Abstract:
An apparatus for minimizing corrosion product build-up within a disc drive incorporates a non-corrosive gas hermetically sealed within the disc drive and a diaphragm chamber that allows the constrained non-corrosive gas to respond to changes in pressure and temperature. The diaphragm chamber includes a diaphragm that partitions the diaphragm chamber into a top and bottom chambers. The top chamber has an aperture for communicating with the external environment and the bottom chamber has an aperture for communicating with the internally constrained non-corrosive gas. The diaphragm is non-permeable and made of an elastic material that responds to changes in air volume or mass on either side of the partition so that the pressure inside the hermetically sealed disc drive is constant throughout the life of the device. The diaphragm chamber can be located inside or outside the disc drive and can be integrally formed within the top cover of the disc drive.

Description:
RELATED APPLICATIONS 
     This application claims the benefit of priority of U.S. Provisional Patent Application Serial No. 60/117,867 entitled “ANTI-CORROSION DIAPHRAGM-SEALED DISK DRIVE,” filed Jan. 29, 1999. 
    
    
     FIELD OF THE INVENTION 
     This application relates to magnetic disc drives and more particularly to a diaphragm-sealed disc drive having increased corrosion resistance. 
     BACKGROUND OF THE INVENTION 
     Disc drives are data storage devices that store digital data in magnetic form on a rotating storage medium on an information storage disc. Modern disc drives comprise one or more rigid information storage discs that are coated with a magnetizable medium and mounted on the hub of a spindle motor for rotation at a constant high speed. Information is stored on the discs in a plurality of concentric circular tracks typically by an array of transducers (“heads”) mounted to a radial actuator for movement of the heads in an arc across the surface of the discs. Each of the concentric tracks is generally divided into a plurality of separately addressable data sectors. The recording transducer, e.g. a magnetoresistive read/write head, is used to transfer data between a desired track and an external environment. During a write operation, data is written onto the disc track and during a read operation the head senses the data previously written on the disc track and transfers the information to a host computing system. The overall capacity of the disc drive to store information is dependent upon the disc drive recording density. It is of particular importance in the disc drive art to maximize the disc drive recording density. 
     One of the most important parameters affecting the recording density of a disc drive is the spacing between the head and the magnetizable medium layer of the information storage disc, this spacing is known as the head media spacing. Closer head to media spacing allows for smaller magnetic signals, i.e., bits, recorded on the information storage disc which in turn allows for narrower track widths and consequent greater recording densities on the drive. As such, one way to maximize the disc drive recording density is to minimize head media spacing. 
     Head media spacing is dependent upon several factors, including: the head&#39;s “flying height,” i.e., the physical separation distance between the top of the disc and the bottom of the recording head, the thickness of a lubricant layer, the thickness of a protective overcoat layer located on top of the magnetizable layer on the information storage disc, the thickness of a protective overcoat layer located on the air bearing surface of the head and the “any distance” that the recording transducers&#39; pole tips are recessed below the level of the air bearing surface of the head. 
     Currently, efforts in the disc drive art have been centered on, among other things, decreasing the head media spacing by minimizing the thickness of the protective overcoat layers on the information storage disc and head. One major limiting factor on decreasing the protective overcoat layer thickness is the ability of the overcoat layer to protect the information storage disc and head from the build-up of corrosion products. 
     Corrosion causes corrosion products to build-up on the disc and head during the normal operating life of the drive. Corrosion products tend to accumulate on surfaces and interfere with the head&#39;s ability to fly over the disc surface. Corrosion occurs in the disc drive due to metals&#39; propensity to be oxidized in the presence of oxygen or other oxidizing agents. The protective overcoat layer found on the information storage disc and head limits corrosion by eliminating the contact between the metal surfaces of the information storage disc and head with oxygen or other oxidizing agents found in the air. 
