Patent Publication Number: US-10783908-B1

Title: Microstructure patterned surfaces for integrated lead disk drive head suspensions

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a division of U.S. patent application Ser. No. 13/690,883, filed Nov. 30, 2012, entitled, MICROSTRUCTURE PATTERNED SURFACES FOR INTEGRATED LEAD DISK DRIVE HEAD SUSPENSIONS, now U.S. Pat. No. 9,361,915, issued Jun. 7, 2016, which claims the benefit of U.S. Provisional Application No. 61/630,007, filed Dec. 2, 2011 and entitled Microstructure Patterned Surfaces For Integrated Lead Head Suspensions, both of which are herein incorporated by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     The invention is an integrated lead or wireless head suspension or component, such as a flexure, having textured surfaces on the conductor layer, insulating layer and/or cover layer. 
     BACKGROUND OF THE INVENTION 
     Disk drive integrated lead head suspensions having a spring metal base layer, an insulating dielectric layer and conductor elements, such as traces or leads and electrical bond or termination pads, in a conductor layer are known and disclosed, for example in the Komatsubara et al. U.S. Pat. No. 6,841,737 and the Shiraishi et al. U.S. Pat. No. 6,891,700. These devices generally include a flexure mounted to a spring metal load beam. The flexure typically includes a spring metal layer with a plurality of conductors, leads or traces extending between terminal pads on opposite ends of the flexure. A layer of insulating material separates the traces from the underlying spring metal layer. A cover layer may be formed over portions of the traces so as to extend from the insulating layer up over the tops and sides of the traces. 
     Subtractive and/or additive processes can be used to manufacture these devices. Subtractive manufacturing processes as disclosed in, for example, the Bennin et al. U.S. Pat. No. 5,839,193 use photolithography and etching processes to form the flexure from laminate material stock having a spring metal layer and conductor layer separated by an insulating layer. Additive manufacturing processes as disclosed, for example, in the Matsumoto et al. U.S. Pat. No. 5,666,717 use photolithography, deposition and etching processes to add the insulating layer, conductor layer and other structures to the spring metal layer. 
     In one example of an additive manufacturing process, a photoimageable insulating layer (e.g., polyimide or other polymer) is deposited onto the spring metal base layer. A photolithography process is then used to pattern the insulating layer. Conductive elements such as traces and terminal pads are subsequently deposited onto the patterned insulating layer. In this manner, the deposited conductor elements follow the contour and surface topography of the patterned insulating layer. An insulating cover layer may subsequently be deposited onto certain areas of the conductor elements. Specific regions of the insulating layer may be removed such as by etching or other processes to expose both surfaces of the conductor layer to create, for example, flying termination leads, head termination pads or flying gimbal leads. The exposed surfaces of the flying leads and termination pads may be electrically connected to disk drive circuitry or magnetic head terminals through soldering or ultrasonic bonding processes. 
     There remains a need for integrated lead head suspensions providing improved interlayer adhesion, reduced tool wear, improved vision system inspection characteristics, and enhanced mechanical, thermal and aerodynamic performance. To be commercially viable, any such suspensions or suspension components must be capable of being efficiently manufactured. 
     SUMMARY 
     One embodiment of the invention is a method for making a disk drive head suspension component having a microstructured surface region. The method includes depositing a layer of photoimageable polymer having an associated set of process parameters including a minimum resolution and exposing the photoimageable polymer through a photomask having a microstructure-producing region with features below the minimum resolution for the photoimageable polymer. The exposed photoimageable polymer is developed to produce a layer of polymer having a thickness and a microstructured surface region with depressions that are less than the thickness of the polymer. In another embodiment of the invention, exposing the polymer through a photomask includes exposing the polymer through a photomask having a microstructure-producing region with features sized and spaced between about 1 μm and 10 μm. Embodiments of the invention can be used to produce microstructured surfaces on structures such as flying leads, flying termination pads, cover coat layers and at insulating layer-trace interfaces and insulating layer-cover coat interfaces. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A-1G  are diagrammatic cross sectional illustrations of a head suspension structure showing a process for forming microstructured surfaces in accordance with one embodiment of the invention. 
