Abstract:
The present invention relate to provide a lapping method and apparatus that increases the yield rate in the magnetic head slider manufacturing process, but does not make output and asymmetry characteristics worse. According to the invention, an apparatus for lapping thin film magnetic heads includes a jig block and a lapping plate. The jig block includes a first jig that holds a bar to be lapped, and second jig that holds a member for load sharing. The lapping plate is movable relative to the first jig and the second jig, and is contactable with the surface to be lapped of the bar held by the first jig and the member for load sharing held by the second jig for lapping.

Description:
PRIORITY CLAIM  
       [0001]     This application claims priority from Japanese patent application No.2003-369205, filed on Oct. 29, 2003, which is incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a lapping apparatus and method used in the lapping process for the manufacture of thin film magnetic heads.  
         [0004]     2. Description of the Related Art  
         [0005]     A magnetic head slider used in a magnetic disc provides at least one thin film head element, which is located at training edge (exhaust side of the air flow) of the magnetic head slider, and the magnetic head slider is provided that it floats in the sky from a surface of the magnetic disc by rotating the magnetic disc.  
         [0006]     In the manufacturing process, a plural of magnetic head elements are formed on a wafer (substrate), and then cut the wafer into a plural of bars, which have a plural of magnetic head elements in line, and then lapping the air bearing surface (ABS) of a bar is performed, whereby air bearing surface is the surface, which faces the surface of the magnetic disc.  
         [0007]      FIG. 1   a  and  1   b  are a plane view of a holding jig, which is used in a lapping method according to the prior art, showing from a lapping plate side.  
         [0008]     For the lapping method according to the prior art, as shown in  FIG. 1   a  and  1   b,  a triangle shaped holding jig  10  or a square shaped holding jig  11  which can rotate themselves around a supporting point  10   a  or  11   b  is used. More specifically, three bars  12  or four bars  13  to be lapped are fixed on the plane  10   b  or  11   b  of the holding jig, whereby the plane  10   b  and  11   b  face the lapping plate, and the surface to be ABS of the bars  12  or  13  are lapped by rotating the holding jig  10  or  11  around the supporting point  10   a  or  11   b  as well as rotating the lapping plate.  
         [0009]     This method makes it possible to lapping a plural of bars at the same time, therefore, efficiency of lapping increases, and machining time can be shortened, and stress applied to each bars spreads, however, since amount of lapping (amount of height) is controlled by the lapping time, it is not possible to change the amount of lapping by each bar to be lapped at the same time, and therefore it causes the serious problem that the characteristics of the magnetic head slider to be manufactured vary widely.  
         [0010]     To solve the above-mentioned problem, according to the prior art, JP laid open 2001-6128 propose a method for lapping control, which is referred as resistance lapping guide (RLG), by measuring the value of resistance of sensors which are formed on the bar.  
         [0011]     However, for the lapping by RLG method, it is required to lap only one bar fixed on one holding jig, which is mounted on one lapping apparatus, based on its principle of operation.  
         [0012]     Therefore following problems are caused by use of RLG method.  
         [0013]     (1) As the thin film magnetic head advances, required characteristics become more severe, so that in the magnetic head slider manufacturing process, yield rate is decreasing, because a lot of magnetic head sliders are rejected in the quasi static test (QST), especially rejected by bad output and asymmetry characteristics. It decreases the yield rate in the head gimbal assembly (HGA) process, in which the magnetic head sliders are attached to suspension arms.  
         [0014]     (2) Similarly, since it is required for ABS surface to finish with high accuracy, processing becomes more difficult.  
         [0015]     Therefore profile about the finished surface of the magnetic head slider, for example recess or crown profile become to vary widely. Wide variability of the profile causes the instability of magnetic spacing such as height of airborne, it increase the variation of electromagnetic conversion transfer characteristic in the HGA process, therefore it leads the decreasing of yield rate in the HGA process.  
       BRIEF SUMMARY OF THE INVENTION  
       [0016]     The invention has been made in view of the above-mentioned problem, and It is therefore an object of the present invention to provide a lapping method and apparatus that increases the yield rate in the magnetic head slider manufacturing process, but does not make output and asymmetry characteristics bad.  
