BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a top view of an embodiment of a hard disk drive;
FIG. 2 is a side view showing an instrument tip creating a scribe line in a surface of a disk;
FIG. 3 is a graph showing different scribe depths;
FIG. 4 is an enlarged side view showing a scribed line in the disk;
FIG. 5 is a top view showing scribe lines in the disk;
FIG. 6 is an enlarged side view showing movement of the lubricant into the scribe line.
DETAILED DESCRIPTION
Disclosed is a method for measuring the mobility of a lubricant located on the top surface of a disk used in hard disk drives. The method includes forming one or more scribe lines in a lubricant layer of the disk. The disk is then spun on a spin stand where lubricant moves in response to the centrifugal forces of the spinning disk. The disk is removed from the spin stand and the height of lubricant that moved into the scribe line is measured to determine lubricant mobility.
Referring to the drawings more particularly by reference numbers, FIG. 1 shows an embodiment of a hard disk drive 10 of the present invention. The disk drive 10 may include one or more magnetic disks 12 that are rotated by a spindle motor 14. The spindle motor 14 may be mounted to a base plate 16. The disk drive 10 may include a plurality of heads 20 located adjacent to the disks 12. The heads 20 are used to magnetize and sense the magnetic field of the disk as is known in the art. The disk drive 10 typically includes an actuator 22 that is used to move the heads 20 relative to the disk.
The disks 12 are covered with a layer of lubricant to minimize friction between the heads 20 and disk surface. During rotation of the disks 12 the lubricant may move in both a radial and circumferential direction due to the centrifugal forces associated with the spinning disk.
FIGS. 2-6 show a method for determining lubricant mobility. A tip 50 of an instrument 52 may be used to cut, at an atomic level, a scribe line(s) in both the radial and circumferential orientations 54 in a layer of lubricant 56 on the disk 12. The instrument 52 may be a product sold by KLA-Tencor of San Jose, Calif. under the designation Candela 6100. Optical X-Beam Surface Analyzer that is equipped with a diamond tip. The instrument 52 can measure surface depths by measuring changes in reflectivity of the disk surface. The scribe line(s) 54 may have different depths as shown by the graph in FIG. 3. The scribe lines may have a width no greater than 10 microns. The small width allows for improved resolution when measuring the movement of the lubricant.
After the scribe line 54 is formed, the disk 12 is placed on a spin stand (not shown). By way of example, the disk 12 may be placed on a Vena spin stand tester and rotated at 20,000 revolutions per minute. Rotation of the disk causes lubricant to move across the disk. As shown in FIG. 6, lubricant 56 moves into the scribe line 54. The height of the lubricant that moves into the scribe line 54 can be measured with the instrument 52. The height of the lubricant is used to determine lubricant mobility. By way of example, the height of lubricant within the scribe line can be used as a lubricant mobility index.
As shown in FIG. 4, scribing the disk with the tip 50 creates a sharp edge at the boundary between the lubricant and the area with no lubricant. This allows for more accurate readings on the amount of lubricant that flows into the scribed area. If the boundary had a slope, the slope would have to be measured and accounted for, or there would be an inaccurate measurement of lubricant flow.
As shown in FIG. 3, a plurality of scribe lines 54 may be formed in the disk. The multiple scribe lines 54 can be measured with a single scan of the instrument 52. This allows for the measurement of multiple data points from a single disk. This is to be distinguished from the prior art where different disks would have to be washed, spun and measured to obtain multiple data points.
The scribe lines 54 can be located at the same radial location on the disk 12. This allows for multiple data points for circumferential movement of the lubricant. Circumferential movement within a scribe line 54 can be determined by measuring lubricant height across the length of the scribe line 54.
When spinning the disk, the head flying can be coupled with the spinning disk to study lube movement under the slider air bearing force and disk spinning centrifugal force. The ratio of these two forces can be adjusted by adjusting the disk RPM and pole-tip protrusion. By adjusting the ratio of the two forces, the lube spreading mechanisms can be fully understood under each lube movement force.
The spin test also could be conducted in different environmental conditions to study the lube mobility property at different temperature and humidity conditions.
While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention, and that this invention not be limited to the specific constructions and arrangements shown and described, since various other modifications may occur to those ordinarily skilled in the art.
Patent Application
20080072662
