Abstract:
Method and apparatus is provided for controlling unwanted flow of slider bonding adhesive from the flexure tongue portion to the flexure outrigger portion including roughening the tongue portion surface opposite the slider, enclosing the locus of slider attachment fully or partially with a trough etched into the tongue portion, and increasing the depth of fluid adhesive at the locus to increase the adhesive mass and improve the bonding at the slider.

Description:
RELATED APPLICATIONS 
     This application claims the benefit of United States provisional Application Serial No. 60/088,684, filed Jun. 9, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to disk drive suspensions, and more particularly, to the bonding of the sliders in such suspensions to the suspension flexure tongues. 
     2. Related Art 
     The flexure tongue of a magnetic or magnetic-optical recording head suspensions has as one of its functions providing a surface for bonding attachment of the slider. This surface is generally flat to provide the maximum bonding surface area between the slider and the flexure tongue. In some designs, this surface also includes a dimple to provide a point of contact and a point of rotation between the flexure and the applied load supplied by the load beam. The adhesive bond between the slider and the flexure tongue is required to carry some of the loads applied to the slider by the external environment. These loads include shear, tension, compression, and bending. 
     Of these loads, three immediately test the adhesive bond. Shear (horizontal) load between the suspension and the slider is due to friction of the disk, acceleration of the slider across tracks during accessing (moving to a new radial location on the disk), and horizontal (in the plane of the disk) shock from movement of the disk drive. The tension load the slider applies to the adhesive bond joint between the slider and the flexure tongue is due to vertical shock, and liftoff, as is the bending load. Tension and shear loads are the most significant. 
     To achieve an adhesive bond between the slider and the flexure tongue, typically one or more small deposits of fluid, curable adhesive, “dots”, are applied to the flexure tongue portion of the suspension before it is moved into contact with the slider in a bonding fixture which holds the assembly in the exact correct position until enough cure of the adhesive has taken place that the assembled slider/suspension combination can be removed from the fixture safely, that is, without relative movement from the correct position. The cure is then continued without fixturing until the cure is complete. The adhesives are chosen for their low outgassing, long pot life, adhesion strength, environmental and safety compatibility, and cost. It is common to have an adhesive that will spot cure under UV light exposure, and then final cure under thermal (oven cure) process. 
     It is known to use a small hole or holes in the flexure tongue as shown in U.S. Pat. No. 5,008,768 to Carlson, Zarouri and Coon to enhance bond strength by forming a rivet-head like structure so that the adhesive will seep through the hole and form a three dimensional bond instead of a two dimensional bond. Other small holes are used to allow UV light to pass through the load beam and flexure to initiate the cure in some types of UV curing adhesives. 
     SUMMARY OF THE INVENTION 
     The requirement for increased bond strength over past requirements stems from the trend toward higher shock loads resistance, i.e. an ability to withstand more “G” forces. The requirement for higher shock load resistance is increasing as more disk drives are being designed for portable/mobile applications. 
     This requirement cannot be met by increasing the adhesive area, and thus the areal amount of adhesive, for even as higher bond strengths are needed the trend is to smaller and smaller sliders, so the bonding area available is getting smaller. 
     The decrease in size of suspensions and their components has created another difficulty beyond maintaining or increasing adhesive bond strength. The adhesive must be fluid to apply to the bonding surfaces, but should not extend into areas where its presence will interfere with the clearance between the slider/flexure tongue and other parts of the flexure such as the outrigger area or the load beam. The adhesive must be confined to its proper application area and not be permitted to flow (by drip, capillary, run, or otherwise) beyond its intended locus. Ongoing size reductions in suspension parts increase the difficulty of controlling adhesive placement since the clearance between the different parts of the assembly becomes less. Insufficient or poorly placed adhesive will cause a failure, but excess adhesive may bridge between the flexure tongue or slider, its intended locus, and the flexure outrigger or other part of the assembly causing a failure of a different sort. 
     Under ideal conditions the bond strength between a slider and flexure tongue will be as high as about 3000 psi. A typical pico or 30% slider provides about 0.002 square inches at most available for bonding. With a 3000-psi adhesive, a slider to flexure tongue bond strength of a maximum of 6 pounds is possible. This is equivalent to several thousand “G”s, and more than sufficient for the applications presently known. Nonetheless, pico slider adhesion sometimes fails, with fatal results to the assembly and a lowering of yields. 
     It is an object therefore of the present invention to provide improvements in the bonding of slider to flexure tongues. It is a further object to provide more secure bonding through increases in bond adhesive mass, confinement of the adhesive in the proper locus, and texturing of the bonding surface opposite the slider. It is a further object to control the flow paths of the adhesive to prevent bridging between the tongue and flexure outriggers. Still another object is to increase the apparent length of the tongue edges adhered to the slider for additional bonding improvement. 
