Abstract:
A system, method, and apparatus for injection molding conductive bonding material into a plurality of cavities in a surface are disclosed. The method comprises aligning a fill head with a surface. The mold includes a plurality of cavities. The method further includes placing the fill head in substantial contact with the surface. At least a first gas is channeled about a first region of the fill head. The at least first gas has a temperature above a melting point of conductive bonding material residing in a reservoir thereby maintaining the conductive bonding material in a molten state. The conductive bonding material is forced out of the fill head toward the surface. The conductive bonding material is provided into at least one cavity of the plurality of cavities contemporaneous with the at least one cavity being in proximity to the fill head.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    The present patent application is related to co-pending and commonly owned U.S. Patent Application No. ______, Attorney Docket No. YOR920060008US1, entitled “Universal Mold For Injection Molding Of Solder”; U.S. patent application No. ______, Attorney Docket No. YOR920060009US1, entitled “Rotational Fill Techniques For Injection Molding Of Solder”; and U.S. patent application No. ______, Attorney Docket No. YOR92006066US1, entitled “CONDUCTIVE BONDING MATERIAL FILL TECHNIQUES”, all filed on even date with the present patent application, the entire collective teachings of which being hereby incorporated by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention generally relates to the field of placement of conductive bonding material such as solder on electronic pads, and more particularly relates to an apparatus for placement of the conductive bonding material. 
       BACKGROUND OF THE INVENTION 
       [0003]    In modern semiconductor devices, the ever increasing device density and decreasing device dimensions demand more stringent requirements in the packaging or interconnecting techniques of such devices. Conventionally, a flip-chip attachment method has been used in the packaging of IC chips. In the flip-chip attachment method, instead of attaching an IC die to a lead frame in a package, an array of solder balls is formed on the surface of the die. The formation of the solder balls is normally carried out by through-mask evaporation, solder paste screening, or injection molding of solder. 
         [0004]    U.S. Pat. No. 5,244,143, which is commonly owned by International Business Machines Corporation, discloses the injection molded solder (IMS) technique and is hereby incorporated by reference in its entirety. One of the advantages of the IMS over other solder bumping techniques is that there is very little volume change between the molten solder and the resulting solder bump. The IMS technique utilizes a solder head that fills boro-silicate glass (or other material) molds that are wide enough to cover most single chip modules. A wiper is sometimes provided behind the solder slit passes the filled holes of the mold to remove excess solder. 
         [0005]    The IMS method for solder bonding is then carried out by applying a molten solder to a substrate in a transfer process. When smaller substrates, i.e., chip scale or single chip modules are encountered, the transfer step is readily accomplished since the solder-filled mold and substrate are relatively small in area and thus can be easily aligned and joined in a number of configurations. For instance, the process of split-optic alignment is frequently used in joining chips to substrates. The same process may also be used to join a chip-scale IMS mold to a substrate (chip) which will be bumped. One problem with current IMS systems are the fill heads uses to place solder in the cavities of the molds. These fill heads are restricted to linear deposition of solder into rectangular molds. That is, the mold and the solder head are moved linearly with respect to each other such that the cavities move perpendicular to a slit in the solder head thereby filling the cavities as they pass. Another problem with IMS is that the molds are limited to a rectangular configuration, which encourages the linear deposition of the solder. 
         [0006]    Another problem with current fill heads used for IMS and other solder bumping techniques is that they do not provide precise temperature control with response time required to accurately control solder melt and solidification. Current fill heads are designed with resistive (electric) heaters in the solder head. The heater is built into the surface of the fill head where the head contacts the substrate being filled. The performance of a heater of this design is limited by a time delay for the heat to be generated in the line and then the conduction of the fill head. Also, there is a time delay for cooling of the solder in the cavities because the fill head does not provide a means for cooling the solder. 
         [0007]    Therefore a need exists to overcome the problems with the prior art as discussed above. 
       SUMMARY OF THE INVENTION 
       [0008]    Briefly, in accordance with the present invention, disclosed are a system, method, and apparatus for injection molding conductive bonding material into a plurality of cavities in a surface. The surface includes a plurality of cavities. The method further includes placing the fill head in substantial contact with the surface. At least a first gas is channeled about a first region of the fill head. The at least first gas having a temperature above a melting point of conductive bonding material residing in a reservoir mechanically coupled to the fill head thereby maintaining the conductive bonding material in a molten state as the conductive bonding material and the at least first gas are in close proximity to one another. The conductive bonding material is forced out of the fill head toward the surface. The conductive bonding material is provided into at least one cavity of the plurality of cavities contemporaneous with the at least one cavity being in proximity to the fill head. 