         [0017]     Another object of the present invention is to provide a lapping method and apparatus that reducing the variation of the profile of magnetic head sliders.  
         [0018]     According to the present invention, an apparatus for lapping thin film magnetic heads including: a jig block having a first jig and at least one second jig, the first jig holding a bar having a plural of thin film magnetic heads in lines, the second jig holding a member for load sharing, and; a lapping plate being movable relative to the first jig and the second jig, and being contactable with the surface to be lapped of the bar held by the first jig and the member for load sharing held by the second jig for lapping.  
         [0019]     According to the another aspect of the invention, a method for lapping thin film magnetic heads which comprises the step of: holding a bar to contact with a lapping plate by use of a holding jig block, the bar having a plural of thin film magnetic heads in lines, holding at least one member for load sharing to contact with the lapping plate by use of the holding jig; and lapping a surface of the bar by moving the lapping plate relative to the bar.  
         [0020]     As mentioned above, it is required to lap only one bar fixed on one holding jig, which is mounted on one lapping apparatus, when the lapping is performed by use of the RLG method. Therefore it applies the strong load or stress to the bar. The study of inventors of this application shows that bad characteristic of the output and/or asymmetry in the manufacturing process and big variation of between profiles are caused by the load or stress applied to the bar during the lapping operation. Therefore to reduce the load applied to the bar, such as the machine load, drag from the lapping plate and frictional force with the lapping plate, at least one member for load sharing, which is lapped together with the bar, is provided to distribute the load or stress. As a result, both playback output and asymmetry characteristic are improved. Also the defect occurring the surface of the lapping plate and the magnetic head slider, such as scratches and abrasions are reduced, and variation between profiles as well as amount of recess are reduced. Therefore yield rate is significantly improved in the manufacturing process of the magnetic head sliders and HGA.  
         [0021]     Favourably, the second jig lies anterior to the first jig on the basis of the relative move direction of the lapping plate, so that means the member for load sharing lies anterior to the bar.  
         [0022]     Preferably, the second jig or the member is attached to the jig block with the fixed or variable angle relative to move direction of the lapping plate.  
         [0023]     Advantageously, the lapping operation for the bar is controlled by the signal from a sensor, which is formed in the bar, such as RLG.  
         [0024]     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 SEVERAL VIEWS OF THE DRAWINGS  
       [0025]      FIG. 1   a,  already described, is a plane view of a holding jig, which is used in a lapping method according to the prior art, showing from a lapping plate;  
         [0026]      FIG. 1   b,  already described, is a plane view of a holding jig, which is used in a lapping method according to the prior art, showing from a lapping plate;  
         [0027]      FIG. 2  is a perspective view showing an embodiment of a lapping apparatus schematically according to the present invention;  
         [0028]      FIG. 3  is an enlarged perspective view of the lapping apparatus shown in  FIG. 2 , for showing the detail of the holding jig block;  
         [0029]      FIG. 4  is a plane view illustrating RLG sensors formed on the bar;  
         [0030]      FIG. 5  is an example of flow diagram used in the lapping process;  
         [0031]      FIG. 6   a  illustrates the amount of recess to be measured;  
         [0032]      FIG. 6   b  illustrates the amount of crown to be measured;  
         [0033]      FIG. 7   a  shows the average amount of recess of samples, which are made by the lapping method according to the present invention, and measured by the surface profiler;  
         [0034]      FIG. 7   b  shows the average amount of recess of samples, which are made by the lapping method according to the prior art, and measured by the surface profiler;  
         [0035]      FIG. 8   a  shows the average amount of crown of samples, which are made by the lapping method according to the present invention, and measured by the surface profiler;  
         [0036]      FIG. 8   b  shows the average amount of crown of samples, which are made by the lapping method according to the prior art, and measured by the surface profiler;  
         [0037]      FIG. 9  is a SEM picture of the lapped surface of the thin film magnetic head made by the lapping method according to the present invention;  
         [0038]      FIG. 10 a  SEM picture of the lapped surface of the thin film magnetic head made by the lapping method according to the prior art;  
         [0039]      FIG. 11  is an enlarged perspective view of the lapping apparatus showing the holding jig block according to another embodiment of the present invention;  
         [0040]      FIG. 12  is an enlarged perspective view showing the holding jig block only according to further embodiment of the present invention; and  
         [0041]      FIG. 13  is an enlarged perspective view showing the holding jig block only according to further embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0042]      FIG. 2  is a perspective view showing an embodiment of a lapping apparatus schematically according to the present invention, and  FIG. 3  is an enlarged perspective view of the lapping apparatus shown in  FIG. 2 , for showing the detail of the holding jig block.  
