Patent Publication Number: US-11651785-B1

Title: Mounting supports that create a bond pad gap for a hard disk slider

Description:
RELATED PATENT DOCUMENTS 
     This application is a divisional of U.S. application Ser. No. 17/317,277 filed on May 11, 2021, which is incorporated herein by reference in its entirety. 
    
    
     SUMMARY 
     The present disclosure is directed to mounting supports that extend a bond pad gap for a hard disk recording head. In one embodiment, a slider includes a slider body with an air-bearing surface and a top surface opposing the air-bearing surface. A plurality of slider bond pads are disposed on or parallel to the top surface and proximate to or at a trailing edge of the slider. The plurality of slider bond pads have an exposed surface facing away from the top surface of the slider body. One or more mounting supports extend from the top surface to a distance of at least 12 μm above the exposed surface of the plurality of slider bond pads. 
     In another embodiment, a trace-gimbal assembly includes a suspension surface and to a plurality of trace bond pads. The trace bond pads are electrically coupled to traces of a flex circuit that deliver signals to and from signal processing circuitry of the apparatus. A slider is coupled to the trace-gimbal assembly and includes a slider body with an air-bearing surface, and a top surface opposing the air-bearing surface. A plurality of slider bond pads are disposed on or parallel to the top surface and proximate to or at a trailing edge of the slider. The plurality of slider bond pads have an exposed surface facing away from the top surface of the slider body. One or more mounting supports extend from the top surface to a distance of at least 12 μm above an exposed surface of the plurality of slider bond pads. The one or more mounting supports are attached to the suspension surface of the trace-gimbal assembly such that slider bond pads and the trace bond pads are parallel to one another and separated by gaps of the distance of at least 12 μm, the gaps being filled with solder that electrically couples the transducer bond pads to the slider bond pads. 
     In another embodiment, a method involves depositing an adhesion layer on at least a portion of a top surface of a slider body having a top surface opposite an air-bearing surface. A first photolithography cycle is performed to deposit a first metal layer having a thickness of at least 8 μm. A second photolithography cycle is performed to deposit a second metal layer having a thickness of at least 8 μm over the first metal layer. The first and second layer form a mounting support on the top surface. 
     In another embodiment, a method involves providing a slider having a slider body formed of a first material. The slider body has an etching surface opposite an air-bearing surface. The slider includes a transducer portion comprising a second material formed at a trailing edge of the slider. The second material has a higher etch rate than the first material. The method involves removing a portion of the etching surface and the transducer portion to form a mounting support above a top surface. In another embodiment, a method involves plurality of bond pads are deposited on the top surface. A top of the mounting support is at least 12 μm above an exposed surface of the plurality of bond pads. In some embodiments, the method may further involve attaching the mounting support of the slider to a suspension surface of a gimbal such that the bond pads are aligned with corresponding pads on the suspension surface. The bond pads are separated from the corresponding pads by a gap defined by the mounting support. The method may further involve introducing individual solder beads in the gap between each of the bond pads and corresponding bond pads, and reflowing the solder beads to create interconnects between the bond pads and corresponding bond pads. 
     These and other features and aspects of various embodiments may be understood in view of the following detailed discussion and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The discussion below makes reference to the following figures, wherein the same reference number may be used to identify the similar/same component in multiple figures. 
         FIG.  1    is a top view of a hard disk data storage device according to an example embodiment; 
         FIG.  2    is a is a side view of a recording head according to an example embodiment; 
         FIG.  3    is a perspective view of a trace gimbal assembly according to an example embodiment; 
         FIGS.  4  and  5    are side views of a slider showing interconnecting of bonding pads according to an example embodiment; 
         FIGS.  6  and  7    are respective top and side views of a recording head showing a mounting support arrangement according to an example embodiment; 
         FIGS.  8  and  9    are respective top and side views of a recording head showing a mounting support arrangement according to another example embodiment; 
         FIGS.  10 A,  10 B,  10 C, and  10 D  are diagrams showing alternate mounting support geometries according to example embodiments; and 
         FIGS.  11  and  12    are flowcharts of methods according to example embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure generally relates to magnetic recording devices such as hard disk drives (HDDs). An HDD generally uses one or more recording heads (also referred to as heads, read heads, write heads, read/write heads, etc.) held over respective one or more surfaces of a disk by an actuator-driven arm Recording heads progressively add more recording head features as technology advances. Electrical interconnects are provided to connect those features from slider bond pads to trace gimbal assembly (TGA) or suspension trace bond pads to connect with data storage device circuitry. As recording head features are added, the number of interconnects used to support those features increases as well. 
