Patent Publication Number: US-7911732-B2

Title: Hermetically sealed head disk assembly and method of sealing with soldering material

Description:
RELATED APPLICATIONS 
     This application is related to U.S. patent application Ser. No. 10/673,593, entitled “HERMETICALLY SEALED ELECTRONICS ARRANGEMENT AND APPROACH”, by David Albrecht, et al, filed Sep. 29, 2003. 
     This application is related to co-pending U.S. patent application Ser. No. 11/351,440, entitled “HERMETICALLY SEALED HARD DISK ASSEMBLY AND METHOD OF SEALING WITH SOLDERING MATERIAL” by Michael Hatchet, et al, filed Feb. 9, 2006, assigned to the assignee of the present invention. 
     This application is related to co-pending U.S. patent application Ser. No. 11/352,086, entitled “HERMETICALLY SEALED HARD DISK ASSEMBLY AND METHOD OF SEALING WITH SOLDERING MATERIAL” by Michael Hatchet, et al, filed Feb. 9, 2006, assigned to the assignee of the present invention. 
     This application is related to co-pending U.S. patent application Ser. No. 11/352,101, entitled “HERMETICALLY SEALED HARD DISK ASSEMBLY AND METHOD OF SEALING WITH SOLDERING MATERIAL” by Michael Hatchet, et al, filed Feb. 9, 2006, assigned to the assignee of the present invention. 
     TECHNICAL FIELD 
     This invention relates generally to the field of direct access storage devices and in particular to a sealed head disk assembly and a method of achieving a semi-hermetic and a hermetic seal through a novel design of existing components. 
     BACKGROUND ART 
     Direct access storage devices (DASD) have become part of every day life, and as such, expectations and demands continually increase for greater speed for manipulating data and for holding larger amounts of data. To meet these demands for increased performance, the mechanical assembly in a DASD device, specifically the Head Disk Assembly (HDA) has undergone many changes. 
     Shown in  FIG. 1A  is the relationship of components and sub-assemblies of HDA  110  and a representation of data tracks  136  recorded on disk surface  135 . The cover is removed and not shown so that the inside of HDA  110  is visible. The components are assembled into base casting  113 , which provides attachment and registration points for components and sub-assemblies. Data is recorded onto disk surface  135  in a pattern of concentric rings known as data tracks  136 . Disk surface  135  is spun at high speed by means of a motor-hub assembly  130 . Data tracks  136  are recorded onto disk surface  135  by means of magnetic head  156 , which typically resides at the end of slider  155 .  FIG. 1A  being a plan view shows only one head and one disk surface combination. One skilled in the art understands that what is described for one head-disk combination applies to multiple head-disk combinations. The embodied invention is independent of number of head-disk combinations. Slider  155  and consequently head  156  are incorporated into head gimbal assembly (HGA)  150 . HGA  150  is incorporated into actuator  140 , which is comprised of at least one arm  146 , pivot bearing  145 , and voice coil  143 . Arm  146  supports HGA  150  over disk surface  135 . Pivot bearing  145  allows for smooth and precise rotation of actuator  140 . Actuator  140  precisely moves HGA  150  over disk surface  135  by means of electro-motive force (emf) produced between voice coil  143  and magnets  125 . Emf is a force that is produced when a current is passed through voice coil  143  and is in close proximity to magnets  125 . Only bottom magnet  125  is shown. Top and bottom magnets  125  are joined as pole piece assembly  120 . Pole piece assembly  120  in conjunction with voice coil  143  constitutes a voice coil motor (VCM). The VCM positions head  156  via actuator  140  by producing a controlled emf. Current is passed through voice coil  143  from controller  117 . The required amount of current from controller  117 , to produce the desired amount of emf, is determined by location information (stored in other electronic components not shown in  FIG. 1A ) for data tracks  136  and location information stored in data tracks  136 . Electronic commands for accessing data tracks  136  pass from controller  117  through flex cable  118  and into voice coil  143 . Small corrections to the position of head  156  are determined from retrieved information from data tracks  136 . This retrieved information is sent back to controller  117  so that small corrections can be made to the location and the appropriate current can be sent from controller  117  to voice coil  143 . Once the desired data track is located, data is either retrieved or manipulated by means of electronic signals that pass through connector  111  and through flex cable  118 . Connector  111  is the electronic interface that allows data to be transferred in and out of HDA  110 . 
     The dynamic performance of HDA  110  is a major mechanical factor for achieving higher data capacity as well as for manipulating this data faster. The dynamic performance of HDA  110  is dependent upon the dynamic performance of its individual components and sub-assemblies. Many factors that influence the dynamic performance are intrinsic to the individual components. Some of these intrinsic factors are in general: mass of the component; stiffness of the component; and geometry of the component. This is not an all-inclusive list and those schooled in engineering or HDA technology will understand that there are many other factors that influence dynamic performance of HDA  110  components and sub-assemblies. 
