Abstract:
A magnetic head comprises a bump electrically connected to a head element on a side wall of a slider, and a pad covering a protective layer and a contact area of the bump exposed from an flat surface of the protective layer. In the magnetic head, since a bonding member for bonding a conductive pattern to the pad is bonded in a bonding area of the pad formed on the protective layer, secure bonding can be obtained regardless of the form of the contact area of the bump, and a highly reliable magnetic head, without bonding defects, can therefore be provided.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a magnetic head having an enhanced bonding strength between a lead wire and a conductive member and having improved reliability, in which the lead wire leads from a head element of a thin film magnetic head and the like, and the conductive member exchanges electrical signals with the head element. 
     2. Description of the Related Art 
     As shown in FIG. 9, the front portion of a flexure  2  is cut away in the form of an approximately U-shape to form a small portion  2   a,  and four conductive patterns  3  composed of copper and coated with gold by plating thereon are formed on the surface of the flexure  2  coated by a polyimide resin. 
     End portions  3   a  of the conductive patterns  3  are formed so as to broaden and are lined up on the small portion  2   a.    
     A slider  1  in the form of a rectangular parallelepiped is fixed by bonding at a bottom surface  1   b  thereof on the small portion  2   a  of the flexure  2  so that the end portions  3   a  of the conductive patterns  3  oppose a side wall  1   a  of the slider  1 . 
     As shown in FIG.  10  and FIG. 11, the side wall  1   a  of the slider  1  has a head element  7  for writing on and/or reading from a magnetic recording medium, and four lead wires  8 , two for writing and two for reading, lead from the head element  7 . An edge  8   a  of each lead wire  8  having a wider area in an approximately rectangular form is formed in the vicinity of the surface of the flexure  2 . Individual edges  8   a  of the four lead wires  8  are disposed so as to oppose the corresponding end portions  3   a  of the conductive patterns  3  in the vicinity thereof. 
     As shown in FIG. 11, a bump  10  composed of nickel or the like is provided on the edge  8   a  of the lead wire  8 . The bump  10  is composed of a cylindrical pillar portion  10   a  having the bottom surface contacting nearly the entire edge  8   a  of the lead wire  8  and an umbrella-like portion  10   b  expanding at the front edge of the pillar portion  10   a.    
     The umbrella-like portion  10   b  of the bump  10  has an excavated top at the top of approximately hemispherical form, and a round area at the center of the umbrella-like portion  10   b  is to be used as a contact area  10   d  of the bump  10 . 
     The contact area  10   d  of the bump  10  has an inclined portion  10   f  at the periphery thereof and is recessed into the spherical portion  10   e  of the umbrella-like portion  10   b.    
     A protective layer  9  composed of alumina covers the head element  7 , the lead wires  8 , and the surfaces of the pillar portions  10   a  and the spherical portions  10   e  of the bumps  10  on the side wall  1   a,  and is formed so as to be flat. The surface of the contact area  10   d  of the bump  10  is exposed from the protective layer  9 , and is recessed from the level of the surface of the protective layer  9  since the inclined portion  10   f  exists at the boundary of the protective layer  9 . 
     The contact area  10   d  of the bump  10  exposed from the protective layer  9  is adjacent to the surface of the flexure  2 . 
     In a polishing process for polishing the protective layer  9  so as to expose the contact area  10   d  of the bump  10 , the form of the umbrella-like portion  10   b  of the bump  10  as described above is formed by polishing the top of the approximately hemispherical umbrella-like portion  10   b  of the bump  10  together with the protective layer  9 . 
     In the polishing process, the bump  10  composed of a metal, such as nickel, is easily polished since the bump  10  is softer than the protective layer  9  composed of alumina, so that the contact area  10   d  of the bump  10  exposed from the protective layer  9  has the inclined portion  10   f  at the boundary of the protective layer  9  and is recessed from the level of the surface of the protective layer  9 . 
     Four rectangular pads  11  composed of thin gold films or the like cover the surfaces of the individual contact areas  10   d  of the four bumps  10  exposed from the protective layer  9 , and are disposed so as to oppose the corresponding end portions  3   a  of the conductive pattern  3  on the surface of the flexure  2  adjacent to each other. 
