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Frequently Asked Questions |
1)How does ionization fit into an S20.20 compliant control program? | - 1)How does ionization fit into an S20.20 compliant control program?
- Ionization provides protection against electrostatic events in areas where typical grounding methodsare not applicable or appropriate. Ionization refers to air that has been exposed to electrical corona, alpha
radiation, or soft x-rays and through exposure has had an electron either added or removed from a small portion of the air molecules. While a low level of ionized air occurs naturally, it is necessary to increase ionization levels to
promote static elimination. Ionized air acts as a charge carrier. By neutralizing electrostatic charge, ionization helps prevent electrostatic events where the risk of exposing an electrostatic sensitive device to static charges
cannot be avoided.
Process equipment often contains quantities of essential insulating materials in their structure that are prone to developing static charges. Packaging materials, such as outer wraps, tapes, and labeling materials, can present
another electrostatic problem. Ionization generally provides rapid neutralization of the static charges produced by these materials.
While ionization neutralizes electrostatic charge quickly, it is not instantaneous. Static neutralization from an ionizer occurs as a logarithmic decay of the charge. Very highspeed
processes, such as automated processes, can outpace the ionizer’s ability to neutralize the electrostatic charge.In high-speed processes it is important to verify that ionization, if used, is suitable to the pace of the process.
Also, ionized air has little persistence; the ions “recombine” quickly, exchanging charge and reverting to normal air molecules. Therefore ionized air must be delivered to its target quickly to be effective. Many air ionizers rely on fans or blowers to deliver the ionized air
to neutralize static charge in the critical area. If you can’t feel the airflow from an ionized air blower in the critical area, it probably isn’t neutralizing charges in that area.
ANSI/ESD S20.20-1999 contains recommendations to
apply “ionization or other charge mitigating techniques” in areas where the risk from electrostatic charge cannot be removed from the proximity of the ESD sensitive parts.
ANSI/ESD S20.20-1999 also provides a recommended
range for maximum ionizer offset voltag(sometimes
referred to as ion balance) for room system ionizers and other types of ionizers. ANSI/ESD S20.20-1999 references ANSI/ESD STM3.1-2000 Ionization as the standard test method to measure the ionizer offset voltage. The maximum discharge time permitted is up to the discretion
of the user. The discharge time specification should include distance, operating parameters (fan speed, air velocity, applied air pressure, etc. as required by the application) and should be commensurate with protecting the ESD sensitive device from electrostatic events.
Discharge time specified by the user would typically reference ANSI/ESD STM3.1-2000 as the standard test method to measure the ionizer discharge time. As part of a compliance verification program, periodic audits or
certifications are required by ANSI/ESD S20.20-1999.This ensures that, where needed, the protection by ionized air is established and maintained.
Ensuring that the protection by ionized air is not interrupted is an important part of any ESD control program. ESD SP3.3-2000 Periodic Verification of Air Ionizers is a good starting point. Once the level of protection required by air ionization is established, it is advisable to benchmark the performance of newly installed
ionizers for future reference. Regularly scheduled periodic testing of the air ionizer will indicate if performance is within acceptable limits. Choice of intervals for testing depends on many variables. In general, 3 to 6 months is often recommended as a starting point. The equipment manufacturer should be able to offer guidance on typical testing intervals. Adjustment of the testing intervals may
be made as confidence in the equipment dictates.
It may be necessary to institute regular maintenance between the testing intervals. Maintenance is a fact of life. For the most part, air ionizer maintenance is simple.
Perhaps the most difficult part is establishing and maintaining the routine. Routine maintenance should include:
An examination for equipment integrity. Is the ionizer positioned as it was installed? If airflow is used, does it seem normal? Are all indicators normal? Are there any alarms? (Tend to those at once!) Are all calibration, test,
and inspection labels up-to-date?
Cleaning as necessary. Air ionizers that use AC or DC corona typically need the ion emitters cleaned on a regular basis. Usually, this task takes little time but ensures expected ion production levels are maintained.
Establishing and maintaining effective protection from ESD with the use of ionized air is just one part of the many faceted electrostatic discharge control program
outlined in ANSI/ESD S20.20-1999.
Provided by the ESDAssociation Q: A:
18 CONFORMITY® JULY 2005 www.conformity.com
ESDOpen Forum Reprinted from Conformity®
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