     It is also possible to limit corrosive product build-up on the disc and head by limiting the availability of oxygen within the disc drive. Here, the oxygen containing air within the disc drive can be replaced with a non-corrosive gas such as argon. The disc drive is then hermetically sealed so as to maintain a non-corrosive environment for the disc drive metal components. Within this non-corrosive environment the protective overcoat layers may be minimized in thickness, or in certain circumstances removed. 
     A major shortcoming of oxygen replacement within the drive is that the constrained non-corrosive gas within the hermetically sealed disc drive is unable to respond, i.e., expand or contract, to external changes in pressure or temperature. As is well known in the art, the volume of a gas is dependent upon its temperature and pressure. In general, a gasses volume is inversely proportional to the pressure applied to it and directly proportional to its temperature. For example, under ideal conditions an atmospheric pressure change from 101.3 kPa at sea level to 69.6 kPa at an altitude of 10,000 feet produces a volume increase of approximately 43% for an unconstrained constant mass of gas. The volume increase inside the disc drive results in increased pressure and has consequent affects on the alignment of components within the drive and potential failure of the seals within the drive. Against this backdrop the present invention has been developed. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention the above problems and other problems have been solved by incorporating a gas constrained within a diaphragm-sealed disc drive. 
     In accordance with one embodiment of the present invention, a disc drive includes a hermetically sealed housing having a baseplate. A gas is constrained within the hermetically sealed housing. A spin motor is mounted to the housing baseplate for rotating an information storage disc. An actuator assembly is also mounted to the baseplate, the actuator assembly swings an actuator arm, carrying a read/write head, over the information storage disc. Additionally, the disc drive includes a diaphragm chamber having a first portion that accommodates changes in the volume of the constrained gas. The first portion defines an aperture that provides an air passage between the disc drive&#39;s external environment and the first portion. A diaphragm hermetically seals the diaphragm chamber&#39;s first portion from the internally constrained gas within the disc drive. Further, the diaphragm responds to the gasses volume changes within the hermetically sealed disc drive. 
     The present invention may also be implemented as a disc drive diaphragm chamber having a constrained gas for reducing the effects of corrosion product build-up within the disc drive. A first portion of the diaphragm chamber is positioned in the disc drive to accommodate changes in the volume of the constrained gas, while a first aperture provides an air passage between the disc drive&#39;s external environment and the first portion. A diaphragm seals the first portion from the constrained gas as well as responds to volumetric changes of the constrained gas. 
     Utilizing the diaphragm-sealed disc drive will allow for a minimization of the protective overcoat layers on the information storage disc and head and potentially an increase in the disc drive&#39;s recording density. Additional benefits of the present invention include: (1) reduced non-repeatable run-out caused by windage excitation, i.e., disc flutter, when the constrained gas has a lower density than air, e.g., helium, hydrogen, etc.; (2) reduced power dissipation by the disc drive due to decreased air resistance when the constrained gas has a lower density than air; and (3) reduced wear on the disc drive components in general, as a result of the fact that many tribochemcial wear reactions require oxygen and other oxidizing agents not found in the constrained gas. 
     These and various other features as well as advantages which characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a disc drive incorporating a diaphragm chamber and diaphragm in accordance with a preferred embodiment of the present invention. 
     FIG. 2 is a representative sectional view of a head-disc interface illustrating a head media spacing showing a head flying height, a lubricant, a protective overcoat layer for the information storage disc and a protective overcoat layer for the head. 
     FIG. 3 is a schematic sectional view taken along  3 — 3  of FIG. 1 under normal disc drive operating conditions. 
     FIG.4 is a schematic sectional view taken along  3 — 3  of FIG. 1 when the disc drive is exposed to relatively low external air pressure and/or high temperature with respect to the constrained non-corrosive gas. 
     FIG. 5 a schematic sectional view taken along  3 — 3  of FIG. 1 when the disc drive is exposed to relatively high external air pressure and/or low temperature with respect to the constrained non-corrosive gas. 
