Understanding Decay Time & Ion Balance in Static Elimination

1. Decay Time (Static Dissipation Time)

Definition:
The time required to reduce the charge on a ±1000V charged object to ±100V when exposed to an ionizer.

Key Points:

• A critical metric for evaluating ionizer performance in ESD control.

• Faster decay times indicate more efficient static elimination.

• Industry benchmarks:

• <1 second (High-performance ionizers for cleanrooms)

• 1–3 seconds (General electronics assembly)

2. Ion Balance (Offset Voltage)

Definition:
The residual voltage on a neutralized object after continuous exposure to balanced positive/negative ions. Closer to 0V indicates superior ion balance.

Key Points:

• Ideal range: ±5V or better for precision electronics.

• Poor ion balance can cause:

• Recharging of sensitive components (ESD risks).

• Particle attraction in cleanrooms.

• Measured per IEC 61340-5-1 or ANSI/ESD STM3.1.

Performance Optimization

• For decay time: Use high-frequency ionizers or pulsed DC systems.

• For ion balance: Regular calibration with a charged plate monitor (CPM) is essential.

Industry Standards:

• ANSI/ESD S20.20: Recommends decay time testing for compliance.

• SEMI E78: Specifies <1 second decay for semiconductor tools.

• Why This Matters

• Faster decay + tighter balance = Reduced ESD defects in PCB/SMT manufacturing.

• Critical for medical devices, aerospace electronics, and flat panel display production.