Abstract:
A system of producing metal cored solder structures on a substrate includes: a decal having a plurality of apertures, the apertures being tapered from a top surface to a bottom surface of the decal; a carrier configured for positioning beneath the bottom of the decal, the carrier having cavities in a top surface and the cavities located in alignment with the apertures of the decal; the decal being configured for positioning on the carrier having the decal bottom surface in contact with the carrier top surface to form feature cavities defined by the decal apertures and the carrier cavities, the feature cavities being shaped to receive a plurality of metal elements therein, the feature cavities configured for receiving molten solder being cooled in the cavities, the decal being separable from the carrier to partially expose metal core solder contacts; and receiving elements of a substrate being configured to receive the metal core solder contacts thereon, and the metal core solder contacts being exposed and positioned on the substrate.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional application of U.S. patent application Ser. No. 13/565,982. This application is related to the following commonly-owned, United States patents, and co-pending United States patent applications, the entire contents and disclosures of which are expressly incorporated by reference herein in their entirety: U.S. patent application Ser. No. 12/121,236, now U.S. Pat. No. 7,780,063, “TECHNIQUES FOR ARRANGING SOLDER BALLS AND FORMING BUMPS”; and U.S. patent application Ser. No. 11/869,573, now U.S. Pat. No. 7,928,585, “SPROCKET OPENING ALIGNMENT PROCESS AND APPARATUS FOR MULTILAYER SOLDER DECAL”; U.S. patent application Ser. No. 12/983,292. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention related to a method and system for producing metal cored solder structures; and the present invention also relates to a metal cored solder decal structure for utilization in manufacturing semiconductor or flip chip interconnections. 
         [0004]    2. Discussion of the Prior Art 
         [0005]    The present state of the art is directed to increasing the Cu/Sn ratio in flip chip semiconductor interconnections in order to be able to exploit the benefits of the copper (Cu) content that is contained therein. Copper possess a high thermal conductivity of about 398 W/m·K and a low electrical resistivity of about 1.69 mΩ·cm. In comparison, pure Sn has a thermal conductivity of about 67 W/m·K and an electrical resistivity of about 11.4 mΩ·cm, whereas eutectic PbSn solder has a thermal conductivity of about 51 W/m·K and an electrical resistivity of about 17.0 mΩ·cm. In the current state-of-the-art, there have been integrated Cu die-side bumps by using a Cu electroplating process in high-volume manufacturing quantities and with disclosed inherent reliability benefits that are related to stress, electromigration and thermal conductivity. Furthermore, it has been ascertained in the technology that the etched Cu post substrate technology can, potentially, reduce the actually expected thermal resistance of the semiconductor or flip chip interconnections. 
         [0006]    Moreover, there is also described in Ference, et al., U.S. Pat. No. 5,244,143, that the C4 NP (controlled collapse chip connect new process) can be readily extended so as to be capable of providing high Cu/Sn ratio chip interconnections through the insertion of copper (Cu) spheres into the center of flip chip joints. U.S. Pat. No. 5,244,143 is commonly assigned to the present assignee, and the disclosure of which is incorporated herein by reference in its entirety. The foregoing concept is currently utilized as described in commonly assigned U.S. patent application Ser. No. 11/733,840, now U.S. Pat. No. 7,786,001, the disclosure of which is incorporated herein by reference in its entirety. In that instance, the application provides for an area array composite interconnect structure that is constituted of a copper core which is connected to respective bond pads on a semiconductor device, and a packaging substrate with a solder. However, pursuant to the foregoing co-pending patent application, a process of transferring is described as being implemented in two steps in a separate manner with the utilization of the solder and copper. 
         [0007]    Moreover, pursuant to copending U.S. Ser. No. 11/733,840, the foregoing is limited to producing Cu cored solder bumps only on the surface of Si (silicon) wafer, whereas contrastingly in the technology there is currently a considerable need to provide for the formation of metal cored solder bumps on a substrate surface, inasmuch as the copper post that is prevalent on the substrate surface reduces the thermal resistance of the electrical interconnection. 
         [0008]    In addition to the foregoing, other aspects known in the art are disclosed in Buchwalter et. Al., US Patent Publication Nos. 2009/0093111 and 2008/0251281; Gruber, U.S. Pat. No. 5,673,846, and Ference, U.S. Pat. No. 5,244,143; all of which are commonly assigned to the present assignee, and the disclosures of which are incorporated herein by reference in their entireties. 
         [0009]    Flip-chip joints are shown in U.S. Pat. No. 7,786,001, commonly assigned to the present assignee, and which disclosure is expressly incorporated by reference herein in its entirety. U.S. Pat. No. 7,786,001 discloses an area array composite interconnect structure made up of a copper core connected to respective bond pads on a semiconductor device and a packaging substrate with solder. However, the method includes two steps of transfer processes of solder and Cu, separately. Also, U.S. Pat. No. 7,786,001 is limited to making Cu cored solder bumps only on the Si wafer side. 
