HP LTE Notebook PC 5250 LTE 5000 Family of Personal Computers Maintenance and - Page 118

Chapter 4. Removal and Replacement Preliminaries Chapter 4.0 Introduction This chapter provides general service information for the computer. Adherence to the procedures and precautions described in this chapter is essential for proper service. Chapter 4.1 Electrostatic Discharge Information A sudden discharge of static electricity from your finger or other conductor can destroy static-sensitive devices or microcircuitry. Often the spark is neither felt nor heard, but damage occurs. An electronic device exposed to electrostatic discharge (ESD) may not be affected at all and can 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 tube 2,000 V 700 V 400 V Removing DIPS from vinyl tray 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 PCB 26,500 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. 4.1.2 Preventing Electrostatic Damage to Equipment