     The pads  11  includes a recessed portion  11   a  covering the surface of the contact area  10   d  of the bump  10  and an inclined portion  11   f  overlaying an inclined portion  10   f  of the bump  10  from the contact area  10   d  thereof to the surface of the protective layer  9 . 
     Since the contact area  10   d  of the bump  10  is adjacent to the surface of the flexure  2 , the recessed portion  11   a  of the pad  11  and the inclined portion  11   f  thereof are also adjacent to the end portion  3   a  of the conductive pattern  3  formed on the surface of the flexure  2 . 
     At an angular portion  12  at which the side wall  1   a  of the slider  1  and the surface of the flexure  2  contact each other, an approximately spherical bonding member  13 , composed of gold or the like, is joined in contact with the recessed portion  11   a  of the pad  11  and the end portion  3   a  of the conductive pattern  3 , so that the pad  11  and the conductive pattern  3  are connected to each other. On the surface of the approximately spherical bonding member  13 , a protruding residual portion  13   a  remains. 
     As shown in FIGS. 12 and 13, there is a conventional example in which wire  15  is used as the bonding member, and in which an edge portion  15   a  of the wire  15  is bonded to the recessed portion  11   a  of the pad  11 , and the other edge portion  15   b  of the wire  15  is bonded to the end portion  3   a  of the conductive pattern  3 . 
     In the magnetic head described above, the surface of the slider  1  is disposed so as to oppose the magnetic recording surface of the magnetic disc, and the slider  1  fixed to the flexure  2  is raised at a predetermined distance over the magnetic recording surface of the magnetic disc during an operation of the magnetic hard disc. The head element  7  is connected to an external circuit through the lead wires  8 , the bumps  10 , and the conductive patterns bonded by the bonding members to the bumps  10  via the pads  11  so as to perform magnetic writing on and reading from the magnetic disc by transmission of electric signals of electric circuits from the head element  7  to the external circuit. 
     In a bonding process for bonding the pad  11  and the conductive pattern  3  by using the spherical bonding member  13 , as shown in FIG. 14, a front edge of a fine gold wire  17  drawn from a capillary  16  for bonding is melted by discharging, whereby the spherical bonding member  13  is formed. When the bonding member  13  contacts the recessed portion  11   a  of the pad  11  and the surface of the end portion  3   a  of the conductive pattern  3 , ultrasonic vibration is imparted to the bonding member  13 , and the bonding member  13  is bonded to the pad  11  and to the end portion  3   a  of the conductive pattern  3  by ultrasonic welding. 
     In this case, since the pad  11  has the recessed portion  11   a  adjacent to the end portion  3   a  of the conductive pattern  3  in the conventional magnetic head, depending on the size of the spherical bonding member  13 , the bonding member  13  may be bonded to the end portion  3   a  of the conductive pattern  3  and an angular portion of the inclined portion  11   f  of the pad  11 , as shown in FIG.  15 . Consequently, there is a problem in that contact defects between the bonding member  13  and the pad  11  may occur. 
     When the spherical bonding member  13  rotates along the inclined portion  11   f  of the pad  11 , as shown in FIG. 16, the bonding member  13  is placed at the pad  11  side and is raised from the end portion  3   a  of the conductive pattern  3 , so that there is a problem in that contact failure with the conductive pattern  3  may occur. 
     When the bonding member for bonding the pad  11  and the conductive pattern  3  is the wire  15 , as shown in FIGS. 12 and 13, the front edge portion  15   a  of the wire  15  is contacted to the recessed portion  11   a  of the pad  11 , and then the front edge portion  15   a  of the wire  15  and the recessed portion  11   a  of the pad  11  are bonded by ultrasonic vibration imparted to the wire  15 . Subsequently, after forming a bending portion  15   c  in the wire  15 , the other edge portion  15   b  of the wire  15  is contacted to the end portion  3   a  of the conductive pattern  3 , and then ultrasonic vibration is imparted to the wire  15 , whereby the other edge portion  15   b  of the wire  15  and the end portion  3   a  of the conductive pattern  3  are bonded to each other. 
