Static Electricity and Electrostatic Discharge (ESD) – Basic

 

What is Static Electricity & Electrostatic Discharge ?

Static electricity is an imbalance of electrical charges within or on the surface of a material. And, what is electrostatic discharge? Electrostatic discharge (ESD) definition is a rapid, spontaneous transfer of electrostatic charge induced by a high electrostatic field. In this article we will discuss about what is and how static charge created then how static electric becomes electrostatic discharge —Omazaki Consulant is an ESD consultant that provides static electricity and electrostatic discharge consulting services. Contact us by sending an email to cs@omazaki.co.id or by filling in the form in contact.

This article is a series of several related articles:

• Static electricity and Electrostatic Discharge (ESD) – Basic
• Causes and Effect of Electrostatic Discharge
• Solutions, Prevention and Control of Electrostatic Discharge

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Static Electricity

Electrostatic charge is defined as “electric charge at rest”. Static electricity is an imbalance of electrical charges within or on the surface of a material. This imbalance of electrons produces an electric field that can be measured and that can influence other objects.

How Static Charges are Created?

Static electricity is the result of something called triboelectric charging which happens whenever the atoms of the surface layers of two materials rub against each other. As the atoms of the two surfaces move together and separate, some electrons from one surface are retained by the other.

All items are made of small atoms. These atoms are made up of even smaller items called protons, neutrons and electrons. The protons are charged positive, the neutrons have no charge and the electrons are charged negative. Under normal conditions, there are the same amount of protons and electrons giving atoms no charge.

However, these electrons can move. When separating or rubbing together materials, electrons can move from atom to atom or from one material to another (triboelectric charges). This can mean that atoms can hold a positive or negative charge. (Dependant on movement and direction of electrons). If the material in question is an insulator, this charge can be held and not move. This is called static electricity.

What Contributes to Charge Generation?

The size of the charge generated also depends upon the following:

• The type of materials subjected to contact or separation.
• How much friction/time.
• What the relative humidity is.
• Charges can accumulate if not controlled.

At lower relative humidity, as the environment is drier, charge generation will increase significantly. Increasing RH lowers charge generation but doesn’t improve decay significantly.

Common Sources of Static Electricity

The following table shows a sample list of sources of static electricity.

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Electrostatic Discharge

Electrostatic discharge (ESD) is defined as the rapid, spontaneous transfer of electrostatic charge induced by a high electrostatic field. ESD is also a build-up of charges over a specific area without current flow. Another definition of electrostatic discharge is an uncontrolled surge of static between objects with different voltage potentials. Note: Usually, the charge flows through a spark between two conductive bodies at different electrostatic potentials as they approach one another.

We experience occurrences of static electricity everyday. For example, walking along a carpeted floor in a heated room during winter generates sufficient static electricity to give us a rather shocking experience when we touch the door knob. While this sudden discharge of static electricity does not result in any harm to the human body, it can be very damaging to electronic devices which are sensitive to electrostatic discharge. It is possible for electronic devices to be damaged by ESD that is imperceptible to the human body.

How Does Static Become Electrostatic Discharge (ESD)?

If two items are at different electrostatic charge levels, as they approach one another, a spark or electrostatic discharge (ESD) can occur. This rapid, spontaneous transfer of electrostatic charge can generate heat and melt circuitry in electronic components.

The sequences of static becomes electrostatic discharge is as follows:

• Charges seek to balance (opposites attract)
• Bigger charge meets smaller charge
• Discharge is instantaneous
• Discharge energy causes heat
• Heat causes damage

ESD Characteristics

According to IEC 61000-4-2, ESD is characterized by:

• Fast rise time
• High peak voltage
• Current up to 30A

However, the damage caused by the effects of ESD is not always so noticeable.

Typical Electrostatic Voltages Generated

Human Awareness Levels

• We feel the discharge if it greater than 3500 volts.
• We hear the discharge if is greater than 5000 volts.
• We see the discharge if is greater than 8000 volts.

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Type of Electro-static Discharge

The most spectacular form of electrostatic discharge is the spark. Spark occurs when a heavy electric field creates an ionized conductive path in air. This can cause minor discomfort to people, damage to electronic equipment, and fires and explosions if the air contains combustible gases or particles.

The spark can be visible and audible. But, many ESD events occur without a visible or audible spark. A person carrying a relatively small electric charge may not feel a discharge that is sufficient to damage sensitive electronic components. Some electronic devices may be damaged by discharges as small as 30V. Those invisible forms of ESD can cause outright device failures, or less obvious forms of degradation that may affect the long term reliability and performance of electronic devices. The degradation in some devices may not become evident until well into their service life.

The best known example of a natural spark is lightning. The electric potential between a cloud and ground, or between two clouds, is typically hundreds of millions of volts.

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Can ESD Cause Damage?

Yes. A relatively small electric charge is sufficient enough to damage sensitive electronic components, and even cause fires and explosions if the air contains combustible gases or particles. Many devices may be damaged by discharges as small as 30V. These invisible forms of ESD can cause outright device failures and may affect the long-term reliability and performance of electronic devices. Electrostatic damage can occur at any time – goods input, production, assembly, testing, storing, packing, shipping or maintenance.

This topic will be discuss more detail in article of Causes and Effect of Electrostatic Discharge.