         FIG. 2  is a magnified photograph of a microstructured surface in accordance with an embodiment of the invention. 
         FIG. 3  is an isometric view of a head suspension gimbal including flying leads having microstructured surfaces in accordance with an embodiment of the invention. 
         FIG. 4  is an illustration of a head suspension flexure dual stage actuator (DSA) paddle having a contact pad with a microstructured surface in accordance with an embodiment of the invention. 
         FIG. 5  is an illustration of a head suspension flexure tail having flying termination pads with microstructured surfaces in accordance with an embodiment of the invention. 
         FIGS. 6A-6E  are diagrammatic cross sectional illustrations of a head suspension structure showing a process for forming microstructured surfaces in accordance with another embodiment of the invention. 
         FIG. 7  is a diagrammatic cross sectional illustration of a head suspension flexure trace having a microstructured insulating layer-trace interface and a microstructured covercoat in accordance with an embodiment of the invention. 
         FIG. 8  is a diagrammatic cross sectional illustration of a head suspension flexure having a microstructured insulating layer with varying depression sizes in accordance with an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Smooth conductor layer and insulating layer surfaces can lead to premature wear of ultrasonic bonding tips and poor adhesion and delamination between the insulating layer and conductor or cover layers. Head suspensions and head suspension components having microstructure patterned surface layers in accordance with the present invention can alleviate premature tool wear and adhesion problems. Embodiments of the present invention utilizes a unique photolithography imaging and exposing or patterning process in conjunction with known subtractive and additive manufacturing processes such as, for example, wet and dry etching, various deposition processes and laminated materials, to form microstructure patterned surfaces on the conductor, insulating and/or cover layers of the components. 
     A method for making a disk drive head suspension component having microstructured surfaces such as head termination pads or flying termination leads in accordance with one embodiment of the invention can be described generally with reference to  FIGS. 1A-1E . As shown in  FIG. 1A , a photoimageable polymer such as insulating polyimide layer  10  is deposited onto the spring metal base layer  12 . Regions  14  of the polyimide layer  10  coinciding with surfaces to be microstructured, such as the conductor termination pads or leads, are exposed through a mask  16  having light blocking or transmitting features below the minimum resolution for the photoimageable polyimide of layer  10  as shown in  FIG. 1B . In one embodiment of the invention the light blocking or transmitting features are sized (e.g., diameter) and spaced (e.g., separated by) from between about 1 μm and 10 μm. After being exposed through the mask  16  the polyimide layer  10  is developed and cured or otherwise hardened as shown in  FIG. 1C . By this process a microstructured region  14  having depressions  18  that are less than the thickness of the polyimide layer  10  is formed in the polyimide layer. 
     The minimum resolution defines the maximum size light blocking or transmitting features that will create patterned depressions  18  in predetermined regions of the polyimide  10  for a given set of material properties and process parameters. The polyimide will etch through when exposed through a mask having light blocking or transmitting features sized above the minimum resolution for the same set of material properties and process parameters. The minimum resolution is dependent on the thickness and material properties of the polyimide along with the exposing and developing processing times among other things. The remaining regions of the insulating polyimide layer are exposed through a mask having conventional light blocking or transmitting features. In this manner, microstructure patterned depressions  18  are formed in selected, predetermined regions  14  during the develop and cure cycles of the insulating polyimide layer  10  patterning process. 
     A conductive material layer  20  (typically copper or copper alloy) that can be formed into conductor elements such as traces or leads and termination or bond pads is deposited, using known methods (e.g., plating following seed layers), onto the patterned insulating layer  10  over the microstructure patterned depressions  18  as shown in  FIG. 1D . Portions of the spring metal base layer  12  and the microstructure patterned insulation layer  10  can then be removed via etching, laser ablation or the like to expose the termination surfaces  22  of the conductive material layer  20  as shown in  FIGS. 1E and 1F . A corrosion resistant material  24  such as nickel-gold can, but need not be, deposited onto the surfaces  22  of the conductive material layer  20  as shown in  FIG. 1G . 