         [0009]    In another embodiment of the present invention a system for injection molding conductive bonding material into a plurality of cavities in a surface is disclosed. The system comprises at least one surface including at least one cavity. The system also includes at least one conductive bonding material placement device for providing conductive bonding material into the at least one cavity of the at least one surface. The conductive bonding material placement device comprises a fill head and a conductive material reservoir. The fill head comprises at least a first gas channel situated about a first region of the fill head. The at least first gas channel is for channeling at least a first gas having a temperature above a melting point of the conductive bonding material thereby maintaining the conductive bonding material in a molten state as the conductive bonding material and the at least first gas are in close proximity to one another. The conductive material reservoir is mechanically coupled to the fill head for providing conductive bonding material to the fill head from the conductive material reservoir. 
         [0010]    In yet another embodiment of the present invention a fill head for injection molding of conductive bonding material into a plurality of cavities in a surface is disclosed. The fill head comprises a reservoir for retaining conductive bonding material. A conductive bonding material channel that is mechanically coupled to the reservoir is also included. The fill head further includes a delivery slot that is situated perpendicular to the conductive bonding channel. The delivery slot accepts conductive bonding material from the reservoir via the conductive bonding material channel for providing the conductive bonding material to at least one cavity on a surface. The fill head also comprises at least a first gas channel situated about a first region. The at least first gas channel for channeling at least a first gas having a temperature above a melting point of conductive bonding material residing in a reservoir mechanically coupled to fill head thereby maintaining the conductive bonding material in a molten state as the conductive bonding material and the at least first gas are in close proximity to one another. 
         [0011]    An advantage of the foregoing embodiments of the present invention is that a fill head that includes at least one gas channel is provided. The gas channel allows for a gas having a temperature above the melting point of the conductive bonding material to be retained within the fill head. The hot gas allows for the conductive bonding material to liquefy or become molten as it is provided to cavities of a mold. Another gas channel within the fill head allows for gas with a temperature below the melting point of the conductive bonding material to be retained within the fill head. This causes the conductive bonding material to solidify as it comes into contact with the gas. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0012]    The accompanying figures where like reference numerals refer to identical or functionally similar elements throughout the separate views, and which together with the detailed description below are incorporated in and form part of the specification, serve to further illustrate various embodiments and to explain various principles and advantages all in accordance with the present invention. 
           [0013]      FIGS. 1-5  are top views of an IMS system illustrating a progressive sequence of filling cavities in a non-rectangular mold with conductive bonding material using a rotational fill technique that implements a fill head of a first type, according to an embodiment of the present invention; 
           [0014]      FIGS. 6-9  are top views of an IMS system illustrating a progressive sequence of transitioning the fill head of the first type from a non-rectangular mold after filling cavities in the mold with a conductive bonding material, according to an embodiment of the present invention; 
           [0015]      FIGS. 10-12  is are top views of an IMS system illustrating a progressive sequence of filling cavities in a non-rectangular mold with a conductive bonding material using a rotational fill technique that implements a fill head of a second type, according to an embodiment of the present invention; 
           [0016]      FIGS. 13-15  are top views of an IMS system illustrating a progressive sequence of transitioning the fill head of the second type from a non-rectangular mold after filling cavities in the mold with a conductive bonding material, according to an embodiment of the present invention; 
           [0017]      FIGS. 16-20  are top views of an IMS system illustrating a progressive sequence of filling cavities in a non-rectangular mold with a conductive bonding material using a rotational fill technique that implements a fill head of a third type, according to an embodiment of the present invention; 
           [0018]      FIGS. 21-22  are top views of an IMS system illustrating a progressive sequence of transitioning the fill head of the third type from a non-rectangular mold after filling cavities in the mold with a conductive bonding material, according to an embodiment of the present invention; 
           [0019]      FIG. 23  is a cross sectional view of a prior art IMS fill head; 
           [0020]      FIG. 24  is a cross-sectional view of a prior art IMS fill head; 
           [0021]      FIG. 25  is an angular view of an exemplary IMS fill head, according to an embodiment of the present invention; 
           [0022]      FIG. 26  is a cross-sectional view of a IMS fill head, according to an embodiment of the present invention; 
           [0023]      FIG. 27  is a planar view of the IMS fill head of  FIG. 23 , according to an embodiment of the present invention; 
           [0024]      FIG. 28  is a cross-sectional view of another IMS fill head, according to an embodiment of the present invention; 
           [0025]      FIG. 29  is a planar cross-sectional view of the IMS fill head of  FIG. 25 , according to an embodiment of the present invention; 
           [0026]      FIG. 30  is an operational flow diagram illustrating an exemplary process of filling molds using rotation of an exemplary fill head including at least one gas channel, according to an embodiment of the present invention; 
       
    
    
     DETAILED DESCRIPTION  
       [0027]    As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which can be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. Further, the terms and phrases used herein are not intended to be limiting; but rather, to provide an understandable description of the invention. 
