ESD Systems - Questions And Answers

What is the specified humidity level for a class 100 clean room to make Hard Disk Assembly? Pomalux is the only plastic material I know as ESD safe, but it is very costly. Would you recommend me some other alternative? Is there any total room ionizers available? If so who is making it? How to monitor whether it gives the right result? Why static sensor shows a wide variability in its reading (I mean no repeatability or swifts over a wide range)? - Anonymous, Madras, India

A1: A good range would be between 40% and 55%. You want to minimize corrosion and maximize ESD protection. There is a paper on Humidity for your convenience. A2: We have vinyl, rubber, cardboard, and polyethylene materials that are ESD safe, depending on your application. ESD safe can also imply the properties of anti-static, dissipative, and shielding, again depending on your application. Please e-mail your application or requirements so I can be of further assistance. A3 and A4: A charge plate analyzer is the preferred instrument to monitor the proper operation of an corona discharge type, air carrier ionizer. Also, static sensors measure a small area at a time and static charges are not necessarily uniform on a conductive or insulative surface. There is an imbalance in the free electrons when a material is subjected to an electric field or triboelectric generation. This imbalance is not always uniform. The spacing from the static meter's sensor to the surface being measured also adds variability. The geometry of the surface being measured can also lead to variations in field strength, e.g., a curved surface (cylindrical pyramid) may have a higher field than a planer surface because charges may accumulate at the edges.

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