5.1 ESD Control Program (ANSI/ESD S20.20)

Electrostatic Discharge (ESD) is the invisible assassin of modern electronics. A human can only feelUnlike a shockshort atcircuit 3,000V, butor a MOSFETbroken gatetrace, canESD bedamage destroyedoften bymanifests lessas thana 100V.latent Thedefect danger is not— the "deadwalking onwounded." arrival" component; it is the Latent Failure—aA component thatmay ispass woundedfinal test today but passes functional test, only to fail in the field weeksafter later.200 Thisthermal chaptercycles definesdue to a compromised gate oxide. As a Quality Engineer, your objective is not merely to enforce "cleanroom etiquette" but to maintain the non-negotiableelectrostatic architecturepotential fordifference between any two items in the Electrostaticprocess Protectedbelow Areathe sensitivity threshold of the most fragile component (EPA)typically in≤ compliance100V withHBM). If you cannot prove the process was compliant at the moment of assembly, you cannot guarantee the reliability of the product.

Program Management & Scope

The ESD Control Program must be technically robust and auditable. Adherence to ANSI/ESD S20.20. is the baseline, not the gold standard.

Define the Administrative Requirement:

The Quality Management System (QMS) must designate a dedicated ESD Coordinator. This individual is responsible for the verification plan, not just the purchasing of supplies.

• Compliance Verification Plan (TR53): You must define how and how often you measure the controls. A wrist strap on a wrist is useless if the coil cord is open.
• Training Registry: No operator, manager, or visitor enters the ESD Protected Area (EPA) without documented training or an escorted protocol.

TheTechnical Elements of the EPA Boundary (The Kill Zone)

The EPAESD Protected Area (EPA) is defined by physics, not yellow tape. It is a hardvolume electrical fortress. It is not a suggestion; it is a discipline.

• Requirement: Clearly markwhere all EPAsurfaces, entrances with yellow/black caution tapeoperators, and official ESD signage.
• Logic:
  • If youequipment are inside the yellow tape -> Then you must be grounded.
  • If you are a visitor -> Then you must wear heel straps and be escorted by a trained operator.
  • If material enters the EPA -> Then it must be removed from cardboard/plastic transport packaging outside the boundary.

Pro-Tip: "Pink" plastic (Dissipative) is not a magic shield. It only prevents charge generation; it does not block external fields. Never use pink bags for shipping outside the EPA.

Personal Grounding Strategy

Gravity holds you to the floor; grounding holds you to zero volts. The method of grounding depends on the operator's posture.equipotential.

1. SeatedGrounding Operations (Bench Work)Systems

• Primary Ground: Wrist Strap connected to a

  The Common Point Ground (CPG) is the reference zero for the entire EPA.

  • AC Equipment Ground: Verify the impedance between the equipment chassis and the 3rd wire electrical ground is < 1.0 Ω.
  • Constraint:Worksurfaces: HeelMatting strapsmust alonebe aredissipative, not conductive, to limit discharge current.
    • Resistance to Ground (RTG): insufficient1 x 10^6 Ω ≤ R ≤ 1 x 10^9 Ω.
    • Pro-Tip: forDo seatednot operatorsdaisy-chain becausemats. liftingEach feetmat breaksneeds theits connectionown direct path to the floor.Common Point Ground to prevent additive resistance.
    • Test: Daily verify wrist strap resistance (Range: 800 kΩ – 35 MΩ).

  2. Standing/MobilePersonnel OperationsGrounding (Logistics/SMT)Strategy

  Human operators are the primary generators of static charge. You must couple them to ground. Use the following decision logic to determine the required method:

  • Primary Ground:IF Operator is Seated:
    • THEN Wrist Strap is Mandatory. Flooring/Footwear is insufficient due to lifting feet or insulating chair wheels.
    • Control: Continuous Monitor (preferred) or Daily Log required.
    • Limit: < 3.5 x 10^7 Ω.
  • IF Operator is Standing/Walking:
    • THEN ESD Footwear + ESD Flooring System is required.
    • Control: Test upon entry (Left Foot / Right Foot independent test).
    • Limit: Product of System (Person + Shoes + Floor) < 1.0 x 10^9 Ω AND Body Voltage Generation < 100V.

  3. Packaging & Material Handling

  Protecting the PCBA inside the EPA differs from protecting it during transport.

