Abstract:
The present invention provides a system, method and apparatus for controlling the coverage of an adhesive bond area between a suspension and a flex circuit interconnect by etching an area of the suspension to create a bonding area. The etching process prevents bonding of the flex circuit interconnect to the suspension in a tail and a side region allowing movement between the flex circuit and suspension, wherein the movement dampens a first torsion resonance mode. Better control of the bonding area between the interconnect and the suspension using the “adhesive down” helps reduce the variation in the roll stiffness of the suspension thereby reducing the fly height variation.

Description:
RELATED APPLICATIONS 
     This application claims priority of U.S. provisional application Ser. No. 60/176,516 filed Jan. 13, 2000. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a suspension system and, more particularly, a suspension system having partial etched areas to limit and control the adhesive coverage between a flex circuit interconnect and the suspension. 
     BACKGROUND OF THE INVENTION 
     Today the demand for high performance, low cost and nonvolatile information storage systems is ever increasing. There are a variety of information storage systems with varying degrees of development and commercialization, including magnetic tape drives, magnetic hard disc drives, magnetic floppy disc drives, magnito-optic (MO) disc drives, phasechange optic disc drives, semiconductor flash memory, magnetic random access memory (RAM), and holographic optical storage. To date, magnetic information storage technology, (hard disc, floppy disc and tape drives) is most widely used. 
     Direct access storage devices (DASD), or disc drives, store information on concentric tracks of an erodable magnetic recording disc. A magnetic head or transducer element is moved from track to track to record and read the desired information. Typically, the magnetic head is positioned on an air bearing slider which flies above the surface of the disc as the disc rotates. A suspension assembly connects the slider to a rotary or linear actuator. The suspension provides support for the slider. 
     The suspension must be flexible and provide a biased force in the vertical direction. This is necessary to provide a compensating force to the lifting force of the air bearing in order to keep the slider at a correct height above the disc. Also, the vertical flexibility is needed to allow the slider to be loaded and unloaded away from the disc. Further, the suspension must be rigid in the lateral direction. This is needed to prevent the head from moving from side to side, which will result in the head reading the wrong track. Further yet, the suspension must have a frequency response that satisfies the requirements of a disc drive system. A desirable frequency response consists of resonances high in frequency and low in gain. The present suspension systems typically use flanged load beams which exhibit undesirable low frequency bending, and sway modes. This is especially true where the flange height of the suspension is relatively small. 
     Systems employing dampening methods have been in use for quite some time. Several such dampening methods are disclosed in Pal et al., U.S. Pat. No. 4,760,478; Erpelding et al., U.S. Pat. No. 5,781,379, and Gifford et al., U.S. Pat. No. 5,483,397. However, the problem with all of these methods is that the use of adhesive is not confined to a predetermined area and may not aid in dampening of a first torsion resonance mode. 
     Resonance is inherent in mechanical structures. The impact of resonance must be minimized in disc drives. A resonance mode may be caused by the high speed rotation of the discs, actuation of the suspension using the coil motor, and air disturbances, created by high spinning disc speeds, against the suspension. Whenever these resonance modes become excited, they cause large gains or high offsets of the slider thereby causing a loss of a signal. A head-gimbal assembly (HGA) first torsion mode mechanical resonance results in significant drive level yield loss. HGA roll stiffness variation is a significant contribution to fly height sigmas in disc drives, which in turn directly impacts the drive yield. Reduction in roll stiffness variation is critical to reduction of fly height sigmas. Both of these issues have been attributed to an excessive bonding area between the flex circuit interconnect and the suspension in the HGA. 
     HGA&#39;s of the prior art are designed without adhesive control features. An adhesive used to bond the interconnect to the suspension is dispensed in an etched area of the suspension until it is full. Because there are no adhesive control features, in many cases the adhesive overflows into unwanted areas such as in a “forward glue dot” area thereby bonding the flex circuit interconnect in this unwanted area. Further, the adhesive being used usually is a high viscosity material. Thus, bonding the flex circuit interconnect in the forward glue dot area results in increased roll stiffness of the HGA which directly impacts its fly height performance in the drive. 
     Present suspension systems have a problem in achieving low enough pitch and roll stiffness for the air bearing flying height tolerances while at the same time achieving high enough lateral stiffness to prevent relative motion between the slider and the supporting end of the suspension. Some sliders may even attempt to compensate for irregularities in manufacture and operation by pitching and/or rolling slightly to maintain the air bearing. 
     However, the current suspension design and the lack of adhesive control allow for very poor control of the flex circuit interconnect/suspension bonding area. This results in the adhesive being dispensed on the suspension in the “forward glue dot” area of the suspension resulting in a higher roll stiffness. Also, the first torsion gains are increased due to the increased amount of interconnect to suspension bonding which in turn reduces the vibrations of the unbonded portions of the interconnect. These vibrations are effective in dampening the suspension vibrations in the first torsion resonance mode. 
