Abstract:
A lapping sensor used in fabrication of a magnetic head with an MR element includes a resistor film with a resistance that varies depending upon a lapping amount, and a pair of connection pads formed on a element-forming surface of the magnetic head and electrically connected to both end sections of the resistor film. The pair of connection pads consist of a first connection pad and a second connection pad located nearer to a lapping surface than the first connection pad. One edge of the first connection pad is faced to one edge of the second connection pad and inclined toward the lapping surface.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a lapping sensor used in a height adjustment of a magnetoresistive effect (MR) film (MR-height adjustment) when a magnetic head with an MR element is fabricated, and to a lapping control method using the lapping sensor. 
     DESCRIPTION OF THE RELATED ART 
     In the MR-height adjustment process, MR heights of a plurality of MR elements are adjusted in one operation by polishing one surface (ABS, Air Bearing Surface) of a bar or block obtained by cutting a wafer so that a plurality of magnetic heads with the MR elements are aligned along the bar. In order to precisely and equally adjust MR heights of MR elements in one bar and MR heights of MR elements in bars, a lapping amount is controlled in response to electrical signals from a plurality of lapping sensors each called ELG (Electric Lapping Guide) or RLG (Resistance Lapping Guide), which are in general formed in each bar for detecting the lapped height of the bar. Bending of the bar may be additionally controlled in response to the electrical signals. 
     The ELG or RLG is substantially configured by a resistor film formed adjacent to and in line with the ABS to be lapped, and by a pair of connection pads electrically connected with both end sections of the resistor film. When lapping the MR height, the resistor film will be also lapped to decrease its height and to increase its electrical resistance. Thus, the lapped amount can be obtained from the change in a terminal voltage of the resistor film. 
     Such lapping sensors are disclosed in for example U.S. Pat. Nos. 5,065,483, 5,210,667, 5,242,524, 5,361,547, 5,997,381, 6,007,405 and 6,03,849. 
     In general, the pair of the connection pads for taking out the electrical signal from the resistor film of the lapping sensor are arranged on an element-forming surface of the bar side by side with terminal electrodes of magnetic heads. 
     FIG. 1 shows a plane view schematically illustrating an element-forming surface of a part of a conventional bar obtained by cutting in lines an wafer on which many magnetic heads are formed in matrix. 
     In the figure, reference numerals  10  denote magnetic head sections, and  11  denote lapping sensor sections adjacent to the respective magnetic head sections  10 . On the element-forming surface of each magnetic head section  10 , four magnetic head connection pads  13   a - 13   d  electrically connected to a composite magnetic head element  12  consisting of an MR element and an inductive element are formed. On the element-forming surface of each lapping sensor section  11 , two resistor-film connection pads  14   a  and  14   b  electrically connected to the resistor film, for extracting an electrical signal from the resistor film are aligned perpendicular to a surface to be lapped (lapping surface)  15  of the bar. 
     Such conventional structure had been applicable to a 30% magnetic head slider with a size of 1.0 mm×1.235 mm×0.3 mm. However, in case of a magnetic head slider with a size smaller than that of the 30% slider such as a 20% slider of 0.7 mm×0.85 mm×0.23 mm, since the space between the upper connection pad  14   a  and the lower connection pad  14   b  and also the space between the lower connection pad  14   b  and the lapping surface  15  became extremely narrow, the following problem had been occurred. 
     In the lapping control process, one end terminals of a printed circuit board (PCB) with the other end terminals to be electrically connected to a lapping control device are electrically connected to the resistor-film connection pads  14   a  and  14   b  by wires in general. If these spaces are too narrow, because a wire bonding machine has a limited accuracy in bonding, a wire  16  bonded to the lower connection pad  14   b  may come into contact with the upper connection pad  14   a  as shown in FIG. 2 causing a short circuit to occur, or a wire  17  bonded to the lower connection pad  14   b  may come into contact with a lapping plate touched with the lapping surface  15  as shown in FIG. 2 
     If the resistor-film connection pads  14   a  and  14   b  are short-circuited by the wire  16 , the measured resistance of the lapping sensor will become lower than its actual resistance and thus an excess lapping may be occurred. Also, if the wire  17  touches the lapping plate, noises may be mixed in the measured signal due to current flowing into the lapping plate via the wire  17 . Then, a correct resistance of the lapping sensor cannot be measured and a correct lapping cannot be expected. 
