Abstract:
A head suspension for a hard disk drive is thin from an arm to a head and involves a minimum step between the arm and a load beam. The head suspension includes a load beam that includes a rigid part and a resilient part. The load beam applies load onto a head that is arranged at a front end of the load beam to write and read data to and from a disk arranged in the hard disk drive. The head is connected to read/write wiring patterns of a flexure. The flexure supports the head and is attached to a disk-facing surface of the rigid part. An arm is attached to a carriage of the hard disk drive and is turned around a spindle. The arm supports the resilient part that is attached to a base end of the rigid part. A disk-facing surface of the arm is arranged within the total of thicknesses of the rigid part and head.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a head suspension for a hard disk drive incorporated in an image processing unit such as a computer. 
     2. Description of Related Art 
       FIG. 1  shows part of a hard disk drive. The hard disk drive includes disks  2  serving as storage media. Data is written to and read from the disk  2  with a magnetic head  11  that is supported with a head suspension  101 . The head suspension  101  is attached to an arm  31 . The arm  31  is attached to a carriage  13 , which is turned around a spindle (not shown) by a positioning motor (not shown). The head suspension  101  includes a base plate  32 , a load beam  102  extending from the base plate  32  to the head  11 , and a flexure  103 . 
     The load beam  102  is made of, for example, a stainless steel (Japanese Industrial Standard: SUS304, SUS301, or the like) plate having a thickness in the range of 30 μm to 60 μm. The flexure  103  includes a substrate made of a stainless steel (SUS304) plate or a spring plate having a thickness of about 20 μm, an insulating layer formed on the substrate from, for example, polyimide resin, and a conductive layer made of, for example, copper by deposition or photolithography on the insulating layer. On the conductive layer, a protective layer is usually made from insulating material such as polyimide or epoxy resin. The total thickness of the flexure  103  is about 40 μm. 
     The arm  31  and base plate  32  are usually discrete parts. There is an integrated arm (called “unamount arm”) that is an integration of an arm and a base plate. The arm and base plate are collectively called “base” ( 12 ) hereinafter. The base plate  32  has a thickness of 200 μm to 300 μm. The bending elastic modulus of the base plate  32  is larger than that of the load beam  102  by one digit. 
     The load beam  102  includes a rigid part  21 , a resilient part  22 , and a joint part  105 . The resilient part  22  is bent by a predetermined amount toward the disk  2 , to apply a gram load onto the head  11  so that the head is pressed against the disk  2 . The joint part  105  of the load beam  102  is laid on and fixed to a surface of the base  12 . The flexure  103  transmits data to and from the head  11 . Between the head  11  and the joint part  105  of the load beam  102 , the flexure  103  is laser-welded at several spots to a surface of the load beam  102  that faces the disk  2 . 
     The head  11  lifts from the surface of the disk  2  due to an air flow when the disk  2  is rotated. It is preferable that a force to lift the head  11  balances with the gram load of the head suspension  101  so that the head  11  is stably kept at a slightly lifted position. For this, adjusting the gram load by bending the load beam  102  is essential to determine the performance of the hard disk drive. If the gram load is determined solely with the bending stress of the resilient part  22  of the load beam  102 , the designing of the head suspension  101  will be easy. 
     In practice, however, the bending stress of a combination of the resilient part  22  of the load beam  102  and the flexure  103  arranged in parallel with the resilient part  22  works on the head suspension  101 .  FIG. 2  is a perspective view showing an example of a head suspension  101  according to a related art. Like the head suspension  101  of  FIG. 1 , the head suspension  101  of  FIG. 2  includes a load beam  102 , a flexure  103 , and a base plate  32  serving as a base  12 . The load beam  102  includes a rigid part  21 , a resilient part  22 , and a joint part  105 .  FIG. 3  is an enlarged sectional view showing the resilient part  22  indicated with arrows III in  FIG. 2 . In  FIGS. 2 and 3 , the flexure  103  and rigid part  21  are fixed together at a joint spot X, the flexure  103  and a flexure attaching face  107  of the joint part  105  are fixed together at a joint spot Y, and the joint part  105  and base  12  are fixed together at a joint spot Z. The joint spot Y is separated away from the joint spot Z toward a disk, and therefore, the flexure  103  restricts movement of the resilient part  22 . Namely, a gram load acting on a head  11  is not determinable only with the bending stress of the resilient part  22  but it is greatly influenced by the bending stress of the flexure  103 . 
