Abstract:
Methods and apparatus to control heat dissipation in hard-disk drives (HDDs) are disclosed. A disclosed example apparatus comprises a semiconductor die, a ground bump positioned on the die, and a hard-disk drive writer head positioned on the die relative to the ground bump based on a thermal impedance.

Description:
RELATED APPLICATIONS 
     This patent claims the benefit of U.S. Provisional Application Ser. No. 60/988,541, entitled “Footprint of Preamp Writer Heads,” filed on Nov. 16, 2007, and which is hereby incorporated by reference in its entirety. 
    
    
     FIELD OF THE DISCLOSURE 
     This disclosure relates generally to hard-disk drives (HDDs), and, more particularly, to methods and apparatus to control heat dissipation in HDDs. 
     BACKGROUND 
     HDDs use one or more disks and/or platters that rotate about a spindle with respect to one or more heads, such as read and/or writer heads. The read or writer heads read information from and/or impart information to the disk platters, but do not, in desired operation, physically contact the platters. Traditionally, a HDD head is implemented by an integrated circuit (IC) that is subsequently mounted (e.g., soldered) to a printed circuit substrate (e.g., a printed circuit board (PCB) and/or a printed circuit cable assembly (PCCA). The printed circuit substrate is affixed to a stiffener and/or armature arm that positions the HDD head relative to a disk platter. 
       FIG. 1  is a plan view of an example of a layout  100  for armature assembly printed circuit substrate  102  for an HDD. In the illustrated example of  FIG. 1 , seats (e.g.,  106 - 1 ) and solder bumps or balls (e.g.,  108 - 1 ) on a printed circuit substrate  102  are shown. In particular, there is an IC seat  104  (which is the position or location for the IC) having sides A, B, C, and D for an IC that implements four HDD writer heads is shown in a broken line. Each of the HDD write heads within the IC includes seats  106 - 1  to  106 - 4  (which are illustrated with broken lines). As shown, the HDD writer head seats  106 - 1  to  106 - 4  are positioned at the edge of side A of the IC seat  104  to, for example, shorten a trace length from solder bumps (e.g., sets of solder balls  108 - 1  to  108 - 4 ) for the writer head seats  106 - 1  to  106 - 4  to other components, circuits and/or devices of the printed circuit substrate  102 . There are also several other sets of solder balls or bumps  110  to  116  associate with seat  104 . 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top view of an example prior art layout for an armature assembly for an HDD; 
         FIGS. 2A to 2C  are diagrams of an example HDD constructed in accordance with the teachings of the invention; 
         FIG. 3  is a side-view showing additional detail of an example manner of implementing the example armature assembly of  FIG. 2 ; 
         FIG. 4  is a top view of an example layout for the armature assembly of  FIG. 3 ; 
         FIG. 5  is a graph illustrating example thermal impedance improvements that may be achieved by positioning a HDD writer head based on thermal conductivity principles described herein; 
         FIG. 6  is a flowchart of an example process that may be carried out to position a HDD writer head on an IC; and 
         FIG. 7  is a schematic illustration of an example processor platform that may be used and/or programmed to execute the example process of  FIG. 6  to place a HDD writer head on an IC as described herein. 
     
    
    
     DETAILED DESCRIPTION 
     As shown in  FIGS. 2A to 2C , an HDD system  200  of a computer in accordance with the teachings of the invention can be seen. As shown, the HDD system  200  generally comprises a motor  204  that controls the movement of an armature assembly  206 , pivoting about pivot points  208  and  210 . This arrangement allows the writer heads  218  to sweep across platters  214  and  216  (which rotates about spindle  212 ) so as to read and write data to the platters  214  and  216 . All of these items are contained within a housing  202 . HDD system  200  may also include one or more platters (e.g., platters  214  and  216 ). There may also be one or more armature assemblies (one of which is designated at reference numeral  206 ). The example armature assembly  206  of  FIGS. 2A and 2B  includes one or more HDD read and/or writer heads (one example writer head is designated at reference numeral  218 ) for reading information from and/or writing information to the platters  214  and  216 . In the write context, the example HDD writer head  218  is coupled to a drive head controller  220 , which processes a write signal  222  and provides one or more signals to the writer head  218  and/or, more generally, the armature assembly  206  to cause data associated with the write signal  222  to be written to one or more of the platters  214  and  216 . 
