Charge Decay Testing
Measuring how quickly static charge dissipates from ESD surfaces and materials.
Charge decay testing evaluates how fast an applied electrostatic charge is reduced to a safe level. Unlike surface resistance, which describes a static property, charge decay captures dynamic behaviour that more closely reflects real-world ESD events.
What charge decay testing measures
In a typical test, a known voltage is applied to a surface or material and the time taken for the charge to decay to a specified fraction of the initial voltage is measured.
Faster decay generally indicates better control of static charge, provided the discharge is not excessively rapid or uncontrolled.
Why decay time matters
Two materials with similar surface resistance values can behave very differently during a discharge event. Charge decay testing helps reveal:
- How quickly charge is removed from the surface
- Whether charge persists long enough to cause damage
- Differences in behaviour that resistance testing alone may miss
Factors affecting charge decay results
- Humidity: higher RH often accelerates decay in hygroscopic materials.
- Surface condition: contamination or wear alters decay behaviour.
- Material structure: bulk vs surface conduction mechanisms.
- Test configuration: electrode geometry and grounding path.
Interpreting results responsibly
Charge decay results should be interpreted alongside other tests, including surface resistance and durability assessments. A single fast decay measurement does not guarantee long-term ESD safety.
- Charge decay testing captures dynamic ESD behaviour.
- Decay time complements surface resistance measurements.
- Environmental and surface conditions influence results.
- Results should be evaluated as part of a broader validation strategy.