Abstract:
A head stack assembly of a disk drive unit including a head arm assembly (HAA) having a head gimbal assembly, a drive arm to be connected with the head gimbal assembly; wherein the drive arm comprises a securing portion, a connection portion and a spacer connecting the securing portion with the connection portion. In the present invention, at least one undercut is formed on the spacer of the drive arm to strengthen the drive arm. The invention also discloses a method of manufacturing such a head stack assembly.

Description:
FIELD OF THE INVENTION 
   The present invention relates to disk drive units and manufacturing method thereof, and more particularly to a HSA (head stack assembly) and manufacturing method thereof. 
   BACKGROUND OF THE INVENTION 
   Disk drives are information storage devices that use magnetic media to store data. Referring to  FIG. 1 , a typical disk drive in prior art comprises a drive arm  5 , a head gimbal assembly (HGA)  4  with a slider  3  being coupled to the drive arm  5  (the drive arm and the HGA with the slider also known as head stack assembly (HSA)), a magnetic disk  1  mounted on a spindle motor  2  which causes the magnetic disk  1  to spin, and a disk drive base plate  13  to enclose the above-mentioned components. The slider  3  flies over the surface of the magnetic disk  1  at a high velocity and is positioned radially by a voice coil  7  embedded (e.g. by epoxy potting or overmolding) in a fantail spacer  8  to read data from or write data to concentric data tracks on the magnetic disk  1 . Generally, a voice coil motor (VCM)  10  is used to drive the voice coil  7 . 
   Referring to  FIGS. 2(   a ) and  3 , a traditional head stack assembly (HSA) comprises an independent fantail spacer  8  which is interposed between two pieces of the drive arms  5  and combines with the drive arms  5  together with a securing means. The securing means is consisted of a pivot member  6 , a washer  25 ′ and a nut  26 ′. In the prior art, the HGA  4  is coupled to the drive arm  5  by laser welding or swaging the suspension of the HGA  4  with the drive arm  5 . The drive arms  5  each have a suspension flexure cable  20  running from the sliders  3  to a plurality of bonding pads  19 . The suspension flexure cable  20  is secured to the suspension of the HGA  4  by laser welding or adhesive. 
   In typical disk drives, referring to  FIGS. 2(   a ) and  2 ( b ), electrical control signals are communicated to the voice coil  7  by a flexible printed circuit assembly (FPCA)  9 . The bonding pads  19  of the suspension flexure cable  20  are electrically connected with the FPCA  9  by using connection balls  15  (e.g., by soldering or ultrasonic bonding) to bond the bonding pads  19  to a plurality of connecting pads  16  of the FPCA  9 . Thus, the FPCA  9  may communicate read/write data to the slider(s)  3 . In addition, referring to  FIG. 1 , a printed circuit board (PCB)  11  mounted on a bracket  12  is provided to control the position of the drive arm(s)  5  with the slider(s)  3 . 
   With reference to  FIG. 2(   a ), the FPCA  9  is aligned with the fantail spacer  8  at an end thereof by an alignment pin  17  protruding from the fantail spacer  8 . After positioning, the FPCA  9  will be electrically coupled to the HGA  4 . 
   However, because the traditional HSA use the independent fantail spacer  8  to partition the two pieces of the drive arms  5 , and manufacturing the fantail spacer  8  takes much time and money, the cost of the HSA becomes higher and the manufacturing process becomes more complicated. 
   It is therefore desirable to provide a HSA of a disk drive unit and manufacturing method thereof to solve the above-mentioned problems. 
   SUMMARY OF THE INVENTION 
   A main feature of the present invention is to provide a low-cost HSA of a disk drive unit which is easily manufactured and a manufacturing method thereof. 
   To achieve the above-mentioned feature, a head stack assembly of a disk drive unit of the present invention comprises a head arm assembly (HAA) having a head gimbal assembly, a drive arm to be connected with the head gimbal assembly; wherein the drive arm comprises a securing portion, a connection portion and a spacer connecting the securing portion with the connection portion. 
