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Question Could you please inform me how the D.I. water can lead to ESD damage? How to avoid it? -Anonymous, Tianjin, China
Answer DI water is by nature, without contaminants and therefor insulative. Spraying an insulative material onto a wafer or electronic device can lead to charging via tribocharging. Also the removal or drying off of DI water can also lead to charging problems.

I know that DI water is made specifically to minimize contamination to the wafers and that making this water dissipative will require putting contaminants into it, thereby nullifying its purpose. I do not know of any process in which to make DI water both dissipative and contaminate free.

The degree to which water can conduct an electric current is dependent on the purity of the water. Pure water has very low conductivity, that is, it does not conduct electrical current very well. As salt or other solids/contaminants are dissolved into the water, the conductivity increases.

One way to treat this problem (drying off parts with DI water on them) is discussed in Q198: Q198: We are a small contract manufacturing Company. We build hybrid (PTH & SMT) circuit boards. After a cleaning process, we use compressed air to blow off excess DI water. I am a mechanical engineer. It seems to me that there could be ES charges developed by this air. Is this true. If so, what can be done to manage this? Wrist straps are worn during this operation. A good answer might be to put an ionizer in the air flow, but, I doubt if that would be very effective with the volume of compressed air used.. - Chuck Dailey, ASAP, Inc., Tucson, AZ

A198: You have a valid concern, but realize that just air doesn’t tribocharge. It is the impurities in the air that has enough molecular weight to cause tribocharging. There are a few solutions. Either use real clean air (maybe an LN2 source for compressed dry nitrogen) or employ a product like out Ion Viper Air Nozzle systems that uses a compressed air source with either a hand gun ionizer or flexible hose.

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