Abstract:
A fill head apparatus includes at least one chamber for holding a fluid. The chamber has an outlet for expelling the fluid. A vacuum device has an inlet for a suction device adjacent to the fluid outlet. A plurality of flexible and resilient sealing devices contact a top surface of a workpiece. The sealing devices are positioned on opposing sides of the chamber outlet and on opposing sides of the vacuum device inlet, such that the sealing devices create at least a partial seal around a cavity defined by the workpiece and the cavity is beneath both the chamber outlet and the vacuum outlet.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to an apparatus having a fill head interface for vacuum and pressure fill, and more particularly, an apparatus having a fill head interface including adjacent vacuum and pressure devices for use in a manufacturing process. 
       BACKGROUND OF THE INVENTION 
       [0002]    Typical precision patterned fill processes, for example, in semiconductor manufacturing (e.g., integrated circuits, chip technology, and chip packaging), provide filling of features (cavities or trenches created, for example, by etching) on a wafer or semiconductor chip. The features may be filled with substances including pastes, inks, liquid metals (such as solder) and solvents. These materials may be at sub-ambient, ambient, or high temperatures such as molten solders. Further, the features may be such features and cavities required in manufacturing of a product, including small features, for example, 5-200 μm wide and/or deep. 
         [0003]    One problem associated with current patterned fill processes is that pressure alone is often not sufficient to inject materials into the features. Moreover, for example, through holes of high aspect ratio, i.e., comparatively large height and diameter, or height and width, can be difficult to fill. Furthermore, blind holes are often very difficult to fill since entrapped gas backpressure can prevent complete filling of the holes. 
         [0004]    Typically, there are problems filling holes or mold features using cavity filling processes due to the presence of ambient atmosphere gas in the features. The gas must be completely displaced by the filling material or gas pockets compromise the filled feature and/or can cause a break in a seal around the feature. The problem is accentuated during high speed fills where the feature or cavity has minimal time to bleed out the entrapped gas while the fill material enters the cavity. Thus, the displacement process often is incomplete in the time desired for filling features, and results in partially filled or in extreme cases empty cavities which become defects in the process. For some operations, no defects, such as partial or unfilled cavities of features are allowable. Entrapped gases in the features may result in a partially filled cavity. A partially filled feature or cavity may result in seal degradation around the feature, especially over extended periods of time at high temperatures, e.g., over 200° degrees Celsius. 
         [0005]    Another problem with current feature filling processes is that current attempt to seal the feature are inadequate to maintain the seal around the feature, as the surface area may be rough. The roughness may be caused by current sealing methods which may drag the fill substance, such as solder, from the cavities leaving streaks on the surface area of the device, e.g., wafer. 
         [0006]    Referring to  FIG. 1 , a known fill head assembly  10  for dispensing molten solder into a mold plate uses a fill head  20 . The fill head assembly  10  further includes a solder reservoir  12  being partially filled with solder  14 . A body portion  30  of the assembly  10  includes two heater  32  for heating the solder  14  in the reservoir  12 . A passageway  18  provides an inlet for the solder and is pressurized with a downward pressure  19 . A solder fill region  16  or solder outlet in the solder fill head  20  provides egress for the solder  14 . Two seals  24  are positioned on opposite sides of the solder fill region  16 . A mold plate  40  (for example, a glass mold plate) includes cavities  44 . Using the assembly  10 , the body portion  30  is heated to above the melting point of solder using built-in cartridge heaters  32 . For example, tin or tin alloy solders melt at approximately 230 degrees C., therefore in this case the body portion is heated to around 250 degrees C. The molten solder  14  is held in the sealed reservoir  12 . The fill head (alternatively FH or solder fill head) assembly  10  rests on the mold plate  40  and a nominal load or downward force is applied (typically 2.5 lbs/linear inch of seal). A seal at the solder in solder outlet  16  prevents the solder  14  from leaking out the bottom of the fill head assembly  10 . The solder reservoir  12  is pressurized, usually to a pressure of between 0 and 20 psi, to ensure that solder enters the mold plate  40  cavities  44  during the mold fill process. The small cavities  44  in the mold plate  40  are filled by moving the mold plate  40  underneath the solder fill head  20 , typically at a speed of between 0.1 to 10 mm/sec. Air is purged from the mold plate cavities as the solder enters the cavities. The air escapes between the seal  24  and a top surface  42  of the mold plate  40 . This process continues until all mold cavities  44  are filled. The mold plate  40  is moved in the direction  41 . The mold plate  40  with the filled cavities  45  is then removed and passed to the next tool where the solder is transferred from the mold to the pads of a silicon wafer. 
         [0007]    Shortcomings with current methods of solder fill described above include the solder must exert pressure on the air in the cavities to force the air from the cavities. This pressure may cause the solder to leak from the seal in the outlet  16 , particularly if there are variations in the seal or variations in the flatness of the mold plate. Another problem is that for air from the cavities to escape across the seal it is helpful if the seal is roughened, textured, or scratched to provide small channels to enable the air to more easily escape between the seal and the top surface of the mold. However, this approach results in increased wear over time, for instance wearing away the channels or scratches, resulting in the same problem as the channels where to prevent, i.e., difficulty in purging the air from the cavities. An additional problem with current approaches is that even with the textured or channeled seal discussed above, pressure alone may not be sufficient to eject air from the cavities, thereby unwanted air remains in the cavities resulting in the undesirable condition of partially filled cavities, i.e., cavities partially filled with solder. 