     In order to solve such problem, there may be an arrangement in which resistor-film connection pads  34   a  and  34   b  of the lapping sensor are aligned in parallel with a lapped surface  35  of a bar by forming the connection pad  34   a  over a lapping sensor section  31  and a magnetic head section  30  as shown in FIG.  3 . However, this arrangement will make the layout design of magnetic head connection pads very difficult and also will expose the section of the resistor-film connection pad  34   a  when the magnetic head section  30  is separated by cutting from the section  31 . 
     There may be another arrangement in which resistor-film connection pads  44   a  and  44   b  of one lapping sensor are aligned in parallel with a surface to be lapped  45  of a bar by forming the connection pad  44   a  in one lapping sensor section  41  and by forming the other connection pad  44   b  in another lapping sensor section  41  as shown in FIG.  4 . However, this arrangement will make the resistance of the lapping sensor to increase because of a long lead conductor  48  for connecting the resistor film of the lapping sensor with the connection pad  44   b,  and also will expose the section of the lead line  48  when the magnetic head section  40  is separated by cutting from the lapping sensor section  41 . 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a lapping sensor which can surely and stably detect a correct lapping amount even when a magnetic head slider is to be fabricated is downsized. 
     Another object of the present invention is to provide a lapping control method using a lapping sensor, whereby an MR height can be surely and stably adjusted to a correct value. 
     According to the present invention, a lapping sensor used in fabrication of a magnetic head with an MR element includes a resistor film with a resistance that varies depending upon a lapping amount, and a pair of connection pads formed on a element-forming surface of the magnetic head and electrically connected to both end sections of the resistor film. The pair of connection pads consist of a first connection pad and a second connection pad located nearer to a lapping surface than the first connection pad. One edge of the first connection pad is faced to one edge of the second connection pad and inclined toward the lapping surface. 
     One edge of the first connection pad formed far side from the lapping surface (upper connection pad) is faced to one edge of the second connection pad formed near side from the lapping surface (lower connection pad) and inclined toward the lapping surface. Thus, when wires are bonded to these connection pads, contact of the wire bonded to the lower connection pad with the upper connection pad can be prevented. Namely, by routing the wire bonded to the lower connection pad run along the inclined edge of the upper connection pad, a possibility of contact of this wire with the upper connection pad can be extremely reduced. As a result, a correct lapping amount can be always provided, and therefore an MR height can be surely and stably adjusted to a correct value even when a magnetic head slider to be fabricated is downsized. 
     It is preferred that the one edge of the first connection pad (upper connection pad) has a linear shape. In this case, more preferably, the one edge of the second connection pad (lower connection pad) has also a linear shape parallel to the one edge of the first connection pad (upper connection pad). Thus, the space between the upper connection pad and the lower connection pad and the space between the lower connection pad and the lapping surface can be widened. Therefore, a possibility of contact of the wire boned to the lower connection pad with the upper connection pad and/or a possibility of contact of this wire with a lapping plate abutted to the lapping surface can be extremely reduced. As a result, a correct lapping amount can be always provided even when a magnetic head slider to be fabricated is downsized. 
     It is also preferred that each of the first and second connection pads is formed in a triangular shape, and that each of the one edge of the first connection pad and the one edge of the second connection pad corresponds to an oblique side of the triangular shape. In this case, more preferably, the triangular shape is a right triangular shape. 
     It is preferred that the one edge of the first connection pad has a curved shape. In this case, it is more preferred that each of the first and second connection pads is formed in a circular or oval shape. 
     It is also preferred that the first and second connection pads are aligned along a direction perpendicular to or inclined toward the lapping surface. 
     According to the present invention, furthermore, a lapping control method using at least one lapping sensor for fabricating a magnetic head with an MR element includes a step of preparing at least one the aforementioned lapping sensor, a step of connecting bonding wires to the first and second connection pads, respectively so that the bonding wires run along the one edge of the first connection pad, and a step of extracting an electrical signal from the at least one lapping sensor to control the lapped amount. 
     It is preferred that the method further includes a step of adjusting a height of an MR film in the MR element in accordance with the electrical signal extracted. 
