Patent Publication Number: US-9421665-B2

Title: Pressure-adjusting lapping element

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims benefit of priority to U.S. Provisional Patent Application No. 61/936,046, entitled “Advanced Rough Lap” and filed on Feb. 5, 2014, which is specifically incorporated by reference herein for all that it discloses or teaches. 
    
    
     BACKGROUND 
     Lapping is a machining process by which two surfaces are abrasively rubbed together. Lapping generally takes one of two forms. The first form generally involves rubbing a work piece (e.g., a bar of hard disc drive heads) against a lapping plate with an abrasive (e.g., aluminum oxide, iron oxide, cerium oxide, other oxides, emery, silicon carbide, diamond) placed there between. This process forms microscopic conchoidal fractures as the abrasive rolls between the work piece and the lapping plate and removes material from both the work piece and the lapping plate. In some implementations, the abrasive is in a powder form and mixed with water or another liquid to form an abrasive slurry. 
     The second form of lapping generally involves rubbing the work piece against a lapping plate with an abrasive embedded in the lapping plate. For example, the lapping plate may be made up of a relatively soft material (e.g., pitch or a ductile metal) or a ceramic that holds the abrasive material and permits it to score the work piece when the work piece is rubbed against the lapping plate. 
     Lapping can be used to obtain a precise surface roughness and/or a very accurate surface contour (e.g., planar, convex, and concave). A lapping tool is used to provide precise dimensional control of the work piece to allow the lapping operations to achieve the desired surface roughness and/or contour on the work piece. The tool holds the work piece while it is lapped and permits precise control of the orientation of the work piece with respect to the lapping plate and fine adjustment of any load applied to the work piece during the lapping process. 
     Variations in surface roughness and/or contour may cause process difficulties or failures during later processing steps performed on the work piece. Further, variations in surface roughness and/or contour may cause poor performance of a resulting device. As a result, improved lapping equipment that makes tighter surface roughness and/or contour tolerances achievable and cost-effective is important to create smaller and more accurately defined devices (e.g., hard disc drive heads). Further, improved lapping equipment may achieve higher rates of material removal during the lapping process while maintaining the aforementioned surface roughness and/or contour tolerances. 
     SUMMARY 
     Implementations described and claimed herein address the foregoing problems by providing a pressure-adjusting lapping element comprising a structural region and a whippletree region. The whippletree region includes two or more actuator nodes, one or more element deflection channels oriented between the actuator nodes and the structural region permitting the whippletree region to deflect in response to an applied force at one or more of the actuator nodes, and one or more node separation channels oriented between the individual actuator nodes and permitting the actuator nodes to deflect independently in response to the applied force at the actuator nodes. 
     Implementations described and claimed herein address the foregoing problems by further providing a method comprising applying a lapping force to a structural region of a pressure-adjusting lapping element, applying a pressure distribution force at one or more actuator nodes of a whippletree region of the pressure-adjusting lapping element, and lapping a work piece attached to the whippletree region of the pressure-adjusting lapping element. The whippletree region includes one or more element deflection channels oriented between the actuator nodes and the structural region permitting the whippletree region to deflect in response to the pressure distribution force, and one or more node separation channels oriented between the individual actuator nodes and permitting the actuator nodes to deflect independently in response to the pressure distribution force. 
     Implementations described and claimed herein address the foregoing problems by still further providing a carrier assembly comprising a pressure-adjusting lapping element and an actuator assembly directly attached to the pressure-adjusting lapping element. The pressure-adjusting lapping element including two or more actuator nodes, one or more element deflection channels oriented between the actuator nodes and the structural region permitting the whippletree region to deflect in response to an applied force at one or more of the actuator nodes, and one or more node separation channels oriented between the individual actuator nodes and permitting the actuator nodes to deflect independently in response to the applied force at the actuator nodes. The actuator assembly including two or more linear actuators, each of which engages one of the actuator nodes and provides the applied force at the one or more actuator nodes. 
