Static electricity is an electrical charge at rest. Electrostatic discharge is the transfer of charges between bodies at different potentials caused by direct contact or induced by a charged field.
The prime method of generating static is by rubbing or separating materials, commonly known as the Triboelectric Method. A triboelectric charge is defined as "an electrical charge generated by frictional movement, or separation of two surfaces".
The electronics industry is concerned with static electricity's inconspicuous discharge currents and their damaging effects on electronic parts.
An immediate failure occurs when ESD damages the part and renders the part useless immediately after the ESD event. This type of failure would require replacement of the damaged part before any further testing could be accomplished.
A latent failure occurs when the ESD damage is not severe enough to require replacement of the part. This type of failure may be noticed as a glitch in the signal, which only occurs for a microsecond. Further testing may not indicate any damage to the part and operators assume the part to be acceptable. The ESD damage caused the part to fail intermittently whereby a defect was not detected; however, over time and use, the part may degrade until it causes a permanent failure.
The following are ESD control requirements to consider:
- Verify conformance of ESD protected areas/grounded workbench.
- Proper use of ESD protective equipment.
- Avoid use of charge generating materials in ESD protected areas.
- ESD audits and inspections.
- Inclusion of ESD requirements on documentation.
- Control the relative humidity.
- Use Faraday Cage containers to store and transport ESDS items.
- Air ionizer.
The best method to control the damage caused by ESD is to eliminate any electrostatic charges in the work place. This is easier said than done. A basic guideline to prevent electrostatic charges is to eliminate any unnecessary materials in the work place. Smoking, eating and drinking are some of the most common activities that shall be prohibited in the work area. The plastic packaging that most foods are wrapped in carries a high probability for electrostatic charges.
In terms of an of ESD training program, the following administration requirements should be followed:
- Develop and maintain an ESD program plan
- Develop a training program
- Establish a compliance verification and validation plan
In terms of an of ESD training program, the following technical requirements should be followed:
- Use grounding/bonding systems
- Use personnel grounding
- Establish ESD protected areas
- Use proper packaging techniques
- Appropriately mark all ESD sensitive items
- Use proper AC powered equipment
- Use proper handling procedures
The following is a good reference for ESD related information: ESD Association Standard for the Development of an Electrostatic Discharge Control Program for Protection of Electrical and Electronic Parts, Assemblies and Equipment (Excluding Electrically Initiated Explosive Devices). ANSI-ESD-S20-20.