By Larry Levit
Electrostatic charge is a contaminant of energy rarely understood by those responsible for and working in cleanrooms. Typically referred to as ESD in most lab and manufacturing environments, it can be controlled through grounding of all conducting objects in the cleanroom, including personnel, by eliminating insulators where possible, and using ionizers to avoid damage to products as workers sit and work at assembly or test benches.
However, people and products in cleanrooms typically move around while working, and airflow and low relative humidity in the clean environment generates a myriad of electrostatic phenomena. This can result in electrostatic discharge (ESD) that damages products. ESD can also manifest in other, more subtle ways to modify the environment and cause spurious particle events, interfere with processing equipment, and create other problems that can hinder productivity or plague equipment maintenance efforts.
Since it is impossible to see electrostatic charge and its associated manifestations, one must be knowledgeable in the science that creates it and be able to analyze the environment to discover weakness that allows the electrostatic event to develop and unfold. But most cleanroom users and managers are unfamiliar with the basics of electrostatics. IEST’s new Recommended Practice, IEST-RP-CC052: Understanding, Identifying and Controlling Electrostatic Charge in Cleanrooms and Other Controlled Environments, will help them solve cleanroom-related electrostatic charge problems by understanding the underlying science. Users of this IEST Recommended Practice can then visualize the “invisible” nature of this form of contamination that affects cleanrooms in many ways.
IEST-RP-CC052 More Extensive, Relevant—Replaces IEST-RP-CC022.2
The old IEST recommended practice, IEST-RP-CC022: Electrostatic Charge in Cleanrooms and Other Controlled Environments, was written more than 20 years ago to address this topic. The overview provided some instructions for describing electrostatic risks and testing developed by the ESD Association. In a sense, it was a light version of the ESDA formulas for addressing static charge. Unfortunately, both the ESDA documents and RP-CC022 have little applicability to the needs of cleanroom operators and managers. Most people responsible for cleanroom operations do not have enough technical background in physics to understand how these charges are generated in the dynamic working environment of the cleanroom. As expected, cleanroom professionals found little use for IEST-RP-CC022.
IEST decided to create a new working group to develop a new, more extensive recommended practice relevant to more users. The new working group developed IEST-RP-CC052, which replaces IEST-RP-CC022. This approach provides managers and operators of all cleanrooms with the background necessary to understand the science of electrostatic charge phenomena and thus understand the basis for charge control protocols.
We hope cleanroom professionals will apply the fundamentals they learn in IEST-RP-CC052 to recognize deficiencies in their own environment and choose appropriate remedies to avoid potential product losses, equipment failures, or spurious particle events.
Larry Levit is chair of IEST WG-CC052.