Going Beyond Color in Static Control

Leaving static control to visual inspection can lead to problems, and clear definitions are essential for troubleshooting electrical events.

Q. What is the difference between a pink static bag and the gray static bag?

A. Although it once was common for manufacturers to distinguish between different types of packaging materials by their color, this distinction has ceased to be practical, if in fact it ever was.

Too often, however, trusting in the simplicity of visual inspection creates more problems than it solves. Certainly, in static control this is more the rule than the exception. Effective static control need not be overly complicated, but we do need to go beyond the simplification of distinction by color.

Although the emergence of ESD standards and general agreement on definitions has helped to provide a degree of clarification, widespread education is needed, as we still find much casual use of terminology. So, how do we reduce the pitfalls of trusting our eyes?

To distinguish between the two bags, it is important to examine product literature provided by each supplier. It may be necessary to conduct your own testing or request independent test lab data from the suppliers. By comparing published data and confirming them as necessary, it is possible to identify the characteristics of different static bags and to select the type most suitable for the application.

A. By definition, electrical overstress (EOS) is "the exposure of an item (an electronic component, for example) to a current or voltage beyond its maximum rating. This exposure may or may not result in a catastrophic failure of the item." Electrostatic discharge (ESD) is a specific type of EOS. ESD is "the rapid, spontaneous transfer of electrostatic charge induced by a high electrostatic field. Usually the charge flows through a spark between two bodies at different electrostatic potentials as they approach one another."¹

Typically, it can be inferred that an overstress has occurred when an item fails to meet its electrical characteristics. Determining whether the failure was caused by an ESD event or some other type of overstress is often more difficult. In addition, overstress may result in latent damage to an item. This damage is not immediately detected in its electrical properties, but could result in a failure of the item later.

1. ESD-ADV 1.0-1994, "Glossary of Terms," ESD Association, Rome, NY.

To submit your questions to the ESD Help Desk or to browse the archives of past questions and answers, go on-line at http://www.ce-mag.com/esdhelp.html. Information on the ESD Association may be found at http://www.esda.org.