         [0028]    The terms “a” or “an”, as used herein, are defined as one or more than one. The term plurality, as used herein, is defined as two or more than two. The term another, as used herein, is defined as at least a second or more. The terms including and/or having, as used herein, are defined as comprising (i.e., open language). The term coupled, as used herein, is defined as connected, although not necessarily directly, and not necessarily mechanically. 
         [0029]    The present invention, according to an embodiment, overcomes problems with the prior art by providing a fill head that includes at least one gas channel. The gas channel allows for a gas having a temperature above the melting point of the conductive bonding material to be retained within the fill head. The hot gas allows for the conductive bonding material to remain molten as it is provided to cavities of a mold. Another gas channel within the fill head allows for gas with a temperature below the melting point of the conductive bonding material to be retained within the fill head. This causes the conductive bonding material to solidify as the fill head pass over the cavity retaining the conductive bonding material. 
         [0030]    Exemplary IMS System for Rotational Fill Techniques 
         [0031]    According to an embodiment of the present invention  FIGS. 1-5  show a progressive sequence of an exemplary IMS system  100  utilizing rotational fill techniques. The exemplary IMS system  100  includes a non-rectangular mold  102 . The non-rectangular mold  102 , in one embodiment, is circular, however, other non-rectangular configurations may also be used according to the present invention. For example, the mold  102  may comprise oval, hexagonal, triangular, star, or any combination of these shapes. Although the foregoing embodiments are directed towards non-rectangular molds, the rotational fill techniques are also applicable to rectangular molds such as rectangular or square molds as well. In one embodiment, the non-rectangular mold  102  corresponds to a silicon wafer. In this embodiment, the non-rectangular mold  102  is comprised of borosilicate glass. In another embodiment, the non-rectangular mold  102  is comprised of glass, silicon, metal, or the like. In one embodiment, the material used to create the non-rectangular mold  102  should have the same coefficient of thermal expansion as the wafer material. For example, borosilicate glass has the same coefficient of thermal expansion as a silicon wafer. However, in another embodiment, a material such as molybdenum is used, which has a very different coefficient of thermal expansion than the wafer material. 
         [0032]    The non-rectangular mold  102  comprises a plurality of cavities  104  corresponding to wetting pads (not shown) on a wafer (not shown). The square boundaries  106  represent chip boundaries and are for illustrative purposes only. In one embodiment, the cavities  104  are formed by applying polyimide to the borosilicate glass surface. The polyimide layer is then laser processed to produce cavities  104  in the polyimide layer only. In another embodiment, wet etching is used to form the cavities  104 . However, the present invention is not limited to these two processes for forming cavities as should be well understood by those of ordinary skill in the art in view of the present discussion. 
         [0033]    A fill head  108  is also included in the IMS system  100 . The fill head  108 , in one embodiment, is made from glass, metal, graphite, or the like. The fill head  108  is configured so that it scans smoothly over a surface  110  of the non-rectangular mold  102 , or alternatively so that the mold  102  scans under the head. An exemplary fill head  108  has a smooth coating (not shown) on the surface of the fill head  108  facing the mold  102  of the fill head  108  with a low friction coefficient to ensure smooth scanning over the non-rectangular mold  102 . A reservoir (not shown) is coupled to the fill head  108  for retaining material to be provided to the cavities  104  via the fill head  108 . For example, a conductive organic material such as a conductive epoxy, a solder paste, an adhesive impregnated with conductors (e.g. metal particles), or the like is retained within the reservoir (not shown). 
         [0034]    Throughout this disclosure the term solder will be used as an example of the type of material to be deposited into the cavities  104 . The fill head  108  also includes a delivery slot (or slit)  112  that allows solder material to flow from the reservoir (not shown) into the cavities  104 . The fill head  108  in one embodiment also includes at least one gas channel (not shown) comprising a gas having a temperature above the melting point of the solder. This causes the solder from the fill head  108  to more fully liquefy (melt) and to flow into the cavities  104 . The fill head  108  will be discussed in greater detail below. 