         [0010]    The known art uses a process utilizing copper Si die bumps by employing a copper electroplating process, and entails the need for an extremely expensive procedure, inasmuch as it necessitates the application of a lithographic process of thick photoresists, whereas other prior art publications disclose the use of copper post bumps on the side of the substrate, and which also require the implementing of lithographic processes for the etching of a copper layer. 
       SUMMARY OF THE INVENTION 
       [0011]    There exists a need in the art to form metal cored solder bumps on the substrate side because the Cu post on the substrate side reduces the interconnection thermal resistance. Further, it would be desirable to form metal cored solder bump structures utilizing a simple one step transfer process. 
         [0012]    Accordingly, in order to improve upon and uniquely evidence the current state of the technology, the invention provides for a novel metal cored solder bump fabrication method that is implemented on Si wafers and/or electronic package substrates. A basic concept of the present invention uses the combination of a polymer film and a Si fixture in order to form metal cored solder bumps through the intermediary of only a single step transfer process. The polymer film which has through-holes found therein, aids in the arrangement of metal balls in the Si mold plate and in the implementation of a solder filled IMS (injection molded solder) process in a simultaneous manner. Moreover, the polymer film renders it possible to form metal cored solder bumps on the surface of the substrate because of a close CTE (coefficient of thermal expansion) match with that of the substrate. 
         [0013]    Hereby, in contrast with known techniques, the present invention is directed to providing for an increase in the Cu/Sn ratio of a solder bump in the absence of requiring the application of a lithography process. Moreover, in further improving the prior art and the state of the current technology, the present invention requires only a single step transfer process, and can be applied in order to form the metal cored bumps on the substrate surface. 
         [0014]    It is, accordingly, an object of the present invention to provide a system for producing metal cored solder structures on a substrate includes: a decal having a plurality of apertures, the apertures being tapered from a top surface to a bottom surface of the decal; a carrier configured for positioning beneath the bottom of the decal, the carrier having cavities in a top surface and the cavities located in alignment with the apertures of the decal; the decal being configured for positioning on the carrier having the decal bottom surface in contact with the carrier top surface to form feature cavities defined by the decal apertures and the carrier cavities, the feature cavities being shaped to receive a plurality of metal elements therein, the feature cavities configured for receiving molten solder being cooled in the cavities, the decal being separable from the carrier to partially expose metal core solder contacts; and receiving elements of a substrate being configured to receive the metal core solder contacts thereon, and the metal core solder contacts being exposed and positioned on the substrate. 
         [0015]    In another aspect of the invention, a method of producing metal cored solder structures on a substrate includes: providing a decal having a plurality of apertures, the apertures being tapered from a top surface to a bottom surface of the decal; positioning the decal on a substrate, the substrate having solder wetting pads in a top surface and the pads located in alignment with the apertures of the decal; positioning the decal on the substrate having the decal bottom surface in contact with the substrate top surface to; positioning a plurality of metal elements in the feature apertures of the decal; filling the feature apertures with molten solder and cooling the solder; and removing the decal. 
         [0016]    In another aspect of the invention, a method of producing metal cored solder structures on a substrate includes: providing a dry film on a substrate, the substrate having solder wetting pads; patterning the dry film and forming a plurality of apertures on the wetting pads; positioning a plurality of metal elements in the feature apertures of the dry film; filling the feature apertures with molten solder and cooling the solder; and removing the dry film. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The features and advantages of the present disclosure will become apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawings. The various features of the drawings are not to scale as the illustrations are for clarity in facilitating one skilled in the art in understanding the disclosure in conjunction with the detailed description. In the drawings: 
           [0018]      FIGS. 1A through 1F  is a sequence of schematic block diagrams illustrating sequentially a method for a single-step transfer in forming metal cored solder bumps on Si wafers or organic substrates according to an embodiment of the invention; 
           [0019]      FIGS. 2A through 2C  is a sequential block diagram illustrating a sequence representing a silicon mold transfer to a semiconductor wafer; 
           [0020]      FIGS. 3A through 3F  are sequential schematic block diagrams illustrating a metal cored solder decal transfer to a decal mold according to an embodiment of the invention; 
           [0021]      FIGS. 4A through 4C  are sequential schematic block diagrams illustrating a decal mold transfer to an organic substrate from  FIGS. 3A-3F ; 
           [0022]      FIGS. 5A-5C  are sequential block diagrams of a process for forming metal contacts using a mask and a mold for selectively inserting metal spheres according to an embodiment of the invention; 
           [0023]      FIG. 6  is a block diagram of the process shown in  FIGS. 5A-5C  showing a second mask; 
           [0024]      FIG. 7  is a block diagram showing injection molding of the mask and mold shown in  FIG. 6 ; 
           [0025]      FIGS. 8A-8E  are sequential schematic block diagrams illustrating a metal cored solder formation on a structure according to an embodiment of the invention; and 
           [0026]      FIGS. 9A-9F  are sequential block diagrams of a process for forming metal contacts using a dry film lamination according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0027]    The present disclosure will now be described in greater detail by referring to the following discussion and drawings that accompany the present application. The drawings of the present application, which are referred to herein below in greater detail, are provided for illustrative purposes and, as such, they are not drawn to scale. 
