Ionizers are a common sight in electronics manufacturing and assembly facilities; but all too often the process of ionization is not well understood. To get the inside scoop on ionization, EE asked advice from industry experts Arnie Steinman, Chief Technology Officer for Ion Systems, and John Begley, Marketing Manager at Simco.
The questions we asked the experts focused on when ionizers are required and what factors determine which ionizer type is best. We start off by determining what we must do to provide a static-free environment.
For any area where static-sensitive devices are handled, make sure you ground all conductors and clear the area of all unnecessary insulators. This sounds easy, but it takes a thorough investigation of both the grounding techniques for your conductive material and the methods that neutralize the charge on your insulator materials. For more information, refer to The Essentials of ESD Grounding in the December 1995 issue of EE.
Grounding an insulator is ineffective because static charges will not migrate to ground. Consequently, passive devices such as heel/wrist straps, mats and conductive boxes ground and safeguard static-sensitive devices but do not prevent static charges from accumulating on insulative materials. This is a job for an ionizer because it makes the air sufficiently conductive to dissipate static charges as well as neutralize static on nearby surfaces.
It is especially important to use ionizers to neutralize static charge if your operation uses insulators. For example, applications such as clean rooms need ionizers because they use glass, plastic, ceramics, quartz and silicon—all insulators. Adding to the difficulty are the HEPA filtration systems that remove particulate and strip the air of its normal ion content, fostering high levels of static charge.
A charged device in a clean room is susceptible to damage from ESD and attracts airborne particulate to its surface. These two events are major contributors to product degradation and device failure, and good reasons to use ionizers to neutralize static charges. Other control methods, such as increasing the humidity and spraying chemicals in clean rooms, cannot be used because they actually increase the potential for particle contamination.
In an automated manufacturing line, the only way to reduce static charge is to isolate the equipment from the products, make the machinery with noninsulative material, or remove any charge build-up. For manufacturing operations that must use insulative materials, the ionizer is a good choice because it eliminates charges from the surfaces of the equipment.
In many automated manufacturing lines that use nonconductive gases and epoxy cases, ionizers are placed inside the equipment to eliminate charge build-up. Any movement in these operations causes the devices to charge and ionizers can keep the static charges under control.
Help Is Available
Some ionizer manufacturers, including Ion Systems and Simco, will survey your work area and make suggestions to keep it static free. They will inspect your process, look at your product and determine what static-control measures are best for you.
Manufacturers also will loan you an ionizer to help determine which type is best, such as laminar flow, room, bench or point-of-use. And they can point out if your process requires an AC, steady-state or pulse DC, or a nuclear ionizer. For example, you may need a unit that decays 1,000 V to 100 V in 1.4 s @ 6″, but other applications may need a slower decay rate over a wider area.
To help you perform a static audit, ionizer vendors will measure the manufacturing process for contamination or static charge before and after placement of the ionizers. Using this process, some companies have realized an 8% increase in yield just 24 h after installing the ionizers.
Each situation is different and you cannot expect a survey to tell you exactly what percent of improvement you should realize. The important point is to be as thorough as possible. Your survey should follow these steps: measure your manufacturing process without ionization, determine which ionization method is best, implement it and measure again to evaluate its effectiveness before making refinements.
Types of Ionizers
Many types of ionizers are available to generate ions. A primary factor that distinguishes one from another is whether the system uses high-voltage AC, DC, pulsing DC current or nuclear elements to create ions.
The AC ionizer applies high voltage to a series of closely spaced emitter points and cycles negative and positive ions at 50 Hz or 60 Hz. This technology uses grids, ionizing blowers, guns and bars. Due to the fast cycling and ion recombination, AC systems must have high levels of airflow to blow ions away from the emitter points.
Steady-state DC ionizers provide separate emitter points for each polarity of ions. Positive high voltage is continually applied to one half of the emitter points while negative high voltage is applied to the other half. They are used in room systems, laminar hoods, ionizing blowers and air guns. Steady-state DC works with low and high airflow if the emitter points are spaced apart enough to reduce ion recombination or hot spots.
Pulsed DC ionizers use positive and negative emitter points that alternately turn on and off, creating clouds of positive and negative ions. They are used in clean rooms, laminar hoods and nonclean rooms. Usually they are not used in ionizing blowers or air guns.
Cycle timing can be adjusted to the airflow conditions. Pulsed DC allows either polarity to be left on as long as needed. Some systems also have times when neither polarity is on, permitting dispersion of existing ions.
Nuclear ionizers are available for ionizing bars, guns and blowers. Typically, they use polonium 210, which emits alpha particles to ionize the air. These units need no external power supply or wiring, and work well in confined spaces because they do not need to compensate for high-voltage emitters.
Ionizers in Leading-Edge Places
The decrease in the geometry of today’s semiconductors has made them more susceptible to static damage. Several years ago, the level of susceptibility was about 200 V. Now with the increasing sophistication of these devices, the levels have plummeted to 20 V.
To meet this exceedingly low level, you may have to rethink your entire ESD-control program. For example, a wrist strap that protects at the 200-V level is an ineffective part of a system required to control static charges at the 20-V level. All your static-control products, including ionizers and passive control devices such as wrist straps and mats, must complement each other by meeting the lower voltage level requirements.
