Abstract:
A dual stage actuated suspension has microactuators that are adhered to the suspension by adhesive such as epoxy. The epoxy is contained within an adhesive containment vessel defined by walls of an insulating material such as polyimide. Adhesive overflow channels are formed within the polyimide to receive and channel any excess epoxy that overflows over the polyimide wall. The channels may have increasing width to help draw the excess epoxy toward a centrally located reservoir.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from U.S. provisional patent application Ser. No. 61/829,167 filed May 30, 2013. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to the field of dual stage actuated suspensions for hard disk drives. More particularly, this invention relates to the field a dual stage actuated suspension having channels to control the overflow of adhesive used to affix microactuators to the suspension. 
     2. Description of Related Art 
     Magnetic hard disk drives and other types of spinning media drives such as optical disk drives are well known.  FIG. 1  is an oblique view of an exemplary prior art hard disk drive and suspension for which the present invention is applicable. The prior art disk drive unit  100  includes a spinning magnetic disk  101  containing a pattern of magnetic ones and zeroes on it that constitutes the data stored on the disk drive. The magnetic disk is driven by a drive motor (not shown). Disk drive unit  100  further includes a disk drive suspension  105  to which a magnetic head slider (not shown) is mounted proximate a distal end of load beam  107 . The “proximal” end of a suspension or load beam is the end that is supported, i.e., the end nearest to base plate  12  which is swaged or otherwise mounted to an actuator arm. The “distal” end of a suspension or load beam is the end that is opposite the proximal end, i.e., the “distal” end is the cantilevered end. 
     Suspension  105  is coupled to an actuator arm  103 , which in turn is coupled to a voice coil motor  112  that moves the suspension  105  arcuately in order to position the head slider over the correct data track on data disk  101 . The head slider is carried on a gimbal which allows the slider to pitch and roll so that it follows the proper data track on the disk, allowing for such variations as vibrations of the disk, inertial events such as bumping, and irregularities in the disk&#39;s surface. 
     Both single stage actuated disk drive suspensions and dual stage actuated (DSA) suspension are known. In a single stage actuated suspension, only voice coil motor  112  moves suspension  105 . 
     In a DSA suspension, as for example in U.S. Pat. No. 7,459,835 issued to Mei et al. as well as many others, in addition to voice coil motor  112  which moves the entire suspension, at least one microactuator is located on the suspension in order to effect fine movements of the magnetic head slider to keep it properly aligned over the data track on the spinning disk. The microactuator(s) provide much finer control and much higher bandwidth of the servo control loop than does the voice coil motor alone, which effects relatively coarse movements of the suspension and hence the magnetic head slider. A piezoelectric element, sometimes referred to simply as a PZT, is often used as the microactuator motor, although other types of microactuator motors are possible. 
       FIG. 2  is a top plan view of the distal end of a suspension in which the PZTs are mounted at the gimbal end of the suspension, according to a previous design by the assignee of the present application. No representation or admission is made herein that that design is “prior art” to the present application within the legal meaning of that term. In the design, a microactuator  18  such as a PZT microactuator is bonded at its proximal side to a relatively fixed portion of the suspension including the flexure, and is bonded at its distal side to stainless steel finger  12  that extends from the gimbal on which magnetic read/write head  14  is mounted. As PZT  18  expands and contracts, that expansion/contraction pivots the suspension gimbal from side to side thus effecting fine lateral movements of a transducer head  14 , which is usually a read/write head. The lateral movements of transducer head  14  constitute radial movements of transducer head  14  relative to the spinning data disk platter  101 . 