         [0043]     In the  FIG. 2  and  FIG. 3 , reference  20  is a lapping plate, which rotates the direction indicated by the arrow, and reference  21  is a holding jig block or assembly, whereby a holding jig in the holding jig block  21  holds the bar to be lapped, and reference  22  is a transfer tool, which supports the holding jig in the holding jig block  21 , and provides the signal line to transmit the signal from a lapping amount sensor, which is described later, to controller of the lapping apparatus.  
         [0044]     The holding jig block  21  mainly includes a rectangular column shaped jig  24  (a first jig), which holds a bar  23  to be lapped, and a dummy bar jig  26  (a second jig), which holds a dummy bar  25 , and a lapping keeper  27 , which is fixed to the dummy bar jig  26  at one end, and fixed to the rectangular column shaped jig  24  at other end. The dummy bar  25  is favorably made of the same material as the bar  23 , such as AlTiC (Al 2 O 3 —TiC).  
         [0045]     The bar  23  has a plural of thin film magnetic heads, which are arranged in one line or several lines, and is obtained by cutting the wafer, on which a plural of thin film magnetic heads are formed. By way of example, mageto-resistive films  40 ,  41  and  42  of the thin film magnetic head are formed on the side of ABS (surface to be lapped)  23 a of the bar  23  as shown in  FIG. 4 , and arranged in line, and MR films  43  and  44  of RLG sensor (hereinafter referred to as RLG sensors for short), which is the sensor of the amount of lapping, are respectively formed between MR films of the thin film head.  
         [0046]     MR height is calculated based on the value of resistance of the RLG sensor  43  and  44 , whereby the value of resistance changes dynamically during the lapping, and lapping operation is controlled. The method for calculating the MR height from the value of resistance of the RLG sensor is well known, therefore, detailed description is omitted. (See JP laid open 2003-91804 for more detail) In the embodiment, the dummy bar jig  26  lies anterior to the rectangular column shaped jig  24  on the basis of the rotation direction, so that means dummy bar  25  lies anterior to the bar  23 .  
         [0047]     The lapping is performed by pressing the lapped surface of the bar  23  to a lapping surface  20 a of the rotating lapping plate  20 . In this case, both the bar  23  and the dummy bar  25  are pressed to the lapping plate, so that the load during the lapping, for example machine load, drag from the lapping plate and frictional force with the lapping plate, is not concentrated to the bar  23 , but distributed to two points. Therefore, output and asymmetry characteristic of the magnetic head slider are improved, it does not lead the defect occurring on the surface of the lapping plate and the slider such as scratches or abrasions, and it reduces the variation between profiles, and it reduces the variation between amount of recess of the magnetic head slider. As a result, the yield rate is significantly improved in the manufacturing process of the magnetic head sliders and HGA.  
         [0048]      FIG. 5  is an example of flow diagram used in the lapping process First, the bar  23  is attached to the rectangular column shaped jig  24  (Step S 1 ). ABS (Surface to be lapped) should face to the lapping plate  20 , and the training edge (exhaust side of the air flow) should place the backside based on the rotation direction of the lapping plate  20 .  
         [0049]     Next a first lapping is performed using RLG sensors (Step S 2 ). The purpose of the first lapping is to adjust the MR height of the bar for desired height. The condition for it, for example, grain diameter of the slurry is about {fraction (1/10)} um, lapping time is about 10 to 20 minutes, the stress is about 1.0 to 2.0 kgf, and rotation speed of the lapping plate is about 10 to 60 rpm.  