     The quantity of data tracks  136  recorded on disk surface  135  is determined partly by how well magnetic head  156  can be positioned and made stable over a desired data track  136 . The quantity of data track  136  is a direct indicator of the amount of data stored. Although the mass, stiffness and geometry of the components in actuator  140  directly affect the stable positioning of magnetic head  156 , vibration energy that acts on actuator  140  and its components is also a major factor in the stable positioning of head  156 . If excessive, vibration energy will impart oscillating motion to actuator  140  and move head  156  from a desired position over data track  136 . 
     There are several sources for vibration energy that act on actuator  140 . There is outside vibration energy that enters HDA  110  through base casting  113  and affects the stability of actuator  140 . There is internal vibration energy that is produced by rotating components and sub-assemblies inside HDA  110 . Motor-hub assembly  130  can transmit vibration energy through base casting  113  and into actuator  140 . Spinning disk surface  135  can impart oscillating motion directly into magnetic head  156  and cause it to move off data track  136 . And pivot bearing  145  can also transmit vibration energy into actuator  140  and thus into magnetic head  156 . Attention is given to all potential sources of vibration energy in the design of these sub-assemblies and components. Another source of vibration energy inside HDA  110  is the motion of the atmosphere inside HDA  110  and its interaction with sub-assemblies and components. 
     Shown in  FIG. 1B  is the relationship of components and sub-assemblies during assembly of HDA  110  as described by  FIG. 1A . Included in  FIG. 1B  are cover  115  and both magnets  125 . 
     It has been recognized by HDA designers that it is desirable to control the atmosphere inside the HDA. The atmosphere can be controlled for its humidity as cited in U.S. Pat. No. 6,762,909 or the atmosphere can be controlled for its gas composition. In light of the aforementioned problem of atmosphere inside the HDA impacting HDA components and imparting vibration energy, it has been recognized that a low-density gas, such as helium (He), has the benefit of imparting less energy into HDA components. It is well known that the aerodynamic forces on an object are proportional to the product of the density and square of the velocity of the impinging fluid. By virtue of the lower density of He, it will impart smaller lift and drag forces into HDA components as the internal gas of the HDA impinges on the internal components of the HDA. 
     Once a desired atmosphere or mixture of gases is introduced inside an HDA, it must be contained or maintained. US Patent Application 2003/0081349 teaches how to replenish the mixture of gases from a reservoir and valve system if the mixture of gases cannot be contained. Emphasis has been placed on containing a mixture of gases once it has been established. The general term for containing and sealing in a gas or atmosphere is a hermetic seal. Partial containment is a semi-hermetic seal. Hermetic seals have taken several forms. Much attention has been given to sealing HDAs by various means of welding. In general, welding is the assembly technique by which two parts to be joined are held together, their mating surfaces heated above their melting temperatures either by applying molten material of similar composition or applying heat directly to the mating surfaces. U.S. Pat. No. 6,762,909 cites welding as a method to achieve a hermetic seal. The high temperatures required for welding has made this approach difficult to apply to the hermetic sealing of an HDA. Other approaches for making a welded hermetic seal are taught in US Patent Application 2003/0223148 and Japanese Patent JP8161881. 2003/0223148 cites laser welding as a means to achieve a welded hermetic seal. Japanese Patent JP8161881 teaches the use of a welded metallic ribbon. 
     Hermetic seals have also been described that use the folding, or hemming of metal in conjunction with a compliant sealing material. Hemming is the process by which thin sheets are placed together so they overlap at an edge and are secured to each other by folding the overlapping edges together. Both U.S. Pat. Nos. 4,367,503 and 6,556,372 teach variations for hemming metal with a compliant material in the hem. 
     Secondary enclosures and covers have also been described in the art. US Patent Application 2003/0179489 teaches the use of a structural cover that provides a semi-hermetic seal, followed by a sealing cover that attaches to the base casting and on top of the structural cover that provides the hermetic seal. Japanese Patent JP5062446 teaches placing a generally conventional HDA inside a hermetically sealed outer container. 
     The challenges to the above cited art include but are not limited to: distortion of HDA components and sub-assemblies due to the high temperature required for welding; restriction of the choice of materials for the base and cover so as to be suitable for welding; the use of multiple components for isolating HDA components and sub-assemblies from welding temperatures; rework procedures that might be required due to failed HDA components or sub-assemblies. 
     SUMMARY OF THE INVENTION 
     Various embodiments of the present invention are described herein. A sealed head disk assembly has a base casting for providing attachment points for the major components of the head disk assembly. The base casting has a semi-hermetic seal encompassing an outer perimeter of the base casting and allows the semi-hermetic seal to be juxtaposed to at least one complementary surface on the cover. The cover for enclosing the major components of the head disk assembly has a hermetic seal outside a perimeter of the complementary surface for the semi-hermetic seal thus allowing the hermetic seal to be juxtaposed to at least one complementary surface on the base casting. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention: 
         FIG. 1A  is a plan view of an HDA with cover and top magnet removed. 
