Patent Publication Number: US-2017365285-A1

Title: Hard disk circuit with direct connection to preamp

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 62/351,157, filed Jun. 17, 2016, the disclosure of which is incorporated herein in its entirety by reference. 
    
    
     BACKGROUND 
     1. Field 
     Apparatuses consistent with exemplary embodiments relate to hard disk drive (HDD) technology, and more specifically, to an HDD suspension, flexure/suspension circuit and the connection to the preamp which is mounted onto the main actuator circuit. 
     2. Description of the Related Art 
     Hard disk drives include flexures/suspension circuits which support the HDD in, for example, a computer. A flexure/suspension circuit is connected to a main actuator circuit, and provides an electrical connection between the main actuator circuit and the read-write head of the HHD. The flexure/suspension circuit consists of a steel layer and one or more intricately patterned copper foil layers with insulating material (for example, polyimide) which separate the conductive layers (for example, the copper and steel layers) from each other. 
     SUMMARY 
     An exemplary embodiment is directed to methods and apparatuses providing direct connections between the flexure/suspension circuit(s) and one or more preamps. On the opposite end of the preamp(s), a separate interposer(s) may connect circuitry from the main actuator circuit to the preamp(s). This simplifies the main actuator circuit pad design connecting to the preamp(s). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and/or other aspects will become more apparent by describing certain exemplary embodiments, with reference to the accompanying drawings, in which: 
         FIG. 1  illustrates a related art the Head Stack Assembly (HSA). 
         FIGS. 2 and 3  illustrate an assembly according to an exemplary embodiment. 
         FIG. 4  illustrates connection circuits disposed between the preamp and the flexure/suspension circuits, according to an exemplary embodiment. 
         FIG. 5  illustrates the main actuator circuit, according to an exemplary embodiment. 
         FIG. 6  illustrates the main actuator circuit with the mounted preamp, according to an exemplary embodiment. 
         FIG. 7  is a top view of an example of the formed interposer circuit, according to an exemplary embodiment. 
         FIG. 8  illustrates a bottom view of the formed interposer circuit of  FIG. 7 , according to an exemplary embodiment. 
         FIG. 9  illustrates an overall view of the flexure/suspension circuit, according to an exemplary embodiment. 
         FIG. 10  illustrates a top surface of a portion of the flexure/suspension circuit, according to an exemplary embodiment. 
         FIG. 11  illustrates a bottom surface of the portion of the flexure/suspension circuit, according to an exemplary embodiment. 
         FIG. 12  illustrates a side view of an assembly, according to an exemplary embodiment. 
         FIGS. 13A and 13B  illustrate solder connections, according to an exemplary embodiment. 
         FIG. 14  illustrates an electrically conductive tape to make electrical connection, according to an exemplary embodiment. 
         FIG. 15  illustrates wire-bondable pads formed on the main actuator circuit, according to an exemplary embodiment. 
         FIG. 16  illustrates wire-bondable pads of the formed interposer circuit, according to an exemplary embodiment. 
         FIG. 17  illustrates an assembly (ready for ultra-sonic tab bonding (USTB)) according to an exemplary embodiment. 
         FIG. 18  illustrates an assembly according to an exemplary embodiment. 
         FIG. 19  illustrates an assembly according to an exemplary embodiment. 
         FIG. 20  illustrates the assembly of  FIG. 19  without a coverlay, according to an exemplary embodiment. 
         FIG. 21  illustrates a top view of a flat preamp interposer, according to an exemplary embodiment. 
         FIG. 22  illustrates a bottom view of the flat preamp interposer of  FIG. 21 , according to an exemplary embodiment. 
         FIG. 23  illustrates a bottom view of the flat preamp interposer of  FIG. 21 , according to an exemplary embodiment. 
         FIG. 24  illustrates a portion of a set of flexure/suspension circuits which may be edge-mounted, according to an exemplary embodiment. 
         FIG. 25  illustrates a conductive film which provides electrical connection, according to an exemplary embodiment. 
