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Guidelines for Handling
Electrostatically Sensitive Devices (ESD)
1 What is ESD?
VSLI chips (MOS technology) are used in practically all SIMATIC S5 and TELEPERM M modules.
These VLSI components are, by their nature, very sensitive to overvoltages and thus to electrosta
tic discharge:
They are therefore defined as
"Electrostatically Sensitive Devices"
"ESD" is the abbreviation used internationally.
The following warning label on the cabinets, subracks and packing indicates that electrostatically
sensitive components have been used and that the modules concerned are susceptible to touch:
ESDs can be destroyed by voltage and energy levels which are far below the level perceptible to
human beings. Such voltages already occur when a component or a module is touched by a per
son who has not been electrostatically discharged. Components which have been subjected to
such overvoltages cannot, in most cases, be immediately detected as faulty; the fault occurs only
after a long period in operation.
An electrostatic discharge
- of 3500 V can be felt
- of 4500 V can be heard
- must take place at a minimum of 5000 V to be seen.
But just a fraction of this voltage can already damage or destroy an electronic component.
The typical data of a component can suffer due to damage, overstressing or weakening caused
by electrostatic discharge; this can result in temporary fault behavior, e.g. in the case of
- temperature variations,
- mechanical shocks,
- vibrations,
- change of load.
Only the consequent use of protective equipment and careful observance of the precautions for
handling such components can effectively prevent functional disturbances and failures of ESD
modules.
1
©
Siemens AG C79000-D8000-C333-01
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