     FIG. 6 is a representative sectional view of a disc drive incorporating a diaphragm chamber having an environmental protection switch in accordance with one preferred embodiment of the present invention. 
     FIG. 7 is a representative sectional view of a disc drive incorporating a diaphragm chamber in accordance with a second preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION 
     A disc drive  100  constructed in accordance with one preferred embodiment of the present invention is shown in FIG.  1 . The disc drive  100  includes a base plate  102  to which various structural components of the disc drive  100  are mounted. A top cover  104  cooperates with the base  102  to form a disc drive housing  105 . The housing  105  forms an internal, sealed environment for the disc drive in a conventional manner. The disc drive components include a spindle motor  106  which rotates one or more information storage discs  108  at a constant high speed. Information is written to and read from tracks on the information storage discs  108  through the use of an actuator assembly  110 , which rotates or swings about a bearing shaft assembly positioned adjacent the discs  108 . The actuator assembly  110  includes a plurality of actuator arms  114  which extend towards the discs  108 , with one or more flexures  116  extending from each of the actuator arms  114 . Mounted at the distal end of each of the flexures  116  is a head  118  which includes an air bearing slider  120  (FIG. 2) enabling the head  118  to fly in close proximity above the corresponding surface of the associated information storage disc  108 . Finally, a diaphragm chamber  122  in accordance with one preferred embodiment of the present invention is positioned adjacent the actuator assembly  110 . 
     The spacing of the head  118  in relation to the recording media  124  of the information storage disc  108 , i.e., the head media spacing  126 , is a critical parameter to the amount of information an information storage disc  108  is able to store. (see FIG. 2) Relative close proximity between the head  118  and information storage disc  108  allows for smaller bits, i.e., magnetic signals, and thus narrower track widths on the discs  108 . Narrower track widths result in more tracks per disc and hence a higher disc drive recording density. Alternatively, relatively larger distances between the head and the information storage disc results in fewer tracks being recordable on the disc and hence a lower disc drive recording density. 
     FIG. 2 is a representative sectional view of a head  118  positioned over an information storage disc  108  showing the head media spacing  126 . The head media spacing  126  includes the head flying height  128 , a lubricant layer (not shown), a corrosion and wear protective overcoat layer  130  for the information storage disc  108  and a corrosion and wear protective overcoat layer  132  for the head  118 . Conventionally, the flying height  128  of the head  118  may be anywhere from 15-30 nm in thickness, the lubricant layer 1-2 nm in thickness, the protective overcoat layer  130  for the information storage disc  108  5-10 nm in thickness and the protective overcoat layer  132  for the air bearing surface of the head  118  5-7 nm in thickness. Thus, the total head media spacing  126  in any one disc drive  100  typically varies between 26-49 nm. Of that 26-49 nm of head media spacing  126 , 10-17 nm of spacing result from the two protective overcoat layers  130  and  132 , one found on the information storage disc and the other on the head. The present invention is concentrated on limiting, and possibly eliminating, the need for having the 10-17 nm spacing  126  dedicated to the two protective layers  130  and  132  by providing an alternative mechanism for corrosion resistance. In the absence of the two protective layers  130  and  132  the head  118  potentially could be positioned in the range of 16-32 nm from the information storage disc recording layer  124 . It should be understood that the numerical spacing distances used above are merely for illustrative purposes and are not meant to define the scope of the present invention. It can be expected that these distances will change in future disc drives. 
     One preferred embodiment of the present invention is shown in top view in FIG.  1  and cross-sectional schematic views in FIGS. 3-5. A diaphragm chamber  122  having a diaphragm  134  positioned within it is located adjacent the actuator assembly  110 . The diaphragm chamber  122  itself is generally a box shaped structure having four sides  136 , a top  138  and a bottom  140 . The top  138  of the diaphragm chamber  122  is simply the top cover  104 . Extending downward from the top cover or top  104  are four sides  136  of relative equal length and width, each forming one side of the box like structure. Preferably, two of the sides  136  are positioned to border the internal environment  142  of the disc drive  100 . The bottom  140  of the chamber  122  combines the fours sides  136  together and completes the compartment. The bottom  140  of the compartment can be a separate wall constructed specifically for the chamber or can be a region of the base plate  102 . 