         [0035]    An optional fill blade (not shown), in one embodiment, is optionally coupled to the fill head  108 . The optional fill blade (not shown) is situated on a portion of the fill head  108  that is in contact with the surface  110  of the mold. The optional fill blade (not shown) is situated so that the cavities  104  are filled prior to passing under the optional fill blade (not shown). The optional fill blade (not shown) prevents solder from leaking beyond the delivery slot (or slit)  112  as solder is provided to the cavities  104 . When the optional fill blade (not shown) is situated against the surface  110  of the non-rectangular mold  102  a seal is created that allows air within the cavities to escape. The optional fill blade (not shown) is comprised of either a flexible or rigid material. If a optional fill blade is not coupled. In another embodiment, the fill head  108  itself acts a optional fill blade. For example, a bottom surface of the fill head  108 , which in one example is flat and smooth, is applied to the mold with enough pressure as to exhibit a squeegee effect across the mold. 
         [0036]      FIGS. 1-5  show a fill head  108  situated along a radius of the non-rectangular mold  102 . In one embodiment, the fill head  108  is slightly longer than the radius of the non-rectangular mold  102 .  FIGS. 2-5  show the IMS system  100  in 45 degree increments as either the fill head  108  is rotated about the center of the mold  102  or the non-rectangular mold  102  is rotated about its center, or both. It should be noted that rotational motion can be imparted to one or both of the non-rectangular mold  102  and the fill head  108 . For example, the non-rectangular mold  102 , in one embodiment, is rotated up to 360 degrees while the fill head  108  remains stationary. In another embodiment, the fill head  108  is rotated up to 360 degrees while the non-rectangular mold  102  remains stationary. In yet another embodiment, both the non- rectangular mold  102  and the fill head  108  are rotated relative to each other. 
         [0037]    The rotational motion, in one embodiment, is continuous so that the non-rectangular mold  102  and/or the fill head  108  smoothly rotates without stopping. In another embodiment, the rotational force is applied in increments. Although the rotation is shown in a counter clockwise manner, the rotational motion can also be applied in a clockwise manner. Throughout this disclosure, an exemplary embodiment will be described wherein the fill head  108  remains stationary while the non-rectangular mold  102  is rotated. Additionally, even though in this example a single non-rectangular mold  102  and a single fill head  108  are shown, it should be understood by those of ordinary skill in the art in view of the present discussion that multiple non-rectangular molds  102  and/or multiple fill heads  108  can be combined in a system according to the present invention. Additionally, it should be understood that the non-rectangular mold  102  can be situated above or below the fill head  108 , according to the present invention. 
         [0038]    As the non-rectangular mold  102  is rotated about its center, the cavities  104  pass under the delivery slot (or slit)  112 . Back pressure is applied to the solder in the reservoir (not shown) by, for example, injecting a gas such as nitrogen or argon into the reservoir (not shown). The back pressure forces molten solder to flow from the reservoir (not shown) to the delivery slot (or slit)  112  whereby the molten solder exits to the surface  110  of the non-rectangular mold  102 . The fill head  108  remains in substantial contact with the surface  110  of the non-rectangular mold  102  as the non-rectangular mold  102  rotates. In one embodiment, the molten solder is directly deposited to a substrate itself such as a circuit supporting substrate without using a mold  102 . In this embodiment, the substrate is non-rectangular and has cavities similar to the cavities  104  on the mold  102 . The same procedure as described above with respect to the mold  102  is applicable when directly depositing solder onto a non-rectangular substrate. 
         [0039]    The optional filling blade (not shown), which is also in substantial contact with the surface  110 , exhibits a squeegee effect and guides the molten solder into the cavities  104  of the non-rectangular mold  102 . Filled cavities are represented by the darkened circles in  FIGS. 2-5 . The fill head  108 , according to one embodiment, also includes at least one gas channel (not shown) comprising a gas with a temperature below the melting point of the solder. This causes the molten or liquefied solder to solidify in the cavity  104  as the cavity passes under a trailing edge  114  of the fill head  108 . The fill head  108  will be discussed in greater detail below. 
         [0040]    One advantage of the present invention is the ability to fill non-rectangular molds with solder. Current IMS systems operate in a linear manner. That is, the mold and fill head move in a linear direction with respect to each other. Non-rectangular molds such as circular molds are desirable for use with circular wafers. The rotational fill techniques of the present invention allow non-rectangular molds such as circular molds to be filled without adapters. For example, prior art techniques place rectangular adapters on circular molds and scan a fill head in a linear direction across the mold. 
