Effects of Static Electricity The effects of ESD are not recognized. Failures due to ESD are often misanalyzed as being caused by electrical  overstress  due  to  transients  other  than  static. Many  failures,  often  classified  as  other,  random, unknown,   etc.,   are   actually   caused   by   ESD. Misclassification of the defect is often caused by not performing  failure  analysis  to  the  proper  depth. COMPONENT SUSCEPTIBILITY All solid-state devices, except for various power transistors and diodes, are susceptible to damage by discharging  electrostatic  voltages.  The  discharge  may occur across their terminals or through subjection of these  devices  to  electrostatic  fields. LATENT FAILURE MECHANISMS The  ESD  overstress  can  produce  a  dielectric breakdown of a self-healing nature when the current is unlimited. When this occurs, the device may retest good, but contain a hole in the gate oxide. With use, metal will eventually migrate through the puncture, resulting in a shorting of this oxide layer. Another  structure  mechanism  involves  highly limited current dielectric breakdown from which no apparent damage is done. However, this reduces the voltage at which subsequent breakdown occurs to as low  as  one-third  of  the  original  breakdown  value. ESD   damage   can   result   in   a   lowered   damage threshold at which a subsequent lower voltage ESD will cause further degradation or a functional failure. ESD ELIMINATION The  heart  of  an  ESD  control  program  is  the ESD-protected  work  area  and  ESD  grounded  work station.  When  you  handle  an  ESD-sensitive  device outside of its ESD protective packaging, you need to provide  a  means  to  reduce  generated  electrostatic voltages  below  the  levels  at  which  the  item  is sensitive. The greater the margin between the level at which  the  generated  voltages  are  limited  and  the ESDS   item   sensitivity   level,   the   greater   the probability  of  protecting  that  item. PRIME GENERATORS All common plastics and other generators should be   prohibited   in   the   ESD   protected   work   area. Carpeting should also be prohibited. If you must use carpet, it should be of a permanently antistatic type. Perform   weekly   static   voltage   monitoring   where carpeting is in use. PERSONAL APPAREL AND GROUNDING An  essential  part  of  the  ESD  program  is grounding personnel and their apparel when handling ESDS material. Means of doing this are described in this  section. Smocks Personnel  handling  ESDS  items  should  wear  long sleeve, ESD-protective smocks, short sleeve shirts or blouses, and ESD-protective gauntlets banded to the bare wrist and extending toward the elbow. If these items are not available, use other antistatic material (such as cotton) that will cover sections of the body that could contact an ESDS item during handling. Personnel Ground Straps Personnel  ground  straps  should  have  a  minimum resistance  of  250,000  ohms.  Based  upon  limiting leakage currents to personnel to 5 milliamperes, this resistance  will  protect  personnel  from  shock  from voltages  up  to  125  volts  RMS.  The  wrist,  leg,  or ankle bracelet end of the ground strap should have some  metal  contact  with  the  skin.  Bracelets  made completely   of   carbon-impregnated   plastic   may burnish  around  the  area  in  contact  with  the  skin, resulting in too high an impedance to ground. ESD-PROTECTIVE  MATERIALS There  are  two  basic  types  of  ESD-protective material—conductive    and    antistatic.    Conductive materials  protect  ESD  devices  from  static  discharges and  electromagnetic  fields.  Antistatic  material  is  a nonstatic   generating   material.   Other   than   not generating static, antistatic material offers no other protection  to  an  ESD  device. Conductive ESD-Protective Materials Conductive  ESD-protective  materials  consist  of metal,    metal-coated,    and    metal-impregnated materials.  The  most  common  conductive  materials used  for  ESD  protection  are  steel,  aluminum,  and carbon-impregnated   polyethylene   and   nylon.   The latter two are opaque, black, flexible, heat sealable, electrically  conductive  plastics.  These  plastics  are 10-17