     Two apertures  144  and  146  are formed in the diaphragm chamber  122 , the first aperture  144  is formed through the top  138  of the chamber  122 . The second aperture  146  is formed through one of the two sides  136  that borders the internal environment  142  of the disc drive  100 . Each aperture  144  and  146  should be of a size and shape to freely allow airflow into and out of the chamber  122 . 
     A flexible diaphragm  134  or partition extends across the interior of the diaphragm chamber  122 . The flexible diaphragm  134  separates the diaphragm chamber  122  into a first portion  148 , that communicates through the aperture  144  formed in the top  138  with the disc drive&#39;s external environment  150 , and a second portion  152 , that communicates through the aperture  146  formed in one of the diaphragm chamber&#39;s  122  internal facing sides  136  with the disc drive&#39;s internal environment  142 . The flexible diaphragm  134  is sealed to the diaphragm chamber sides  136  by adhesive or other attachment means so that the two portions  148  and  152  are hermetically sealed from each other by the diaphragm  134 . The diaphragm  134  is positioned approximately half way between the two apertures  144  and  146  so as to create substantially two equally sized portions  148  and  152 . However, the diaphragm  134  may be positioned anywhere within the chamber  122  as long as it partitions the disc drive&#39;s external environment  150  from the disc drive&#39;s internal environment  142 . 
     The diaphragm  134  itself is preferably a flexible or elastic material, responsive to small changes in pressure, on the order of a kPa, and having low propensities for outgassing. Additionally, the diaphragm is substantially non-permeable to air. A thin metal coating can be added to the diaphragm to help prevent gas diffusion. An example of one such diaphragm material is a polyester film, such as Mylar™. 
     Potential non-corrosive gases for use inside the disc drive  100  include: argon, hydrogen, helium, nitrogen, fluorocarbon and hydrocarbon. Oxygen, water vapor and acid gases (e.g., nitric oxide) are specifically excluded from the internal environment of the drive. It is also envisioned that a chemically-reactive oxygen-scavenging material, “getter,” could also be included within the disc drive. The oxygen-scavenger would remove oxygen that infiltrates the drive during the disc drive&#39;s manufacture or due to subsequent disc drive leaks. Examples of such “getter” materials include magnesium and copper. 
     FIG. 3 shows a disc drive  100  where the air pressure and temperature of the external air and internal non-corrosive gas are approximately the same. The diaphragm  134  maintains a non-stressed position within the chamber  122  due to the unchanged volume of the non-corrosive gas. FIG. 4 shows a disc drive  100  where the external air pressure is lower than the non-corrosive gas pressure or, alternatively, where the external air temperature is greater than the internal non-corrosive gas temperature. In either case, the non-corrosive gas expands in volume to respond to the change in pressure and temperature and exerts pressure on the flexible diaphragm  134 . The diaphragm  134  flexes or expands into the first portion  148  to accommodate the increased gas volume—thus keeping the pressure relatively constant within the disc drive  100 . FIG. 5 shows a disc drive  100  where the external air pressure is greater than the internal non-corrosive gas pressure or, alternatively, where the air temperature is lower than the internal non-corrosive gas temperature. In these cases, the diaphragm  134  flexes or expands into the second portion  152  to accommodate the decreased volume—thus keeping the pressure relatively constant within the disc drive  100 . 