         [0041]    After the non-rectangular mold  102  has been rotated up to 360 degrees all of the cavities  104  are filled. The fill head  108  then can transition to an adjacent mold (not shown). In one embodiment, as the fill head  108  is transitioning from mold to mold, the back pressure is released thereby causing the solder to retract back from the delivery slot (or slit)  112 . However, in some instances the fill head  108  or a portion of the fill head  108  will extend beyond the non-rectangular mold  102  thereby exposing the delivery slot (or slit)  112  as it is transitioning. This can result in solder leaking out of the fill head either comprising the filled cavities and/or wasting the solder. To avoid this problem a parking blade  644 , in one embodiment, is coupled to the edges of the non-rectangular mold  102  where the fill head  108  transitions to the next non-rectangular mold  102 . 
         [0042]      FIGS. 6-9  illustrate the embodiment where a parking blade  602  is coupled to the non-rectangular mold  102 . Once the cavities  104  on the non-rectangular mold  102  have been filled with solder, the non-rectangular mold  102  is shuttled so that the fill head  108  transitions to the next mold (not shown). As the non-rectangular mold  102  is shuttled, a portion of the fill head  108  or the entire fill head  108  extends beyond the non-rectangular mold  102  as shown in  FIGS. 8 and 9 . The fill head  108  remains in substantial contact with the parking blade  602  thereby preventing spillage of the solder. 
         [0043]    Exemplary IMS System Utilizing a Fill Head of a Second Type 
         [0044]      FIGS. 10-12  illustrate another embodiment of the present invention wherein the fill head  1008  is slightly longer than a diameter of the non-rectangular mold  1002 .  FIGS. 10-12  show a progressive sequence at 90 degree intervals of the non-rectangular mold  1002  being rotated up to 180 degrees. The fill head  1008  is aligned along the diameter of the non-rectangular mold  1002 . As the non-rectangular mold  1002  is rotated about its center, molten solder flows from the delivery slot  1012  and onto the surface  1010  of the non-rectangular mold. As the non-rectangular mold  1002  is rotated, the optional filling blade (not shown) guides the molten solder into the cavities  1004 . In this embodiment, the fill head  1008  is bi-directional. In other words, the fill head  1008  fills the cavities  1004  in two directions. For example, cavities  1004  situated on the upper half  1016  of the non-rectangular mold  1002  are filled from an opposite direction as the cavities  1004  situated on the bottom half  1018  of the non-rectangular mold  1002 . 
         [0045]    The non-rectangular mold  1002  only needs to be rotated up to 180 degrees in order for all of the cavities  1004  to be filled. Therefore, one advantage of the present invention is that the fill time of cavities  1004  is controllable by using different fill heads  108 ,  1008 . In one embodiment, the fill head  1008  includes a set of gas channels  1122 ,  1124 ,  1126 ,  1128  ( FIG. 11 ) on a first edge  1014  and a second edge  1020  of the fill head  1008 . For example,  FIGS. 11 -12  show a first gas channel  1122  and a second gas channel  1124  on a first edge  1014  of the fill head  1008  and a third gas channel  1126  and a fourth gas channel  1128  on a second edge  1020  of the non-rectangular mold  1002 . In one embodiment, the first and fourth gas channels  1122 ,  1128  include a gas with a temperature above the melting point of the solder and the second and third gas channels  1126  include a gas having a temperature below the melting point of the solder. This configuration of the gas channels  1122 ,  1124 ,  1126 ,  1128  allows for the cavities  104  to be filled in a counter clockwise direction and have the molten solder solidified in the cavities as the pass under the opposite edge of the fill head  108  The gas channels  1122 ,  1124 ,  1126 ,  1128  are inversed when the rotation is clockwise. In another embodiment the first and fourth gas channels  1122 ,  1128  and the second and third gas channels  1126 ,  1128  are mechanically coupled to each other, respectively. 
         [0046]      FIGS. 13-15  show another embodiment of the present invention wherein a parking blade  1344  is coupled to the non-rectangular mold  1002  so that the non-rectangular mold  1002  can transition to an adjacent non-rectangular mold (not shown) without spillage of the solder. The parking blade  1344  has a width greater than the fill head  1008 . As the non-rectangular mold  1002  is shuttled so that narrower portions of the non-rectangular mold  1002  pass under the filler head  1008 , the fill head  1008  extends beyond the edges of the non-rectangular mold  1002 . Without the parking blade  1344 , solder will spill out of the fill head  1008  causing waster and/or the filled cavities  104  to be compromised. The parking blade  1344  allows for a smooth transition of the fill head  1008  to the next non-rectangular mold  1002  by keeping substantial contact with the fill head  1008 . 