     Other implementations are also described and recited herein. 
    
    
     
       BRIEF DESCRIPTIONS OF THE DRAWINGS 
         FIG. 1  is a perspective view of an example advanced lapping machine incorporating a pressure-adjusting lapping element. 
         FIG. 2  is an exploded front perspective view of an example carrier assembly including a pressure-adjusting lapping element. 
         FIG. 3  is an assembled front perspective view of an example carrier assembly including a pressure-adjusting lapping element. 
         FIG. 4  is a front perspective view of an example pressure-adjusting lapping element. 
         FIG. 5  is a front view of an example pressure-adjusting lapping element. 
         FIG. 6  illustrates example operations for assembling a lapping head assembly incorporating a pressure-adjusting lapping element. 
         FIG. 7  illustrated example operations for lapping a work piece using an advanced lapping machine incorporating a pressure-adjusting lapping element. 
     
    
    
     DETAILED DESCRIPTIONS 
       FIG. 1  is a perspective view of an example advanced lapping machine  100  incorporating a pressure-adjusting lapping element  132 . The lapping machine  100  includes a baseplate  102  with a lapping plate assembly  120  mounted thereon. The lapping plate assembly  120  includes a spindle  106  that rotates a lapping plate  104  about axis  108 , which is oriented generally in a vertical or z-direction, as illustrated by arrow  110 . Typically, rotation of the lapping plate  104  about axis  108  is motor controlled and may also be feedback controlled to achieve and maintain a desired rotational speed. A support frame  112  is also attached to the baseplate  102  and provides a fixed attachment structure for one or more lapping head rails  114 ,  122  upon which a lapping head assembly  116  is mounted. In other implementations, a greater or fewer number of rails may be used to secure the lapping head assembly  116 . 
     During lapping operations, the lapping head assembly  116  oscillates back and forth along the rails  114 ,  122  generally in a horizontal or x-direction, as illustrated by arrow  118 . The range of travel of the lapping head assembly along the rails  114 ,  122  lies between a location near the inside diameter of the lapping plate  104  and a location near the outside diameter of the lapping plate  104  and in a radial direction extending from the axis of rotation  108 . In some implementations, the travel of the lapping head assembly  116  extends beyond the inside diameter and/or outside diameter of the lapping plate  104 . 
     Precise movement of the lapping head assembly  116  may be accomplished using any of mechanical, electric, and/or electronic systems. For example, movement of the lapping head assembly  116  along the rails  114 ,  122  may be controlled by a synchronized mechanical or electro mechanical system (e.g., a servo motor controlled rack and pinion with sensors monitoring the travel of the lapping head assembly  116 ). The servo motor may be feedback controlled by the sensors to achieve and maintain a desired lapping head assembly  116  oscillation profile (e.g., rate and distance) across the lapping plate  104 . 
     A carrier assembly  130  is suspended within a lapping head frame  162  of the assembly  116 . The lapping head assembly  116  provides fine pitch, roll, and yaw control to the carrier assembly  130 . The pressure-adjusting lapping element  132  is attached to the carrier assembly  130  and serves as a mounting structure for a work piece (e.g., a bar of hard disc drive heads or other microelectronic structure, not shown). The pressure-adjusting lapping element  132  may also form a structural component that strengthens and simplifies construction of the carrier assembly  130 . The pressure-adjusting lapping element  132  may also include features (not shown) that provide enhanced bending force and deflection capabilities to achieve a desired surface contour to the work piece. 
       FIG. 2  is an exploded front perspective view of an example carrier assembly  230  including a pressure-adjusting lapping element  232 . The pressure-adjusting lapping element  232  is a structural component of the carrier assembly  230  and is used to secure (e.g., glue or otherwise attach) a work piece  224  (e.g., a slider chunk). The work piece  224  may include, for example, slider material that is to be sliced into individual bars of multiple sliders. The carrier assembly  230  also includes a PCB (printed circuit board) assembly  226  that includes a base plate  244 , a top plate  234 , and various internal components  236  (e.g., a moisture seal, a spring, a flex connector, a PCB, etc.) are arranged as shown in  FIG. 2  and clamped together to form the PCB assembly  226 . 
