Abstract:
A disc drive is encapsulated by having a thermal bonding adhesive disposed between two housing components. The adhesive is selected for its ability to provide a sufficiently strong bond for forming sealed enclosure capable of withstanding a given external shock load applied to the disc drive. The sealing is effected without the need for mechanical fasteners coupling the two housing components.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims benefit from U.S. Provisional Application No. 60/347,453, filed Jan. 11, 2002. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates generally to disc drives. More particularly, the present invention relates to an improved apparatus and method for sealing disc drives.  
         BACKGROUND OF THE INVENTION  
         [0003]    Disc drives are commonly used to store large amounts of data for easy retrieval. The conventional disc drive enclosure is generally made tip of a base deck and a cover fastened together by screws and other such fasteners. The housing provides a relatively clean and controlled environment in which the various disc drive components operate. Currently, a cover may be secured to the base deck by six or more screws threaded through holes in the cover and threadably engaging tapped holes in the base deck. During the manufacture of disc drives, the various components are mounted to the base deck before the cover is assembled thereto and the screw&#39;s driven in to complete the housing.  
           [0004]    In the past, improvements to the sealing of disc drives have generally been directed towards providing gaskets and sealants in addition to the use of fasteners such as screws, to ensure that the cover will not be loosened from the base deck even when the disc drive is subject to a given maximum external shock load. Should the sealing fail, contaminants such as air borne particulates, acidic gases, and volitile organics will be able to enter easily into internal environment of the disc drive and damage the delicate components therein.  
           [0005]    As conventional mechanical fasteners are well known to provide measurable and secure coupling, and with increasing precision required of the read/write process and the ever present pressure to improve overall drive performance, drive manufacturers invariably rely on mechanical fasteners (such as screws) as the primary coupler between the cover to the base deck. Methods that are based on the use of chemicals have been avoided for fear of outgassing. This is because it is generally believed that outgassing can contribute significantly to contamination in the internal environment of the disc drive, and may therefore adversely impact drive performance.  
           [0006]    Yet, despite the general expectation that mechanical fasteners are necessary, alternative solutions are provided by the present invention that not only overcome the difficulties described above but also offer other advantages over the prior art.  
         SUMMARY OF THE INVENTION  
         [0007]    Embodiments of the present invention provides a method of effecting disc drive encapsulation. The method involves providing an adhesive to the first housing component, mating the first housing component with the second housing component to form an enclosure, and effecting an adhesive bond between the first housing component and the second housing component such that reinforcements to seal the enclosure are not necessary. The enclosure formed is one that is suitable for providing an internal environment within which a disc stack assembly and an actuator assembly may operate. This presents manufacturing advantages over the prior art since the tapping of holes and threading in of screws and other mechanical fasteners is a time-consuming part of disc drive manufacture.  
           [0008]    The adhesive chosen is preferably one that is changeable between a less adhesive state and a more adhesive state. Thus, the adhesive may be provided in the less adhesive state on one of the two housing components to facilitate handling, and later changed to the more adhesive state after the two housing components have been properly aligned or mated. This further provides, additional advantages in that the adhesive may be changed back to the less adhesive state to allow the two housing components to be separated, thereby allowing access to the various disc drive components during rework. A disc drive relying solely on the adhesive to effect a sealed enclosure is further advantageous because of the opportunities for greater design flexibility. The two housing components need not be constrained by a need to allow for mechanical fasteners to be distributed along the length of the joint between the two housing components.  
           [0009]    These and various other features as well as advantages which characterize the present invention will be apparent upon reading of the following detailed description and review of the associated drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 is a top view of a conventional disc drive.  
         [0011]    [0011]FIG. 2 is a partially exploded isometric view of a disc drive according to one embodiment of the present invention.  
         [0012]    [0012]FIG. 3 is a partial cross-sectional view of the disc drive of FIG. 2.  
         [0013]    [0013]FIG. 4 is a partially exploded isometric view of a disc drive according to one embodiment of the present invention.  
         [0014]    [0014]FIG. 5 is a partial cross-sectional view of the disc drive of FIG. 4.  
