Abstract:
A lubricant is applied to swage contact surfaces in a disk drive of the type including a suspension arm connected to an actuator arm by a swaging process. A preferred thin film lubricant may be applied to the contact surfaces by immersion and draining, immersion and raising the part out of the solution, localized spraying, or various deposition processes. Application of the lubricant reduces chipping during de-swaging, particularly with nickel plated metal components. Application of the lubricant has also shown to improve gram load uniformity, reduce adverse distortion to the actuator assembly and reduces torque out retention values. Improved gram load uniformity enhances overall disk drive functioning, reduced distortion preserves intended attitude and flatness of the actions for assembly and reduced torque out retention values improves reworkability of the disk drive.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This present application is a divisional of application Ser. No. 09/975,593, filed on Oct. 10, 2001, now U.S. Pat. No. 7,024,754, Entitled “Suspension Swage Plate With Applied Solid Film Lubricant and Method of Assembling the Same”, which claims the benefits of U.S. Provisional Application Ser. No. 60/239,159, which was filed on Oct. 10, 2000, and is incorporated herein by this reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates in general to disk drives, and more particularly, to application of a solid film lubricant to components in a disk drive assembled by a swage process. 
     BACKGROUND OF THE INVENTION 
     Magnetic-disk drives generally utilize rotary actuators to position one or more magnetic read/write heads (also known as transducers) with respect to a similar number of magnetic disks rotatably mounted on a hub driven by a motor. The read/write heads are moved among particular tracks of the magnetic disk to gain access to the information recorded on that track and/or to write information to a particular location on the disk. 
     The read/write heads are mounted on an air bearing slider. The slider positions the read/write heads above the data surface of the disk by a cushion of air generated by the rotating disk. Alternatively, the slider may operate in contact with the surface of the disk. The slider is mounted to a suspension load beam or suspension arm assembly. The suspension arm maintains the read/write heads and the slider adjacent to or in contact with the data surface of the disk with as low a loading force as possible. The combination of the read/write heads, slider and suspension arm is sometimes referred to as the head gimbal assembly (HGA). 
     The suspension arm is connected to the distal end of a rotary actuator arm pivotally installed within the housing of the disk drive. A voice coil motor pivots the actuator arm to position the read/write heads over desired tracks at selected radii of the magnetic disks. 
     Currently, ball swaging is the preferred method of attachment of the suspension arm to the actuator arm. Generally, swaging is a process for connecting metallic components. The wall of a thin tubular component is expanded in compression against a complementary component wherein the thin tubular component experiences some degree of plastic deformation. More specifically, with respect to this invention, the process of swaging a suspension arm to an actuator arm involves pressing and fastening the periphery of a boss or sleeve of the suspension arm to the inner face or wall of a through-hole formed in the actuator arm. The boss or sleeve is typically integral with a mounting plate or baseplate attached to the suspension arm. To attach the suspension arm to the actuator arm, the boss is inserted into the through-hole formed in the actuator arm. Then, a swage ball having a diameter larger than the inner diameter of the opening of the boss is passed completely through the opening of the boss, forcing the boss against the inner wall of the through-hole. Depending upon the size of the swage ball relative to the through-hole, the inner wall defining the through-hole in the actuator arm will undergo a range of deformation from little to extensive. The swaging process generally provides a stronger connection than a press fit because the boss is work hardened by the deformation which actually increases tensile strength. Nevertheless, the deformation must be sufficient to reliably hold the separate pieces together. Unfortunately, the swage ball can tear away metal as it is forced through the through-hole and cause cracking and metal failure. The loose metal pieces may adhere to the perimeter of the exit side of the through-hole, like a metal burr, which may then dislodge after assembly of the drive, thereby placing metal debris on the surface of a disk. Such debris, if it breaks away, can cause extensive damage to the disk. Moreover, the quantity of the debris can increase if the pieces are plated, such as nickel-plated pieces. In addition, the swaging process can alter the attitude of the suspension, thereby changing the position of the slider relative to the disk in the final assembly. If the flying characteristics of the slider are changed as a result, the flying dynamics of the slider and the overall performance of the drive may be adversely affected. Thus, it can be seen that there is a need for a lubricant in the swaging process. 
     Deswaging is the process of disconnecting components that have been joined by swaging. It is often desirable to deswage components when a drive needs to be reworked, as in the case when testing reveals problems in operation or function of the disk drive. For example, testing may reveal that a transducer is not performing properly and needs replacing. In such a circumstance, it is desirable to deswage the suspension arm from the actuator arm and replace it with a new suspension arm, slider and transducer; however, it is desirable to re-use the original actuator arm. 
