US3233308A

US3233308A - Method of manufacturing magnetic heads having very short gap lengths

Info

Publication number: US3233308A
Application number: US175536A
Authority: US
Inventors: Simon Duinker; Marinus Josephus Johannes Schoones
Original assignee: US Philips Corp
Current assignee: US Philips Corp; North American Philips Co Inc
Priority date: 1961-03-30
Filing date: 1962-02-26
Publication date: 1966-02-08
Anticipated expiration: 1983-02-08
Also published as: GB996957A; SE323818C; ES275904A1; DK104577C; AT242389B; NL263099A; CH415091A; SE323818B

Description

Feb. 8, 1966 s. DUINKER ET AL METHOD OF MANUFACTURING MAGNETIC HEADS HAVING VERY SHORT GAP LENGTHS Filed Feb. 26, 1962 smow DUINKERINVENTOR JULES OS MABRJINBS J J SCHOONES I? AGENT United States Patent 3,233,308 METHOD OF MANUFAQTURING MAGNETIC HEADS HAVlNG VERY SHORT GAP LENGTHS Simon Duinker, Jules Bus, and Martinus Josephus .lo-

hannes Schoones, Eindhoven, Netherlands, assignors to North American Philips (Iompany, Inc., New York, N.Y., a corporation of Delaware Filed Feb. 26, 1962, Ser. No. 175,536 Claims priority, application Netherlands, Mar. 30, 1.961, 263,099 3 Claims. (Cl. 29155.5)

This invention relates to a method of manufacturing magnetic heads. More particularly, it relates to a method of manufacture of such heads which have very short gap lengths, the method providing a head which is mechanically strong and magnetically efficient.

The recording density required of some magnetic recordings has become such that they can only be recorded and reproduced with the aid of heads having very short gap lengths, for example from 1 to 2 microns. To enable the gap walls to resist the forces occurring during the process of shaping the pole face of the head by grinding and polishing, their depth, corresponding to the height of the gap, has to be at least 150 microns. If both walls consist of a material having a high magnetic reluctance which is generally used in manufacturing heads of the type under consideration, for example ferrite, the efiiciency of the head is appreciably lower than that of heads having longer gap lengths. This is due to the fact that in the head having a short but comparatively deep gap the magnetic reluctance of the useful path of the lines of magnetic flux, i.e., the path through the magnetic record carrier, is large compared with the magnetic reluctance of the gap. To obtain a satisfactory efficiency with a gap length of from 1 to 2 microns the gap height consequently has to be limited to about microns; this value of gap height, however, is only a fraction of the value required in order to give the head sufiicient mechanical strength, the latter value being at least 150 microns.

It is the object of the present invention to provide a magnetic head having a very short gap length which is mechanically strong and magnetically eflicient. In accordance with one aspect of the invention, one of the two plates from which the pole pieces of the head are made is scored by grinding for part of the surface by which it engages the other plate; the depth of scoring appreciably exceeds the desired gap length of the finished head, and the recess formed by scoring is filled with a strengthening material having a comparatively high melting point, for example glass, after which the said surface is ground and polished; after the other plate has been ground and polished, it is pressed against the first plate with the interposition of a thin layer of non-magnetic filling material having a lower melting point than the strengthening material and having a thickness equal to the desired gap length; finally the poleface of the head is given the desired outline and the gap height is given the desired value by grinding and polishing. As used herein, the gap length is to be understood as the dimension indicated in the drawing; the gap height is the dimension of the gap in the vertical direction of the plane of the drawing. This dimensional nomenclature is that employed and shown in an article by S. Duinker, Durable High-Resolution Ferrite Transducer Heads Employing Bonding Glass Spacers in Philips Research Reports, vol. 15, 1960, pages 342-367; see especially FIG. 1 of this article.

The above mentioned recess provided by grinding the surface of one plate is preferably shaped so as to be rounded at the end nearer the future poleface of the head, the radius of the rounded end preferably being a few times greater than that corresponding to the depth of the recess in the said surface.

In order that the invention may readily be carried into effect, it will now be described more fully, by way of example, with reference to the accompanying drawing in which the single figure is a cross-sectional view to an enlarged scale of two plates of ferrite material prepared with the use of the invention and'secured to one another.

The figure shows two ferrite plates 1 and 2, the lefthand plate 1 being recessed as shown generally by reference numeral 4 by grinding to a depth of about microns. At the end adjacent the future poleface of the head, which is shown by a broken line 3, this recess 4 terminates in a rounded part 5 through a distance exceeding the desired gap height, for example through a distance of from 100 to 200 microns. The rounded part 5 serves to limit the magnetic reluctance of the flux lines traversing the gap 9 to a value which is not unnecessarily large.

