Automation is a boon to electronic manufacturing as it speeds devices through the assembly line. It’s also a bust when ESD takes charge of the process.
Manufacturers must scramble for solutions when ESD causes the assembly line to come to a grinding halt. To combat the problem of static-charge buildup, the best product often is the ionizer.
The ionizer wasn’t always the best choice. Early attempts to use electric ionizers to control unwanted charges in production facilities were unsuccessful because the emitters were placed directly in the process chambers. This positioning was futile because the ionizers were too close to the products and the distance to ground was too short, forcing the ions to ground too quickly, and the supply of ions needed to neutralize unwanted charges was limited.
The proximity made it possible for the ionizer emitter current to increase, which in turn caused particle contamination of the emitter points. Generally, products should come no closer than 12″ to the exposed ion emitter points.1
Precautions on Automated Lines
An automated production line can be an ESD nightmare if it isn’t fully evaluated for ESD-generating conditions before the ionization equipment is installed, said Bradford Jubin, Vice President of Semtronics. For example, if the line contains a large number of insulators and ungrounded conductors, it will perform like an enormous Van de Graaff generator, storing large amounts of static electricity, he explained.
Conductive material and ground paths must be provided to counter this effect, said Mr. Jubin. Once this is done, you can evaluate the need for ionization.
To avoid ESD problems, consider the sensitivity of the product and the capability of the ionizer to provide protection, observed Carlos De La Isla of Desco. An ionizer that does not incorporate an effective means of monitoring or ensuring ion balance can damage the very product it is designed to protect.
Proper installation of ionizers in automated equipment requires careful study of the whole area and the processes of the equipment, said Jim Curtis, Product Manager at NRD. Start by determining where destructive voltage levels are generated and where the damage occurs.
Next, determine where and how to install appropriate ionizers. Then, verify that the problem is solved. Finally, design a monitoring or periodic verification method with a frequency interval to track the operation. This sounds simple, but it’s not, said Mr. Curtis.
The ionizing equipment for a clean room-level manufacturing process with HEPA filtration and laminar airflow includes a ceiling-style ionizer with ultra-clean emitters, said Clark Taylor of Ion Systems. A low-voltage pulse DC ionizer with silicon emitter points works well in semiconductor, flat-panel display and disk-drive manufacturing. This unit offers an adjustable off time to optimize ion output and ion recombination and to lessen voltage swings to help minimize discharge times, he added.
Large, open-area production lines without laminar airflow can use ceiling emitters or ionizing bars, but the performance is less effective than in an environment with airflow, continued Mr. Taylor. Place ionizing blowers near the critical operations to contain static discharge.
Use ionization at the location where the static causes a problem, agreed Mr. Curtis. Often, that is inside the automated equipment. Any ionization system that does not target the area is ineffective. The longer it takes to get ions to the problem, the longer it takes to eliminate the charge.
NRD’s nuclear-based technology offers a solution for the difficult point-of-use applications because it provides alpha energy within the ionizer and needs no external power supplies or wiring, said Mr. Curtis. This product works well in confined spaces because you do not need to compensate for high-voltage emitters, ion mix or ion balance.
Small, confined areas also can use ionizing bars with either pulse DC or steady-state DC ion emission, said Mr. Taylor. The closer the workpiece and the more susceptible it is to voltage swings, the more useful is a steady-state DC technology. But it must control hot spots, provide inherently balanced ion emission and be UL-listed to provide the necessary reliability, he said.
Ionizers are only one step in a comprehensive static-control program, observed Mr. Taylor. An expert can help determine what measures should be taken and what sort of ionizers are required for a specific problem.
When an ionizer is installed, test it to confirm its effectiveness, continued Mr. Taylor. A hand-held verification device is sufficient for ion-blower testing, but a clean-room application requires a charged plate monitor for calibration and performance verification. ISO 9000 and FDA applications also may require performance verification of ionizers on a regular basis.
