MAGNETIC HEAD COMPRISING A MAIN ELEMENT AND A SUB-ELEMENT, AND METHOD OF MANUFACTURING THE MAGNETIC HEAD

Abstract: Magnetic head comprising a main element (2) formed in a thin-film technique, with at least a transducing element (5) and a sub-element (4) arranged against the main element. An adhesive (21) is present between a face of the main element facing the sub-element and a face of the sub-element facing the main element. A thin but strong adhesive layer is obtained by providing at least one of said faces with a structure of parts which are either re-entrant or projecting with respect to the relevant face so that the adhesive is present both on and between said parts.

Description: Magnetic head comprising a main element and a sub-element, and method of manufacturing the magnetic head. The invention relates to a magnetic head comprising a main element with at least a transducing element and a sub-element arranged against the main element, an adhesive being present between a face of the main element facing the sub-element and a face of the sub-element facing the main element. The invention also relates to a method of manufacturing a magnetic head comprising a main element with at least a transducing element and a sub-element arranged against the main element, in which a face of the main element facing the sub-element and a face of the sub-element facing the main element are secured together by means of an adhesive. Such a magnetic head and a method are known from NL-A 9002344. The known magnetic head has a head face and comprises a substrate with a plurality of layers applied in a thin-film technique, which layers jointly constitute a number of integrated head sensors with transducing elements terminating in the head face. A counter block protecting the head sensors and constituting a tape contact face is placed on the substrate provided with the layers. The substrate and the counter block are made of a wear-resistant ceramic material. Dependent on their function, the layers present are made of an insulating, electrically conducting or magnetically conducting material. A flat insulation layer is provided on the side of the head sensors facing the counter block, which insulation layer serves as a bonding layer for an adhesive layer which is present between the head sensors and a flat surface of the counter block. In a known method of securing the counter block on the insulation layer, small quantities of adhesive are locally deposited on said surface of the counter block, whereafter the counter block with the surface provided with the adhesive is placed against the insulation layer, while the adhesive which is present is distributed by moving the counter block across the insulation layer. A drawback of this known method is that the adhesive dose is critical because a too large quantity of adhesive leads to a relatively thick adhesive layer and adhesive protruding from the edges of the counter block, and a too small quantity of adhesive leads to a deficient bond. The thickness of the adhesive layer formed is generally limited due to mechanical and/or electrical requirements such as the strength of the bond and the wear-resistance on the head face. In a magnetic head which is provided on its head face with a wear-resistant, electrically conducting coating, a relatively thick adhesive layer may give rise to a mechanically and electrically weak bond. Moreover, from a manufacturing- technical point of view, moving the counter block, which is necessary during manufacture, is a cumbersome activity which leads to poorly reproducible bonds. It is an object of the invention to provide a magnetic head of the type described in the opening paragraph, in which the main element and the sub-element are spaced apart by an accurately defined distance. To this end, the magnetic head according to the invention is characterized in that at least one of said faces is provided with a structure of parts which are either reentrant or projecting with respect to the relevant face, while the adhesive is present both on and between said parts. The expression 'either re-entrant or projecting' is herein understood to mean offset with respect to the relevant face. The structure may comprise, for example parallel ducts or ducts intersecting each other. An advantage of the magnetic head according to the invention is that at the areas where the sub-element and the main element, which is usually built up in layers particularly in a thin-film technique, are most proximate to each other, an adhesive layer which is present and is formed during manufacture is thin so that the bond has an optimum strength, also at the head face. The sub-element serves as a protective element for the main element and is often mentioned counter block. A further advantage is that the realized bond is effected on a relatively large surface so that the bond has a relatively large adhesive strength. An embodiment of the magnetic head according to the invention is characterized in that the structure comprises a pattern of recesses. The shape and dimensions of the recesses are dependent on various factors, such as the properties of the material of the main element and the sub-element at the faces and the properties of the adhesive. An embodiment of the magnetic head according to the invention is characterized in that the structure is present in a non-magnetic material. The structure may be present in an insulation layer of the main element, which layer is formed from, for example SiO 2 or Al 2 O 3 . The structure may be alternatively, or additionally, present in the sub-element. The sub-element may be formed from, for example a ceramic material such as TiC/Al 2 O 3 , in which the structure is provided in the ceramic material. It is alternatively possible that the sub-element of, for example a ceramic material or a ferrite comprises a layer of, for example quartz in which the structure is