         [0050]     Next a second lapping is performed using solvent (step S 3 ). The purpose of the second lapping is to complete the adjusting the MR height. The condition for it, for example, using diamond slurry and oil solvent, grain diameter of the slurry is about ⅛ um, lapping time is about 3 to 7 minutes, the stress is about 1.5 to 2.3 kgf, rotation speed of the lapping plate is about 2 to 4 rpm.  
         [0051]     Then a third lapping is performed using solvent (step S 4 ). The purpose of the third lapping is for mirror finish. The condition for it, for example, using diamond slurry and oil solvent, grain diameter of the slurry is about {fraction (1/10)} um, lapping time is about 1 to 3 minutes, the stress is about 3.5 to 4.5 kgf, rotation speed of the lapping plate is about 2 to 3 rpm.  
         [0052]     Next the lapped bar  23  is detached from the rectangular column shaped jig  24  (Step S 5 ).  
         [0053]     Then rails are formed on the ABS of bar  23  (Not shown in  FIG. 5 ), cut the bar  23  into a plural of single magnetic head slider. Finally, the magnetic head slider is mounted on a suspension to complete the HGA.  
         [0054]     In accordance with the above-mentioned lapping process, bars were lapped, and the rails were formed on the each bar, and then output and asymmetry characteristic of giant magneto resistance (GMR) head elements were measured by QST. Also amount of recess and amount of crown were measured as a profile by the surface profiler. For comparison, the same measurement was performed for the bars, which were lapped using the lapping apparatus according to the prior art. Hereupon, amount of recess means a distance between the ABS  61  of the magnetic head slider and magnetic head element  60  as shown in  FIG. 6   a,  and amount of crown means amplitude of a bend of ABS of the magnetic head slider  62  as shown in  FIG. 6   b.    
         [0055]     Table 1 shows the playback output characteristic, asymmetry characteristic and yield rate of the QST for the samples made by the lapping method according to the embodiment shown in  FIG. 2  as well as the prior art.  
         [0056]     The number of lots used was  10 , whereby each lot had  100  samples. The condition for QST is, sense current for GMR reading head is 3.0 mA, and writing current for inductive recording head element is the value when 60 mV0p voltage is applied to each writing head element, frequency of the writing current is 80 MHz, frequency of the applied magnetic field is 1.0 kHz with 10 us applied time, and measurement was done when amplitude of the applied magnetic field was 700 e. Asymmetry is calculated by (V 1 −V 2 )/(V 1 +V 2 )*100 (%), wherein V 1  is the positive amplitude, and V 2  is the negative amplitude of the playback output. Acceptance criterion for the QST is playback output characteristic, which has equal or greater than 500 uVpp, and asymmetry characteristic, which has equal or greater than −40% and equal or less than +40%.  
                                                         TABLE 1                                       Playback                   output (uV)   Asymmetry (%)                    Standard       Standard   Yield rate           Average   deviation   Average   deviation   of QST               Embodiment in   865.8   377.1   1.5   24.5   80.3               Prior art   811.2   400.0   2.5   28.7   70.2       Comparison   Increase   Decrease   Improved   Decrease   Improved           by 6.7%   by 5.7%   by 1.0%   by 4.2%   by 10.1%                  
 
         [0057]     As shown in the Table 1, average playback output characteristic according to the embodiment shown in  FIG. 2  increases by 6.7%, and the standard deviation of playback output decreases by 5.7%, so that means the variation is reduced, in comparison with the ones according to the prior art. For asymmetry, average value decreases by 1.0%, so that means the symmetry is improved, and standard deviation decreases by 4.2%, so that means the variation is reduced. As a result, yield rate of QST increases by about 10%.  
         [0058]      FIG. 7   a  shows the average amount of recess of samples, which are made by the lapping method according to the embodiment shown in  FIG. 2 , and measured by the surface profiler, and  FIG. 7   b  shows the ones according to the prior art.  