       FIG. 3  is a cross section view of the suspension of  FIG. 2 , taken along section line  3 - 3  and showing the details of how PZT  18  is mounted at its proximal end to the relatively fixed part of the suspension, and more specifically to a relatively fixed part of the flexure. The flexure includes a support layer  20  such as stainless steel, an insulating material  22 / 24  such as polyimide, and a signal conductor such as copper or copper alloy  26 . A void or gap  23  is formed in the polyimide  22 / 24 , to create what is effectively a containment vessel into which a non-conductive adhesive such as non-conductive epoxy  30  is dispensed, the non-conductive epoxy  30  being contained by first polyimide section  22  on one side, second polyimide section  24  on a second side, and stainless steel support layer  20  on the bottom. Conductive epoxy  34  is dispensed so as to form a conductive bridge from copper contact pad  26  which is part of the signal conductor layer to the top surface of PZT  18  which is metallized to constitute an electrode. Second polyimide section  24  thus forms not only one side of an epoxy containment vessel, but also acts as an insulation layer that prevents the bottom surface of PZT  18  from electrically shorting to stainless steel  20 . 
     Although it is contemplated that copper contact pad  26  will normally provide the driving voltage for PZT  18  on its top surface, and a ground potential lead (not shown) will normally be electrically connected to the bottom surface of the PZT, it is not necessary that the drive voltage is on top and the ground is on bottom. Those positions could be reversed, with copper contact pad  26  providing the ground potential to the top surface of PZT  18  and the driving voltage being connected to the bottom surface of the PZT. 
     SUMMARY OF THE INVENTION 
     The inventors of the present application have discovered that sometimes non-conductive epoxy  30  can intrude undesirably across second polyimide section  24  toward the right hand side of the figure. Enough epoxy  30  must be dispensed in order to fill in gap  23 , both because epoxy  30  performs the structural function of bonding PZT  18  to the suspension, and because epoxy  30  serves as an electrical insulator to prevent the bottom surface of PZT  18  from making electrical contact with stainless steel  20  and conductive epoxy  34  which would short out PZT  18 . Epoxy  30  can be drawn into the region above polyimide  24  by a combination of the wicking effect between the surfaces of polyimide  24  and the bottom surface of PZT  18 , too much epoxy  30  being dispensed into gap  23 , and/or PZT  18  being pressed down too far into epoxy  30  during assembly. 
       FIG. 4  is the same view as  FIG. 3 , but also showing overflowing portion  31  of adhesive  30 . Overflowing adhesive  31  extends over second polyimide section  24 , spilling onto stainless steel  20  and possible even dripping off the suspension. 
     It is advantageous to control that flow of excess adhesive  31 . Adhesive flowing too far and/or unrepeatably can degrade the static attitude attributions of the head suspension assembly, affect the dynamic resonance attributes of it, create variations in the gram load attributes in it, affect the gimbal stiffness, and degrade the stroke length of the microactuator. The inventors of the present application discovered that it can be very difficult to dispense epoxy  30  and assemble the suspension such that flow of epoxy into the region above polyimide  24  is minimized and repeatably controlled. 
     In order to address these problems, according to the invention second insulating section  24  is provided with one or more adhesive control features in the form of an adhesive overflow channel to contain and/or channel excess epoxy toward a more benign area of the suspension for that excess epoxy to be. 
     In one aspect therefore, the invention is of a dual stage actuated suspension having one or more adhesive control channels to control and/or contain flow of excess epoxy used to adhere the microactuator(s) to the suspension. The suspension has a base portion comprising a metal support layer, an insulation layer comprising an insulating material on the metal support layer, and a signal conductor layer on the insulation layer. The suspension further has a gimbaled portion on which a transducer head is mounted; a microactuator adhered to the support layer, the microactuator configured to effect fine movements of a transducer head disposed on the gimbaled portion; an adhesive containment structure, the adhesive containment structure comprising a first portion of the insulating material and a second portion of the insulating material, the second portion of the insulating material at least partially disposed underneath the microactuator, the first and second portions of insulating material being separated by a gap; and adhesive disposed within the gap, the adhesive adhering the microactuator to the support layer. The suspension further has an adhesive overflow channel formed in the second portion of insulating material, the adhesive overflow channel being configured to hold adhesive that overflows from the adhesive containment structure over a top surface of the second portion of insulating material during a process of adhering the microactuator to the support layer via the adhesive. The adhesive control channel may extend from underneath the microactuator to an area that is lateral to the microactuator on one or both lateral sides thereof. The channel may become wider in a direction in which it is desired to direct the flow of excess adhesive, including toward a longitudinal axis of the suspension, and may extend to a reservoir that is located on the longitudinal axis of the suspension. The central reservoir may be connected to both a first adhesive control channel that extends underneath a first microactuator, and to a second adhesive control channel that extends underneath a second microactuator, such that any excess epoxy from the bonding of either of two microactuators is channeled to the central reservoir. 
