Step-by-step guide to choosing the right ESD equipment

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Gemma Squire Own Brand Manager RND

Gemma and team are dedicated to sourcing high-quality, compliant and cost-efficient tools and components for engineers and technicians in maintenance, repair and operations. Passionate about product, she has extensive experience as a Product Manager identifying the best lines and the best deal for our own brand range, RND.

Step-by-step guide to choosing the right ESD equipment

Electrostatic Discharge (ESD) is a sudden flow of electric current between two differently charged objects. It occurs when the exchange of electrons creates a large electrostatic field build up and it is hugely problematic in a high-tech manufacturing environment.

Static electricity and electrostatic induction are the most common causes of ESD. In order to avoid it, procedures should be followed and correct shielding material should be used to reduce or eliminate electrical current.

Figure 1: ESD Strike

The two types of risk to electronic equipment are: 

  1. Catastrophic failure: which causes a permanent damage such as a metal melt, junction breakdown or oxide failure and is usually easy to detect upon inspection.                                                                                                      
  2. Latent defect: results in partial degradation, where the device will usually continue to perform and the fault may be harder to detect. However, partial degradation tends to lead to intermittent failure or permanent failure at a later date.

How can ESD protection be provided?

ESD protection is important in manufacturing, shipping and operational processes.

As the range of ESD protection devices is extensive, it is important to pick the right option for your application. An inappropriate device will be ineffective and is likely to interfere with the normal operation of the circuit. An optimum ESD device must:

  • React quickly to stop dangerous current and voltage spikes during ESD events.
  • Have the ability to remain unaffected by repetitive ESD strikes.
  • Not disturb the functionality of the system that it is protecting. 

ESD protection devices serve to protect sensitive electronic products and equipment from ESD during storage and transit and prevent static build-up and contamination from dust or humidity. Types of ESD protection include:

1. Packaging and Storage

2. ESD Accessories

This category encompasses an array of ESD devices that can be used to provide additional protection. It includes, but is not limited to:

3.  Grounding Systems

Grounding systems are used to safely ground anyone working with sensitive electronic equipment. By using grounding products, the build-up of static electricity can be prevented, reducing ESD. Examples of ESD grounding systems include:

Figure 2: Coiled Earth Lead

Considerations when choosing the right ESD equipment

1. Understand where a strike is likely to come from to determine what  level of protection your device requires.When considering the level of protection needed, three standards can be used to determine the overall immunity of integrated circuits (ICs) to ESD.

  • Human contact – Human Body Model –  This model simulates the ESD of a human onto an electrical component. A person can accumulate static electricity from walking or moving, which is then discharged through the IC.
  • Normal use of the device – Charged Device Model –  The CDM test simulates how a device acts when the device itself has an electrostatic charge and comes into contact with a metallic surface. This is the most common type of ESD. CDM discharge depends largely on the size and type of the component package.
  • Other equipment – Machine Model –  This simulates the discharge of static electricity accumulated from machines and equipment.  
ModelHBMMMCDM

Test levels
 

2,4,8 and 15kV

100,150 and 200V

250, 500, 750 and 1000V

Peak current (A)
 

1.5

+3

5 to 6

Pulse width (nsec)
 

Approximately 150

Approximately 80

Approximately 1

Rise time
 

2 to 10 nsec

Approximately 1 nsec

Less than 400 psec

Typical ESD failures
Junction damage, metal penetration, metal melting, contact spiking, and gate-oxide damage
 
Junction damage, metal melting, and gate-oxide damageGate-oxide damage, charge trapping, and junction damage

Table 1: Comparison ESD testing
2. Ascertain what/who you are aiming to protect.

What are you protecting?

In order to provide effective ESD protection, any items handled that are susceptible to ESD and which require protection must be identified. For example, external ESD protection devices are ideal for interfaces that are particularly susceptible to ESD damage but may not be suitable for highly advanced systems on a chip (SoC).

