Static control is the technique of controlling static electricity. Static electricity is defined as being electricity at rest, and is generated by an unbalance of the construction of non-conductive insulators at a molecular level. A method of static control is necessary in the semiconductor industry because it keeps unwanted charges from affecting the resulting outcome.
Static control is used in many different industries, thus having many means of being achieved. There are two general types of control: passive control and active control. In passive control, the static electricity is removed naturally, and so the technique is not as effective. Active control, however, uses methods that would not normally been found in nature, and is much more effective than passive control.
One of the simplest techniques via passive static control is induction. In induction, static electricity is removed by a metal or source that will take away the unnecessary charges. Tinsel is often used for this, and is the most common tool, but sometimes does not produce successful results if misused. Induction devices, unfortunately, cannot reduce or neutralize static electricity to the zero potential level, as there is a threshold voltage necessary in order to begin the process.
Another form of passive static control is called grounding. In grounding, the molecular construction of the operator is disturbed, sending the voltage through that individual. This can be eliminated by having the operator stand on a grounded conductive mat. It is also important to ground plant machinery and related equipment so that those pieces of equipment do not get damaged by the high amount of electricity. It also helps to alleviate the high charges.
The most effective form of static control is active control. A typical method of active control is ionization. It ionizes the units that produce both the positive and negative ions to be attracted by unbalanced material. This way, neutralization occurs and tones down the high voltage of static electricity. This, however, does not eliminate the static electricity, due to the fact that if the material were to experience friction once this process had been completed, it would generate static electricity once more.
Due to thresholds and the principles of electricity, static electricity can never be entirely eliminated. Through the above processes, however, it can be reduced greatly in order to be maximally effective.
Electrostatic discharge (ESD) control is used for cleanroom and laboratory safety in semiconductor manufacturing. It is very important for maintaining a safe environment and, of course, controlling dangerous amounts of static electricity. This can be done through the use of different geometric shapes and with current technology, more effective techniques can be created through smaller designs and faster production methods. Control methods, however, are still a difficult problem in today’s market.
There are a few basic facts one should know about ESD in order to best understand controlling it. Virtually any material can be charged triboelectrically. How high this charge is relies on the type of material, humidity and other impending factors. Electrostatic discharge can create catastrophic failures as well as occur throughout the operational processes, and thus needs to be watched out for. All components vary in their sensitivity to ESD, and so each should be treated differently.
When designing an ESD control program, it is important to focus on six basic principles. The first of these is the ESD Immunity Design-in. After that, one needs to focus on the definition of the desired level of ESD control, the identification of electrostatic protected areas, reduction or elimination of static generation, the static neutralization and dissipation, and the protection of products from ESD. Though all are essential to the overall control, three principles are particularly important.
ESD Immunity Design-in is needed for the prevention of ESD related problems. It begins by creating devices with the ability to withstand ESD events that would be otherwise dangerous if not kept in check. Proper determination of ESD sensitivity levels prior to production release is required in order to achieve the best possible results. ESD sensitivity testing is thus used for examining whether the model is device has adequate immunity to ESD and that it will not create problems. There are several necessary procedures in today’s assembly.
Identification of electrostatic protected areas is also a highly important part of ESD control. The ESD control program must be stable to begin with before ESD immunity can be designed into the product. An electrostatic protected area, or an EPA, is an area in which ESD-sensitive devices are going to be handled. All electrostatic protected areas must first be designated within a given factory and then adequately protected by the ESD controls.
Most important to proper ESD control is the reduction of static generation as well as the dissipation of static through proper grounding. This is the backbone for ESD control. The primary means by which items that are prone to ESD are grounded is through providing electrically conductive paths between the items as well as a common ground. Every factory that wishes to be approved for its ESD control program must have a common grounding point. This way a maximum safety can be established.