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An ESD Protected area or rather known as EPA is an area where workers work and deal with ESD sensitive items in a safe environment from harmful electrostatic charges. From a quick glance, this EPA is decorated with many and different type of ESD protective materials and equipments which are used to control the generation and accumulation of electrostatic charges, such as ESD mat, ESD wrist strap, ESD tote box, ESD air ionizer, ESD chair, ESD flooring etc. The EPA is normally identified with a clear signage to indicate that the area is an ESD Protected area.
Controls at EPA
When working in an EPA, workers are required to wear wrist strap while handling the ESD sensitive parts in a seated position.
Tailoring could be made when workers are dealing with hazardous voltage. The use of wrist strap can be exempted with some technical justifications.
The work surface shall be grounded and both conductive and dissipative work surfaces are allowed to be in the EPA, depending on the product’s requirement.
Non essential process insulator such as coffee cup, plastic bottle and personal plastic bag are not allowed to be in an ESD Protected workstation. When essential process insulators are needed on the workstation, the 2kV/inch rule is applied.
When scanning the workstation with a static field meter, a source that gives any reading above the 2Kv in an inch distance shall be kept in a distance at least 30 cm away from the ESD sensitive parts.
Alternatively, ESD air ionizers can be used to neutralize the electrostatic charges on the insulative source or other mitigating ways such as shielding technique can be applied.
Workers shall be trained periodically while working in an EPA. Any untrained visitors such as vendors, customers and external auditors shall be accompanied by a trained worker while in the EPA.
Jigs, tools or surface of automated equipment that has direct contact with the ESD sensitive parts shall be dissipative or conductive in nature and grounded.
ESD garments that are worn by workers shall be checked periodically to ensure
continuous functionality during use in the EPA.
Most established organizations have installed ESD flooring in the EPA. While the presence of ESD flooring definitely make ESD controls much easier, it must be noted that ESD flooring does not work alone and in fact it only works effectively with the presence of ESD footwear.
It is the role of the ESD Coordinator to ensure ESD controls at the ESD Protected area is complying with ANSI/ESD S20.20 standard requirements.
ESD Personnel grounding
Still up to today, people remains as the main culprit contributing the most in destroying the sensitive electronic chips used in electronic equipments and gadgets. Because of this reason, ESD Association established an ANSI/ESD S20.20 standard to provide guidelines to organizations across the globe on the protection of their ESD sensitive items from ESD damage greater than or equal to 100 Volts Human Body Model (HBM).
When a person walks, electrostatic charges continuously build up on the person body through the contact and separation process that takes place between the person’s shoe sole and the flooring material.
The electrostatic charges start to discharge from the person when he touches a conductive material. That explains the reason why a person would feel a jolt when he touches a conductive door knob in a cold and dry weather.. Static jolt is felt when static electricity of at least 3000 Volt build up in a person body. But a mere 10 Volts can kill a Tunneling Magnetoresistive head(TMR)straight away without the person knowledge.
In any organization, ESD personnel grounding are given the most attention.
There are two common ways where ESD personnel grounding are controlled:
• Wearing an ESD wrist strap
• Wearing an ESD shoes
ESD wrist strap
When wearing an ESD wrist strap, the wearer has to ensure that the wrist strap band is making an intimate contact with his bare skin. This is to ensure the wearer is really bonded to the ground via the wrist strap.
A good wrist strap usually comes with a 1 Megohm +/- 10%, ¼ Watt resistor to protect the wearer from the hazardous current or electrical shock.
The ESD wrist strap is used to drain the electrostatic charges from the wearer body to the ground.
The lower the resistance measured from the wearer to the ground when the ESD wrist strap is in use, the lower the body voltage would be. This is because the electrostatic charges flow faster to the ground when the total wrist strap resistance is lower.
The total wrist strap system resistance when wrist strap is in use has to be less than 35 Megohm to get a body voltage less than 100 Volts.
ESD shoes
Before buying any ESD shoes, the organization has to ensure that the esd shoes are evaluated with the presence of the ESD flooring. This is because the esd shoes and esd flooring has to work hand in hand like husband and wife to ensure full effectiveness.
To get a body voltage less than 100 Volts, the total system resistance from the wearer through the esd shoes and esd flooring to the ground shall be less than 35 Megohm.
If the organization has a total system resistance greater than 35 Megohm but less than 1000 Megohm, this condition is still acceptable as long as the body voltage of a person is less than 100 Volts.
When an organization is dealing with a more sensitive device which can be easily damaged by a 50 Volts human body voltage, then a total system resistance of the ESD personnel grounding device when in use to ground must be less than 10 Megohm.
When a person walks, electrostatic charges continuously build up on the person body through the contact and separation process that takes place between the person’s shoe sole and the flooring material.
The electrostatic charges start to discharge from the person when he touches a conductive material. That explains the reason why a person would feel a jolt when he touches a conductive door knob in a cold and dry weather.. Static jolt is felt when static electricity of at least 3000 Volt build up in a person body. But a mere 10 Volts can kill a Tunneling Magnetoresistive head(TMR)straight away without the person knowledge.
In any organization, ESD personnel grounding are given the most attention.
There are two common ways where ESD personnel grounding are controlled:
• Wearing an ESD wrist strap
• Wearing an ESD shoes
ESD wrist strap
When wearing an ESD wrist strap, the wearer has to ensure that the wrist strap band is making an intimate contact with his bare skin. This is to ensure the wearer is really bonded to the ground via the wrist strap.
A good wrist strap usually comes with a 1 Megohm +/- 10%, ¼ Watt resistor to protect the wearer from the hazardous current or electrical shock.
The ESD wrist strap is used to drain the electrostatic charges from the wearer body to the ground.
The lower the resistance measured from the wearer to the ground when the ESD wrist strap is in use, the lower the body voltage would be. This is because the electrostatic charges flow faster to the ground when the total wrist strap resistance is lower.
The total wrist strap system resistance when wrist strap is in use has to be less than 35 Megohm to get a body voltage less than 100 Volts.
ESD shoes
Before buying any ESD shoes, the organization has to ensure that the esd shoes are evaluated with the presence of the ESD flooring. This is because the esd shoes and esd flooring has to work hand in hand like husband and wife to ensure full effectiveness.
To get a body voltage less than 100 Volts, the total system resistance from the wearer through the esd shoes and esd flooring to the ground shall be less than 35 Megohm.
If the organization has a total system resistance greater than 35 Megohm but less than 1000 Megohm, this condition is still acceptable as long as the body voltage of a person is less than 100 Volts.
When an organization is dealing with a more sensitive device which can be easily damaged by a 50 Volts human body voltage, then a total system resistance of the ESD personnel grounding device when in use to ground must be less than 10 Megohm.
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