Humidity is not an effective way to control ESD in an electronics production environment. While the ability to generate static electricity increases when the air gets dryer (the % RH decreases), increased humidity does not eliminate the ESD event entirely or provide protection to ESD susceptible devices . As an example, walking across a carpet can yield a charge of 35kV at 10% RH (very dry air), but will drop significantly to 7.5kV at 55% RH. However, even the reduced charge at 55% RH would not be safe to most modern electronic devices that are susceptible to 100 volts or less.
The ESD Association also covers the importance of RH in a few documents. These include:
- ESD Handbook ESD TR20.20-2008 section 2.3 Nature of Static Electricity: However, it is impractical to use humidity control alone to provide static control since static charges are developed even at relative humidity levels of 90% and greater.
- ESD Handbook ESD TR20.20-2008 section 5.3.16 Humidity: Relative humidity above 30% in ESD protective areas is desirable as long as other adverse conditions are not created as a result of humidity levels. Generally speaking an upper limit of 70% is desirable to prevent corrosive effects on the metal portions of electronic devices and assemblies.