     To form an interconnect, a slider (which includes the read/write head at one end) is placed on a suspension with suspension trace bond pads such that the head bond pads are aligned with and perpendicular to the suspension trace bond pads. A mechanical system may be used to jet solder spheres to connect the slider bond pads to the suspension trace bond pads in a thermal interconnect (TIC) process. The present disclosure generally describes a recording head design with parallel or opposing bond pad interconnects, and describes slider features that allow increasing the density of the interconnects. 
       FIG.  1    shows an illustrative hard disk data storage apparatus  100  in which certain slider interconnect embodiments disclosed herein may be incorporated. The data storage apparatus  100  includes a data storage disk  102  and a slider  104 . The slider  104  includes transducer elements (not shown in  FIG.  1   ) such as a reader (e.g., magnetoresistive stack) and writer (e.g., magnetic write coil and poles) The slider  104  is positioned above the disk  102  to read data from and/or write data to the disk  102 , which is rotated by a spindle motor (not shown). An actuator  106  rotates an arm  108  upon which the slider  104  is mounted. The rotation induced by the actuator  106  positions the slider  104  relative to data tracks on the rotating disk  102 . Both the spindle motor and actuator  106  are connected to and operated through drive circuitry  110 , e.g., a circuit card. 
     In  FIG.  2    is a side view of the slider  104  above the medium  102  shows additional details of the data storage apparatus  100 . Transducer elements  200  within the head portion of the slider  104  include read and write elements encapsulated in an insulating structure to form a transducer portion  104   b  of the slider  104 . As shown, the slider  104  includes a media-facing surface  202 , e.g., configured as an air bearing surface (ABS). The slider  104  is coupled to the arm  108  through a gimbal  204  coupled to a top surface  206  of the slider  104  facing away from the disk  102 . Note that the term “top surface” is used for convenience of description, and does not require any particular orientation of the slider with respect to a reference point, e.g., the ground. The disk  102  can be a continuous storage medium, a discrete track medium, a bit patterned medium or other magnetic storage medium including one or more magnetic recording layers. 
     During operation, rotation of the disk  102  creates an air or gas flow along the media-facing surface  202  of the slider  104  from a leading edge  208  to a trailing edge  210  of the slider  104 . The air or gas flow along the media-facing surface  202  creates a pressure cushion to support the slider  104  above the disk  102  for read and/or write operations. As shown, the transducer portion  104   b  is formed at or near the trailing edge  210  of the slider  104 . The transducer portion  104   b  may include elements such as read and write transducers, writer and/or reader heaters, a thermal asperity sensor, heat-assisted recording optics, etc., which are not shown in the interest of simplification. The transducer portion  104   b  is joined with a slider body  104   a . The slider body  104   a  may be formed of a metal, e.g., AlTiC, and provides a structural attachment for the slider  104  as well as including air bearing features. 
     In  FIG.  3   , a perspective view shows a trace gimbal assembly (TGA)  300  according to an example embodiment. The TGA  300  provides an electrical interface to electrical elements of the transducer portion  104   b  of the slider  104 , which is shown with its media-facing surface  202  facing upwards. The TGA  300  includes a plurality of trace bond pads  302  on a suspension surface  304  coupled to the traces  306  of a flex circuit extending along opposed sides of the slider  104 . The slider  104  is also attached (e.g., bonded) to the suspension surface  304 , and this provides a mechanical coupling between the slider  104  and a gimbal suspension (not shown). 