         [0015]    [0015]FIG. 6 is a flow-chart showing a method of sealing a disc drive according to one embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0016]    [0016]FIG. 1 shows a top view of a conventional disc drive  100  with the cover  102  partially cut-away to reveal the components in the disc drive  100 . There is typically one or more discs  104  mounted to a spindle motor  106  that is in turn mounted to the base deck  108 . Data is read from or written to the disc surfaces  110  by read/write heads  112  supported by a suspension  114  extending cantilever-fashion from one or more actuator arms  116  of an actuator assembly  118 . The actuator assembly  118  supports a voice coil  120  in proximity to one or more permanent magnets  122  such that when a current is provided to the voice coil  120 , the actuator assembly  118  is motivated to rotate about its pivot  124  and thereby controllably position the read/write heads  112  with respect to data tracks on the disc surfaces  110 . Flexible circuit cables  126  run from the read/write heads  112  to a printed circuit board assembly (hidden from view) attached to the base deck  108  via a connector  128 . The base deck  108  is provided with tapped holes  130  corresponding to holes  132  in the cover  102 , and these two housing components  102 , 108  are joined together by fasteners  134  such as screws to create a sealed enclosure  136 . In the example shown, six fasteners  134  distributed about the perimeter of the cover  102  are used to ensure that the disc drive  100  is properly sealed. A gasket  138  may sometimes be located between the base deck  108  and the cover  102  to improve the seal. The gasket  138  is provided with holes  140  for the fasteners  134  to pass through in order that the gasket  138  may be held in place together with the cover  102  and the base deck  108 .  
         [0017]    [0017]FIG. 2 is a partially exploded isometric view of a disc drive  200  according to one embodiment of the present invention. The base deck  202  provides a major surface  204  for the mounting of a disc stack assembly  206  formed by a plurality of discs  208  carried by a spindle motor  210 . An actuator assembly  212  is shown with its array of actuator arms  214 , suspensions  216  and read/write heads  218  interleaved with the discs  208 . The voice coil is substantially hidden from view, but it will be understood that it is sandwiched between pole plates  220  to close the magnetic flux associated with the voice coil motor  222 . Also shown is a flexible circuit cable  224  leading from the actuator assembly  212  to a connector  226  in communication with a printed circuit board hidden from view under the base deck  202 .  
         [0018]    Around the perimeter of the major surface  204  of the base deck  202  runs a wall  230  substantially transverse to a base plane that is defined by the major surface  204  of the base deck  202 . The wall  230  includes a shelf  232  offering a surface substantially parallel to the base plane. The wall  230  may continue to extend further beyond the shelf  232 , as shown, to form a skirting  234  around an outer boundary of the shelf  232 .  
         [0019]    The disc drive  200  includes a cover  240  shaped and sized to mate fittingly with the shelf  232  such that the cover  240  rests within the skirting  234 . The cover  240  itself may be substantially flat such that in assembly with the base deck  204 , the cover  240  is substantially parallel to the base plane. In assembly, the cover  240  presents an outer surface  242  to the environment external to the disc drive and an inner surface  244  to the internal environment  246  of the disc drive  200 .  
         [0020]    The cover  240  is attached to the base deck  202  without the aid of mechanical fasteners such as screws. Instead, an adhesive  250  is provided near the perimeter of the cover  240  such that, in assembly, the adhesive  250  is between the shelf  232  and the inner surface  244  of the cover  244 , as illustrated by the cross-sectional schematic of FIG. 3. The adhesive  250  may be shaped or applied such that it varies in width along its length, as shown in FIG. 2. The cover  240  and the base deck  202  are in this fashion effectively bonded together (that is, the disc drive  200  is encapsulated) to provide a sealed enclosure within which the various disc drive components reside.  
         [0021]    Referring to FIGS. 4 and 5, an alternative embodiment of the present invention is described. The wall  230  of the base deck  202  may optionally end in a terminal surface  260  without a further skirting or flange running around the perimeter. The width of the terminal surface  260  is such that it provides sufficient surface area for effective bonding with the inner surface  244  of the cover  240 . The cover  240  shown here includes a flange or boundary portion  262  substantially complementary to the terminal surface  260 . In assembly, an adhesive film  264  is located between the boundary portion  262  of the cover  240  and the terminal surface  260  of the base deck  202  such that the cover  240  and the base deck  202  are effectively bonded together to form a sealed enclosure.  
