Abstract:
The present invention relates to preformed seals used in the manufacture of low density gas filled disk drives. The seals may be preformed to facilitate positioning in the disk drive and eliminate the need for manually applied or semi-automatically applied epoxies, thereby reducing manual labor costs, non-uniform seals, waste and inefficiencies due to equipment malfunction. The epoxy seals may soften and seal after being positioned, thereby forming an in-place hermetic or substantially hermetic seal.

Description:
BACKGROUND OF THE INVENTION 
     Hard disk drives incorporate magnetic storage disks and read/write heads which are capable of reading data from and writing data onto the rotating storage disks. Data is typically stored on each magnetic storage disk in a number of concentric tracks on the disk. The read/write heads, also referred to as read/write transducers or read/write elements, are integrated within a slider. The slider, in turn, is part of an actuator assembly which positions the heads relative to the surface of the storage disks. This may be at a predetermined height above the corresponding storage disk or, in some instances, in contact with the surface of the storage disk. The actuator assembly is typically positioned by a voice coil motor which acts to position the slider over a desired track. One or more read/write heads may be integrated within a single slider. In the case of non-contact sliders, a cushion of air is generated between the slider and the rotating disk. The cushion is often referred to as an air bearing. 
     Hard disk drives are an efficient and cost effective solution for data storage. Depending upon the requirements of the particular application, a disk drive may include anywhere from one to a plurality of hard disks and data may be stored on one or both surfaces of each disk. While hard disk drives are traditionally thought of as a component of a personal computer or as a network server, usage has expanded to include other storage applications such as set top boxes for recording and time shifting of television programs, personal digital assistants, cameras, music players and other consumer electronic devices, each having differing information storage capacity requirements. 
     A primary goal of disk drive assemblies is to provide maximum recording density on the storage disk. In order to provide greater storage capacity on a storage disk, track widths have become increasingly narrower. However, decreasing the width of tracks makes it more difficult for the read/write heads to accurately read and write information to and from the narrowing tracks. Not only is it difficult to physically position the read/write element over a narrow width track, but it is increasingly difficult to maintain the read/write element over the track at an optimal position for accurate data transfer. Air turbulence created by the spinning disks, disk flutter and spindle vibrations, temperature and altitude can all adversely effect registration of the read/write element relative to the tracks. Moreover, increasing the speed of the rotating disks to achieve increased data access times increases air turbulence, which increases misregistration between the read/write element and the tracks on the storage disks (track misregistration or TMR). Higher rotational speeds can also increase disk flutter and spindle vibrations further increasing TMR. Higher rotational speeds can also increase spindle motor power and idle acoustics. 
     Accuracy can be further adversely effected if the read/write heads are not maintained within an optimum height range above the surface of the storage disk. Thus, a related goal is to increase reading efficiency or to reduce reading errors, while increasing recording density. Reducing the distance between the magnetic transducer and the recording medium of the disk generally advances both of those goals. Indeed, from a recording standpoint, the slider is ideally maintained in direct contact with the recording medium (the disk) to position the magnetic transducer as close to the magnetized portion of the disk as possible. Contact positioning of the slider permits tracks to be written more narrowly and reduces errors when writing data to the tracks. However, since the disk rotates many thousands of revolutions per minute or more, continuous direct contact between the slider and the recording medium can cause unacceptable wear on these components. Excessive wear on the recording medium can result in the loss of data, among other things. Excessive wear on the slider can result in contact between the read/write transducer and the disk surface resulting, in turn, in failure of the transducer, which can cause catastrophic failure. 
     Similarly, the efficiency of reading data from a disk increases as the read element is moved closer to the disk. Because the signal to noise ratio increases with decreasing distance between the magnetic transducer and the disk, moving the read/write element closer to the disk increases reading efficiency. As previously mentioned, the ideal solution would be to place the slider in contact with the disk surface, but there are attendant disadvantages. In non-contact disk drives there are also limitations on how close a read/write element may be to the surface of a disk. A range of spacing is required for several reasons, including the manufacturing tolerances of the components, texturing of the disk surface and environmental conditions, such as altitude and temperature. These factors, as well as air turbulence, disk flutter and spindle vibration, can cause the read/write element flying height to vary or even cause the read/write element to contact the spinning disk. 
