Compaq dc5850 Service Reference Guide: HP Compaq dc5850 Business PC - Page 65

Microtower (MT) 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 appear to be affected at all and can work perfectly throughout a normal cycle. The device may function normally for a while, but it has been degraded 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. Generating Static The following table shows that: ● Different activities generate different amounts of static electricity. ● Static electricity increases as humidity decreases. Event 55% Walking across carpet 7,500 V Walking across vinyl floor 3,000 V Motions of bench worker 400 V Removing DIPs* from plastic tube 400 V Removing DIPs* from vinyl tray 2,000 V Removing DIPs* from Styrofoam 3,500 V Removing bubble pack from PCB 7,000 V Packing PCBs in foam-lined box 5,000 V *These are then multi-packaged inside plastic tubes, trays, or Styrofoam. Relative Humidity 40% 15,000 V 5,000 V 800 V 700 V 4,000 V 5,000 V 20,000 V 11,000 V 10% 35,000 V 12,000 V 6,000 V 2,000 V 11,500 V 14,500 V 26,500 V 21,000 V Electrostatic Discharge Information 53