How does Ionisation fit into an ESD Control Programme?

Setting up an ESD-safe workstation is often more challenging than it first appears. There are many methods of controlling ElectroStatic Discharge (ESD), and typically, it requires a combination of these to curb all static problems. Unfortunately, there is no single method that will fill all requirements.

Wrist straps and work surface mats are probably the most familiar to everyone, draining charges from operators as well as from the product being worked on. But what if the static charge in question is on an insulator? Electronic products, by nature, will normally consist of conductors and insulators. Insulators at the workstation can be found on the product itself, tools being used, tapes for masking, even circuit boards. A static charge on an insulator cannot be drained by grounding, as you could with a conductive material.

Ionisation
To effectively remove charges from insulators, we need to make the surrounding air more conductive. We have all seen a balloon cling to a wall because of a static charge, and we know that, after a period of time, it will drop. That is because the air is somewhat conductive and the charge eventually drains off. The problem with this concept is that it takes too long. The more conductive the air is, the faster the charge will be neutralised.

A balloon “stuck” on a wall by static charge.A balloon “stuck” on a wall by static charge.

The method most frequently used to increase the conductivity of the air is ionisation.
Ionisers are useful in preventing electrostatic charge generation, ElectroStatic Discharge, ElectroStatic Attraction, as well as preventing equipment latch-up. EN 61340-5-1 clause 5.3.4.2 Insulators states: “If the measured electrostatic field or surface potential exceeds the stated limits, ionization or other charge mitigating techniques shall be used.

How do Ionisers work?
Most ESD workstations will have some insulators (e.g. product plastic housing) or isolated conductors (e.g. PCB board components not in contact with ESD worksurface) that cannot be removed or replaced. These should be controlled using ionisation.

Ionisers create great numbers of positively and negatively charged ions. Fans help the ions flow over the work area. If there is a static charge present on an item in the work area, it will be reduced and neutralised by attracting opposite polarity charges from the air.
Ionisation can neutralise static charges on an insulator in a matter of seconds, thereby reducing their potential to cause ESD damage.

Electronic enclosures are process-essential insulatorsElectronic enclosures are process-essential insulators.

The charged ions created by an ioniser will:

  • neutralise charges on process required insulators,
  • neutralise charges on non-essential insulators,
  • neutralise isolated conductors and
  • minimise triboelectric charging.

How does Ionisation fit into an ESD Control Programme?
Ionisation is just one component of your ESD Control Programme. Before utilising ionisation, you should follow the fundamental principles of ESD Control:

  • Ground all conductors (including people) using conventional grounding methods (e.g. wrist straps or footwear/flooring system).
  • Remove all insulators, e.g. coffee cups, food wrappers etc.

“Air ionization is not a replacement for grounding methods. It is one component of a complete static control program. Ionizers are used when it is not possible to properly ground everything and as backup to other static control methods. In clean rooms, air ionization may be one of the few methods of static control available.” (User Guide CLC/TR 61340-5-2 clause 4.7.6 Ionization)

  • Ionisers can be critical to reduce induction charging caused by process necessary insulators
  • Ionisers can be critical in eliminating charges on isolated conductors like devices on PCBs
  • Ionisation can reduce ElectroStatic Attraction (ESA) and charged particles clinging and contaminating products.

The SCS Ioniser 9110-NO in use.The SCS Ioniser 9110-NO in use.

It is recommended to use ionisers with feedback mechanisms, so you’re notified if the offset voltage is out of balance.
Ionisers should be pieces of equipment that have serial numbers and are included in the company’s maintenance and calibration schedules. This is particularly critical to ensure that the offset voltage or balance is within acceptable limits. Otherwise, instead of neutralising charges the out of balance ioniser will charge insulators and isolated conductors. The user, depending on the value and function of their products, must determine the appropriate frequency of maintenance and calibration.

Summary
The best way to keep electrostatic sensitive devices (ESDs) from damage is to ground all conductive objects and remove insulators. 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. Applications include:

  • eliminating charges on process essential insulators,
  • neutralising workstations where ESDS are handled,
  • removing charged particulates to create a static free work area.

For more information and to select the right ioniser for your application, check out our Ioniser Selection Guide.

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 2019-02-18, in ESD Information, Ionisation, Question & Answers, Resources. Bookmark the permalink. Leave a comment.

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