     These and other objects of the invention, to become apparent hereinafter are realized in basic form by imposing a partial etch pattern on the bonding side, that is the slider-facing side of the flexure tongue to increase the contact area available for the adhesive by roughening it. The etching also serves to diminish or prevent capillary flow of the adhesive toward areas where it is not desired. The area of the flexure tongue where the dimple force is applied on the far (non-slider) side is not etched or otherwise changed so that the contact area of the dimple is as smooth, flat, and stiff as possible. In addition, in a further embodiment, the perimeter of the flexure tongue is increased with etch-formed fingers such that the adhesive will flow across the fingers for increased adhesion but not flow out from the tongue area to the opposing outriggers. 
     In particular, the invention provides a disk drive suspension flexure and slider assembly, the flexure comprising an outrigger portion and a tongue portion, the tongue portion having a slider-attaching surface extending in a surface plane, the slider being fluid adhesive-attached to the tongue portion at a predetermined attachment locus on the tongue slider-attaching surface, the slider-attaching surface being surface-etched in surface roughening relation opposite the slider in slowing relation to fluid adhesive flow from the attachment locus. 
     In this and like embodiments, typically, the etched slider-attaching surface and the slider are substantially coextensive, and the slider-attaching surface is etched below the surface plane to increase the mass of fluid adhesive at the slider and the strength of the adhesive bond. 
     In a further embodiment, the invention provides a disk drive suspension flexure and slider assembly, the flexure comprising an outrigger portion and a tongue portion, the tongue portion having a slider-attaching surface extending in a surface plane, the slider being fluid adhesive-attached to the tongue portion at a predetermined attachment locus on the tongue slider-attaching surface, the slider-attaching surface being surface-etched below the surface plane opposite the slider and at least partially circumferentially of the attachment locus in trough-forming relation against fluid adhesive flow beyond the trough. 
     In this and like embodiments, typically: the trough is of uniform depth throughout its length; the trough has a roughened surface for slowing flow of adhesive fluid therethrough; the trough extends fully circumferentially about the attachment locus; the trough defines a repository for the fluid adhesive, whereby the adhesive is locally of a depth greater than the distance between the slider and the surface plane for increased strength in adhering the slider and the attachment surface together; and/or the tongue portion has a perimeter, the tongue portion perimeter being repeatedly reversely deflected for increased perimeter length over a given length of tongue for enhanced adhesion of the fluid adhesive to the tongue portion. 
     In yet another embodiment, the invention provides a disk drive suspension flexure and slider assembly, the flexure comprising an outrigger portion and a tongue portion, the flexure tongue portion having a slider-attaching surface extending in a surface plane, the slider being fluid adhesive-attached to the tongue portion at a predetermined attachment locus on the tongue portion slider-attaching surface, the attachment locus being surface-etched opposite the slider in fluid adhesive-containing relation. 
     In this and like embodiments, typically: at least one section of the attachment locus is etched below the surface plane in fluid adhesive receiving relation to increase the depth of adhesive to greater than the distance between the slider and the surface plane; the etched attachment locus section has a roughened surface for slowing flow of fluid adhesive in the section; the etched attachment locus section defines a recess extending normal to the surface plane and adapted to receive and retain fluid adhesive in slider-adhering relation; the recess has in a plane parallel to the surface plane a circular or polygonal shape in cross-section; the recess in a plane parallel to the surface plane is cruciform in shape; and/or the recess in a plane parallel to the surface plane has in cross section the shape of a geometric figure of from three to six sides. 
     In a further embodiment, the invention provides a disk drive suspension flexure and slider assembly, the flexure comprising an outrigger portion and a tongue portion, the tongue portion having a slider-attaching surface extending in a surface plane, the slider being fluid adhesive-attached to the tongue portion at a predetermined attachment locus on the tongue slider-attaching surface, the slider-attaching surface being surface-etched in recess-defining relation within the attachment locus and surface etched beyond the attachment locus in trough-forming relation against fluid adhesive flow beyond the trough. 
     In its method aspects, the invention provides the method of assembling a slider and a flexure having an outrigger portion and a tongue portion having a surface opposite the slider and defining an intended attachment locus for the slider, including etching the tongue portion opposite the slider to form a fluid adhesive receptacle, depositing fluid adhesive onto the attachment locus, and containing the fluid adhesive within the etched portion of the tongue portion against contact of the fluid adhesive with the flexure outrigger portion and to increase locally the depth of the adhesive. 