     Further objects and advantages of the present invention will be apparent from the following description of the preferred embodiments of the invention as illustrated in the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 already disclosed shows a plane view schematically illustrating the element-forming surface of a part of the conventional bar; 
     FIG. 2 already disclosed shows a plane view illustrating the element-forming surface where the wires are bonded to the connection pads shown in FIG. 1; 
     FIG. 3 already disclosed shows a plane view illustrating a layout example of the conventional connection pads; 
     FIG. 4 already disclosed shows a plane view illustrating another layout example of the conventional connection pads; 
     FIG. 5 shows a plane view schematically illustrating an element-forming surface of a part of a bar obtained by cutting in lines an wafer on which many magnetic heads are formed in matrix as a preferred embodiment according to the present invention; 
     FIG. 6 shows a plane view schematically illustrating an MR film and lead conductors in each magnetic head section and a resistor film and lead conductors in each lapping sensor section in an inwardly located plane from the element-forming surface shown in FIG. 5; 
     FIG. 7 shows an oblique view illustrating an inward structure of the lapping sensor section; 
     FIG. 8 shows an A—A line sectional view of FIG. 5, illustrating an inward structure of the magnetic head section; 
     FIG. 9 shows an exploded oblique view illustrating fixing of a bar and a PCB to a lapping jig; 
     FIG. 10 shows an oblique view illustrating the bar and the PCB fixed to the lapping jig; 
     FIG. 11 shows an oblique view illustrating wire-bonding between the resistor-film connection pads of the bar and connection terminals of the PCB; 
     FIG. 12 shows a plane view illustrating a wiring direction of the bonding wires bonded to the resistor-film connection pads of the bar; 
     FIG. 13 shows an oblique view illustrating actual lapping of the bar; and 
     FIGS. 14 a  to  14   g  show plane views illustrating various shapes of resistor-film connection pads in modifications according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 5 schematically illustrates an element-forming surface of a part of a bar obtained by cutting in lines an wafer on which many magnetic heads are formed in matrix as a preferred embodiment according to the present invention, FIG. 6 schematically illustrates an MR film and lead conductors in each magnetic head section and a resistor film and lead conductors in each lapping sensor section in an inwardly located plane from the element-forming surface shown in FIG. 5, FIG. 7 illustrates an inward structure of the lapping sensor section, and FIG. 8 is an A—A line sectional view of FIG. 5, illustrating an inward structure of the magnetic head section. 
     In FIG. 5, reference numerals  50  denote magnetic head sections and  51  denote lapping sensor sections adjacent to the magnetic head sections  50 . Each lapping sensor section  51  is formed between the magnetic head sections  50 . The lapping sensor section  51  may be additionally formed at both end sections of the bar. 
     On the element-forming surface of each magnetic head section  50 , four magnetic head connection pads  53   a - 53   d  electrically connected to a magnetic head element  52  consisting of an MR element and an inductive element are formed. On the element-forming surface of each lapping sensor section  51 , two resistor-film connection pads  54   a  and  54   b  electrically connected to the resistor film, for extracting an electrical signal from the resistor film are aligned substantially perpendicular to a surface to be lapped (lapping surface)  55  of the bar. 
     In this embodiment, the resistor-film connection pads  54   a  and  54   b  are formed in a right triangular shape to align along a direction perpendicular to the lapping surface  55 . The hypotenuses of the right triangle pads  54   a  and  54   b  are faced in parallel with each other. 
     In FIG. 6, reference numerals  60  denote MR films formed in the respective magnetic head sections  50  to run along a direction parallel to the lapping surface  55 ,  61   a  and  61   b  denote lead conductors with one ends connected to the both end sections of the respective MR films  60 ,  62   a  and  62   b  denote connection conductors or via hole conductors connected to the other ends of the respective lead conductors  61   a  and  61   b,    63  denote resistor films formed in the respective lapping sensor sections  51  to run along a direction parallel to the lapping surface  55 ,  64   a  and  64   b  denote lead conductors with one ends connected to the both end sections of the respective resistor films  63 , and  65   a  and  65   b  denote connection conductors or via hole conductors connected to the other ends of the respective lead conductors  64   a  and  64   b,  respectively. The connection conductors  62   a  and  62   b  in each magnetic head section  50  are electrically connected to the respective magnetic head connection pads  53   a  and  53   b  shown in FIG. 5, and the connection conductors  65   a  and  65   b  in each lapping sensor section  51  are electrically connected to the respective resistor-film connection pads  54   a  and  54   b  shown in FIG.  5 . 
