The Role of ESD
In ordinary circumstances, static electricity is little more than an annoyance. However, in an increasingly technological and integrated age, that familiar static shock we receive when walking across a carpet can be costly or even dangerous. This same static shock, referred to as electrostatic discharge (ESD), can ignite flammable mixtures and damage electronic components. Static electricity can also attract contaminants in clean environments or cause products to stick together.
ESD and ESD damage play a role in many of today’s industries as technology becomes more complex and vital. The cost of ESD-damaged electronic devices alone ranges from only a few cents for a simple diode to several hundred dollars for complex hybrids. Loss of production time in web processing industries due to static attraction is significant. When associated costs of repair and rework, shipping, labor, and overhead are included, the opportunities for significant improvements in reducing losses to ESD and static electricity become evident.
According to industry experts, “ESD control, other than a dramatic increase in sales, is the single most profitable opportunity for industry under today’s economic conditions. Independent consultants have found that ESD costs the average electronics manufacturer 4 to 8 percent of total annual corporate revenue.”1 Also “internal studies in telecommunications and other electronic firms have revealed losses equal to, or in excess of, 10 percent of annual revenues. At an estimated average impact of 6.5 percent of revenues, this means that the international electronics industry is losing in excess of $84 billion (USD) every year based on production data from 1997 through 2001.”1 According to the Electrostatic Discharge (ESD) Technology Roadmap, produced by EOS/ESD Association, the devices of today and in the future will be more sensitive to ESD than those used from 1997 to 2001. Indeed, since the mid-’90s, ESD immunity levels of electronic devices have steadily declined. By 2020, it is estimated that device sensitivities will be below 125V CDM for the most sensitive devices.2
What is ESD?
Static electricity is defined as an electrical charge caused by an imbalance of electrons on the surface of a material. This imbalance of electrons produces an electric field that can be measured and that can influence other objects even at a distance. Electrostatic discharge is defined as the transfer of charge between bodies at different electrical potentials.
Electrostatic charge is most commonly created by the contact and separation of two materials. For example, a person walking across the floor generates static electricity as shoe soles contact and then separate from the floor surface. In the same manner, an electronic device sliding into or out of a bag, magazine, or tube generates an electrostatic charge as the device’s housing and metal leads make multiple contacts and separations with the surface of the container. While the magnitude of the electrostatic charge may be different in these two examples, static electricity is generated in both situations.
Just as the circumstances and objects in the above examples differ, so do the results. The first example may end in the person experiencing a small shock when they reach the door and touch a metal doorknob. In the second situation, however, the outcome can be far more lasting. Electrostatic discharge can change the electrical characteristics of a semiconductor device, degrading or destroying it. Electrostatic discharge also may upset the normal operation of an electronic system, causing equipment malfunction or failure.
Another problem caused by static electricity occurs in cleanrooms. Charged surfaces can attract and hold contaminants, making removal from the environment difficult. When attracted to the surface of a silicon wafer or a device’s electrical circuitry, these particulates can cause random wafer defects and reduce product yields.