Abstract:
A plurality of through-substrate holes is formed in each of at least one substrate. Each through-substrate hole extends from a top surface of the at least one substrate to the bottom surface of the at least one substrate. The at least one substrate is held by a stationary chuck or a rotating chuck. Vacuum suction is provided to a set of through-substrate holes among the plurality of through-substrate holes through a vacuum manifold attached to the bottom surface of the at least one substrate. An injection mold solder head located above the top surface of the at least one substrate injects a solder material into the set of through-substrate holes to form a plurality of through-substrate solders that extend from the top surface to the bottom surface of the at least one substrate. The vacuum suction prevents formation of air bubbles or incomplete filling in the plurality of through-substrate holes.

Description:
BACKGROUND 
       [0001]    The present invention generally relates to apparatuses and methods for forming seamless solder structures through at least one substrate. 
         [0002]    As consumer products such as mobile phones become thinner, highly integrated semiconductor chips are needed to provide multiple functions within a single portable device. In such devices, power and ground interconnects as well as signal interconnects extend not only across a single substrate including a semiconductor chip, but also across multiple substrates that include multiple semiconductor chips that are vertically stacked. Such vertically stacked substrates are typically called “multistacks.” Providing conductive interconnect structures for such multistacks is a costly and time-consuming process. 
         [0003]    Typically, line cavities and via holes in each dielectric layer are patterned and filled with a conductive material for each substrate to form conductive lines and conductive vias. Patterning and filling of the line cavities and via holes is typically effected by a combination of lithographic processes, anisotropic etching, and deposition of a conductive material. The deposition of a conductive material includes deposition of an adhesion/seed layer by means such as chemical vapor deposition (CVD) or physical vapor deposition (PVD), a subsequent via fill by a CVD, PVD, or a plating process, and a planarization process to remove excessive material from a top surface of the topmost dielectric layer. The conductive materials commonly used for conductive lines and conductive vias include polysilicon, tungsten, and copper. 
         [0004]    Once each substrate is provided with conductive lines and conductive vias, inter-substrate electrical connection is provided typically in the form of metallic bumps, which can be a solder ball. Such bump interconnects usually require compatible under-bump metallurgies (ubm) to be formed on each substrate surface followed by deposition of the metallic bumps on at least one of the two mating substrate surfaces. The two substrates are then interconnected by aligning interconnect bumps and/or ubm pads of each mating substrates then forming metallurgical connections by means of solder reflow or thermoconipression. As such, any use of solder for interconnection is limited to the space between two substrates but not extending into any of the two substrates. 
       BRIEF SUMMARY 
       [0005]    In an embodiment of the present invention, a plurality of through-substrate holes is formed in at least one substrate. Each through-substrate hole extends from a top surface of the at least one substrate to the bottom surface of the at least one substrate. The at least one substrate is held by a stationary chuck or a rotating chuck. Vacuum suction is provided to a set of through-substrate holes among the plurality of through-substrate holes through a vacuum manifold attached to the bottom surface of the at least one substrate. An injection mold solder head located above the top surface of the at least one substrate injects a solder material into the set of through-substrate holes to form a plurality of through-substrate solders that extend from the top surface to the bottom surface of the at least one substrate. The vacuum suction prevents formation of air bubbles or incomplete filling in the plurality of through-substrate holes. 
         [0006]    According to an aspect of the present invention, an apparatus for forming at least one seamless conductive solder structure through at least one substrate is provided. The apparatus includes an upper assembly, a lower assembly, and a vacuum pump. The upper assembly and the lower assembly are configured to move relative to each other. The upper assembly, which is located above the lower assembly, is configured to provide a solder material through an opening on a bottom surface of the upper assembly. The lower assembly includes a chuck including a vacuum pumping line that is connected to the vacuum pump. The lower assembly is configured to laterally confine the at least one substrate. A filter structure, located within a recessed region of the chuck, is configured to vertically support a bottom surface of the at least one substrate. The filter structure is connected to the vacuum pumping line. The upper assembly injects the solder material through at least one through-substrate hole extending from a top surface of the at least one substrate to the bottom surface of the at least one substrate to form at least one through-substrate seamless conductive solder structure that extends from the top surface of the at least one substrate to the bottom surface of the at least one substrate. 
