Abstract:
A method of manufacturing a thin-film magnetic head slider suppresses the production of damaged areas during lapping, reduces the lapping time, produces high-quality products, and is suited to mass production. The method of manufacturing a thin-film magnetic head slider laps an end surface of a row bar, which has been produced by cutting a wafer substrate on which magnetic sensor parts have been formed into strips, to expose an end surface of magnetic sensor parts to a floating surface, wherein a high processing rate is set in an initial part of a lapping process that laps the row bar and a lower processing rate is set in a later part of the lapping process.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a method of manufacturing a thin-film magnetic head slider, and in particular to a method of manufacturing a thin-film magnetic head slider characterized by a lapping method used on a floating surface of the thin-film magnetic head slider.  
         [0003]     2. Related Art  
         [0004]     In the manufacturing process of a thin-film magnetic head slider, after magnetic sensor parts for reading and writing have been formed on a wafer substrate, the wafer substrate is cut into strips in accordance with the arrangement of elements formed on the wafer substrate and a lapping process is then carried out on the end surfaces of a row bar of cut-out sliders. The process that laps the end surface of a row bar exposes the magnetic sensor parts to the floating surface, with the lapping also having an object of producing predetermined characteristics for the magnetic sensor parts.  
         [0005]      FIG. 4  is a diagram useful in explaining the construction of the magnetic sensor part of a composite-type thin-film magnetic head slider. An MR element  11  is formed between a base shield layer  10  and an upper shield layer  12  as a read head. The write head is constructed by winding a conductive coil  13  between the upper shield layer  12 , which acts as a bottom magnetic pole, and a top magnetic pole  14 , and forming the magnetic pole tips  12   a,    14   a  at the tips of the bottom magnetic pole and the top magnetic pole  14 .  
         [0006]     During the process that laps the end surface of the row bar to expose the magnetic sensor parts to the floating surface, as described above it is also necessary to control the characteristics of the magnetic sensor parts. A method is therefore used where a lapping process is carried out while monitoring the resistance of the magnetic sensor parts (the MR elements) and the lapping is stopped when the resistance of the magnetic sensor parts has reached a predetermined value. 
    Patent Document 1    
 
         [0008]     Japanese Laid-Open Patent Publication No. S62-199354 
    Patent Document 2    
 
         [0010]     Japanese Laid-Open Patent Publication No. H11-121410 
    Patent Document 3    
 