     Disk drives are assembled in a clean room to reduce contamination from entering the drive prior to final assembly. Thus, the air that is trapped within the drive once it is finally sealed is filtered room air. Accordingly, seals or gaskets used in disk drives between the housing components, such as between the base plate and cover, are designed to prevent contaminants from entering the drive. Such seals are not designed to prevent internal air and other gases from exiting through the seal and out of the drive. Loss of gas in this manner is anticipated and accommodated by use of a filtered port to maintain equalized air pressure within the drive compared to that of air pressure outside of the drive. 
     As an alternative to air-filled drives, advantages may be achieved by filling disk drives with gases having a lower density than air. For example, helium has a lower density than air at similar pressures and temperatures and can enhance drive performance. As used herein, a low density gas or a lower density gas means a gas having a density less than that of air. When compared with air, lower density gases can reduce aerodynamic drag experienced by spinning disks within the drive, thereby reducing power requirements for the spindle motor. A low density gas-filled drive thus uses less power than a comparable disk drive that operates in an air environment. Relatedly, the reduction in drag forces within the low density gas-filled drive reduces the amount of aerodynamic turbulence that is experienced by drive components such as the actuator arms, suspensions and read/write heads. Some low density gases also have greater thermal conductivity, which results in better motor efficiencies and therefore lower power consumption for a given performance level. Reduction in turbulence allows drives filled with low density gas to operate at higher speeds compared with air-filled drives, while maintaining the same flying height and thereby maintaining the same range of read/write errors. Low density gas-filled chives also allow for higher storage capacities through higher recording densities due to the fact that there is less turbulence within the drive which allows the tracks to be spaced more closely together. 
     Despite these advantages, low density gas-filled drives have not been commercially successful. Low density gas-filled drives, in order to function, must be effectively sealed over an acceptable lifetime of the drive. It has been difficult to prevent the low density gas from escaping from the sealed drive environment. Unlike air-filled drives, a port may not be used to equalize pressure outside and inside the drive. As a result, the seal between the cover and base plate must minimize or prevent leakage and maintain a threshold level of low density gas within the sealed environment over the expected lifetime of the drive. Conventional rubber seals used in air-filled drives are inadequate at preventing leakage of low density gas due to the smaller atom size of low density gases, such as helium, compared to air. The smaller helium atoms diffuse through the rubber seals, thereby reducing the volume of low density gas within the drive. Thus, over time, the necessary threshold quantity of low density gas may be lost within the drive environment and may or may not be replaced with ambient air. In either case, the performance of the drive will change from the design specifications, namely, a low density gas-filled sealed environment. As the low density gas leaks out of a drive and is replaced by air, the drive is subject to undesirable operational effects possibly leading to unacceptable error rates and/or failure of the drive. For example, the increased concentration of air may increase the turbulent forces on the heads due to the increased drag forces within the drive which may further cause the heads to fly at too great a distance above the disks and potentially increasing instances of read/write errors. If the low density gas leaks from the sealed environment over time and is not replaced by ambient air, problems will occur such as the heads flying at a distance too close or in contact with the disks, thereby increasing instances of read/write errors as well as damage to the disk surface and head and higher operating temperatures due to a reduction in conduction cooling. Each creates a reliability risk. The risk of unanticipated failures due to inadequate amounts of low density gas within the drive is a draw back to low density gas-filled drives. Indeed, data stored within the drive may be irretrievably lost if the drive fails due to the loss of the low density gas environment. 