       FIG. 3  illustrates a side-view showing additional details of an example manner of implementing the example armature arm assembly  206  of  FIGS. 2A to 2C . The example armature assembly  206  of  FIG. 3  includes an armature arm  302 , a stiffener  304 , a printed circuit substrate  306  (e.g., a printed circuit board (PCB) and/or PCCA) having one or more copper and/or ground planes  312 , and an IC  308 . As shown, the IC  308  includes the example HDD writer head  218 . The example HDD writer head  218  of  FIG. 3  is positioned within the IC  308  to control the manner in which heat is conducted from the HDD writer head  218  to other portions of the armature assembly  206  (e.g., along path  318 ). That is, how well the heat is being conducted from the HDD writer head  218  to one or more of the copper and/or ground plane  312  of the substrate  306 , the stiffener  304  and/or the armature arm  302 . In some examples, the HDD writer head  218  is positioned within the IC  308  to minimize a thermal impedance from the HDD writer head  218  to the armature arm  302 . However, the HDD writer head  218  may be positioned within the IC  308  to decrease the thermal impedance subject to other design constraints, such as clock speed, signal skew, noise, and so forth. 
     As described above, to implement the example HDD writer head  218 , the example armature assembly  206  of  FIG. 3  includes the example IC  308 . The example IC  308  may be, for example, a semiconductor die onto which circuits (e.g., the example HDD writer head  218 ), components, devices, traces, etc. are depositing using any number and/or type(s) of silicon manufacturing processes. The example IC  308  is constructed as a so-called “flip-chip”, which is also referred to in the industry as a controlled collapse chip connection (C 4 ) type of mounting. However, any type of package and/or mounting may be used to construct the IC  308 . For example, the IC  308  may include one or more semiconductor dice, one or more bonding wires and a semiconductor package. Compared to some other types of chip packages, the example IC  308  of  FIG. 3  has a plurality of solder bumps (one of which is designated at reference numeral  310 ) instead of wire bonds. The example solder bumps or balls  310  of  FIG. 3  may be, for example, constructed by depositing solder onto chip pads of the IC  308 , which are located on the top side of the IC  308 , during a final wafer processing step. The example IC  308  is mounted to the printed circuit substrate  306  by “flipping” the chip such that the top of the IC  308  is facing down towards a mounting area of the example printed circuit substrate  306 . The solder bumps  310  are then re-melted (e.g., using ultrasound) to adhere the IC  308  to the printed circuit substrate  306 . Once the IC  308  is affixed to the printed circuit substrate  306 , circuits (e.g., the example HDD writer head  218 ), nodes, devices and/or traces of the IC  308  become electrically coupled to circuits, nodes, traces (two of which are designated at reference numerals  314  and  316 ), and/or copper and/or ground planes (one of which is designated at reference numeral  312 ) of the example printed circuit substrate  306 . In some examples, the mounted IC  308  is then under filled using an electrically-insulating adhesive (not shown). 
     Typically, there is a subset of solder bumps  310  of the IC  308  are dedicated to and/or used to provide coupling of ground signals and/or ground traces of the example IC  308  to a ground plane (e.g., the example plane  312 ) of the example printed circuit substrate  306 . These solder bumps can be referred to as “ground bumps,” to delineate their purpose from other solder bumps (e.g., the solder bump  310 ) used to electrically couple other types of signals. As described more fully below in connection with  FIG. 4 , the example HDD writer head  218  of  FIG. 3  is positioned within and/or located on the IC  308  to control how well heat can be conducted from the HDD writer head  218  to the ground plane  312  and, thus, to other portions of the example armature assembly  206 . Subject to any other design and/or layout constraints (e.g., clock speed, signal skew, noise, etc.), the example writer head  218  of  FIG. 3  is located relative to (e.g., as close as possible to) one or more ground bumps  311  to increase (e.g., maximize) the amount of heat (generated by operation of the writer head  218 ) that is conducted by the nearby ground bumps to the ground plane  312  (e.g., through trace  316 ). That is, the example writer head  218  is purposefully located on the IC  308  to lower the thermal impedance of the silicon junctions that comprise the writer head  218 . Such a lowering of the thermal impedance allows, for example, that the writer head  218  may be operated at higher clock frequencies and/or facilitates better thermal stability of the printed circuit substrate  306  and/or, more generally, the entire armature assembly  206 . In contrast, traditional HDD ICs have their writer heads placed within the IC without regard to thermal constraints. For example, placing them at the edges of an IC for ease of routing within the IC and/or a printed circuit substrate to which the IC is mounted, as describe above in connection with  FIG. 1 . 