     As previously described, swaging is a severe process, particularly with nickel-plated metal actuators and suspension arms. The swaging process creates a retention torque between the mating metal pieces that must be overcome to separate or free the metal pieces from each other. As a result, deswaging of parts can cause damage to both the actuator arm and the boss of the suspension arm manifesting in the form of cracking and other material failures. Such failures can contribute to undesirable contamination due to creation of particles. Accordingly, it can be seen that there is also a need for providing a lubricant which helps to prevent the failure of contact services in a deswaging process. 
     It is known in the art of swaging to apply an isopropyl alcohol to members which come into contact with one another during the swaging process. Presumably, the purpose of applying the isopropyl alcohol during the process is to provide some type of lubrication among the members in contact, and then the isopropyl alcohol evaporates leaving no residue. Although a liquid lubricant of this type may have certain advantages in the swaging process, it is also known that isopropyl alcohol is not a very effective lubricant. Regardless, isopropyl alcohol applied in the swaging process does not provide lubrication in later de-swaging because the alcohol will have evaporated. 
     The U.S. Pat. No. 5,879,578 discloses a lubricated swage ball for use in swaging a head gimbal assembly to an actuator arm in a disk drive. The purpose of using a lubricated swage ball in this reference is to reduce transfer of aluminum oxide, or other hard materials which can be deposited on a disk during the swaging process. The swage balls are first pretreated by cleaning and then by etching to remove residual alumina from their surfaces. The cleaned, etched swage balls are then lubricated in a fluorocarbon lubricating system. Although this reference may address lubrication of a swage ball, this reference does not disclose the need to lubricate mating parts of the actuator arm and the suspension arm. Also, the inventors of the present application have learned from experimentation that swage balls may not rotate upon insertion into the through-hole, if the tolerances are sufficiently small to attain proper swaging. As a result, any lubrication is quickly scraped off by initial contact between the swage ball and side walls of the through-hole, leaving metal on metal contact. 
     SUMMARY OF THE INVENTION 
     The present invention involves the application of a lubricant to metal parts of a disk drive prior to swaging. In one aspect of the invention, an improved disk drive is provided which includes a lubricant polymer coating applied to components of the actuator arm and suspension arm which come into contact during the swage process. The portions of the components which come into contact with one another can be defined as swage contact surfaces. 
     In another aspect of the invention, a method of assembling an actuator assembly is provided including the step of depositing a polymer film or a solid film to selected elements of an actuator arm and suspension arm prior to swaging. 
     In yet another aspect of the invention, various methods may be used in applying the lubricant coating to the respective components of the disk drive. Such methods contemplated herein include localized spray, vacuum deposition, CVD (chemical vapor deposition), PE-CVD (plasma enhanced chemical vapor deposition), ion beam deposition, cathodic arc deposition, and sputter deposition. 
     One lubricant which has been found to provide good results is a fluorocarbon polymer made from a diluted solution of a 3M® polymer FC722 (fluoroalkylmethacrylate). In testing performed, the polymer film was applied in thicknesses ranging from 20 angstroms to 175 angstroms to a number of actuators and suspension arms by a drain coating process, leaving a uniform layer of the lubricant on the inside surfaces of the through-hole of the actuator arm and the exterior surface of the boss of the suspension arm. Deswaging showed a pronounced decrease in retention torque, the torque needed to separate the two metal pieces. The testing further revealed a pronounced decrease in chipping of the metal components and improved deformation characteristics of the metal components following swaging. Surprisingly, use of the polymer coating also provided better uniformity in gram load throughout the head gimbal assembly. 
     Although this range of thicknesses, between 20 and 175 angstroms, has proven to be adequate for providing a desired amount of lubricant, it shall be understood that this is not a critical minimum or maximum thickness. Rather, thinner or thicker films are still advantageous for use in lubrication with the invention herein disclosed. Indeed, the inventors believe a monolayer, namely a film layer one molecule thick, will provide sufficient lubrication. Such a monolayer would be on the order of 5-7 angstroms depending upon the lubricant used. 
     Another lubricant that provides good results is solid films, such as solid fluorocarbon films. In testing using fluorocarbon solid films, a coating having a thickness ranging from 25 to 2700 angstroms was applied to a number of swage plates by plasma enhanced chemical vapor deposition of CHF 3 . As with the polymer films, deswaging showed a pronounced decrease in retention torque. The testing further revealed a pronounced decrease in chipping of the metal components and improved deformation characteristics of the metal components following swaging. The use of the solid film coating also provided better uniformity in gram load throughout the head gimbal assembly. Similarly, the inventors believe a single monolayer film will provide adequate lubrication. 
     In general, fluorocarbon containing films are relatively inert, provide excellent lubrication, and take the form of polymer or solid films. The FC 722 is a solid like, lubricating film composed of a polymer with a distribution of molecular weights. In the deposition processes mentioned above, the solid lubricant precursor is a fluorocarbon containing gas, a fluorocarbon containing solid substance, or a combination of fluorocarbons containing gases with fluorocarbon solids, depending upon the deposition technique used to deposit the lubricant film. 