         [0022]    A method  300  of sealing a disc drive  200  according to one embodiment of the present invention is further described with reference to FIG. 6. A disc stack assembly  206  and an actuator assembly  212  are mounted to a base deck  202  of a disc drive  100  (step  302 ). An adhesive  250 , 264  is chosen from a family of thermoplastics that exhibit adhesive properties of variable strength and low outgassing characteristics, such as Thermo-Bond Films 668 and 668 EG available from 3MTM of Minnesota. The adhesive  250 , 264  can be first applied to either the cover  240  or the base deck  202  (step  304 ).  
         [0023]    For example, the adhesive  250 , 264  may be a film cut to line the inner surface  244  of the cover  240  along its sides or its boundary portion  262 . The entire cover  240  and adhesive  250 , 264  may be subject to tacking conditions where the adhesive  250 , 264  is made to adhere lightly to the cover  240 . This may involve subjecting the cover  240  to pressure of about 10 pounds per square inch (psi) and temperature of around 70 degree Celsius for about 2 seconds, through the use of an oven or ultrasonic device. At the end of this tacking process, the cover  240  can be moved without the adhesive  250 , 264  dropping off. This easier handling is a manufacturing advantage, especially when compared to mechanical fasteners which could only be secured to either housing component after it is secured to both housing. The cover  240  can then be prepared in advance to reach the disc drive assembly line with the adhesive  250 , 264  already in place. The tacking conditions may optionally be applied locally, that is to say, only where the adhesive  250 , 264  is in contact with the cover  240 .  
         [0024]    Alternatively, the base deck  202  may be provided with the adhesive  250 , 264  lightly tacked on. For example, the adhesive  250 , 264  can be shaped to rest neatly on the terminal end  260  or a shelf  232  of the wall  230  of the base deck  202 . The base deck  202  is then subjected to tacking conditions favorable to the formation of a bonds between the adhesive  250 , 264  and the base deck  202  (step  304 ). The disc stack assembly  206  and the actuator assembly  212  can then be mounted to the base deck  202  (step  302 ), or depending on the design of the assembly line, the various disc drive components can be assembled before or simultaneously as the adhesive  250 , 264  is applied to the base deck  202  (steps  302 , 304 ). A heated ring could be used to apply localized heating and pressure to effect the tacking.  
         [0025]    Continuing with the description of the sealing process  300 , the cover  240  and the base deck  202  are mated with the adhesive  250 , 264  in contact with both the inner surface  244  of the cover  240  and the wall  230  of the base deck  202  (step  306 ). The assembly is then subjected to bonding conditions conducive to the formation of stronger bonds between the adhesive  250 , 264  and the cover  240  and between the adhesive  250 , 264  and the base deck  202  (step  308 ). Such bonding conditions may be applied locally with the use of a heated ring or a hot shoe so as not to affect the other components of the disc drive  200 . The bonding conditions may include a dwell time of about 15 seconds at a temperature of about 150 degree Celsius and pressure of about 20 psi. Comparatively, this may be more efficient than to drive in six screws in a conventional assembly of a disc drive.  
         [0026]    Customer expectations of drive performance and reliability demand that certain requirements to be met. For example, a disc drive must be able to withstand a certain amount of external shock load without the cover becoming detached from the base deck or the seal between the cover and the base deck being broken. Tests were therefore conducted to confirm that the bond formed is suitable for use in a disc drive housing, especially to house a fully assembled disc drive having a disc stack assembly and actuator assembly mounted to the base deck. The peel strength was found to be at least 10 ounces for a 0.25 inch wide sample of adhesive that was tested after a 20-minute dwell time. To test the shear strength, a 250 gram weight was applied to an adhesion area of about 0.25 square inches for 24 hours at 60 degree Celsius. The adhesive was applied to a clean cover material. It was found that the creep did not exceed 0.125 as measured from a reference (top of the sample). Therefore, it was ascertained that using an adhesive alone can provide the required sealing strength without reducing the reliability of the disc drive. In addition to the fear that adhesives may generate unacceptable levels of outgassing, the traditional view is that an adhesive alone could not provide proper sealing of a disc drive. Unexpectedly, the contrary is found. Tests conducted showed that certain acrylic adhesives (such as ×4643 and ×4615 from Avery Dennison) would be suitable because they have acceptably low outgassing properties. Other types of adhesives which may be used include TH 434 (epoxy/propylene based) and TH 496 (polyester based) materials from Alcan, as well as some polyolefin and EVAs (ethylene vinyl acetates).  