formed. It is another object of the invention to provide a method of the type described in the opening paragraph, with which the sub-element can be secured to the main element in an accurate and reproducible manner. To this end, the method according to the invention is characterized in that at least one of said faces is provided with a structure of parts which are either re-entrant or projecting with respect to the relevant face, whereafter the main element and the sub- element, with said faces facing each other, are pressed together and the adhesive is provided on an interface between the two faces for forming an adhesive layer between the main element and the sub-element. An advantage of the method according to the invention is that the sub-element can be secured to the main element while using a static clamping force. When the main element and the sub-element are being pressed together and after the adhesive has been provided, the structure has a capillary effect on the adhesive. The main element and the sub-element thus constitute a capillary structure during pressing, in which the adhesive, such as a liquid glue, can be distributed by means of capillary action, while the adhesive soaks in to a minimal extent in the areas where the faces are most proximate, so that the adhesive layer will have an optimum thickness in these areas. The adhesive dose in the method according to the invention is not critical, while the thickness of the adhesive layer to be formed is still fully controllable. An embodiment of the method according to the invention is characterized in that the structure is formed by providing recesses. The recesses, for example intersecting ducts, may be formed by means of known photolithographic methods such as etching, or with mechanical techniques. An embodiment of the method according to the invention is characterized in that a substrate of sub-elements is used, a face of which is provided with structures of reentrant or projecting parts, whereafter separate sub-elements each provided with a structure are separated from the substrate. The substrate may consist, for example, entirely of a nonmagnetic material or of a base of a ceramic material or another material on which a non- magnetic layer of, for example Al 2 O 3 or SiO 2 is provided. The separate sub-elements may be separated in the conventional manner by means of, for example a sawing operation. An embodiment of the method according to the invention is characterized in that the sub-elements are provided with a non-magnetic layer provided on the substrate, in which layer recesses, which do not extend as far as the substrate, are provided for forming the structures. An embodiment of the method according to the invention is characterized in that a wafer of main elements is used, in which a face of a non-magnetic layer is provided with structures of either re-entrant or projecting parts, whereafter separate main elements each provided with a structure are separated from the wafer. For example, a layer of Al 2 O 3 or a layer of SiO 2 may be used as a non-magnetic final layer. The separate main elements may be separated by means of known sawing techniques. It is to be noted that the magnetic head according to the invention, as well as the magnetic head obtained by means of the method according to the invention may be a read and/or write head. The magnetic head may therefore be provided with one or more magnetoresistive and/or inductive transducing element. The magnetic head may be adapted to cooperate with tape-shaped and/or disc-shaped agnetic media, may be formed as single- channel or multichannel magnetic head or may be suitable for audio, video, data and/or multimedia applications. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. In the drawings: Fig. 1 shows, in a diagrammatic cross-section, an embodiment of the magnetic head according to the invention, Fig. 2 shows a part of the magnetic head, as shown in Fig. 1 , in a larger form, Fig. 3 shows a part of the cross-section, taken on the line V-V in Fig. 1 , in a larger form, Fig. 4 shows a first variant of the part shown in Fig. 2, and Fig. 5 shows a second variant of the part shown in Fig. 2. The magnetic head according to the invention, shown in Figs. 1 , 2 and 3 comprises a main element 2 and a sub-element, or protective element, 4 which jointly constitute a head face 1. The main element 2, which is constructed by means of a known thin-film technique, comprises a base 3 provided with a magnetic head structure with a transducing element. In this example, the base 3 is formed from a magnetic material such as an NiZn ferrite. In this example, the magnetic head structure comprises a read element as a transducing element, which is a magnetoresistive element 5, and also two flux guides 7a and 7b, an electric conductor 9 for driving the magnetoresistive element 5 and various insulation layers 1 1a, l ib, l ie and 13 of, for example quartz. In this example, the magnetoresistive element 5 is provided with equipotential strips 5a, and bridges a space 15 between the flux guides 7a and 7b. The insulation layer l ie forms a read gap 17 terminating in the head face 1 and extending between the base 3 and the flux guide 7a. Instead of one read element, the magnetic head may also be provided with several, for example juxtaposed, read elements. The magnetic head may not only be provided with one read element but also additionally with one or more read elements or one or more write elements, particularly inductive elements. In this example, the sub-element 4 comprises a non-magnetic plate- shaped block 19, also referred to as counter block, of Al- > O 3 /TiC. An adhesive 21 is present between a face 2a of the main element 2 facing the sub-element 4 and a face 4a of the sub- element 4 facing the main element 2, which adhesive secures the two elements together. The face 2a is formed by the planed surface of the insulation layer 