Reference
1. Steinman, A., “Ionization For Production Tools,” EOS/ESD Symposium, 1994, pp. 28-33.
Ionizer Products
Air Curtain Eliminates
Static to 20′ Away
The Ionizing Air Curtain is a long-range static eliminator that generates a uniform sheet of neutralized ions. The curtain uses air pressure from 20 psi to 30 psi to neutralize static up to 20′ away. The unit is available in six lengths ranging from 6″ to 36″. The Air Research Technology Co., Ltd., (800) 307-7475.
Blower Controls ESD
In Area Up to 80 ft2
The I-VSE 5000 Volume Static Eliminator controls ESD in areas up to 80 ft2. It uses a passive ionization circuit, and has a variable-speed fan, a replaceable filter and a built-in diffuser for eliminating ESD. The unit maintains a balanced ion flow within ±5 V. A cleaning kit is included and the emitter assembly can be removed for cleaning. Chapman Corp., (207) 773-4726.
Compact Ionizer
Provides Autobalancing
The A60455 Chargebuster Jr. is an autobalancing benchtop ionizer. An active feedback balance circuit maintains the ion balance despite variations in line voltage, air speed or the conditions of the emitter electrode. The feedback circuit also has a visual alarm, indicating when maintenance is required. Desco Industries, Inc., (909) 598-2753.
Flowbar Controls Static
Without Disrupting Airflow
The Nilstat® 5285 AeroBar is an ionizing flowbar that provides static control without disrupting laminar airflow and the evacuation of particulate matter. A patented DC ion output helps adjust the airflow to maximize ionization efficiency. The unit is programmed to turn off for short periods to provide a space between ions of opposite polarity and to reduce recombination of charged ions. Mounting brackets with snap-in installation are available in several sizes and shapes. Ion Systems, (510) 548-3640.
Compact Ion Air Blower
Offers Installation Options
The Model 4060 Ionmaster Mini Ion Air Blower removes static charges that cannot be controlled by grounding. It delivers an even flow of ionized air kept in balance by an alpha-energy source. The compact unit supports a variety of installation options including a tabletop stand or assembly that attaches to the underside of a work bench. The ionizer requires no calibration and needs only general cleaning. NRD Inc., (800) 525-8076.
Benchtop Ionizer Provides
Constant Display of Balance
The DSN-100 Benchtop Ionizer controls balance (offset voltage) and output (ion current). Discharge time is less than 1 s. The unit automatically shuts down and an alarm sounds when the balance voltage exceeds the limits. An indication of ion current is displayed and an alarm sounds when output falls below 20% of capacity. An integral 300-W heater and adjustable air-speed control provide operator comfort. Airflow reaches targets within 12″ to 18″. Pinion, A Division of PSG Industries, Inc., (215) 257-3621.
System Incorporates
Fluorescent Lighting
The EN136-HD Airpro III Ionization System features built-in fluorescent lighting. It uses steady-state DC ionization technology and senses and maintains ion balance from 0 V to +20 V at the work surface. The system provides continuous ionization coverage for areas with turbulent or no airflow. It is also effective in areas where sensitive device work, such as gold-wire bonding or surface mounting, is conducted. Semtronics Corp., (800) 247-4863.
Benchtop Ionizer Has
Emitter Point Cleaner
The Aerostat PC Ionizing Air Blower offers adjustable heated air flow, an integral emitter point cleaner and ±5-V inherent balance. The discharge time from 1,000 V to 100 V is 1.5 s at a distance of 1′. The air-volume output ranges from 35 cfm to 70 cfm. An ionization status light indicates the presence of high voltage on the emitter points. The SIMCO Co., Inc., (215) 822-2171.
Workstation Ionizer
Features Three Fan Speeds
The 962 Ionized Air Blower is a self-contained, bipolar, intrinsically balanced unit that has 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 units never need calibration or adjustment. 3M Electrical Specialties Division, (800) 328-0016.
Copyright 1995 Nelson Publishing Inc.
April 1995