Measurement of the effects of ionizer imbalance and proximity to ground in MR head handling

Ionizers are employed to neutralize the static charge on parts used in disk drive manufacturing. Corona ionizers reduce static charges, lowering the voltages on sensitive components such as MR heads to a small but nonzero voltage. ANSI EOS/ESD S3.1-1991 attempts to characterize this voltage by defining the offset voltage measured with a charged plate monitor. Unfortunately, the voltage on the MR head can be either higher or lower than the offset voltage, depending upon its location and the proximity of grounded objects. In this presentation, the relationship between the location of the part, the offset voltage and the damage threshold are measured and discussed. For objects located more than 15 cm (6") above the work surface, the accepted 10 V damage threshold may underestimate the hazard. When the object is located a few mm (/spl sim/1/8-1/4") from the work surface, considerably more than 10 V of offset voltage is required to damage an MR head.