     It can be seen that there is a need to reduce the first torsion gains in a suspension system. 
     It can also be seen that there is a need to limit and control the adhesive coverage between the flex circuit interconnect and the suspension. 
     SUMMARY OF THE INVENTION 
     To overcome the limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention generally discloses a suspension system and, more particularly, a suspension system having an adhesive control feature. 
     The present invention solves the above-described problems by limiting and controlling the bonding area between the flex circuit interconnect and the suspension thereby reducing gains in the first torsion resonance mode and reducing roll stiffness. 
     A method in accordance with the principles of the present invention provides a bonding surface located on a first side of the suspension. An etched area surrounding the bonding surface, wherein the etched area is recessed with reference to the bonding surface. 
     The bonding area between the flex circuit interconnect and the suspension terminates at the etched portion of the suspension. This bonding area terminates because the flex circuit interconnect does not contact the bonding surface of the suspension in the etched areas. These etched areas are generally referred to as adhesive dams. 
     Other embodiments of a system in accordance with the principles of the invention may include alternative or optional additional aspects. One such aspect is to create a bonding surface having a cross-shaped area and island-shaped area located towards a center area of the suspension. Further, the suspension includes an etched area creating a forward dam located remotely from the bonding area. The suspension also prevents bonding of the flex circuit interconnect to the suspension in a tail and a side region allowing movement between the flex circuit and suspension, wherein the movement dampens a first torsion resonance mode. In addition, adhesive bonding in specific areas may decrease the rigidity of the suspension and roll stiffness of a head-gimbal assembly. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a top view of a suspension system in accordance with a preferred embodiment of the present invention. 
     FIG. 2 is a side view of the system shown in FIG.  1 . 
     FIG. 3 illustrates a top view of a prior art design of an HGA without adhesive control features. 
     FIG. 4 illustrates the HGA shown in FIG. 3 with a non-uniform adhesive coverage according to the prior art design. 
     FIG. 5 illustrates one embodiment of adhesive control features on the suspension in accordance with a preferred embodiment of the present invention. 
     FIG. 6 illustrates a flex interconnect circuit bonded to the suspension of FIG. 5 in accordance with a preferred embodiment of the present invention. 
     FIG. 7 illustrates the standard suspension design without adhesive control features of FIG.  3 . 
     FIG. 8 illustrates one embodiment of a suspension design with an “crosspattern” adhesive control feature in accordance with the present invention. 
     FIG. 9 illustrates a preferred embodiment of a suspension design with adhesive control features in accordance with the present invention. 
     FIG. 10 illustrates a comparison of the first torsion gain variance for three designs, one without any adhesive control feature and the other two designs having different adhesive control features. 
    
    
     DETAILED DESCRIPTION 
     In the following description of various preferred embodiments of the invention, reference is made to the accompanying drawings in which like reference numerals represent like parts throughout the drawings. It is to be understood that embodiments other than those described herein may be utilized. Accordingly, structural and functional modifications may be made without departing from the scope and spirit of the present invention. 
     The present invention provides a system for a suspension and, more particularly, a suspension system having partial etched dams to limit and control the adhesive control feature to control the bonding area between the flex circuit interconnect and the suspension. 
     If the bonding area between the suspension and flex circuit interconnect is reduced and better controlled, it results in reduced gains in first torsion resonance mode of the head-gimbal assembly (HGA). This is because the rubbing of the unbonded flex circuit interconnect against the suspension results in reduced gains in the first torsion resonance mode. In addition, reduced roll stiffness variation is realized when the adhesive does not encroach on the HGA (therefore reducing fly height variation). This is accomplished by an innovative design of an etched feature in the suspension in conjunction with the use of a commercial adhesive such as EMCAST712-5K from Electronic Materials, Inc. of St. Peters, Mo. EMCAST712-5K is a low viscosity adhesive providing a less rigid bond between the flex circuit and the suspension. 
     FIG. 1 illustrates a top view of a magnetic disc drive suspension system  100  in accordance with a preferred embodiment of the present invention. A magnetic disc drive is mainly composed of four components, a slider  5  on which a read/write head (not shown) is mounted, a disc  25 , a spindle  15  and a suspension  10 . Each write/read head (not shown) is located on the trailing edge of the slider  5 . The slider  5  is mounted to the end of the suspension  10 , forming a so-called HGA. Data detection electronics and a write circuit may be located on a printed circuit board (not shown) with many very large scale integration (VLSI) chips. A mechanical server and control system, including spindle  15 , actuators, suspensions  10 , and control chips are used to position the slider  5  over a data track  20  on the disc&#39;s  25  recording surface. A microprocessor interface is located at one edge of a printed circuit board (now shown). The microprocessor interface provides a path to the disc drive for I/O (input/output) information. 