     During the manufacture of the drive, the trace bond pads  302  are electrically coupled to bond pads  303  of the slider&#39;s transducer portion  104   b . This electrically connects the transducer portion  104   b  of the slider  104  to the traces  306 . The traces  306  deliver signals to and from the trace bond pads  302  to and from signal processing circuitry of the drive after the drive is fully assembled, coupling the transducer portion  104   b  to this circuitry. Note that different routings of the traces  306  as well as other physical configuration (e.g., shape, location) of the traces  306  and the rest of the flex circuit may be possible in the embodiments described herein. 
     A factory system or device is used to deposit conductive material, such as solder balls (also referred to as spheres, pellets, droplets, beads) to form the connection between slider bond pads  303  and trace bond pads  302 . The operation of an assembly system and device according to an example embodiment is shown in  FIGS.  4  and  5   . As seen in  FIG.  4   , the system uses one or more capillary tubes  400  that send solder spheres  402  to be deposited in a gaps  404  between the bond pads  302 ,  303  to form interconnects. As seen in  FIG.  5   , heat  500  is applied to the solder sphere  402 , causing it to melt and reflow. The reflowing results in both bond pads  302 ,  303  being wetted (e.g., the solder is molten and will adhere to the bond pads) which forms an electrical interconnect, and provides additional mechanical bonding as well. 
     As new recording technologies are implemented, there may be a need to increase the number of bond pads  303  on the slider  104 . For example, technologies such as heat-assisted magnetic recording (HAMR) involve integrating a laser (not shown) with the slider  104 , which require at least electrical lines for current supply and current return. A HAMR recording head may include additional optical sensors to control the laser, e.g., a bolometer, which may involve adding additional signal lines to the head. In other cases, multiple transducers, e.g., readers, may be incorporated into the head, each requiring additional signal lines. 
     Existing production TGA configurations have typically used 10 or fewer bond pads at the recording head. Newer designs are expected to increase this to 12, 14, or higher. For example, the implementation shown in  FIG.  3    shows 14 trace bond pads  302  and corresponding slider bond pads  303  (also referred to as recording head bond pads). As the density of bond pads on an interconnect increases, the cost and risk of defects during the interconnect process increases. Bond pads may be reduced in size (for example, pads may be 30 μm wide) and the spaces between the pads may be reduced (for example, spaces may be 23.75 μm wide) to create high density pads (for example, recording heads with 11 bond pads or greater). 
     To connect high density interconnects, smaller solder spheres (for example, approximately 40 μm wide) may be used, but there may be issues with using smaller solder spheres. Smaller solder spheres pose various operational challenges and the process cost per head increases as solder sphere diameter decreases. Challenges for the mechanical system that deposits the solder spheres may include blocked chutes or capillaries; sheared off solder spheres, debris, or smears; or doubling of solder spheres. Capillaries may also need to be replaced with increased frequency and cost. Reducing the amount of solder and/or the space between bond pads also increases the risk of soldering defects. Interconnects with bond pads that are too close together or that use too little solder risk poor connections, cracks, or missed interconnects. Bond pads that are too close together also risk bridging, such that a bond is formed between adjacent bond pads. 
     In reference again to  FIGS.  4  and  5   , the reflowed solder ball  402  has been formed in the gap  404  between opposing bond pairs of slider bond pads  303  and trace bond pads  302 . Forming the interconnect between opposing bond pairs, rather than perpendicular bond pairs, may allow a strong joint to be formed without an outward bulge toward adjacent bond pads. By reducing outward bulges, the risk of bridging between adjacent bond pads is decreased. Thus, utilizing opposing bond pads may allow for an increased interconnect density and reduces the limitations of using smaller solder spheres or the risk of defective joints. Thus the slider bond pads  303  and trace bond pads  302  have at least some parts that are parallel to one another separated by the gap  404  between the pair of pads  302 ,  303 . Note while the slider bond pad  303  is shown with parts that are both parallel and perpendicular to the trace bond pad  302 , the perpendicular parts are optional. 
     In order to increase the density of bond pads on the TGA, it is expected that size of the gap  404  will be on the order of 11 μm or more. A gap may be formed in some designs by forming a notch in the slider  104  at the intersection of the trailing edge  210  and the top surface  206  of the slider  104 . Such an approach could be problematic for a gap  404  larger than 11 μm, however. As such, embodiments described herein include a mounting support  406  can be formed between the top surface  206  and the suspension surface  304 . The mounting support  406  acts both as a structural support and a spacer that creates gaps between an exposed surface  303   a  of slider bond pads  303  and a corresponding (e.g., parallel) surface  302   a  of the trace bond pads  302 . 