     These and various other advantages and features which characterize the invention are pointed out with particularity in the claims annexed hereto, and form a part of the disclosure hereof. Additionally, other advantages and features of the invention are disclosed in the description which follows, taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         FIG. 1  is a plan view disclosing an example of a typical hard disk drive including at least one actuator assembly; 
         FIG. 2  is a greatly enlarged fragmentary, exploded, perspective view of an actuator arm, a head gimbal assembly (HGA), and a swage plate including a swage boss extending therefrom; 
         FIG. 3  is another greatly enlarged fragmentary perspective view of the components illustrated in  FIG. 2 , but said components being assembled; and 
         FIG. 4  is a greatly enlarged vertical section taken along line  4 - 4  of  FIG. 3  illustrating the actuator arm and the suspension arm prior to swaging. 
     
    
    
     DETAILED DESCRIPTION  
       FIG. 1  shows a plan view of a disk drive assembly  10 , with the top cover removed.  FIG. 1  is representative of any number of common disk drives. The disk drive assembly  10  illustrated herein includes at least one disk  12 , typically having magnetic media on both the upper and lower surfaces thereof. The disk  12  along with other components of the disk drive are contained within a housing  14 . The disk  12  is mounted over a hub  16  which is driven by a motor (not shown) enabling the disk to rotate at high revolutions per minute during operation. An actuator assembly  18  is shown rotatably mounted to an actuator pivot  24 . Basic components of the actuator assembly  18  shown include one or more read/write heads  20  mounted on a flexure arm or suspension arm assembly  21 . Suspension arm  21 , in turn, is attached to an actuator arm  22 , as further discussed below. In solid lines, the actuator assembly  18  is shown parked over the landing zone. The landing zone has been represented by the area of the disk  12  on or adjacent disk track  30 . The landing area of the disk is allocated for takeoff and landing of the read/write heads  20  during spin-up and spin-down of the disk. The actuator assembly  18  is rotated to a desired disk track by a voice coil motor shown as voice coil  26 . The voice coil  26  is immersed in a magnetic field generated by the magnet  28 . An actuator control circuit (not shown) causes current flow in the voice coil motor  26 , and ultimately controls the position of the actuator assembly  18  by varying current through the voice coil. The dotted position of actuator assembly  18  illustrates the manner in which actuator assembly  18  rotates about actuator pivot  24  in response to the voice coil motor  26 . The magnet  28  is mounted to a mounting plate  32 .  FIG. 1  also shows other common elements of a disk drive including a communications bus  36  which transfers electronic signals to and from the read/write heads  20 . 
     Now referring to  FIG. 2 , the distal end of the actuator arm  22  is illustrated, along with the head gimbal assembly (HGA), and a swage plate. More specifically, the distal end of the actuator arm  22  includes a through-hole or opening defined by inner face or wall  38 . The proximal end of the suspension arm  21  includes a base portion  41  having an opening or hole formed therethrough, defined by inner face or wall  40 . Other components of the suspension arm are also shown including a flexure member  42  which is attached to the distal end of the suspension arm  21 , and a slider  44  mounted to the flexure member  42 . The slider  44  houses the transducer/read/write heads  20 . 
     Although a specific design is shown for the actuator arm and suspension arm, it shall be understood that the invention is not limited by this specific design, and the methods and apparatuses claimed herein apply to any actuator arm assembly including a swage-type connection. 
     One form of a swage plate  46  is also illustrated in  FIG. 2 . The swage plate  46  includes an integral swage boss  48  extending from the swage plate  46 . The swage boss  48  is a cylindrical shape member which is inserted through openings  40  and  38  when assembled with the actuator arm and suspension arm. Swage plate  46  may be welded to the base portion  41 , or may be attached by other known means in the art. As shown in  FIG. 3 , the boss  48  has been inserted through openings  40  and  38  for attachment of the suspension arm  21  to the actuator arm  22 . 
       FIG. 4  illustrates the suspension arm  22  and the actuator arm  21  along with the swage boss  48  and swage plate  46  prior to swaging. As shown, there is a definable gap between the exterior surface of the swage boss  48 , and the openings  38  and  40 . A swage ball  60  is forced through the opening in the swage boss  48 . The swage boss  48  opening may include a larger diameter portion  50 , a smaller diameter portion  54 , and a stepped or interconnecting portion  52 . The swage ball  60  is forced through the opening and because the diameter of the swage ball  60  is larger than portions  54  and  52 , the boss is deformed to accommodate passage of the swage ball. This deformation results in expansion of the swage boss  48  so that the exterior surface thereof is pressed in contact with surfaces  38  and  40 . Absent an applied lubricant as described herein, swaging is a harsh process that generates significant debris, due to the severe metal deformation. By lubricating the surfaces that come in contact during swaging, damage to the components is lessened and chipping or creation of metal debris is reduced. The swaging process can also impart a bend or curve into the actuator arm thereby altering its performance. The lubrication described herein also reduces the forces that tend to distort the actuator arm and help maintain the actuator arm within its design criteria. 
