ESD Protection–How ESD Creates an Anti-Static Environment

What is ESD and Why is ESD Protection Important?

Electrostatic discharge, or ESD, is the sudden flow of electricity between two objects caused by contact, an electrical short, or dielectric breakdown. ESD can be very damaging to electronic components and cause product defects, failures, and reduced reliability.

ESD protection is critical in manufacturing, production, and handling of electronics to prevent damage and ensure high quality and reliability. An ESD event as small as 30 volts can destroy a sensitive electronic device. Common causes of ESD include:

Human body model (HBM) ESD from a person becoming charged then touching an electronic device
Charged device model (CDM) ESD from an imbalanced charge buildup on the device itself
Field induced model from the electric fields generated by the buildup of static charge on surfaces and objects

Implementing proper ESD protection protocols creates an anti-static environment to safeguard electronics from the damaging effects of electrostatic discharges. Key aspects include:

Grounding workers, work surfaces, floors, and equipment to the same electrical ground point
Using static dissipative or conductive materials and coatings
Controlling humidity to 30-70% RH
Neutralizing charges with ionization
Implementing ESD-safe packaging, handling, and transportation methods

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The Basics of ESD and Charge Generation

Triboelectric Charging

One of the primary causes of electrostatic charge buildup is triboelectric charging – the transfer of electrons that occurs when two materials make contact then separate. The level of charge generated depends on the type of materials and how easily electrons migrate from one to the other.

The triboelectric series ranks materials based on their tendency to gain or lose electrons. When two materials far apart on the series touch, the material higher on the positive end will pull electrons from the one closer to the negative end:

Most Positive	Intermediates	Most Negative
Air	Cotton	PVC
Human skin	Wool	Polyurethane
Asbestos	Nylon	Polyethylene
Glass	Aluminum	Polypropylene
Mica	Paper	Teflon

For example, walking across a wool carpet generates a high charge on a person because wool is much more positive than human skin. The static charge will then discharge to the next thing the person touches.

Conductive vs Insulative Materials

Materials are categorized based on their resistivity or ability to prevent or allow electric current flow:

Material Type	Resistivity Range (ohms/square)	Charge Behavior
Conductive	<10^5	Charges flow easily and dissipate quickly
Static Dissipative	10^5 to 10^12	Charges flow slowly and take time to dissipate
Insulative	>10^12	Charges do not flow and remain in place

In an ESD protective environment, conductive and static dissipative materials allow charges to flow to ground and neutralize. Insulative materials should be avoided as they prevent charge dissipation and can build up high voltages.

Key Elements of an ESD Protective Work Environment

ESD-Safe Flooring

ESD flooring materials prevent the buildup of static charges as people walk and move equipment around the workspace. The floor provides a path for charges to dissipate to ground.

Types of ESD flooring include:

Conductive vinyl, rubber, or epoxy
Static dissipative carpet
Interlocking conductive floor tiles
Conductive floor coatings applied over existing floors

For proper function, ESD floors must be electrically connected to ground with grounding strips typically placed around the perimeter or at entryways. The floor also needs to be kept clean as dirt, wax, and residues can create an insulative layer.

ESD-Safe Workstations and Benches

Work surface mats made of conductive or static dissipative rubber or vinyl prevent charges from building up where sensitive devices are handled. The mats connect to dedicated ESD ground points with a grounding wire.

Other key elements of an ESD-safe workstation setup include:

Grounding the worker with a wrist strap tethered to the mat
Grounded dissipative chairs and stools
Ionization to neutralize charges
Grounded dissipative storage bins and shelving
Dissipative table coverings and floor mats around the workstation

All grounded elements should have a common connection point to avoid differences in electrical potential.

Ionization

Ionizers generate positive and negative ions that attract and neutralize opposite charges on objects and surfaces. They are very effective at eliminating static in areas that are difficult to ground like on insulative objects or isolated conductors.

Ionizers come in several configurations including:

Overhead ionizing blowers
Ionizing guns and nozzles
Ionizing bars and air knives
Benchtop ionizing fans and blowers

Balanced ionization requires good air flow and ion delivery to the surface. Ionizers need to be kept clean and may require periodic calibration to ensure equal production of positive and negative ions.

Personal Grounding for ESD Protection

Grounding workers is a critical step for ESD protection, as people can easily build up charges from clothing and movement that transfer to electronic devices they handle.

Options for personal grounding include:

Wrist straps tethered to a grounded cord
Conductive footwear on an ESD floor
Conductive garments like lab coats, smocks, and gloves

Wrist straps are the most common and effective, as they provide a consistent, dedicated ground path. They should be worn snug to maintain skin contact. Conductive shoes and clothing rely on contact with an ESD floor and can be compromised by dirt and residues.

Regular testing of personal grounding equipment is important to verify proper functionality. Wrist straps and cords should be tested daily before use. Conductive footwear and floors should be tested regularly according to an ESD program plan.

ESD-Safe Packaging, Handling and Transportation

Outside of ESD protective work areas, sensitive electronics need to be handled and transported in a manner that shields them from charge generating sources.