     FIG. 2 is a side view of the system shown in FIG.  1 . It illustrates the operation of the head disc assembly which is based on a self-pressurized air bearing  30  between the slider  5  and the spinning disc  25 , which maintains a constant separation, called the fly height  40 , between them. By positioning the head-slider along the radial direction, different data tracks can be read from or written to the disc  25 . 
     FIG. 3 illustrates a top view of a prior art design of an HGA without an adhesive control feature. The suspension has an etched area  230  that is trapezoidal in shape. The etched area  230  is recessed compared to the area of suspension around the etched area  230 . A flex circuit interconnect  210  is coupled to the suspension  10  through an adhesive disposed in the etched area  230  of the suspension  10 . The flex circuit interconnect  210  is used to couple the read/write head (not shown) located at the end of the slider to the electronics of the drive. The adhesive is dispensed in the etched area  230  of the suspension  10  until it is full. The flex circuit interconnect is then laid on the suspension and pressure is applied to bond the interconnect to the suspension. This pressure usually causes the adhesive to overflow outside the etched area  230  bonding the flex circuit interconnect  210  in unwanted areas. The adhesive being used may be of a high viscosity material and does not flow readily. The interconnect needs to be bonded down again in the forward glue dot area  225  to keep it below the rails of the suspension  245 . Bonding the flex circuit interconnect  210  in the forward glue dot area  225  results in increased HGA roll stiffness which directly impacts its fly height performance in the drive. 
     FIG. 4 illustrates the HGA shown in FIG. 3 with a non-uniform adhesive coverage according to the prior art design. Shown in gold is the flex circuit interconnect  210 . An adhesive is disposed in the etched area  230  of the suspension located under the flex circuit interconnect. The adhesive coverage is not uniformly distributed, i.e., its thickness and coverage are not uniform when dispensed in the etched area  230 . 
     The flex circuit interconnect is thus bonded to the suspension  10  over a large area. This results in increases in torsion gains because of the large bonding area which in turn reduced the vibration of the unbonded portions of the interconnect. 
     FIG. 5 illustrates a preferred embodiment of adhesive control features on a suspension  10  in accordance with the present invention. The invention introduces a structure in the suspension to physically control the adhesive coverage between the suspension  10  and a flex circuit interconnect  210 . More particularly, a cross-pattern  220  is etched into the suspension. The cross-pattern  220  defines the bonding area of the suspension. Bonding does not occur in the portion surrounding the cross-pattern  220 , e.g., since the etched areas  230  are recessed compared to the cross-pattern  220 . The etched areas  230  act as dams and prevent the adhesive from migrating outside of the etched areas towards the tail region (preload bend region)  235  and towards areas of the suspension rails  245  that should not be bonded. The suspension rails  245  are bent up portions of the suspension  10 , and are bent up perpendicular to the plane of the suspension  10 . The suspension rails run lengthwise along each side of the suspension  10  between the rail region  235  and the head area  240 . The dam  280  is etched in a forward portion of the suspension and extending between the side rails  245 . The forward dam  280  prevents the bonding of the flex circuit  210  in the front of the suspension towards the gimbal  250  (in the head area  240 ) thereby reducing roll stiffness of the HGA  290  and improving fly height performance in the drive. The overall uniformity (i.e. consistency) of the bond coverage reduces roll stiffness variation and thus the fly height variation in the drive. 
     Overall, these features are designed to allow optimum bonding of the flex circuit interconnect  210  to the suspension  10  such that the area of the flex circuit interconnect  210  that is bonded to the suspension  10  is limited and strategically positioned. This limitation provides gain reduction in the first torsion resonance mode and, at the same time, prevents the flex circuit interconnect  210  to be raised above the suspension rails  245  and effected by forces such as air movement created by the spinning disc. For example, the resonance in the suspension  10  may cause the flex circuit interconnect  210  to rise and fall in areas where the flex circuit interconnect  210  is not bonded to the suspension  10 . When the flex circuit interconnect  210  rises, it may rise higher than the suspension rails  245  and is disturbed by the air movement created by the spinning disc. 
     FIG. 6 illustrates a flex circuit interconnect bonded to the suspension of FIG. 5 in accordance with a preferred embodiment of the present invention. A low viscosity adhesive is placed on the cross-pattern  220  surface and flows substantially uniformly over the cross-pattern  220  surface up to forward dam  280 . Excessive adhesive may flow into the etched areas  290 , but since those areas are recessed with respect to cross-pattern  220  surface, bonding of the flex circuit interconnect  210  to the suspension  10  in those etched areas  290  is prevented. Thus the flex circuit interconnect is only bonded at certain locations. 
