Head slap characterization using optical surface analyzer

Details Head slap characterization using optical surface analyzer Head slap characterization using optical surface analyzer

2001-06-12

2003-04-29

Dang, Hung Xuan (Department: 2873)

Optics: measuring and testing

Inspection of flaws or impurities

Surface condition

C356S237300, C356S237100

Reexamination Certificate

active

06556292

ABSTRACT:

FIELD OF THE INVENTION
This application relates generally to the inspection of data storage disc surfaces and more particularly to a method and system for characterizing damage caused during a head slap event to a data storage disc surface using an optical surface analyzer.
BACKGROUND OF THE INVENTION
Disc drive reliability and performance have become increasingly important in today's technology marketplace. Original Equipment Manufacturers (OEMs), as well as end consumers, place high demands on disc drives, requiring the disc drives to function under a variety of environmental conditions and stresses.
During the installation and use of a disc drive, the disc drive may be subjected to a multitude of stresses. One such stress is a shock to the disc drive. OEMs routinely conduct and require that disc drives pass a battery of shock tests. Shock tests can include such tests as topple drop shock, non-operational shock, operational shock, etc. A disc drive is required to endure these shock tests and continue to perform to the customer's satisfaction. In addition, during product research and development stages, as well as during reliability testing, disc drive manufacturers routinely perform shock tests to ensure that current design and changes to the current design of the disc drive (e.g. actuator change, suspension change, slider process change, air-bearing surface design change, etc.) can meet or exceed shock test performance requirements.
One method of performing a shock test on a disc drive is termed “topple drop.” During a topple drop shock test, a first edge of the disc drive is placed on a resting surface and a second edge of the disc drive is elevated to a specified angle above the resting surface. The second edge of the disc drive is then allowed to drop from this elevated height to the resting surface below, thereby causing a shock to the disc drive. Topple drop shock tests can include drops from such angles as 60, 75, and 110 degrees. Topple drop shock tests may be performed while the disc drive is operational or while the disc drive is non-operational (i.e. the data storage disc may not be spinning and the heads may be in the parked position).
One of the failure modes in shock-induced stress testing such as topple drop is head slap. Head slap is a phenomenon in which a disc drive head, which is mounted on an actuator arm positioned within the disc drive, comes into contact with the magnetic recording media of the data storage disc. During normal operation, the head is mounted on the actuator arm so that the head can read the information stored on the magnetic recording media of the data storage disc. The head includes an air-bearing slider that allows the head to fly in close proximity, approximately 1 micro inch, above the surface of the data storage disc without actually contacting the surface. When a head slap event occurs, the head is caused to come into contact with the magnetic recording media of the disc drive. A head slap event can typically occur during a shock test such as topple drop because the motion created by the shock can cause the actuator arm on which the head is mounted to pivot, thereby causing the head to contact the magnetic recording media one or more times.
A head slap event is detrimental to a data storage disc because it can lead to mechanical damage to the head and magnetic recording media surface. Damage caused during a head slap event can also create debris from the destruction to the head and magnetic recording media surface that can become trapped underneath the air-bearing surface of the head. Particles trapped in this position while the disc drive is spinning can lead to deep scratches on the datastorage disc surface as well as a head crash.
One of the preferred methods to understand shock test performance in a disc drive is to analyze the severity of the damage caused during a head slap event to the magnetic recording media of the data storage disc surface. In general, if the damage caused to the surface is severe, it can be assumed that the slapping motion produced by the actuator arm and head is also severe and that damage to the head itself will be severe. As a result, the greater the severity of damage caused during the head slap event, the greater the chance that the disc drive will fail a shock test. Therefore, the ability to characterize the severity of the damage caused during a head slap event is very critical to the prediction of overall reliability of the disc drive from both a design and cost point of view.
A current method used to analyze a head slap event requires disassembly of the disc drive and placement of the data storage disc under an optical microscope for both low and high magnification surface scan analysis. Although this method can provide qualitative information on the severity of the head slap event, a disadvantage is that the results are crude, involving only a two-dimensional analysis of the data storage disc surface. Further, such an analysis is very subjective, requiring the operator conducting the analysis to make a determination as to the severity of damage to the surface using only this two-dimensional representation of the damage caused to the surface during the head slap event. Because different operators use different standards when evaluating and ranking the severity of a head slap event, significant variations in the analysis of the severity of a head slap event can occur. Finally, an analysis using an optical microscope can vary depending on microscope settings and lighting conditions.
Another method employed to analyze the severity of a head slap event is through the use of a contact profilometer. The contact profilometer includes a stylus that contacts and traces the surface of the data storage disc and thereby measures any imperfections on the data storage disc's surface. While this method can provide an accurate measurement of the surface damage, the process is slow, requiring a significant amount of time to characterize the damage depth of an entire head slap event region on a data storage disc. In addition, the stylus on the contact profilometer can potentially scratch the surface of the data storage disc as it traces the surface during analysis, thereby causing additional damage to the surface.
Accordingly there is a need for a system and method that can provide both accurate and efficient characterization of the severity of a head slap event.
SUMMARY OF THE INVENTION
Against this backdrop the present invention has been developed. A system and method have been created in which a commercial non-contact optical surface analyzer is utilized to characterize the severity of a head slap event through examination of the surface of a data storage disc. The optical surface analyzer selected has the capability of detecting surface topography using a high-resolution scanning head. When performing the analysis, the data storage disc may be removed from the disc drive and placed on a spindle of the optical surface analyzer. The scanning of the data storage disc surface topography takes place while the disc is spinning. A full scan of the entire data storage disc surface can be done, as well as a zoomed scan on a specific area of the data storage disc surface, thereby allowing for a higher resolution scan on the surface encompassing a head slap event. Data captured by the optical surface analyzer can then be exported to a commercial mathematical program for analysis and presentation.
There are several advantages to this system and method. First, the system and method are relatively fast and efficient, requiring less than one minute for a full data storage disc surface scan and approximately 45 seconds for a zoomed scan. Second, the optical surface analyzer equipment is capable of a sub-angstrom sized vertical resolution and a sub-micron sized lateral resolution scan range. This allows for higher resolution and a three-dimensional qualitative analysis of the head slap event area. Further, the data collected by the optical surface analyzer can allow for a quantitative analysis to be performed

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