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ESD Environment Considerations for Cleanrooms

noviembre 30, 2022
ESD damaged printed circuit board, chips on pcb
Figure 1. ESD damage to electronics

People encounter static electricity in everyday life – crackling when you pull your sweater off, walking on carpet then getting a shock when you touch the doorknob, or your hair standing up when the air is low in humidity.

ElectroStatic Discharge (ESD) is when an electric charge is released which can severely damage electronics. As electronic feature sizes have shrunk from mils to microns to 0.1 microns, electronic device features have become more and more sensitive to ESD damage. These fine line widths have pushed electronics manufacturing into cleanrooms in order to maintain an acceptable manufacturing yield.

A static charge occurs when two surfaces come into contact with each other. It can also come from environmental conditions, such as exposure to light, heat and cooling. Mobile processes in semiconductor manufacturing such as spinning, coating and plasma processes also cause static charge. Humans can cause static charge by moving. HEPA filtration is a major contributor to static charge due to the friction of large amounts of air passing thru dense HEPA filters. Static charges cause contamination. Once a surface is charged, it will attract and hold small particles in the air having an opposite electrical charge.

As cleanroom classifications levels are reaching ISO5 and ISO6 in non-electronics manufacturing cleanrooms such as pharma and medical device cleanrooms, companies are realizing that static charge (ionic attraction) of submicron contamination makes removal of these particles much more difficult. Therefore, reducing static electricity in these non-electronics industry cleanrooms has also become a priority. 

Most common methods to reduce ESD in cleanrooms:

Cleanroom Humidity Control

Cleanroom humidity control is one of the most important factors in controlling static in cleanrooms. Low humidity environments (below 40%) can have serious static build up problems. Keeping humidity in the 40-60 percent range will allow static charge to leak to the ground thru the air.

Cleanroom Personnel Equipment

You can reduce ESD by using some specific cleanroom personnel equipment like wrist grounding tabs and cleanroom booties grounding tabs. However, the booties only work if they are used on cleanroom static dissipative flooring.

Cleanroom Furniture Grounding Tabs/Drag Chains

Cleanroom furniture grounding tabs/drag chains can also help remove ESD however this method will only work if placed on cleanroom static dissipative flooring. These tabs can be placed on furniture such as:

  • Cleanroom chairs
  • Cleanroom tables
  • Cleanroom floor mats

Cleanroom Static Dissipative Flooring

  • Static dissipative heat welded vinyl cleanroom flooring (grounded)
  • Static dissipative vinyl cleanroom tiles (grounded)
  • Static dissipative epoxy flooring
gray cleanroom vinyl flooring, copper grounding tab from flooring to electrical outlet
Figure 3. Static dissipative cleanroom vinyl flooring with copper going to electrical ground

Cleanroom Static Dissipative Walls

  • The modular cleanroom walls are painted aluminum on aluminum honeycomb. The paint has conductor added to it to make it static dissipative.
  • Cleanroom vinyl soft walls curtains can be made of static dissipative vinyl to reduce electrostatic buildup

Cleanroom Deionizing Systems

Another approach to reducing ESD in cleanrooms is to measure static electricity in air and deploy deionizing systems which put out oppositely charged ions in the problem areas of cleanroom.

interior of cleanroom, clean room ceiling, deionizer modules mounted to cleanroom ceiling
Figure 4. Cleanroom de-ionizing system
Property American Cleanroom Systems 2022

The author Anthony Chien has worked at American Cleanroom Systems for the past 10 years. He has more than 40 years of cleanroom experience. Anthony has a BS and MS in Electrical Engineering specializing in semiconductor manufacturing from the University of Illinois. American Cleanroom Systems is a design-build modular cleanroom manufacturer based in Rancho Santa Margarita CA. American Cleanroom Systems is your expert in ISO-5 thru ISO-8 (class 100 to class 100k) modular cleanrooms for pharmaceutical cleanrooms, medical device cleanrooms, and industrial cleanrooms.

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