Test Results
Body Voltage Generation - Charge generation varied between 50 volts and 1,000+ volts. Using the formula for a Gaussian probability distribution:
Body voltage generation was calculated within a 0.1% maximum probability range. Tests were conducted using insulative soles and verified ESD footwear, with both feet in contact with the floor and then one foot elevated to create a worst case scenario, representative of a walking motion. Reported data reflects the one foot elevated scenario. The environment in which the floor is to be used would determine what the proper combination of flooring, test criteria and footwear should be. Figure #5 shows results from Month 31 using approved ESD footwear as well as insulative footwear.
Surface Resistivity - Readings typically fell in the range of 5 x |
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to 20 x 
(maximum measureable charge). See Figure #6 for a view of the overall surface resistivity results. Month #24 results are broken out for comparison by flooring "type" in Figures #7, #8 and #9.
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Based on these results; Floors "C", "A", "B", "E", "G", "N", "H", "J", "O", "F", and "P" were typically less than |
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and more than 
as of Month #24. Installation requirements: All of the floors installed were connected to ground (typically using copper foil or wire). In addition, the tile & rubber flooring were installed using conductive adhesive. For purposes of this study, very little prep was necessary. All floors were installed directly over the existing standard vinyl floor tiles. It should be noted that subfloor material may affect test results and the results in this study may not necessarily mimic those performed with a different subfloor, such as concrete or wood.
The epoxies & urethanes required more time & training to install than the tile or rubber flooring. In addition, one of the epoxies & urethanes required evacuation of people in the immediate area due to strong odors. MSDS sheets did not reveal any strong health concerns with limited exposure during installation, but personnel in the area have reported throat irritation and other related ailments up to 48 hours after exposure.
From a cost perspective, the conductive adhesive used during tile & rubber installations was considerably more expensive than standard adhesive. It must be applied, in most cases, such that the layer of adhesive is spread evenly & thick enough to allow for even resistance across the surface of the flooring material. Some of the tile manufacturers in stalled their products using too much adhesive, which later bled through the seams. One of the epoxies, Floor "K", dried with extensive bubble formations across its surface.
Floor "L", an epoxy quartz floor appeared to have "Puddles" after final application of the top coat. Floor "F", another type of epoxy floor, was thin enough that the subfloor outlines could be easily seen through it.
Appearance - From a user's perspective, ESD flooring is expected to meet not just electrical criteria, but mechanical as well. The floor should be able to withstand daily usage and maintain a level of appearance acceptable to the user. The floors were rated on a 1 -1 10 scale, with 1 being best cosmetic appearance. Below are the results as of Month 24 for each of the floors:
These ratings were based on the amount of dirt retention, change in appearance over the one year period, scuffing and other measures of general appearance. Floors "C", a rubber floor, and "H", a quartz, were rated best in terms of appearance. |
Maintenance- During the study, all of the floors received once per week cleaning and buffing. For some, such as the rubber and Floor "H", a quartz, this was more than adequate. After the cleaning, the floors' appearance was similar to that of the day of original installation. Others, such as the vinyl tile products appeared to need more than daily sweepings in addition to weekly cleaning and buffing. For the remainder, harsh cleaning agents and extreme buffing would have been necessary for removal of ground in dirt and scuffing. The ratings on degree of necessary maintenance, with a 1 - 10 scale (1=least amount) follow:
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Odor - As discussed earlier, odor was a major consideration. Besides running into odor problems during installation, one of the floors emitted a slight odor for approximately three months after installation. Large fans had to be brought into the area to relieve the area of odors presumably emitted from one of the epoxies. Floor "C", a rubber floor, also emitted a slight odor that dissipated within a few weeks and two cleanings. None of the floors in the study had any long-term problems with odor, although the short-term problems could have been monumental had the area been larger.
Static Decay - During the second week of the study, all of the test sites were tested per Fed Test Standard 101C, method 4046 and a modified version, including the introduction of the human body. All of the floors tested passed the test without the human body. However, some of the floors showed a disconcerting change in decay times when the human body was introduced into testing. This particular test, without the use of the human body, is one of the three traditional approaches to testing & advertising ESD flooring . Other test methods, including body voltage generation & footwear interactions must also be considered.