         FIG. 26  illustrates the flat preamp interposer attached to the main actuator circuit via the conductive layer, according to an exemplary embodiment. 
         FIG. 27  illustrates the preamp, according to an exemplary embodiment. 
         FIG. 28  illustrates a bottom view of the preamp, according to an exemplary embodiment. 
         FIG. 29  illustrates the preamp attached to the main actuator circuit via the preamp module, according to an exemplary embodiment. 
         FIG. 30  illustrates the flexure/suspension circuits edge-mounted to the preamp module, according to an exemplary embodiment. 
         FIG. 31  illustrates a top surface of the preamp, according to an exemplary embodiment. 
         FIGS. 32 and 33  illustrate an exemplary embodiment of the preamp. 
         FIGS. 34A and 34B  illustrate an assembly of an exemplary embodiment and of related art, respectively. 
         FIGS. 35A and 35B  illustrate a detailed assembly of an exemplary embodiment and of related art, respectively. 
         FIG. 36  illustrates the thermal simulation models of an exemplary embodiment and of the related art. 
         FIG. 37  illustrates the thermal simulation results. 
         FIG. 38  illustrates Dual stage actuator (DSA) lines formed in the main actuator circuit, according to an exemplary embodiment. 
         FIG. 39  illustrates the flexure/suspension circuits provided with the flaps to connect with the DSA lines, according to an exemplary embodiment. 
         FIG. 40  illustrates the solder bumps which electrically connect the DSA lines with the flexure/suspension circuits, according to an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Certain exemplary embodiments are described in greater detail below with reference to the accompanying drawings. 
     In the following description, the same drawing reference numerals are used for the same elements even in different drawings. The matters defined in the description, such as detailed construction and elements, are provided to assist in a comprehensive understanding of exemplary embodiments. Thus, it is apparent that exemplary embodiments can be carried out without those specifically defined matters. Also, well-known functions or constructions are not described in detail since they would obscure exemplary embodiments with unnecessary detail. 
       FIG. 1  illustrates a related art Head Stack Assembly (HSA)  10 . It consists of the main actuator circuit  12  and a preamp  14  mounted to the main actuator circuit  12 . Flexure/suspension circuits  16  are connected to pads  18  in the main actuator circuit  12 . The main actuator circuit  12  and flexure/suspension circuits  16  are mounted to the E-block  19 . 
     The preamp  14  is electrically connected to the main actuator circuit  12  via a series of conductive pads  18 , for example, copper. The conductive path continues via a set of conductive pads on the other side of the preamp  14  and a set of flexure/suspension circuits  16  is connected to the conductive pads. That is, the main actuator circuit  12  is connected to both the preamp  14  and flexure/suspension circuits  16  and the related art does not provide direct connection of the flexure/suspension circuits to the preamp. 
       FIGS. 2 and 3  illustrate an assembly  20  including a main actuator circuit  12  and flexure/suspension circuit or circuits  21 , according to an exemplary embodiment. Stiffeners  24  may be formed of aluminum or steel, but this is not limiting. For example, other materials may be used as, for example, polyimide. 
     A first dielectric layer  28  is disposed on the stiffener  24  and a conductive material  26 , such as copper, is disposed on the first dielectric layer  28  and provides a set of contacts, conductive traces, and/or conductive pads. A second dielectric layer may be disposed to cover portions of the conductive material  26 . 
       FIG. 4  illustrates connection circuits  40 , according to an exemplary embodiment, which provide connection between the preamp  14  and the flexure/suspension circuits  21 , and an interposer circuit  42  having a body  64  disposed on the preamp  14  on the opposite side of the connection circuits  40 , to provide connection between the preamp  14  and the main actuator circuit  12 . The electrical connection between the elements may be achieved by solder bumps  44 , as described in greater detail below. As seen in  FIG. 4 , the flexure/suspension circuits  21  are directly connected to the preamp  14 , unlike the apparatus of the related art which exhibits undesirable impedance discontinuities at the extra solder joints. Although  FIG. 4  illustrates one interposer and four flexure/suspension circuits, a greater number of interposers and a greater or smaller number of flexure/suspension circuits may be implemented. 
