ElectroStatic charges and ElectroStatic discharges are different. All material can tribocharge (generate ElectroStatic charges). This is static electricity which is an electrical charge at rest. When an electrical charge is not at rest, but discharges (i.e. ESD), problems can occur. All matter is constructed from atoms which have negatively charged electrons circling the atom’s nucleus which includes positively charged protons. The atom having an equal number of electrons and protons balances out having no charge.
Electrostatic charges are most commonly created by contact and separation; when two surfaces contact then separate, some atom electrons move from one surface to the other, causing an imbalance. One surface has a positive charge and one surface has a negative charge.
Charge Generation, or Tribocharging Examples
The simple separation of two surfaces, as when tape is pulled off a roll, can cause the transfer of electrons between surfaces, generating an ElectroStatic charge.
- Unwinding a roll of tape
- Gas or liquid moving through a hose or pipe
- A person walking across a floor with heels and soles contacting and separating from the floor
The amount of static electricity generated varies and is affected by materials, friction, area of contact, and the relative humidity of the environment. At lower relative humidity, charge generation will increase as the environment is drier. Common plastics generally create the greatest static charges.
Typical Electrostatic Voltages
Many common activities may generate charges on a person’s body that are potentially harmful to electronic components. (A higher charge is generated at low humidity, in a dry environment.)
- Walking across carpet: 1,500 to 35,000 volts
- Walking over untreated vinyl floor: 250 to 12,500 volts
- Vinyl envelop used for work instructions: 600 to 7,000 volts
- Worker at bench: 700 to 6,000 volts
- Picking up a common plastic bag from a bench: 1,200 to 20,000 volts
Electrostatic Discharge (ESD)
If two items are at the same electrostatic charge or at equipotential, no discharge will occur. However, if two items are at different levels of ElectroStatic charge, they will want to come into balance. If they are in close enough proximity, there can be a rapid, spontaneous transfer of electrostatic charge. This is called discharge, or ElectroStatic Discharge (ESD).
Examples in daily life:
- Lightning, creating lots of heat and light
- The occasional zap felt when reaching for a door knob
- The occasional zap felt when sliding out of an automobile and touching the door handle
In a normal environment like your home, there are innumerable ESD events occurring, most of which you do not see or feel. It takes a discharge of about 2,000 volts for a person to feel the “zap”. It requires a much larger ESD event to arc and be seen. While a discharge may be a nuisance in the home, ESD is the hidden enemy in a high-tech manufacturing environment. Modern electronic circuitry can be literally burned or melted from these miniature lightning bolts. Even less than 100 volts might damage a sensitive Class 0A component! ESD control is necessary to reduce and limit these ESD events.
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