Subsequently the recess 4 is filled with a layer 6 of glass or other non-magnetic strengthening material having a high melting point. The surface of the plate 1 to be engaged by the plate 2, which surface consequently largely consists of glass, now is ground fiat and polished and then coated with a film It of enamel or other suitable filling material for the future gap having substantially the thickness of the desired gap length, the melting point of this material being lower than that of the above mentioned strengthening material.

After the plate 2 has been ground flat and polished it is pressed against the plate 1 while heating until it firmly adheres thereto. The pressure employed is not so great as to force any appreciable amount of the gap forming material from between the plates. The poleface of the head is then given the desired outline and the gap is given the desired height of, for example, 25 microns by grinding and polishing, during which process the glass or other strengthening material 6 prevents the tapering part of the plate 1 from collapsing under the mechanical pressure inevitable in grinding and polishing. Owing to its high melting point the glass 6 retains the required strength during this operation. In order to prevent the gap edges from being chipped during this operation, the coetficient of expansion of the enamel in the gap 9 has to be matched to that of the ferrite.

Finally the plates may be firmly secured, with the poleface down, in a jig which is shaped in accordance with the pole-face, after which with the aid of asuitable grinding tool capable of being lowered in the plane of the gap so much material is removed by grinding as to produce the outline shown in the figure. It should be ensured that at the gap end a part of the plate 2 of at least microns high is left and that at this point the two plates are kept together by the portion 6 of the strengthening material which is not removed by grinding. The poleface outlines may be produced by any convenient method and they may alternatively be produced before the parts 1 and 2 are secured to one another. Between the extending legs 7 and 8 of the plates an amount of space is thus produced sufiicient to accommodate the windings of the head.

In the foregoing, the invention has been described solely in connection with a specific embodiment. Many modifications in the method will be readily obvious to those skilled in the art without departing from the spirit of the inventive concept, the scope of which is set forth in the appended claims.

What is claimed is:

l. A method of manufacturing a magnetic head having a very short gap length and composed of at least two magnetic plates forming the head pole pieces each having a surface and an adjoining edge, comprising: grinding a recess in the part of the edge of one of said plates which is adapted to confront the edge of the other plate to form the gap, said recess being ground to a depth substantially exceeding the desired gap length of the completed head and being located at a portion of said plate remote from where the surface and edge are joined, said grinding leaving intact a conjoining portion of said edge where the surface and edge are joined, filling said recess with a non-magnetic strengtheing material having a comparatively high melting point, said filling being done at said high melting point such that said strengthening material is fusion bonded to the plate and has an exposed part in approximate alignment with said conjoining portion, grinding and polishing said conjoining part of said one edge and said exposed part of the strengthening material, grinding and polishing said edge of said other plate, interposing a thin layer of gap filler material between said exposed part and conjoining portion of said one plate and said edge of the other plate, and pressing them together, said gap filler material having a comparatively low melting point and having a thickness substantially equal to the desired gap length, said pressing being done at said low melting point such that the parts which are pressed together are fusion bonded to each other and thereby leaving a portion of said thin layer thus forming the gap of the head, and grinding the surfaces of the plates in the vicinity of the gap to achieve the desired poleface outline and the desired gap height.

2. A method of manufacturing a magnetic head having a very short gap length and composed of at least two magnetic plates forming the head pole pieces each having a surface and an adjoining edge, comprising: grinding a rounded recess in the part of the edge of one of said plates which is adapted to confront the edge of the other plate to form the gap, said recess being ground to a depth substantially exceeding the desired gap length of the completed head and being located at a portion of said plate remote from where the surface and edge are joined, said grinding leaving intact a conjoining portion of said edge where the surface and edge are joined and being rounded at the portion remote from the edge, filling said recess with a non-magnetic strengthening material having a comparatively high melting point, said filling being done at said high melting point such that said strengthening material is fusion bonded to the plate and has an exposed part in approximate alignment with said conjoining portion, grinding and polishing said conjoining part of said one edge and said exposed part of the strengthening material, grinding and polishing said edge of said other plate, interposing a thin layer of gap filler material between said exposed part and conjoining portion of said one plate and said edge of the other plate, and pressing them together, said gap filler material having a comparatively low melting point and having a thickness substantially equal to the desired gap length, said pressing being done at said low melting point such that the parts which are pressed together are fusion bonded to each other and thereby leaving a portion of said thin layer thus forming the gap of the head, and grinding the surfaces of the plates in the vicinity of the gap to achieve the desired poleface outline and the desired gap height.