     Another preferred embodiment of the flexible diaphragm is shown in FIG.  6 . Here, an environmental protection switch  154  is placed within the diaphragm chamber  122  to alert the user when external conditions, i.e., temperature and altitude, have caused the diaphragm  134  to flex to a predetermined position or threshold. An electrical contact  156  is adhered to the top side  158  of the diaphragm  134 . A second electrical contact  160  is adhered to the bottom side  162  of the top  138  of the chamber  122 . The two electrical contacts  156  and  160  are aligned so that at a predetermined expansion of the diaphragm  134 , the two contacts  156  and  160  will meet and complete an electrical circuit. Any number of signals could be tripped when the circuit is connected: flashing light, audio alarm, etc. It is further envisioned that a like switch could be arranged with electrical contacts on the bottom side of the diaphragm and top side of the bottom of the diaphragm chamber. 
     FIG. 7 is a sectional view through another preferred embodiment of the present invention. In this embodiment the diaphragm chamber  164  is formed within a two-piece stamped aluminum top cover  166 . The top stamping  168  of the top cover  166  is the same shape and size as conventional disc drive top covers  104  (see FIG.  1 ). A bottom stamping  170  of the top cover  166  defines the bottom surface of the diaphragm chamber  164 . The bottom stamping  170  would be of a shape and size to contour along the disc drive components. The area between the top and bottom stampings  168  and  170  respectively forms the diaphragm chamber  164 . Aperture  172  is formed in the top stamping  168  and aperture  174  is formed in the bottom stamping  170 . The apertures  172  and  174  must be of a size and shape to freely allow airflow into and out of the chamber  164 . 
     A flexible diaphragm  176  partitions the diaphragm chamber  164  into two compartments a top and a bottom compartment  178  and  180  respectively. The diaphragm  176  could be sealed in the chamber  164  with an adhesive or other attachment means. Alternatively, the diaphragm  176  could be fit between a peripheral flange (not shown) defined along a peripheral edge  182  of the top stamping  168  and along a peripheral flange (not shown) defined along a peripheral edge  184  of the bottom stamping  170 . The diaphragm  176  is positioned between the top and bottom stamping flanges (not shown) and the flanges are sealed together by heat, pressure or adhesive. It is also noted that a non-continuous diaphragm could be positioned within the two-piece top cover  166  as long as each diaphragm segment sealed off a portion of the bottom chamber and each portion of the bottom chamber has an aperture for communication with the internally constrained gas. 
     As can be seen from a comparison between FIG.  1  and FIG. 6, the diaphragm chamber  164  in FIG. 7 provides a greater volume to accommodate potential non-corrosive gas expansion or contraction. Preferably, as much as possible of the unoccupied space within the disc drive  100  is utilized for the diaphragm chamber  122  and  164 . Thus, dependent on the drive configuration, number of discs within the drive and diameter of the discs, the chamber should be designed to maximize chamber volume. For example, it is estimated that the diaphragm chamber  122  embodiment shown in FIG. 1, positioned in a Bali-4 disc drive, would have a volume of approximately 33 cm 3 . This compares to a total disc drive internal air volume of approximately 112 cm 3 . As such, this chamber  122  volume would be sufficient to allow for a roughly 35% overall change in internal gas volume. 
     Other diaphragm chamber designs are contemplated to be within the scope of the present invention. For example, the diaphragm chamber could be built into the base plate with the diaphragm partitioning the two chambers so that one of the two chambers communicates with the external environment through an aperture formed in the base plate. Additionally, since the chambers function to accommodate changes in gas volume, the chambers can have any number of sides or different shapes as long as the chamber fits within the configuration of the drive. In fact, the chamber could be formed in the absence of a bottom as long as the diaphragm sealed the external environment from the internally constrained non-corrosive gas. It is further envisioned that multiple diaphragm chambers could be positioned within the disc drive, positioned wherever the disc drive has unoccupied space. Alternatively, the chamber or chambers could be separate structures built on the exterior housing of the disc drive as long as they function to accommodate the expansion or compression of the constrained non-corrosive gas and do not interfere with the functioning of the disc drive. Finally, it should be understood that a diaphragm covered opening in the disc drive could be sufficient to allow the constrained internal gas to expand and/or contract in accordance with the present invention and is thus also within the present invention&#39;s scope. 