     The PCB assembly  226  attaches to a work piece back support  228  with the pressure-adjusting lapping element  232  secured there between. More specifically, the pressure-adjusting lapping element  232  is secured between the PCB assembly  226  and the back support  228  and constrained from movement in the x-y plane. The pressure-adjusting lapping element  232  is able to move in the z-direction with reference to the PCB assembly  226  and the back support  228 . In one implementation, fasteners (not shown) extend through holes  254 ,  256  in the base plate  244 , slots  250 ,  252  in the pressure-adjusting lapping element  232 , and are secured to holes  258 ,  260  in the back support  228 , respectively. The pressure-adjusting lapping element  232  may move in the z-direction with reference to the PCB assembly  226  and the back support  228  by action of the fasteners sliding within the slots  250 ,  252 , respectively. 
     The carrier assembly  230  also includes a lapping pressure actuator assembly  246 , which includes male protrusions  264 ,  266  that engage with female receptacles  268 ,  270 , respectively. When the carrier assembly  230  is assembled, the actuator assembly  246  is secured in the x-z plane via the protrusions  264 ,  266  engaging with the receptacles  268 ,  270 . The actuator assembly  246  is secured in the y-direction by compressing the entire carrier assembly  230  together in the y-direction. For example, one or more actuators (not shown) may compress the carrier assembly  230  in the y-direction against a fixed structure (also not shown). Further, planar surface  248  of the pressure-adjusting lapping element  232  engages a similar planar surface (rear-facing, not shown) of the actuator assembly  246  to ensure secure interfacing between the pressure-adjusting lapping element  232  and the actuator assembly  246 . As a result, the actuator assembly  246  is substantially constrained from movement and/or rotation is all directions with respect to the pressure-adjusting lapping element  232 . 
     Utilizing the pressure-adjusting lapping element  232  as a structural component of the carrier assembly  230  allows the back support  228  to be u-shaped rather than solid across. The u-shaped back support  228  allows the actuator assembly  246  to be intimately and directly attached to the pressure-adjusting lapping element  232  without any other structure there between and without interference with the actuator nodes and an array of channels in the pressure-adjusting lapping element  232 . 
     The actuator assembly  246  also includes an array of linear actuators (e.g., linear actuator  272 ) that may independently move in the z-direction as desired. The linear actuators each engage with a corresponding actuator node (e.g., actuator node  274 ) in the pressure-adjusting lapping element  232  when the carrier assembly  230  is assembled. As a result, actuation of the linear actuators in the z-direction causes a corresponding deflection of the pressure-adjusting lapping element  232 , as described in further detail below. 
       FIG. 3  is an assembled front perspective view of an example carrier assembly  330  including a pressure-adjusting lapping element  332 . The pressure-adjusting lapping element  332  is a structural component of the carrier assembly  330  and is used to secure a work piece  324 . When in operation, the PCB assembly  326  and the back support  328  remain in a fixed position, as does the pressure-adjusting lapping element  332  and the work-piece  324  with the caveat that the work-piece  324  is permitted to make small correcting movements within the assembly  330  in the z-direction, as shown by the arrow  310 . As layers of the work piece  324  (e.g., wafer bars of a wafer chunk) are lapped, the carrier assembly  300  is disassembled and the next layer of the work piece  324  is advanced by sliding the pressure-adjusting lapping element  332  and its attached work-piece  324  between the PCB assembly  326  and the back support  328  to allow lapping operations to continue until the work-piece  324  is consumed. The pressure-adjusting lapping element  332  forms a part of the structure of the carrier assembly  330  and is fixedly attached to a lapping pressure actuator assembly (not shown, see e.g., lapping pressure actuator assembly  246  of  FIG. 2 ). The pressure-adjusting lapping element  332  maintains alignment between the work piece  324  and the remainder of the carrier assembly  330 . 