     Detail structure of the above-mentioned resistor film  63 , lead conductors  64   a  and  64   b,  connection conductors  65   a  and  65   b,  and resistor-film connection pads  54   a  and  54   b  in the lapping sensor section  51  are indicated in FIG.  7 . The resistor films  63  are made of the same material as that of the MR films  60 , and the lead conductors  64   a  and  64   b , connection conductors  65   a  and  65   b  and resistor-film connection pads  54   a  and  54   b  are made of the same material as that of the lead conductors  61   a  and  61   b,  connection conductors  62   a  and  62   b  and magnetic head connection pads  53   a  and  53   b . These constituent elements in each lapping sensor section  51  are formed in the same wafer processes as the corresponding constituent elements in each magnetic head section  50 . 
     The magnetic head section  50  are fabricated, as shown in FIG. 8 in detail, by forming a lower shield layer  82  on an under film  81  deposited on an wafer substrate  80 , by forming thereon the MR film  60  and lead conductors (not shown in FIG. 8) via a lower shield gap layer  83 , by forming thereon an upper shield layer  85  via an upper shield gap layer  84 , by forming thereon an inductive element  86  which uses this upper shield layer  85  as a lower pole layer, and by forming other elements such as connection pads (not shown in FIG.  8 ). 
     Many magnetic head sections and lapping sensor sections are thus formed on the wafer in matrix, and then the wafer is cut into bars each having aligned magnetic heads and lapping sensors, as shown in FIGS. 5 and 6. Thereafter, lapping control of the MR height (height of the MR film) of each bar is executed as follows. 
     First, as shown in FIGS. 9 and 10, a printed circuit board (PCB) for connection  91  is attached to a side surface  90   a  of a lapping jig  90 , and a bar  92  to be lapped is adhered to the bottom face  90   b  of the jig  90 . In this case, the lapping surface of the bar  92  is a surface  92   a  opposite to the jig  90 . 
     Then, as its part is shown in FIG. 11, the resistor-film connection pads  54   a  and  54   b  formed on the bar  92  are electrically bonded to connection terminals  93   a  and  93   b  on the PCB  91  by wires  94   a  and  94   b , respectively. The connection terminals  93   a  and  93   b  of the PCB  91  are electrically connected to a lapping control device (not shown) via connection terminals  95  (FIG.  10 ), respectively. 
     When bonding the wires  94   a  and  94   b  to the resistor-film connection pads  54   a  and  54   b  on the bar  92 , the wires  94   a  and  94   b  are routed substantially in parallel with the respective hypotenuses of the right triangle pads  54   a  and  54   b  as more clearly shown in FIG.  12 . Thus, the wire  94   b  connected to the lower connection pad  54   b  will not contact with the upper connection pad  54   a  in most cases. 
     Since the resistor-film connection pads  54   a  and  54   b  in this embodiment are formed in a right triangular shape so that their hypotenuses are faced to each other, sufficiently effective area of each connection pad can be provided even if the area of the element-forming surface of the lapping sensor section is small. In other words, the space between the upper connection pad  54   a  and the lower connection pad  54   b  and/or the space between the lower connection pad  54   b  and the lapping surface  55  can be widened. Therefore, even if the wire bonding machine has a limited accuracy in bonding, no short circuit of the wire  94   b  will occur. Furthermore, since the two right triangle connection pads  54   a  and  54   b  are aligned along a direction perpendicular to the lapping surface  55  in this embodiment, these connection pads  54   a  and  54   b  can be formed to have a large area with effectively utilizing the lateral width of each lapping sensor section  51 . As a result, short circuit between these connection pads and the wires can be more effectively prevented. 
     The bar  92  attached and electrically connected to the lapping jig  90  as aforementioned is then lapped as shown in FIG.  13 . Namely, the lapping surface  92   a  of the bar  92  is abutted to the surface of a rotating lapping plate  130  and thus this surface  92   a  is lapped to adjust the MR height. During this lapping, the lapped amount is detected by the resistor film in the lapping sensor section and an electrical signal representing the detected lapped amount is applied to the lapping control device through the resistor-film connection pads  54   a  and  54   b , the wires  94   a  and  94   b  and the PCB  91  so that the lapped amount is feedback-controlled. 
