3.2 The ESD Protected Area (EPA)

The EPA is not merely a room with a sign; it is a precisely engineered equipotential volume. Inside this zone, all conductive elements—floors, operators, equipment, and workbenches—are electrically bonded to a common ground point. This ensures that the voltage potential difference between any two objects is effectively zero, preventing the rapid discharge (spark) that destroys gate oxides. If an object cannot be grounded (insulator), it must be excluded or neutralized.

Perimeter & Physical Boundaries

An EPA is defined by physics, not policy. The boundary represents the "Line of Death" for static control.

Demarcation Logic

• Visual Standard: Use high-contrast Yellow/Black ESD warning tape to define the floor perimeter.
• Vertical Signage: Install "ATTENTION: ESD PROTECTED AREA" signage at eye level (1.5m) at every access point.
• Buffer Zone: Maintain a 1-meter "buffer" between the EPA boundary and any uncontrolled static sources (e.g., cardboard storage, plastic packing stations).

Decision Logic: Entry Control

• IF entry is a main personnel corridor → THEN Install hard physical barriers (turnstiles/gates) linked to test equipment.
• IF entry is for material transport (AGV path) → THEN Mark with floor tape and install "Stop & Test" stations for human operators.

Environmental Controls (Temperature & Humidity)

Physics dictates that low humidity increases static generation. Dry air acts as an insulator, allowing charge to accumulate rapidly on surfaces.

• Target: 40% – 60% Relative Humidity (RH).
• Lower Limit (Risk): < 30% RH.
  • Consequence: Triboelectric charging efficiency triples. Walking across a floor generates >5kV instead of <1kV.
• Upper Limit (Risk): > 70% RH.
  • Consequence: Moisture absorption leads to corrosion, "popcorning" in reflow, and solderability defects.

Pro-Tip: Do not rely on the main HVAC sensor. Install independent T/RH loggers directly above the SMT lines where the product is exposed.

Workstation Architecture

Every surface touching the product must provide a controlled path to ground.

Essential Configuration

1. Work Surface: Static Dissipative Mat (Rtg: 1.0 x 10^6 – 1.0 x 10^9 Ω). Do not use conductive mats (risk of hard short).
2. Common Point Ground (CPG): A single terminal grounding the mat, the wrist strap, and the equipment chassis.
3. No Insulators: The "12-Inch Rule" (30 cm).
   • IF item is an insulator (plastic cup, scotch tape, personal phone) → THEN Keep >30 cm away from open PCBA.
   • IF item is essential process plastic (traveler folder) → THEN Use ESD-safe version or neutralize with air ionization.

Final Checklist