  • Inside EPA: Materials should be Dissipative (HeelPink StrapsPoly/Black orCarbon). ESDThis Shoes)slows +the charge transfer.ESD Flooring.
  • Constraint:Outside EPA (Transport): Both feetMaterials must be grounded. One strap is zero straps.
  • Test:Shielded Verify(Metal-in/Metal-out conductivitybags).
    • Rule: uponNever entrytransport usingESD-sensitive adevices combo-tester(ESDS) gate.outside the EPA in merely "Pink Poly" bags. They offer no shielding against external fields.

  Managing

  4. Insulators (The 12-Inch Rule)

  Ionization

  Insulators (standard plastic, styrofoam, scotchplastics, tape, acrylic)housings) cannot be grounded. TheyIf hold charge until it arcs to your PCBA. You have three tactical options to neutralize them:

  1. Remove: Keep all non-essential plasticsinsulators (coffeeare cups,present wrappers,within personal binders) > 30 cm (12of inches)ESDS:
     • Action: awayDeploy from open electronics.
     • Replace: Substitute standard tools with ESD-safe versions (e.g., ESD mats, conductive bins).
     • Ionize: If the insulator is essential (e.g., connector housing, label liner), use an Air Ionizer to flood the area with positive/negative ionsIonizers to neutralize the charge.
• Verification: Measure Offset Voltage (Balance) and Decay Time.
  • IfLimit: Ionizer is used -> Then verify offsetOffset voltage < ±35V monthly.

  Packaging Logic (The Shield)

  Material movement is the highest risk event for triboelectric charging (friction). Use the correct armor for the environment.

  • Inside EPA (Work in Progress):
    • Use Static Dissipative (Pink) bags or totes.
    • Function: Prevents charge buildup during handling.
  • Outside EPA (Storage/Shipping):
    • Use Static Shielding (Metallized/Silver) bags or Conductive Black Totes.
    • Function: Creates a Faraday Cage to block external static fields.
    • Rule: A pink bag outside the EPA is a failure.35V.

  Compliance Verification (Audit or Fail)Auditing)

  A grounding system that isn't measured isAs a hallucination.QE, you do not trust; you verify. Verification must follow ESD TR53 test methods.

  The Auditor's Cadence:

  • Daily: Operator tests wrist/heel straps. Log resultsself-check (Pass/Fail)Wrist straps/Footwear).
  • Weekly: Visual inspectioncheck of ground cords (check for fraying/disconnection).wires.
  • Monthly: MeasureIndependent Workaudit Surfaceof Resistanceworksurfaces, (Rtg)floor resistance, and Floorionizer Resistance (Rtg).balance.
    • Limit: < 1 x 10^9 Ω.
  • Quarterly: IonizerFull balancesystem audit (RTG of shelving, carts, chairs, and decay time verification.garments).

  Pro-Tip: Humidity affects conductivity. If Relative Humidity (RH) drops below 30%, dissipative materials may become insulative. Increase audit frequency during dry winter months or humidify the facility.

  Final Checklist

  Control PointElement	RequirementParameter	Critical Limit / Threshold	Non-NegotiableFrequency Rule(Min)
  EPAPersonnel Entry(Wrist)	Visual BoundaryResistance	< 3.5 x 10^7 Ω	NoDaily ungrounded/ personnel past the yellow tape.Continuous
  SeatedPersonnel Ground(Shoe/Floor)	WristSystem StrapResistance	< 1.0 x 10^9 Ω	HeelDaily straps do not ground seated operators.(Entry)
  InsulatorsWorksurface	30Resistance cmto (12 inch) SeparationGround	< 1.0 x 10^9 Ω	Keep standard plastics away from open PCBA.Monthly
  ShieldingIonizers	SilverOffset BagVoltage (Faraday Cage)Balance)	< ±35V	PCBs leaving the EPA must be in Shielding Bags, not Pink Bags.Monthly
  HumidityMobile Carts	>Resistance 30%to RHGround	< 1.0 x 10^9 Ω	Low humidity increases charge generation risk. Monitor continuously.Quarterly
  TestingFields	DailyStatic LogField	< 2000V / inch (at 30cm)	IfMonthly
  Packaging	Shielding	Visual thecheck tester(No doesn'tholes/tears)	Per print a pass, the operator cannot touch hardware.Use