generally range from 104 to 106 for conductive and 106 to 109 for static-dissipative types. The triboelectric charge generation varies with formulation, but the best of these floors maintain an average of less than 100 V. Epoxy and urethane also perform effectively in relative humidity as low as 12%.
The preparation of surfaces for epoxy finishes is critical for effective performance, said Mr. Cohen. Epoxy is vulnerable to moisture, so problems of this nature must be eliminated before installation.
Tile flooring systems generally have the same static-control properties as epoxy systems. There are two types of tile systems: welded seamless and vinyl tile. The seamless version is well-suited for clean rooms as long as the hardness values are sufficient to prevent particulate shedding, said Mr. Campion.
The majority of tile systems are installed in low-traffic or office areas. High-traffic areas should be avoided because the material is susceptible to deformation under heavy compressive loads or moderate impact loads.
What’s New
Electrical specifications for flooring are in transition, according to Mr. Fowler. No true industry standard is in place for surface resistance, resistance to ground and body voltage generation. In fact, there isn’t even a definition of dissipative vs conductive with regard to flooring, he said.
As the specifications for static-safe work areas evolve, a few similarities are emerging, said Mr. Fowler. Most likely, the specifications will be:
o Surface resistance: 2.5 x 104 to 2.5 x 108
o Surface-to-ground resistance: 5.0 x 104
o Body voltage with proper footwear: <50 V
A holistic approach to ESD protection is another trend in the flooring industry, said Bruce Lampert of United Technical Products. For example, each generation of ICs is more susceptible to ESD than the previous one, some to less than 100 V. Manufacturers realize that the effectiveness of an ESD program depends on having grounding throughout the entire facility.
Rather than producing islands of protection, manufacturers are using conductive flooring to create a continuous path to ground. When equipment is grounded with conductive casters and personnel are equipped with conductive footgear, damage from ESD becomes negligible.
Flooring is in step with the changing environment of electronic manufacturing, and provides you with several viable selections to resolve your ESD needs.
Flooring Products
Carpet Offers Range of
Point-to-Point Resistances
Ten-SixTM is an ESD carpet with average point-to-point and point-to-ground resistances of 1 M per the requirements of ESD Association Standard 7.2. However, the product can be specified for resistances ranging from 25 k to several hundred megohms. Walking on the carpet with ESD-protective shoes meets voltage requirements of AATCC 134. The nylon carpet is offered in roll, tile or mat versions and several colors. ESD Flooring Systems, Inc., (800) 803-4569.
Chemically Resistant Flooring
Has Static Decay of <0.1 s
Chemi-CoteTM ESD Urethane Coating is an aliphatic polyester urethane flooring that can be applied over nonconducting floor surfaces, including concrete or static-control tiles. The coating provides <15-V body voltage generation and has a body voltage decay from 5,000 V to 0 in <0.1 s. It resists a variety of fluids, including hydrazine, jet fuels, hydraulic fluids and organic/inorganic acids as well as alkalis and chlorinated solvents. Garland Floor Co., (800) 321-2395.
Seamless Flooring Reduces
Charge Generation to <100 VStonlux AT is a seamless ESD flooring. It decreases the effects of triboelectric charge generation to <100 V for Class 0 applications. The conductive pathway of the system is the conductive primer, which carries a charge from the surface of the floor to a ground source. Stonlux AT is neither temperature nor humidity dependent, and resists chemicals, impacts and abrasions. Stonhard, Inc., (800) 257-7953.Water-Based Conductive Paint
Has Charge Decay of <0.01 s
Statproof Conductive Paint is an acrylic polymer floor coating formulated to produce controlled dissipation of static charges. The water-based paint is abrasion resistant, and has a surface resistivity of 3.87 x 105 /sq and a charge decay of <0.01 s per FTMS 101C, Method 4046. The gray coating covers 250 to 300 ft2 at a 1-to 2-mil thick film per gallon. Plastic Systems, (508) 485-7390.
Vinyl Tile Is Used
In Solder-Wave Areas
VersaTile ESDTM, a hardtop antifatigue ESD-safe vinyl tile, is used in solder-wave areas or wherever there is potential for chemical spillage. The tile is constructed with an antiskid surface and a cushioned backing. It installs over most existing floors with the company’s conductive adhesive, providing a resistance to ground of 106 to 108 . Tile colors include navy blue, graphite, teal and jet black. United Technical Products, Inc., (800) 225-6052.
Copyright 1995 Nelson Publishing Inc.
February 1995