     In this case, since the pad  11  has the inclined portion  11   f  in a conventional magnetic head, as shown in FIG. 17, the front edge portion  15   a  of the wire  15  contacts the angular portion of the inclined portion  11   f  of the pad  11  and is raised from the pad  11 . Consequently, the bonding area between the wire  15  and the pad  11  is small, and contact defects occur therebetween. 
     SUMMARY OF THE INVENTION 
     As a first means for solving the problem described above, a magnetic head according to the present invention comprises a slider having a head element for performing writing on and/or reading from a magnetic recording medium, and a bump composed of metal and having an electrical contact area, the bump being electrically connected to the head element, the head element and the bump being formed at a side wall of the slider; a protective layer composed of an insulating material; a pad composed of a metal film; a bonding member; and a conductive pattern for electrically connected to an external circuit. The magnetic head has a construction, in which the protective layer covers over the side wall of the slider except for the contact area of the bump, the pad covers the surfaces of the protective layer and the contact area of the pad, and is bonded to the conductive pattern with the bonding member therebetween, and the bonding member is bonded in a bonding area of the pad formed on the surface of the protective layer. 
     In the magnetic head according to the present invention, the contact area of the bump formed on the side wall of the slider and electrically connected to the head element is exposed at the flat surface of the protective layer covering the side wall of the slider, and the pad composed of metal and covering the surfaces of the contact area of the bump and the protective layer is bonded with the bonding member to the conductive pattern for electrically connected to an external circuit. In this construction, since the bonding member is bonded in the flat bonding area of the pad formed on the protective layer, the bonding member and the pad, and the bonding member and the conductive pattern, are securely bonded to each other regardless of the form of the contact area of the bump, a highly reliable magnetic head without any bonding defects can be provided. 
     As a second means for solving the problems described above, a magnetic head according to the present invention has a construction, in which the slider and the conductive pattern are disposed so that end portions of the conductive pattern oppose the side wall of the slider on a flexure, and the bonding member is approximately spherical, and contacts the bonding area approximately at the center thereof of the pad and the end portion of the conductive pattern. 
     In the case in which the end portion of the conductive pattern is formed to oppose the side wall of the slider and the bonding member is composed of metal and is approximately spherical, the bonding member is designed to be bonded to the bonding area at approximately the center thereof. Consequently, since the bonding area and the area adjacent thereto at which the approximately spherical bonding member is bonded is flat, and the bonding member can securely be bonded to the pad without any slippage of the bonding member during a bonding process, a highly reliable magnetic head without any bonding defects can be provided. 
     As a third means for solving the problems described above, a magnetic head according to the present invention has a construction, in which the slider and the conductive pattern are disposed so that end portions of the conductive pattern oppose the side wall of the slider on a flexure, and the bonding member is a wire, and contacts the bonding area at the front edge portion of the wire and the conductive pattern at the other edge portion of the wire. 
     In the case in which the end portion of the conductive pattern is formed to oppose the side wall of the slider and the bonding member is a wire, the bonding area of the pad at which the front edge portion of the wire  15  is bonded is flat and the front edge portion thereof is not raised. Consequently, the bonding member in the form of a wire can securely be bonded to the pad, and a highly reliable magnetic head without any bonding defects can be provided. 
     As a fourth means for solving the problems described above, a magnetic head according to the present invention has a construction, in which the bonding area is a part of the pad, being at least a half of the height of the pad from the conductive pattern and being adjacent thereto. 
     More preferably, since the bonding area of the pad is at least a half of the vertical height thereof from the conductive pattern as shown in the drawings, the bonding area is wide, sufficient contacting area for the bonding member for electrical contact can be obtained, the size of the bonding member can be increased, and the stable bonding can be achieved within the bonding area even when the position of the bonding member is slightly moved. 