   In the present invention, at least one undercut is formed on the spacer of the drive arm to strengthen the drive arm. The head stack assembly further comprises an additional HAA having a second head gimbal assembly (HGA), a second drive arm to be connected with the second HGA, and a voice coil embedded in the second drive arm. The additional HAA is coupled with the HAA by a securing means. In addition, a bracket is positioned on one side of the second drive arm, which comprises a bracket body having at least one bracket clamp extending from one side thereof and at least one alignment pin formed thereon, and a guiding rail extending from one end of the bracket body. 
   In the present invention, the additional HAA further comprises a flexible printed circuit assembly (FPCA) having a flexible printed circuit (FPC) having at least one alignment hole corresponding to the at least one alignment pin, a U-shaped connector attached to one end of the FPC, and a connection leg extending from one side of the FPC; the FPCA is aligned with the bracket by the alignment pin and fixed by the bracket clamp. The connection leg has two voice coil pads and a grounding pad formed thereon, the second drive arm is provided with a grounding pin and two connection pins near the bracket which are electrically coupled with the connection pins and the grounding pin, respectively. In addition, each of the two head gimbal assemblies has a suspension flexure cable with a plurality of bonding pads provided thereon, and the U-shaped connector comprises two connection plates each having a plurality of connecting pads thereon to electrically connect with the bonding pads of the two suspension flexure cables. 
   According to the present invention, a method for manufacturing a head stack assembly of a disk drive unit comprising a step of forming a head arm assembly, which comprises the steps of: forming a head gimbal assembly; providing a raw drive arm and stamping it to form a spacer; and coupling the head gimbal assembly with the stamped drive arm together. In the present invention, forming the head arm assembly further comprises forming at least one undercut on the spacer. 
   Also, the method further comprises the steps of forming an additional head arm assembly (HAA) and assembling the two head arm assemblies together by a securing means. Forming the additional head arm assembly comprises the steps of: forming a second head gimbal assembly, a second drive arm and a voice coil; coupling the second head gimbal assembly, the second drive arm and the voice coil together. In the present invention, forming the second drive arm comprises forming a bracket on one side thereof. Forming the bracket comprises a step of forming a guiding rail and a bracket body having at least one bracket clamp and at least one alignment pin. Forming the additional head arm assembly further comprises forming a flexible printed circuit assembly thereon. Hereinto, forming the flexible printed circuit assembly comprises the steps of: forming a flexible printed circuit having at least one alignment hole and a connection leg; forming a U-shaped connector; and coupling the flexible printed circuit with the U-shaped connector together. 
   In the present invention, forming the additional HAA further comprises the steps of aligning the flexible printed circuit assembly with the bracket by the at least one alignment pin and fixing it by the at least one bracket clamp. And, forming the connection leg comprises forming two voice coil pads and a grounding pad thereon, and forming the second drive arm comprises forming a grounding pin and two connection pins thereon. In addition, forming the additional head arm assembly further comprises electrically coupling the two voice coil pads and the grounding pad with the connection pins and the grounding pin, respectively. 
   In the present invention, forming the U-shaped connector comprises forming two connection plates each having a plurality of connecting pads thereon, and forming each of the two head gimbal assemblies comprises forming a suspension flexure cable having a plurality of bonding pads thereon. Also, forming the additional HAA further comprises electrically coupling the connecting pads of the two connection plates with the bonding pads of the two suspension flexure cables, respectively. 
   Comparing with the prior art, the head stack assembly of the present invention has the drive arm formed a step thereon as a spacer to partition the two head arm assemblies. Therefore, an independent fantail spacer is saved and accordingly the manufacturing process of the HSA becomes easier and the cost thereof becomes lower. In addition, by forming a step on the drive arm, the securing means does not protrude from the HAA as a traditional HSA. Thus, the HSA of the present invention can be made thinner. Furthermore, the design of the special bracket on the first HAA and the corresponding FPCA makes the electrical and physical connection therebetween more reliable. 