Scuff Resistance - Intricately tied to appearance, scuffing was checked per ASTM D 3714 at the beginning of the study. In addition, each floor was then rated on a 1 -1 0 basis (1=best) weekly, based upon the amount of scuffing found within 24 hours after the weekly cleaning. One of the two quartz poured floors, along with the rubber flooring showed remarkable resistance to scuffing. All of the vinyl tiles reflected a higher than expected amount of scuffing & dirt retention. These phenomena can be possibly attributed to the softness of the vinyl and the natural tendency to mark. The majority of urethane, acrylic & epoxy floors had excessive scuffing and marking which became so embedded in the flooring that buffing at 5000 rpm could not remove it. These type of floors experienced a higher rate of scuffing, even more so than the vinyl tiles, especially in areas where chairs were located.
Wear - A combination of both electrical and mechanical properties were looked at to determine the exact rate of wear among various floors. Some of the epoxy, acrylic & urethane based floor systems showed distinct wear problems. The manufacturers recommend a repeat application every 1 - 3 years in most cases. More specifically, the latex epoxy was in need of reapplication after approximately 11 months, while floors "F" and "D", had even earlier signs of wear.
Among the other test sites, wear seemed to improve the appearance of the rubber flooring, presumably removing any residual coating left during the manufacture process (which impeded earlier electrical readings). One of the two quartz floors did not show signs of extreme wear like the other "poured & rolled' types of flooring. However, the other quartz floor (Floor "L") had problems with "puddle formation" a presumed accumulation of "top coat" during the initial application process. This floor also displayed extreme path wear which resulted in statistically significant variation of electrical attributes.
Required Maintenance - In many manufacturing areas, floor maintenance may not be a top priority. Maintenance has traditionally been linked to aesthetics, not ESD prevention. In addition, floor cleanings & waxing may interfere with the manufacturing process and delays are typically costly. A floor which would require as little maintenance as possible was preferable. The cost of maintenance could be extremely high due to the typically large square footage of most IC manufacturing and assembly plants (i.e. 1,000,000+ sq ft).
The vinyl floors included in the study displayed various degrees of necessary maintenance, but all had one common requirement: the need for an ESD wax application to inhibit dirt retention & prevent marking. This was not particularly surprising based on reports detailing performance of standard (non-ESD) vinyl tiles available on the commercial market. Even vinyl's advertised as "NO WAX", typically require a coating of wax at some point in time. ESD vinyl tiles included in this study were no exception.
Slip Resistance - As per UL specifications, all floors must have a minimal average coefficient of friction of 0.50. All of the floors included in the study met this requirement.
Fowler, S.L. and Klein, W.G., "Static Phenomena and Test Methods for Static Controlled Floors," EOS/ESD Symposium Proceedings, 1992.
iv EOS/ESD-DS7.2, DS7.1, EOS/ESD Association Standards, EOS/ESD Association, 200 Liberty Plaza, Rome, NY 13440.
v ASTM Stds D257, D4078, D3714, D2047-69, D1044, and F150, American Standards for Testing and Materials, 1916 Race St. Philadelphia, Pa. 19103.
vi UL Std 779, Underwriters Laboratories, 333 Pfingsten Rd. Northbrook, Ill 60062.
vii NFPA 99, National Fire Protection Assn, 60 Batterymarch St., Boston, MA 02110.
viii FTS 101C, Method 4046, Federal Supply Service, General Services Administration, Washington, DC.
ix Freeman, P.S. & Moss, R.Y., Hewlett-Packard, "Sources of Error in Resistance Measurements on Conductive Flooring", 1991 EOS/ESD Symposium Proceedings.
x Chase, E.W. and Unger, B.A., "Triboelectric Charging of Personnel from Walking on Tile Floors," 1986 EOS/ESD Symposium Proceedings.
Introduction | Experiment Overview | Procedures | Results | Economics | Summary | Conclusion | Credits