       FIG. 5  illustrates the main actuator circuit  12  having a circuitry  50  terminated at pads  52 , e.g., contacts, according to an exemplary embodiment. The pads  52  connect to a single interposer circuit  42  ( FIG. 7 ), and, thus, the size and shape of the main actuator circuit can be simplified, thereby making the main actuator circuit easier and cheaper to manufacture. An opening  54  may be formed in the main actuator circuit  12  to accommodate the preamp  14 . According to the present exemplary embodiment only one set of pads  52  for a single interposer circuit is shown, but this is not limiting. 
       FIG. 6  illustrates the preamp  14 , according to an exemplary embodiment, which is mounted into the opening  54 , so that preamp contacts  60  and  61 , e.g., conductive pads, are disposed on a top surface  63  and are facing in an upward direction  62 . Since the body of the preamp  14  is mounted directly onto the metal, the heat dissipation may be improved. 
       FIG. 7  is a top view of an example of the formed interposer circuit  42 , according to an exemplary embodiment, which has the body  64 , formed of metal, such as stainless steel, having a top surface  65  and contact sets  66 ,  68 ,  69 , and  70 . Each contact set has openings  72  surrounded by a dielectric layer  74 , such as polyimide. A conductive material  76 , such as copper, is exposed on the inner walls of the openings  72 , to provide electric conductivity. 
     The body  64  of the formed interposer circuit  42  has a step-up shape in which the contact sets  66  and  68  are disposed on a lower plate  77  for connecting to the circuitry  50  of the main actuator circuit  12 , and the contact sets  69  and  70  are disposed on an upper plate  78  for connecting to the flexure/suspension circuits  21 . 
       FIG. 8  illustrates a bottom view of the formed interposer circuit  42  of  FIG. 7 , according to an exemplary embodiment. The step-up shape of the interposer circuit  42  is held in place by the body  64  formed of metal, for example, steel, having a boundary portion  80  that protrudes from the top surface  65  so that the boundary portion  80  overhangs the dielectric layer  74 , as seen at a bottom surface  81 . 
     A circuitry  82 , e.g., copper traces, is disposed on the dielectric layer  74  at the bottom surface  81  of the interposer circuit  42  for providing electrical connection between conductive pads  84  disposed on the upper plate  78  and conductive pads  86  disposed on the lower plate  77 . However, this is only an example, and an exemplary embodiment is not limited thereto. 
       FIG. 9  illustrates an overall view of the flexure/suspension circuit  21  which has body members  90  formed of, for example, steel, which define a shape of and support the flexure/suspension circuit  21 , according to an exemplary embodiment. A first dielectric material  92  and conductors extend in between the body members  90 . 
       FIG. 10  illustrates a top surface  100  of a first portion  102  of the flexure/suspension circuit  21  that is connected to the preamp  14 , according to an exemplary embodiment. A connecting portion  104  is formed at the end portion of the first portion  102  and includes the first dielectric material  92  disposed in the body member  90 . Openings  106  are formed in the first dielectric material  92  of the connecting portion  104  and may include copper disposed on the inner walls, as described above, for providing electrical connectivity to the preamp contacts  60 . 
     As seen in  FIG. 10 , the body members  90  provide a supporting frame for the first dielectric material  92  that extends in the supporting frame. 
       FIG. 11  illustrates a bottom surface  110  of the first portion  102  of the flexure/suspension circuit  21  having pads  103  for electrically connecting to the preamp  14 , according to an exemplary embodiment. A second dielectric material  112  covers at least a portion of the copper circuitry  114 . The flexure/suspension circuit described above is only an example, and an exemplary embodiment is not limited thereto. 
       FIG. 12  illustrates a side view of an assembly including the formed interposer circuit  42 , preamp  14 , and flexure/suspension circuit  21 , according to an exemplary embodiment. 
