A complete static control program must also deal with isolated conductors that cannot be grounded and insulating materials (e.g., most common plastics). If an insulator cannot be removed from the ESD Protected Area, substituted with an ESD protective version, or controlled with a topical antistat, ionization must be used. These insulators are often referred to as process necessary insulators. Common process necessary insulators used for manufacturing electronics include flex cables, product enclosures, test fixtures, and the PCB substrate substrate itself*.
Neutralization of charges on insulators does occur naturally as positive and negative charged ions are in the atmosphere. As opposite charged ions are attracted to the charge on the insulator, the charges will be neutralized over time (same charged ions will be repelled). However, the process is much too slow for ESD susceptible components.
Examples of some common process necessary insulators are PC board substrate, insulative test fixtures, and product plastic housings. Examples of isolated conductors can be conductive traces or components loaded on a PC board that are not in contact with ESD worksurface.
The primary functions of ionizers are to:
- Discharge / Neutralize process necessary insulators that can charge ESDS devices / assemblies via induction, thus creating potential CDM damage, and/or
- Discharge / Neutralize ESDS devices / assemblies that are not grounded, thus are an isolated conductor, thus creating potential CDM damage, and/or
- Discharge / Neutralize insulators where particulate contamination can cause visual defects (for example – dust on plastic or glass lenses, attracted to / held in place by Electrostatic Attraction [ESA])
*Note. The PCB substrate is a process necessary insulator and can become charged during automated handling processes and the ESD susceptible components on the PCB may be isolated or floating conductors as well.
Desco offers a variety of ionizers:
Contact Desco for more information about when you need to ionize or how to choose the right ionizer for your application.