     In some embodiments, the mounting support  406  formed integrally with the slider  104 , e.g., via deposition of materials on the top surface  206  or by removal of materials from the top surface  206 . The mounting support  406  includes sufficient adhesion area to support the slider  104 , and also has can firmly support the slider  104  in response to external forces, e.g., air-bearing forces, head-to-disk impacts. Thus the mounting support  406  may be at least partly located around the periphery of the top surface  206 , as this provides a good resistance against torques applied to the slider  104 . 
     In  FIGS.  6  and  7   , top and side views of a slider  104  show a slider standoff arrangement according to an example embodiment. As indicated in this view, the head is formed of a metallic slider body  104   a  and a transducer portion  104   b . The metallic slider body  104   a  is formed, e.g., from AlTiC or the like. When the slider  104  is formed, the AlTiC slider body  104   a  serves as a substrate on which the transducer portion  104   b  is formed. The transducer portion  104   b  includes electrical, magnetic, and in some cases optical components. The transducer portion  104   b  may be filled mostly with an oxide such as Al 2 O 3 , but may include a wide variety of other oxides, metals, and other materials that are used to form the transducers, sensors, and other components of the transducer portion  104   b.    
     In this embodiment, a mounting support  600  formed as single contiguous structure that covers a majority of the top surface  206 . As seen in  FIG.  7   , single contiguous structure of the mounting support  600  includes an adhesion layer  600   a  on the metal (e.g., AlTiC) of the slider body  104   a . Layers  600   b  are formed of a second metal that is formed on the adhesion layer. The second metal is different than the first metal (e.g., second metal may include Sn, for example. The adhesion layer  600   a  may also include metals, such as Ti and Ni. Also shown is a protective top layer  600   c , which may be an oxide such as Al 2 O 3 , which passivates the mounting support  600 , protecting it from corrosion. 
     In some embodiments, a height  700  of the mounting support  600  above the slider bond pads  303  may be between 16 μm and 24 μm, although may be below or above this range in some embodiments, e.g., by adjusting process, material, patterns, etc. In one embodiment, the mounting support is added after depositing the slider bond pads  303 . Note that in this view the bond pads  303  are shown formed over an insulator layer  602  on the slider body  104   a , which keeps the bond pads  303  from shorting to the metal body  104   a . Note that a dimension  702  of the mounting support  600  above the top surface  206  may be larger than the height  700  of the mounting support  600  above the slider bond pads  303 , due to the thickness of the bond pads  303  and insulator layer  602 . 
     After formation of the bond pads  303 , the adhesion layer  600   a  is deposited, 800 Å Ti+3,000 Å Ni in one example. The adhesion layer  600   a  is followed by one or more metal layers, e.g., a plurality of 80,000 Å Sn layers. For a 16 μm dimension  700 , this may involve depositing two such layers  600   b , which involves two cycles of photolithography, deposition, and stripping of photoresist. For a 24 μm dimension  700 , this may involve depositing three such layers  600   b , which involves three cycles of photolithography, deposition, and stripping of photoresist. After building up of the metal layers  600   b , the protective top layer  600   c  is added, e.g., by depositing 3,000 Å Al 2 O 3 . It will be understood that different shapes and materials may be used to create a similar mounting support and spacer structure. 
     In  FIGS.  8  and  9   , top and side views of a slider  104  show a slider standoff arrangement according to another example embodiment. As before, the head is formed of a metallic slider body  104   a  and a transducer portion  104   b . One or more mounting supports  800  are formed on the top surface  206  of the slider body  104   a . As indicated by the cross-section in  FIG.  9    corresponding to cross-section line  804 , the slider body  104   a  and mounting supports  800  can be made of the same material, e.g., AlTiC. The mounting supports  800  can be formed by etching into the slider body  104   a , e.g., by depositing and patterning an etch-resistant mask that defines the shape of the mounting supports  800  and creates the top surface  206 . This results in the mounting supports  800  and slider body  104   a  being a monolithic structure, e.g., formed or composed of a single block of homogenous material without joints or seams. 