     In addition, due to temperature and humidity, the flexure  103  extends or contracts, and the elastic modulus thereof varies. If a proportion of the flexure  103  in the gram load is large, the gram load easily varies to raise a severe problem in designing the head suspension  101 . 
     The related art mentioned above is disclosed in Japanese Unexamined Patent Application Publication No. 11-514780. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to solve the problem that a flexure of a head suspension for a hard disk drive has a large contribution rate with respect to a gram load acting on a head of the head suspension. 
     In order to accomplish the object, an aspect of the present invention provides a head suspension having a base attached to a carriage. The head suspension is provided with a flexure attaching face in the base side. The flexure attaching face is stepped away from the disk-side surface of a joint part of a load beam. A flexure is fixed to a rigid part of the load beam as well as to the flexure attaching face. 
     According to this aspect of the present invention, the head suspension has the flexure attaching face, in the base side, that is stepped away from the disk-side surface of the joint part of the load beam. The flexure is fixed to the rigid part as well as to the flexure attaching face. Without regard to the presence of the joint part of the load beam, the flexure is fixed to the flexure attaching face in the base side, so that a resilient part of the load beam may act as a simple support beam. This configuration can reduce the contribution rate of the flexure with respect to a gram load, i.e., the bending stress of a combination of the load beam and flexure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional view showing a hard disk drive; 
         FIG. 2  is a perspective view showing a head suspension having a one-piece load beam according to a related art; 
         FIG. 3  is a view showing a part indicated with arrows III in  FIG. 2 ; 
         FIG. 4  is a perspective view showing a head suspension according to a first embodiment of the present invention; 
         FIG. 5  is a view showing a part indicated with arrows V in  FIG. 4 ; 
         FIG. 6  is a perspective view showing a unamount (integrated) head suspension according to a second embodiment of the present invention; 
         FIG. 7  is a perspective view showing a head suspension according to embodiments 3 and 4 of the present invention; 
         FIG. 8  is a perspective view showing a base plate of the head suspension of  FIG. 7 ; 
         FIG. 9  is a view showing a part indicated with arrows IX in  FIG. 7 ; 
         FIG. 10  is a perspective view showing a head suspension according to a fifth embodiment of the present invention; 
         FIG. 11  is a view showing a part indicated with arrows XI in  FIG. 10 ; 
         FIG. 12  is a perspective view showing a head suspension according to a sixth embodiment of the present invention; 
         FIG. 13  is a view showing a part indicated with arrows XIII in  FIG. 12 ; and 
         FIG. 14  is a table showing flexure contribution rates. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Head suspensions according to embodiments of the present invention will be explained. Each of the head suspensions reduces the contribution rate of a flexure with respect to a gram load by adjusting a joint of the flexure with respect to a base. 
     First Embodiment 
       FIGS. 4 and 5  show a head suspension  1  for a 2.5-inch hard disk drive according to the first embodiment of the present invention.  FIG. 4  is a perspective view showing part around a resilient part  22  of a load beam  14  of the head suspension  1  and  FIG. 5  is a sectional view showing a part indicated with arrows V in  FIG. 4 . In  FIGS. 4 and 5 , parts corresponding to those of  FIGS. 1 to 3  are represented with like reference numerals. 
     In  FIGS. 4 and 5 , the head suspension  1  of the first embodiment includes a base  12 , the load beam  14 , and a flexure  15 . The load beam  14  includes a rigid part  21 , the resilient part  22 , and a joint part  23 . The resilient part  22  is made of a stainless steel plate of 51 μm thick. The rigid part  21  is made of the same stainless steel plate and has a high rigidity by box-bending to a height of 200 μm to 300 μm in a direction opposite to a disk. The joint part  23  is laid on a flat surface of a base plate  32  or the base  12  and fixed to a joint part fixing surface which is a part of the flat surface at joint spot Z by laser-welding. Therefore, the joint part  23  serves as a base side together with the base  12 . The flexure  15  includes a stainless steel substrate of 20 μm thick, a wiring layer, and a resin layer. The total thickness of the flexure  15  is 43 μm. The flexure  15  has an extension  17  on each side edge. The extensions  17  are extended in an across-the-width direction of the flexure  15 . The load beam  14  is cut off a portion of the joint part  23  adjacent to the resilient part  22  to form a hole  16 . The hole  16  is extended from a first end of the joint part  23  to which the resilient part  22  is connected toward a second end opposite to the first end in the longitudinal direction of the load beam  14 . The hole  16  exposes a partial area of the flat surface of a base plate  32  or the base  12  to define a flexure attaching face  41 . Namely, the flexure attaching face  41  is recessed in the base  12  so that the flexure attaching face  41  is separated away from a disk-side surface of the joint part  23  of the load beam  14 . 