       FIG. 13A  illustrates solder connections  130  between the preamp  14  and flexure/suspension circuits  21 , solder connections  132  between the preamp  14  and formed interposer circuit  42 , solder connections  134  between the formed interposer circuit  42  and the main actuator circuit  12 , according to an exemplary embodiment. For example, molten solder can be jetted into the openings in the interposer and into the openings of the flexure/suspension circuits connecting the conductive surfaces of the preamp to the conductive surfaces of the main actuator circuit and flexure/suspension circuits. 
     As shown in  FIG. 13B , solder may be deposited as solder bumps  134  on the main actuator circuit  12 , for example, by using solder paste, solder plating, or solder jetting methods known to those skilled in the art, prior to the interposer assembly. However, this is not limiting. 
       FIG. 14  illustrates an electrically conductive tape  140  which may be applied to the main actuator circuit prior to the formed interposer assembly to make electrical connection, according to an exemplary embodiment. For example, the conductive tape may be an anisotropic conductive film (ACF). 
       FIG. 15  illustrates rectangular wire-bondable pads  150  formed on the main actuator circuit, according to an exemplary embodiment. However, the shape of the wire-bondable pads  150  is not limited thereto. 
       FIG. 16  illustrates rectangular wire-bondable pads  160  formed on the formed interposer circuit  42  that may provide the electrical connection between the main actuator circuit and the preamp  14 , according to an exemplary embodiment. However, the shape of the wire-bondable pads  160  is not limited thereto. 
       FIG. 17  illustrates an assembly in which the rectangular wire-bondable pads  150  of the main actuator circuit are connected to the rectangular wire-bondable pads  160  of the formed interposer circuit, while the raised portion of the formed interposer circuit  42  is connected via solder bumps  132  to the preamp  14 , according to an exemplary embodiment. 
       FIG. 18  illustrates an exemplary embodiment in which the preamp  14  is connected to the main actuator circuit  12  via a flat interconnected circuit  190 , according to an exemplary embodiment. For example, the flat interconnected circuit may include a hybrid type, edge mount pads  180  disposed on a first side surface  181  of the preamp  14  that provide electrical connectivity to the main actuator circuit. For example, the edge mounted preamp pads  180  are connected to main actuator circuit pads  182  using solder, such as solder jet bond (SJB), solder paste, reflow, etc., but this is not limiting. The preamp  14  may be connected to the flexure/suspension circuits as described above with reference to exemplary embodiments. 
       FIG. 19  illustrates an exemplary embodiment of an assembly in which the preamp  14  may be connected to the main actuator circuit  12  via the flat interconnected circuit  190  having exposed copper pads  192 . A polyimide layer  194  is disposed on the aluminum stiffener  196  which supports the main actuator circuit circuitry. 
       FIG. 20  illustrates the assembly of  FIG. 19  without a coverlay. The pads  200  and traces  202  may be formed of copper. 
       FIG. 21  illustrates a top view  210  of a flat preamp interposer  212 , which may be used with the flat interconnected circuit and may be formed of polyimide, according to an exemplary embodiment. A top layer  213  may be formed on the polyimide as a coverlay. A copper layer may be exposed to form preamp contacts  214 , e.g., concentric pads, for a flipchip-mount preamp. On a side of the flexure/suspension circuits, contacts  216 , e.g., exposed copper, may be formed to connect with the pads or contacts of the edge-mounted flexure/suspension circuits. Optionally, an opening  218  may be formed, to accommodate at least a portion of the preamp  14 . However, the arrangement of an exemplary embodiment described above is not limiting. 
       FIG. 22  illustrates a bottom view  220  of the flat preamp interposer  212  of  FIG. 21 , according to an exemplary embodiment. On a side of the main actuator circuit, contacts  222  may be formed to connect with the pads  192  of the flat preamp interposer. For example, an inner copper layer may be exposed to form the contacts  222 . 