ESD-safe packaging options include:

Static shielding bags
Conductive and dissipative totes and containers
Foam and cushioning made of dissipative polyethylene and polyurethane
Humidity control dessicant packs
ESD-safe tape, labels, and stretch wrap

All packaging should be grounded when in use. Transport carts made of conductive metal or dissipative plastic will prevent charge buildup during movement. For shipping, packing in ESD-safe boxes with dissipative filler materials and sealing in a static shielding bag provides optimal protection.

ESD Protected Area (EPA) Protocols

An ESD Protected Area (EPA) is a designated space in which all surfaces, objects, people and ESD sensitive devices are kept at the same electrical potential through ESD protective measures. Implementing proper EPA protocols is essential for consistently effective ESD control.

Key EPA protocols include:

Clearly defining EPA boundaries with signs and markings
Requiring all personnel to be grounded before handling ESD sensitive devices in the EPA
Grounding all surfaces and conductors to the same common ground point
Using ESD-safe packaging for storing and transporting sensitive devices within the EPA
Eliminating charge generating sources like common plastics and styrofoam
Periodic verification of ESD ground functionality and resistivity measurements
ESD awareness and prevention training for all personnel working in an EPA

Auditing for compliance to ESD protocols is important to find and correct issues that compromise an EPA. Audits should include:

Wrist strap and footwear testing logs
Resistivity measurements of work surfaces, floors, and packaging
Ionizer balance and offset voltage checks
Inspection for proper signage and labels
Observation of personnel for correct ESD practices

ESD Training and Awareness

Proper training is a critical part of an ESD control program, as people are common sources of ESD events when correct protocols are not understood and followed. All personnel that handle ESD sensitive devices or work in an EPA should complete training on ESD basics and specific proper procedures for their role.

ESD training should cover topics including:

Basics of charge generation and ESD
Potential sources of ESD in the work environment
Proper use of wrist straps and conductive footwear
Handling ESD sensitive devices only at grounded workstations
Transporting devices in ESD-safe packaging
Grounding protocols for working in an EPA
Proper cleaning and maintenance of ESD protective materials

Regularly scheduled retraining sessions are important to refresh knowledge and update personnel on any changes to protocols or standards. Incorporating ESD awareness into daily operations through signage, informational posters, and compliance checks will further reinforce training and promote the right habits.

ESD Standards and Testing

Meeting industry standards for ESD control ensures the right protective measures are in place. The most widely used ESD standards include:

ANSI/ESD S20.20 – Development of an ESD Control Program
ANSI/ESD S541 – Packaging Materials for ESD Sensitive Items
ESD TR53-01-06 – Compliance Verification of ESD Protective Equipment and Materials
IEC 61340-5-1 – Protection of Electronic Devices from Electrostatic Phenomena

Many electronics manufacturers and suppliers require compliance to one or more of these standards. Each outlines specific requirements for ESD control including:

Personnel grounding methods
Packaging and marking of sensitive devices
Grounding and resistivity of surfaces and materials
Ionization for charge neutralization
Periodic verification testing of ESD equipment and EPAs

Performing compliance verification testing on a regular basis is important to maintain ESD control and meet standard requirements. This involves checking the key parameters of ESD protection including:

Element	Parameters	Test Frequency
Wrist Straps	Resistance <10 megohms	Before each use
Footwear	Resistance <100 megohms	Daily
Garments	Resistance <1 gigohm	Weekly
Surfaces	Resistance <1 gigohm	Monthly
Floors	Resistance <1 gigohm	Monthly
Ionizers	Offset voltage <±50V	Weekly
EPAs	All ESD elements in spec	Monthly

Records of test results should be documented and reviewed to identify any out-of-spec conditions for correction. Many ESD monitoring systems offer software for automated data logging and reporting to meet compliance verification requirements efficiently.

Frequently Asked Questions

What is the difference between ESD and EMI?

ESD is a single, fast, high-voltage discharge while EMI (electromagnetic interference) is a continuous radiated disturbance across a range of frequencies. EMI shielding is often incorporated with ESD protection as the fast voltage changes of an ESD pulse can induce EMI.

How long can static charges last?

Static charges can remain on an ungrounded surface or object for a very long time, even days or weeks. The charge will slowly decay from humidity and air ionization but may still have sufficient voltage to cause ESD damage.

What is the typical human body voltage?

People can easily generate several thousand volts of charge from normal activity like walking across a carpet. Voltages over 10,000V are possible in dry environments. A human body capacitance model of 100 picofarads is used to simulate human ESD in testing.

What happens if I don’t wear my ESD smock?

An ESD garment is one component of ESD protection and should always be worn when working in an EPA and handling sensitive devices. A smock shields charges on clothing worn underneath. With no smock on, charges on the clothing could transfer to sensitive devices and cause damage.

How do I check my ESD workstation?

Test wrist strap and work surface resistance with an ESD ohmmeter. Ensure all elements are connected via grounding wire to a common ground point. Check for no loose connections. Verify ionizers are balanced and delivering air flow to the area. Inspect the area to ensure no unauthorized materials or objects are present.