What Is Static Electricity And How is It Generated?

Static electricity refers to the buildup of electric charge on the surface of an object. Static charges are usually generated in the following three ways:

1. Friction
2. Two objects sperate after contact
3. Electrostatic Induction

Almost every object in working station can generate static electricity, such as:

• Mobile objects: Handcarts and chairs
• Materials: Adhesive tape, turnaround boxes, and other items used for material handling
• Clothing: gloves, cloths used in cleanrooms, shoe and regular clothing
• Workstation components: Workbench surfaces, CRT computer monitors, hand tools, paper, notebooks, folders, and pens
• Infrastructure: Walls, floors, and alcohol bottles
• Packaging: regular plastics, paper, and cardboard.

What Does ESD Stand For?

ESD stands for Electrostatic Discharge, which is the sudden flow of electricity between two electrically charged objects caused by contact, an electrical short, or dielectric breakdown. When this electrostatic charge transfer process is strong enough, it may damage components and products.

Factors Influencing Static Electricity Creation

Static electricity generation is influenced by various factors, Understanding these factors is essential for managing ESD effectively.

• Material Conductivity: The conductivity of materials directly impacts static electricity generation. Conductive materials and antistatic substances produce minimal static charge, while insulating materials generate significant static electricity.
• Relative Humidity: The relative humidity of the environment exerts a substantial influence on static electricity production. Higher relative humidity, indicative of a moist atmosphere, leads to reduced static charge generation and fewer ESD concerns. Conversely, lower relative humidity amplifies ESD issues by promoting increased static electricity generation.

Ambient Relative Humidity	10-20% RH	40-50% RH	70-90% RH
walking on carpet	35000V	8000V	1500V
walking on ESD floor with regular shoes without wrist strap	10000V	4000V	200V
walking one ESD floor with ESD shoes and wrist strap	50V	10V	0V
Friction insulation materials	4000V	1500V	300V

• Impact of Movement: Walking on the floor generates more static electricity than remaining stationary, underscoring the significance of movement in static charge accumulation.
• ESD Control Measures: The utilization of ESD flooring, ESD-safe footwear, ESD armband, ESD combo tester , ESD turnstile and other protective equipment is highly effective in minimizing human-generated static electricity.

Unstanding how ESD is created and how do they damage components and products, we have to learn the most impoartant part-How to manage and prevent ESD ?

The Electrostatic Properties of Different Materials

The magnitude of static electricity varies depending on the material. All objects can generate static electricity, and the phenomena induced by static electricity can differ greatly depending on the object, which is related to the conductivity of the corresponding material.

Conductive, Insulative and Dissipative Materials

Based on electrical conductivity, materials are typically categorized into three types: conductors, dissipative materials, and insulators. In ESD ADV 1.0, specific definitions for surface and volume resistivity for these three categories are provided as below. For uncertain materials, a specialized surface resistance meter can be used to measure either their surface or volume resistivity.

	Surface Resistance/volume resistance
Conductive Materials	＜1.0 × 104 ohms
Dissipative Materials	≥1.0 × 104 ohms and ＜1.0 × 1011 ohms
Insulative Materials	≥1.0 × 1011 ohms

When two objects come into contact, static electricity is generated, regardless of whether the objects are conductors or insulators. However, there are differences in the nature of the static electricity generated between conductors and insulators.

The Dissipation of Static Electricity on Conductive Materials

When a conductive object becomes charged, it will continue to hold that charge unless some action is taken. The action that can instantly restore the object to a neutral, non-charged state is “grounding”.

Grounding refers to connecting the charged conductive object to the earth (ground). The earth is a large, stable conductive body that can act as a charge reservoir. By connecting the object to ground, a conductive path is formed, allowing the object’s charge to dissipate.

For a positively charged object, grounding allows the earth’s negative charges to be supplied to the object. For a negatively charged object, grounding provides a path for the negative charges to flow into the earth. Through the grounding process, the object is able to transition to a stable, non-charged state.

The Dissipation of Static Electricity on Insulative Materials

For insulators, the dissipation of static electricity is different from that of conductors. Since insulators are poor conductors, even if they are grounded, the accumulated static electricity will not be able to flow away easily.

The Dissipation of Static Electricity on Dissipative Materials

Dissipative materials have resistivity values that fall between insulators and conductors. While electrons can flow through dissipative materials, their movement is governed by the materials’ surface or volume resistivity. The rate of charge transfer in these materials is noticeably faster than in insulators, yet slower than in conductors.

ESD Event

ESD events include three scenarios: the discharge of a charged conductor (including the human body) to an electrostatic discharge susceptible(ESDS) item, the transfer of charge from the ESDS to a conductor, and from charge transfers resulting from electrostatic fields. Each of these scenarios can potentially damage or destroy electronic components, leading to failures in devices and systems.

How Electrostatic Discharge Damage Components?

When a substantial static charge swiftly moves between an object (be it a person or a machine) with a varying potential and a product, it induces a high current within a short span, surpassing the product’s tolerable current level. This can result in severe consequences, such as circuit damage, rendering the product unusable. In less severe cases, it can lead to circuit overheating and impairment, ultimately affecting the product’s longevity and reliability.

Electrostatic discharge (ESD) is a pervasive phenomenon that surrounds us, with the human body only capable of sensing ESD at levels exceeding 3000 volts. Surprisingly, ESD within the range of only 100 to 500 volts can damage ESD sensitive devices. What exacerbates the issue is that only 10% of instances of immediate component failure are detectable within the factory setting, while a significant 90% of potential defects that may lead to impairment of these sensitive devices remain challenging to uncover during the manufacturing process. This imbalance highlights why comprehensive ESD control for electronic manufacturing becomes crucial.

To safeguard products from damage due to electrostatic discharge (ESD), it is necessary to establish a thorough ESD control program.

How to Avoid Electrostatic Discharge?

• Grounding: Connect personnel and equipment to a common ground point to neutralize static charges. Use grounded wrist straps, footwear, or conductive flooring to direct charges safely to earth.
• ESD-Safe Materials: Use conductive or dissipative materials (e.g., antistatic work surfaces, containers) to prevent charge accumulation. Avoid insulative materials like regular plastics or untreated fabrics.
• Humidity Control: Maintain relative humidity between 40-60% to reduce static buildup. Dry air increases charge generation.
• Personal Protection: Wear ESD-safe apparel (e.g., smocks, gloves) and avoid rapid movements or contact with unprotected surfaces.
• Daily Checks: Use ESD personnel grounding tester to verify personal protective devices (e.g., wrist straps, footwear) daily to ensure proper functionality and grounding.
• Component Handling: Store and transport static-sensitive components in shielded packaging (e.g., metallized bags, conductive foam). Use ionizers to neutralize charges on insulative surfaces.
• ESD-Protected Areas (EPAs): Designate zones with grounding systems, antistatic tools, and signage. Restrict non-essential insulative items (e.g., coffee cups, paper) from EPAs.
• Training & Compliance: Educate personnel on ESD risks and protocols, including key standards such as ANSI/ESD S20.20 and IEC-61340-5-1.

By combining these measures, static charges are controlled, minimizing ESD risks to sensitive components.