3. A method of manufacturing a magnetic head having a very short gap length and composed of at least two ferrite plates forming the head pole pieces each having a surface and an adjoining edge, comprising: grinding a rounded recess in the part of the edge of one of said plates which is adapted to confront the edge of the other plate to form the gap, said recess being ground to a depth substantially exceeding the desired gap length of the completed head and being located at a portion of said plate remote from where the surface and edge are joined, said grinding leaving intact a conjoining portion of said edge where the surface and edge are joined and being rounded at the portion remote from the edge, filling said recess with glass having a comparatively high melting point, said filling being done at said high melting point such that said glass is fusion bonded to the plate and has an exposed part in approximate alignment with said conjoining portion, grinding and polishing said conjoining part of said one edge and said exposed part of the glass, grinding and polishing said edge of said other plate, interposing a thin layer of gap filler material between said exposed part and conjoining portion of said one plate and said edge of the other plate, and pressing them together, said gap filler material having a comparatively low melting point and having a thickness substantially equal to the desired gap length, said pressing being done at said low melting point such that the parts which are pressed together are fusion bonded to each other and thereby leaving a portion of said thin layer thus forming the gap of the head, grinding the surfaces or" the plates in the vicinity of the gap to achieve the desired poleface outline and the desired gap height, and grinding away a portion of said plates and said glass at a point remote from the surface.

References Ziterl by the Examiner UNITED STATES PATENTS 2,915,812 12/1959 Rettinger 29-15559 2,933,565 4/1960 Neumann 179-1002 3,079,470 2/1963 Camaras 179-1002 3,094,772 6/1963 Duinker 29-15556 3,104,455 9/1963 Frost 29-1555 FOREIGN PATENTS 1,031,020 5/ 1958 Germany.

827,335 2/1960 Great Britain.

852,533 10/1960 Great Britain.

WHITMORE A. WILTZ, Primary Examiner.

LESTER M. SWINGLE, JQHN F. CAMPBELL,

Examiners,

Claims

1. A METHOD OF MANUFACTURING A MAGNETIC HEAD HAVING A VERY SHORT GAP LENGTH AND COMPRESSED OF AT LEAST TWO MAGNETIC PATES FORMING THE HEAD POLE PIECES EACH HAVING A SURFACE AND AN ADJOINING EDGE, COMPRISING: GRINDING A RECESS IN THE PART OF THE EDGE OF ONE OF SAID PLATES WHICH IS ADAPTED TO CONFRONT THE EDGE OF THE OTHER PLATE TO FORM THE GAP, SAID RECESS BEING GROUND TO A DEPTH SUBSTANTIALLY EXCEEDING THE DESIRED GAP LENGTH OF THE COMPLETED HEAT AND BEING LOCATED AT A PORTION OF SAID PLATE REMOTE FROM WHERE THE SURFACE AND EDGE ARE JOINED, SAID GRINDING LEAVING INTACT A CONJOINING PORTION OF SAID EDGE WHERE THE SURFCE AND EDGE ARE JOINED, FILLING SAID RECESS WITH A NON-MAGNETIC STRENGTHENING MATERAL HAVING A COMPARATIVELY HIGH MELTING POINT, SAID FILLING BEING DONE AT SAID HIGH MELTING POINT SUCH THAT SID STRENGTHENING MATERIAL IS FUSION BONDED TO THE PLATE AND HAS AN EXPOSED PART IN APPROXIMATE ALIGNMENT WITH SAID CONJOINING PORTION, GRINDING AND POLISHING SAID CONJOINING PART OF SAID ONE EDGE AND SAID EXPOSED PART OF THE STRENGTHENING MATERIAL, GRINDING AND POLISHING SAID EDGE OFF SAID OTHER PLATE, INTERPOSING A THIN LAYER OF GAP FILLER MATERIAL BETWEEN SAID EXPOSED PART AND CONJOINING PORTION OF SAID ONE PLATE AND SAID EDGE OF THE OTHER PLATE, AND PRESSING THEM TOGETHER SAID GAP FILLER MATERIAL HAVING A COMPARATIVELY LOW MELTING POINT AND HAVING A THICKNESS SUBSTANTIALLY EQUAL TO THE DESIRED GAP LENGTH, SAID PRESSING BEING DONE AT SAID LOW MELTING POINT SUCH THAT THE PARTS WHICH ARE PRESSED TOGETHER ARE FUSION BONDED TO EACH OTHER AND THEREBY LEAVING A PORTION OF SAID THIN LAYER THUS FORMING THE GAP OF THE HEAD, AND GRINDING THE SURFACES OF THE PLATES IN THE VICINITY OF THE GAP TO ACHIEVE THE DESIRED POLEFACE OUTLINE AND THE DESIRED GAP HEIGHT.