In today's electronic manufacturing environment, static electricity must be controlled. Without effective control, static electricity will lead to electrostatic discharge (ESD) of components, as well as electrostatic attraction (ESA) of particles to critical product surfaces. The static control program starts with grounding. Anything that conducts electricity or dissipates static electricity must be grounded. However, in most manufacturing areas, there are conductive and insulating items that cannot be grounded. Grounding does not eliminate static electricity on insulators.
When insulating conductors or insulators are present in the manufacturing process, static electricity can only be neutralized by the use of bipolar ionization. Bipolar ionizers create positive and negative charges in the gases in the air. These positive and negative "ions" in the air can neutralize the static charge on any surface they touch. Having two polarities ensures that any polar charges on the insulator or insulated wire are effectively neutralized. But effective neutralization also requires that the number of positive and negative ions must be kept in balance. An unbalanced ionizer can actually create a static charge on an ungrounded object. The net effect of ionizer imbalance on the object is measured in volts. Creating a charge on an object is the opposite of what you want to do with ionization. The electrostatic discharge sensitivity of today's complex electronic components is usually less than 250 volts, with some components being as low as 1 volt. Protecting these ESD sensitive elements requires a way to ensure ionizer balance.
Electronic (corona) ionizers have various methods to adjust the ionizer balance, including manual and automatic. Manual adjustments were initially used to set the balance, but frequent readjustments or calibrations are required due to voltage variations, emitter pole corrosion, emitter cleanliness, and environmental variations. This means that the long-term stability of the ionizer balance can only be achieved by frequent maintenance. Eventually, the maintenance cost will exceed the ionizer cost.
Automatic adjustment of the ionizer balance can be achieved by using sensor feedback. This involves the use of internal or external sensors to monitor and adjust the operation of the ionizer. Based on the information provided by the sensor, the ionizer power supply can be adjusted to maintain the ionizer balance. The internal sensor only monitors the ionizer output and cannot correct environmental effects such as nearby ground or air flow. External sensors installed in the work area can adjust the ionizer to maintain a balance between electronic and environmental concerns. This reduces maintenance and improves the long-term stability of the ionizer. Unfortunately, both feedback methods require a large number of additional components, which can increase the cost of the ionizer, especially if it has to reach extremely low equilibrium voltages, such as 5 volts or less. The additional components and complexity of the feedback system inevitably reduce the long-term reliability of the ionizer.
AP&T DJ28 serious use an intrinsic self-balance method to achieve ionizer balance. It starts with an understanding of the basic physical law, Conservation of Charge. Simply stated, Conservation of Charge requires that in an isolated environment you can neither create nor destroy charge. With respect to ionizers, if you produce ions of one polarity in an isolated environment, you must produce the same number of ions of the opposite polarity. Therefore, the net charge created is zero. This also means that the ionizer balance will be zero. How well this intrinsic self-balance method works depends on the success of isolating the ionization process.
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As manufacturing process requirements for ESD control to extremely low levels become more widespread, the features of AP&T ionization will become increasingly important. Self-balance at low levels (5 volts or lower) assures that static charge will be reduced below the level at which CDM or CBE ESD damage occurs. Auto-cleaning reduces maintenance costs and production downtime and enables applications inside production equipment. Monitoring and alarms assure reliable operation over long periods of time. These features will find increasing importance as the trend to more ESD-sensitive devices continues over time.
