How to establish an ESD protected area (EPA)

1. What is an EPA?

EPA stands for ESD Protected Area: a controlled area that protects electrostatic-discharge-sensitive items, or ESDS items, against electrostatic discharge.

Typical areas requiring ESD protection include:

• Surface-mount technology (SMT) production.
• Electronic assembly.
• Circuit-board testing and inspection.
• Storage of electronic components and assemblies.
• Incoming quality control (IQC) for electronic materials and components.

Within the EPA, personnel and conductive or dissipative objects are bonded and grounded as appropriate to control potential differences. Unnecessary insulators should be removed; essential insulators require suitable charge-control measures, such as ionisation, based on the assessed risk.

2. Establishing the EPA

A practical EPA implementation plan includes:

• Identify the operations that require ESD protection.
• Define the EPA boundaries on the layout.
• Display EPA entry and control signs.
• Control grounding of personnel, workstations, chairs, trolleys, flooring and equipment as applicable.
• Install an appropriate grounding and bonding system.
• Provide ionisation equipment where required.
• Select partitions and curtains suitable for the ESD-control requirements.
• Provide suitable instruments to check wrist straps, garments, mats, footwear and work surfaces.
• Display the ESD rules that apply within the EPA.
• Perform routine compliance checks, such as daily personnel-grounding checks, according to the control plan.
• Schedule periodic compliance verification; frequency, including any monthly checks, must be defined in the control plan.

ESD floor-marking tape for EPA boundaries.

EPA entry warning and ESD-sensitive-area signs.

3. Operating principles within the EPA

EOS/ESD Association - standards and current documents

Insulators: use a suitable electrostatic field meter, such as the illustrated DZ4, and the measurement method specified in the applicable standard. The original article cited 2,000 V/inch at 30 cm and 125 V/inch at 2.5 cm. These archived figures must not be used as a complete current acceptance rule: voltage, field strength and measurement distance are different quantities. Verify the applicable requirements and the sensitivity of the ESDS items.

DZ4 electrostatic field meter.

Conductors: bond and ground conductive items where practicable. Isolated conductive tools, such as pliers, scissors and tweezers, require a defined control method and verification. Selecting an ESD-labelled tool alone does not establish compliance; confirm its electrical characteristics and how it is used.

Ionisers neutralise charge on essential insulators and other items that cannot be grounded effectively. They complement grounding. Check ion balance and discharge time periodically; the original article specifies a ±35 V balance limit. Confirm the applicable limits, method and measurement positions in the ESD-control plan.

DP ioniser test instrument.

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