The size of the workplace and nature of the work carried out will also determine the ESD grounding requirements of a company. Typically, smaller work environments will adhere to basic ESD requirements whilst larger facilities will need to follow more stringent grounding requirements.

Within a large working environment, the creation of an ESD protected area (EPA) may be required, where all surfaces, objects, people and ESD devices are kept at the same electrical potential. This is achieved by:

  • Grounding all conductors (including people).
  • Removing all insulators – either directly or by replacing them with an ESD alternative.
  • Using an ioniser to neutralise essential insulators.

Who are you protecting?

Grounding is an essential form of protection as it ensures safe operation of equipment and protects users from ESD strikes. All components of a work area should be grounded, including work surfaces, personnel and equipment. The type of grounding system used is determined by the worker who requires it. For instance, those who are seated when working should use a wrist strap whilst those who work on their feet should use a foot grounding system. In some situations, a combination of the two might be applicable.Additionally, the best ESD protection for a user in a manufacturing environment will differ from the protection required by those working remotely. Field service engineers, for instance, will require portable equipment that can provide extensive protection to compensate for the absence of an EPA.

Figure 6: Field service kit

3. Calculate the required ESD protection specifications.

Once the subject requiring protection has been determined, it will then be necessary to ensure that ESD equipment with appropriate specifications is chosen. Factors to consider include:

Capacitance

Capacitance refers to a component’s or circuit’s ability to collect and store energy in the form of an electrical charge. As signal frequency increases, the capacitance effect changes. A mismatch between the capacitance of a suppressor and the signal speed of a circuit can result in the degradation of the signal. Ideally, the maximum capacitance for the diode without interfering with the interface signal should be determined. 

To increase capacitance the conductors can be positioned closer together and larger plates with a greater surface area can be used. Further, capacitors can be added as ESD protection to divert or store charge.

Figure 7: Capacitor

ESD clamping voltage

This determines the level of safety that a protection diode can guarantee. Reducing the voltage that an IC will be exposed to in the event of an ESD strike is essential for the protection of more sensitive components within the IC. Devices that have a low clamping voltage therefore tend to be more effective.

Leakage current

The leakage current refers to the amount of current that passes through the ESD suppressor whilst the circuit is operating normally. This consideration is of particular importance to battery-driven applications. Here, suppressors that allow for as little leakage as possible are desirable so that battery drain time is not increased.

System operating voltage

Suppressors have varied system operating voltage specifications according to their construction. These specifications determine the suitability of parts within given circuit parameters and are used to ensure that appropriate parts are used. For example, a 5 VDC-rated part would not be appropriate for use in a 9 VDC bus as excess voltage could cause degradation of the part.

Location of ESD suppressor

The most effective suppressors are those that are located near the ESD source and are as close as possible to the line that they are protecting. The greater the distance between them, the higher the impact of the transient voltage will be on the IC.

ESD protection is of huge importance in high-tech industries to ensure product reliability, to reduce costs where damage would otherwise occur and as a health and safety precaution for users. As technology progresses, the likelihood of an ESD strike increases. This gives rise to a greater need for ESD protection. Integrated circuitry is the “brains” of all electronic products and so protecting these components is crucial. As technological progress develops rapidly in this area, the need for ESD protection will increase, bringing with it a greater, more advanced offering of ESD protection devices.

ESD Field Service Kit with CH Plug

Creates an instant EPA for safe working, even remotely. For use in the field where there isn’t an EPA. Red pouch ensures the kit is easily visible .Self-contained kit keeps everything safely stored and neatly to hand.

ESD Workstation Kit with CH Plug

Reflection breaking surface to reduce glare and improve operator comfort. Prevention of sliding of delicate components thanks to excellent friction coefficient. Heat resistance: does not melt or burn coming into contact with hot metal parts or soldering debris. Suitable for loose laying: does not require application with adhesive. Good resistance to scratches and excellent flexibility and comfort.

ESD Earth Bonding Plug

Easy connection to mains earth for operators and other elements of the EPA. Moulded from ABS. For use in the factory and in the field.

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