         [0047]    Exemplary IMS System Utilizing a Fill Head of a Third Type 
         [0048]      FIGS. 16-20  show an IMS system  1600  implementing a substantially curved fill head  1608 , according to an embodiment of the present invention.  FIGS. 16-20  show a progressive sequence in 90 degree increments of the non-rectangular mold  102  being filled with molten solder while rotating 360 degrees. The substantially curved fill head  1608 , in one embodiment, is substantially curved relative to the curvature of the perimeter  1630  of the non-rectangular mold  1602 . The substantially curved fill head  1608  is aligned along a radius of the non-rectangular mold  1602 . As the non-rectangular mold  1602  is rotated up to 360 degrees, the cavities  1604  pass under the delivery slot  1612 . Back pressure is applied to the reservoir (not shown) causing molten solder to flow out of the fill head  1612  and onto the top surface  1610  of the non-rectangular mold  1602 . The optional fill blade (not shown) forces the molten solder into the cavities  1604 . As the cavities  1604  with molten solder pass under the trailing edge  1614  of the substantially curved fill head  1608 , the molten solder is solidified. 
         [0049]    After the cavities  1604  have been filled, the substantially curved fill head  1608  is transitioned to the next non-rectangular mold  1602  by pivoting the substantially curved fill head  1608 . For example,  FIGS. 21-22  show the substantially curved fill head  1608  being pivoted so that the substantially curved fill head  1608  passes over the outer perimeters  1630  of the non-rectangular mold  102 . The delivery slot  1612  is aligned with the outer perimeter  1630 , as shown in  FIGS. 21-22 . The substantially curved fill head  1608  is able to maintain substantial contact with the non-rectangular mold  1602  throughout the transition to an adjacent mold (not shown) without the use of a parking blade. In this embodiment, the non-rectangular molds  1602  are situated with respect to one another so that a minimal gap is produced between the molds  1602 . In another embodiment, the substantially curved fill head  1608  remains stationary as the next non-rectangular mold (not shown) is transitioned under the substantially curved fill head  1608 . 
         [0050]    Prior Art Fill Head with an Electric Resistive Heating Element 
         [0051]      FIGS. 23 and 24  show a prior art fill head  2308 . The prior art fill head  2308  includes a reservoir  2346  for retaining solder. A solder channel  2332  is coupled to the reservoir  2346  for guiding the solder to a delivery slot  2312 . The prior art fill head  2308  also includes an electric resistive heating element  2450 . The electric resistive heating element  2450  is built into the surface of the prior art fill head  2308  where the prior art fill head  2308  contacts the mold being filled. The electric resistive heating element  2450  causes mold and the solder to be heated allowing the solder to flow into cavities on the mold. 
         [0052]    One problem with the prior art fill head  2308  is the use of an electric resistive heating element  2450 , which is used to heat the mold and solder. The performance of the electronic resistive heating element  2450  is limited by a time delay for the heat to be generated in the line and then the conduction of the prior art fill head  2308 . Additionally, the prior art fill head  2308  does not provide a means for the solder to be cooled within the cavities of the mold. A time delay in the filling process is also experienced while waiting for the solder to cool within the cavities. 
         [0053]    Exemplary Fill Head 
         [0054]      FIG. 25  shows an angular view of an exemplary fill head  2508  and  FIGS. 26 and 27  show a cross sectional view and a bottom planar view, respectively, of the fill head  2508  according to an embodiment of the present invention. The fill head  2508  has a conductive bonding material reservoir  2546  for retaining conductive bonding material to be deposited into cavities of a mold. A back pressure is applied by injecting gas through a back pressure port  2548  and into the reservoir  2546 . As conductive bonding material such as solder is heated, it flows from the reservoir  2546  through a channel  2632  and into a delivery slot (or slit)  2512 . The delivery slot (or slit)  2512  allows the molten solder to flow onto a top surface of a rectangular or non-rectangular mold. 
         [0055]    In one embodiment, the fill head  2508  also includes an optional fill blade  2552 . In another embodiment, the fill head  2508  does not include an optional fill blade. The optional fill blade  2552  guides the molten solder into the cavities of the rectangular or non-rectangular mold and prevents leakage of the molten solder, leaving a surface clean of solder residue. If the mold is non-rectangular, the fill head  2508  is either slightly longer than a radius of the mold, slightly longer than a diameter of the mold, or is substantially curved to match a curvature of the mold, as described above. Also, in one embodiment, the fill head  2508  is configured so that it can provide conductive bonding material to a rectangular or non-rectangular mold bi-directionally. The solder, in one embodiment, is provided into the cavities contemporaneous with the cavities being in proximity to the fill head  2508 . 