     In summary, a preferred embodiment of the invention described herein is directed to a hermetically sealed disc drive (such as  100 ) responsive to volumetric changes in an internally constrained gas. The disc drive includes a hermetically sealed housing (such as  105 ) that constrains a gas, the housing (such as  105 ) further defines a baseplate (such as  102 ). A spin motor (such as  106 ) is mounted to the baseplate (such as  102 ) to rotate an information storage disc (such as  108 ). An actuator assembly (such as  110 ) is also mounted to the baseplate (such as  102 ) to swing an actuator arm (such as  114 ), carrying a read/write head (such as  118 ), over the information storage disc (such as  108 ). Additionally, the disc drive (such as  100 ) includes a diaphragm chamber (such as  122 ) for responding to changes in the internally constrained gas volume. The diaphragm chamber (such as  122 ) includes a first portion (such as  148 ) that accommodates changes in the volume of the constrained gas, a first aperture (such as  144 ) that provides an air passage between the disc drive&#39;s external environment (such as  150 ) and the first portion (such as  148 ), and a diaphragm (such as  134 ) that hermetically seals the first portion (such as  148 ) of the diaphragm chamber (such as  122 ) from the constrained gas. The disc drive (such as  100 ) may also include a second diaphragm chamber (such as  122 ) for responding to changes in the volume of the constrained gas. 
     In another preferred embodiment of the present invention, an environmental protection switch (such as  154 ) is operatively engaged by the diaphragm (such as  134 ) to cause a signal when the diaphragm (such as  134 ) has flexed a predetermined amount. 
     In another preferred embodiment of the present invention, the constrained gas within the disc drive (such as  100 ) is non-corrosive. The gas may be argon, nitrogen, hydrogen, helium, a fluorocarbon or a hydrocarbon. Additionally, an oxygen scavenger, like magnesium or copper, may be included with the constrained gas. 
     In another preferred embodiment of the present invention, the diaphragm (such as  134 ) is a polyester film and can have a thin metal coating. 
     In another preferred embodiment of the present invention, the diaphragm chamber includes a second portion (such as  152 ) that is separated from the first portion (such as  148 ) by the diaphragm (such as  134 ). A second aperture (such as  146 ) is positioned in the second portion (such as  152 ) to provide an air passage between the disc drive&#39;s internally constrained gas and the second portion (such as  152 ). 
     In yet another preferred embodiment of the present invention, the diaphragm chamber (such as  164 ) is housed between a top stamping (such as  168 ) and a bottom stamping (such as  170 ) of the top cover (such as  166 ). A first aperture (such as  172 ) may be positioned through the top stamping (such as  168 ) and a second aperture (such as  174 ) may be positioned through the bottom stamping (such as  170 ). 
     A further exemplary preferred embodiment of the present invention includes a diaphragm chamber (such as  122 ) for responding to internal changes in gas volume in a hermetically sealed disc drive (such as  100 ). The diaphragm chamber (such as  122 ) includes a constrained gas for reducing the effects of corrosion build-up within the disc drive (such as  100 ). Additionally, the diaphragm chamber includes a first portion (such as  148 ) that accommodates changes in the volume of the constrained gas and a first aperture (such as  144 ) that provides an air passage between the disc drive&#39;s external environment (such as  150 ) and the first portion (such as  148 ). A diaphragm (such as  134 ) seals the first portion (such as  148 ) from the constrained gas and is able to respond to volumetric changes in the disc drive&#39;s constrained gas. 
     It will be clear that the present invention is well adapted to attain the ends and advantages mentioned as well as those inherent therein. While a presently preferred embodiment has been described for purposes of this disclosure, numerous changes may be made which will readily suggest themselves to those skilled in the art Accordingly, all such modifications, changes and alternatives are encompassed in the spirit of the invention disclosed and as defined in the appended claims.