     Low density gas-filled drives also must be designed to permit testing and rework, if necessary. Thus, the ability to seal openings in the base plate and/or cover plate on a temporary basis and on a long-term basis must exist. Such openings include, but are not limited to, openings for securing ends of the spindle and actuator shafts to the cover or base plate, or openings to permit self servo-writing. These openings must be adequately sealed to permit testing of the drive under normal conditions and, if possible, unsealed to permit rework. Thus, it is desirable to minimize waste and optimize efficiencies when sealing a disk drive housing to allow rework when needed. 
     Seals are a critical component for any disk drive, particularly low density gas filled disk drives. One critical sealing location is around electrical connectors in the disk drive base plate. For example, multi-pin input/output connectors are used to connect the printed circuit board, typically secured to the exterior of the base plate, to the electrical components within the sealed interior portion of the drive housing, such as the flex circuit. Prior to the present invention, an epoxy sealant was dispensed either manually, such as with a hand-operated syringe, or semi-automatically using a dispensing machine which mixes and applies adhesives and sealants during the assembly process. Because manual labor is involved in each of these processes, these application methodologies are relatively costly. Moreover, it is also difficult to maintain uniform consistency in the application, placement and quantity of the sealing epoxy due to the use of manual labor and/or due to the need to continuously add component epoxies to mixing and dispensing machines and simultaneously maintain operation of the machines which tend to clog over time. These methods require additional processing time for mixing and dispensing of component epoxies and require specialized equipment to apply the sealing epoxy and to try to accurately control volume and placement of the epoxy. These techniques also require regular and frequent equipment cleanup and maintenance which is labor-intensive. These methods are also inefficient in terms of material usage. Not only does the quantity of epoxy applied vary, possibly resulting in the waste of epoxy, but a large quantity of epoxy remains unused in the dispensing equipment, cannot be subsequently used and is discarded. 
     Another drawback of these techniques is contamination of the electrical or input/output pins by the sealing epoxy. Either the epoxy is applied first, requiring the pins of the connector to push through the pre-existing epoxy, or the epoxy is applied following assembly of the connector, in which case the application methodology causes the epoxy to contact and contaminate the pins. In each scenario, the epoxy-coated pins may no longer create a reliable electrical connection between electrical components on opposite sides of the base plate. In turn, this can cause electrical failures in the disk drive. 
     SUMMARY OF THE INVENTION 
     Various embodiments of the present invention are generally directed to a method for establishing an electrical interconnect through a hermetically sealed housing. 
     In accordance with some embodiments, the method generally comprises positioning an epoxy seal member adjacent a housing aperture extending through a housing member, the epoxy seal member having a first shape and a pin aperture; placing an electrical connector onto the epoxy seal member so that an electrical pin extending from the electrical connector extends through the pin aperture in the epoxy seal member and into the housing aperture of the housing member; and curing the epoxy seal member so that the epoxy seal member changes to a second shape and respectively adheres to the electrical pin and the housing member to form a substantially hermetic seal of the housing aperture while permitting an electrical connection between components on opposite sides of said housing member. 
     In accordance with other embodiments, the method generally comprises placing an uncured epoxy seal member, having a first temperature, adjacent a housing aperture in a housing member so that an electrical pin of a connector extends through a preformed pin aperture in the seal member and into the housing aperture; and increasing the temperature of the seal member to a second temperature to cure the seal member so as to sealingly adhere to the electrical pin and form a hermetic seal of the housing aperture. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded perspective view of a hard disk drive manufactured using the present invention. 
         FIG. 2  is an exploded perspective view of a printed circuit board connector and seal and a hard disk drive base plate. 
         FIG. 3  is an enlarged exploded perspective view of the printed circuit board connector, seal and base plate of  FIG. 2 . 
         FIG. 4  is a top plan view of the seal illustrated in  FIGS. 2 and 3 . 
         FIG. 5  is a partial exploded perspective view of a flex circuit, connector and base plate. 
         FIG. 6A  is a cross-section view of a printed circuit board connector and seal prior to assembly. 
         FIG. 6B  is a cross-section view of the printed circuit board connector and seal of  FIG. 6A  following assembly and reformation of the seal. 