       FIG. 4  is a front perspective view of an example pressure-adjusting lapping element  432 . The pressure-adjusting lapping element  432  includes a structural region  476  (or area of increased thickness) for attaching the pressure-adjusting lapping element  432  to other structures of a corresponding carrier assembly (not shown) and a flexible region  478  (or an area of decreased thickness) for permitting fine adjustment of pressure applied to a work piece  424  attached to the pressure-adjusting lapping element  432 . In various implementations, the flexible region  478  thickness is substantially equivalent (i.e., less than 5% variance) to the work-piece/chunk thickness. Further, the various implementations, the flexible region  478  thickness is 10-30% of the structural region  476  thickness. The flexible region  478  may include a whippletree structure as depicted in  FIG. 4  or any other arrangement (including one or more of material, thickness, and physical features, for example) that achieves sufficient flexibility to allow actuator nodes (e.g., actuator node  474 ) to manipulate the pressure-adjusting lapping element  432  as described herein. 
     More specifically, the structural region  476  includes a pair of slots  450 ,  452  through which fasteners (not shown) extend and attach the pressure-adjusting lapping element  432  to a PCB assembly (not shown) and a back support (not shown), while allowing the pressure-adjusting lapping element  432  to move in the z-direction with reference to the PCB assembly and the back support by action of the fasteners sliding within the slots slots  450 ,  452 . The structural region  476  further includes a pair of receptacles  468 ,  470  that engage with corresponding protrusions (not shown) of a precision actuator assembly (not shown) and compressively secures the precision actuator assembly intimately and directly to the pressure-adjusting lapping element  432  without any other structure there between and without interference with the actuator nodes and an array of channels (e.g., channel  480 ) in the pressure-adjusting lapping element  432 . 
       FIG. 5  is a front view of an example pressure-adjusting lapping element  532 . The pressure-adjusting lapping element  532  includes a structural region  576  (or area of increased thickness) for attaching the pressure-adjusting lapping element  532  to other structures of a corresponding carrier assembly (not shown) and a flexible region  578  (or an area of decreased thickness) for permitting fine adjustment of pressure applied to a work piece  524  attached to the pressure-adjusting lapping element  532 . The flexible region  578  may include a whippletree structure as depicted in  FIG. 5  or any other arrangement (including one or more of material, thickness, and physical features, for example) that achieves sufficient flexibility to allow actuator nodes (e.g., actuator node  574 ) to manipulate the pressure-adjusting lapping element  532  as described herein. 
     More specifically, the flexible region  578  includes actuator nodes (e.g., actuator node  574 ) and an array of channels (e.g., channel  580 ). Corresponding linear actuators (not shown) on a precision actuator assembly (not shown) engage the actuator nodes and provide the force for fine adjustment of the flexible region  578  primarily in the z-direction. The array of channels provides the requisite flexibility of the flexible region  578  to deflect a desired amount and direction in response to the force applied to the actuator nodes via the linear actuators. 
     Pressure-adjusting lapping element  532  includes 5 actuator nodes, each of which corresponding to a linear actuator (not shown). The linear actuators allow the pressure-adjusting lapping element  532  to be manipulated in the z-direction in 5 separate regions separated by vertical node separation channels (e.g., channel  580 ) to achieve a desired lapping surface pressure profile. Further, the pressure-adjusting lapping element  532  includes an array of horizontal element deflection channels (e.g., channel  582 ) oriented substantially between the actuator nodes and the structural region  576  that allow the pressure-adjusting lapping element  532  to deflect under force from the actuator nodes. As a result, lapping plate pressure can be manipulated via the  5  actuator nodes to achieve a desired pressure profile on the lapping plate. Since pressure on the lapping plate is directly related to the rate of material removal, the desired pressure profile permits a desired work piece surface contour (e.g., planar, a upward-facing curve, a downward-facing curve, or any complex contour geometry) to be achieved. 