13 remote from the base 3 and the face 4a is a surface of the block 19. In this example, the face 4a is provided with a structure of parts 4ab which are re-entrant with respect to the face 4a. In this example, these re-entrant parts form a pattern of ducts 23 having a width w, in the range between 5 and 10 μms and a depth d in the range between 0.05 and 0.5 μms. As a result of the structure which is present, the adhesive has only a small thickness between the faces outside the ducts. An epoxy glue is used as an adhesive. During manufacture of the magnetic head according to the invention, the face 2a and the face 4a provided with the structure of re-entrant parts 4ab are moved towards each other and subsequently pressed together, whereafter the adhesive 21 is provided on an interface 25, in this example on the head face 1 , between the two faces. Due to capillary action, the adhesive 21 moves in and between the ducts 23 so that a very rigid adhesion between the elements 2 and 4 is obtained, while the adhesive layer formed may have a very small layer thickness t, for example, of the order of 0.05 μms. The ducts 23 present in the sub-element 4 are constituted by recesses which are provided by means of known techniques, such as etching, in the non-magnetic block 19. Fig. 4 shows an alternative embodiment for the measures used in the magnetic head shown in Figs. 1 , 2 and 3 according to the invention. In Fig. 4, a main element 2' and a sub-element 4' are secured together by means of an adhesive 21. The main element 2' has a face 2'a facing the sub-element 4', opposite which face 2'a a face 4'a of the sub-element 4' extends. A structure of projecting parts 4'ab is formed by means of a lithographic process on the face 4'a. The adhesive 21 ' is present both on and between these parts. Fig. 5 shows a further alternative embodiment. In this embodiment, the magnetic head according to the invention has a main element 2" and a sub-element 4" secured thereto by means of an adhesive 21 ". The main element 2" has a structured face 2"a facing the sub-element 4" and forming part of a non-magnetic layer 13" , while the sub- element 4" has a smooth face 4"a facing the main element 4". The face 2"a is provided with a structure of parts 2"ab which are re-entrant with respect to the face 2"a, while the adhesive 21 " is present both on and between these parts. In a method in which large numbers of magnetic heads of the type as shown in Figs. 1 , 2 and 3 or in Fig. 4 are manufactured, it is favourable to start from a substrate of sub-elements 4, 4', whose faces 4a, 4'a are provided with structures of reentrant parts 4ab and 4'ab, respectively, whereafter separate sub-elements each provided with a structure are sawn or cut from the substrate. In a method in which large numbers of magnetic heads of the type as shown diagrammatically in Fig. 5 are manufactured, it is advantageous to start from a wafer of main elements 2", in which the face 2 "a of the non-magnetic layer 13" is provided with structures of either re-entrant parts 2"ab or projecting parts, whereafter separate main elements each provided with a structure are sawn or cut from the wafer. It is to be noted that the invention is not limited to the embodiments shown.

Claims: CLAIMS: 1. A magnetic head comprising a main element with at least a transducing element and a sub-element arranged against the main element, an adhesive being present between a face of the main element facing the sub-element and a face of the sub-element facing the main element, characterized in that at least one of said faces is provided with a structure of parts which are either re-entrant or projecting with respect to the relevant face, while the adhesive is present both on and between said parts. 2. A magnetic head as claimed in Claim 1 , characterized in that the structure comprises a pattern of recesses. 3. A magnetic head as claimed in Claim 1 or 2, characterized in that the structure is present in a non-magnetic material. 4. A method of manufacturing a magnetic head comprising a main element with at least a transducing element and a sub-element arranged against the main element, in which a face of the main element facing the sub-element and a face of the sub-element facing the main element are secured together by means of an adhesive, characterized in that at least one of said faces is provided with a structure of parts which are either re-entrant or projecting with respect to the relevant face, whereafter the main element and the sub- element, with said faces facing each other, are pressed together and the adhesive is provided on an interface between the two faces for forming an adhesive layer between the main element and the sub-element. 5. A method as claimed in Claim 4, characterized in that the structure is formed by providing recesses. 6. A method as claimed in Claim 4 or 5, characterized in that a substrate of sub-elements is used, a face of which is provided with structures of either re-entrant or projecting parts, whereafter separate sub-elements each provided with a structure are separated from the substrate. 7. A method as claimed in Claim 6, in which the sub-elements are provided with a non-magnetic layer provided on the substrate, in which layer recesses, which do not extend as far as the substrate, are provided for forming the structures. 8. A method as claimed in Claim 4 or 5, characterized in that a wafer of main elements is used, in which a face of a non-magnetic layer is provided with structures of either re-entrant or projecting parts, whereafter separate main elements each provided with a structure are separated from the wafer.

Inventors: DRAAISMA EELTJE AIZE, FRANSSEN JOHANNES HENRICUS COR, DRAAISMA, EELTJE, AIZE, FRANSSEN, JOHANNES, HENRICUS, CORNELIS
Applicants: PHILIPS ELECTRONICS NV, PHILIPS NORDEN AB, PHILIPS ELECTRONICS N.V.
Application year: 1997
Main classification: G11B5
IPC codes: G11B5