Electric heating – Metal heating – Cutting or disintegrating
Reexamination Certificate
1999-01-13
2001-06-05
Evans, Geoffrey S. (Department: 1725)
Electric heating
Metal heating
Cutting or disintegrating
C219S069120
Reexamination Certificate
active
06242709
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to respective methods for manufacturing conductive wafers, thin-plate sintered compacts and ceramic substrates for a thin-film magnetic head and to a method for machining conductive wafers.
In recent years, a thin-film magnetic head has been used for various types of magnetic recording devices such as a hard disk drive (HDD) and a floppy disk drive (FDD) for a computer. As a thin-film magnetic head has been downsized, the thickness of a wafer, used as a substrate for such a head, has also been reduced. Since a substrate for a magnetic head is required to have high hardness and high abrasion resistance, Al
2
O
3
—Ti, SiC and ZrO
2
ceramics are currently used therefor. For example, an ALTIC wafer, widely used currently as a ceramic substrate for a magnetic head, is manufactured by sintering a powder green compact of raw materials such as alumina (Al
2
O
3
) and titanium carbide (TiC). An ALTIC wafer having a thickness of about 1.2 mm is practically used today as a substrate for a magnetic head. In order to realize magnetic recording with even higher density, however, the development of an even thinner and further planarized ceramic substrate is awaited.
A sintering process is indispensable for manufacturing a ceramic substrate. However, in accordance with currently available techniques, a sintered ceramic substrate is often deformed, e.g., warped, during the sintering process. One of the main reasons is the non-uniform temperature distribution of the sintered compact during the sintering process. It is now known that the thinner the thickness of a ceramic substrate to be formed is (e.g., if the thickness is equal to or smaller than 2 mm), the more warped the substrate is likely to get. Conventionally, such a “warp” has been eliminated by planarizing the surface of a substrate through polishing.
A sintered compact used as a substrate for a thin-film magnetic head has extremely high hardness (the Vickers hardness thereof is 2,000 or more). Accordingly, it takes a very long time to polish such a sintered compact. For example, sometimes it takes several tens of hours to reduce the thickness of a plate sintered compact from 2 mm to 1.2 mm by polishing it. On the other hand, the thinner a sintered compact is, the less rigid and the more warped the sintered compact gets. Thus, if an even thinner ceramic substrate is required in the near future, the conventional method for forming a ceramic substrate will take an enormous amount of time to perform various post-sintering processes like polishing. Accordingly, it is expected that the productivity will drastically decrease in such a case. In other words, this problem constitutes a great obstacle to further increasing the productivity of a thin-film magnetic head.
It is noted that the “warp” problem is not unique to a ceramic substrate for a thin-film magnetic head, but possibly happens during the formation of any thin-plate sintered compact in general. Therefore, the above-described problems (that is, polishing for eliminating such a warp takes a lot of time and increases the manufacturing cost) are generally true of any method for manufacturing a sintered compact involving a sintering process (e.g., a method for manufacturing a sintered magnet).
SUMMARY OF THE INVENTION
In view of these problems, the present invention was made to provide respective methods for manufacturing conductive wafers, thin-plate sintered compacts and ceramic substrates for a thin-film magnetic head, and a method for machining conductive wafers, with a long polishing time, conventionally required for eliminating a “warp”, shortened by reducing the “warp” of a sintered compact.
A method for manufacturing thin-plate sintered compacts according to the present invention includes the steps of: forming a conductive sintered compact to have such a thickness as to cause a warp to a negligible degree; and slicing the conductive sintered compact, thereby cutting and dividing the conductive sintered compact into at least two wafers.
A method for manufacturing conductive wafers according to the present invention includes the steps of: forming a conductive sintered compact having two surfaces that are substantially parallel to each other; and slicing the conductive sintered compact along at least one plane substantially parallel to the two surfaces of the conductive sintered compact, thereby cutting and dividing the conductive sintered compact into at least two conductive wafers.
Another method for manufacturing thin-plate sintered compacts according to the present invention includes the steps of: forming a conductive sintered compact having a Vickers hardness of 2,000 or more by sintering raw material powder; and slicing the conductive sintered compact by wire electrical-discharge machining, thereby forming at least two thin-plate sintered compacts, each said thin-plate sintered compact having a thickness smaller than that of the conductive sintered compact.
Still another method for manufacturing thin-plate sintered compacts according to the present invention includes the steps of: forming a sintered compact having a Vickers hardness of 2,000 or more by sintering a raw material powder; and slicing the sintered compact, thereby forming at least two thin-plate sintered compacts, each said thin-plate sintered compact having a thickness smaller than that of the sintered compact.
A method for manufacturing ceramic substrates for a thin-film magnetic head according to the present invention includes the steps of: forming a conductive sintered compact having two surfaces that are substantially parallel to each other by sintering raw material powder and polishing a resulting sintered compact; and slicing the conductive sintered compact along at least one plane substantially parallel to the two surfaces of the conductive sintered compact, thereby cutting and dividing the conductive sintered compact into at least two ceramic substrates for a thin-film magnetic head.
A method for machining conductive wafers according to the present invention includes the steps of: setting a conductive sintered compact into an electrical-discharge wire cutting machine; and cutting and dividing the conductive sintered compact into a plurality of conductive wafers by slicing the conductive sintered compact with the application of a voltage between a wire of the electrical-discharge wire cutting machine and the conductive sintered compact while one of the wire and the conductive sintered compact is moved against the other. Each said conductive wafer has a crown of 50 &mgr;m or less and a thickness that is one half or less of the thickness of the conductive sintered compact.
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Chikuba Masanori
Fukuda Makoto
Costellia' Jeffrey L.
Evans Geoffrey S.
Nixon & Peabody LLP
Sumitomo Special Metals Co. Ltd.
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