         [0012]     Japanese Laid-Open Patent Publication No. H6-246602  
         [0013]     During the manufacturing process of a thin-film magnetic head slider, extremely high lapping precision is required to lap the floating surface of the sliders while monitoring the resistance of the magnetic sensor parts. Due to the construction of a thin-film magnetic head slider, there are problems such as electrical short circuits easily occurring at the magnetic sensor parts and deterioration occurring in the output of the magnetic sensor parts due to damaged areas (positions where fine scratches have been formed by the lapping) and/or distorted parts being formed. For this reason, the lapping process is normally carried out with the lowest possible processing rate.  
         [0014]     However, since the processing time is increased when the processing rate of the lapping process is decreased, there is a limit on how slow the processing rate can be made when products need to be mass produced. Also, for a thin-film magnetic head slider used for recording and reproducing extremely high-density information, a process that produces even fewer damaged areas is required, and therefore the lapping needs to be carried out with an even lower processing rate. Accordingly, when such products are manufactured, an even longer processing time is required, resulting in the problem of mass-production being hindered.  
       SUMMARY OF THE INVENTION  
       [0015]     The present invention was conceived to solve the problem described above, and it is an object of the present invention to provide a method of manufacturing a thin-film magnetic head slider that suppresses the occurrence of damaged areas during lapping, does not increase the lapping time, produces high-quality products, and is suited to mass production.  
         [0016]     To achieve the stated object, the present invention is a method of manufacturing a thin-film magnetic head slider that laps an end surface of a row bar, which has been produced by cutting a wafer substrate on which magnetic sensor parts have been formed into strips, to expose an end surface of the magnetic sensor parts to a floating surface, wherein a high processing rate is set in an initial part of a lapping process that laps the row bar and a lower processing rate is set in a latter part of the lapping process.  
         [0017]     The lapping process may be divided into a plurality of stages in which the processing rate changes in steps, and the processing rate may be set high in an initial stage out of the plurality of stages and set lower in latter stages.  
         [0018]     Also, the lapping process may be set so that the processing rate continuously changes, and the processing rate may be set high in an initial part of the lapping process and may decrease as the lapping process proceeds.  
         [0019]     The processing rate may be changed by changing a relative velocity of a lapping plate and the row bar, by changing a pressure applied by the row bar to a lapping plate, and/or by changing a velocity with which the row bar is moved on the lapping plate.  
         [0020]     The entire lapping process on the row bar may be carried out using a single lapping device so that the lapping process can be carried out efficiently.  
         [0021]     With the method of manufacturing a thin-film magnetic head slider according to the present invention, it is possible to effectively lap thin-film magnetic head sliders, to suppress the occurrence of damaged areas and distorted parts, and to carry out lapping with high quality, thereby manufacturing non-defective thin-film magnetic head sliders. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]     The aforementioned and other objects and advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying drawings.  
         [0023]     In the drawings:  
         [0024]      FIG. 1  is a diagram useful in explaining a method of lapping a workpiece using a lapping plate;  
         [0025]      FIG. 2  is a graph showing the required processing time when the pressure is changed;  
         [0026]      FIG. 3  is a graph showing the required processing time when the relative velocity is changed; and  
         [0027]      FIG. 4  is a diagram useful in explaining the construction of a magnetic sensor part of a thin-film magnetic head slider. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]     Preferred embodiments of the present invention will now be described in detail with reference to the attached drawings.  
         [0029]     The method of manufacturing a thin-film magnetic head slider according to the present invention is characterized in that when an end surface of a row bar, which has been cut out in a strip from a wafer substrate on which magnetic sensor parts have been formed, is lapped, the lapping process is carried out while conditions (relative velocity and applied pressure) are changed either in accordance with stages in the lapping process or continuously as the lapping process proceeds.  
         [0030]      FIG. 1  shows a state where a row bar as a workpiece  22  is pressed onto a lapping plate  20  and lapped. When the lapping process is carried out on the workpiece  22  using the lapping plate  20 , as shown in  FIG. 1 , the lapping plate  20  is rotated in one direction and the workpiece  22  is pressed onto a lapping surface of the lapping plate  20  with a predetermined pressure and also moved on the lapping surface, resulting in the workpiece  22  being lapped.  
         [0031]     The workpiece  22  is moved on the lapping plate  20  so that the workpiece  22  is lapped uniformly. When the row bar is lapped, the row bar is moved on the lapping plate  20  so as to trace a circle with a fixed radius of rotation.  
         [0032]     When a workpiece is lapped using a lapping plate, the processing rate increases as the rotational velocity of the lapping plate increases. The processing rate also increases as the pressure with which the workpiece is pressed onto the lapping plate increases.  
         [0033]     If the relative velocity of the lapping plate  20  and the workpiece is set at ν (m/min) the pressure applied on the workpiece is set as p (kgf/cm 2 ), and the processing time is set at t (min), the lapped amount h (μm) is governed by Preston&#39;s Law. 
 
 h=η   w   ·ν·p·t  (where η w  is a constant of proportionality)
 
         [0034]     The processing rate is therefore h/t=η w ·v·p. That is, the processing rate is proportionate to the relative velocity ν and the pressure p of the lapping plate and the workpiece. The lapped amount can also be calculated by integrating the processing rate with respect to time.  
         [0035]      FIG. 2  is a graph showing how the required lapping time changes when the applied pressure is changed and  FIG. 3  is a graph showing how the required lapping time changes when the relative velocity is changed.  FIG. 2  shows that the lapping time increases as the applied pressure is reduced and  FIG. 3  shows that the lapping time increases as the relative velocity falls.  
         [0036]     In the method of manufacturing a thin-film magnetic head slider according to the present embodiment, the lapping time can be controlled by adjusting the relative velocity of the lapping plate  20  and the workpiece  22  and by adjusting the pressure with which the workpiece  22  is pressed onto the lapping plate  20 .  
         [0037]     In the actual method of lapping a row bar as the workpiece  22  in the present embodiment, lapping is first carried out with a high processing rate as a first stage and lapping is then carried out with a low processing rate as a second stage.  
         [0038]     Table 1 shows the lapping characteristics when a row bar has been actually lapped and the results of measuring an MR ratio for evaluating the quality characteristics of a thin-film magnetic head slider after lapping.  
         [0039]     Condition “a” in Table 1 shows the case where the relative velocity and applied pressure do not change from the start of lapping to the end of lapping. Condition “b” in Table 1 shows the case where the lapping process is divided into two stages referred to as a first stage and a second stage and the relative velocity and applied pressure are changed.  
                                   TABLE 1                               Plate   Workpiece   Applied           Condition   Stage   Velocity   Velocity   Pressure   MR Ratio                   a   —   1.0 rpm   15 rpm   0.20 kgf/cm 2     4.2%       b   1   1.0 rpm   15 rpm   0.20 kgf/cm 2     7.0%           2   0.5 rpm   15 rpm   0.02 kgf/cm 2                    
 