         FIG. 1B  is an isometric blow-apart of an HDA. 
         FIG. 2  is an isometric blow-apart of the cover and base casting embodied in the present invention. 
         FIG. 3  is a plan view of the cover embodied in the present invention. 
         FIG. 4  is a plan view of the base casting embodied in the present invention. 
         FIG. 5  is a cross-section view through the base casting, cover and a screw embodied in the present invention. 
         FIG. 6  is a process flow diagram embodied in the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     It is the goal of the embodied invention to address the challenges presented by the cited prior art while achieving flexibility in the assembly and test process, minimizing the number of required components, and minimizing the cost impact associated with producing a hermetically sealed HDA. 
     The embodied invention teaches a component design and assembly technique by which a semi-hermetic and hermetic seal are in series with each other. A semi-hermetic seal in series with a hermetic seal allows the build and test of the HDA to occur under a desired atmosphere using the temporary semi-hermetic seal. Atmosphere is defined as a mixture of gases, a particular gas, or gases that are typically found in air. Once the HDA has finished its build and test processes, the hermetic seal is activated and the desired atmosphere is permanently sealed inside the HDA. Referring to  FIG. 2 , cover  215  is similar to the current art of sealing HDA  110 . A hermetic seal (not visible in  FIG. 2 ) is incorporated onto surface  208  of cover  215 . Said hermetic seal  305 , visible in  FIG. 3 , is attached to an outer perimeter of the inside surface  208  of cover  215 . The hermetic seal  305  is juxtaposed to complementary surface  212  on base casting  213 . 
       FIG. 5  shows semi-hermetic seal  244  and hermetic seal  305  registered against respective complementary surfaces  322  and  212 . Hermetic seal  305  incorporated in cover  215  is aligned and registered against surface  212  on base casting  213 . Semi-hermetic seal  244  incorporated in base casting  213  is aligned and registered to surface  322  on cover  215 . Multiples of screw  201  and multiples of coinciding screw hole  202  fabricated in cover  215  align and register hermetic seal  305  and semi-hermetic seal  244  against at least one complementary surface on base casting  213  and against at least one complementary surface on cover  215 . Multiples of screw hole  202  fabricated in cover  215  are unsupported on at least one edge. It can be seen in  FIG. 5  that screw  201  causes deflection in zone  515   a  of cover  215  and thus provides spring force that allows registering hermetic seal  305  incorporated in cover  215  against complementary surface  212  on base casting  213  and semi-hermetic seal  244  incorporated in base casting  213  against complementary surface  322  on cover  215 . The material for semi-hermetic seal  244  is an elastomeric polymer. 
     A major challenge of the cited prior art is the extreme heat required to weld a cover and base casting together to produce a hermetic seal. The invention presented accomplishes a hermetic seal by two methods. 
     The first method for achieving a hermetic seal is to use a joining technique known in the industry as soldering. Soldering involves the melting of a tertiary material to join two materials. The soldering material typically melts at a temperature below the melting point of the materials to be joined. A hermetic seal using soldering will produce an inviolable atmosphere within the HDA once melting has activated the soldering material. 
     It is possible that the two materials are of a different composition. If one or both surfaces to be joined are incompatible with the soldering material, a coating is applied which makes the surfaces complementary to the soldering material. The preferred method taught in this invention is to use a solder alloy as the soldering material. The common element in solder alloy is the presence of tin (Sn). Solder alloys include, but are not limited to Sn—Pb, Sn—Ag, Sn—Ag—Cu, and Sn—Bi. If required, the surfaces of the cover and base casting are made complementary to solder alloy via plating or vacuum deposition processes well known in the industry. 
     This invention is not limited to solder as a soldering material. One schooled in the art will recognize there are numerous methods of soldering with various metals, alloys, and plastics.  FIG. 3  depicts one embodiment by which soldering material comprising hermetic seal  305  is applied around a perimeter of cover  215 . It is to be understood that the application of soldering material comprising hermetic seal  305  can be accomplished by a variety of techniques that include but are not limited to plating, vacuum processing, solder paste, placing a preform of soldering material comprising hermetic seal  305  onto complementary surface  522   a  of  FIG. 5 , or dipping complementary surface  522   a  into molten soldering material. 
     The second method for achieving a hermetic seal is to use an appropriate liquid bonding material. In general an appropriate liquid bonding material is a reactive cross-linking polymer. A common type of reactive cross-linking polymer is epoxy, but for the purpose of this invention, a reactive cross-linking polymer also includes adhesives that react and are solidified in the presence of heat or a catalyst that causes the cross-linking process to take place. 
