Dynamic magnetic information storage or retrieval – Head – Core
Reexamination Certificate
1997-01-03
2001-04-17
Renner, Craig A. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Core
C360S122000, C360S234700, C360S235100, C360S235400
Reexamination Certificate
active
06219200
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a thin-film magnetic head, and a method of manufacturing the magnetic head. More particularly, it relates to a method of polishing a surface to-be-worked made up of different kinds of materials having unequal hardness values, such as the air bearing surface or floating surface of a thin-film magnetic head. Especially, it relates to a method of manufacturing a thin-film magnetic head so as to be able to protrude the end face of a magnetic film beyond the air bearing surface of the head.
2. Description of the Related Art
In recent years, as an expedient for enhancing the record density of a magnetic record medium in a magnetic recording/reproducing system, research has been carried out on the approach of a magnetic head to the magnetic record medium.
FIG. 3
illustrates the positional relationship between the magnetic head and the magnetic record medium in the magnetic recording/reproducing system in the prior art. As clearly shown in
FIG. 3
, the air bearing surface
2
of the thin-film magnetic head
1
is afloat above the magnetic record medium
21
by a certain flying height
29
. In this regard, it has been known that a recorded bit length on the magnetic record medium
21
is in a proportional relationship with the flying height
29
of the magnetic head
1
as illustrated in FIG.
4
. In the case of
FIG. 4
mentioned by way of example, the bit length increases 0.05 [&mgr;m] as the flying height
29
increases 0.01 [&mgr;m]. For the increase of the record density, therefore, it is desired to decrease the flying height
29
of the magnetic head
1
as much as possible.
Meanwhile, the thin-film magnetic head
1
includes a protective film
12
and a magnetic film
11
which are stacked on a substrate
13
as illustrated in
FIGS. 2A and 2B
and FIG.
3
. The air bearing surface
2
of the magnetic head
1
is formed by so-called “lapping”. Lapping is a method wherein, while a lapping fluid which contains diamond abrasive grains is being dropped onto a lap (lapping plate) made of a soft metal, the workpiece (the magnetic head
1
as a semi-finished product) held in position by a holder is slid under pressure so as to polish and form the air bearing surface
2
of the magnetic head
1
. The lapping method is stated in, for example, “TRIGGER 88-1 (1988)” published by Kabushiki-Kaisha Nikkan K{overscore (o)}gy{overscore (o)} Shinbun-sha, p. 51.
Besides, as disclosed in the official gazette of Japanese Patent Application Laid-open No. 178910/1992, there has been proposed a method wherein the air bearing surface of a thin-film magnetic head is formed so as to protrude a magnetic film beyond this air bearing surface by so-called “float polishing” which polishes the workpiece (the magnetic head as a semi-finished product) without pressing abrasive grains against the workpiece.
All of the prior-art techniques, however, have been problematic as stated below.
When the surface of the workpiece made up of the plurality of members or constituents of the substrate
13
, protective film
12
and magnetic film
11
having hardness values unequal to one another, such as the air bearing surface
2
of the thin-film magnetic head
1
, is polished by the conventional lapping method utilizing the diamond abrasive grains, there arises the problem that a pole tip recession
22
appears in the worked or finished surface as shown in FIG.
2
B and FIG.
3
.
The appearance of the pole tip recession
22
is attributed to the fact that, while the workpiece made up of the plurality of members having the unequal hardness values is subject to the finish working under an identical lapping pressure, the intrusional depths of the abrasive grains (namely, the amounts to which the abrasive grains bite into the members) become different due to the differences of the hardness values of the materials of the individual members. Generally in the thin-film magnetic head, the material of the magnetic film (
11
in
FIG. 2B
or
FIG. 3
) is softer than those of the protective film (
12
) and substrate (
13
). By way of example, the thin-film magnetic head
1
in the prior art is constructed of the magnetic film
11
whose Vickers' hardness number is about 200 [kgf/mm
2
], and the protective film
12
and substrate
13
whose Vickers' hardness numbers are 1300 [kgf/mm
2
] or above. In this magnetic head
1
, the pole tip recession
22
having appeared between the magnetic film
11
and the substrate
13
is in the order of 0.03 [&mgr;m].
As seen from
FIG. 3
, when such a pole tip recession
22
exists, the magnetic film
11
cannot approach the record medium
21
in correspondence with the recession
22
, and hence, the flying height
29
of the thin-film magnetic head
1
cannot be, in effect, reduced. More specifically, in the example mentioned in
FIG. 4
, when the pole tip recession of 0.03 [&mgr;m] exists in the air bearing surface of the magnetic head, the bit length becomes 0.15 [&mgr;m] greater than in the nonexistence of this recession, and the record density of the magnetic record medium (
21
in
FIG. 3
) is lowered correspondingly.
On the other hand, according to the float polishing method as disclosed in the official gazette of Japanese Patent Application Laid-open No. 178910/1992, the magnetic film can be protruded beyond the air bearing surface, whereby the flying height of the magnetic head can be decreased. Since, however, the float polishing method does not press the abrasive grains against the surface to-be-worked or workpiece, it has the problems of a low abrasion working rate and a low production efficiency. Moreover, the float polishing method features that the edges of the air bearing surface are worked more efficiently. This leads to the problem that the edges of the air bearing surface of the magnetic head are abrasively rounded, so that it is difficult to form a protective film of carbon, silicon or the like at a uniform thickness on the air bearing surface.
SUMMARY OF THE INVENTION
The present invention has for its first object to provide a method of efficiently manufacturing a thin-film magnetic head in which the end face of a magnetic film lies even with, or projects beyond, that of a substrate within the air bearing surface of the magnetic head.
Further, the present invention has for its second object to provide a method of polishing a surface made up of a plurality of members of unequal hardness values, without recessing a surface part which corresponds to the member of lower hardness.
The inventors studied the mechanisms of the working processes of individual members of unequal hardness values during a lapping operation, and have attained to the present invention.
When the plurality of members to-be-worked exhibiting unequal hardness values are lapped with a predetermined lapping force (a force with which the lap or the lapping plate is pressed), the intrusional depths of abrasive grains become different in the respective members to-be-worked, and the abrasion working rates of the respective members are different. On the other hand, when any of the members are lapped with various lapping forces, the lapping forces and the abrasion working rates of the member are in a substantially proportional relationship.
Nevertheless, in the case of lapping the surface of a workpiece which is constructed of the plurality of members of unequal hardness values, the lapping force cannot be changed for the respective members, and the intrusional depths of the abrasive grains become different in the respective members, so that pole tip recessions appear.
Meanwhile, it is known that chip or removal material made by lapping are not made of the material of the workpiece itself intruded and scratched by the abrasive grains, but that a hydroxide is flushed as the chip due to a chemical reaction in which the surface of the piece to-be-lapped is turned into the hydroxide, as illustrated in FIG.
5
.
The inventors have discovered out that, using t
Fujisawa Masayasu
Isono Yukihiro
Waki Yoshiharu
Hitachi , Ltd.
Mattingly Stanger & Malur, P.C.
Renner Craig A.
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