         [0027]    In the event that rework of a disc drive is desired (decision  310 ), the housing components  202 , 240  are again subjected to elevated temperatures to soften the adhesive  250 , 264 . The housing components  202 , 240  can then be separated for access to the disc drive components housed therein. This is made possible by the choice of an adhesive  250 , 264  that does not undergo curing during heating or aging. Examples of a suitable adhesive include thermoplastics such as that described above. In this and other aspects, the present invention offers advantages over the prior art by providing for a bond between the cover and the base deck such that mechanical fasteners are superfluous to the proper sealing of the disc drive.  
         [0028]    Other advantages that may follow in the wake of doing away with mechanical fasteners include the possibility of making smaller disc drives as well as allowing greater flexibility in the design of the housing components, since allowance for mechanical fasteners will not be essential. Possibly the base deck can be manufactured at lower cost because there is now no necessity to provide tapped holes in the base deck.  
         [0029]    Alternatively described, one embodiment of the present invention involves providing an adhesive (such as  250 , 264 ) to the first housing component (such as  202 , 240 ; such as step  304 ), mating the first housing component (such as  202 , 240 ) with the second housing component (such as  202 , 240 ) to form an enclosure (such as step  306 ), and effecting an adhesive bond between the first housing component (such as  202 , 240 ) and the second housing component (such as  202 , 240 ) such that reinforcements to seal the enclosure are not necessary (such as step  308 ).  
         [0030]    The method  300  may include mounting a disc stack assembly (such as  206 ) to a selected one of the first housing component (such as  202 , 240 ) and the second housing component (such as  202 , 240 ), and also mounting an actuator assembly (such as  212 ) to the selected housing component (such as  202 , 240 ; such as step  302 ). Optionally, a step (such as step  304 ) of subjecting the first housing component (such as  202 , 240 ) and the adhesive (such as  250 , 264 ) to tacking conditions favorable to formation of an initial bond between the first housing component (such as  202 , 240 ) and the adhesive (such as  250 , 264 ) may be performed. The tacking conditions may include a dwell time of about 2 seconds at temperature of about 70 degree Celsius and pressure of about 10 psi. The method may further involve a step (such as  308 ) of subjecting the first housing component (such as  202 , 240 ), the second housing component (such as  202 , 240 ) and the adhesive (such as  250 , 264 ) to bonding conditions favorable to formation of a final bond between the adhesive (such as  250 , 264 ) and the first housing component (such as  202 , 240 ) and between the adhesive (such as  250 , 264 ) and the second component (such as  202 , 240 ). The bonding conditions may include a dwell time of about 15 seconds at temperature of about −150 degree Celsius and pressure of about 10 psi. The adhesive (such as  250 , 264 ) may be one that is changeable between a less adhesive state and a more adhesive state. The adhesive (such as  250 , 264 ) may be a thermoplastic.  
         [0031]    Another embodiment of the present invention provides a disc drive (such as  200 ) having a sealed enclosure formed by a method (such as  300 ) described in the foregoing.  
         [0032]    Yet another embodiment of the present invention provides a disc drive (such as  200 ) having a first housing component (such as  202 , 240 ), a second housing component (such as  202 , 240 ), and an adhesive (such as  250 , 264 ) disposed between the first housing component (such as  202 , 240 ) and the second housing component (such as  202 , 240 ), where the adhesive (such as  250 , 264 ) provides the only bonding mechanism between the first housing component (such as  202 , 240 ) and the second housing component (such as  202 , 240 ). Optionally, the first housing component (such as  202 , 240 ) and the second housing component (such as  202 , 240 ) are complementarily mated to form a sealable enclosure for housing disc drive components (such as  206 ,  212 ).  
         [0033]    It is to be understood that even though numerous characteristics and advantages of various embodiments of the present invention have been set forth in the foregoing description, together with details of the structure and function of various embodiments of the invention, this disclosure is illustrative only, and changes may be made in detail, especially in matters of structure and arrangement of parts within the principles of the present invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.