         [0008]    Other known fill head assemblies include a solder dispensing region, a vacuum region, a flat seal, and channels or slots that enable communication between the vacuum region and the solder region. The vacuum region is intended to remove the air from the mold plate cavities prior to fill. However, several deficiencies of known designs include difficulty in maintaining desired contact between the solder fill head assembly and the mold plate by using a flat seal. For example, even if a compliant seal material is used, irregularities in the mold plat e surface and alignment errors between the fill head assembly and the mold plate result in solder leaking across the seal. It is also difficult to maintain a vacuum in the mold plate cavities prior to solder fill due to air leaking into the vacuum region. Another problem with current designs is that as the seal wears, small slots between the vacuum region and the solder region tend to disappear, thus making it difficult to maintain a good vacuum in the mold plate cavities prior to solder fill. Another problem with current designs is that a flat seal does not provide adequate wiping as it moves across the mold plate, and therefore tends to leave streaks of solder on the mold surface. 
         [0009]    It would therefore be desirable to provide a localized vacuum environment to remove ambient gas and encourage backfilling of a material used to fill features during manufacturing. It would also be desirable to provide an apparatus and method for filling features with material at high speed, without material overfill, bridging, or streaking. Further, there is a need for a reliable mold filling process which ensures that each cavity or feature is accurately filled by a fill head device. 
       SUMMARY OF THE INVENTION 
       [0010]    In an aspect of the invention a fill head apparatus includes at least one chamber for holding a fluid. The chamber has an outlet for expelling the fluid. At least one vacuum device has an inlet adjacent to the fluid outlet. A plurality of flexible and resilient sealing devices contact a top surface of a workpiece. The sealing devices are positioned on opposing sides of the chamber outlet and on opposing sides of the vacuum device inlet. The sealing devices create at least a partial seal around a cavity defined in the workpiece and beneath both the chamber outlet and the vacuum inlet. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0011]    These and other objects, features and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawings, in which: 
           [0012]      FIG. 1  is a cross-sectional front elevational view of a prior art solder fill head assembly, the solder fill head assembly includes a solder reservoir, a solder dispensing region, seals, and a work piece or plate with cavities being filled with molten solder; 
           [0013]      FIG. 2  is a cross-sectional view of a fill head apparatus according to an embodiment of the present invention including a solder fill head assembly, the solder fill head assembly includes a solder reservoir, a solder dispensing region, a vacuum region, a vacuum and seals, a mold plate is depicted being filled with molten solder; 
           [0014]      FIG. 3  is a detail side elevational view of the seal shown in  FIG. 2 ; 
           [0015]      FIG. 4  is a bottom view of a solder fill head assembly, including a solder dispensing region, a vacuum region, and a solder and vacuum seal; 
           [0016]      FIG. 5  is a cross-sectional view of a bi-directional fill head apparatus according to another embodiment of the present invention similar to the embodiment shown in  FIG. 2  and further including a second vacuum region and vacuum, and the apparatus being capable of filling the mold plate bi-directionally; and 
           [0017]      FIG. 6  is a schematic block diagram of a cavity and vacuum inlets according to the embodiment of  FIG. 5   
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    Referring to  FIG. 2 , an embodiment of a fill head apparatus  100  according to the present invention includes a body portion  104  and a fill head  108  attached to the body portion  104 . The body portion  104  includes a sealed solder reservoir  112 , internal heaters  116 , a solder fill region  114  or outlet including a solder head  136  for egress of the solder  113  from the solder reservoir  112 . The solder reservoir contains solder  113  filled through an inlet  116  in a passageway  118 . The passageway in under pressure from a pressure source  119 , to maintain positive pressure on the solder  113  in the solder reservoir  112 . The fill head  108  includes a vacuum region or vacuum inlet  130 . The vacuum region  130  communicates with a vacuum source  131  through a vacuum tube  134 . The fill head  108  further includes a plurality of seals  140 . The seals  140  are positioned on each side of the vacuum inlet  130  and on each side of the fill region  114 , as shown in  FIG. 2 . The seals  140  include an arcuate seal head  142 , as show in more detail in  FIG. 3 . The arcuate seal head  142  has a specified radius  146  and dimension  144 . The arcuate seal head  142  of the seal  140  provide superior sealing between the top surface  152  of a mold plate  150 . The mold plate  150  includes cavities or features  154 . 
