# Why is the balance voltage of the ion fan set at -35V \< V \< 35V?
**URL:** https://forum.esda.org/t/why-is-the-balance-voltage-of-the-ion-fan-set-at-35v-v-35v/777
**Category:** Uncategorized
**Created:** [July 18, 2024, 3:17am UTC](https://forum.esda.org/t/why-is-the-balance-voltage-of-the-ion-fan-set-at-35v-v-35v/777 "2024-07-18T03:17:12Z")
**Posts on this page:** 6
**Page:** 1
### Author:  [@Yang](https://forum.esda.org/u/Yang)
#### Post date: [July 18, 2024, 3:17am UTC](https://forum.esda.org/t/why-is-the-balance-voltage-of-the-ion-fan-set-at-35v-v-35v/777/1 "2024-07-18T03:17:12Z")
Dear all experts,
Why is the balance voltage of the ion fan defined at -35V \< V \< 35V?
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### Author:  [@AndyN](https://forum.esda.org/u/AndyN)
#### Post date: [July 18, 2024, 2:10pm UTC](https://forum.esda.org/t/why-is-the-balance-voltage-of-the-ion-fan-set-at-35v-v-35v/777/2 "2024-07-18T14:10:33Z")
Yang,
ANSI/ESD S20.20 sets a limit to the ionizer offset voltage of less than +/- 35V based on the requirement of limiting isolated conductors to less than +/- 35V. The basis for this, I believe, came from experiments that showed that isolated conductors at +/- 35V have similar characteristics as HBM at 100V, which is the limit in S20.20.
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### Author:  [@Yang](https://forum.esda.org/u/Yang)
#### Post date: [July 19, 2024, 1:19am UTC](https://forum.esda.org/t/why-is-the-balance-voltage-of-the-ion-fan-set-at-35v-v-35v/777/3 "2024-07-19T01:19:40Z")
Dear AndyN：
Thank you very much for your reply. Can I understand that if the ion fan generates more than 35V voltage, it will cause device damage in the process of continuous blowing of the device?
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### Author:  [@AndyN](https://forum.esda.org/u/AndyN)
#### Post date: [July 19, 2024, 11:18am UTC](https://forum.esda.org/t/why-is-the-balance-voltage-of-the-ion-fan-set-at-35v-v-35v/777/4 "2024-07-19T11:18:22Z")
Yang,
The ESD risk is not in the voltage generated by the ionizer. The danger comes from the devices being exposed to the ion stream and then being grounded. That is where the ESD event could occur.
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### Author:  [@AndyN](https://forum.esda.org/u/AndyN)
#### Post date: [July 19, 2024, 4:15pm UTC](https://forum.esda.org/t/why-is-the-balance-voltage-of-the-ion-fan-set-at-35v-v-35v/777/5 "2024-07-19T16:15:10Z")
Yang,
To give you an example, suppose you were working on a worksurface with an ionizer and your ESDS item is grounded on the worksurface. If you were to touch the ESDS item with an isolated conductor (like a screwdriver or tweezers), the isolated conductor would be charged to the offset voltage of the ionizer. If this is above the limit of +/- 35V, you could have a discharge that may damage your device if the HBM sensitivity is 100V or less. Hope this helps
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### Author:  [@Yang](https://forum.esda.org/u/Yang)
#### Post date: [July 22, 2024, 12:46am UTC](https://forum.esda.org/t/why-is-the-balance-voltage-of-the-ion-fan-set-at-35v-v-35v/777/6 "2024-07-22T00:46:48Z")
Dear AndyN,
Ok, got it. Thank you very much for your reply!