     To increase the rigidity of the example printed circuit substrate  306 , the example armature assembly  206  of  FIG. 3  includes a stiffener  304 . In modern HDDs, sufficient rigidity of the printed circuit substrate  306  is important, while the HDD is operating, to controlling and/or maintaining a separation between the example writer head  218  and a platter (e.g., the example platter  216  of  FIG. 2B ). The example stiffener  304  of  FIG. 3  includes one or more mounts (e.g., holes and associated screws that allow the example printed circuit substrate  306  to be mechanically attached to the stiffener  304 . In addition to increasing the rigidity of the printed circuit substrate  306 , the example stiffener  304  also serves as part of a thermal conductivity path  318  between the writer head  218  and an armature arm  302 . 
     The example armature arm  302  of  FIG. 3  is controlled by, for example, the drive head controller  220  of  FIG. 2C , to position the writer head  218  relative to a HDD platter, such as the example platter  216 . The example armature arm  302  also serves as a thermal sink for heat generated by the writer head  218  and conducted to the armature arm  302  via the thermal conduction path  318 . 
     Turning to  FIG. 4 , an example layout for IC  308  of the armature assembly  206  of can be seen. As shown in this example, four writer heads (e.g., head  218 ) are positioned within the IC  308  so that the writer heads (e.g.,  218 ) are close to one or more sets of ground bumps  408 - 1 ,  408 - 2 , and  408 - 3  (which can be collectively referred to as a set of ground bumps  408 ). By locating the writer heads (e.g.,  218 ) near to the ground bumps  408 - 1 ,  408 - 2 , and/or  408 - 3 , heat can be readily conducted from the writer heads to the ground bumps  408 - 1 ,  408 - 2 , and/or  408 - 3 , and from the ground bumps  408 - 1 ,  408 - 2 , and/or  408 - 3  via one or more traces (one of which is designated at reference numeral  410 ) of the printed circuit substrate  306  to a ground plane  312  of the printed circuit substrate  306 . As shown in this example, IC  308  has a seat or positioning location  402  (having sides I, II, III, and IV) with seats or positioning locations  404 - 1  to  404 - 4  for the four write heads (which each have a width W and a length L). Each of these seats  404 - 1  to  404 - 4  includes a set of bumps  406 - 1  to  406 - 2  (where, collectively, sets  406 - 1  to  406 - 4  can be referred to as set  406 ). An example thermal design constraint and/or rule lays out, designs, locates, positions and/or orients the writer heads seats  404 - 1  to  404 - 4  within seat  402  such that a distance (e.g., distances D 1 , D 2 , D 2 , or D 4 ) from any significant heat generating solder bump (such as set of bumps  406 - 1 ) to a set of ground bumps (e.g.,  408 - 1 ) is no greater than a dimension (e.g., length L or width W) of the seat (e.g.,  404 - 1 ). Seat  402 , as shown, also includes a set of bumps  412  (which are coupled to ground plane  312 ) located in proximity to side or edge II. 
     While an example manner of implementing the example armature apparatus  206  of  FIG. 2  is illustrated in  FIGS. 3 and 4 , an armature apparatus may be implemented using any number and/or type(s) of alternative and/or additional logic, devices, components, circuits, modules, interfaces, etc. Further, the logic, devices, components, circuits, modules, elements, interfaces, etc. illustrated in  FIGS. 3  and/or  4  may be combined, divided, re-arranged, omitted, eliminated and/or implemented in any other way. For example the example stiffener  304  and the example armature arm  302  could be combined into a single module, and/or a different number of writer heads (e.g., eight) could be implemented by an IC and/or an armature assembly. Moreover, an armature assembly may include additional logic, devices, components, circuits, interfaces and/or modules instead of, or in addition to those illustrated in  FIGS. 3  and/or  4 . 
       FIG. 5  is a graph illustrating example thermal impedance improvements that may be achieved by positioning HDD writer heads as described herein. Thermal impedance values are shown for combinations of the number of writer heads per the example IC  308  (four and eight), and whether the writer heads (e.g.,  218 ) are placed near the edge of the IC  308  (as illustrated in  FIG. 1 ) or within an interior portion of the IC  308  near to ground bumps (e.g., the example ground bumps  408 - 1  to  408 - 4 ). As illustrated in  FIG. 5 , a five to ten percent decrease in thermal impedance can be achieved by positioning HDD writer heads (e.g.,  218 ) based on thermal conductivity principles. 
