COMBINED MANUFACTURING GLIDE TEST AND IN-SITU LOAD/UNLOAD DISK DAMAGE DETECTION
Original Publication Date: 2004-Jul-13
Included in the Prior Art Database: 2004-Jul-13
A method of detecting disk damage that has resulted from a faulty load/unload operation is disclosed.
COMBINED MANUFACTURING GLIDE TEST AND IN -SITU LOAD/UNLOAD DISK DAMAGE DETECTION
The use of a load/unload device in a disk drive to unload a slider with an integrated magnetoresistive (MR) read and a thin-film write head (referred to as the slider/head) from a disk surface when the disk drive is not in operation, eliminates at least two important failure modes. Firstly, slider-disk stiction failures are eliminated by removing the slider/head from the disk surface. Secondly, failures due to disk damage caused by the slider/head during non-operating shocks are eliminated. However, the load/unload process can still create disk damage if the slider/head for some reason makes contact with the disk during the load/unload operation. This can, for example, happen if the slider/head becomes contaminated with hard particles that contact the disk during loading. With the head/disk clearance only a few micro-inches in current state-of-the-art disk drives, it will be appreciated that only a minuscule particle on the slider/head can damage the disk surface when the slider/head is loaded. Similarly, a minuscule disk defect protruding above the disk surface can cause a damaging contact with the slider/head. Any slider/head contact with the disk surface is detrimental to reliability in the disk drive which is expected to operate flawlessly for more than hundreds of thousands hours.
The disk drive design problem is, therefore, twofold. It is necessary to design a disk drive so that head-disk contact is avoided or at least minimized. It is also necessary to detect any disk damage created by the load/unload process. This invention is focused on an in-situ device that can detect disk damage occurring during manufacturing or in the field.
Disk drives that use MR read heads can take advantage of the thermal response or baseline modulation of the MR head for measuring the head-to-disk spacing change. The thermal response is generated by variations in temperature of the MR element. The resistive MR element is supplied by a current from a constant current source which produces a voltage across the element. The MR head was designed to change its resistance in response to magnetic transitions written in tracks on the disk surface. The changes in resistance with a constant current passing through the MR element will cause a proportional change in the voltage across the MR element. There is, however, another independent cause of variation in the MR resistance which is due to changes temperature. The temperature changes are being caused by changes in spacing between the MR head and the disk surface. If the head-disk spacing decreases below nominal, the head cools and its resistance decreases (assuming a positive temperature coefficient) causing the voltage across the MR element to decrease. If the head-disk spacing increases above nominal, the head heats up and its resistance increases causing the voltage across the MR element to increase. The thermal response...