     In an example implementation, a 10-40N lapping force is applied to the pressure-adjusting lapping element  532  as illustrated by arrow  510 . A responsive normal 10-40N force (or pressure) is exerted by a lapping plate (not shown) on the work piece  524 , as illustrated by arrows  584 . In order to achieve a desired pressure profile of the normal pressure exerted by the lapping plate, one or more of the actuator nodes are deflected by the linear actuators applying a +/−0-80N corrective force in the positive or negative z-direction, as illustrated by arrows  586 . The resulting pressure profile influences the rate of material removal during lapping operations, which ultimately yields a desired work piece lapping surface profile. The aforementioned example is for illustration purposes, lapping forces, normal forces, and corrective forces outside the aforementioned ranges are contemplated in the presently disclosed technology. 
     A number, placement, orientation, and size of the channels and the actuator nodes is specifically chosen to provide desired pressure-adjusting lapping element  532  bending characteristics. Further, the pressure-adjusting lapping element  532  is configured to operate with a work piece  524  with a widely varying z-direction thickness and stiffness (e.g., a slider chunk with 44 slider bars remaining vs. a slider chunk with only 1 slider bar remaining). Still further, electronic lapping guides (not shown) embedded within the work piece  524  may monitor work piece surface contour and the pressure on the lapping plate and the surface geometry of the work piece  524  can be manipulated in real time by monitoring the electronic lapping guides to achieve the desired work piece surface contour over time. Furthermore, the number, placement, and size of the channels delineating the flexible region  578  or flexure arrangement and its actuator nodes may be precisely tailored to control pressure distribution and reaction force along a length of the work-piece  524 . The channels may minimize or eliminate the introduction of work-piece dimensional errors created by shortcomings in the overall system design. 
     In one implementation, the work piece  524  is a slider chunk with a lapping surface on the bottom surface. The pressure-adjusting lapping element  532  is specifically configured to provide a desired pressure profile against a lapping plate (not shown) during lapping operations to achieve a desired quantity of material removal and a planar lapping surface. The pressure profile is varied via the actuator nodes and feedback from the electronic lapping guides pressure is used to achieve the desired quantity of material removal and the planar lapping surface, regardless of the thickness of the slider chunk (i.e., how many slider bars remain on the slider chunk  1268 ) or any overall downward pressure applied against the lapping plate. 
     In various implementations, the flexible region  578  of the pressure-adjusting lapping element  532  enables more uniform reaction force and pressure characteristics in response to overall lapping forces than prior-art designs. As a result, the application of an overall lapping force to the pressure-adjusting lapping element  532  does not contribute to any dimensional errors in the work-piece  524 . Conceptually, the flexible region  578  is a complex spring arrangement with a stiffness along a length of the work piece  524  precisely tailored to create a substantially uniform spring constant along the length of the work piece  524 . Therefore, given an outwardly applied, overall down-force upon the lapping plate, the responsive pressure distribution on the work-piece  524  lapping surface is substantially uniform or has a desired pressure response profile. 
     Prior-art designs fail to recognize the positive effect of this uniform spring rate/uniform pressure distribution/uniform deflection characteristic on work piece  524  lapping operations. As a result, in prior-art designs, the work-piece  524  lapping surface would experience an inconsistent responsive pressure profile, and thus uneven lapping rates across the work piece  524  lapping surface under the overall lapping force. This inconsistent responsive pressure profile of prior art designs may be corrected by providing and manipulating the actuator nodes of the pressure-adjusting lapping element  532 . 
       FIG. 6  illustrates example operations  600  for assembling a lapping head assembly incorporating a pressure-adjusting lapping element. A bonding operation  605  bonds a work piece to be lapped to a pressure-adjusting lapping element. In implementations where the work piece is a wafer chunk, the bonding operation occurs once per wafer chunk at the beginning of wafer chunk processing operations. 