         FIG. 6C  is a partial cross-section perspective view of the embodiment of  FIG. 6B , illustrated from the bottom of  FIG. 6B . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is an exploded perspective view of one embodiment of a low density gas filled disk drive  10 . In general terms, the disk drive comprises a base plate  12 , cover plate  14 , disk stack assembly  16 , actuator assembly  18 , flex circuit  20 , connector wiring harness and mounting bracket  22 , voice coil motor  24 , capture plate  26  and metal seal  28 . The individual storage disks  30  are mounted on a rotating hub  32 . The base plate and cover include aligned apertures  34  evenly spaced around their perimeters for securing the cover and base plate together using approved fasteners. When sealed together, the base plate and cover create an inner cavity or chamber  36 . Following final assembly, the inner chamber is filled with a low density gas, such as helium. 
     Turning to  FIGS. 2-4 , a preformed epoxy insert or epoxy preform seal  40  is shown. Also shown is a 24-pin connector  42  comprising 24 individual pins  44 . For purposes of manufacturability and assembly, the electrical connector pins  44  are affixed in a predetermined orientation in a plastic base. The pins electrically connect components mounted on a printed circuit board (not shown) secured to the underside or exterior of the base plate through the base plate to the flex circuit  20  within the inner chamber  36  of the disk drive housing. The base plate is provided with an opening or pass-through  48  for the multi-pin connector. In one embodiment, the pass-through comprises a recess or trough  50  formed on the inside surface of the base plate with an array of cylindrical openings  52  passing completely through the base plate. In the preferred embodiment, the number and size of the array of apertures  52  correspond to the number and orientation of pins  44  in the desired electrical connector. As shown more clearly in  FIG. 5 , the connector wiring harness and mounting bracket  22  engages the pins  44  at contact portion  54 . The contact portion  54  creates a direct electrical connection between the individual pins  44  and the flex circuit  20 . The mounting bracket is secured to the inside surface of the base plate by appropriate fasteners. 
     One embodiment of a preformed epoxy insert or seal  40  is shown in  FIGS. 3 ,  4  and  5 . The preform  40  is made from an epoxy and includes an array of apertures  56  which correspond to the configuration of pins  44  in the electrical pin connector  42 . The configuration of the preform  40  may vary to accommodate most any configuration of pin connector  42 , or any opening  52  in the base plate or cover of a disk drive. As those of skill in the art will appreciate upon review of this disclosure, the preform has substantial versatility to adapt to shapes and openings, and successfully seal those openings. 
     An example of an acceptable epoxy is LCA4 from Bacon Industries, which is mixed with catalyst BA5 and is limestone-filled. In one embodiment, LCA4 cures at room temperature within 24 to 48 hours. In this example, the epoxy preform may be created and stored at temperatures lower than room temperature to avoid curing and to facilitate handling and assembly. With LCA4 epoxy, the preforms are stored at −40° C. to avoid curing. Thus, the epoxy preform may be easily handled and positioned relative to the connector pins  44  and the pass-through  48  in the disk drive base plate. Within 24 to 48 hours of assembly, sitting in a room temperature environment, the epoxy will flow around the pins  44  and between the base  46 , apertures  52  and cavity  50  to create a hermetic or substantially hermetic seal. Alternatively, the curing may be accelerated by elevating the temperature, for example, to 200° F. for two hours. Thus, following subassembly of the epoxy preform, electrical connector and base plate, the subassembly may be placed in storage at the appropriate curing temperature where over an appropriate period of time the epoxy flows to fill the voids and cures into a hard hermetic seal. Further assembly of components into the base plate may then proceed without risk of damaging the seal. 
     Filling the epoxy with limestone or other filler reduces the coefficient of thermal expansion (CTE) to match aluminum and also inhibits migration or diffusion of low density gas, such as helium. Glass and other fillers could be used as would be appreciated by those of skill in the art. Catalyst BA5 provides a good adhesion to pins that are gold-plated. Gold plating enhances conductivity of the pins. The epoxy and its constituent components should not be conductive, which could short the pin connectors. 
