3.2 The ESD Protected Area (EPA)

ElectrostaticThe Discharge (ESD)EPA is thenot primarymerely latenta failureroom mechanismwith ina modernsign; electronics. Damage occurs at voltages below human perception (< 3000V). The ESD Protected Area (EPA)it is a definedprecisely zoneengineered whereequipotential volume. Inside this zone, all surfaces,conductive people,elements—floors, operators, equipment, and devices workbenches—are keptelectrically atbonded to a common ground point. This ensures that the same electricalvoltage potential difference between any two objects is effectively zero, preventing the rapid discharge (equipotentialspark) bonding).that destroys gate oxides. If an object cannot be grounded (insulator), it must be excluded or neutralized.

EPA BoundariesPerimeter & SignagePhysical Boundaries

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

Demarcation Logic

• PhysicalVisual Demarcation: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 EPA"12-Inch mustRule" be(30 clearlycm).
   • IF visibleitem viais yellow/blackan aisleinsulator tape(plastic orcup, physicalscotch barriers.tape, personal phone) → THEN Keep >30 cm away from open PCBA.
   • Signage:IF "Attention:item ESDis Protectedessential Area"process signsplastic must(traveler befolder) posted→ at all entry points.
   • The "3-Foot Rule":THEN StaticUse generatingESD-safe materialsversion (regularor plastic,neutralize Styrofoamwith cups,air packing tape) are prohibited within 1 meter (3 feet) of any exposed PCBA.ionization.

   Entry Protocols

   • Mandatory Testing: No person (employee or visitor) may enter the EPA without passing a resistance test for footwear and wrist straps.
   • Data Logging: Test results must be logged electronically. Failure to pass restricts door access (Smart Gate system).

Final Checklist

ElementControl Parameter	RequirementSpecification / Limit	Verification Frequency	Owner
BoundariesEnvironmental	Visual40% Tape– /60% SignageRH	MonthlyContinuous AuditAlert	Facilities
ProhibitedBoundary ItemsIntegrity	Tape intact, Signs visible	Monthly	ESD Lead
Workstation Ground	Mat Rtg < 1.0 x 10^9 Ω	Quarterly	ESD Lead
Insulator Proximity	No Insulatorsstatic generators < 30cm30 from ESDScm	Daily Visual	Operations
AccessPersonnel ControlEntry	Pass/Fail100% Verified (Gate TestLog)	Daily (Every Entry)	Security/Ops