     A first attaching operation  610  fixedly attaches an actuator assembly directly to the pressure-adjusting lapping element. In various implementations, the actuator assembly and the lapping element include matching male/female alignment devices that secure the actuator assembly to the lapping element when pressed together. Further, when pressed together, individual linear actuators on the actuator assembly each engage an actuator node on the lapping element. 
     A second attaching operation  615  slidably attaches a printed circuit board (PCB) assembly and a back plate to the pressure-adjusting lapping element to form a carrier assembly. In various implementations, the PCB assembly and the back plate are oriented on opposing sides of the lapping element and the lapping element includes two or more slots. Fasteners extend from the PCB assembly, through the slots in the lapping element, and secure within holes in the back plate. As a result, the PCB assembly and the back plate are fixedly attached to one another, with the lapping element able to move axially with respect to the PCB assembly and the back plate. 
     An assembling operation  620  assembles the carrier assembly as a component of an overall lapping head assembly and a precision lapping machine. The carrier assembly is compressed within the lapping head assembly, which provide precise pitch, roll, and yaw control to the work piece. The lapping head assembly is attached to one or more rails on the precision lapping machine, which allows the lapping head assembly to oscillate the work piece across a lapping pate assembly of the precision lapping machine during lapping operations. 
       FIG. 7  illustrated example operations  700  for lapping a work piece using an advanced lapping machine incorporating a pressure-adjusting lapping element. A first force application operation  705  applies a lapping force to the pressure-adjusting lapping element of a lapping head assembly. The lapping force is directed at achieving a desired rate of material removal from a work piece during lapping operations. A second force application operation  707  applies a balance correcting force to the pressure-adjusting lapping element of the lapping head assembly. The balance correcting force corrects for slope and/or linear errors (e.g., least-squares line fit angle correction) along a length of the work piece. 
     A third force application operation  710  applies a pressure distribution force to the pressure-adjusting lapping element. The lapping element includes two or more actuator nodes that permit fine adjustment of the pressure distribution profile on the work piece on a lapping plate. The pressure adjustment force is applied at one or more of the actuator nodes, at desired magnitude(s) and direction(s) to achieve a desired pressure profile on the lapping plate. 
     A lapping operation  715  laps a surface of the work piece. More specifically, the work piece is pressed against a rotating lapping plate with a pressure profile resulting from a combination of the first force application operation  705  and the second force application operation  710 . The lapping plate abrasively removes material from the work piece at a rate corresponding to the pressure profile of the work piece on the lapping plate. A monitoring operation  720  monitors an array of lapping guides embedded within the work piece. More specifically, the lapping guides are resistive elements, each of which indicates thickness of the work piece in the region of the work piece that is monitored by each lapping guide. In combination, the lapping guides can be used to measure a work piece surface profile. 
     A decision operation  725  determines if lapping operations are complete. The measured work piece profile is compared against a desired work piece profile. If the measured work piece profile does not match the desired work piece profile within an acceptable tolerance, the operations  705 - 725  are repeated with modified pressure distribution force defined to modify the measured work piece profile to more closely match the desired work piece profile. Further, if a sufficient quantity of material overall has not been lapped from the work piece, regardless of the work piece profile, operations  705 - 725  may also be repeated. Until lapping is complete, operations  705 - 725  may be repeated iteratively. Once lapping is complete, removing operation  735  removes the lapped work piece from the pressure-adjusting lapping element for further processing. 
     The logical operations making up the embodiments of the invention described herein are referred to variously as operations, steps, objects, or modules. Furthermore, it should be understood that logical operations may be performed in any order, adding and/or omitting operations as desired, unless explicitly claimed otherwise or the claim language inherently necessitates a specific order. 
     The above specification, examples, and data provide a complete description of the structure and use of exemplary embodiments of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended. Furthermore, structural features of the different embodiments may be combined in yet another embodiment without departing from the recited claims.