     Exemplary embodiments of the invention will be further described below with reference to the drawings, in which like numbers refer to like parts. The drawing figures might not be to scale, and certain components may be shown in generalized or schematic form and identified by commercial designations in the interest of clarity and conciseness. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an oblique view of a prior art disk driving having a dual stage actuated suspension. 
         FIG. 2  is a top plan view of the distal end of a dual stage actuated suspension according to a previous design by the assignee of the present application. 
         FIG. 3  is a cross section view of the suspension of  FIG. 2 , taken along section line  3 - 3 . 
         FIG. 4  is the same view as  FIG. 3 , but also showing overflowing adhesive. 
         FIG. 5  is a top plan view of the distal end of a dual stage actuated suspension according to one embodiment of the present invention. 
         FIG. 6  is a cross section view of the suspension of  FIG. 5 , taken along section line  6 - 6 . 
         FIG. 7  is the same view as  FIG. 6 , but also showing overflowing adhesive. 
         FIG. 8  is a top plan view of a suspension according to a second embodiment of the invention. 
         FIG. 9  is a top plan view of a suspension according to a third embodiment of the invention. 
         FIG. 10  is the same view as  FIG. 9 , but also showing overflowing adhesive. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 5  is a top plan view of the distal end of a dual stage actuated suspension according to one embodiment of the present invention, and  FIG. 6  is a cross section view thereof taken along section line  5 - 5 . According to one embodiment second polyimide section  24  is provided with a recess that defines an adhesive overflow channel into which excess epoxy can flow. Void  43  is defined between first polyimide wall  42  and second polyimide wall  44  that defines second polyimide section  24 . Polyimide walls  42  and  44  rise up from support layer  20  but do not rise all the way up to microactuator  18 , and extend generally transversely to the suspension. In this embodiment, adhesive overflow channel  43  takes the form of a slit, the slit extending in a generally transverse direction relative to the length of the suspension, the slit also curving at its ends in general conformance to the shape of gap  23 , the slit being of approximately uniform width through its length. Epoxy  30  defines a first mass of adhesive that adheres a first end of microactuator  18  to support layer  20 . Epoxy  30  that spills out from void  23  over the top of polyimide wall  42  and into epoxy overflow channel  43  will be captured and channeled transversely therein. Epoxy overflow channel  43  acts as both a channel and an adhesive containment structure or reservoir to transversely direct and thereby longitudinally limit the flow of excess epoxy. Channel  43  extends from underneath the microactuator  18  to an area that is not underneath the microactuator. In this embodiment, channel  43  extends from underneath microactuator  18  to areas on either lateral side of microactuator  18  that are not underneath the microactuator. 
     In a preferred embodiment, epoxy overflow channel  43  has a width that is less than 10% of the length of microactuator  18 , and more preferably less than 5% of the length of the microactuator. 
       FIG. 7  is the same view as  FIG. 6 , but also showing overflowing adhesive  31 ′ spilling into the adhesive containment vessel defined by stainless steel substrate  20  on the bottom, and polyimide walls  42  and  44  on either side. The containment vessel contains overflow adhesive  31 ′ and channels it laterally outward from the overflow location. In this context, “laterally outward” means laterally in a direction that is either toward the suspension&#39;s central longitudinal axis and/or away from that central longitudinal axis. 
