Main stream of magnetic heads mounted on a hard disc drive of a computer are thin film magnetic heads such as composite MR-inductive type heads in which inductive elements are used to write records and MR (magnetoresistive) elements or GMR (giant MR) elements are used to read records.
As shown in JP 2001-20044A, these thin film type magnetic heads are composed of a composite material comprised of a plurality of materials which have different hardness, for example, a substrate such as ALTIC (Al2O3—TiO2), a ceramic protective and/or insulation film such as alumina (Al2O3), and a metallic film which is a magnetic material such as permalloy (Fe—Ni) and Sendust (Fe—Al—Si) and the like.
In the process of producing thin film magnetic heads, a bar having a row of sliders is cut out from a wafer in which a number of electromagnetic transducing elements are arranged in the form of a matrix and an area of the surface of the bar that becomes ABS (air bearing surface) is lapped to obtain a flat surface.
The conventional grinding process of ABS of a slider is conducted while controlling the throat height (TH) and MR height.
The TH is one of the factors which affect recording performance of the thin film magnetic head and is a distance at a magnetic pole portion between the ABS and the terminus of the insulator which electrically isolates a thin film coil (TH shown in FIG. 3)
The MR height (MR-h) is one of the factors which affect reading performance of the thin film magnetic head and is a length of the MR element measured from the ABS (indicated as MR-h in FIG. 3). The details are described in JP2001-200244 A. In FIG. 3, the respective parts are as follows. 1: an ALTIC substrate, 2: an alumina insulation film, 3: a bottom shield film (Sendust, permalloy or the like), 4: an alumina film, 5: an MR element, 6: an alumina film, 7: a head shield film (permalloy or the like), 8: an alumina film, 9: write pole tip (permalloy or the like), 10: an alumina protective film, and 11: a coil conductor.
Conventionally, the lapping treatment of the surface which would become the ABS was performed by dripping a free abrasive slurry composition using diamond abrasive particles onto a face plate formed from a soft metal such as tin, and reciprocating a workpiece (which may be cut into a bar if necessary) to be polished on the face plate.
For examples, patent documents 1 and 2 disclose free abrasive slurry compositions suitable to form a flat surface which is to be used as ABS of thin film magnetic heads.
However, during the grinding operation using such free abrasive slurry composition, it was necessary to continue supplying the slurry composition without cessation and thus the consumption of the slurry composition was enormous, the cost was high and a particle problem that the abrasive particles pierce the surface to be polished occurred.
On the other hand, during the finish grinding operation of surfaces or end faces of precision parts, it is possible to use a grinding or polishing sheet which is composed of an abrasive layer formed on a substrate sheet. Since the grinding sheet retains fixed abrasive particles and accordingly any expensive free slurry composition is not necessary, one sheet may be used repeatedly. Therefore, the production cost can be reduced. For example, patent document 3 discloses a grinding sheet adapted to be used to finish surfaces or end faces of precision parts.
[Patent document 1] JP 11-302636 A
[Patent document 2] JP 2000-087011 A
[Patent document 3] JP 2003-103470 A