     In this and like embodiments, typically, there is further included etching the fluid receiving receptacle to a depth below the surface of the tongue portion within the attachment locus to increase locally the depth of the adhesive, etching a roughened surface into the tongue beyond the attachment locus against flowing contact of the fluid adhesive with the flexure outrigger portion, and/or etching a fluid adhesive recess into the tongue inward of the etch-roughened surface and within the attachment locus to increase locally the depth of the adhesive. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be further described in connection with the attached drawings in which: 
     FIG. 1 is a PRIOR ART Figure showing a bonded slider and tongue in which the adhesive is bridging the gap between the tongue and the outrigger portion of the flexure; 
     FIG. 2 is an exploded view of a flexure tongue and slider combination according to the invention; 
     FIG. 3 is a side elevation view thereof; 
     FIG. 4 is bottom plan view of the bonded tongue and slider in one embodiment; 
     FIG. 5 is a view like FIG. 4 of a different embodiment of the invention; 
     FIG. 6A is a view like FIG. 4 of a different embodiment of the invention; 
     FIG. 6B is a view taken on line  6 B in FIG. 6A; 
     FIG. 6C is a view taken on line  6 C in FIG. 6A; 
     FIG. 7A is a view like FIG. 6A of a different embodiment of the invention; 
     FIG. 7B is a view taken on line  7 B in FIG. 7A; 
     FIG. 7C is a view taken on line  7 C in FIG. 7A; 
     FIG. 8 is bottom plan view of a different embodiment of the invention; 
     FIG. 9 is a view like FIG. 8 of a different embodiment of the invention; 
     FIG. 10 is an isometric view of a slider tongue assembly in which the tongue has a reversely deflected perimeter edge. 
    
    
     DETAILED DESCRIPTION 
     With reference now to the drawings in detail, In FIG. 1 the PRIOR ART suspension assembly  1  comprises a load beam  2 , a flexure  3  carried by the load beam, a flexure tongue  4  cantilevered from the outrigger portion  5  of the load beam. A slider  6  is glued to the flexure tongue  4  by adhesive  7 . The adhesive is shown somewhat exaggeratedly as overflowing the intended gluing area  8  and entering he gap  9  between the tongue  4  and the outrider portion  5 . This bridging of the adhesive will interfere with the proper operation of the suspension. The adhesive area may be adequate if the thickness of adhesive is sufficient, but the present invention improves on the mass or adhesive  7  used for bonding by etching the smooth tongue surface opposite the slider  6  and provides means of capturing the adhesive in its proper place. 
     In FIGS. 2 and 3, the disk drive suspension comprises the load beam  10  and the flexure  12  fastened to the load beam generally opposite the dimple  13 . The flexure  12  comprises outrigger portions  14 ,  16  joined at their distal ends  17 ,  19  to vertically offset flexure terminal portion  18  and a central flexure tongue portion  22  cantilevered from the flexure terminal portion to extend between the vertical planes of the outrigger portions of the flexure. Slider  24  containing the magnetic or magneto-optical head (not shown) is fixed to the surface  26  of the flexure tongue portion. A mass of adhesive  28  shown representationially as a solid flat mass but actually applied as a fluid mass, fixes the slider  24  to the tongue portion surface  26 . 
     The tongue portion surface  26  is modified as shown in FIG. 2, and in subsequent Figures to be described, by defining at the proposed locus  30  of slider attachment one or more adhesive flow control elements including inner rectangular trough  32 , outer rectangular trough  34 , each generally circumferentially distributed about the attachment locus  30 , and etched surfaces  36  in these troughs or elsewhere on the tongue surface  26  which act to slow adhesive flow through the troughs or across the tongue surface. 
     In FIGS. 4 and 5, the size relationship of the slider  24  to the adhesive mass  28  is depicted. In general both the size of the slider  24  and the adhesive locus are variable to accommodate different design requirement. There may be excess width or excess length of slider or both in a given assembly of a slider and tongue, but every assembly will have an overlapping area, an area of registration between the slider  24  and the opposing surface  26  of the tongue portion  22 , which area usually less a perimetrical margin  27  is termed the attachment locus  30  herein. Thus, in FIG. 4, the tongue portion  22  defines an attachment locus  30  which is central to the tongue portion and central to the slider  24 , with the slider profile extending laterally of the locus on either side and longitudinally thereof in both front and rear. Within the attachment locus  30  an area is crosshatched to represent the adhesive mass  28  which is generally coincident with a surface-etched portion of the tongue  22 . The etching is carried out in the manner of etching load beams generally in the art by applying a suitable etchant to an unmasked surface portion corresponding to the locus  30  and etching until there is a surface roughening tangible to the touch and visible but not necessarily to any measurable depth into the surface  26 . This level of surface roughening is sufficient to limit the rate of flow of the fluid adhesive across the surface  26  in the etched areas, and serves to limit out-of-bounds flow of the adhesive, concentrating the adhesive mass  28  in the intended area FIG. 5 shows a different profile relationship between the slider, the attachment locus  30  and the adhesive mass  28 . There the adhesive mass  28  extends beyond the distal end  38  of the slider  24 . This arrangement will produce a fillet  42  at tg distal end that improves the bonding of the slides  24  to the surface  26  and moderately increases the amount of adhesive mass  28 . 