     As mentioned above, according to this embodiment, since no short circuit will occur on the wires  94   a  and  94   b  connected to the resistor-film connection pads  54   a  and  54   b , correct lapping amount can be always measured and thus the MR height can be surely and stably adjusted to a correct value. 
     FIGS. 14 a  to  14   g  illustrate various shapes of resistor-film connection pads in modifications according to the present invention. 
     In the modification shown in FIG. 14 a , resistor-film connection pads  144   a  and  144   b  in each lapping sensor section  141  are formed in a right triangular shape so that their hypotenuses are faced to each other, and are aligned in a slanting direction with respect to a lapping surface  145 . Therefore, in this modification, effective utilization of the lateral width of each lapping sensor section  141  cannot be expected as the embodiment of FIGS. 5 and 6. However, since the space between the upper connection pad  144   a  and the lower connection pad  144   b  and the space between the lower connection pad  144   b  and the lapping surface  145  can be more widened, short circuit between these connection pads and the wires can be more effectively prevented. 
     In the modification shown in FIG. 14 b,  resistor-film connection pads  154   a  and  154   b  in each lapping sensor section  151  are formed in a triangular shape other than a right triangle so that their oblique sides are faced to each other, and are aligned in a slanting direction with respect to a lapping surface  155 . Therefore, in this modification, effective utilization of the lateral width of each lapping sensor section  151  cannot be obtained as the embodiment of FIGS. 5 and 6. Except for this, the same advantages as the embodiment of FIGS. 5 and 6 can be expected in this modification. 
     In the modification shown in FIG. 14 c,  resistor-film connection pads  164   a  and  164   b  in each lapping sensor section  161  are formed in a rectangular shape so that their oblique linear sides slanting with respect to a lapping surface  165  are faced to each other. The same advantages as the embodiment of FIGS. 5 and 6 can be expected in this modification. 
     In the modification shown in FIG. 14 d,  resistor-film connection pads  174   a  and  174   b  in each lapping sensor section  171  are formed in a rectangular shape so that their oblique curved sides slanting with respect to a lapping surface  175  are faced to each other. The same advantages as the embodiment of FIGS. 5 and 6 can be expected in this modification. 
     In the modification shown in FIG. 14 e,  resistor-film connection pads  184   a  and  184   b  in each lapping sensor section  181  are formed in a circular shape, and are aligned in a slanting direction with respect to a lapping surface  185 . Therefore, in this modification, effective utilization of the lateral width of each lapping sensor section  181  cannot be expected as the embodiment of FIGS. 5 and 6. However, since the space between the upper connection pad  184   a  and the lower connection pad  184   b  and the space between the lower connection pad  184   b  and the lapping surface  185  can be more widened, short circuit between these connection pads and the wires can be more effectively prevented. 
     In the modification shown in FIG. 14 f,  resistor-film connection pads  194   a  and  194   b  in each lapping sensor section  191  are formed in an oval shape with a long axis perpendicular to a lapping surface  195 , and are aligned in a slanting direction with respect to the lapping surface  195 . Therefore, in this modification, effective utilization of the lateral width of each lapping sensor section  191  cannot be expected as the embodiment of FIGS. 5 and 6. However, since the space between the upper connection pad  194   a  and the lower connection pad  194   b  and the space between the lower connection pad  194   b  and the lapping surface  195  can be more widened, short circuit between these connection pads and the wires can be more effectively prevented. 
     In the modification shown in FIG. 14 g , resistor-film connection pads  204   a  and  204   b  in each lapping sensor section  201  are formed in an oval shape with a long axis in a slanting to a lapping surface  205 , and are aligned in a slanting direction with respect to the lapping surface  205 . Therefore, in this modification, effective utilization of the lateral width of each lapping sensor section  201  cannot be expected as the embodiment of FIGS. 5 and 6. However, since the space between the upper connection pad  204   a  and the lower connection pad  204   b  and the space between the lower connection pad  204   b  and the lapping surface  205  can be more widened, short circuit between these connection pads and the wires can be more effectively prevented. 
     It is apparent that the shape of the resistor-film connection pads in the lapping sensor section according to the present invention will not limited to the above-mentioned embodiment and modifications but various shapes can be adopted. 
     Many widely different embodiments of the present invention may be constructed without departing from the spirit and scope of the present invention. It should be understood that the present invention is not limited to the specific embodiments described in the specification, except as defined in the appended claims.