     In the vicinity of the joint part  23 , the extensions  17  and an adjacent body of the flexure  15  are arranged on the flexure attaching face  41  in the hole  16 . Each extension  17  of the flexure  15  is laser-welded to the flexure attaching face  41  at a joint spot Y. Additionally, the adjacent body of the flexure  15  may be also laser-wedled to the flexure attaching face  41 . The flexure  15  is fixed to the rigid part  21  of the load beam  14  at a joint spot X. Namely, the flexure  15  is fixed to the rigid part  21  and to the flexure attaching face  41  of the base plate  32 . 
     The bending elastic modulus of a combination of the resilient part  22  and flexure  15  and the bending elastic modulus of the resilient part  22  without the flexure  15  are measured, to calculate a flexure contribution rate, i.e., the influence of the flexure  15  on the combinational bending elastic modulus. To verify the effect of the present invention, a table shown in  FIG. 14  compares values measured on the head suspensions according to the present invention with values measured on the related art of  FIG. 3  that laser-welds the load beam  14  and flexure  15  together without the flexure attaching face  41 . 
     The flexure contribution rate is a percentage obtained by subtracting the bending elastic modulus of a resilient part from a combinational (resilient part plus flexure) bending elastic modulus to provide a difference (which may correspond to the bending elastic modulus of a flexure) and by dividing the difference by the combinational bending elastic modulus. In the table of  FIG. 14 , the flexure contribution rate of the related art is 34.3% and that of the first embodiment is 9.3%. In this way, the first embodiment can reduce the flexure contribution rate. This is because the first embodiment forms the joint spot Y where the flexure  15  is fixed to the flexure attaching face  41  and the joint spot Z where the joint part  23  is fixed to the base  12  on the same plane as shown in  FIG. 5 . Namely, without regard to the presence of the joint part  23  of the load beam  14 , the first embodiment can fix the flexure  15  to the flexure attaching face  41 , i.e., the base  12 . 
     When a head  11  arranged at a front end of the load beam  14  lifts, the resilient part  22  bends in a direction opposite to a disk. At this time, the flexure  15  according to the first embodiment receives no unreasonable tension between the rigid part  21  and the base  12  and naturally bends in the direction opposite to a disk, thereby minimizing the contribution rate of the flexure  15  with respect to a gram load. 
     Hard disk drives are gradually reduced in size from those for server computers to those for desktop computers, notebook computers, and mobile computers. They must be further downsized when used for household appliances and cellular phones. A miniaturized hard disk drive needs small head suspensions. The small head suspensions involve light gram loads. To improve the shock property of a small head suspension involving a light gram load, a load beam of the head suspension must be lightweight. To reduce the weight of a load beam, the load beam must be thinned or must have a seamlessly integrated body including a rigid part ( 21 ), resilient part ( 22 ), and joint part ( 23 ) made of the same material. In this case, a flexure is laser-welded to the load beam and to a base like the related art shown in  FIGS. 2 and 3 , to increase a flexure contribution rate with respect to a gram load. A head suspension with a high flexure contribution rate hardly allows to compute a correct gram load and easily looses resilience. The first embodiment can solve these problems. 
     Second Embodiment 
       FIG. 6  is a perspective view showing a head suspension  1 A according to the second embodiment of the present invention. In  FIG. 6 , parts corresponding to those of  FIGS. 1 to 3  are represented with like reference numerals with “A”. This head suspension  1 A is for a 1-inch hard disk drive and is of an unamount (integrated) type. 
     According to the second embodiment, a base plate  32 A is integral with an arm  31 A, to form a base  12 A. The head suspension  1 A has a load beam  14 A and flexure  15 A. The load beam  14 A of the head suspension  1 A is 30 μm thick. The load beam  14 A includes a rigid part  21 A, a resilient part  22 A, and a joint part  23 A. The rigid part  21 A is box-bent to a height of 100 μm to 200 μm in a direction opposite to a disk. The resilient part  22 A is formed from a pair of resilient plates  30 A separated from the rigid part  21 A. The resilient plates  30 A are disposed along the side edge of the rigid part  21 A to form a gap therebetween in an across-the-width direction of the load beam  14 A. A first end of the resilient plate  30 A is fixed to an end of the rigid part  21 A. A second end of the resilient plate  30 A is integrated with the joint part  23 A fixed to an end of the base plate  32 A. 
