Electricity: measuring and testing – Magnetic – Magnetic information storage element testing
Reexamination Certificate
1999-11-04
2001-08-28
Snow, Walter E. (Department: 2862)
Electricity: measuring and testing
Magnetic
Magnetic information storage element testing
C360S031000, C369S053130
Reexamination Certificate
active
06281677
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to methods for marking defects in thin film hard disks, and more particularly to the use of precise coordinates and DC erase on the hard disk to locate and identify the defect and utilizing ferromagnetic fluid for visual identification of the defect.
2. Description of the Prior Art
The detection, location and analysis of defects on the surface of hard disks has become an increasingly difficult problem where data bit sizes have decreased such that sub-micron sized asperities are of sufficient size to constitute defects. A read/write head may be used for the detection and location of such defects, as is taught in U.S. Pat. No. 4,635,139, entitled Asperity Burst Writer, issued Jan. 6, 1987 to Nguyen et al. Such asperity location and marking methods have provided adequate results in the past, however, the difficulty in locating and marking sub-micron sized defects has necessitated improved methods for disk marking for defect location. The present invention avoids writing, or erasing over a defect and avoids the application of ferromagnetic fluid on top of the defect where steps are taken to visually locate the defect.
SUMMARY OF THE INVENTION
The present invention is a method for defect locating, marking and analysis of thin film hard disks. Initially, the hard disk is disposed in a disk drive and the disk is formatted with sector identification lines and data written into data tracks. During the data writing process a disk surface defect is identified by its sector, track and byte location. The hard disk is then marked such that the defect can be located at a later time. The disk marking process includes erasing certain portions of the disk in the sector in which the defect is located. Significantly, the precise location of the defect is not erased. The disk marking process includes erasing the inner tracks of the sector in which the defect is located, erasing individual data tracks within the sector at intervals of approximately 30 tracks out to the track where the defect is located, and erasing a portion of the track in which the defect is located out to but not including the defect. Additionally, a band of adjacent tracks may be erased radially inwardly from the track in which the defect is located, and a second band of adjacent tracks may be erased radially outwardly from the track in which the defect is located. The erased bands aid in later locating the defect. After the defect locating erasures have been completed for each defect found on the disk, the disk is removed from the hard disk drive for further analysis.
The disk is then placed on the stage of a microscope and ferromagnetic fluid is applied to the disk in order to make the erased tracks visible. Initially, ferromagnetic fluid is applied to the inner tracks of the disk to locate sectors with inner track erasures as an indication that a defect exists in that sector. Next the ferromagnetic fluid is applied proximate the sector identification line radially outwardly such that the erased index lines visually appear. The ferromagnetic fluid is applied radially outwardly until the two erased bands of adjacent tracks become visible, such that the track containing the defect is disposed between the two erased bands. Thereafter the ferromagnetic fluid is applied to the erased portion of the track that includes the defect. The ferromagnetic fluid is applied out to the end of the track erasure, without application of ferromagnetic fluid to the defect itself.
As a result, the specific defect is visually located for further analysis in its original condition, without disk erasure over it, and without the application of ferromagnetic fluid upon it. Because the defect is in its original condition a more precise and accurate analysis of the nature of the defect can be made.
It is an advantage of the present invention that a disk having defects thereon can be marked for later location and analysis of the defects.
It is another advantage of the present invention that a disk having defects located thereon can be marked with DC erasure and exposed to ferromagnetic fluid, without DC erasure over the defect and without the application of ferromagnetic fluid to the defect.
It is a further advantage of the present invention that a method for locating defects on a hard disk in a disk drive has been developed in which the marking of defect locations is simple and automatically accomplished by the hard disk drive.
It is yet another advantage of the present invention that a method for marking and analysis of defects on a hard disk has been developed that is relatively rapid and simple to accomplish.
It is yet a further advantage of the present invention that a method for marking and analyzing defects on a hard disk has been developed in which the defects are analyzed in the original condition.
These and other advantages of the present invention will be well understood by those skilled in the art upon reviewing the following detailed description which makes reference to the several figures of the drawings.
REFERENCES:
patent: 4635139 (1987-01-01), Nguyen et al.
patent: 4896277 (1990-01-01), Fountain et al.
patent: 5168412 (1992-12-01), Doan et al.
patent: 5247254 (1993-09-01), Huber et al.
patent: 5581021 (1996-12-01), Flechsig et al.
Cosci Michael Craig
Green Paul Marion
Oliver Lisa Ann
Guillot Robert O.
International Business Machines - Corporation
Oppenheimer Wolff & Donnelly LLP
Snow Walter E.
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