         [0056]    The fill head  2508  also includes gas channels  2634 ,  2736  for retaining gas provided by gas ports  2740 . Each gas channel is situated along an edge  2620 ,  2714  of the fill head  2508 . The gas(es), in one embodiment, is retained in a gas reservoir(s) (not shown) external to the fill head  2508 . Gas lines  2738  coupled to gas ports  2740  transport gas to the gas channels  2634 ,  2736 . In one embodiment, the gas channels  2634 ,  2736  channel the gases about respective output regions of the fill head  2508 . In another embodiment, the at least one of the gas channels  2634 ,  2736  is situated within the fill head  108  so that solder remains molten as it travels through the delivery slot  2512  and into a cavity  104 . Also, one of the gas channels  2634 ,  2736  is situated within the fill head  108  so that solder solidifies within the cavity  104  as the cavity passes under the fill head  108 . 
         [0057]    As described above, the fill head  2508  can provide conductive bonding material to cavities either in one direction or bi-directionally. Depending on the filling direction, one of the gas channels  2634 ,  2736  retains a gas having a high heat capacity and thermal conductivity such as helium. This gas is held at a constant temperature above the melting point of the material in the material reservoir  2546 . The edge  2620 ,  2714  of the fill head  2508  that is situated in close proximity to the gas channel  2634 ,  2736  with the hot gas, in one embodiment, is grooved for maximum heat transfer. The hot gas is injected from the external gas reservoir (not shown) into a leading edge, which is the edge the cavities first pass under before they are filled with conductive bonding material. Either of the edges  2620 ,  2714  described above can be the leading edge or the trailing edge depending on the filling direction. 
         [0058]    The hot gas heats at least the leading edge  2620  causing the conductive bonding material to remain molten/liquefied as it passed through the delivery slot (or slit)  2512 . The other gas channel  2634 ,  2736  retains a gas having a temperature below the melting point of the material. A second external gas reservoir (not shown) retains this cool gas, which is injected in the other gas channel  2634 ,  2736  via the gas lines  2738  and gas ports  2740 . The trailing edge  2614  including the gas channel  2634 ,  2736  with the cool gas is cooled below the melting point of the conductive bonding material. This allows the molten material in the cavities to solidify as the cavities pass under the trailing edge  2714  of the fill head  108 . In another embodiment, the cool gas contacts the conductive bonding material in the cavities  104  thereby solidifying the material. 
         [0059]    Channeling a hot gas and a cool throughout the fill head  108  (at least in specific regions of the fill head  108 ) allows for more control over the temperature of the fill head  108  and the solder. For example, the heat/cool load from the mold  102  can change the temperature of the solder. Without the channeling of gases, the reservoir needs to be heated at a much higher temperature so that the solder does not solidify prematurely. In another embodiment, thermocouple probes (not shown) are situated in at least one of the leading edge  2620  and trailing edge  2714  to provide accurate temperature monitoring and feedback. 
         [0060]    Another Exemplary Fill Head 
         [0061]      FIGS. 28-29  show a fill head  2808  according to another embodiment of the present invention. The fill head  2808  of  FIGS. 28 and 29  includes a reservoir  2846 , a back pressure port (not shown) similar to the back pressure port  2548  of  FIG. 25 , and a delivery slot  2812  similar to the fill head  2508  of  FIGS. 26 and 27 . However, at least two gas channels  2922 ,  2924 ,  2826 ,  2828  are included at each edge  2820 ,  2914  of the fill head  2808 . For example, a first edge  2914  of the fill head  2808  includes a first gas channel  2922  and a second gas channel  2924  similar to the fill head  1008  as described with respect to  FIG. 11 . A second edge  2820  of the fill head  2808  includes a third gas channel  2826  and a fourth gas channel  2828  similar to the fill head  1008  as described with respect to  FIG. 11 . The first gas channel  2922  of the first edge  2914  of the fill head  2808  is coupled to the fourth gas channel  2828  of the second edge  2820  of the fill head  2808  via a first coupling channel  2842 . Similarly, the second gas channel  2924  of the first edge  2914  of the fill head  2808  is coupled to the third gas channel  2826  of the second edge  2820  of the fill head  2808  via a second coupling channel  2844 . For simplicity,  FIG. 28  shows only a portion of the coupling channels  2842 ,  2844 . However, the coupling channels  2842 ,  2844 , in one embodiment, cross over/under each other to connect the first gas channel  2922  to the third gas channel  2828  and the second gas channel  2924  to the fourth gas channel  2826 , respectively, as shown in  FIG. 29 . 