       FIG. 23  illustrates a bottom view  220  of the flat preamp interposer  212  of  FIG. 21 , according to an exemplary embodiment. On a side of the main actuator circuit, pads  230 , e.g., rectangular pads, may be formed to connect with the pads  192  of the interposer circuit. For example, the pads  230  may be formed of stainless steel, to increase a total surface area for bonding, by either solder or ACF, with the pads  192  of the flat interposer circuit. On the side of the flexure/suspension circuits, a plate  232 , e.g., a spacer may be placed, to maintain an even height of the flat preamp interposer. For example, the plate  232  may be formed of stainless steel. 
       FIG. 24  illustrates a set of flexure/suspension circuits  21  which may be edge-mounted, according to an exemplary embodiment. Although only a portion of the flexure/suspension circuits  21  is illustrated for convenience of description, the flexure/suspension circuits  21  extend beyond the cutoff point shown in  FIG. 24 . Contacts  240 , e.g., exposed copper, are formed on an edge of the flexure/suspension circuits  21  to connect to the contacts  216  of the preamp module  212 . However, this is not limiting, and the contacts  240  may be used to edge mount directly to the preamp  14 . Although  FIG. 24  illustrates four flexure/suspension circuits  21 , the number of flexure/suspension circuits  21  is not limiting. 
       FIG. 25  illustrates a conductive film  250 , e.g., an anisotropic conductive film, according to an exemplary embodiment, which is placed over at least a portion  252  of the copper pads  192  and provides electrical connection between the copper pads  192  and the preamp module  212 , for example. One or more cutouts in conductive film  250  could be added to improve heat release of the preamp  14  to the metal stiffener  340  ( FIG. 34A ). 
       FIG. 26  illustrates the flat preamp interposer  212  attached to the main actuator circuit  12  via the conductive film  250 , according to an exemplary embodiment. The preamp assembly may be done before or after the flat preamp interposer  212  is attached to the main actuator circuit. Reference numeral  260  indicates a portion of the conductive film  250  or metal stiffener  340  (if conductive film cutout is employed), exposed in the opening  218 . 
       FIG. 27  illustrates a body  270  of the preamp  14 , according to an exemplary embodiment. 
       FIG. 28  illustrates a bottom side  280  of the body  270  of the preamp  14 , according to an exemplary embodiment. A contact set  282  is disposed on the side of the main actuator circuit  12  and has bumps  284  for connecting to the preamp contacts  214  disposed on the preamp module  212  on the side of the main actuator circuit  12 . A contact set  286  is disposed on the side of the flexure/suspension circuits  21  and has bumps  288  for connecting to the preamp contacts  214  disposed on the preamp module  212  on the side of the flexure/suspension circuits  21 . Although  FIG. 28  illustrates the contact set  282  having two groups of contacts and the contact set  286  having four groups of contacts, the number of group of contacts and the arrangement of contacts are not limiting. 
       FIG. 29  illustrates the preamp  14  attached to the main actuator circuit  12  via the preamp module  212 , according to an exemplary embodiment. 
       FIG. 30  illustrates the flexure/suspension circuits  21  edge-mounted to the preamp module  212 , according to an exemplary embodiment. As shown, the contacts  240  of the flexure/suspension circuits are inserted into the spaces formed between the contacts  216  of the flat preamp interposer  212 , so that the contacts  240  of the flexure/suspension circuits alternate with the contacts  216  of the flat preamp interposer  212  and make one on one contact with a corresponding contact  216  of the flat preamp interposer  212 . 
       FIG. 31  illustrates an exemplary embodiment of the preamp  14  having contacts  60  disposed on the top surface  63  of the preamp  14 , for connecting to the flexure/suspension circuits, and edge contacts  312  disposed on the first side surface  181  for connecting to the main actuator circuit  12 . For example, the edge contacts  312  may be similar to the edge contacts  180  described above with reference to an exemplary embodiment of  FIG. 18 . Note that this type of preamp has conductive areas on the face and edge of the device. 
       FIGS. 32 and 33  illustrate an exemplary embodiment of the preamp  14  having edge contacts  312 ,  322  disposed on first and second side surfaces  181 ,  324 , for connecting to the flexure/suspension circuits and to the main actuator circuit  12 , respectively. Note that this type of preamp has conductive areas on 2 opposing edges and is suitable for edge-mounted connections. 