     During a deswaging process to separate the actuator arm from the suspension arm, a forcing implement or tool (not shown) presses the swage boss  48  back through the openings defined by surfaces  38  and  40 . This forcing action can also result in damage to the actuator arm and suspension arm, and therefore can result in disk drive contamination due to particles generated by chipping and other material failures. By lubricating the surfaces that come in contact during swaging, torque retention values are reduced, which provides better predictability in application of a load to deswage the actuator arm from the suspension arm. This predictability can therefore prevent overloading, underloading, and multiple loading attempts to deswage. Accordingly, there is less of a chance that damage will occur to the suspension arm and actuator arm. 
     Various methods are contemplated in applying the lubricating film. Additionally, it is also contemplated that application of the lubricating film can be conducted prior to attaching the swage plate to the suspension arm, as well as selected application of the lubricant to different components. 
     One method in which to apply the lubricant film is to first attach the swage plate  46  to the base portion  41  of the suspension arm  21 , immerse the entire base portion  41  in a dilute solution of the FC 722 (for example, a 1.0% fluorine containing polymer in 99.0% PF 5060 fluorocarbon solvent), and then drain away the dilute solution from the base portion  41  at a preselected, constant rate (for example, 200 mm/sec) leaving a uniform film of the polymer on the surfaces of the base portion  41 . Of course, the surface which is desired to be coated is the outer surface of the swage boss  48  which will inherently become coated by dipping of the base portion  41 . Increasing or decreasing the drain rate and adjusting the concentration of the coating solution will determine the thickness of the coating applied. As mentioned above, it has been found that a polymer film having a thickness ranging from 20 to 175 angstroms is adequate and, in the case of solid films, a lubricant having a thickness ranging from 20 to 2700 angstroms is adequate; however, thinner or thicker films can be applied as desired, including a layer one molecule thick. An additional advantage of utilizing a fluorocarbon solvent is the cleaning effect upon the components. Application of the thin film lubricant can be conducted in a two step drain process, with the first step providing solvent cleaning and an initial coating, and the second step providing the final desired thickness of coating. 
     Another method in which to coat the components would be to only immerse the swage plate  46  and boss  48 , prior to attaching the swage plate to the suspension arm. In this method, there would be no film lubricant applied to any surfaces of the suspension arm. This method may be preferred if it is desired to also limit the components of the disk drive subject to coating. Alternatively, the inner face or wall  38  of the actuator arm  22  may be coated with the film lubricant to provide the desired lubrication. Accordingly, the distal end of the actuator arm  22  may also be immersed in a dilute solution of the FC 722, or any other acceptable polymer or solid film. Examples of such include thin films formed from organic sulphurs, organic phosphorus, oxygen containing organics (such as carboxylic, esters and alcohols), nitrogen containing organics, organic boron compounds and metal containing compounds. 
     Depending upon the type of materials making up the actuator arm and suspension arm, as well as desired torque out retention-values, it is also contemplated that one may select only the inner face  38  to be lubricated, only the outer surface of the swage boss  48  to be lubricated, or both surfaces may be lubricated. 
     In addition to immersing, other methods of applying the lubricant are also contemplated for each of the components to include localized spraying, and the various deposition processes listed above. 
     An unexpected result of lubrication of the swage contact surfaces is that gram load uniformity was also improved. As understood by those skilled in the art, gram load uniformity refers to the normal load placed on the disk by the suspension elements of the actuator assembly (i.e., the suspension arm, and complimentary elements). It is desirable to have gram load uniformity among each of the actuator assemblies in a disk drive. Gram load uniformity affects a number of disk drive operation variables, to include fly height of the read/write heads. It is believed that by lubricating the swage contact surfaces by a solid lubricant, the lubricant minimizes deleterious effects which the swage process may impart upon the structure of the actuator arm and suspension arm, thus improving gram load uniformity. 
     Coating the swage contact surfaces with a thin film lubricant enhances the deformation characteristics of the swage boss, facilitates reduction in the retention torque, and provides better consistency in torque out retention values. Each of these attributes contributes in reducing chipping and other potential material failure of the swage contact surfaces. Because of the many methods available in applying thin film lubricants, many options are available for application of the lubricant. Additionally, one or more selected surfaces may be lubricated to achieve desired results. 
     This invention has been described with respect to a particular disclosed embodiment; however, it will be understood that various other modifications can be made which fall within the spirit and scope of this invention.