Are your Ionisers working correctly?

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 ionisation systems.
However, if an ioniser is out of balance, instead of neutralising 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 ionisers and verify their functionality. Below we have put together a list of tasks that need to be performed with ionisers 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.” (User Guide CLC/TR 61340-5-2 clause 4.7.6.7 Maintenance and cleaning)
EIA-625, recommends checking ionisers 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. EN 61340-5-1 clause 5.2.4 Compliance Verification Plan  states: “Process monitoring (measurements) shall be conducted in accordance with a compliance verification plan that identifies the technical requirements to be verified, the measurement limits and the frequency at which those verifications shall occur.
Under normal conditions, an ioniser will attract dirt and dust (especially on the emitter points). To maintain optimum neutralisation efficiency and operation, cleaning should be performed on a regular basis.

1. Case
Wipe the case with a soft cloth and deionised 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 deionised 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 ioniser’s manual.

  • Turn the unit OFF and unplug the power cord.
  • Open the top screen by loosening the screw and swinging the grill to one side.
  • Clean the emitter points using an emitter point cleaner or a swab dampened with Isopropyl alcohol.
  • Re-attach the top screen.
  • Plug in the power cord and turn the unit ON.

Verify the performance of the ioniser by using a charged plate monitor or ionisation test kit (see below).

Cleaning of Emitter Points using SCS 9110-NO as an exampleCleaning 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
EN 61340-4-7 provides test methods and procedures for evaluating and selecting air ionisation equipment. It is recommended to measure the offset voltage and discharge times, clean the unit, including emitter points and air filters if present, offset the voltage to zero (if adjustable), and then repeat offset voltage and discharge time testing. Should the unit not meet offset voltage specifications or minimum established discharge time limits, further service is required. Manufacturers should provide details on service procedures and typical service intervals.
Most companies will assign a number or otherwise identify each ioniser and setup a Compliance Verification / Maintenance / Calibration schedule. If the ionisers all test good, the data can justify lengthening the calibration period. If ionisers require adjustment, the calibration period should be shortened.

Verification should be performed in accordance with EN 61340-4-7.
Below are general instructions on how to verify your ioniser’s offset voltage and discharge time. Always refer to the User Guide accompanying your charge plate monitor or ionisation test kit for proper operation and setup.

1. Testing Ioniser Offset Voltage:
The required limit per EN 61340-5-1 is less than ± 35 volts. Check your ioniser’s operating manual or consult with the ioniser manufacturer to determine what the offset voltage should be for your ioniser.

Charge Plate Monitor (CPM)

  • Position the ioniser and charge plate monitor as shown below.
  • Set the CPM to Decay/Offset mode.
  • 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.
  • Start the decay/offset test sequence on the CPM. This will take a few seconds.
  • Record the decay time, and offset voltage as displayed on the CPM.

Positioning your Charge Plate Monitor for Overhead and Benchtop Ionisers

Ionisation Test Kit

  • 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.
  • Hold the meter approximately one foot (30.5 cm) in front of the ioniser.
  • Monitor the display. The value displayed is the offset balance of the ioniser, which is the difference between the number of positive and negative ions being emitted.

Auditing ionisation equipment with the Digital Static Field Meter and Conductive PlateAuditing ionisation equipment with the Digital Static Field Meter and Conductive Plate

2. Testing Ioniser Discharge Time:
The required limit per EN 61340-5-1 is “(1 000 V to 100 V and –1 000 V to –100 V) < 20 s or user defined”. Please refer to the ioniser’s operating manual or consult with the ioniser manufacturer to determine what this discharge time should be.

Charge Plate Monitor (CPM)

  • Set the CPM to Decay/Offset mode.
  • 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.
  • Start the decay/offset test sequence on the CPM. This will take a few seconds.
  • Record the decay time, and offset voltage as displayed on the CPM.

Ionisation Test Kit

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

Some ionisers offer adjustment options (e.g. trim pots) which allow modification of the offset voltage.
However, if your ioniser is out of balance (and cannot be adjusted) or if the discharge time is out of specification, the ioniser will require service/repair by an authorised company.

Conclusion
Ionisation is one of the best methods of removing charges from insulators and as a result plays an important role in controlling ESD.
Remember though: ionisers require periodic cleaning of emitter pins and verifying of the offset voltage and discharge time. Otherwise, instead of neutralising charges, the ioniser will primarily produce positive or negative ions. The ioniser will therefore place an electrostatic charge on items that are not grounded, potentially discharging and causing ESD damage to nearby sensitive items.

About descoeurope

Desco Europe is the newest brand in the Desco Industries family, consolidating our two previous UK-based brands, Charleswater and Vermason. Charleswater, originally located in W. Newton, MA, was acquired in 1990. After several years of offering both Desco and Charleswater products in the US, Charleswater was set up to be the leading brand in the UK with the acquisition of Conductive Products in 1998. Vermason was a manufacturer of ESD protection products and was founded in Letchworth in 1979. In April 2007 Desco Industries, Inc. of Chino California acquired 100% of the shares of Vermason Ltd. Vermason is now a division of Desco Industries, Inc. Today, as Desco Europe, we retain our manufacturing capability in Letchworth, Hertfordshire, with sales and administration being split between Letchworth and our Crowborough, East Sussex office. Desco Europe sells the full range of DII products, manufactured in our facilities in the USA and UK, servicing the European market via trained distributors who will sell the Desco Europe value package and complete ESD solution to all ESD users in their territory, leading with hi-end solutions that mark us out from the competition. Desco Europe’s UK-based inventory coupled with that of our distributors means that we are in a unique position to support our Customers across Europe no matter what their needs.

Posted on 2019-02-20, in Articles, ESD Information, How-To, Ionisation. Bookmark the permalink. Leave a comment.

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