Conformity Magazine - September 2007 - (Page 48)

the ones that make the transition before they actually begin working with ultra-sensitive components. And that can only happen if they begin re-educating themselves immediately. Fortunately, interest in ESD has been increasing over the past couple years. Internet searches on engines like www. google.com indicate a significant rise in ESD-related searches. Attendance at ESD-related events and conferences is up. Both indicate a growing need for technical information and advice. The following seven issues are only the tip of the iceberg. They are however the place to begin. 1st Consideration: Understand the Limitations of ANSI/ESD S20.20-2007 Today, technological advances are outpacing the human ability to respond. It could take years for standards to be modified and new standards to be generated by volunteerled organizations. It is imprudent to rely solely on industry standards and benchmark recommendations that neither fully anticipate nor adequately prescribe solutions to problems specific to state-of-the-art technology. The responsibility to do things right— which may mean exceeding the recommendations of generally accepted methods—always falls on the implementer. In the case of ANSI/ESD S20.202007, two limitations are clearly identified by the document’s authors. First, as stated in the forward to ANSI//ESD S20.20-2007, “This standard covers the requirements necessary to design, establish, implement and maintain an Electrostatic Discharge (ESD) Control Program for activities that manufacture, process, assemble, install, package, label, service, test, inspect or otherwise handle electrical or electronic parts, assemblies and equipment susceptible to damage by electrostatic discharges greater than or equal to 100 volts Human Body Model (HBM).” By design, the standard does not offer a prescription for handling sensitive components with HBM thresholds below 100 volts. S20.20 also fails to address applications where the use of ESD controlled footwear is impractical—such as in server rooms, data centers or call centers. In applications where static protective footwear will not be used, buyers should consider the recommended specifications in S20.20, and also analyze any unusual performance parameters that apply to their specific application. In the case of flooring, a buyer should look at the antistatic properties of the floor not only when it’s used in conjunction with conductive footwear, but also when it’s used with conventional nonconductive footwear. Second, this standard does not cover the handling of electrically initiated explosive devices. The handling of explosives is obviously of greater concern than the handling of ESDS components, since there is little margin for error where safety is concerned. The fact that S20.20 does not address these concerns does not diminish its applicability to the industry it was written to serve. It merely points out that there are situations and applications where static must be controlled at different levels and possibly in a more rigorous manner. As with explosives, the handling of class 0 devices requires redundant process controls and the use of better performing static preventive materials. Readers can download a free copy of ANSI/ESD S20.20-2007 at http://esda.org/documents/S20.20-2007FINAL_000.pdf. 2nd Consideration: Understand the Charge Device Model Most ESD program managers understand the human body discharge model. We encounter this model everyday, whether we realize it or not. When humans move, slide in chairs, remove or put on items of clothing, they generate some amount of static electricity. When they touch another object, that static electricity discharges; this is called the human body model discharge. While discharges below 3500 volts are dangerous to components, they cannot be felt by humans. HBM threats can usually be addressed by implementing a continuous system of grounding and electrical bonding. The three most common examples of HBM precautions are wrist straps, conductive footwear and ESD flooring. Properly selected and monitored, these three precautions will eliminate almost all HBM threats. (This may require educating skeptical personnel who, because they cannot see or feel static electricity, question its existence.) Figure 1: Class 0 devices per factory. (Copyright 2007, Dangelmayer Associates) 48 Conformity September 2007 A less understood but potentially more destructive threat to components is a failure model called the http://www.google.com http://www.google.com http://esda.org/documents/S20.20-2007FINAL_000.pdf

Table of Contents Feed for the Digital Edition of Conformity Magazine - September 2007

Contents Editor’s Note FCC Extends Disability Access Requirements to VOIP Commission Fines Importer $3 Million Over Non-Compliant TVs FCC Gets Tough on Retailers Over Analog TV Tuner Labeling Analog Cellular Service Sunset Date Reaffirmed Commission Adopts Recommendations of Katrina Panel Free-Space Antenna Factors Through the Use of Time-Domain Signal Processing Editorial Correction ESD Open Forum An Update on Revisions to IEC 61000-4-2, the Basic Standard on ESD Practical Advice for Meeting the DFS Testing Requirements of the FCC The EMC Impact of Embedded Software ESD Design Buyer's Guide Tate Renominated to the FCC EPA Releases Report on U.S. Electronic Waste Additional Standards For The EU’s Toy Directive Medical Device Manufacturer Enters Consent Order Updated Guidance Document on Laser Products Issued FDA Offers Advice on Defective Heating Pads CPSC Issues China Product Safety Program Report Other CPSC Actions In The News IEC Standards Update Product Reviews Product News UL Standards Update From Our “You Can’t Make This Stuff Up” Department Looking Back: Items from Past Issues of Conformity Advertisers

Conformity Magazine - September 2007

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