         [0007]    According to another aspect of the present invention, an apparatus for forming at least one seamless conductive solder structure through at least one substrate is provided. The apparatus includes a set of an upper assembly and a lower assembly, a middle assembly, and a vacuum pump. The middle assembly and the set of the upper and lower assemblies are configured to move relative to each other, while the upper assembly maintains a same relative position with respect to the lower assembly. The upper assembly, which is located above the middle assembly, is configured to provide a solder material through an opening on a bottom surface of the upper assembly. The middle assembly includes a first chuck configured to laterally confine the at least one substrate. The first chuck maintains a same relative position with respect to the at least one substrate. The lower assembly includes a second chuck including a vacuum manifold that is connected to the vacuum pump. The upper assembly injects the solder material through at least one through-substrate hole extending from a top surface of the at least one substrate to a bottom surface of the at least one substrate to form at least one through-substrate seamless conductive solder structure that extends from the top surface of the at least one substrate to the bottom surface of the at least one substrate. 
         [0008]    According to yet another aspect of the present invention, a method of forming at least one seamless conductive solder structure through at least one substrate is provided. The method includes providing an apparatus including an upper assembly, a lower assembly, and a vacuum pump. The upper assembly and the lower assembly of the apparatus are configured to move relative to each other. The lower assembly of the apparatus includes a chuck and a filter structure, and the chuck includes a vacuum pumping line that is connected to the vacuum pump. The filter structure is located within a recessed region of the chuck. At least one substrate, which includes at least one through-substrate hole extending from a top surface of the at least one substrate to the bottom surface of the at least one substrate, is placed on the filter structure. The chuck laterally confines the at least one substrate, and the filter structure vertically supports the bottom surface of the at least one substrate. A solder material is injected from the upper assembly into the at least one through-substrate hole. During the injection, the pump provides vacuum environment to an unfilled portion of a through-substrate hole into which the solder material is injected. At least one through-substrate seamless conductive solder structure that extends from the top surface of the at least one substrate to the bottom surface of the at least one substrate is provided. 
         [0009]    According to still another aspect of the present invention, a method of forming at least one seamless conductive solder structure through at least one substrate is provided. The method includes providing an apparatus including a set of an upper assembly and a lower assembly, a middle assembly, and a vacuum pump. In this apparatus, the middle assembly and the set of the upper and lower assemblies are configured to move relative to each other while the upper assembly maintains a same relative position with respect to the lower assembly. The middle assembly includes a first chuck configured to laterally confine the at least one substrate and maintain a same relative position with respect to the at least one substrate. The lower assembly includes a second chuck including a vacuum pumping line that is connected to the vacuum pump. At least one substrate, which includes at least one through-substrate hole extending from a top surface of the at least one substrate to the bottom surface of the at least one substrate, is placed on the second chuck. The first chuck laterally confines the at least one substrate and the second chuck vertically supports the bottom surface of the at least one substrate. A solder material is injected from the upper assembly into the at least one through-substrate hole. During the injection, the pump provides a vacuum environment to an unfilled portion of a though-substrate hole into which the solder material is injected. At least one through-substrate seamless conductive solder structure that extends from the top surface of the at least one substrate to the bottom surface of the at least one substrate is provided. 
     
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
         [0010]      FIG. 1A  is a schematic top-down view of a first exemplary apparatus according to a first embodiment of the present invention. 
           [0011]      FIG. 1B  is a schematic vertical cross-sectional view of the first exemplary apparatus in  FIG. 1A  along the plane B-B′. 
