Why is low RH a cause of ESD?

Posted: Tue Aug 19, 2026 10:09 am Post subject: Why is low RH a cause of ESD?

I heard low RH can cause ESD. What is the explanation for this?

PZC

Posted: Tue Aug 26, 2026 2:04 pm Post subject:

Hi PZC,

A high RH reduces ESD risks because the moisture content of the air reduces the surface resistivity of dielectric materials and inhibits the tendency of materials to undergo triboelectric charging. The lower resistivity of ‘moist’ surfaces allow a gradual discharge of static charges to the common ground (assuming that the workplace has an ESD-protective grounding system), preventing any ESD build-up. For comparison, an activity at 20% RH can generate a voltage that’s 2 to 20 times the voltage generated by the same activity at 80% RH.

‘Moist’ air itself can also serve as discharge path of static build-up to ground. On the other hand, dry air flow over an insulative surface can increase triboelectric charging.

Note that a high RH can trigger corrosion and delamination issues, so increasing the RH without limit is also undesirable. An RH of 40% to 60% seems to be the best RH for semicon production.

EE