     Consequently, a highly reliable magnetic head without any bonding defects can be provided. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an overall view of a magnetic head according to the present invention; 
     FIG. 2 is an enlarged perspective view of a front portion of the magnetic head according to the present invention; 
     FIG. 3 is a plan view of a side wall of a slider of the magnetic head according to the present invention; 
     FIG. 4 is a cross-sectional view of a side wall of the slider of the magnetic head taken along the line  4 — 4  in FIG. 3; 
     FIG. 5 is a plan view of a side wall of the magnetic head of another embodiment according to the present invention; 
     FIG. 6 is a cross-sectional view of the side wall of the magnetic head taken along the line  6 — 6  in FIG. 5; 
     FIG. 7 is an explanatory drawing showing a bonding process for the magnetic head according to the present invention; 
     FIGS. 8A to  8 F are explanatory drawings showing a manufacturing method of a bump and a pad of the magnetic head according to the present invention; 
     FIG. 9 is an enlarged perspective view of a front portion of a conventional magnetic head; 
     FIG. 10 is a plan view of a side wall of a slider of the conventional magnetic head; 
     FIG. 11 is a cross-sectional view of the side wall of the slider of the conventional magnetic head taken along the line  11 — 11  in FIG. 10; 
     FIG. 12 is a plan view of a side wall of a slider of a conventional magnetic head of another embodiment; 
     FIG. 13 is a cross-sectional view of the side wall of the slider of the conventional magnetic head taken along the line  13 — 13  in FIG. 12; 
     FIG. 14 is an explanatory drawing showing a bonding process for the conventional magnetic head; 
     FIG. 15 is an example explanatory drawing showing a bonded state of a pad and a bonding member of the conventional magnetic head; 
     FIG. 16 is an example explanatory drawing showing a bonded state of a pad and a bonding member of the conventional magnetic head; 
     FIG. 17 is an example explanatory drawing showing a bonded state of a pad and a bonding member of the conventional magnetic head of another embodiment. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in FIG. 1, a typical structure used for a magnetic hard disc apparatus includes a resilient load beam  4  composed of stainless steel, a mount  5  composed of stainless steel and fixed at the back end of the load beam  4 , a flexible cable  6  mounted to the mount  5  and extended to the rear of the load beam  4 , and a flexure  2  composed of a thin flexible stainless steel plate and extended from the front to the back of the load beam  4 . 
     As shown in FIG. 2, the front portion of the flexure  2  is cut away in the form of an approximately U-shape to form a small portion  2   a,  and four conductive patterns  3  composed of copper and coated with gold by plating thereon are formed on the surface of the flexure  2  coated by a polyimide resin. 
     End portions  3   a  of the conductive patterns  3  are formed so as to broaden and are lined up on the small portion  2   a,  and the other end portions  3   b  are connected to a wiring pattern (not shown) of the flexible cable  6  at the back portion of the flexure  2 . 
     A slider  1  in the form of a rectangular parallelepiped is fixed by bonding at a bottom surface  1   b  thereof on the small portion  2   a  of the flexure  2  so that the end portions  3   a  of the conductive pattern  3  oppose a side wall  1   a  of the slider  1 . 
     In FIG. 2, the end portions  3   a  of the conductive pattern  3  formed on the flexure  2  and the side wall  1   a  of the slider  1  are not necessarily to be opposed orthogonally to each other, and they may be formed to oppose each other at any freely selected angle. 
     As shown in FIG.  2  and FIG. 3, the side wall  1   a  of the slider  1  bonded at the bottom surface  1   b  thereof to the flexure  2  has a head element  7  for writing on and/or reading from a magnetic recording medium, and four lead wires  8 , two for writing and two for reading, lead from the head element  7 . Edges  8   a  of individual lead wires  8 , in approximately rectangular form, are disposed in an area which is sufficiently distant from the surface of the flexure  2  so as to be lined up adjacent to corresponding end portions  3   a  of the conductive patterns  3 . 
     As shown in FIG. 4, a bump  10  composed of nickel or the like is provided on the edge  8   a  of each lead wire  8 . The bump  10 , which has a form similar to that of a conventional one but is smaller, is composed of a cylindrical pillar portion  10   a  having the bottom surface contacting nearly the entire edge  8   a  of the lead wire  8  and an umbrella-like portion  10   b  expanding at the front edge of the pillar portion  10   a.    
     The umbrella-like portion  10   b  of the bump  10  has an excavated top at the top of the approximately hemispherical form, and a round area at the center of the umbrella-like portion  10   b  is to be used as a contact area  10   d  of the bump  10 . 
