Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
1998-11-10
2001-11-27
Hughes, S. Thomas (Department: 3726)
Metal working
Method of mechanical manufacture
Electrical device making
C029S407010, C029S407050, C029S593000, C029S603090, C029S603120, C029S254000, C029S254000
Reexamination Certificate
active
06321440
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to laser scribing tools for scribing semiconductor chips and the like. More particularly, it relates to a method for scribing magnetic sliders so that they have an accurate curvature on the air bearing surface (crown curvature and camber curvature).
BACKGROUND OF THE INVENTION
Hard drives utilizing magnetic data storage disks are used extensively in the computer industry. Each magnetic data storage disk in a hard drive has an associated slider which is used to magnetically read and write on a disk surface. In operation, the magnetic data storage disks are rotated and a slider is held very close to the surface of each disk surface. The motion of the disk past the slider allows data communication between the slider and disk surface.
The distance between the slider and disk must be accurately controlled. Typically, the slider is shaped to fly upon a cushion of moving air formed by the rapidly moving disk surface. The surface of the slider closest to the disk surface is called an air bearing surface. The air bearing surface has a shape which is designed to provide a small but stable flying height between the slider and disk. The slider must not touch the disk surface during operation because damage can result. Also, it is desirable to maintain as small a flying height as possible, because this increases the amount of data which can be stored. As flying height is reduced, it becomes increasingly difficult to maintain the flying height accuracy to the degree required for reliable recording and reading of data.
The shape of the slider has a substantial effect upon fly height. More specifically, the flying height is dependent upon the average curvature of the air bearing surface of the slider. The curvature of the air bearing surface is often affected by the manufacturing processes used to make the slider. Lapping of the slider (either the air bearing surface or a surface opposite to the air bearing surface) often causes stress variations in the slider which distort the shape of the air bearing surface. After lapping, it is almost always necessary (for high storage density applications) to adjust the curvature of the air bearing surface to a desired target curvature.
U.S. Pat. No. 5,266,769 to Deshpande et al. discloses a method of adjusting the curvature of the air bearing surface of a slider by scribing a back surface of the slider. The scribing removes material from the back surface, thereby releasing internal stress in the slider and controllably changing the curvature of the air bearing surface. Scribing may be performed with a laser, sandblasting tool or the like. A curvature measuring tool may monitor the curvature of the air bearing surface as material is removed, thereby providing feedback control if desired. A problem with the method of Deshpande is that sliders are most efficiently made in rows, and each slider in a row may have a different amount of stress. This means that each slider must have a different amount of material removed in order for the sliders to have the same air bearing surface curvature. Deshpande does not disclose a method for individually controlling the curvature of sliders in a row. Deshpande assumes that all sliders in a row require the same curvature adjustment. It would be an advance in the art to provide a row of sliders with individually controlled curvature.
Further, Deshpande does not disclose specific, advantageous methods of implementing curvature control. The curvature of a slider may only be changed ‘in one direction’ by removal of material from the back side of the slider and so the target curvature must not be overstepped. Deshpande does not disclose a method for curvature adjustment which assures that the target curvature is not overstepped. Also, the changes in curvature caused by material removal from the back surface of the slider are not entirely predictable. When large changes in curvature are necessary, the final curvature of the slider may be rather inaccurate. Deshpande does not disclose a method which provides the same accuracy in curvature control for large and small curvature adjustments. Therefore, there are many improvements which can be made to the method of Deshpande.
OBJECTS AND ADVANTAGES OF THE INVENTION
Accordingly, it is a primary object of the present invention to provide a method of adjusting curvature of a slider that:
1) can be used to adjust the curvature of individual sliders still joined in a row;
2) assures that a target curvature is not overstepped;
3) provides the same accuracy in final curvature for a wide range in the amount of curvature adjustment required.
These and other objects and advantages will be apparent upon reading the following description and accompanying drawings.
SUMMARY OF THE INVENTION
These objects and advantages are attained by a method for adjusting the curvature of an air bearing surface (ABS) of a slider to match a final target curvature. The slider has a back surface opposite the ABS. The method includes the steps of measuring the ABS curvature, determining a curvature difference between the measured curvature and final target curvature, and scribing lines to correct for a predetermined percentage of the curvature difference. The steps of measuring, determining, and scribing are repeated in at least two installments. The predetermined percentage may be different or the same in succeeding installments. The final installment corrects for 100% of the remaining curvature difference.
Preferably, the scribe lines are spaced apart by a distance sufficient to ensure that the scribe lines act independently to affect the curvature of the ABS. The scribe lines are spaced apart by a distance in the range of about 5-200 microns, preferably in the range of about 20-80 microns, and most preferably in the range of about 35-55 microns.
Preferably, the method includes the step of establishing a set of scribe line locations on the back surface where scribe lines can be located. The scribe line locations are spaced apart by a distance sufficient to ensure that neighboring scribe lines act independently. Also preferably, in each installment, the average curvature change per scribe line is substantially equal to an average curvature contribution for all the scribe line locations.
In an alternative embodiment of the present method, each installment has the same steps of measuring, determining and scribing, but each installment changes the curvature to an intermediate target curvature. The intermediate target curvatures are predetermined. In a process using three installments, for example, there will be two intermediate target curvatures. The target curvature for the third and final installment is the final target curvature. Scribe lines are scribed at the predetermined scribe line locations.
The present invention also includes a method for providing a desired curvature change in an ABS surface of a slider. The method includes the steps of establishing scribe line locations on the back surface of the slider. The scribe line locations are sufficiently spaced apart such that neighboring scribe lines at neighboring scribe line locations act independently. Next, a curvature contribution for each scribe line location is determined. Next, scribe line locations are selected such that a sum of the curvature contributions of the selected locations is equal to the desired curvature change. Finally, scribe lines are scribed at the selected locations.
Preferably, the scribe line locations are spaced apart by a distance sufficient to ensure that neighboring scribe lines at neighboring locations act independently.
Also preferably, scribe line locations are selected such that the average curvature change per scribe line is substantially equal to an average curvature contribution for all scribe line locations.
All methods of the present invention can be applied to both crown curvature and camber curvature.
REFERENCES:
patent: 3685216 (1972-08-01), Frey et al.
patent: 4835361 (1989-05-01), Strom
patent: 4912883 (1990-04-01), Chang et al.
patent: 4914868 (1990-04-01),
Crawforth Linden James
Poon Chie Ching
Tam Andrew Ching
Hughes S. Thomas
International Business Machines - Corporation
Omgba Essama
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