The ESD-control industry is also faced with a challenge to persuade manufacturers that ESD is a real threat to sensitive electronic circuitry. The industry has been trying to convince manufacturers that their field failures are very often the result of ESD. It weakens devices but often not enough to cause a complete failure until weeks or even months later.
Today’s more knowledgeable ionizer customers ask for equipment with the appropriate decay rate for their process as well as low maintenance models, such as the electric models with easy-to-clean emitter points. Customers also want ionizers that incorporate self-balancing technology for automated production facilities. Automated lines need ionizers that are self-cleaning and self-calibrating. These newer self-balancing and easy-access units meet these requirements by making your job easier and your process free of charge.
Worksite Ionizer Delivers
The 6400 family of ionizers provides a range of capabilities from pinpoint accuracy in tight workspaces to high output for long-range uses. The ionizers never need calibrating and are self-balancing. The 6420 is used at a 1-ft working distance; the 6450 provides ionized air at 15 ft. The 6440 has three speeds and a heater. Arbell, (905) 332-7755.
Air Gun Maintains
± 10-V Balance AutomaticallyThe Silencer SE is a static-eliminating air gun with a patented circuit to automatically maintain a ± 10-V balance. It is made of cast aluminum and features a reinforced ionizing-point assembly. The unit provides a decay rate of 1,000 V to 100 V in <0.5 s per EOS/ESD-S3.1. Shielded cables and an emitter assembly minimize capacitance and EMI. The air gun produces <80 dBa at 2 ft @ 30 psig. Chapman, (207) 773-4726.
Overhead Ionizer Features
Control Panel, Status LEDs
The Model A60429 High-Output Deluxe Overhead Ionizer employs pulse-width-modulated bipolar DC operation with closed-loop monitoring on each fan output. The soft-touch control panel has LED status indicators for the power, the fan speed and the alarm modes. A lockout key prevents tampering with ionizer settings. The ionizer has internal emitters for user safety and is configurable to operate on 120-V or 220-V lines. The airflow is adjustable from 90 cfm to 260 cfm. It shuts down automatically when the power supply fails or when the emitters become contaminated or damaged. Desco, (909) 598-2753.
Balanced Unit Neutralizes
1,000 V Charge in 4 s
The Dynastat® 16EI Ionizing Air Blower is an inherently balanced system that neutralizes 1,000-V electrostatic charge in 4 s. The ionizer has a balance indicator and optional swivel-stand or gooseneck mountings. ElectroStatics, (215) 513-0850.
Particle Blow-Off Gun
Dissipates Charge in <0.5 s
AirForce is an ionizing particle blow-off gun that dissipates static charge in <0.5 s. The power source is encapsulated within the hand-held unit and provides flexible air-hose attachments. The low level of electromagnetic emissions of the ionizer prevents interference with other electronic equipment. It implements the company’s IsoStat™ technology to ensure balanced ionization without the need for calibration. Ion Systems, (510) 548-3640.
Air Gun Controls
Static in Clean Rooms
The Alpha Clean II Model 4056 Ion Air Gun uses the company’s Nuclecel™ ionizing cartridge for emitting a stream of ions to neutralize static charges and prevent particles from clinging to surfaces. Filtered nitrogen is ionized as it passes through the nozzle and is balanced at the source. The tip is vented to achieve OSHA’s flow standards. The gun connects to the compressed gas line and does not need a power supply to operate. Alpha Clean II can stop particles of 0.5 microns, and 0.2 microns optionally. NRD, (800) 525-8076.
Unit Moves Ionized Air
With No Turbulence
The Air Ring™ 1000 is a steady-state DC ionizer that moves ionized air from 1 ft to 6 ft with compressed gas. It is powered by the company’s Intelligent Balance Controller™ 20. A built-in sensor continuously monitors the ion balance. The 4″ ´ 5″ ionizer is used for applications such as hard-disk manufacturing, MR head production, ESD-sensitive assembly, medical manufacturing, and film extrusion and lamination in converting operations. Richmond Technology, (800) 538-0750.
Overhead Unit Has
Inherent Balance, Lighting
The Aerostat® Guardian™ Overhead Ionizing Air Blower has an integrated heater and task lighting. It features a patented inherent balance and built-in emitter-point cleaners. The AC-operated unit has airflow diffusers which contribute to effective charge decay rates. Discharge time is 3 s at 18″. The variable air-volume output ranges from 150 cfm to 300 cfm. Simco, (215) 822-2171.
Workstation Ionizer Has
Three Fan Speeds
The 962 Ionized Air Blower is a self-contained, bipolar, intrinsically balanced system with three fan speeds and a heater. It neutralizes static charge on nonconductors such as insulative tapes, plastics and circuit-board substrates. The proprietary power supply delivers a balanced ion stream even if the emitter points are dirty or corroded. The ionizer never needs calibration or adjustment. 3M Electrical Specialties, (800) 328-0016.
Overhead Ionizer Provides
The Overhead Bench Ionizer features closed-loop auto balancing with a balance indicator and touchpad controls for alarm, fan speed and power. The ionizer has an audible alarm, an automatic shutdown function and a switch for 120-V or 220-V operation. Emitter needles are enclosed to prevent shock hazard to the user. A lockout key switch provides a tamper-resistant setting. Plastic Systems, (508) 485-7390.
Copyright 1996 Nelson Publishing Inc.