           [0012]      FIG. 1C  is a schematic vertical cross-sectional view of the first exemplary apparatus in  FIG. 1A  along the plane C-C′. 
           [0013]      FIG. 2  is a schematic top-down view of a second exemplary apparatus according to a second embodiment of the present invention. 
           [0014]      FIG. 3A  is a schematic top-down view of a third exemplary apparatus according to a third embodiment of the present invention. 
           [0015]      FIG. 3B  is a schematic vertical cross-sectional view of the third exemplary apparatus in  FIG. 3A  along the plane B-B′. 
           [0016]      FIG. 3C  is a schematic vertical cross-sectional view of the third exemplary apparatus in  FIG. 3B  along the plane C-C′. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    As stated above, the present invention relates to apparatuses and methods for forming seamless solder structures through at least one substrate, which are now described in detail with accompanying figures. Throughout the drawings, the same reference numerals or letters are used to designate like or equivalent elements. The drawings are not necessarily drawn to scale. 
         [0018]    As used herein, “at least one substrate” refers to a single substrate or a plurality of substrates that are vertically stacked together. 
         [0019]    As used herein, a “through-substrate hole” refers to a cavity that extends from a topmost surface of at least one substrate to a bottommost surface of the at least one substrate. A through-substrate hole extends from a top surface of a single substrate to a bottom surface of the single substrate, or from a top surface of a topmost substrate in a plurality of substrates to a bottom surface of a bottommost substrate in the plurality of substrates. 
         [0020]    As used herein, a “through-substrate solder structure” refers to a contiguous solder structure that extends from a topmost surface of at least one substrate to a bottommost surface of the at least one substrate. A through-substrate solder structure extends from a top surface of a single substrate to a bottom surface of the single substrate, or from a top surface of a topmost substrate in a plurality of substrates to a bottom surface of a bottommost substrate in the plurality of substrates. 
         [0021]    As used herein, a “partially-filled through substrate hole” refers to a solder structure that partially fills a through-substrate hole but does not completely fill the through-substrate hole. 
         [0022]    As used herein, a “seamless conductive solder structure” refers to a structure of a conductive solder material that is in one contiguous piece without a seam or an interface therein. 
         [0023]    Referring to  FIGS. 1A-1C , a first exemplary apparatus according to a first embodiment of the present invention is shown, which can be employed to form at least one seamless conductive solder structure through at least one substrate  30 . The first exemplary apparatus includes an upper assembly  55 , a lower assembly  15 , and a vacuum pump (not shown). The upper assembly  55  and the lower assembly  15  are configured to move relative to each other. The lower assembly  15  is configured to hold the at least one substrate  30 , which may include, for example, a stack of a first substrate  30 A, a second substrate  30 B, and a third substrate  30 C. While the present invention is illustrated employing the at least one substrate  30  that includes the first, second, and third substrates ( 30 A,  30 B,  30 C) that are vertically stacked, the present invention can be employed for a single substrate or a plurality of substrates of any number that are vertically stacked together. 
         [0024]    Each of the at least one substrate ( 30 A,  30 B,  30 C) may be any type of substrate that requires an electrical interconnection or a structural interconnection by at least one through-substrate seamless conductive solder structure  46 . For example, the at least one substrate ( 30 A,  30 B,  30 C) can be a plurality of semiconductor substrates, each including semiconductor chips. The at least one substrate ( 30 A,  30 B,  30 C) may include a first semiconductor substrate including a plurality of processor core dies, a second semiconductor substrate including a plurality of memory dies, etc. 