       FIGS. 34A and 34B  illustrate an assembly of an exemplary embodiment and of the related art, respectively. As shown in  FIG. 34A , the preamp  14  according to an exemplary embodiment is disposed directly on a stiffener  340  which can be made of metal, e.g., aluminum. As shown in  FIG. 34B , the preamp  14  according to the related art assembly is disposed on one or more additional layers  342  which are disposed on the stiffener  340 . There is typically an underfill material  350  injected and cured to aid heat release and reduce stress of the solder bumps However, as shown by a reference numeral  344  in  FIG. 34A , there are no such additional layers in an exemplary embodiment. Therefore, as compared to the related art, heat dissipation in an exemplary embodiment may be improved and underfill material  350  is eliminated. 
       FIGS. 35A and 35B  illustrate a detailed assembly of an exemplary embodiment and of related art, respectively.  FIG. 35A  shows direct connection of the suspension circuit  42  to the preamp  14  whereas related art  FIG. 35B  illustrates the flexure/suspension circuit not attached to the preamp. 
       FIG. 36  illustrates the thermal simulation model  360  of an exemplary embodiment and the thermal simulation model  362  of the related art. As shown, the thermal simulation model  362  of the related art includes the additional layers  342  and underfill material  350 , so that the preamp of the related art is not in direct contact with the stiffener  340 . The thermal simulation model  360  of an exemplary embodiment does not include any layers between the preamp and the stiffener  340 , i.e., the preamp of an exemplary embodiment is in direct contact with the stiffener  340 . 
     The thermal simulation was performed under the following conditions: prescribe a fixed 25° C. temperature under stiffener; apply internal heat generation for preamp volume (1.5 W/mm 3 ); apply thermal symmetry conditions; ignore convection. 
       FIG. 37  illustrates the thermal simulation results according to  FIG. 36 . As shown, the temperature of the preamp of the thermal simulation model  362  of the related art registered at approximately 74° C., while the temperature of the preamp of the thermal simulation model  360  of an exemplary embodiment registered at approximately 42° C. 
       FIG. 38  illustrates DSA lines  380  formed in the main actuator circuit, according to an exemplary embodiment. 
       FIG. 39  illustrates the flexure/suspension circuits  21  provided with the copper flaps  390  to connect with the DSA lines  380 , according to an exemplary embodiment. 
       FIG. 40  illustrates the solder bumps  400  which electrically connect the DSA lines  380  with the flaps  390  of the flexure/suspension circuits  21 , according to an exemplary embodiment. 
     As described above, an exemplary embodiment is directed to methods and apparatuses providing direct connections between the flexure/suspension circuit and one or more preamps. On the opposite end of the preamp(s) a separate interposer(s) may connect the main actuator circuit&#39;s circuitry to the preamp(s). This simplifies the main actuator circuit pad design connecting to the preamp(s). 
     This approach eliminates the need for a second set of conductive pads in the main actuator circuit since the flexure/suspension circuits are connected directly to the preamp(s). 
     Connection between the different components (main actuator circuit, interposer circuit, preamp(s), and flexure/suspension circuits) can be made using different methods: i.e. soldering, anisotropic conductive film, ultrasonic bonding etc. 
     The resulting reduction in the number of conductive pads in the main actuator circuit allows for simplification of the main actuator circuit design. 
     The direct connection between the preamp(s) and the flexure/suspension circuits reduces the potential for signal impedance discontinuity between the preamp(s) and the flexure/suspension circuit(s). 
     Since the preamp is mounted with the conductive pads facing up, the body of the preamp can be mounted directly to a metal part (stiffener) which is attached to the main actuator circuit resulting in improved thermal release/dissipation. 
     The foregoing exemplary embodiments and advantages are merely exemplary and are not to be construed as limiting. The present teaching can be readily applied to other types of apparatuses. Also, the description of the exemplary embodiments is intended to be illustrative, and not to limit the scope of the claims, and many alternatives, modifications, and variations will be apparent to those skilled in the art.