Question: What does an ionizer do?
Answer: The primary function of an ionizer is to neutralize electrostatic charges on insulators and isolated (non-grounded) conductors to reduce the magnitude of electrostatic discharges in the ESD protected area. Point-of-use compressed air ionizers combat electrostatic attraction neutralizing charges on particles causing contamination or visual defects on products.
Question: Does ANSI/ESD S20.20-2007 require the use of ionizers in an ESD control program?
Answer: No, ionizers are not required. But general information in the ANSI/ESDS20.20-2007 Foreword states: “Necessary non-conductors in the environment cannot lose their electrostatic charge by attachment to ground. Ionization systems provide neutralization of charges on these necessary non-conductive items (circuit board materials and some device packages are examples of necessary non-conductors).”
Question: When should ionizers be used?
Answer: Per ESD Association ESD Handbook ESD TR20.20 Ionization, section 18.104.22.168 Introduction and Purpose / General Information “A complete static control program must also deal with isolated conductors that cannot be grounded, insulating materials (e.g., most common plastics), and moving personnel who cannot use wrist or heel straps or ESD control flooring and footwear. 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.”
Question: After installation, do ionizers need to be checked? How frequently?
Answer: Ionizers 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 neutralizing charges the out of balance ionizer 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.
Question: What should ionizers be checked for? What are acceptable limits?
Answer: Per S20.20-2007, Compliance Verification of Ionizers per Table 3 should be per ESD TR53. The ionizers should be tested for offset voltage (balance) and for discharge times. The required limit for offset voltage per S20.20 is less than +/- 50 volts (less than +/- 150 volts for room ionization). Per S20.20, the required limit for discharge time is user defined. Note: discharge time for both polarities are to be tested, from +1,000 volts to +100 volts and from -1,000 volts to -100 volts.
Question: What is the advantage of steady state DC ionization?
Answer: Experience has found that steady state ionizers work effectively with a modest air flow suitable for sensitive items, soldering operations, and where operator comfort is a concern. “Steady state DC Systems consist of separate negative and positive ion emitters connected by a pair of high voltage cables to their respective high voltage power supplies. The spacing between emitters will vary depending on the design, and DC power is constantly applied to the emitter points.
Emitters of opposite polarities are spaced farther apart in the DC systems than in the AC systems. Ion recombination occurs at a lower rate and steady state DC systems will operate at a lower airflow than AC systems. In some situations, it may not be desirable to place sensitive components close to the emitter points. The electric field of the ionizer is used to move ions in the absence of high airflow.” [ESD Handbook ESD TR20.20 section 22.214.171.124.1.3]
Question: What is the advantage of AC systems?
Answer: “AC systems utilize emitters that are switched rapidly between positive and negative high voltage, usually at the power line frequency. Ion recombination is high, as both polarities are produced in rapid succession at each emitter point. The electrostatic field from the emitter points also changes direction rapidly. In some situations, it may not be desirable to place sensitive components close to the emitter points. For these applications, moving ions away from the emitter points will require airflow. AC systems are often mounted at the output of an air delivery system.” [ESD Handbook ESD TR20.20 section 126.96.36.199.1.2]