         [0062]    The coupling channels  2842 ,  2844  allow for different gases to be placed in different areas of the fill head  2808  and for the gas locations to be inversed depending on the fill direction of the fill head  2808 . The gases are supplied to the gas channels  2822 ,  2824 ,  2826 ,  2828  via the gas lines  2938  and the gas ports  2940 , as described with respect to  FIG. 26  and  FIG. 27 . In one embodiment, the gas channels  2922 ,  2924 ,  2826 ,  2828  channel the gases about respective regions of the fill head  2808  that are in close proximity to the conductive bonding material and/or a bottom surface of the fill head  108  that contacts the mold  102 . 
         [0063]    For example, as described with respect to the fill head  1008  of  FIG. 11 , when a fill head  1008  is used that runs the diameter of a non-rectangular mold  1002 ; solder is deposited in two different directions. Having the gas channels configured as in  FIGS. 28 and 29  allows for solder to remain molten as one gas is channeled in close proximity of the solder in the fill head  103  and solidified by channeling a gas in close proximity to a surface of the fill head  108  that contacts the mold  102 . Coupling the gas channels via the coupling channels  2842 ,  2844  also allows for the cooling and heating gases to be placed in different channels according to the rotation of the mold  1002  and/or the fill head  1008 . Alternatively, when the mold is rectangular, having gas channels configured as shown in  FIG. 28  and  FIG. 29  allows for solder to be heated and cooled irrespective of the linear fill direction. 
         [0064]    The fill heads  2508  and  2808  as described in  FIGS. 25-29  are not only advantageous for use with non-rectangular molds but are also advantageous for use with rectangular molds. Current fill heads have resistive heaters within the head. The heater is built into the surface of the fill head where the head contacts the mold being filled. A time delay is experienced because of the time it takes for the heat to be generated in the line and then the conduction of the head. Furthermore, these fill heads do not have any means for cooling the solder within the cavities. The fill heads of the present invention do not experience the time delays as described above. Furthermore, the fill heads of the present invention provide a means to cool the molten solder as the cavities pass under the fill head. 
         [0065]    Exemplary Process of Filling a Mold With Solder Using an Exemplary Fill Head 
         [0066]      FIG. 30  is an operational flow diagram showing the exemplary process of filling cavities in a mold using the fill head  2508  including gas channels  2634 ,  2736 . Although the following discussion is with respect to the fill head  2508  of  FIG. 25 , it is also applicable to the fill head  2808  of  FIG. 28 . The operational flow diagram of  FIG. 30  begins at step  3000  and flows directly to step  3002 . The fill head, at step  3002 , is aligned with a mold. For example, the fill head  108  is aligned along a radius or a diameter of a non-rectangular mold depending on the type of fill head used or is aligned across the width of a rectangular mold. The fill head  2508 , at step  3004 , is placed in substantial contact with the mold. A gas, at step  3006 , having a temperature above the melting point of the solder is provided to the fill head  5608 . This allows the solder to remain liquefied or molten as the gas is channeled in close proximity of the gas. For example, a gas such as helium kept at a constant temperature above the melting point of the solder is transferred from an external reservoir (not shown) to a gas channel  2634  within the fill head  2508 . Solder, at step  3008 , is forced out of the fill head  2508  towards the mold. For example, a back pressure is applied to a reservoir  2546  forcing the solder to flow through a channel  2632  and out of the fill head  2508 . 
         [0067]    Solder, at step  3010 , is provided to at least one cavity on the mold as the at least one cavity passes under the fill head  2508 . An optional fill blade (not shown) exhibits a squeegee effect and guides the molten solder down into the cavity. A gas, at step  3012 , having a temperature below the melting point is provided to the fill head  2508 . For example, a cool gas is transferred from an external reservoir (not shown) to another gas channel within the fill head  2508 . This causes solder in the at least one cavity to solidify as the cavity pass under the area of the fill head  2508  where the cool gas is being channeled. The control flow then exits at step  3014 . 
         [0068]    Non-Limiting Examples 
         [0069]    The foregoing embodiments of the present invention are advantageous because they provide a fill head that includes at least one gas channel. The gas channel allows for a gas having a temperature above the melting point of the conductive boning material to be retained within the fill head. The hot gas allows for the conductive bonding material to remain liquid, liquefy, or become molten as it is provided to cavities of a mold. Another gas channel within the fill head allows for gas with a temperature below the melting point of the conductive bonding material to be retained within the fill head. This causes the conductive bonding material to solidify as it comes into contact with the gas. 
         [0070]    Although specific embodiments of the invention have been disclosed, those having ordinary skill in the art will understand that changes can be made to the specific embodiments without departing from the spirit and scope of the invention. The scope of the invention is not to be restricted, therefore, to the specific embodiments, and it is intended that the appended claims cover any and all such applications, modifications, and embodiments within the scope of the present invention.