       FIG. 6  is a flowchart representative of example process that may be carried out to locate and/or place HDD writer heads on an IC. The example process of  FIG. 6  may be carried out by a processor, a controller and/or any other suitable processing device. For example, the example process of  FIG. 6  may be embodied in coded instructions stored on a tangible medium such as a flash memory, a read-only memory (ROM) and/or random-access memory (RAM) associated with a processor (e.g., the example processor P 105  discussed below in connection with  FIG. 7 ). Alternatively, some or all of the example process of  FIG. 6  may be implemented using any combination(s) of circuit(s), application specific integrated circuit(s) (ASIC(s)), programmable logic device(s) (PLD(s)), field programmable logic device(s) (FPLD(s)), discrete logic, hardware, firmware, etc. Also, some or all of the example process of  FIG. 6  may be implemented manually or as any combination of any of the foregoing techniques, for example, any combination of firmware, software, discrete logic and/or hardware. Moreover, the example process of  FIG. 6  may be incorporated in design rules enforced by an IC design and/or layout tool and/or software. Further, although the example operations of  FIG. 6  are described with reference to the flowchart of  FIG. 6 , many other methods of implementing the operations of  FIG. 6  may be employed. For example, the order of execution of the blocks may be changed, and/or one or more of the blocks described may be changed, eliminated, sub-divided, or combined. Additionally, any or all of the example process of  FIG. 6  may be carried out sequentially and/or carried out in parallel by, for example, separate processing threads, processors, devices, discrete logic, circuits, etc. 
     The example process of  FIG. 6  begins by positioning grounds bumps  405  on a IC  308  of an IC  308  (block  605 ). Writer heads (e.g.,  218 ) are then positioned on the IC  308  relative to the ground bumps (e.g.,  408 - 1 ) to improve a thermal characteristic of the IC  308  (e.g., reduce a thermal impedance) (block  610 ). The remainder of components, circuits, devices and/or traces of the IC  308  are then placed and/or laid out on the IC  308  (block  615 ). Control then exits from the example process of  FIG. 6 . 
     Additionally or alternatively, the example process of  FIG. 6  may be applied iteratively wherein one or more layout constraints are verified upon completion of block  615 . If one or more of the constraints are not met, the process could be repeated after one or more design rules are relaxed (e.g., a maximum distance between a writer head  218 ,  420 - 422  and ground bumps  405  is increased). Moreover, a portion of the IC  308  may be laid out prior to the ground bumps  405  and/or writer heads  218 ,  420 - 422  being placed. 
       FIG. 7  is a schematic diagram of an example processor platform P 100  that may be used and/or programmed to layout a HDD IC in accordance with the writer head placement methods and apparatus described herein. The example process platform P 100  may, additionally or alternatively, be used and/or programmed to implement an IC design and/or layout tool that includes the writer head placement methods and apparatus described herein. The example processor platform P 100  can be implemented by one or more general purpose processors, processor cores, microcontrollers, etc. 
     The processor platform P 100  of the example of  FIG. 7  includes at least one general purpose programmable processor P 105 . The processor P 105  executes coded instructions P 110  and/or P 112  present in main memory of the processor P 105  (e.g., within a RAM P 115  and/or a ROM P 120 ). The processor P 105  may be any type of processing unit, such as a processor core, a processor and/or a microcontroller. The processor P 105  may execute, among other things, the example process of  FIG. 6  to implement the example methods and apparatus described herein. 
     The processor P 105  is in communication with the main memory (including a ROM P 120  and/or the RAM P 115 ) via a bus P 125 . The RAM P 115  may be implemented by dynamic random access memory (DRAM), synchronous dynamic random access memory (SDRAM), and/or any other type of RAM device, and ROM may be implemented by flash memory and/or any other desired type of memory device. Access to the memory P 115  and the memory P 120  may be controlled by a memory controller (not shown). 
     The processor platform P 100  also includes an interface circuit P 130 . The interface circuit P 130  may be implemented by any type of interface standard, such as an external memory interface, serial port, general purpose input/output, etc. One or more input devices P 135  and one or more output devices P 140  are connected to the interface circuit P 130 . 
     Although certain example methods, apparatus and articles of manufacture have been described herein, the scope of coverage of this patent is not limited thereto. On the contrary, this patent covers all methods, apparatus and articles of manufacture fairly falling within the scope of the appended claims either literally or under the doctrine of equivalents.