Abstract:
Systems and methods for pre-heating adjacent bond pads for soldering are provided. In one embodiment, the invention relates to a method for soldering adjacent bond pads, the method including directing an ultraviolet light beam onto the bond pads from a first angle relative to the bond pads for a preselected duration, heating a solder, and depositing the solder onto the bond pads from a second angle relative to the bond pads during the preselected duration, wherein the second angle is different from the first angle.

Description:
FIELD 
     The present invention relates to information storage devices, and more specifically to systems and methods for pre-heating adjacent bond pads for soldering. 
     BACKGROUND 
     Information storage devices use magnetic media to store data and a movable read head or slider positioned over the magnetic media to selectively read data from and write data to the magnetic media. In a modern magnetic hard disk drive device, each read head is a sub-component of a head-gimbal assembly (HGA). The HGA also includes a suspension assembly for holding the read head and providing a plurality of electrical connections thereto. The suspension assembly typically includes a fragile laminated flexure to carry the electrical signals to and from the head. The HGA, in turn, is a sub-component of a head-stack assembly (HSA) that typically includes a plurality of HGAs, an actuator, and a flex cable. The plurality of HGAs are attached to various arms of the actuator, and each of the laminated flexures of the HGAs has a flexure tail that is electrically connected to the HSA&#39;s flex cable. 
     The read head is typically bonded to a tongue portion of the fragile laminated flexure by an adhesive, for example by an epoxy adhesive, and a soldering process for electrically coupling a pad on the flexure/suspension with a pad on the read head/slider. Conventional soldering processes use solder jet bonding to deposit a molten solder ball on the slider and suspension bond pads at room temperature. However, the molten solder ball can cause thermal shock at the bond pads, which can lead to solder creep, solder joint undercut, pitch static variations and other undesirable results. As such, an improved system and method for bonding adjacent bond pads is needed. 
     SUMMARY 
     Aspects of the invention relate to systems and methods for pre-heating adjacent bond pads for soldering. In one embodiment, the invention relates to a method for soldering adjacent bond pads, the method including directing an ultraviolet light beam onto the bond pads from a first angle relative to the bond pads for a preselected duration, heating a solder, and depositing the solder onto the bond pads from a second angle relative to the bond pads during the preselected duration, wherein the second angle is different from the first angle. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1   a - 1   e  show a sequence of side views of a soldering assembly and a work piece illustrating a process for pre-heating adjacent pads of the work piece using ultraviolet light before bonding the pads in accordance with one embodiment of the invention. 
         FIG. 2  is a side view of a solder joint for adjacent pads that were pre-heated using ultraviolet light in accordance with one embodiment of the invention. 
         FIG. 3  is a table illustrating a comparison of the contact angle of each solder joint on the adjacent pads for a conventional process versus a process using pre-heating and ultraviolet light in accordance with one embodiment of the invention. 
         FIG. 4  is a perspective view of a soldering assembly that includes a solder dispenser, a nitrogen shower, and an ultraviolet light source in accordance with one embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings, embodiments of systems and processes for pre-heating adjacent pads of a work piece using ultraviolet light are illustrated. In several embodiments, a soldering apparatus is controlled to direct an ultraviolet light beam onto adjacent pads from a first angle and for a preselected duration. The soldering apparatus can heat solder for a joint to be formed between the adjacent pads. The soldering apparatus can then deposit the solder onto the adjacent bond pads from a second angle during the preselected duration, where the second angle is different from the first angle. In a number of embodiments, the solder joint that results from the processes described herein are more robust than a solder joint formed by conventional processes. In several cases, the improved process avoids the thermal shock at the bond pads, thereby avoiding solder creep, solder joint undercut, pitch static variations and other undesirable results common to the conventional processes. 
       FIGS. 1   a - 1   e  show a sequence of side views of a soldering assembly  100  and a work piece  102  illustrating a process for pre-heating adjacent pads of the work piece  102  using an ultraviolet light source  108  before bonding the pads in accordance with one embodiment of the invention. The soldering assembly  100  includes a laser  104 , a nitrogen dispenser  106 , and the ultraviolet heat source  108 . The work piece  102  includes a slider  102   b  mounted to a suspension  102   a , where the slider  102   b  and suspension  102   a  each have one or more pads (not visible) positioned near a point (e.g., bonding target) where the two components meet. In several embodiments, this point will become the location of the solder joint. 
