When two objects are rubbed together, one loses electrons and becomes positively charged while the other gains electrons and becomes negatively charged, creating static electricity. As the negatively charged object comes into contact with another positively charged object, it rapidly releases electrons to achieve neutrality, resulting in electrostatic discharge (ESD).
The polarity and magnitude of the charge depend on the materials' positions in the triboelectric series. The further apart they are, the greater the charge.
The Triboelectric Series
Types of Materials
ESD materials are classified based on how quickly electricity moves through the material:
|Electrons can easily flow across its surface or through its volume due to its low electrical resistance, which is less than 1 x 10^4 Ω-cm. When it comes into contact with another conductive object, charges will flow uniformly across its surface or to the ground.
|Electrons flow at a controlled speed through the material, slower than in a conductive material but faster than in an insulative material. Its resistivity is in the range of 1 x 10^4 – 1 x 10^11 Ω-cm, which is ideal for ESD materials.
|It prevents or limits the flow of electrons across its surface or through its volume due to its high electrical resistance of at least 1 x 10^11 Ω-cm. Hence, they are more difficult to ground, and static charges can remain in place for a long period of time.
We often feel, hear, or see ESD in everyday situations such as the shock you get when you touch a metal doorknob, the crackling sound you hear when you remove your sweater, or even lightning. While ESD is not harmful to humans, it can cause severe damage to electronic components or even cause fire and explosion in hazardous areas.
Find out more about the dangers of ESD to electronic devices here.