   Other objects, advantages and novel features of the invention will become more apparent from the following detailed description of a preferred embodiment thereof when taken in conjunction with the accompanying drawing. accompanying drawings, wherein: 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a traditional disk drive; 
       FIG. 2(   a ) is a perspective view of a traditional head stack assembly (HSA); 
       FIG. 2(   b ) is an enlarged, cross-sectional view of an electrical connection between suspension flexure cables and FPCA of the HSA of  FIG. 2(   a ); 
       FIG. 3  is an exploded, perspective view of the HSA in  FIG. 2(   a ); 
       FIG. 4  is a perspective view of a HSA according to the present invention; 
       FIG. 5  is an exploded, perspective view of the HSA of  FIG. 4 ; 
       FIG. 6  is a perspective view of a second HAA of the HSA in  FIG. 5 ; 
       FIG. 7(   a ) is an enlarged, perspective view of a FPCA of the HSA in  FIG. 5 ; 
       FIG. 7(   b ) is an enlarged, perspective view of the FPCA with a bracket of the second HAA in  FIG. 6 ; 
       FIG. 8  is a perspective view of a first HAA of the HSA showing in  FIG. 5 ; 
       FIG. 9  is a partial, enlarged perspective view of the second HAA in  FIG. 6 ; 
       FIG. 10  is a partial, enlarged perspective view of the HSA in  FIG. 4  showing an electrical connection between the suspension flexure cables and the FPCA; and 
       FIG. 11  is a schematic view showing a process of electrical connection between the suspension flexure cable and the FPCA. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to the drawings in detail,  FIG. 4  shows an HSA of a disk drive unit according to an embodiment of the present invention. The HSA comprises a first head arm assembly (HAA)  21  and a second head arm assembly (HAA)  22  coupled to the first HAA  21  by securing means (not labeled). In an embodiment of the present invention, see  FIG. 5 , the securing means comprises a pivot  6 ′, a washer  25 , a nut  26  and a screw  23 . 
   With reference to  FIG. 8 , the first HAA  21  comprises a first head gimbal assembly (HGA) having a first suspension  4 ″ and a first slider  3 ″, and a first drive arm  5 ″ to be connected with the first suspension  4 ″. The first suspension  4 ″ is provided a first suspension flexure cable  20 ″ coupled thereon. In an embodiment of the present invention, the first suspension  4 ″ is overmolded onto the first drive arm  5 ″ and the first suspension flexure cable  20 ″ are coupled with the first suspension  4 ″ by overmold as well. The first drive arm  5 ″ is stamped to form a step constructed by a securing portion  51 , a connection portion  53  and a spacer  52  connecting the securing portion  51  with the connection portion  53 . Two undercuts  32  are made on the spacer  52  to strengthen the first drive arm  5 ″. In the present invention, because a step is formed on the first drive arm  5 ″, so the pivot  6 ′ does not protrude from the first HAA  21  as a traditional HSA. Thus, the HSA of the present invention can be made thinner because the height of the pivot  6 ′ contributes to the total height of the HSA. Additionally, the first suspension flexure cable  20 ″ is also provided with a plurality of bonding pads  19 ″ on an end thereof. 
   Referring to  FIG. 6 , the second HAA  22  comprises a second head gimbal assembly having a second suspension  4 ′ and a second slider  3 ′(see  FIG. 9 ), a second drive arm  5 ′ to be connected with to the second suspension  4 ′, a bracket  24  positioned on one side of the second drive arm  5 ′, and a voice coil  7 ′ embedded in the second drive arm  5 ′ for controlling the motion of the second drive arm  5 ′. In an embodiment of the invention, the bracket  24 , the second suspension  4 ′, and the voice coil  7 ′ are overmolded onto the second drive arm  5 ′. 
