Abrading – Work holder – Clamp
Reexamination Certificate
2000-07-24
2001-07-17
Hail, III, Joseph J. (Department: 3723)
Abrading
Work holder
Clamp
C451S028000, C451S405000
Reexamination Certificate
active
06261165
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a row carrier that is used for handling the heads during lapping of disk drive heads and is also used for handling the heads throughout the slider fabrication operation. A row of heads is bonded to the row carrier, which is, in turn, bonded to a row tool used on lapping machines. Due to the decrease in the overall dimensions of the advanced technology hard disk heads, there has be a long-standing need for better handing of the heads during the slider fabrication operation since direct handling of the heads can lead to significant yield losses. Heretofore, automated handling has not provided the improvement required for the slider fabrication operation. The row carrier has special importance during the lapping operation since it provides the opportunity to “dice” the heads prior to stripe height lapping. As the requirements for stripe height, crown, twist, PTR (pole tip recession), surface roughness, and cavity depth increase, there has been a long-standing need for improved lapping equipment and processes. The present row carrier permits “single-slider” lapping at the row level by dicing the rows prior to lapping. Lapping at the row level can increase the stresses in the row so that when the row is diced into individual heads, the head twist and the crown of the head change. This slight amount of twist and crown change is unacceptable after dicing for the emerging advanced heads being used in the hard disk drives. These emerging advanced heads will be in full production by 1999.
BACKGROUND OF THE INVENTION
The magnetic devices used to read and write data from the media on a hard disk are called sliders or heads. The previous generation of heads used a single inductive head for both the reading and writing, but such technology could not provide the necessary performance improvements for higher capacity hard disks in high volume production.
Winchester style sliders having thin film, magneto-resistive (MR), giant magneto-resistive (GMR), spin valve, or other types are now being used in magnetic hard disk storage systems to read information magnetically encoded in the magnetic media of the hard disk, with MR elements being the most popular. GMR heads are emerging quickly. A magnetic field extending from magnetic media caused by the spinning of the disk directly modulates the resistivity of the MR element. The change in resistance of the MR element normally is detected by passing a sense current through the MR element and then measuring the changes in voltage across the MR element. The resulting signal is used to recover the digital magnetically encoded information.
Read/write heads are produced by forming the separate read and write elements on a ceramic wafer in a deposition process somewhat similar to that used in the semiconductor industry. The wafer is cut into rows and the slider surfaces are then machined and lapped for proper magnetic and flying height characteristics as described in U.S. Pat. Nos. 5,607,340 and 5,620,356 both by Lackey et al. Tolerances are in the millionths of an inch and are getting tighter as areal densities (the storage bits per unit area) increase. The top surface of the wafer eventually becomes the back surface (trailing end) of the slider, perpendicular to the slider surface (air bearing surface) of the head that forms an air bearing with the media. The electrical resistance of the magneto-resistive material changes when a magnetic field sweeps there through. Normally, a MR head includes a MR stripe having upper and lower sides parallel to the spinning disk media, and conductors that overlay the ends of the stripe at right angles thereto. The conductors define the ends of the stripe and provide the electrical path for the sense current that is used to read the bits of magnetically information. The bits are recorded on the magnetic media by a separate inductive element. The inductive element is formed on the back surface of the head during the wafer process spaced from the MR element.
The change in resistance in a MR element occurs because the magnetic field causes the impedance vector of the material to rotate from a pure resistance, which has the effect of changing the resistance portion of the impedance vector. The effect in the present generation MR elements results in a maximum change in resistance, from 2 to 10%. In the next generations of multi-layer elements, each provide significant improvement, that is the newly available giant MR elements produce a &Dgr;R of about 10 to 30% and the planned colossus MR elements are expected to produce a &Dgr;R of over 30%. The more an MR element changes its resistance when exposed to a magnetic field, the smaller the MR sensor element can be, allowing narrower tracks and smaller magnetized areas, so that more data can be stored per unit area of magnetic media.
The signal to noise ratio of a MR element varies with ratio between the resistance, R, of the stripe and the change in resistance, &Dgr;R, of the element when subjected to the sweeping magnetic field. The thickness and to a lesser extent, the composition of a stripe are difficult to precisely control during the wafer fabrication process and therefore a precision lapping process that removes material from the flying surface of the slider is used to trim the height of the stripe to obtain maximum signal to noise ratio. If the stripe is too tall, the resistance is to low with respect to &Dgr;R and the voltage variations due to passing magnetic fields are too low, while if the stripe is too short, the resistance is too high, and the voltage variations due to passing magnetic fields again are too low. In the next generation of heads for drives with even higher areal densities (number of bits per square inch) requiring smaller MR elements, stripe height control to maximize signal output will become ever more critical, requiring lapping to magnetic performance and control on the order of a millionth of an inch. In addition, the stripe height lap and a final crown lap need to be combined since stripe height is reduced by the final crown lap.
MR elements are constructed by laying down thin stripes of MR material using wafer fabrication techniques similar to those developed in the semiconductor industry. The wafer is then sliced so that the MR stripes are positioned adjacent what will become the slider air bearing surface along what will become the trailing or back edge of the slider. Two conductors are formed over each end of the stripes so that the changing resistances due to magnetic fields impinging therein can be measured by a sensing current fed there across.
The most common control approach for lapping uses magneto-resistive electrical lapping guides (MR ELGs) that are formed at intervals along each row of MR elements. Generally MR ELGs are long MR elements with separate connections to the control systems for the lapping machines. In order to find the proper relationship between the stripe height and the measured resistance, it is necessary to calculate the “sheet resistance” of the MR element by finding the sheet resistance of the surrounding MR ELGs. There are many circuit designs for performing this type of calibration of the sheet resistance.
Unfortunately, the resistivity of the MR film varies over each wafer and more particularly over the length of a row of elements on the wafer. Therefore, the resistivity of MR elements distant from a MR ELG and the MR ELG may be different, creating an electrical offset error from head to head and from MR element and the MR ERG. Also, feedback from a MR ELG, which is physically offset from the MR element whose height it is trying to control, creates a physical offset error. This may seem minor, but if the distance between a MR ELG and the MR element whose height its is controlling is 0.008 inches and the desired control is 1 microinch, this is a ratio of 1 to 8,000. Some data scatter is also attributable to imprecise formation of the MR stripes.
One solution for variations in sheet resistivity and stripe variations suggested in the past, was to measure the r
Lackey Lauren D.
Lackey Stanley A
Advanced Imaging
Finch George W.
Hail III Joseph J.
Wilson Lee
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