The Institute of Environmental Sciences and Technology recently published a revision of IEST-RP-CC0022.2, “Electrostatic Charge in Cleanrooms and Other Controlled Environments.” It is an excellent resource to enable you to improve control in your cleanroom. Additional information and ESD standards are available from the ESD Association.

Controlling ESD in the cleanroom should be a multi-faceted approach. Each individual parameter supports the total ESD program. The most common components in a complete ESD control program are: personnel, personnel apparel, shoes and grounding straps, ionizers, temperature and humidity control, flooring, work surfaces, and packaging. It is impossible for any one of the above components to individually control static electricity.

People working in the cleanroom are the major generators of static electricity. Therefore the training of personnel to control movement in the cleanroom in-and-around ESD sensitive devices is imperative.

Static dissipative cleanroom garments and shoes may impart some ESD control in the cleanroom. Grounded static dissipative garments, when worn correctly, are designed to minimize the charges that may or may not be present on an operator’s undergarments. However, it is recommended that other measures of ESD control are also used.

Wrist straps are typically used to control static electricity on personnel working in and around ESD sensitive materials. When properly worn and connected to ground, a wrist strap keeps the person wearing near ground potential. Daily testing and/or continuous monitoring of the wrist straps is recommended.

Insulative grounders, casters and wheels prevent static charge and enable control of static electricity on carts. These are used in combination with grounding foot straps and ESD protective flooring to reduce triboelectric charging when movement of carts and personnel is required during the production process.

Air Ionizers are used to neutralize static charge in the cleanroom by charging the molecules of the gases on the air.

Temperature and relative humidity are usually controlled in the cleanroom for operator comfort. The cleanroom temperature should remain at approximately 60°F with a relative humidity of 30-50%. If the relative humidity is less than 30%, the incidence of static discharge is increased. Therefore, it is advised to control relative humidity in the cleanroom as a part of the complete ESD program.

Packaging materials (shielding bags or boxes) provide direct protection of the ESD sensitive device if it is constructed of antistatic materials. The inside of the packaging is usually a layer of conductive material with the outside surface constructed of static dissipative material.

Regular auditing of your cleanroom is the best method for assessing the status and effectiveness of your ESD program.