clean room re ESD

An excerpt from this long article

Unlike wafer makers who can watch the incremental effects of static
discharge with each reduction of product size and adjust their ESD efforts
accordingly, disk drive makers were blindsided by its effect in 1995. Before
then, disk drive heads could withstand 500 to 1000 volts of discharge with
little impact to their functionality. ESD was a non-issue for that industry,
until the introduction of magneto-resistive (MR) heads into mass production
in 1995. The MR head was a seemingly revolutionary advance because it
allowed much higher areal densities to be used on the platters than was
possible with older head designs, greatly increasing the storage capacity
and the speed of the drive. Because the MR head was not generating a current
directly the way standard heads did, it was several times more sensitive to
magnetic flux changes in the media, allowing the use of weaker written
signals, which let the bits be spaced closer together without interfering
with each other, improving capacity by a large amount.



What the disk drive manufacturers didn't realize was that the new MR
heads were at much greater risk of damage to even the smallest ESD event.
They were completely unprepared to handle the new technology's sensitivity
to ESD-which dropped from 1000 volts to less than 20 volts. The result was
catastrophic.

Complete article at


http://cr.pennnet.com/Articles/Artic...ICLE_ID=210414