     The termination surfaces  22  of the conductor elements in the conductive material layer  20  include microstructure patterned raised areas formed by the patterned depressions  18  in the removed insulating layer  10 . The microstructure patterned termination surfaces  22  increase the coefficient of friction between an ultrasonic bonding tool and the termination surfaces resulting in reduced slippage between the tool and termination surfaces thus decreasing tool wear. The microstructure patterned termination surfaces also concentrate the ultrasonic bonding tool tip force to a smaller effective area which increases the localized pressure during bonding and results in greater coupling between the bonding tool and the termination surfaces. The higher effective pressure at the surface can be achieved with lower bulk ultrasonic bonding tool aggressiveness which results in decreased tool wear for the same effective bonding robustness. 
       FIG. 2  is an photograph of a magnified (500×) microstructured surface  22  in a conductive material layer  20  manufactured in accordance with the present invention using a photomask having 5 μm features. 
       FIG. 3  is an illustration of a gimbal  30  of a head suspension flexure having flying leads or traces  32  with microstructured surfaces  22  in accordance with an embodiment of the invention. Also shown in  FIG. 3  are portions of the gimbal  30  formed from the polyimide layer  10  and the spring metal base layer  12 . The microstructure patterned flying gimbal traces  32  provide improved aerodynamic performance. During operation of the disk drive, as the head suspension flies over the rotating disk, the microstructure pattern on the flying gimbal traces  32  causes the air flow over the leads to transition from laminar to turbulent which reduces the pressure drag and improves aerodynamic performance of the gimbal leads. 
     Another embodiment of the invention includes integrated lead flexures manufactured by additive and/or subtractive processes (e.g., a so-called TSA or TSA+ flexure) configured for use with dual stage actuated (DSA) suspensions having piezoelectric or other motors. The flexures include one or more traces terminating at contacts (also sometimes referred to as DSA paddles) configured for electrical interconnection to the DSA motors. Microstructure patterned surfaces of the types described above can be incorporated into the DSA contacts of this embodiment of the invention.  FIG. 4 , for example, is an illustration of a dual stage actuation (DSA) motor contact  40  of a head suspension flexure having a microstructured surface  22  in accordance with an embodiment of the invention. Also shown in  FIG. 4  is a trace  42  extending from the contact  40  and portions of the contact formed from the polyimide layer  10  and the spring metal base layer  12 . 
       FIG. 5  is an illustration of a tail  50  of a head suspension flexure having flying termination pads or contacts  52  with microstructured surfaces  22  in accordance with an embodiment of the invention. Also shown in  FIG. 5  are the traces  54  extending from the contacts  52  and portions of the tail formed from the spring metal base layer  12 . Still other embodiments of the invention include head suspension flexures having other contacts with microstructured surfaces, such as for example bond pads on the head suspension gimbal for connection to a read/write head on a slider. The microstructured surfaces can improve interfacial effects such as increased surface area for adhesion of non-ultrasonic bonds (e.g., solder, conductive epoxy, gold ball bonds, and the like). The roughness of the microstructured surface can also change the surface morphology to increase mechanical locking of the layers. The increased surface area and morphology can improve DSA paddle and other contact joint reliability. Similarly, other contact pads on traces of integrated lead flexures (e.g., those on the tail and gimbal) will benefit from this feature. 
     A method for making a disk drive head suspension component having microstructured surfaces in accordance with another embodiment of the invention that provides improved adhesion between the conductor element-insulating layer interface and between the cover layer-insulating layer interface can be described generally with reference to  FIGS. 6A-6E . As shown in  FIG. 6A , the photoimageable insulating polyimide layer  110  is deposited onto the spring metal base layer  112 . Regions  114  of the polyimide layer  110  coinciding with surfaces to be microstructured such as the insulating layer-conductor elements interface and the cover layer-insulating layer interface are exposed through a mask  116  having light blocking or transmitting features below the minimum resolution for the photoimageable polyimide of layer  110  as shown in  FIG. 6B . After being exposed through the mask  116  the polyimide layer  110  is developed and cured or otherwise hardened as shown in  FIG. 6C . By this process a microstructured region  114  having depressions  118  that are less than the thickness of the polyimide layer  110  is formed in the polyimide layer. 
