HP Armada 4200 Armada 4100 and 4200 Families of Personal Computers Maintenance - Page 83

Chapter 4 Removal and Replacement Preliminaries This chapter provides general service information for the Compaq Armada 4100 and 4200 Families. Adherence to the procedures and precautions described in this chapter is essential for proper service. 4.1 Electrostatic Discharge A sudden discharge of static electricity from a finger or other conductor can destroy static-sensitive devices or microcircuitry. Often the spark is neither felt or heard, but damage occurs. An electronic device exposed to electrostatic discharge (ESD) may not be affected at all and will work perfectly throughout a normal cycle. Or it may function normally for a while, then degrade in the internal layers, reducing its life expectancy. Networks built into many integrated circuits provide some protection, but in many cases, the discharge contains enough power to alter device parameters or melt silicon junctions. 4.1.1 Generating Static Table 4-1 shows how different activities generate static electricity and at different electrostatic voltage levels. Table 4-1 Typical Electrostatic Voltages Relative Humidity Event 10% 40% 55% Walking across carpet 35,000 V 15,000 V 7,500 V Walking across vinyl floor 12,000 V 5,000 V 3,000 V Motions of bench worker 6,000 V 800 V 400 V Removing DIPS from plastic tubes 2,000 V 700 V 400 V Removing DIPS from vinyl trays 11,500 V 4,000 V 2,000 V Removing DIPS from Styrofoam 14,500 V 5,000 V 3,500 V Removing bubble pack from PCBs 26,000 V 20,000 V 7,000 V Packing PCBs in foam-lined box 21,000 V 11,000 V 5,000 V NOTE: 700 volts can degrade a product. Removal and Replacement Preliminaries 4-1