Insulators and isolated conductors in the EPA: when is ionization needed?
Insulators and isolated conductors cannot be discharged through a ground connection. Ionization is needed when a process-essential insulator can be neither removed, replaced nor kept at least 30 cm from the device, or when an ungrounded conductor touches sensitive parts. A field meter at the device location shows whether the field is critical.
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Why can an insulator not be grounded?
An insulator has such a high surface and volume resistance that charge on it stays practically where it is. A ground lead only discharges the spot it touches; the rest of the surface keeps its charge. This is why IEC 61340-5-1 does not ask for insulators to be grounded but for their electrostatic field to be assessed and controlled.
In conductors and dissipative materials, charge moves through the material to the ground point. Plastics such as polystyrene, PET film or acrylic offer no such path: charge from rubbing, peeling or separation can persist for a long time, depending on humidity.
The real risk is the field, not contact. When a sensitive device sits in the field of a charged insulator, the charges inside the device shift (induction). If the device then touches a grounded conductor, charge flows off abruptly: a CDM event (Charged Device Model). If the device is afterwards taken out of the field and grounded again, a second discharge of opposite polarity follows.
What are process-essential insulators and isolated conductors?
Process-essential insulators are materials that the product or process genuinely requires and for which no dissipative alternative exists, such as PCB base material, plastic housings, films and operating controls. Isolated conductors are metal parts without a ground connection that touch devices, for example test probes, bond wires, hand tools and transport rollers.
The difference determines the measure. On an insulator the charge is fixed. An isolated conductor collects mobile charge and releases all of it very quickly at the first contact. In return, it can usually be grounded afterwards; an insulator never can.
| Object | Classification | First measure |
|---|---|---|
| PCB base material | Process-essential insulator | Ionization at the handling point |
| Plastic housings, component carriers | Process-essential insulator | Distance, otherwise ionization |
| Protective films, covers | Insulator | Dissipative version, otherwise ionization |
| Controls, displays, keys | Process-essential insulator | Distance or ionization |
| Test probes, bond wires | Isolated conductor | Grounding or bonding |
| Hand tools, transport rollers | Isolated conductor | Dissipative version, otherwise ionization |
In what order should insulators be dealt with?
Ionization is the last step, not the first. First check whether the insulator can be removed, then whether a dissipative alternative exists, then whether a distance of at least 30 cm from the device can be maintained. Only when none of these works does an ionizer neutralize the charge directly where the process takes place.
- Remove: anything not needed for the work step leaves the workstation.
- Replace: use dissipative films, containers and tool handles; ground or bond isolated conductors.
- Distance: keep remaining insulators with a significant field at least 30 cm from the device; the field drops markedly with distance.
- Ionize: when none of this is possible, for instance because the insulator is part of the product.
Which ionizer type suits which case?
Benchtop ionizers cover one workstation, and compact units also fit inside machines. Overhead ionizers supply the whole bench from above, even where objects would block the airflow of a benchtop unit. Compressed-air ionizers act at a single point, for example at placement stations, and also release attracted particles.
IonizersBenchtop, overhead and compressed-air ionizers for insulators that must stay in the process.
View productsField metersMeasure the field at the device location and show whether distance is enough.
View productsHow do you find out whether an insulator is critical?
What matters is the electrostatic field where the device sits or is processed, not somewhere on the bench. It is measured with a field meter held by a grounded person. The result shows whether distance is sufficient or ionization is needed. The assessment follows IEC 61340-5-1; IEC TR 61340-5-2 gives guidance on how to carry it out.
- Measure in the real process state, for example right after peeling the film or during handling.
- The person measuring is grounded; otherwise the instrument lacks a reference.
- Small objects relative to the measuring distance give readings that are too low: measure closer or treat the value as a lower limit.
- Record location, distance, date and value, and measure again after installing an ionizer.
A field meter measures without contact and does not change the charge on the insulator. What matters for measuring range, distance sensing and grounding of the instrument is covered in the guide Choosing an electrostatic field meter.
What must an ionizer achieve for insulators?
An ionizer does not replace grounding; it complements it for whatever cannot be grounded. It must be balanced so that it does not deposit charge itself (offset voltage within ± 35 V per IEC 61340-5-1), and it must remove charge fast enough. Both are checked regularly according to IEC 61340-4-7 and IEC TS 61340-5-4.
Most units use corona discharge at emitter points. AC units need high airflow because many ions recombine. Steady-state DC units with separate emitters reach high ion density at moderate airflow, which suits soldering and sensitive parts.
Dirty emitter points shift the balance, and an unbalanced ionizer charges insulators instead of discharging them. Every unit belongs in the test plan with its serial number and is measured before and after cleaning. Units with sensor feedback readjust their balance automatically.
How ionization worksIon generation, ionizer types and the limits of neutralizing insulators.
Read the guideTesting an ionizerMeasure offset voltage and discharge time, adjust balance, set intervals.
Read the guideFrequently asked questions
Can an insulator be discharged with a ground lead?
No. On an insulator the charge is fixed, so a ground lead only discharges the contact point and the rest of the surface stays charged. Insulators are removed, replaced, kept at a distance or neutralized with an ionizer.
Does an ionizer replace the wrist strap?
No. Ionization complements the grounding of people, work surfaces and conductive parts; it does not replace it. Ionizers are used where something cannot be grounded and as an additional safeguard within the ESD control program.
Is a printed circuit board an insulator?
The base material is a process-essential insulator and can become charged during automated handling. The mounted components behave like isolated conductors: they pick up charge by induction and discharge at the next ground contact as a CDM event.
When is distance enough instead of ionization?
When the insulator can be kept permanently at least 30 cm away from the device and the field measured at the device location is not critical. If the insulator is part of the product or must stay close to the device, ionization is used.
Insulators in the process that have to stay?
Ionizers neutralize charge on process-essential insulators and isolated conductors; field meters show where this is needed.
Standards-based
According to IEC 61340-5-1 and IEC TR 61340-5-2.
Measurable
Field measurement at the device location.
Reviewed
Content technically reviewed by ESD specialists.
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