We often hear our customers say they want to “de-ionize” or “ionize” air flow to protect ungrounded electronics and work surfaces from holding a static charge.
95% of ionizers used in the world are electrically powered. 5% are plutonium-based, which is not covered in this article.
As an authorized re-seller of Simco-Ion products and manufacturer of cleanrooms, Elimstat.com is one of the few distributors with trained sales staff who can recommend proper specifications for the use of ionization in your ESD Control Program and your cleanroom class.
In this article, I review the example workplaces where static can only be discharged using ionization and the differences between using alternating current (AC) and direct current (DC) to ionize air molecules.
What type of workplace environments need ionization?
Static electricity is a problem for insulative materials and electrically isolated conductors.
Objects made from insulative materials like plastic, glass, and coated paints are the most prone to holding a charge.
At a molecular level, insulators can hold positive and negative charges in various pockets distributed across their surface.
Insulative materials are triboelectrically charged- charged when coming into contact with differing materials. Rubbing an insulator will build up charge on it.
Insulators cannot be charged by electrostatic induction (coming near the field of a charged object), or electrostatic conduction (coming into contact with a charged object).
The second type of material to be concerned about are conductors. Humans, circuit boards, and metals all conduct electricity. Conductive materials used for static control often use carbon, which gives them a black tone.
Conductors are uniformly charged across their surface.
Conductors can become charged by triboelectrification (rubbing), electrostatic induction, and electrostatic conduction.
If a conductor is electrically isolated (as opposed to being electrically bonded), ionization is needed. When the isolated conductor (including a person) comes into contact with a neutrally charged object an electrostatic discharge (ESD) will occur.
Machines that use tools to assemble circuit boards are particularly prone to building charge and conducting it onto the boards.
Since circuitry can be as small as 15 nanofibers (1/5 the width of a human hair), they can be damaged by a charged object holding as little as 100 volts.
Micro ionizing blowers are used inside of machines dealing with circuitry manufactured at this level by placing the ionizer as close as possible to the tool the machine is using.
Ionization should also be used at workstations where electronics are assembled, tools are laid out, or products are packaged.
While the person assembling the parts may be grounded, the materials they are handling may hold a charge.
For example, assembling an electronics part to go into a plastic bag is always best done with ionization nearby.
How does ESD Air Ionization work?
Since charge sits on the surface of an object, we can use charged air molecules to dissipate the static on it.
Ionization is this process of positively and negatively charging thousands of air molecules so that when they come into contact with the charged molecules they attract them off the charged object, or push them off the charged object.
The most important consideration when choosing an ionizer is whether you need the charge to be rapidly dissipated, the balance of the charged environment, and the physical dimensions of the place where you will be using ionization.
We can either use alternating current (AC) or direct current (DC) to charge the emitter points.
When current is applied to the emitter point, it creates an electric field or “corona” around the emitter.
This high voltage corona of ions then interacts with electrons in nearby gas molecules.
Here’s a quick rule of thumb:
Use AC ionizers in fast-paced work environments where the ionizer can be as close as possible to the charged objects.
Use DC ionizers in rooms or workstations where the ionizer sits at a distance from the charged objects.
How does AC Corona Ionization Work?
When an air ionizer utilizes alternating current (AC) the high voltage is applied to a single emitter point that cycles between negative and positive at the line frequency (50/60 Hz).
The advantage of using AC ionizers is that they are “plug and play.”
Popular models like the Simco-Ion Aerostat XC are used because they run at specification whether or not all the emitter points are working.
The most frequent cause of failure for AC ionizers is not cleaning the emitter points weekly. Just because there is air coming out, does not mean the emitter points are working.
The emitter point cleaner is usually a knob or button on the ionizer that cleans off debris. Simco-Ion has done studies showing where over months the difference between cleaning an emitter point every week versus not cleaning it for months is upwards of 90% in machine efficiency.
Essentially, AC ionizers are great at “blasting” a charged object instantaneously but have limited range.
In assembly-line applications where you need to ensure charge is dissipated evenly across the surface of an object and done so that you are not waiting for the charge to dissipate the only option is to use AC ionizers.
If you were to use DC ionization in a fast-paced assembly line, “streaking” can occur: one side of an object can be reduced of its charge, and the other side of the object can be left untouched.
This is because DC ionizers have emitter points spaced apart, and are forced to shoot ions in sequence to achieve the same effect as AC ionizers running at line frequency.
However, because the emitter points are placed so close together on AC ionizers, the ions will eventually recombine at some point over distance.
How Does DC Corona Ionization Work?
The advantage to using DC ionization is that you can place the emitter points apart thus reducing recombination of ions. If AC ionizers are brushes, DC ionizers can be thought of as cannons that cover large swathes of a work area from a distance.
Direct current (DC) ionizers shoot both positive and negative ions through their emitter points at constant rates. Since the ions are emitted from separate points, there is much less recombination of ions- which can cause charge to accumulate in the air.
This is particularly useful for applications where the ionizer cannot be placed close to the work area.
In fact, some DC ionizers are used without using air flow at all.
Simco-Ion has placed ionizers as far as 6 feet above a work area without air flow.
Steady State DC Corona Ionization continuously applies a positive high voltage to half of the emitter points and negative high voltage to the other half.
Pulsed DC ionizers allow positive and negative emitter points to be turned on and off, creating clouds or waterfalls of positive and negative ions. Ionizers using pulsed DC may be finely tuned to allow timing cycles and polarities to operate as exactly needed for a specific application, usually in a time period of seconds.