       FIG. 8  is a top plan view of a suspension according to a second embodiment of the invention. In this embodiment, adhesive overflow channel  43  leads to a reservoir  50  that is wider than the channel and is located closer to the longitudinal axis L-L of the suspension than its associated PZT. Adhesive overflow channel  43  is thus in fluid communication with the reservoir  50 . In this embodiment reservoir  50  is a central reservoir that is located on the longitudinal axis L-L of the suspension, and is connected to a first adhesive overflow channel associated with the first PZT and is also connected to a second adhesive overflow channel associated with the second PZT. In this way, excess epoxy from the area of both PZTs will be channeled to central reservoir  50 . Because excess epoxy is channeled to a centrally located reservoir, the suspension will be more evenly mass balanced about the longitudinal axis than if the overflow epoxy associated with one of the PZTs all stayed on the lateral side of the suspension from which it originated. Any excess epoxy within reservoir  50  will thus be more benign from a static and dynamic mass balancing perspective, having less of an impact on the suspension&#39;s performance. 
       FIG. 9  is a top plan view of a suspension according to a third embodiment of the invention. In this embodiment adhesive overflow channels  43  are not of uniform width. Instead, the channels widen in the direction in which it is desired to direct the adhesive overflow, in this case, to a reservoir that is centrally located relative to the longitudinal axis of the suspension, and is located laterally between the two microactuators. The widths of the channels may be smoothly tapered (widening) toward the central longitudinal axis. Selectively widening and narrowing the channel allows the overflow adhesive to be more effectively channeled into a desired area, due to the surface tension of the adhesive which tends to draw the adhesive from the narrower portion(s) of the channel into the wider portion(s) of the channel. The channel geometry including the width of the channel and the angle of the channel walls relative to parallel (i.e., the transition slope of the channel) can be adjusted depending on the viscosity of the adhesive. As with the embodiment of  FIG. 8 , the central reservoir  50  is wider as the first and second channels  43  at the points that those channels extend underneath microactuators  18 . Central reservoir  50  may be at least two, three, or four times as wide as channels  43  at their widest respective points underneath their respectively associated microactuators  18  under which they extend. 
       FIG. 10  is the same view as  FIG. 9 , but also showing overflowing adhesive. Epoxy  30  that overflows from void  23  over the top of polyimide wall  42 , thus defining overflow adhesive  31 ″ is caught within epoxy overflow channel  43 . Channel  43  will stop at least a significant percentage of the excess epoxy from flowing longitudinally past channel  43 , the overflow adhesive  31 ″ instead being directed and channeled laterally, and preferably laterally inwardly toward the central longitudinal axis of the suspension, thus reducing or minimizing the affects from overflowing epoxy as discussed in the Summary of the Invention herein. 
     It will be understood that the terms “generally,” “approximately,” “about,” and “substantially,” and the like as used within the specification and the claims herein allow for a certain amount of variation from any exact dimensions, measurements, and arrangements, and that those terms should be understood within the context of the description and operation of the invention as disclosed herein. 
     It will further be understood that terms such as “top,” “bottom,” “above,” and “below” as used within the specification and the claims herein are terms of convenience that denote the spatial relationships of parts relative to each other rather than to any specific spatial or gravitational orientation. Thus, the terms are intended to encompass an assembly of component parts regardless of whether the assembly is oriented in the particular orientation shown in the drawings and described in the specification, upside down from that orientation, or any other rotational variation. 
     All features disclosed in the specification, including the claims, abstract, and drawings, and all the steps in any method or process disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. Each feature disclosed in the specification, including the claims, abstract, and drawings, can be replaced by alternative features serving the same, equivalent, or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features. 
     It will be appreciated that the term “present invention” as used herein should not be construed to mean that only a single invention having a single essential element or group of elements is presented. Similarly, it will also be appreciated that the term “present invention” encompasses a number of separate innovations which can each be considered separate inventions. Although the present invention has thus been described in detail with regard to the preferred embodiments and drawings thereof, it should be apparent to those skilled in the art that various adaptations and modifications of the present invention may be accomplished without departing from the spirit and the scope of the invention. Accordingly, it is to be understood that the detailed description and the accompanying drawings as set forth hereinabove are not intended to limit the breadth of the present invention, which should be inferred only from the following claims and their appropriately construed legal equivalents.