Method for detection of end of grinding of a thin layer magnetic

Details Method for detection of end of grinding of a thin layer magnetic Method for detection of end of grinding of a thin layer magnetic

1989-06-26

1991-05-07

Powell, William A.

Adhesive bonding and miscellaneous chemical manufacture

Delaminating processes adapted for specified product

Delaminating in preparation for post processing recycling step

29603, 156645, 156656, 156664, 156667, B44C 122, C23F 100, C03C 1500, C03C 2506

Patent

active

050133942

DESCRIPTION:

BRIEF SUMMARY
The present invention concerns a method for the detection of the end of grinding of a magnetic head made according to the so-called thin layer techniques.
Thin layer magnetic heads are made by successive deposits of magnetic, dielectrical and conductive materials. These layers undergo final operations for etching and grinding the magnetic poles.
The depth of the gap is a geometrical characteristic, the checking of which is fundamental for magnetic heads and, especially, for those using technologies for the deposition and etching of thin layers. In effect whereas, in a massive magnetic head (VHS or audio head for example) or in a head of the type having, on each side of the gap, a magnetic metal alloy (also called a magnetic metal alloy in gap head), the efficiency hardly varies with the depth of the gap (typically 0.05 dB/.mu.), this is not so for heads using thin layer technologies (variation typically around 0.2 dB/.mu.). In the latter case, it proves to be necessary to perform very precise controls on this dimension while making the head. Furthermore the values of the depth of the gap differ greatly according to the technological method used: they are of the order of 20 to 40.mu. for a massive head and of the order of 2 to 10.mu. for a thin layer head. For thin layer heads, this small depth causes a very appreciable reduction in the section of the gap and, hence, a reduction in the thermal noise related to the real part of the impedance of the head. For, the thermal noise is proportionate to the section of the gap.
It is therefore very important to be able to perform, repetitive, reliable and precise controls on the depth of the gap during the stage for finishing the active face of the head. In order to achieve this result, many methods are presently used by those skilled in the art. It is possible, during the grinding step, to measure the impedance of the head to adjust it to the desired value. It is also possible to detect the opening of the magnetic circuit of the head by measuring the inductance at the terminals of the coil. There are also optical methods for checking the depth of the gap. All these methods are generally well mastered, but they have major drawbacks: they are difficult to implement and the measured values change constantly during the process of establishing the size of the depth of the gap. The precision obtained is relatively low: about 0.5.mu. for a gap depth of the order of 2.mu..
In order to overcome these drawbacks, the invention proposes a method for the detection of the end of grinding by measurement of the variation of a signal, the sizing of the depth causing an all or nothing type of variation in the signal. The variation in the signal comes into play at the precise instant when the desired dimension is achieved.
The invention therefore has, as an object, a method for the detection of the end of grinding of at least one thin layer magnetic head, said head comprising, at the stage of implementation of said method, an active face, formed by two magnetic poles separated by a gap, the detection being obtained through the interruption of an electrical circuit, characterized in that it comprises the following steps:
deposition of a conductive layer on the entire active face to form said electrical circuit;
etching of the active face coated with said conductive layer;
deposition of a layer of dielectric material on the etched active face;
grinding of the active face starting from the face that is free of the layer of dielectric material until total removal of that part of the conductive layer located above said gap, said removal being detected by the sudden variation in resistivity between the two magnetic poles.
The invention will be better understood and other advantages will emerge from the following description, given as a non-restrictive example, and through the appended figures, of which:
FIG. 1 shows a simplified structure of a planar head;
FIGS. 2 to 6 represent different steps of the method according to the invention applied to the structure shown in FIG. 1.
The method ac

REFERENCES:
patent: 3495049 (1970-02-01), Humphreys et al.
patent: 3938193 (1976-02-01), Sargunar
patent: 4670972 (1987-06-01), Sakakima
Patent Abstracts of Japan, vol. 10, No. 312, (P-509)(2368), Oct. 23, 1986, & JP, A. 61122909 (Sanyo) Jun. 10, 1986.

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