         [0025]    The various semiconductor substrates in the at least one substrate ( 30 A,  30 B,  30 C) may be aligned prior to loading onto the chuck  20  so that a plurality of through-substrate holes may be formed while each die in a semiconductor substrate is vertically aligned to all other dies directly above or below in the stack of the at least one substrate ( 30 A,  30 B,  30 C). The plurality of through-substrate holes are vertically aligned through all substrates in the at least one substrate ( 30 A,  30 B,  30 C). The horizontal cross-sectional area of each through-substrate hole may be constant across the entirety of each through-substrate hole. The at least one through-substrate seamless conductive solder structure  46  provides electrical connection among the plurality of semiconductor substrates in the at least one substrate ( 30 A,  30 B,  30 C) such that each vertical stack of semiconductor dies are electrically wired. The horizontal cross-sectional area of each at least one through-substrate seamless conductive solder structure  46  may be constant between the top surface and the bottom surface of the at least one substrate ( 30 A,  30 B,  30 C). 
         [0026]    Upon formation of the at least one through-substrate seamless conductive solder structure  46 , stacks of vertically connected dies may be diced out from the at least one substrate ( 30 A,  30 B,  30 C). Each stack of vertically connected dies includes electrical connections enabled by the at least one through-substrate seamless conductive solder structure  46 , which may be employed to provide a power supply grid network, an electrical ground grid network, and/or at least one signal grid network cross multiple dies located at different levels of the vertical stack. 
         [0027]    The upper assembly  55  is located above the lower assembly  15  and the at least one substrate  30 . The upper assembly  55  is configured to provide a solder material through an opening on a bottom surface of the upper assembly  55 . For example, the upper assembly  55  may include an injection mold system having an enclosure  50  with an opening on a bottom surface and a movable extrusion actuator  52  on another opening therein. As the movable extrusion actuator  52  moves, for example, downward in the direction of an arrow in  FIGS. 1B and 1C , a solder material  60  within the enclosure  52  extrudes into at least one through-substrate holes in the at least one substrate. Alternatively, the upper assembly  55  may be any other type of device that is configured to extrude a solder material from an opening on a bottom surface. 
         [0028]    The lower assembly  15  includes a chuck  10 . The chuck  10 , which includes a vacuum pumping line  12 , is configured to laterally confine the at least one substrate  30 . For example, the chuck  10  may have a recessed region having a substantially same horizontal cross-sectional shape as the at least one substrate  30  that is laterally confined by the chuck  10 . The vacuum pumping line is connected to the vacuum pump through the vacuum pumping line  12 . A filter structure  20  is located within a recessed region of the chuck  10 . The filter structure  20  can be a mesh of any solid material, or can be a porous material that retards flow of the solder material therethrough. Preferably, the pumping line is connected directly to a surface of the filter structure  20 . 
         [0029]    Preferably, the filter structure  20  is made of a heat-resistant material to withstand an elevated temperature of the solder material during extrusion from the upper assembly  55 . Typically, the temperature of the solder material from the upper assembly  55  can be from 200° C. to 400° C. during the extrusion depending of the melting point of the solder material, which is a metallic compound including metals such as Sn, Ag, Cu, etc. The filter structure  20  is configured to vertically support a bottom surface of the at least one substrate  30 . The filter structure  20  is connected to the vacuum pumping line  12  so that any gas flowing into the filter structure  20  is pumped through the vacuum pumping line  12  into the vacuum pump. 
         [0030]    The upper assembly  55  injects the solder material through at least one through-substrate hole extending from a top surface of the at least one substrate  30  to the bottom surface of the at least one substrate  30 . At least one through-substrate seamless conductive solder structure  46  that extends from the top surface of the at least one substrate  30  to the bottom surface of the at least one substrate  30  is thereby formed. 
         [0031]    The at least one substrate  30  may include a plurality of through-substrate holes. A first group of through-substrate holes may include only an ambient gas. The first group of through-substrate holes is herein referred to as “unfilled through-substrate holes under ambient conditions”  40 . A second group of through-substrate holes can be under vacuum when a bottom surface of the upper assembly completely covers an opening on the topmost surface of the at least one substrate  30  while most gas in the second group of through-substrate holes is pumped out through the filter structure  20  and the vacuum pumping line  12  into the vacuum pump. The second group of through-substrate holes is herein referred to as “unfilled though-substrate holes under vacuum”  42 . The unfilled through-substrate holes under ambient conditions  40  and the unfilled though-substrate holes under vacuum  42  are collectively referred to as “unfilled through-substrate holes” ( 40 ,  42 ). 
