Conclusions
The intent of this study was to determine which ESD flooring types and test specifications would be acceptable for us in an IC manufacturing and assembly environment. Seventeen parameters were considered, including cost, maintenance, appearance, mechanical and electrical properties. The task of determining which of the floors to recommend was complex and time consuming.
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Many ESD flooring manufacturers were invited to participate. Most accepted while others declined. Reasons for not participating were varied from “we don’t give out free samples” to “we’re reformulating-call us in 6 months”. Sales and technical support was minimal in some cases. Available material pricing varied from approx. $2.00 per square foot up to approx. $9.00 per square foot. Electrical test results ranging from triboelectric propensity to surface resistivity were varied and sometimes surprising. Appearance after 24 months was contradistinctive. Based on the data accumulated, taking into consideration critical vs. non-critical requirements, the following conclusions can be made:
- In order to properly analyze an ESD product, be it ESD flooring or a static dissipative finger cot, a multitude of tests, including, but not limited to, electrical, mechanical, sales, support, pricing, aesthetics, warranty and ecological evaluations should be considered. All too often, protects are chosen based entirely on electrical data with little or no consideration given to other criteria. This study attempted to take into account all aspects of ESD flooring materials in order to achieve a complete and thorough engineering evaluation.
- Some “poured” and “rolled-on” type floors displayed a wide variation in electrical readings. In one case, depending upon where the probes are placed on the test site, the floor’s electrical resistivity could range from 10 to the fourth ohms to ten to the eleventh ohms. This type of floor’s mechanical and electrical properties appeared to be too dependent upon the method of application. In addition, with only one exception, this type of floor displayed extensive wear after only a few months.
- Most ESD flooring manufacturers test and advertise their flooring products based on three widely-used electrical tests; the static decay test, body voltage generation & electrical resistance. These approaches are limited and not well defined in many cases. Additional tests must be performed, in conjunction with ESD footwear & “street” footwear in order to determine the floor’s true capability of preventing ESD induced damage.
- Traffic levels need to be considered before purchasing any ESD flooring. In areas with very little traffic, such as an engineering lab, vinyl tile with infrequent ESD wax applications may be appropriate. In heavy traffic areas, with round-the-clock operations, the use of vinyl tile is not recommended if aesthetics are a priority. rubber flooring successfully maintained their original appearance after 24 months with no sign of wear. In fact, one of the two rubber flooring, Floor “C”, appeared more aesthetically “pleasing” AFTER 24 months than when it was originally installed. Maintenance requirements for most of the “poured” and “rolled-on” floors were above average. In addition, this type of floor may need reapplication after a one to two year period.
- When analyzing test data, probability distributions need to be considered. All too often, “average” or “median” readings are reported.
- The human body needs to be considered during testing. Static decay tests currently specified in ESD floor applications were originally designed for ESD packing material testing & evaluation. In addition, NFPA 99 procedures were intended for medical applications, not the IC industry. Modifications in applied voltages and test gear are appropriate.
- There was very little statistically significant change in electrical test results among most of the vinyl tile, rubber and one of the “poured” quartz floors after a two year period of time. Variations among some of the “poured” or “rolled-on” floors could be attributed to: 1) wear, 2) dirt build-up and 3) inconsistencies in application during installation.
- The area and application must be considered. If the floor is intended for office use, in the prevention of ESD-induced failure to electronic office equipment, the requirements may be less stringent than that of an IC manufacturing and assembly area. Cleanroom applications have additional particle count requirements that weren’t considered during this study. However, the quartz floors, based on a granular “sand” system, shed noticeably small particles, assumed to be sand, over the course of the study and did not appear to meet strict Class 10 criteria. Additional testing would be necessary on any floor intended for cleanroom applications.
- ESD flooring advertised as “conductive”, defined by Jedec as a material that has a surface resistivity less than 1 x 10 to the 5th ohms or a volume resistivity less than 1 x 10 to the 4th ohms/cm, may in fact be “static-dissipative”. A few of the floors included in this study were advertised as “conductive”, with resistivity readings as high as 9 x 10 to the 9th ohms.
- With few exceptions, almost all of the ESD floors included in this study displayed considerably high body voltage generation when “street” shoes were used during testing. vinyl tiles used in conjunction with street shoes demonstrated the lowest body voltages. It can be concluded from these results that all ESD flooring systems should be tested for body voltage generation using street shoes (Neolite soles or equivalent) or used only in conjunction with approved ESD footwear in order to keep body voltage generation below 200 volts.
Introduction | Experiment Overview | Procedures | Results | Economics | Summary | Conclusion | Credits
