ionization test kit

The best way to keep electrostatic sensitive devices (ESDs) from damage is to ground all conductive objects and remove insulators from your ESD Protected Area (EPA). This is not always possible because some insulators are “process-essential” and are necessary to build or assemble the finished product. The only way to control charges on these necessary non-conductive items is the use of ionization systems.

However, if an ionizer is out of balance, instead of neutralizing charges, it will produce primarily positive or negative ions. This results in placing an electrostatic charge on items that are not grounded, potentially discharging and causing ESD damage to nearby sensitive items.

It is therefore essential to regularly clean your ionizers and verify they function correctly. Below we have put together a list of tasks you need to perform with your ionizers on a regular basis.

Maintenance

All ionization devices will require periodic maintenance for proper operation. Maintenance intervals for ionizers vary widely depending on the type of ionization equipment and use environment. Critical clean room uses will generally require more frequent attention. It is important to set-up a routine schedule for ionizer service. Routine service is typically required to meet quality audit requirements.” (ESD Handbook TR20.20 section 5.3.6.7 Maintenance / Cleaning)

EIA-625, recommends checking ionizers every 6 months, but this may not be suitable for many programs particularly since an out-of-balance may exist for months before it is checked again. ANSI/ESD S20.20 section 6.1.3.1 Compliance Verification Plan Requirement states: “Test equipment shall be selected to make measurements of appropriate properties of the technical requirements that are incorporated into the ESD program plan.

Under normal conditions, an ionizer will attract dirt and dust (especially on the emitter points). To maintain optimum neutralization efficiency and operation, cleaning should be performed on a regular basis.

1. Case

Wipe the case with a soft cloth and deionized water. Fully squeeze the wiping cloth or sponge to remove any excess liquid. If a stronger cleaning solution is required, dab a soft cloth with mixture of isopropyl alcohol and deionized water (70% IPA and 30% DI water).

2. Emitter Points

The emitter points should be cleaned using specific emitter point cleaners or a swab dampened with Isopropyl alcohol. Below are general instructions on how to clean emitter points. However, each unit is slightly different so always refer to the ionizer’s manual.

  1. Turn the unit OFF and unplug the power cord.
  2. Open the top screen by loosening the screw and swinging the grill to one side.
  3. Clean the emitter points using the an emitter point cleaner or a swab dampened with Isopropyl alcohol.
  4. Re-attach the top screen.
  5. Plug in the power cord and turn the unit ON.
  6. Verify the performance of the ionizer by using a charged plate monitor or ionization test kit (see below).

Cleaning of Emitter Points using SCS 9110-NO as an example

With normal handling, the emitter points should not require replacement during the life of the unit.

Verification

Per ESD TR53 section 5.3.6.7.1 “The best practice is to measure the offset voltage and discharge times, clean the unit, including emitter points and air filters if present, offset voltage to zero (if adjustable), and then repeat offset voltage and discharge time testing. If the unit does not meet offset voltage specifications or minimum established discharge time limits, further service is indicated. Manufacturers should provide details on service procedures and typical service intervals.

Most companies will assign a number or otherwise identify each ionizer and setup a Compliance Verification / Maintenance / Calibration schedule. If the ionizers all test good, the data can justify lengthening the calibration period. If ionizers require adjustment, the calibration period should be shortened. Although ESD TR53 does not advise a test frequency, JESDD625-A (Revision of EIA-625) recommends ionizers be tested semi-annually, noting to use “S3.1 except the number of measurement points and locations may be selected based on the application.

Verification should be performed in accordance with the ESD Association ionization standard ANSI/ESD STM3.1.

Below are general instructions on how to verify your ionizer’s offset voltage and discharge time. Always refer to the User Guide accompanying your Charge Plate Monitor or Ionization Test Kit for proper operation and setup.

1. Testing Ionizer Offset Voltage:

The required limit per ANSI/ ESD S20.20 is less than ± 35 volts. Check your ionizer’s operating manual or consult with the ionizer manufacturer to determine what the offset voltage should be for your ionizer.

Charge Plate Monitor (CPM)

  1. Position the ionizer and charge plate monitor as shown below.
  2. Set the CPM to Decay/Offset mode.
  3. Set the CPM to decay and offset voltage mode with a starting charge at either + or – 1 KV and a stopping charge at either + or -100 Volts.
  4. Start the decay/offset test sequence on the CPM. This will take a few seconds.
  5. Record the decay time, and offset voltage as displayed on the CPM.

Positioning your Charge Plate Monitor for Overhead and Benchtop Ionizers

Ionization Test Kit

  1. Zero the charge plate by touching it with a grounded object. This can either be the finger of a grounded person or some other item which is connected to electrical ground. In either case, zeroing the charge plate should make the display on the field meter read zero.
  2. Hold the meter approximately one foot (30.5 cm) in front of the ionizer.
  3. Monitor the display. The value displayed is the offset balance of the ionizer, which is the difference between the number of positive and negative ions being emitted.
Testing Ionizer Offset Voltage using the SCS 718A Air Ionizer Test Kit

2. Testing Ionizer Discharge Time:

The required limit per ANSI/ESD S20.20 is “user defined”. Please refer to the ionizer’s operating manual or consult with the ionizer manufacturer to determine what this discharge time should be.

Charge Plate Monitor (CPM)

  1. Set the CPM to Decay/Offset mode.
  2. Set the CPM to decay and offset voltage mode with a starting charge at either + or – 1 KV and a stopping charge at either + or -100 Volts.
  3. Start the decay/offset test sequence on the CPM. This will take a few seconds.
  4. Record the decay time, and offset voltage as displayed on the CPM.

Ionization Test Kit

  1. After charging the plate of the ionization test kit, hold the field meter approximately one foot (30.5 cm) away from the ionizer.
  2. Monitor the display of the meter to see how quickly the 1.1 kV charge is dissipated to 0.1 kV.
  3. The speed at which this occurs (the discharge time) indicates how well the ionizer is operating.
  4. Repeat this procedure for both a positively and a negatively charged plate.

Some ionizers offer adjustment options (e.g. trim pots) which allow modification of the offset voltage.

However, if your ionizer is out of balance (and cannot be adjusted) or if the discharge time is out of specification, the ionizer will require service/repair by an authorized company.

Conclusion

Ionization is one of the best methods of removing charges from insulators and as a result plays an important role in controlling ESD.

Remember though: ionizers require periodic cleaning of emitter pins and verifying of the offset voltage and discharge time. Otherwise, instead of neutralizing charges, the ionizer will primarily produce positive or negative ions. The ionizer will therefore place an electrostatic charge on items that are not grounded, potentially discharging and causing ESD damage to nearby sensitive items.