AVIONICS R. Fred Polak | Editor
AVIONICS & ELECTROSTATIC
DISCHARGE
The growth and change in helicopter aviation over the past 50 years has been nothing short of breathtaking.
Helicopters can be found to play an important role in industries as diverse as off-shore oil support to emergency medical transport to airborne law enforcement to executive transport. The systems found on these helicopters have also gone through significant changes, and nowhere is this truer than in the realm of avionics. From vacuum tubes to transistors to integrated circuits, microelectronics and microprocessors, the transformation seems to be continuously moving forward towards smaller and more capable devices. Along the way, the size, weight and power consumption of these devices have decreased and their performance and reliability increased. From an aviation perspective, this is great! Unfortunately, we never get something for nothing when dealing with these newer systems. When dealing with microelectronics that utilize semiconductor devices that measure a few millionths of an inch in thickness, new forces come into play that the helicopter maintenance professional has not had to deal with in the past. Static electricity, or electrostatic discharge (ESD) as it is more commonly referred to, is a major concern when handling many of the newer avionics systems. Estimates tell us that thousands of unnecessary failures and billions of dollars worth of microelectronics and circuit boards are scrapped annually due to damage from static electricity.
Components that are ESD sensitive are commonly referred to as ESDS parts. These parts are found on a wide variety of avionics systems and on many circuit card assemblies (such as the one shown in the lower left) and are field replaceable.
Electrostatic Discharge (ESD) ESD is the sudden flow of electricity between two electrically-charged objects caused by contact, an electrical short or dielectric breakdown. A buildup of static electricity can be caused by tribocharging or by electrostatic induction. Examples of tribocharging include walking on a rug, rubbing a plastic comb against dry hair, rubbing a balloon against a sweater, ascending from a fabric car seat, or removing some types of plastic packaging. In all these cases, the friction between two materials results in tribocharging, thus creating a difference of electrical potential that can lead to an ESD event.
Another cause of ESD damage is through electrostatic induction. This occurs when an electrically-charged object is placed near a conductive object isolated from ground. The presence of the charged object creates an electrostatic field that causes electrical charges on the surface of the other object to redistribute. Even though the net electrostatic charge of the object has not changed, it now has regions of excess positive and negative charges. An ESD event may occur when the object comes into contact with a conductive path. For example, charged regions on the surfaces of styrofoam cups or bags can induce potential on nearby ESD-sensitive components via electrostatic induction, and an ESD event may occur if the component is touched with a metallic tool. Just about all of us have walked across a nylon carpet and generated static electricity. If the relative humidity is low, a charge in excess of 25,000 volts can be generated. We don’t realize that we have done this until we touch something else, like a doorknob. When we do, we experience a static electricity discharge and it will probably generate a spark. Although this discharge is not harmful to us, it would critically damage ESDS parts. Many ESD events occur without a visible or audible spark.
Circuit Card Assembly 12
HelicopterMaintenanceMagazine.com April | May 2014
A person carrying a relatively small electric charge may not feel a discharge that is sufficient to damage sensitive electronic
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