     To meet an example targeted x μm mounting support offset height  900 , y μm of the metal slider body is targeted for removal, wherein y=x*a/b and a/b is the relative mill rate of the metal of the slider body  104   a  to the oxide used in the transducer portion  104   b . For example, where AlTiC and alumina are used for the respective slider body  104   a  and transducer portion  104   b , the alumina to AlTiC mill rate is 1.59/1. Thus for a target gap of 16 μm, y=16*1/1.59≈10 μm of AlTiC is etched away to form the mounting supports  800 . In such an example, a 30 μm resist process enables a single mill run with 10 um AlTiC/16 μm alumina depth. After milling, the insulator layer  602  and bonding pads  303  are deposited. This can be done using bi-layer photolithography process with 9 μm resist, which enables depositing an 8 μm metal layer. As with the embodiment shown in  FIGS.  6  and  7   , the height  902  of the mounting supports  800  above the top surface (which corresponds to the etch depth) may be increased in order to account for thickness of the bond pads  303  and insulator layer  602 . 
     The specific mounting support shapes and layouts shown in  FIGS.  6  and  8    can be made using either described process. Other materials can be used instead of or in addition to the described materials. For example, using a deposition process as described for  FIGS.  6  and  7   , the mounting support can be made from other materials, such as Al, Ti, Ag, Au, Ta 2 O 5 , and SnO 2 . Also, other shapes and arrangements may be used. For example, in  FIGS.  10 A,  10 B,  10 C, and  10 D , a number of mounting support shapes (shaded regions) may be used, each shown on commonly referenced slider body  104   a  and transducer portion  104   b . These shapes may be made using either of the fabrication methods described above. 
     In  FIG.  11   , a flowchart shows a method according to an example embodiment. The method involves depositing  1100  bonding pads on a top surface of a slider that is opposite an air-bearing surface of the slider. The bonding pads extend to a trailing edge of the slider. An adhesion layer is deposited  1101  on at least a portion of the top surface of the slider. A first photolithography cycle is performed  1102  to deposit a first metal layer having a thickness of at least 8 μm. A second photolithography cycle is performed  1103  to deposit a second metal layer having a thickness of at least 8 μm over the first metal layer. The first and second metal layers are coated  1104  with an oxide to form a mounting support that includes at least the first and second metal layers. 
     The method optionally involves attaching  1105  the mounting support to a suspension surface of a gimbal such that the bond pads are aligned with corresponding pads on the suspension surface. The bond pads are separated from the corresponding pads by a gap defined by the mounting support. Individual solder beads are introduced  1106  in the gap between each of the bond pads and corresponding bond pads. The solder beads are reflowed  1107  to create interconnects between the bond pads and corresponding bond pads. 
     In  FIG.  12   , a flowchart shows a method according to another example embodiment. The method involves providing  1201  a slider body comprising a first material. The slider body has an etching surface opposite an air-bearing surface and a transducer portion comprising a second material formed at a trailing edge of the slider. The second material has a higher etch rate than the first material. A portion of the etch surface is removed  1202  (e.g., etched) to form at least one mounting support and a top surface. A plurality of bond pads is deposited  1203  on the top surface, where a top of the at least one mounting support is at least 12 μm above an exposed surface of the plurality of bond pads. 
     Note that after deposition  1203  of the bond pads, the method of shown in  FIG.  12    may include steps  1105 - 1107  in  FIG.  11   , which involve attaching the slider bond pads to the trace bond pads. Other methods steps described elsewhere may also be performed, e.g., adding an oxide passivation layer over the mounting supports after etching  1202  the top surface. 
     Unless otherwise indicated, all numbers expressing feature sizes, amounts, and physical properties used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein. The use of numerical ranges by endpoints includes all numbers within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5) and any range within that range. 
     The foregoing description of the example embodiments has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the embodiments to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. Any or all features of the disclosed embodiments can be applied individually or in any combination are not meant to be limiting, but purely illustrative. It is intended that the scope of the invention be limited not with this detailed description, but rather determined by the claims appended hereto.