     To understand the resonance benefits of the reduced and more controlled bonding of the flex circuit interconnect  210  to the suspension  10 , a comparison of three designs will be described. FIG. 7 illustrates the standard suspension design without adhesive control features of FIG.  3 . The standard design provides a partial etched area  610  wherein an adhesive may be applied. In this design, the adhesive coverage is not uniformly distributed when dispensed in the partial etch area  610 , i.e., in thickness and coverage. Also, there is no control on the area over which the adhesive bonds the flex circuit interconnect  210  to the suspension  10 . 
     FIG. 8 illustrates one embodiment of a suspension design in accordance with the present invention. The adhesive control feature includes the cross-pattern design, as explained in FIGS. 5-6, etched areas  255 , and forward dam  280 . The etched area borders  255  and dam  280  limit the area where bonding between the suspension  10  and the flex circuit interconnect  210  can occur. This is accomplished by preventing the flow of the low viscosity adhesive to unwanted areas thereby bonding a larger area of the flex circuit interconnect  210  then desired. For example, when the adhesive is applied onto the cross-pattern area  220 , it will flow evenly into the etched area  230  and up into the partial etched dam  280 . It will, however, be prevented from flowing past those points. 
     FIG. 9 illustrates a preferred embodiment of a suspension design with adhesive control features in accordance with the present invention. This design, call an island pattern has an “island”  810  etched into the suspension as well as a forward dam. The island  810  is surrounded by etched area  230 . As with the other design, the forward dam and etched area  230  limit the flow of the adhesive and thus the area of the interconnect that will be bonded to the suspension. 
     The designs of FIG.  8  and FIG. 9 illustrate preferred embodiments of the suspension  10  which aids in dampening of the resonance modes. This dampening is accomplished by the movement of a portion of the flex circuit interconnect  210  which is not bonded to the suspension  10 . In FIG. 8, the flex circuit interconnect  210  is bonded to the cross-pattern area  220  and the non-etched area between area  220  and forward dam  280 . In FIG. 9, the flex circuit interconnect  210  is bonded to the island pattern area  810  and the non-etched area between the area  810  and forward dam  280 . Preferably, a low viscosity adhesive is used which displays elastic characteristics that aid in the dampening of the resonance modes. 
     To understand the resonance performance of the different designs of suspensions, a plurality of HGAs of each of the above designs was tested on a bode tester, such as a HRT-1 bode tester (harmonics resonance test machine), for z-heights varying from 0.0145″ to 0.0405″ in 0.002″ increments. The graph in FIG. 10 compares the average first torsion gain variation  910  with z-height  920  for the designs shown in FIGS. 7-9. The z-height  920  is dictated by the spacing between the sliders  5  in a multiple disc system. 
     The gain  910 , as described by the graph  905 , is a normalized displacement at the head area  240  of the suspension  10  with respect to the displacement at the tail area  235 . This movement may be described as the amount of motion the slider  5  is experiencing as a result of the excitation at the tail area  235  of the suspension. The goal is to make the resonance gain  910  as low as possible. High gain causes the read/write head  35  to move away from the disc  25  thereby interrupting the read/write process. 
     The error bars  930 ,  935  on each of the curves show the standard deviation about the mean  940  of the corresponding z-height  920 . The standard design shown in FIG. 7 has the highest first torsion gains among the three designs tested. The gains for the standard design  950  are significantly higher than those of the cross-pattern  960  shown in FIG.  8  and island pattern  970  shown in FIG. 9 designs for all z-heights  920  greater than 0.0265″ (based on a 95% confidence interval). The island pattern design  970  exhibits the best performance with the lowest gains (significantly lower than those of the cross-pattern design  960  based on a 95% confidence interval) for all designs greater than 32.5 mils. The island pattern design  970  also has the lowest standard deviations of the gains for all z-heights  920 . Therefore, the graph  905  shows that the gain is reduced by the movement of the unbonded FOS (flex-on-system) movement of the flex circuit interconnect  210  relative to the suspension  10  in relation to the suspension. 
     While the adhesive control feature has been illustrated as either a cross-pattern or island etched into the suspension, other shapes such as circles, ovals, T-shape, etc., may be etched into the suspension to provide adhesive control. 
     It will be clear that the present invention is well adapted to attain the ends and advantages mentioned as well as those inherent therein. While preferred embodiments have been described for purposes of this disclosure, numerous changes may be made which will readily suggest themselves to those skilled in the art and which are encompassed in the spirit of the invention disclosed and as defined in the appended claims.