Conformity Magazine - September 2008 - (Page 19)

ESD Open Forum It can be seen very clearly in Figure 1 that, if the grounding strap on ESD protective shoe covers loses good body contact, the charge from the person is not drained as well. ESD shoes seldom lose body contact and serve well to drain charge from the person wearing the ESD shoes. Figure 2 displays a comparison of airborne particles generated by new disposable shoe covers and used, but freshly cleaned, static dissipative rubber soled ESD shoes. Airborne particle counts were taken as shoe cover samples and ESD shoe samples respectively were scuffed against each other 30 times per minute, directly over the isokinetic sample probe of a calibrated, portable airborne particle counter. Each sample on the chart represents the average of three (3) one minute sampling sessions. The data from the airborne particle counts clearly show that this particular brand of disposable ESD protective shoe covers generate a greater number of airborne particles in each of the particle size categories. Lastly, a cost comparison between disposable shoe covers and individual pairs of ESD protective shoes has been made. ESD shoes are available from many different suppliers with various styles and features with varying costs. Two examples follow which demonstrate alternatives. Expensive ESD shoes costs approximately $80.00 - $120.00 per pair. There are also inexpensive ESD shoes that cost approximately $20.00 - $30.00 per pair. One pair of ESD shoes should last 1 – 5 years (this will vary with quality of shoe construction and materials, amount of actual wear, the wearer’s body weight and foot/walking abnormalities). If each member of the workforce used one pair of disposable shoe covers per day, it would cost over $100.00 per year for disposable shoe covers for each person. This is much more expensive than supplying the same person with a pair of ESD shoes lasting several years. (Calculations based on a 5 day workweek, 48 workweeks per year). Of course, if a facility decides to have their employees wear ESD protective shoes (restricted to the ESD protected area only), street shoe storage and change facilities are required. In summary, lower human body voltages can be maintained, foreign material in the work area can be reduced, and considerable cost saving can be achieved by using ESD shoes verses disposable shoe covers in certain ESD protected work areas. Notes The equipment used to evaluate body voltage generation and airborne particle generation included the following items: • 711A Electrostatic Field Meter with body voltage probe attachments with current calibration • PGA-710 and Autoanalysis System 1.5 (Version 1.5.1.0) with current calibration • Model 3016 Airborne Particle Counter Calibration with current calibration About the Author Jay Hamlin is principal product engineer and ESD Control Program Manager at Medtronic Microelectronics Center in Tempe, AZ. Jay earned a BSEE from the University of Colorado, Colorado Springs, CO, and has held engineering positions at Intel, Motorola, Qualcomm, and Orbital Sciences. A member of ESDA since the mid-1990s, Jay has also served as a vice-president of the Arizona chapter of the ESD Association. About the ESDA Founded in 1982, the ESDA is a not-for-profit, professional organization directed by volunteers dedicated to furthering the technology and understanding of electrostatic discharge. The Association sponsors education programs, develops ESD standards, holds an annual technical symposium, and fosters the exchange of technical information among its members and others. Additional information may be obtained by contacting the ESD Association, 7900 Turin Rd., Bldg. 3, Rome, NY 13440-2069 USA. Phone: 315-339-6937. Fax: 315-339-6793. Email: info@esda.org. Website: www.esda.org. Figure 2: Airborne particle counts from footwear September 2008 Conformity 19 http://www.esda.org

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Conformity Magazine - September 2008 Contents Editor’s Note Commission Adopts Regulations for Internet-Based TRS Services Another Company Fined for Non-Compliance with HAC Requirements FCC Extends “Do-Not-Call” Registry Compliance Requirements Marketing Company Gets $1.4 Million Fine for Junk Faxes EU Commission Codifies Directive on TTE Market Competition EU Commission Releases Updated Standards List for the R&TTE Directive Updated Standards List for the “New” Low Voltage Directive Released New Standards List Released for the EU’s Machinery Directive The ESD Association: Voluntary Standards in Action ESD Open Forum Medical EMC Standards: Towards the 4th Edition of IEC 60601-1-2 iNARTE Informer Pre-Pulse Voltage in the HBM ESD Model Digital Interfaces and EMC Performance ESD Design Buyer’s Guide Product News Commission Publishes Updated Standards List for the EU’s Personal Protective Equipment Directive FDA Links “Human Factors” to Adverse Events with Medical Devices CPSC Actions in the News IEC Standards Update UL Standards Update Product Reviews Telcordia Standards Update From Our “You Can’t Make This Stuff Up” Department Looking Back: Items from Past Issues of Conformity Advertisers

Conformity Magazine - September 2008

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