     The flexure  15 A is extended from the rigid part side to the base side through the gap of the resilient part  22 A. The flexure  15 A has an extension  17 A on each side edge. The thickness of the flexure  15 A is the same as that of the first embodiment. 
     Like the first embodiment, the head suspension  1 A of the second embodiment has a flexure attaching face  41 A defined in a partial area of the flat surface of the base plate  32 A to which the extension  17 A of the flexure  15 A is welded. The partial are is adjacent to the joint part  23 A. 
     Therefore, weld spots are not adjacent to a resilient part  22 A of the load beam  14 A according to the second embodiment. In the table of  FIG. 14 , the second embodiment provides a flexure contribution rate of 8.9%. 
     Third Embodiment 
       FIGS. 7 ,  8 , and  9  show a head suspension  1 B according to the third embodiment. The head suspension of a third embodiment has the same basic structure as the first embodiment. In  FIGS. 7-9 , therefore, parts corresponding to those of  FIGS. 1 to 5  are represented with like reference numerals with “B”.  FIG. 7  is a perspective view mainly showing a resilient part  22 B of a load beam  14 B of the head suspension  1 .  FIG. 8  shows a base plate  32 B having a flexure attaching face  41 B. This head suspension  1 B is for a 2.5-inch hard disk drive. The base plate  32 B is fixed to a joint part  23 B of the load beam  14 B, and the flexure attaching face  41 B is fixed to a flexure  15 B. The flexure attaching face  41 B is formed by partially etching the base plate  32 B so that the flexure attaching face  41 B is separated away from a disk.  FIG. 9  is a sectional view showing a part indicated with arrows IX in  FIG. 7 . 
     The resilient part  22 B according to the third embodiment is made of a stainless steel plate of 51 μm thick. The flexure  15 B includes a stainless steel substrate of 20 μm thick, a wiring layer, and a resin layer. The total thickness of the flexure  15 B is 43 μm. The load beam  14 B is cut out a portion of the joint part  23 B adjacent to the resilient part  22 B to form a hole  16 . The hole  16  exposes a partial area of the surface. The partial area of the surface has a recess  40 B defining the flexure attaching face  41 B. The recess  40 B including the flexure attaching face  41 B is formed by partially etching the surface of the base plate  32 B by 20 μm that corresponds to the thickness of the stainless steel substrate of the flexure  15 B. In the vicinity of the joint part  23 B of the load beam  14 B, the extensions  17 B and an adjacent body of the flexure  15 B are arranged on the flexure attaching face  41 B in the recess  40 B. Each extension  17 B of the flexure  15 B is laser-welded at a joint spot Y to the flexure attaching face  41 B that is lower than the joint part  23 B. The joint spot Y is adjacent to the resilient part  22 B. 
     According to the third embodiment, the flexure attaching face  41 B is formed in the base plate  32 B (base  12 B) and is separated away from a disk-side surface of the joint part  23 B of the load beam  14 B. The flexure  15 B is fixed to a surface of the rigid part  21 B of the load beam  14 B at a joint spot X and to the flexure attaching face  41 B of the base plate  32 B at the joint spot Y. 
     In the table of  FIG. 14 , the third embodiment provides a flexure contribution rate of 6.1%. According to the third embodiment, the joint spot X between the flexure  15 B and the rigid part  21 B of the load beam  14 B is on the surface of the load beam  14 B, and the joint spot Y between the flexure  15 B and the flexure attaching face  41 B of the base  12 B is lower than a joint spot Z where the joint part  23 B of the load beam  14 B is fixed to the base  12 B. This configuration further decreases the flexure contribution rate. 
     Fourth Embodiment 
     A head suspension  1 C of a fourth embodiment has the same basic structure as the third embodiment. Therefore, the head suspension  1 C of a fourth embodiment will be explained with  FIGS. 7-9  using reference numerals with “C” instead of “B” within a parenthesis. 
     The fourth embodiment further cuts the flexure attaching face  41 B of the third embodiment by partial etching to a depth of 43 μm from the surface of the base plate  32 C to form a recess  40 C defining a flexure attaching face  41 C. In this case, the flexure  15 C is completely within the base  12 C and is fixed thereto without no protruding from the surface of the base plate  32 C. This configuration realizes a flexure contribution rate of 5.8% as shown in the table of  FIG. 14 . This rate is nearly equal to the bending elastic modulus of the flexure  15 C alone. 