       FIGS. 6A-C  generally illustrate the subassembly and curing process for the preferred embodiment. During assembly, the preform  40  is taken from storage, where it is maintained at a temperature below its curing temperature, and placed within the recess  50  of the base plate. As shown in  FIG. 6A , the openings  56  in the preform are dimensioned to be of essentially the same cross-sectional shape as the pins  44 . As illustrated, the openings  56  are smaller than the openings  52  in the base plate. The connector  42  is then forced through the preform until the base  46  abuts the preform and the pins  44  are fully extended through the openings  52  in the base plate. At this point, the epoxy has not softened and it does not adhere to the pins  44  as they are pressed through the openings  56 . With reference to  FIG. 6B , the temperature of the preform is then elevated, causing it to soften and flow into the openings  52  in the base plate and fully surround the electrical pins to create a substantially hermetic seal around each pin. As previously mentioned, this may be accomplished by subjecting the preform and base plate to an accelerated elevated temperature, such as in an oven with exposure to a heat lamp, or the preform may be made to soften and cure slowly at room temperature. Similarly, the epoxy adheres to the base  46  and to the side walls  58  of the cavity  50  to complete the seal. A cured seal is illustrated from the exterior side of the base plate in  FIG. 6C . Unlike manual epoxy fill or machine epoxy fill, uniformity in application and a complete seal is achieved. In addition, waste is substantially reduced as is the need for maintenance of application equipment. 
     Epoxies can be generally described as having three stages: A, B and C. The A stage is when the epoxy is being formed, the B stage is prior to setting, and the C stage is after it is set. The present invention allows use of any epoxy that can be maintained and handled in its B stage, preferably at or about room temperature, and if its C stage curing temperature is around room temperature or higher. As previously mentioned, the preform  40  can be formed in any shape, in any volume, and is not limited to use in intricate situations such as around connector pins. The seals may be preformed in large sheets or individually as required for a particular application. Preforms may be cut from larger sheets of epoxy in its B stage. The preform may be made by molding the epoxy into a desired shape or by stamping out preforms in a B stage state, if the material is not too brittle. The preforms can be maintained or inventoried at a temperature below the curing temperature (C stage), which is preferably in a cool environment, such as in a refrigerator, cooler or freezer. Preforms as described herein may be assembled into disk drives using automated equipment to lower assembly line costs and reduce the need for manual labor or may be inserted manually. Such preforms will provide a constant or uniform fill and avoid clogged needles and variable or non-uniform flow as presently occurs with automated equipment. Waste is reduced by molding preforms with the precise volume of epoxy needed or by remelting and reusing excess epoxy if the preforms are cut from large sheets. 
     Other examples of where the preformed epoxy seal may be used to seal openings in a disk drive, including a low-density gas-filled disk drive, include between the spindle motor and base plate, between the spindle or actuator and cover plate and between the cover and base plate. Other locations will be apparent to those of skill in the art upon reading the foregoing and such applications are considered within the scope of the present invention. 
     The foregoing discussion of the invention has been presented for purposes of illustration and description. The foregoing is not intended to limit the invention to the form or forms disclosed herein. In the foregoing Detailed Description for example, various features of the invention are grouped together in one or more embodiments for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the following claims are hereby incorporated into this Detailed Description, with each claim standing on its own as a separate preferred embodiment of the invention. 
     Moreover, though the description of the invention has included description of one or more embodiments and certain variations and modifications, other variations and modifications are within the scope of the invention, e.g. as may be within the skill and knowledge of those in the art, after understanding the present disclosure. It is intended to obtain rights which include alternative embodiments to the extent permitted, including alternate, interchangeable and/or equivalent structures, functions, ranges or steps to those claimed, whether or not such alternate, interchangeable and/or equivalent structures, functions, ranges or steps are disclosed herein, and without intending to publicly dedicate any patentable subject matter.