     Activation of hermetic seal  305  is dependent upon the material from which hermetic seal  305  is made. The embodied invention is independent of the method of activating hermetic seal  305 . Some common examples of activation by heat are: laser heating, hot iron, inductive heating, oven, and infrared radiation. Other examples of activation are applying a chemical to make a surface complementary for activation with hermetic seal  305 . A chemical used in this manner is typically known as a primer. 
       FIG. 2  and  FIG. 4  shows semi-hermetic seal  244  positioned around an outer perimeter of base casting  213 . It is to be understood that a semi-hermetic seal in series with a hermetic seal can be designed in a variety of combinations. Examples, and the embodied invention not being limited to these examples, are: both hermetic seal and semi-hermetic seal integral to cover; both hermetic seal and semi-hermetic seal integral to base casting; hermetic seal integral to base casting and semi-hermetic seal integral to cover; hermetic seal integral to cover and semi-hermetic seal integral to base casting. 
     In conjunction with providing a hermetic seal between base casting  113  and cover  115 , a hermetic seal must also be provided between base casting  113  and connector  111  and base casting  113  and motor-hub assembly  130 . The sealing of these components is taught in other art and is beyond the scope of the embodied invention. 
     Independent of hermetic seal  305  being integral to cover  215 , or hermetic seal  305  being integral to base casting  213 , or semi-hermetic seal  244  being integral to cover  215 , or semi-hermetic seal  244  being integral to base casting  213 , the assembly process follows the flow chart shown in  FIG. 6 . 
       FIG. 6  is a flow chart of a process  600  in which particular steps are performed in accordance with an embodiment of the present invention for hermetically sealing a head disk assembly with a soldering material.  FIG. 6  includes processes of the present invention, which in one embodiment, are carried out by processors, electrical components and assembly mechanisms under the control of computer readable and computer executable instructions. The computer readable and computer executable instructions reside, for example, in data storage features such as a computer usable volatile memory and/or a computer usable non-volatile memory and/or a data storage device. However, the computer readable and computer executable instructions may reside in any type of computer readable medium. Although specific steps are disclosed in process  600 , such steps are exemplary. That is, the present invention is well suited to performing various other steps or variations of the steps recited in  FIG. 6 . Within the present embodiment, it should be appreciated that the steps of process  600  may be performed by software, by hardware, by an assembly mechanism, through human interaction, or by any combination of software, hardware, assembly mechanism and human interaction. 
     In step  610  of process  600 , HDA components and subassemblies of a hard disk drive  110  are assembled in a base casting  113  (as shown in  FIGS. 1A and 1B ), in an embodiment of the present invention. 
     In step  620  of process  600 , a cover  215  is attached to a base casting  213  (as shown in  FIG. 2 ) in an embodiment of the present invention. 
     In step  630  of process  600 , an atmosphere is introduced into the HDA, in an embodiment of the present invention. One schooled in the art will recognize that there are many various methods and techniques to introduce an atmosphere into an HDA. 
     In step  640  of process  600 , upon introduction of the atmosphere into the HDA, the HDA is tested. One schooled in the art is cognizant that there are many various criteria, methods and techniques that are specified to test the HDA. 
     In step  680  of process  600 , if the HDA passes the specified test, process  600  proceeds to step  690 . If the HDA fails the specified test, process  600  proceeds to step  660 . 
     In step  690  of process  600 , the hermetic seal is activated in an embodiment of the present invention. In an embodiment, laser heating may activate the hermetic seal. Alternatively, activation of the hermetic seal may be achieved by, but is not limited to, a hot iron, an oven, infrared radiation or application of a chemical or primer, in another embodiment of the present invention. 
     In step  650 , if the HDA fails the specified test, process  600  proceeds to step  660 . 
     In step  660  of process  600 , the cover, e.g., cover  115  of  FIG. 1B  or cover  215  of  FIG. 2 , is removed from the base casting, e.g., base casting  113  of  FIG. 1B  or base casting  213 , respectively, in an embodiment of the present invention. 
     In step  670  of process  600 , those elements and/or components of the HDA that failed the specified test are repaired accordingly. Once the faulty elements and components are properly repaired, process  600  returns to step  620 , in which the cover is again attached to a base casting. 
     Subsequent to the completion of step  620  of process  600 , process  600  returns to step  630 , in an embodiment of the present invention. 
     Advantageously, the present invention, in the various presented embodiments allows for the hermetic sealing of an HDA without precluding reworking the HDA in the event of failure during testing. The present invention in the various presented embodiments advantageously allows for cost effective hermetic sealing of an HDA through the novel design of components that are similar to the current art and by not adding more components to the HDA. 
     The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the Claims appended hereto and their equivalents.