ESD: Another kind of lethal contaminant?
As recently pointed out in this magazine, it only takes about 25 V of static electricity to functionally destroy an MR head.
As recently pointed out in this magazine, it only takes about 25 V of static electricity to functionally destroy an MR head. Indeed, for the most part, the poor yields for MR heads (reportedly between 18% and 25%) are attributed to electrostatic discharge (ESD). Moreover, trends in MR head design (i.e., the use of thinner films, higher current densities, and narrower structures) — not to mention the advent of more sensitive giant magneto-resistive (GMR) technology — seem to indicate that static electricity will pose an even greater threat in the near future. So, it’s clear that the drive industry will have to learn how to deal with this “energy contaminant” as they have with other contaminants in the past.
There’s a catch, though: Care must be taken to ensure that standard contamination-control
measures do not compromise ESD management and vice versa. Garments that are cleaner than the driven snow may pose an unsuspected threat if, like wipers and swabs, they are made of pure polymers on which static charges tend to accumulate. Such problems can be avoided by choosing materials that are neither insulators (which prevent the static charge from being transferred to other objects, resulting in a buildup of static electricity) nor conductors (which allow the charge to dissipate so rapidly that an electrostatic discharge occurs).
Better choices are intermediate materials that are “static dissipative”—that is, materials that
allow the charge to gradually drain to ground. Static dissipative fabrics, for example, are used in dry wipers to minimize static buildup or discharge when cleaning tabletops and equipment that are not grounded.
Such fabrics can be made out of various fibers. One option is to use moderately conductive
polymer fibers. The technology is well developed; however, it’s also expensive.