     The minimum resolution defines the maximum size light blocking or transmitting features that will create patterned depressions  118  in predetermined regions of the polyimide  110  for a given set of material properties and process parameters. The polyimide will etch through when exposed through a mask having light blocking or transmitting features sized above the minimum resolution for the same set of material properties and process parameters. The minimum resolution is dependent on the thickness and material properties of the polyimide along with the exposing and developing processing times among other things. The remaining regions of the insulating polyimide layer are exposed through a mask having conventional light blocking or transmitting features. In this manner, microstructure patterned depressions  118  are formed in selected, predetermined regions  114  during the develop and cure cycles of the insulating polyimide layer  110  patterning process. 
     A conductive material layer  120  (typically copper or copper alloy) that can be formed into conductor elements such as traces or leads and termination or bond pads is deposited, using known methods (e.g., plating following seed layers), onto the patterned insulating layer  110  over the microstructure patterned depressions  118  as shown in  FIG. 6D . A photoimageable cover layer  140  can be deposited and patterned to extend from the microstructure patterned insulating layer  110  over the tops and sides of the conductor elements in the conductive material layer  120  as shown in  FIG. 6E . In an alternate embodiment (not shown), the microstructure patterned depressions are formed only in regions of the insulating polyimide layer coinciding with the conductor element-insulating layer interface. The microstructure patterned insulating layer creates a stronger bond to the conductor elements and/or cover layer. 
       FIG. 7  is an illustration of an embodiment that is similar to the embodiment described above, except that the photoimageable cover layer  140 ′ is exposed through a mask having light blocking or transmitting features sized and spaced below the minimum resolution of the photoimageable cover layer, e.g., from e.g., between about 1 μm and 10 μm. The resulting cover layer  140 ′ has a matte finish  142  which provides for increased vision inspection yields by reducing false rejects of otherwise functional product due to cosmetic blemishes. 
     Another embodiment utilizes the microstructure patterning process to control mechanical properties such as stiffness by modifying the insulating layer in selected, predetermined regions of the suspension. For example, it may be desirable to modify the stiffness in the gimbal and/or hinge regions of the head suspension by controlling the amount of the insulating layer in these regions. The insulating layer could be transitioned from regions having, for example, 1 μm microstructure patterns (more stiffness) to regions having, for example, 10 μm microstructure patterns (less stiffness). The transition from larger to smaller microstructure patterns may be gradual or in discreet steps. By way of example,  FIG. 8  is an illustration of a polyimide layer  210  microstructured region  214  having depressions  218  of continuously varying depth. 
     Embodiments of the invention include an integrated lead suspension having a spring metal base layer, a conductor layer and an insulation layer between the spring metal base and conductor layers. The conductor layer includes at least one lead having at least one microstructure patterned termination surface. In another embodiment of the invention, the integrated lead suspension further includes a cover layer extending from the insulating layer over the conductor layer. The insulating layer includes microstructure patterned surfaces at the lead to insulating layer interface and/or at the cover layer to insulating layer interface. In yet another embodiment of the invention, the integrated lead suspension further includes a cover layer extending from the insulating layer over the conductor layer. The cover layer includes a microstructure patterned matte surface finish. In still another embodiment of the invention, the integrated lead suspension further includes flying gimbal leads having microstructure patterned surfaces. In another embodiment of the invention, the insulating layer includes microstructure patterned regions of varying size, spacing and depth. 
     Advantages provided by this invention include microstructure patterned lead termination regions that reduce wear of ultrasonic bonding tools; microstructure patterned insulating layer regions that improve adhesion and provide tailored mechanical properties; microstructure patterned cover layer regions that improve machine vision inspection; and, microstructure patterned leads that improve aerodynamic performance. 
     Although the present invention is described and shown with reference to preferred embodiments, those skilled in the art will recognize that changes can be made in form and detail without departing from the spirit and scope of the invention. For example, the microstructure patterns may have rectangular, triangular, oval or other shapes. Other embodiments of the invention can have other combinations of the microstructure patterned features described above.