     The contact area  10   d  of the bump  10  has an inclined portion  10   f  at the periphery thereof and is recessed into the spherical portion  10   e  of the umbrella-like portion  10   b.    
     A protective layer  9  composed of alumina covers the head element  7 , the lead wire  8 , and the surfaces of the pillar portion  10   a  and the spherical portion  10   e  of the bump  10  on the side wall  1   a,  and is formed so as to be flat. The surface of the contact area  10   d  of the bump  10  is exposed from the protective layer  9  and is recessed to the level below the surface of the protective layer  9  since the inclined portion  10   f  exists at the boundary of the protective layer  9 . 
     The contact area  10   d  of the bump  10  exposed from the protective layer  9  is disposed so as to be sufficiently distant from the surface of the flexure  2 . 
     In the polishing process for polishing the protective layer  9  covering the entire bump  10  so as to expose the contact area  10   d  of the bump  10 , the form of the umbrella-like portion  10   b  of the bump  10  described above is formed by polishing the top of the approximately hemispherical umbrella-like portion  10   b  of the bump  10  together with the protective layer  9 . 
     In the polishing process, the bump  10  composed of a metal such as nickel, is easily polished since the bump  10  is softer than the protective layer  9  composed of alumina, so that the contact area  10   d  of the bump  10  exposed from the protective layer  9  has the inclined portion  10   f  at the boundary of the protective layer  9  and is recessed from the level of the surface of the protective layer  9 . A method for manufacturing the bump will be described later in detail. 
     Four pads  11  in the form of thin rectangular films composed of gold or the like cover the corresponding contact areas  10   d  of the four bumps  10  exposed from the protective layer  9  at areas which are sufficiently distant from the surface of the flexure  2 . The pad  11  is formed from the contact areas  10   d  of the bump  10  to the surface of the protective layer adjacent to the flexure  2  through the peripheral inclined portion  10   f  of the contact area  10   d  of the bump  10  and the surface of the protective layer  9 . 
     Among areas of the pad  11  covering the surface of the protective layer  9 , the area closer to the surface of the flexure  2  than that to the contact area  10   d  of the bump  10  is designated as a bonding area  11   c.  The pad  11  has a sufficiently large bonding area  11   c  at the end portion  3   a  side of the conductive pattern  3  formed on the surface of the flexure  2 . 
     At an angular portion  12  at which the side wall  1   a  of the slider  1  and the surface of the flexure  2  contact each other, an approximately spherical bonding member  13 , composed of gold or the like, is joined in contact with the bonding area  11   c  of the pad  11  and the end portion  3   a  of the conductive pattern  3 , so that the pad  11  and the conductive pattern  3  are connected to each other. On the surface of the approximately spherical bonding member  13 , a protruding residual portion  13   a  remains. 
     FIGS. 5 and 6 show another embodiment of the present invention, in which a wire  15  is used as the bonding member. A front edge portion  15   a  of the wire  15  composed of gold or the like is bonded to the bonding area  11   c  of the pad  11 , and the other edge portion  15   b  of the wire  15  is bonded to the end portion  3   a  of the conductive pattern  3 . 
     Next, in the method for manufacturing the magnetic head described above, a bonding process for bonding the pad  11  and the conductive pattern  3  by using the approximately spherical bonding member  13 , will be described. 
     As shown in FIG. 7, a fine gold wire  17  is drawn from a capillary  16  for bonding and is melted at a front edge of the fine gold wire  17  by discharging, whereby the approximately spherical bonding member  13  is formed. 
     When the flexure  2  having the slider  1  and the conductive pattern  3  is in the state of being fixed by a fixture (not shown), the bonding member  13  contacts the bonding area  11   c  of the pad  11  and the surface of the end portion  3   a  of the conductive pattern  3 . Then, ultrasonic vibration is imparted to the bonding member  13  through capillary  16 , and the bonding member  13  is bonded to the bonding area  11   c  of the pad  11  and to the end portion  3   a  of the conductive pattern  3  by ultrasonic welding. 
     At the end of the process, the fine wire  17  is torn off by pulling. In this stage, a part of the fine wire  17  torn off remains as the residual portion  13   a.    