         [0059]     In these figures, horizontal axis shows the amount of recess, and vertical axis shows the numbers corresponding to the amount of recess. The number of samples is 100. According to the embodiment shown in  FIG. 2 , average is −2.7 nm, and standard deviation is 1.35 nm, however, according to the prior art, average is −6.03 nm, and standard deviation is 1.8 nm. So the recess can be formed with high accuracy, and less variation by use of the method according to the embodiment shown in  FIG. 2 .  
         [0060]      FIG. 8   a  shows the average amount of crown of samples, which are made by the lapping method according to the embodiment shown in  FIG. 2 , and measured by the surface profiler, and  FIG. 8   b  shows the ones according to the prior art.  
         [0061]     In these figures, horizontal axis shows the amount of crown, and vertical axis shows the numbers corresponding to the amount of crown. The number of samples is 100. According to the embodiment shown in  FIG. 2 , average is 4.7 nm, and standard deviation is 1.29 nm, however, according to the prior art, average is 13.64 nm, and standard deviation is 4.6 nm. So crown can be formed with high accuracy and less variation by use of the method according to the embodiment shown in  FIG. 2 .  
         [0062]      FIG. 9  is a SEM picture (×40,000) of the lapped surface of the thin film magnetic head made by the lapping method according to the embodiment shown in  FIG. 2 , and  FIG. 10  is the one according to the prior art.  
         [0063]     The surface of the head shown in  FIG. 10  has many scratches or abrasions, but one shown in  FIG. 9  has less ones.  
         [0064]     As described above, according to the embodiment shown in  FIG. 2 , providing the dummy bar decreases the load to the bar to be lapped, so that it reduces the strain of the head element, whereby the strain is caused by the stress after the lapping, therefore, the average playback output increases, and variation of the playback output is reduced. Moreover, the average asymmetry can be closed to the desired value, and the variation of asymmetry is reduced. As a result, QST yield rate is improved. Furthermore, the variation between profiles of each magnetic head slider is also improved, and the defect occurring on the surface of the lapping plate and the magnetic head during the lapping process, such as the scratches or abrasions, can be reduced substantially.  
         [0065]      FIG. 11  is an enlarged perspective view of the lapping apparatus showing the holding jig block or assembly according to another embodiment of the present invention.  
         [0066]     In the  FIG. 11 , reference  110  is a lapping plate, which rotates the direction indicated by the arrow, and reference Ill is a holding jig block, whereby a holding jig in the holding jig block  111  holds the bar to be lapped, and reference  112  is a transfer tool, which supports the holding jig in the holding jig block  111 , and provides the signal line to transmit the signal from a lapping amount sensor to controller of the lapping apparatus.  
         [0067]     The holding jig block  111  mainly includes a rectangular column shaped jig  114  (a first jig), which holds a bar  113  to be lapped, and a dummy bar jig  116  (a second jig), which holds a dummy bar  115 , and a lapping keeper  117 , which supports the dummy bar jig  116  as rotatable at one end, and fixed to the rectangular column shaped jig  114  at other end. The dummy bar  115  is favorably made of the same material as the bar  113 , such as AlTiC (Al 2 O 3 —TiC).  
         [0068]     The bar  113  has a plural of thin film magnetic heads, which are arranged in one line or several lines, and is obtained by cutting the wafer, on which a plural of thin film magnetic heads are formed. The same as the embodiment shown in.  FIG. 2 , MR film  40 ,  41  and  42  (See  FIG. 4 ) of the thin film magnetic head are formed on the side of ABS (surface to be lapped) of the bar  113 , and arranged in line, and RLG sensor are respectively formed between MR films. MR height is calculated based on the value of resistance of the RLG sensor  43  and  44 , whereby the value of resistance changes dynamically during the lapping, and lapping operation is controlled based on it.  
         [0069]     In the embodiment, the dummy bar jig  116  is placed in front of the rectangular column shaped jig  114  in accordance with the rotation direction, so that means dummy bar  115  is placed in front of the bar  113 .  
