The right humidity for ESD protection

ESD protection can also be achieved by controlling the humidity. A relative humidity of around 50 percent ensures that the conductivity of the air and on material surfaces is increased, which means that any charges that arise are reduced and charges on materials are dissipated more effectively.

How humidity affects ESD protection

One measure for ESD protection, i.e. protection against uncontrolled electrostatic discharges, is to establish a constant level of humidity suitable for ESD protection. Such humidity is achieved at a relative humidity of around 50 %.

But why does humidity have an impact on ESD protection at all? The reason is that a relative humidity of around 50% increases the conductivity of the air, which means that electrical charges can be dissipated via the air. Higher humidity means a higher water content in the air and water is a good conductor of electricity. When materials are surrounded by air with a relative humidity of around 50%, these materials are unable to maintain their static charge. Instead, they release excess charges to the water molecules in the air, and do so continuously.

However, it is not only the conductivity of the air itself that is increased at this level of humidity. The conductivity of material surfaces in rooms with these high relative humidities is also increased. This is because a thin film of moisture forms on the surfaces of these materials at a relative humidity of around 50 %. This film of moisture makes the respective material surface conductive, which reduces the accumulation of electrostatic charges.

A positive side effect of surfaces that are not electrostatically charged is that fewer particles are deposited on these surfaces. This is because surfaces that are electrostatically charged develop a higher dust attraction force.

Another positive side effect of higher humidity is that it improves the working environment for employees. This is because too little humidity can dry out the nasal septum, for example, and even lead to nosebleeds. The risk of catching a cold or flu virus also increases with dry mucous membranes.

However, humidity also influences the voltage levels generated by activities in which friction or the separation of materials leads to electrostatic charges. A high level of humidity prevents a large proportion of the resulting charge by lowering the voltage generated. The following table shows the different voltages depending on the activity and humidity:

Is there an ESD humidity standard?

There are various ESD protection standards that also contain versions on humidity. One such ESD humidity standard is contained in the IPC J-STD-001F (Requirements for Soldered Electrical and Electronic Assemblies) guideline from the IPC standardization organization:

“If the humidity drops to 30% or less, the manufacturer must ensure that the electrostatic discharge is adequately controlled.”

The DIN EN 61340-5-1 standard also takes humidity into account in its specifications. This standard requires that some of the cyclical measurements also take place in winter, as the humidity is lower in winter due to the heating systems in operation, especially in environments in which the humidity is not constantly regulated by a room climate control system.

ESD measuring devices for humidity measurement

There are also ESD measuring devices that can be used to measure not only surface, volume and leakage resistance, but also humidity, such as the ESD measuring device “Resistivity-Meter Safe STAT RM 1000“.

If you would like more information on humidity and ESD protection or suitable ESD measuring devices, our experts at abovo can help you. You can either contact us by telephone on +41 32 552 44 44. Or send us an email to info@abovo.ch and we will get back to you as soon as possible.