     Fifth Embodiment 
       FIGS. 10 and 11  show a head suspension  1 D according to the fifth embodiment of the present invention. The head suspension of a third embodiment has the same basic structure as the first embodiment. In  FIGS. 10-11 , parts corresponding to those of  FIGS. 1 to 5  are represented with like reference numerals with “D”.  FIG. 10  is a perspective view showing the head suspension  1 D and  FIG. 11  is a sectional view showing a part indicated with arrows XI in  FIG. 10 . 
     This head suspension  1 D is for a 2.5-inch hard disk drive. The head suspension  1 D includes a base  12 D, a load beam  14 D, and a flexure  15 D. The load beam  14 D includes a rigid part  21 D, a resilient part  22 D, and a joint part  23 D. The resilient part  22 D is made of a stainless steel plate of 51 μm thick. The flexure  15 D includes a stainless steel substrate of 20 μm thick, a wiring layer, and a resin layer. The total thickness of the flexure  15 D is 43 μm. The flexure  15 D has an extension  17 D on each side edge. A surface of the joint part  23 D of the load beam  14 D is partially etched to a depth of 43 μm to form a recess  40 D defining a flexure attaching face  41 D. The depth 43 μm of the flexure attaching face  41 D corresponds to the total thickness of the flexure  15 D. 
     According to the fifth embodiment, the extensions  17 D and an adjacent body of the flexure  15 D are arranged on the flexure attaching face  41 D in the recess  40 D of the joint part  23  D. Each extension  17 D of the flexure  15 D is laser-welded to the flexure attaching face  41 D at a joint spot Y. Namely, the flexure  15 D is fixed to a surface of the rigid part  21 D and to the flexure attaching face  41 D. 
     Therefore, the flexure attaching face  41 D is formed on the base  12 D side and is spaced away from a disk-side surface of the joint part  23 D in a direction opposite to a disk. 
     According to the fifth embodiment, a joint spot Y where the flexure  15 D is fixed to the flexure attaching face  41 D is separated from a joint spot Z where the joint part  23 D of the load beam  14 D is fixed to the base  12 D by 8 μm compared with 51 μm of the related art. The fifth embodiment achieves a flexure contribution rate of 11.3% as shown in the table of  FIG. 14 . 
     Sixth Embodiment 
       FIGS. 12 and 13  show a head suspension  1 E according to the sixth embodiment of the present invention. The head suspension of a third embodiment has the same basic structure as the first embodiment. In  FIGS. 12 and 13 , parts corresponding to those of  FIGS. 1 to 5  are represented with like reference numerals or like reference numerals with “E”. This head suspension  1 E is for a 2.5-inch hard disk drive.  FIG. 12  is a perspective view mainly showing a resilient part  22 E of a load beam  14 E of the head suspension  1  and  FIG. 13  is a sectional view showing a part indicated with arrows XIII in  FIG. 12 . 
     The resilient part  22 E of the load beam  14 E is made of a stainless steel plate of 51 μm thick. A flexure  15 E includes a stainless steel substrate of 20 μm thick, a wiring layer, and a resin layer. The flexure  15 E has an extension  17 E on each side edge. The total thickness of the flexure  15 E is 43 μm. Like the first embodiment, the load beam  14 E is cut out a portion of the joint part  23 E adjacent to the resilient part  22 E to form a hole  16 E. The hole  16 E exposes a partial area of the flat surface defining the flexure attaching face  41 E. 
     A rigid part  21 E of the load beam  14 E has a second recess  44 E formed by partially etching a portion of the rigid part  21 E adjacent to the resilient part  22 E by 20 μm. The recess  44 E defines a second flexure attaching face  42 E. To the second flexure attaching face  42 E, the flexure  15 E is laser-welded in the rigid part side. According to the sixth embodiment, a joint spot Y at which the flexure  15 E is fixed to the flexure attaching face  41 E and a joint spot Z at which a joint part  23 E of the load beam  14 E is fixed to the base  12 E are on the same plane. A joint spot X at which the flexure  15 E is fixed to the rigid part  21 E is within the thickness of the load beam  14 E. This configuration realizes a flexure contribution rate of 7.8% as shown in the table of  FIG. 14 .