         [0070]     The lapping is performed by pressing the surface to be lapped of the bar  113  against a lapping surface  110   a  of the lapping plate  110 , which is rotating. In this case, both the bar  113  and the dummy bar  115  are pressed against the lapping plate  110 , so that the load during the lapping, for example machine load, drag from the lapping plate and frictional force with the lapping plate, is not concentrated only to the bar  113 , but dispersed to two points. Therefore, output and asymmetry characteristic of the magnetic head slider are improved, and it does not lead the scratch onto the surface of the lapping plate and the slider, furthermore, it reduces the variation of the profile, and it reduces the deviation of the amount of recess. As a result, the yield rate is significantly improved in the manufacturing process of the magnetic head sliders and HGA.  
         [0071]     Especially, frictional force applied to the bar  113  is reduced significantly in the embodiment, because the dummy bar jig  116  is attached to the lapping keeper  117  as rotatable around a rotation axis  117   a.  Therefore, the load to the bar  113  is also reduced.  
         [0072]     The lapping process of the bar is the same as the embodiment shown in  FIG. 2 .  
         [0073]     After the lapping process, rails are formed on the ABS of bar  113  (Not show in  FIG. 11 ), cut the bar  113  into a plural of single magnetic head slider. Finally, the magnetic head slider is attached to a suspension to complete the HGA.  
         [0074]     In accordance with the above-mentioned lapping process, bars were lapped, and the rails were formed on the each bar, and then playback output and asymmetry characteristic of the GMR head element were measured by QST. For comparison, the same measurement was performed for the bars made by use of the lapping apparatus according to the prior art.  
         [0075]     Table  2  shows the playback output characteristic, asymmetry characteristic and yield rate of the QST for the samples made by the lapping method according to the embodiment shown in  FIG. 11 , shown in  FIG. 2  and the prior art.  
         [0076]     The number of lots used was  10 , whereby each lot had 100 samples. The condition for QST is sense current for GMR reading head is 3.0 mA, and writing current for inductive recording head element is the value when 60 mV0p voltage is applied to each writing head element, frequency of the writing current is 80 MHz, frequency of the applied magnetic field is 1.0 kHz with 10 us applied time, and measurement was done when amplitude of the applied magnetic field was 700 e. Asymmetry is calculated by (V 1 −V 2 )/(V 1 +V 2 )*100 (%), wherein V 1  is the positive amplitude, and V 2  is the negative amplitude of the playback output. Acceptance criterion for the QST is playback output characteristic, which has equal or greater than 500 uVpp, and asymmetry characteristic, which has equal or greater than −40% and equal or less than +40%.  
                                                                                   TABLE 2                                       Playback                   output (uV)   Asymmetry (%)                    Standard       Standard   Yield rate           Average   deviation   Average   deviation   of QST                    Embodiment in   865.8   377.1   1.5   24.5   80.3               Embodiment in   870   375.8   1.6   23.7   80.7               Prior art   811.2   400.0   2.5   28.7   70.2       Comparison the   Increase   Decrease   Improved   Decrease   Improved       embodment in   by 7.2%   by 6.1%   by 0.9%   by 5.0%   by 10.5%         FIG. 11  with       the prior art                  
 
         [0077]     As shown in the Table 2, average playback output characteristic according to the embodiment shown in  FIG. 11  increases by 7.2%, and standard deviation of playback output decreases by 6.1%, in comparison with the ones according to the prior art, so that means the variation is reduced. In comparison with ones according to the embodiment shown in  FIG. 2  (dummy bar is fixed), playback output increases by 4.2 uV, and standard deviation decreases by 1.3 uV, so that means the variation is reduced. For asymmetry, In comparison with the ones according to the prior art, average value decreases by 0.9%, so that means the symmetry is improved, and standard deviation decreases by 5.0%, so that means the variation is reduced. In comparison with the ones according to the embodiment shown in  FIG. 2 , average value is almost the same, but standard deviation decreases by 0.8%, so that means the variation is reduced. As a result yield rate of QST increases by about 10.5% in comparison with the one according to the prior art, and by 0.4% in comparison with the one according to the embodiment shown in  FIG. 2 .  