         [0032]    A third group of through-substrate holes includes a volume under vacuum  44 A and a solder material portion  44 B that does not completely fill a through-substrate hole. The third group of through-substrate holes is referred to as “partially-filled through-substrate holes”  44 , each of which includes a volume under vacuum  44 A and a solder material portion  44 B. A fourth group of through-substrate holes are completely filled with a solder material so that a through-substrate solder structure fills each of the fourth group of through-substrate holes. Each through-substrate solder structure is a seamless conductive solder structure including a conducive solder material of a single contiguous piece without an interface or a seam therein. 
         [0033]    The filter structure  20  is configured to draw in the ambient gas through unfilled through-substrate holes under ambient conditions  40 , each of which is one of the at least one through-substrate hole prior to injection of the solder material and prior to complete covering by the bottom surface of the upper assembly  55 . Further, the filter structure  20  is configured to provide a vacuum environment to unfilled though-substrate holes under vacuum  42 , each of which is one of a through-substrate hole that a bottom surface of the upper assembly  55  covers prior to injecting the solder material. 
         [0034]    Yet further, the filter structure  20  is configured to provide a vacuum environment to an unfilled portion of a partially-filled through-substrate hole  44 , i.e., a volume under vacuum, in the at least one substrate  30  while the upper assembly  55  injects the solder material into the partially-filled through-substrate hole  44  to expand a solder material portion  44 B, which is a filled portion of the partially-filled through substrate hole  44  that includes the solder material. 
         [0035]    The upper assembly  55  can be configured to remain stationary while the lower assembly  15  and the at least one substrate  30  rotate around an axis of the chuck  10 . In this case, the chuck  10  and the at least one substrate  30  rotate around the axis of the chuck  10 . Preferably, the axis of the chuck  10  is perpendicular to an interface between the upper assembly  55  and the top surface of the at least one substrate  30 , which can be parallel to the interface between the filter structure  20  and the at least one substrate  30 . The top surface of the at least one substrate  30  can be, but does not need to be, parallel to the bottom surface of the at least one substrate  30 . 
         [0036]    Alternatively, the lower assembly  15  can be configured to remain stationary and keep the at least one substrate  30  stationary as well, while the upper assembly  55  rotates around an axis of the upper assembly. 
         [0037]    The upper assembly  55  is configured to contact the top surface of the at least one substrate  30  without a gap between the upper assembly  55  and the at least one substrate  30 . The absence of any gap between the upper assembly  55  and the at least one substrate  30  is maintained during the relative movement between the upper assembly  55  and the at least one substrate  30 . Thus, the upper assembly  55  is configured to continuously inject the solder material during a relative movement between the upper assembly  55  and the at least one substrate, while the upper assembly  55  contacts the at least one substrate  30  without a gap. 
         [0038]    During the operation of the first exemplary apparatus, the at least one substrate  30 , which includes at least one through-substrate hole extending from a top surface of the at least one substrate  30  to the bottom surface of the at least one substrate  30 , is placed on the filter structure  20 . The chuck  10  laterally confines the at least one substrate  30  and the filter structure  20  vertically supports the bottom surface of the at least one substrate  30 . The solder material is injected from the upper assembly  55  into the at least one through-substrate hole. Each of the at least one through-substrate hole changes its state from an unfilled through-substrate holes under ambient conditions  40 , to an unfilled though-substrate holes under vacuum  42 , then to a partially-filled though-substrate hole  44 , and then to a filled through-substrate hole including a through-substrate seamless conductive solder structure  46  until all of the at least one through-substrate hole becomes filled with a through-substrate seamless conductive solder structure  46 . 
