AN055
ESD Static Protection Manual
7
Table 1-2. Common Behavior Electrostatic Strength
Source
Electrostatic Voltage (V)
10-20% Relative Humidity
65-90% Relative Humidity
Walking on the carpet
35000
1500
Walk on polyethylene floor
12000
250
Staff on seat
6000
100
Polyethylene envelope
(work instruction booklet)
7000
600
Pick up the plastic bag from the
work surface
20000
1200
Work seat with foam pad
18000
1500
1.2.
Electrical Overstress EOS
Electronic components can be damaged by many different sources of harmful electrical
energy, either from ESD voltages or from electrical spikes generated by human-operated tools
such as soldering irons, solder extractors, test instruments, or other electronic equipment.
Some devices are more sensitive than others. Sensitivity was originally an indicator of device
functional design. In general, faster, smaller devices have higher sensitivity than their slower,
larger predecessors. The use or type of device plays a decisive role in sensitivity. This is
because some devices are designed to respond to small electrical signals or over a wide
frequency range. With the reduction of the
process technologies
, the problem of EOS will
become more and more serious.
When considering the sensitivity of a product, we must look at the sensitivity of the most
sensitive components in the assembly. Harmful electrical energy is conducted or processed
as normal signals are applied to the circuit. Periodic testing of equipment, as required by most
ESD specifications, prevents damage from degraded performance over time. Since both EOS
damage and ESD damage are destructive consequences of harmful electrical energy, they
are very similar in nature.
1.3.
Warning Signs
Warning signs can be hung and posted on plants, components, assemblies, equipment and
packaging to alert people that they may be damaged by static electricity or electrical
overloading of the components they operate.
