HP A4500A Hardware Manual - rp24xx, Customer Viewable - Page 37

ESD Safety Standards ESD Safety Standards Static charges (voltage levels) occur when objects are separated or rubbed together. The voltage level of a static charge is determined by the following factors: • Types of materials • Relative humidity • Rate of change or separation Effect of humidity on ESD charge levels The following table lists charge levels based on personnel activities and humidity levels. Activitya Humidityband charge levels (voltages)c 26% 32% 40% 50% Person walking across a linoleum floor 6,150 V 5,750 V 4,625 V 3,700 V Person walking across a carpeted floor 18,450 V 17,250 V 13,875 V 11,100 V Person getting up from a plastic chair 24,600 V 23,000 V 18,500 V 14,800 V a. Source: B.A. Unger, Electrostatic Discharge Failures of Semiconductor Devices (Bell Laboratories, 1981) b. For the same relative humidity level, a high rate of airflow produces higher static charges than a low airflow rate. c. Some data in this table has been extrapolated. Static protection measures - computer room environments Follow these precautions to minimize possible ESD-induced failures in the computer room: • Maintain recommended humidity level and airflow rates in the computer room. • Install conductive flooring (conductive adhesive must be used when laying tiles). • Use conductive wax if waxed floors are necessary. • Ensure that all equipment and flooring are properly grounded and are at the same ground potential. • Use conductive tables and chairs. • Use a grounded wrist strap (or other grounding method) and antistatic mats when handling circuit boards. • Store spare electronic modules in antistatic containers. Static protection measures - office environments Office areas generally do not offer the same degree of environmental control possible in a computer room. However, some of the same precautions should be followed: • Maintain recommended humidity level and airflow rates in the office. Chapter 45