     When the bonding member for bonding the pad  11  and the conductive pattern  13  is the wire  15 , as shown in FIGS. 5 and 6, the front edge portion  15   a  of the wire  15  is contacted to the bonding area  11   c  of the pad  11 , and then the front edge portion  15   a  of the wire  15  and the bonding area  11   c  of the pad  11  are bonded by ultrasonic vibration imparted to the wire  15 . Subsequently, after forming a bending portion  15   c  in the wire  15 , the other edge portion  15   b  of the wire  15  is contacted to the end portion  3   a  of the conductive pattern  3 , and then ultrasonic vibration is imparted to the wire  15 , whereby the other edge portion  15   b  of the wire  15  and the end portion  3   a  of the conductive pattern  3  are bonded to each other. 
     Next, in the method for manufacturing the magnetic head described above, a method for forming the bump  10  and the pad  11  will be specifically described with reference to FIG.  8 . 
     The head element  7  and the lead wires  8  extending from the head element  7  are formed on the side wall  1   a  of the slider  1 . In this stage, the lead wires  8  are formed approximately rectangularly and the edges  8   a  thereof are disposed at positions being sufficiently far from the bottom  1   b  of the slider  1  to be bonded to the flexure  2  in a subsequent process. 
     FIG. 8A shows a cross-sectional view of the edge  8   a  of the lead wire  8  formed on the side wall of the slider  1 . 
     In a process for forming a resist film, shown in FIG. 8B, a resist film  14  is formed on the surface of the side wall  1   a,  and then by using photolithographic etching, a round window  14   a,  which nearly conforms to the edge  8   a  of the lead wire  8 , is formed in the resist film  14 . 
     In a process for forming the bump, shown in FIG. 8C, the edge  8   a  of the lead wire  8  is plated with nickel, aluminum, copper or the like at the window  14   a  of the resist film  14 . In this stage, the plating layer for the bump  10  is formed so as to protrude in the window  14   a  of the resist film  14  and so as to spread at the periphery of the window  14   a,  whereby the approximately hemispherical umbrella-like portion  10   b  is formed. 
     Concerning the bump  10 , similarly to the lead wire  8 , the bump  10  is formed so as to be distant from the bottom surface of the slider  1 . After forming the bump  10 , the resist film is removed. 
     Next, in a process for forming the protective layer, shown in FIG. 8D, by using a vacuum deposition method such as sputtering, the protective layer  9  composed of alumina is formed on the side wall  1   a  of the slider  1  so as to cover the entire bump  10 . 
     In a polishing process shown in FIG. 8E, the bump  10  is exposed from the protective layer  9  by polishing the surface of the protective layer  9 , and simultaneously, the top in the form of a hemisphere of the umbrella-like portion  10   b  of the bump is polished, whereby the round contact area  10   d  is formed at the center of the umbrella-like portion  10   b  of the bump  10 . In this polishing process, the bump  10  composed of a metal such as nickel, is easily polished since the bump  10  is softer than the protective layer  9  composed of alumina, and the contact area  10   d  of the bump  10  exposed from the protective layer  9  is recessed from the level of the surface of the protective layer  9  and has the inclined portion  10   f  at the boundary of the protective layer  9 . 
     In a process for forming the pad shown in FIG. 8F, by plating using gold or the like, the contact area  10   d  of the bump  10  exposed from the protective layer  9  is covered, and the pad  11  in the form of a rectangle extended to the vicinity of the bottom surface of the slider  1  is formed. In this stage, the sufficiently large bonding area  11   c  of the pad  11  formed on the surface of the protective layer  9  is formed adjacent to the bottom surface  1   b  of the slider  1 . 
     In the magnetic head described above, even though the following are not shown, a mount  5  is mounted to a driving arm of the magnetic hard disc device, a surface of the slider  1  is disposed so as to oppose the magnetic recording surface of the magnetic disc, and the slider  1  fixed to the flexure  2  is raised at a predetermined distance over the magnetic recording surface of the magnetic disc during an operation of the magnetic hard disc. The head element  7  is connected to the outside through the lead wires  8 , the bumps  10 , and the conductive pattern  3  bonded by the bonding member to the bump  10  via the pad  11  so as to perform magnetic writing on and reading from the magnetic disc.