         [0039]    During the extrusion and filling process, the pump provides a vacuum environment to an unfilled portion  44 A of a partially-filled though-substrate hole  44  into which the solder material is injected. Each of the at least one through-substrate seamless conductive solder structure  46  extends from the top surface of the at least one substrate  30  to the bottom surface of the at least one substrate  30 . 
         [0040]    In case the at least one substrate  30  is a plurality of substrates, each of the at least one through-substrate hole extends through each substrate in the plurality of substrates. 
         [0041]    Referring to  FIG. 2 , a second exemplary apparatus according to a second embodiment of the present invention includes the same elements as the first exemplary apparatus described above with a difference that the upper assembly  55  (See  FIGS. 1B and 1C ) and/or the lower assembly  15  (See  FIGS. 1B and 1C ) move relative to each other in a one-dimensional linear motion or in a two-dimensional linear motion. Preferably, the relative motion is designed to provide filling of all through substrate holes in the at least one substrate  30 . 
         [0042]    Referring to  FIGS. 3A-3C , a third exemplary apparatus according to a third embodiment of the present invention is shown, which can be employed to form at least one seamless conductive solder structure through at least one substrate  30 . The third exemplary apparatus includes a set of an upper assembly  155  and a lower assembly  125 , a middle assembly  105 , and a vacuum pump (not shown). The middle assembly  105  and the set of the upper and lower assemblies ( 155 ,  125 ) are configured to move relative to each other while the upper assembly  155  maintains a same relative position with respect to the lower assembly  125 . Thus, in a frame of reference that moves with the upper assembly, the lower assembly  125  looks stationary, while the middle assembly  105  moves relative to the upper assembly  155 . 
         [0043]    The middle assembly  105  includes a first chuck  110  that is configured to laterally confine at least one substrate  30 . Further, the first chuck  110  is configured to maintain a same relative position with respect to the at least one substrate  30 . Further, the middle assembly  105  can move relative to the set of the upper and lower assemblies ( 155 ,  125 ) by laterally sliding at two interfaces that are marked by two sets of lateral arrows shown in  FIG. 3B . 
         [0044]    The upper assembly  155  is located above the middle assembly  105  and the at least one substrate  30 . The upper assembly  155  is configured to provide a solder material through an opening on a bottom surface of the upper assembly  155 . 
         [0045]    The lower assembly  125  includes a second chuck  120 . The second chuck includes a vacuum manifold  122  that is connected to the vacuum pump via a vacuum pumping line  112 . An opening in the vacuum manifold  122  at the top surface of the second chuck  120  does not extend across the entirety of the top surface of the second chuck  120 , but is limited to an area that corresponds to the area of the opening from which the solder material is extruded on the bottom surface of the upper assembly  155 . It is critical for the vacuum manifold  122  to evacuate the vias and disengage from the vias before the molten solder is injected to avoid solder getting sucked into the vacuum manifold. In other words, the relative position of the vacuum manifold  122  preceeds the opening slot  52  from which the solder material is extruded. Optionally, a filter structure (not shown) may be placed within the vacuum manifold to retard the flow of the solder material that accidentally extrudes out of the bottom surface of the at least one substrate  30 . 
         [0046]    The second chuck  120  is configured to vertically support the bottom surface of the at least one substrate  30 , and to move relative to the first chuck  110  while the bottom surface of the at least one substrate  30  covers the vacuum manifold  122 . 
         [0047]    The upper assembly  120  injects the solder material through at least one through-substrate hole extending from a top surface of the at least one substrate  30  to a bottom surface of the at least one substrate  30  to form at least one through-substrate seamless conductive solder structure  46  that extends from the top surface of the at least one substrate  30  to the bottom surface of the at least one substrate  30 . The second chuck  120  is configured to provide a vacuum environment to an unfilled portion  44 A of a partially-filled through-substrate hole  44  in the at least one substrate  30  while the upper assembly  155  injects the solder material into the partially-filled through-substrate hole  44  to expand a filled portion  44 B of the partially-filled through substrate hole  44  that includes the solder material. 
