Circuits Assembly - March 2008 - (Page 36)

Controlling Static As an alternative solution, miniature barcode readers are now available with a unique nickel coating and ESD-resistant labels. These units are rated for discharges up to 8kV and feature a surface resistivity of less than 10 * 10-9 /in2. Evaluating ESD Handling Capabilities According to the ESD Association’s (esda.org) Technology Roadmap released in 2005, sensitivity levels to ESD in devices are expected to drop so low assemblers must act quickly to ensure they will be able to handle the new levels.7 Assemblers certified to the ANSI/ESD S20.20, the ESDA standard covering electrostatic discharge programs, already have done much of the work in preparing for the next generation of sensitive devices. For those manufacturers unsure of the voltage capabilities of their automated equipment, the ESD roadmap provides direction in how to get there: • Determine the ESD-control capabilities of the facility’s handling processes. • Ensure all conductive fixtures or tooling that contact sensitive devices are grounded. • Ensure maximum voltage induced on devices is kept below 50V. Following the requirements outlined in S20.20 will help managers assess component sensitivity levels and identify ESD issues at each stage in the process, from receiving and inventory through assembly, test, rework and shipping. By using the appropriate ESD countermeasures, managers will have the data to articulate their facility’s capabilities by voltage level. ■ Figure 4. In a device tracking system, 2-D barcodes are applied to devices to improve unit WIP visibility. Automated Tracking If an ESD event does occur, the data provided from a device tracking system can help assemblers quickly identify damaged components and contain the impact. In a device tracking system model, a barcode reader is installed at various points throughout the manufacturing process to read the barcodes (or 2-D codes) applied to the devices (Figure 4). Typically, readers scan the barcodes on the device before it enters a station and again after it exits. This documents the type of procedure performed, the equipment that performed it and attaches a time/date stamp for when it occurred. While ESD monitoring instruments output all types of data, the barcode reader provides the only link between each device’s serial number and the data supplied from the instrument. For example, when equipment calibration is altered due to EMI from an ESD event, data generated from the device tracking system can help identify specifically which boards were damaged after the equipment’s calibration was altered. Entire lots no longer have to be pulled, scrapped or reworked because of insignificant data. When selecting a barcode reader, ensure it does not introduce additional risk for ESD events. PCBs, ICs and other electrically sensitive components typically use small, high-density barcodes to conserve space, making it difficult for some readers to scan over long distances. When the scanner is mounted within close proximity of the product, the barcode reader may build up a static charge, depending on whether it is used on a nonconductive surface. If the reader itself has built up a charge and is brought into close proximity with a sensitive component, an ESD event could occur, potentially damaging the component. Some manufacturing environments use a workaround by mounting the scanner after applying a special anti-static spray, which is not without its own risk. First, the coating must completely cover the area for maximum effectiveness; uncovered areas remain at risk. In addition, anti-static sprays can wear off and require timely replacing. Without an accurate measure of a spray’s efficacy period, companies either waste money by applying too much, or put their components at risk by using them in an unprotected environment. References 1. ESD Association, “Basics of Electrostatic Discharge Part 1: An Introduction to ESD,” Compliance Engineering, January 2000. 2. Donn G. Bellmore, “ESD Design Concerns in Automated Assembly Equipment,” July 2004. 3. Roger J. Pierce, “The Most Common Causes of ESD Damage,” Evaluation Engineering, November 2002. 4. Semiconductor Equipment and Materials International (SEMI), E78-0706: “Guide to Assess and Control Electrostatic Discharge (ESD) and Electrostatic Attraction (ESA) for Equipment,” May 2006. 5. Roger J. Piece, “The Most Common Causes of ESD Damage,” Evaluation Engineering, November, 2002. 6. Arnie Steinman, et al, “Detecting ESD Events in Automated Processing Equipment,” Compliance Engineering, Sept./Oct. 2000. 7. ESD Association, “Electrostatic Discharge (ESD) Technology Roadmap,” 2005. Bibliography Arnold Steinman and Lawrence B. Levit, Ph.D., “Coping with ESD: Ionization for Production Equipment,” Evaluation Engineering, April 1997. Curtis Maynes, “Technology Roadmap Sees Higher Sensitivity to ESD,” Evaluation Engineering, MARCH 2006. Bob Taplett is manager of applications engineering at Microscan Systems (microscan. com); btaplett@microscan.com. 36 Circuits Assembly MARCH 2008 circuitsassembly.com http://esda.org http://microscan.com http://microscan.com http://circuitsassembly.com

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Circuits Assembly - March 2008 Caveat Lector Letters Industry News Market Watch Talking Heads Focus on Business On the Forefront Screen Printing What Drives the Crowd? Mastering ESD Control in Automated Handling Systems Beating the RoHS Heat Trade Secrets True to Its Roots The Road Abroad - Strategic Alliance or Greenfield Facility? Tech Tips Wave Soldering Test and Inspection Process Doctor Pb-Free Lessons Learned Getting Lean Materials World Equipment Advances Apex Product Preview Ad Index Assembly Insider Technical Abstracts

Circuits Assembly - March 2008

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