Static electricity is an everyday phenomenon - there can be few of us who have not experienced an electrostatic discharge shock after walking across a carpeted room and touching the metal door handle, or on getting out of a motorcar and touching the metal bodywork.
Other nuisance electrostatic effects include the clinging of synthetic fabrics to the body, the sticking of a plastic document cover, or the attraction of dust to a TV or Computer monitor.
While we can feel some of these effects, static electricity is normally present at lower levels that we cannot feel, hear or see, but may nevertheless damage sensitive electronic components. It can build up rapidly on objects, in unexpected ways, to produce surprisingly high voltages that can cause damage to electronic circuitry.
If two charged objects that contain different voltages approach each other closely enough, charges may pass from one object to the other in a quick electrostatic discharge or spark. While this only lasts a microsecond or less, the peak discharge current can be several Amps and the peak power can be in the KiloWatt range!
Principles for Electro Static Discharge (ESD) safe handling of sensitive electronic components:
There are two simple principles that one must apply to protect electrostatic discharge sensitive (ESDS) electronic components from ESD damage:
· Only handle (ESD or other) sensitive electronic components in an ESD Protected Area (ESDPA) under protected and controlled conditions
· Protect sensitive electronic devices outside of the ESDPA using ESD protective measures and packaging
What is an EPA? (ESD Protected Area)
An EPA (ESD Protected Area) is an area that is managed under an ESD Prevention Program and maintained as safe for handling static sensitive components by keeping electrostatic discharges, electrostatic fields and voltages to an insignificantly low level.
An EPA should have well defined and clearly marked boundaries, defining clearly where the safe area is and all of the ESD protection measures must be clearly marked within the safe area.
Insulating materials are strong sources of ESD that can cause damage to sensitive electronic components and devices. These Insulating materials must be excluded or removed from the EPA where possible. Where this is not possible special protection measures such as ionisers must be installed to neutralise electrostatic charges that may be generated within the area.
All non-insulating and conductive objects must be grounded, so that damaging levels of electrostatic charges (ESD) cannot build up on these surfaces. All personnel within the EPA (people are conductive objects!) must be grounded to prevent the build up of electrostatic charges to a level of such high voltages that can cause damage. There are two ways in which people can be grounded:
· Wearing a grounded wrist strap (this is the preferred method)
· Wearing conductive footwear (conductive or dissipative shoes, or heel & toe straps on both feet) in conjunction with a grounded conductive floor surface.
Three key elements of an effective ESD Protection Program (ESD PP)
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