         [0078]     As described above, according to the embodiment shown in  FIG. 11 , providing the dummy bar, which can rotate, leads to the decrease of the frictional force to the bar, therefore the loads to the bar to be lapped is also further reduced, and it effectively reduces the strain of the head element, whereby the strain is caused by the stress after the lapping, so that the average playback output increases, and variation of the playback output decreases. Moreover, the average asymmetry can be closed to the desired value, and variation of asymmetry decreases. As a result, QST yield rate is improved. Furthermore, the variation between profiles of each magnetic head slider is also improved, and the defect occurring on the surface of the lapping plate and the magnetic head during the lapping process, such as the scratches or abrasions, can be reduced substantially.  
         [0079]      FIG. 12  is an enlarged perspective view showing the holding jig block only according to further embodiment of the present invention.  
         [0080]     In the  FIG. 12 , reference  121  is a holding jig block, whereby a holding jig in the holding jig block  121  holds the bar to be lapped. The holding jig block  121  mainly includes a rectangular column shaped jig  124  (a first jig), which holds a bar  123  to be lapped, and a first dummy bar jig  126   a  (a second jig), which holds a first dummy bar  125   a,  and a second dummy bar jig  126   b  (a second jig), which holds a second dummy bar  125   b,  and a lapping keeper  127 , which is fixed to the dummy bar jig  125   a  at one end to support it, and fixed to the rectangular column shaped jig  124  at other end, and is fixed to the dummy bar jig  125   b  at the middle to support it. The first dummy bar  125   a  and second dummy bar  125   b  are favorably made of the same material as the bar  123 , such as AlTiC (Al 2 O 3 —TiC).  
         [0081]     The bar  123  has a plural of thin film magnetic heads, which are arranged in one line or several lines, and it is obtained by cutting the wafer, on which a plural of thin film magnetic heads are formed. Same as the embodiment shown in  FIG. 2 , MR film  40 ,  41  and  42  (See  FIG. 4 ), which are arranged in line, of the thin film magnetic head are formed on the side of ABS (surface to be lapped) of the bar  123 , and RLG sensor are respectively formed between the MR films. MR height is calculated based on the value of resistance of the RLG sensor  43  and  44 , whereby the value of resistance changes dynamically during the lapping, and lapping operation is controlled.  
         [0082]     In the embodiment, jigs are placed in the order of the dummy bar jig  126   a,  the dummy bar jig  126   b,  and the rectangular column shaped jig  124  on the basis of the rotation direction, so that means dummy bar  125   a  and  125   b  lie anterior to the bar  123 .  
         [0083]     The lapping is performed by pressing the surface to be lapped of the bar  123  to a lapping surface of the rotating lapping plate. In this case, the bar  123 , dummy bar  125   a  and  125   b  are pressed together to the lapping plate, so that the load during the lapping, for example machine load, drag from the lapping plate and frictional force with the lapping plate, is not concentrated to the bar  123 , but distributed to three points. Therefore, output and asymmetry characteristic of the magnetic head slider are improved, and it does not lead to the defect on the surface, such as scratches, of the lapping plate and slider, moreover, it reduces the variation between profiles, and it reduces the variation between amount of recess of each magnetic head slider. As a result, the yield rate is significantly improved in the manufacturing process of the magnetic head sliders and HGA.  
         [0084]     Especially, the load applied to the bar  123  is further reduced in this embodiment, because the  2  dummy bars are provided.  
         [0085]     The lapping process of the bar is the same as the embodiment shown in  FIG. 2 .  
         [0086]     After the lapping process, rails are formed on the ABS of the bar  123  (Not show in  FIG. 12 ), and then cut the bar  123  into a plural of single magnetic head slider. Finally, the magnetic head slider is mounted on a suspension to complete the HGA.  
         [0087]     As described above, according to the embodiment shown in  FIG. 12 , By providing the two dummy bars, the loads to the bar to be lapped is further reduced, so that it effectively reduces the distortion of the head element, whereby the distortion is caused by the stress after the lapping, so that the average playback output increases, and variation of the playback output decreases. Moreover, the average asymmetry can be closed to the desired value, and variation of asymmetry decreases. As a result, QST yield rate is improved. Furthermore, the distribution of the profile of the magnetic head slider is also improved, and the defect occurring on the surface of the lapping plate and the magnetic head during the lapping process, such as the scratches or abrasions, can be reduced substantially.  