         [0048]    The middle assembly  105  can be configured to remain stationary with the at least one substrate  30  while the set of the upper and lower assemblies ( 155 ,  125 ) rotates around an axis of the second chuck  120 . In this case, the set of the upper and lower assemblies ( 155 ,  125 ) rotates around the axis of the second chuck  120 . The axis of rotation is perpendicular to an interface between the first chuck  110  and the second chuck  120 , i.e., perpendicular to the interface between the lower assembly  125  and the at least one substrate  30 . Further, the axis of the second chuck  120  is perpendicular to an interface between the upper assembly  155  and the top surface of the at least one substrate  30 . The top surface of the at least one substrate  30  is parallel to the bottom surface of the at least one substrate  30  in this case. 
         [0049]    Alternatively, the set of the upper and lower assemblies ( 155 ,  125 ) can be configured to remain stationary, while middle assembly  105  and the at least one substrate  30  rotate around an axis of the middle assembly  105 . 
         [0050]    The upper assembly  155  is configured to contact the top surface of the at least one substrate  30  without a gap between the upper assembly  155  and the at least one substrate  30 . The absence of any gap between the upper assembly  155  and the at least one substrate  30  is maintained during the relative movement between the upper assembly  55  and the at least one substrate  30 . Thus, the upper assembly  155  is configured to continuously inject the solder material during a relative movement between the upper assembly  155  and the at least one substrate  30 , while the upper assembly  155  contacts the at least one substrate  30  without a gap. 
         [0051]    During the operation of the third exemplary apparatus, the at least one substrate  30 , which includes at least one through-substrate hole extending from a top surface of the at least one substrate  30  to the bottom surface of the at least one substrate  30 , is placed on the second chuck  120  and within the first chuck  110 . The first chuck  110  laterally confines the at least one substrate  30  and the second chuck  120  vertically supports the bottom surface of the at least one substrate  30 . The solder material is injected from the upper assembly  155  into the at least one through-substrate hole. Each of the at least one through-substrate hole changes its state from an unfilled through-substrate hole under ambient conditions  40 , to an unfilled though-substrate hole under vacuum, then to a partially-filled though-substrate hole  44 , and then to a filled through-substrate hole including a through-substrate seamless conductive solder structure  46  until all of the at least one through-substrate hole becomes filled with a through-substrate seamless conductive solder structure  46 . 
         [0052]    During the extrusion and filling process, the pump provides a vacuum environment through the vacuum pumping line  112  and the vacuum manifold  122  to an unfilled portion  44 A of a partially-filled though-substrate hole  44  into which the solder material is injected. Each of the at least one through-substrate seamless conductive solder structure  46  extends from the top surface of the at least one substrate  30  to the bottom surface of the at least one substrate  30 . The vacuum manifold  122  evacuates the unfilled through-substrate hole under ambient conditions  40  and the partially-filled though-substrate hole  44 , but is disengaged from the through-substrate seamless conductive solder structure  46  before the molten solder is injected into the vacuum manifold  122 . During rotation of the upper assembly  155  relative to the middle assembly  105 , the position of the vacuum manifold  122  azimuthally precedes the opening slot  52  from which the solder material is extruded. 
         [0053]    In case the at least one substrate  30  is a plurality of substrates, each of the at least one through-substrate hole extends through each substrate in the plurality of substrates. 
         [0054]    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 the foregoing and other changes in forms and details can be made without departing from the spirit and scope of the present invention. For example, the substrate need not be a circular wafer in rotation, but square or rectangular shaped substrate with the injection molded solder scanning in a linear motion. It is therefore intended that the present invention not be limited to the exact forms and details described and illustrated, but fall within the scope of the appended claims.