   In the present invention, with reference to  FIGS. 5 ,  6  and  9 , the second suspension  4 ′ has a second suspension flexure cable  20 ′ coupled thereon by overmold which runs from the second slider  3 ′ toward the bracket  24 . To make the invention easily understood, a detailed view of overmold status of the second HAA  22  is shown in  FIG. 9 . There are at least two overmold pins  33  used for the attachment of the second suspension  4 ′, and at least two overmold pins  33  used for the attachment of the second suspension flexure cable  20 ′. In the present invention, an overmold status of the first HAA  21  is similar to that of the second HAA  22  and a detail view thereof is omitted herefrom. A plurality of bonding pads  19 ′ is provided on an end of the second suspension flexure cable  20 ′. The second drive arm  5 ′ is provided with a grounding pin  29  and two embedded connection pins  28  near the bracket  24 . The voice coil  7 ′ is driven by a VCM (not shown), which is provided two voice coil leads (not shown) soldered with the connection pins  28 . Also, a balance plate  27  is mounted in the voice coil  7 ′ to balance the motion of the second drive arm  5 ′. The connection pins  28 , the voice coil  7 ′ and the balance plate  27  are overmolded onto the drive arm  5 ′ together. 
   Referring to  FIG. 7(   b ), the bracket  24  comprises a bracket body  241  and a guiding rail  242  extending from one end of the bracket body  241 . The bracket body  241  has a bracket clamp  31  extending from one side thereof and an alignment pin  30  formed thereon. A FPCA  9 ′ is aligned with the bracket  24  by the alignment pin  30  and fixed by the bracket clamp  31 . Referring to  FIG. 7(   a ), the FPCA  9 ′ comprises a flexible printed circuit (FPC)  92 , a U-shaped connector  91  formed to one end of the FPC  92 , and a connection leg  93  extending from one side of the FPC  92 . The FPC  92  has an alignment hole  98  formed therein corresponding to the alignment pin  30  to receive the alignment pin  30 . The connection leg  93  has two voice coil pads  931  and a grounding pad  932  formed thereon, the two voice coil pads  931  are provided for the connection pins  28  to extend through, and the grounding pad  932  is provided for the grounding pin  29  to extend through. The U-shaped connector  91  comprises two connection plates  161 ,  162  with a plurality of connecting pads  16 ′ and  16 ″ (see  FIG. 5)  thereon, respectively. To satisfy the configuration of the guiding rail  242 , the flexible printed circuit (FPC)  92  is folded to contact with the inner surface of the guiding rail  242 . 
   Referring to  FIGS. 7(   a ) and  7 ( b ), in the present invention, the voice coil pads  931  and the grounding pad  932  of the FPCA  9 ′ are electrically coupled with the connection pins  28  and the grounding pin  29  by soldering. At the same time, the voice coil leads (not shown) are electrically connected with the voice coil pads because the voice coil leads (not shown) are soldered with the connection pins  28 . 
   In the present invention, the bonding pads  19 ′,  19 ″ of the first and second suspension flexure cable  20 ′ and  20 ″ are electrically coupled with the connecting pads  16 ′,  16 ″ of the FPCA  9 ′ by epoxy. Referring to  FIG. 11 , in an embodiment, the epoxy is a tacky electrical conductive film  34 , such as Anisotropic Conductive Film (ACF), which adheres to and cover the bonding pad  19 ′ of the second suspension flexure cable  20 ′. Then, the conductive film  34  is pressed against the connecting pad  16 ′ of the FPCA  9 ′ by a bonding tip  35  to bond the bonding pad  19 ′ with the connecting pad  16 ′ together. The bonding tip  35  is heated and then compresses the conductive film  34  to start the curing process. In an embodiment, an additional support plate  36  is inserted into the U-shaped connector  91  for support. Similarly, the bonding pads  19 ″ of the first suspension flexure cable  20 ″ are electrically coupled with the connecting pads  16 ″ of the FPCA  9 ′ and a detailed description thereof is omitted herefrom. 
   It is understood that the invention may be embodied in other forms without departing from the spirit thereof. Thus, the present example and embodiment are to be considered in all respects as illustrative and not restrictive, and the invention is not to be limited to the details given herein.