         [0019]    The fill head apparatus  100  operates according to a method of the present invention by initially heating the fill head body portion  104  above the melting point of the solder  113  using the built-in cartridge heaters  120 . Solders may include Tin or Tin alloy solders, which melt at approximately 230 degrees C., therefore, for the case where Tin or Tin alloy solders are used, the solder fill head is heated to around 250 C. The molten solder is held in a sealed reservoir. The solder fill head (or FH)  136  rests on mold plate  150  and a nominal load or down force is applied (typically 2.5 lbs/linear inch of seal) to ensure satisfactory contact between the fill head  136  and the mold plate  150  top surface  152 . The seals  140  surround the solder fill region  114  preventing the solder  113  from leaking out the bottom of the fill head  136 . The seals  140  surrounding the vacuum region ensure that a quality specified vacuum is maintained. The middle seal  140 , i.e., the seal  140  between the solder fill region  114  and the solder outlet  130  performs two functions, encouraging confinement of the solder and maintaining a vacuum region  132 . The seal  140  material is highly compliant, typically with a height of about 3 mm or more, thus ensuring adequate contact is maintained between the fill head  136  and the mold top surface  152 , even though the mold top surface  152  may not be flat or an imperfect alignment is realized between the fill head  136  and the mold plate top surface  152 . 
         [0020]    The mold plate cavities  154  are filled by moving the mold underneath the solder fill head  136 , for example, at a speed of between 0.1 to 10 mm/sec. Air is removed from the cavities  151  as the cavities enter the fill head&#39;s vacuum region. The cavities  151  proceed directly to the solder fill region, transitioning across the common middle seal section. No slots or scratches on the middle seal are required since a short distance is traversed and the seal is highly compliant. The cavities are filled with solder in the solder fill region. A small pressure may be applied to the solder reservoir (0 psi to 10 psi) to ensure complete cavity fill. The fill process continues until all mold cavities are filled. The mold plate is then removed and passed to the next tool where the solder is transferred from the mold to the pads of a silicon wafer. 
         [0021]      FIG. 4  shows a bottom view of the fill head assembly  10 . A unified seal consists of a solder fill region  162  and a vacuum region  164 . As shown in  FIG. 4 , the solder fill region  162  may be elongated with rounded ends. The solder fill region is of sufficient length to cover the cavities (or cavity region) on the mold plate. For example, for 300 mm wafers, the solder fill region may need to be approximately 300 mm in length for all solder balls (mold plate cavities) to be filled. The vacuum region  164  is defined by an additional seal section which extends from the ends of the solder fill seal region  162 , around to the leading edge of the fill head. Vacuum feed channels  130  (e.g., slots, holes, etc.) are connector to a vacuum source. 
         [0022]    Further, referring to  FIG. 4 , a cavity  154  of the mold plate  150  includes a vacuum inlet  130  passing over the cavity  154 . A seal  140  is also passing over the cavity  154  providing a seal between the top surface  152  of the mold plate  150  and the seal  140 . The seal also wipes clear the top surface  152  of solder. 
         [0023]    Referring to  FIG. 5 , another embodiment of the present disclosure invention includes a bi-directional fill head apparatus  200 . The fill head apparatus  200  includes like elements of the fill head apparatus  100  shown in  FIG. 2 , wherein the same reference numerals are used. Additionally, the bi-directional fill head apparatus  200  includes a second vacuum source  131  and another seal  140  such that opposing seals  140  are on opposite sides of the second vacuum source inlet  130 . The apparatus  200  is capable of filling the cavities with solder in either direction while maintaining the seal about the cavity and initially vacuuming the cavity. 
         [0024]    Referring to  FIGS. 5 and 6 , the fill head apparatus  200  includes another vacuum source  131  and another vacuum tube  134  on the opposing side of the solder reservoir  112 . As shown in  FIG. 6 , the cavity  151  has vacuum outlets  130  on opposing sides of the cavity  151 , separated by a vacuum/pressure containment wall  204 . Thus, a fill head  108  is designed to realize a structure with a vacuum region on both sides of a cavity or fill region for solder (or other material) application. In this embodiment, it is possible to fill mold plates in both directions, thus improving throughput. 
         [0025]    Using the present disclosure, a seal surface does not need to be structured or sanded, greatly improving operating window and relaxing the requirements on tight fill head down pressure and solder reservoir pressure controls. The unified compliant seal of the present disclosure is pressed into a groove in the fill head assembly and is easily replaced as the seal reaches its end of life. 
         [0026]    Benefits of the present disclosure include increased fill speeds, for example, 3-5 times faster than typical without a leading edge vacuum. The vacuum according to the present disclosure improves both vacuum and solder seals on the mold surface since it contributes additional downward force on the seal surface. Additionally, defects were reduces due to partially filled cavities. The seal surface finish was not critical to the process in the present disclosure, since venting no longer controlled the removal rate of gas from the cavities before solder fill. Further, solder leaks were reduces, and wiping was improved, with no streaking, and the need to vent channels between the vacuum and solder regions was eliminated. 
         [0027]    While the present invention has been particularly shown and described with respect to preferred embodiments thereof, it will be understood by those skilled in the art that changes in forms and details may be made without departing from the spirit and scope of the present application. It is therefore intended that the present invention not be limited to the exact forms and details described and illustrated herein, but falls within the scope of the appended claims.