       FIG. 1   a  illustrates the soldering assembly  100  and work piece  102  as a solder capillary tube  110  of the soldering assembly  100  is positioned over a bonding target of the work piece  102 . In several embodiments, the soldering assembly  100  receives instructions from a control program directing it to move such that the capillary tube  110  is positioned over the bonding target. 
       FIG. 1   b  illustrates the soldering assembly  100  and work piece  102  as a solder ball  112  is extended to the capillary tube  110 . A singulation disk, shown directly above laser  104 , is configured to receive solder balls within the solder assembly  100 , like solder ball  112 , and rotate them such that they are positioned above the capillary tube  110 . 
       FIG. 1   c  illustrates the soldering assembly  100  and work piece  102  as the UV heat source  108 , the nitrogen dispenser/shower  106 , and laser  104  are activated at about the same time. In several embodiments, each component can be activated for a preselected duration. 
       FIG. 1   d  illustrates the soldering assembly  100  and work piece  102  as a solder ball  112  is expelled from the capillary tube of the laser  104  toward the bonding target. In several embodiments, the solder ball  112  is urged from the capillary tube toward the bonding target by nitrogen pressure applied by the nitrogen source  106 . In some embodiments, the laser  104  does not allow the solder ball  112  to be expelled until a preselected duration for the UV pre-heating has expired. 
       FIG. 1   e  illustrates the soldering assembly  100  and work piece  102  as a solder ball  112  has melted and formed a solder joint  114  between the adjacent bond pads positioned on the suspension  102   a  and slider  102   b . In several embodiments, the soldering apparatus  100  can repeat the process for another set of adjacent pads. In one embodiment, there are several sets of adjacent pads along the line where the suspension  102   a  and slider  102   b  meet and the soldering apparatus  100  moves along that line to solder each of the sets of adjacent pads, thereby forming several electrical connections between the suspension  102   a  and the slider  102   b.    
     In  FIGS. 1   a - 1   e , the work piece is a suspension and slider for a head gimbal assembly of a storage drive. In other embodiments, the process can be used with other work pieces having adjacent pads that need to be soldered. 
       FIG. 2  is a side view of a solder joint  214  for adjacent pads ( 203 ,  205 ) of a work piece  202  that were pre-heated using ultraviolet light in accordance with one embodiment of the invention. The work piece  202  includes a first substrate  202   a  having first pad  203  positioned on a top surface of the first substrate  202   a . The work piece  202  also includes a second substrate  202   b  having second pad  205  positioned on an outer surface of the second substrate  202   b . The adjacent pads ( 203 ,  205 ) were pre-heated using ultraviolet light and a robust solder joint  214  was formed. As can be seen from  FIG. 2 , the contact angle, or angle at which the solder meets the substrate surface, for each pad is relatively small. In general, the smaller the resulting contact angle, the more robust the solder joint will be. 
       FIG. 3  is a table illustrating a comparison of the contact angle of a number of solder joints on adjacent pads for a conventional process versus a process using pre-heating and ultraviolet light in accordance with one embodiment of the invention. As can be observed from  FIG. 3 , the use of ultraviolet light to pre-heat adjacent bond pads in the improved process fairly significantly reduces the contact angle of the resulting solder joints as compared to conventional processes. 
       FIG. 4  is a perspective view of a soldering assembly  100  that includes a solder dispenser/laser  104 , a nitrogen shower  106 , and an ultraviolet light source  108  in accordance with one embodiment of the invention. 
     While the above description contains many specific embodiments of the invention, these should not be construed as limitations on the scope of the invention, but rather as examples of specific embodiments thereof. Accordingly, the scope of the invention should be determined not by the embodiments illustrated, but by the appended claims and their equivalents. 
     In  FIGS. 1   c - 1   e , the UV heat source  108  is positioned at a preselected distance from the bonding target of the work piece  102 . In one embodiment, the preselected distance is about 0.5 to 1.5 centimeters (cm). In other embodiments, the preselected distance can be increased or decreased beyond 0.5 to 1.5 cm. In several embodiments, the intensity of the UV heat source can varied for best results.