         [0088]      FIG. 13  is an enlarged perspective view showing the holding jig block only according to further embodiment of the present invention.  
         [0089]     In the  FIG. 13 , reference  131  is a holding jig block, whereby a holding jig in the holding jig block  131  holds the bar to be lapped. The holding jig block  131  mainly includes a rectangular column shaped jig  134  (a first jig), which holds a bar  133  to be lapped, and a first dummy bar jig  136   a  (a second jig), which holds a first dummy bar  135   a,  and a second dummy bar jig  136   b  (a second jig), which holds a second dummy bar  135   b,  and a third dummy bar jig  136   c  (a second jig), which holds a third dummy bar  135   c,  and a lapping keeper  137 , which is fixed to the dummy bar jig  135   a  at one end to support it, and fixed to the rectangular column shaped jig  134  at other end, and is fixed to the dummy bar jig  135   b  and  135   c  at the ends, which are vertical to the end of supporting the jig  135   a,  to support them. The first dummy bar  135   a,  second dummy bar  135   b  and the third dummy bar  135   c  are favorably made of the same material as the bar  133 , such as AlTiC (Al 2 O 3 —TiC).  
         [0090]     A plural of thin film magnetic heads, which are arranged in one line or several lines, are formed in the bar  133 , and the bar  113  is obtained by cutting the wafer, on which a plural of thin film magnetic heads are formed. Same as the embodiment shown in  FIG. 2 , MR film  40 ,  41  and  42  (See  FIG. 4 ) of the thin film magnetic head are formed on the side of ABS (surface to be lapped) of the bar  123  in a line, and RLG sensors are respectively formed between MR films. MR height is calculated based on the value of resistance of the RLG sensor  43  and  44 , whereby the value of resistance changes dynamically during the lapping, and lapping operation is controlled.  
         [0091]     In the embodiment, the dummy bar jig  136   a,    136   b  and  136   c  are placed ahead of the rectangular column shaped jig  134  on the basis of the rotation direction, so that means dummy bar  135   a,    135   b  and  135   c  are placed ahead of the bar  133 .  
         [0092]     The lapping is performed by pressing the surface to be lapped of the bar  133  to a lapping surface of the rotating lapping plate. In this case, the bar  133 , dummy bar  135   a,    135   b  and  135   c  are pressed together to the lapping plate, so that the load during the lapping, for example machine load, drag from the lapping plate and frictional force with the lapping plate, is not concentrated only to the bar  133 , but distributed to four points. Therefore, output and asymmetry characteristic of the magnetic head slider are improved, and it does not lead to the defect occurring on the surface of the lapping plate and slider, such as scratches, and it reduces the variation between profiles, and it reduces the variation between amount of recess of each magnetic head slider. As a result, the yield rate is significantly improved in the manufacturing process of the magnetic head sliders and HGA.  
         [0093]     Especially, the load applied to the bar  133  is further reduced in this embodiment, because the  3  dummy bars are provided.  
         [0094]     The lapping process of the bar is the same as the embodiment shown in  FIG. 2 .  
         [0095]     After the lapping process, rails are formed on the ABS of the bar  133  (Not show in  FIG. 13 ), and cut the bar  133  into a plural of single magnetic head slider. Finally, the magnetic head slider is attached to a suspension to complete the HGA.  
         [0096]     As described above, according to the embodiment shown in  FIG. 13 , By providing the three dummy bars, the loads to the bar to be lapped is further reduced, and it effectively reduces the strain of the head element, whereby the strain is caused by the stress after the lapping, so that the average playback output increases, and variation of the playback output is reduced. Moreover, the average asymmetry can be closed to the desired value, and variation of asymmetry decreases. As a result, QST yield rate is improved. Furthermore, the variaton between profiles of each magnetic head slider is also improved, and scratches or abrasions on the lapping plate and surface of the magnetic head can be reduced substantially.  
         [0097]     It is clear that the number of the dummy bars can be more than  4 , and the shape of each jig and/or configuration or assemble of the jig block is not limited to above-mentioned embodiment.  
         [0098]     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.