     In FIGS. 6A,  6 B and  6 C the use of combined troughs and surface roughening is shown. Load beam  10  supports flexure  12  by its outrigger portions  14 ,  16 . Flexure tongue portion  22  is cantilevered from the flexure distal end  18  as in the previous embodiments. Tongue portion surface  26  is etched to define generally opposite the slider  24 , and within the attachment locus  30  a series of congruent, closed-figure. rectangular troughs including inner trough  32  and outer tough  34 . Troughs  32 ,  34 , serve to trap and limit outward adhesive flow so as to slow such flow and to contain any excess amount beyond that desired in the bonding process. The width of each or both of the troughs  32 ,  34  or similar additional troughs (not shown) is not narrowly critical and will be such that etch-formation of the trough is feasible, and the fluid adhesive being used will flow ilto the trough and remain therein. The depth of the troughs  32 ,  34  is not narrowly critical either and will be such that etch-formation is feasible, and the fluid adhesive being used will flow into and be retained therein. A uniform width and depth of trough will be usefull in forming a rib  44  of adhesive of suitable cross-section, and more readily gauging the amount adhesive mass provided and is preferred herein. The spacing of the inner rough  32  from the outer trough  34  defines the tongue portion rib  46  whose sides  48 ,  52  and top face  54  lend bonding area and greater bond strength. See FIG.  6 B. The configuration of tongue portion rib  46  is not narrowly critical and will be selected to maximally increase bonding of the slider  24  to the tongue portion  22  without substantial adverse effect elsewhere in the system. As previously noted, it is preferred to maintain in the troughs  32 ,  34  a roughened surface  56 ,  58  such as above described as being obtained for the etching process to promote adhesion of the cured adhesive, and to control the rate of flow of the uncured, fluid adhesive in forming the adhesive mass  28  so as to fill the troughs but not more with adhesive. See FIG.  6 C. 
     FIGS. 7A,  7 B and  7 C in which like parts have like numerals to FIGS. 1-6, the tongue portion  22  is provided, by etching, with an illustrative variety of trough configurations, including in cross section in a plane parallel to the tongue portion surface  26  circular shape troughs  62 , and polygonal shaped troughs  64 ,  66 , cruciform shaped troughs  68 , and combinations of these figures such as a ribbed trough  72 . In each instance, the individual width and depth dimension, the pattern of shape, the proximity of one shape to another all can be varied to provide not only anchors for the fluid adhesive when cured but flow control through the reception of the flowing adhesive in one or more troughs. Sec FIG. 7 b  and C. As in the FIG. 6 embodiment, the trough bottom  73  and side walls  75  too if desired are roughened during the etching process for increased adhesion and increased resistance to flow of fluid adhesive. 
     FIGS. 8 and 9 illustrate a further feature of the invention. In FIG. 8 the perimeter  74  of the tongue portion  76  is repeatedly reversely deflected to form fingers  78  which increase greatly the perimeter edge  82  and thus the bonding surface available and the level of bonding strength obtain. The fingers  78  are formed by etching and can be surface-etched. In FIG. 9 the tongue portion  22  is again repeatedly reversely deflected, this time to form inlets  84  between peninsulas  86  with the same effect of increasing the length of the tongue portion perimeter  82  and affording better bonding. See FIG. 10 where the pattern of fluid adhesive distribution in, on and around the inlets  84  and peninsulas  86  is depicted. The adhesive mass  28  tends to incorporate the tongue portion edge in the mass and thus a stronger bond is formed. 
     The several described treatments of the tongue portion  22  all tend to limit the flow of fluid adhesive, and positively prevent adhesive flow across the gap  90 , and resultant interference of the adhesive with the proper operation of the flexure. 
     The invention thus provides improvements in the bonding of slider to flexure tongues, affording more secure bonding through increases in bond adhesive mass, confinement of the adhesive in the proper locus, and texturing of the bonding surface opposite the slider. Moreover, the invention controls the flow paths of the adhesive to prevent bridging between the tongue and flexure outriggers, and increases the apparent length of the tongue edges adhered to the slider for additional bonding improvement. The foregoing objects are thus met.