         [0040]     As shown in Table 1, in Condition b, the lapping conditions of the first stage are the same as in Condition a, while in the lapping conditions of the second stage, the rotational velocity of the lapping plate is reduced and the applied pressure is reduced to around one tenth of the pressure in the first stage.  
         [0041]     By comparing the experiment results for Conditions a and b, there is a clear difference in the MR ratio of the thin-film magnetic head sliders between the case (Condition a) where the relative velocity and the applied pressure do not change and the case (Condition b) where the relative velocity and the applied pressure are changed between the first stage and the second stage. Compared to Condition a, a larger MR ratio is achieved for the thin-film magnetic head sliders with Condition b, which means that quality is improved.  
         [0042]     It should be noted that Condition a shown in Table 1 shows the normal processing conditions when lapping a row bar in a conventional manufacturing process for thin-film magnetic head sliders (a processing rate used to avoid producing damaged areas). In both Conditions a and b, the velocity by which the workpiece moves relative to the lapping plate is fixed. However, it is also possible to change the processing rate by changing this velocity by which the workpiece moves relative to the lapping plate.  
         [0043]     The experiment results in Table 1 show that compared to a process where fixed lapping conditions are used from the start of lapping to the end, the characteristics of a thin-film magnetic head slider can be effectively improved by lapping with a high processing rate in a first stage and then lapping with a low processing rate in a second stage.  
         [0044]     That is, even when lapping has been carried out with the processing rate set comparatively high in the first stage, by setting a low processing rate in the second stage, it is possible to achieve a favorable lapping result. It is thought that by setting a low processing rate in the second stage, damaged areas that occur when the lapping has been carried out with a high processing rate can be removed.  
         [0045]     In this way, instead of performing the entire lapping process with the same lapping conditions, by setting a high processing rate at the start of lapping and then setting a low processing rate for a latter part of the lapping process as the lapping proceeds, compared to the case where a low processing rate is used for the entire process, the lapping can be carried out efficiently with a reduced lapping time, with it also being possible to improve the lapping quality.  
         [0046]     Since thin-film magnetic head sliders have an extremely fine structure, sliders are susceptible to electrical short circuits occurring during lapping and the characteristics can easily deteriorate due to damaged areas being formed. This means that lapping has to be carried out with high precision. Since it is possible to effectively reduce the lapping time and the characteristics of the lapped workpiece can be improved, the present invention can be effectively used as a method of processing thin-film magnetic head sliders.  
         [0047]     It should be noted that in the present embodiment, the lapping process is divided into two stages referred to as the first stage and the second stage, but it is also possible to divide the lapping process into three or more stages. When lapping is carried out in a plurality of stages, the processing rate is set so as to decrease as the process moves to the latter stages.  
         [0048]     It is also possible to change the lapping conditions gradually and continuously instead of changing the conditions in steps. In this case also, the processing rate is set so as to decrease toward the end of the process, with it being possible to carry out lapping so that the workpiece and the lapping plate finally stop (the velocity reaches zero) and the applied pressure reaches zero.  
         [0049]     In the lapping method according to the present invention, lapping is carried out by changing the lapping rate while using the same lapping device. By using the same lapping device, it is possible to efficiently carry out lapping while changing the processing rate as the lapping proceeds.  
         [0050]     It should be noted that in the lapping process of thin-film magnetic head sliders, lapping is carried out by controlling the lapped amount while monitoring the resistance of the magnetic sensor parts as described above. In this case, there is a method that monitors the magnetic sensor parts themselves and a method that uses resistors such as metal films embedded for monitoring purposes. In either case, since the resistance falls as the lapping process proceeds, by setting in advance a processing range where the high processing rate is set and a processing range where the low processing rate is set for the intended resistance value, it is possible to carry out lapping while controlling the lapping conditions in accordance with the monitored resistance value, which makes it possible to carry out lapping with higher precision.