The newly installed static-dissipative flooring in the AlliedSignal General Aviation Avionics Plant in Lawrence, KS, provides the right amount of electrical conductivity while contributing other benefits not provided by bare concrete. The new floor also makes the 10-year-old plant much brighter, cleaner and easier to maintain.
Concrete did an acceptable job of dissipating static electricity, but keeping the 75,000 sq. ft. plant clean was a problem. The concrete was porous and attracted dirt. The dirt also seriously compromised the conductivity of the ESD heel straps worn by production workers.
According to some estimates, 25% of latent failures in electronic devices are ESD-related. So while making the plant cleaner and easier to maintain were good incentives, preventing damage to circuit boards and electronic assemblies during production was the overriding concern of our manufacturing managers.
We knew that putting a finish on the bare concrete could interfere with the surface resistance properties, so we were very careful in selecting new flooring. Our choices included floor tiles, latex-based coatings and several different types of poured floors. Tile was ruled out because of the maintenance cost over the long term, and latex-based coating did not stand up to traffic in a trial application in the plant.
Most poured floors are conductive, and we were concerned about too much conductivity. We wanted something that offered a little more resistance to ground. A highly conductive floor just doesn’t provide the same degree of safety for our associates as one that is dissipative.
Resistance below 105 W is usually considered conductive. We were looking for a resistance between 105 W and 109 W as a true static-dissipative floor. The best solution we found was the UltraPlex ESD floor topping.
This flooring material, made by Rust-Oleum Concrete Protection Systems, offers a surface resistance of 106 W to 109 W . It is a two-component formulation of epoxy resin and cycloaliphatic curative with conductive elements added to provide the required degree of conductivity, and is available in a variety of colors. The result is an attractive, long-lasting and easily maintained floor.
White was chosen for the plant floor because it brightens our plant. The flooring also wears well and the high-gloss finish resists scuffing. Any marring is easy to remove. From an ESD standpoint, this floor meets all the requirements every time we check.
Installation
Because the plant continued to operate at capacity during installation, the application period extended over several months. In fact, the project began in December 1993, and was not completed until October 1994.
It’s a good idea to do a job like this all at once, making the entire floor available to the application crew. We didn’t have that luxury, however, because we had to keep operating.
Fortunately, this type of self-leveling topping lends itself to piecemeal application. As a result, we have some seams where we didn’t really want them, but the finish is smooth and the ESD protection is continuous.
Equipment was relocated so the contractor could work during off-hours and over weekends to accommodate our production requirements. When a section was cleared, the concrete floor was shotblasted on a Wednesday or Thursday night to remove previously applied sealers or hardeners and to create a profile for adhesion of the new topping. The shotblasting equipment vacuumed concrete dust as it moved along, so minimal dirt was created in the plant.
Patching the concrete, where necessary, came next, followed by a coat of sealing primer, a coat of ESD primer and one coat of UltraPlex ESD floor topping for a total thickness of 110 mils. By Monday morning, the equipment could be moved back into position.
Recommendations
If the casters on the equipment in your plant are not rubber, replace them. Casters can cause marks and scratches. Marks are a temporary cosmetic issue, but scratches are permanent and may become a long-term wear problem if multiple and deep scratches are made in a small area. As a minimum, use a nonscratching caster material, such as rubber or a softer polyurethane.
Do not overlook the moving equipment used by your plant maintenance or contract riggers. Typically, these loads are heavier than the normal traffic; so unless their wheels or casters are made of a compatible material, damage to the floor can occur.
Cleanliness of the floor is also important. Sand or mud tracked into the plant can become an abrasive as casters and shoes grind the dirt into the floor in high-traffic areas. Use long floor mats on all entrances to allow workers to walk off the dirt on their shoes as they enter the facility.
To date, our testing has shown no performance degradation due to any of these conditions.
Application over such an extended period was difficult because it kept the plant disrupted for a long time. If you are building an electronic manufacturing facility and thinking about an ESD floor, do it immediately.
If you’re thinking about installing an ESD floor on an existing area, put down samples and test them for a while. If the wrong material is used, chances are it will fail quite soon in a high-traffic area. That happened with us when we tried a water-based coating, and the experience helped us avoid a lot of headaches later.
We took our time, and the floor we selected is doing a better job than the bare concrete in meeting our ESD requirements.
About the Author
Bruce Monro is an Industrial Engineer at AlliedSignal. Before joining the company four years ago, he was an Industrial Engineer and Quality Assurance Engineer with IBM for 10 years. Mr. Monro earned a B.S. degree in industrial engineering from Arizona State University, and an M.S. degree in industrial engineering from the University of Arizona. AlliedSignal General Aviation Avionics, 400 N. Rogers Rd., Olathe, KS 66062-1212, (913) 768-2019.
Copyright 1995 Nelson Publishing Inc.
August 1995