         [0028]    In the following description, numerous specific details are set forth, such as particular structures, components, materials, dimensions, processing steps and techniques, in order to provide a thorough understanding of the present disclosure. However, it will be appreciated by one of ordinary skill in the art that the present disclosure may be practiced without these specific details. In other instances, well-known structures or processing steps have not been described in detail in order to avoid obscuring the present disclosure. 
         [0029]    It will be understood that when an element as a layer, region or substrate is referred to as being “on” or “over” another element, it can be directly on the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” or “directly over” another element, there are no intervening elements present. It will also be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. 
         [0030]    Referring to  FIGS. 1A-1F  and  2 A- 2 C, according to an illustrative embodiment of the present disclosure, a method  10  and system for processing metal cored solder contacts (bumps or structures) on an Si wafer includes providing a decal  14  having apertures  18  or holes therethrough. The apertures  18  are tapered from a top surface  22  of the decal  14 , to a bottom surface  24  of the decal  14  which define the apertures  18 . In the embodiment of the invention shown in  FIGS. 1A and 1B , the decal  14  has a narrower top portion  26  of each of the apertures  18 , and a wider bottom portion  28  of each of the apertures  18 , as defined by the geometry of the decal  14 , and shown in  FIG. 1B . 
         [0031]    A carrier embodied as a Silicon (Si) fixture or silicon carrier  40  includes cavities  44 . The carrier  40  has a top surface  46 . The cavities  44  have a wider top portion  52  and a bottom point  54  thereby being generally “V” shaped forming cavities  44 , as shown in  FIGS. 1A and 1B . The cavities  44  may be, for example, V, U, or pyramidal shaped. 
         [0032]    The decal  14  is moved toward the carrier  40  in direction  60  as shown in  FIG. 1B , and positioned on the carrier  40  as shown in  FIG. 1C  to form feature cavities  62 . The feature cavities  62  are defined by the decal apertures  18  and the carrier cavities  44  of the decal  14  and the carrier  40 , respectively. 
         [0033]    Referring to  FIG. 1D , a metal element embodied as a metal ball  72  is positioned in the feature cavities  62 . The metal ball  72  may be comprised of, for example, Cu (copper), Au (Gold), or Ni (Nickel). The feature cavity is filled with molten solder  76  as shown in  FIG. 1E . The solder may be injection molded. The molten solder  76  is cooled. The decal  14  is moved away from the carrier  40  in the direction  80  as shown in  FIG. 1F . Metal core solder contacts  78  are comprised of the solder  76  surrounding the metal ball  72 . The metal core solder contacts  78  are partially exposed when the decal  14  is removed, specifically, a top portion  79  of the metal core solder contacts  78  are exposed. 
         [0034]    Referring to  FIG. 2A , the metal core solder contacts  78  are positioned on receiving elements  86  of a substrate, which may be embodied as a silicon wafer  82 . The carrier  40  is flipped over to be positioned over the wafer  82  as shown in  FIG. 2A . The metal core solder contacts  78  are aligned with the receiving element  86 . The receiving elements  86  can include Ball Limiting Metallurgy (BLM), positioned in the wafer  82  for receiving the metal core solder contacts  78 , as shown in  FIG. 2B . Ball-limiting metallurgy (BLM) is also known as under bump metallization (UBM) and involves the evaporation onto a wafer surface of solder through mask openings, the electroplating, or sputtering in an area array fashion. The combined carrier  40  and wafer  82 , as shown in  FIG. 2B  is heated, thereby reflowing the solder  76  of the solder contacts  78 , to arrive at the generally spherical shaped metal core solder contacts  78  shown in  FIG. 2C . 
         [0035]    Referring to  FIG. 2C , the carrier  40  is removed, in direction  80 , after heating as above, from contact with the metal core solder contacts  78  to expose the metal core solder contacts  78  on the wafer  82 . 
         [0036]    Referring to  FIGS. 3A-3C , a method  100  and system according to another embodiment of the present invention for processing metal cored solder contacts includes a decal  104  having apertures  108  or holes therethrough. The apertures  108  are tapered from a top surface  112  of the decal  104  to a bottom surface  114  of the decal  104 . In the embodiment of the invention shown in  FIGS. 3A and 3B , the decal  104  has a narrower top portion  116  of each of the apertures  108 , and a wider bottom portion  118  of each of the apertures  108 , as defined by the geometry of the decal  104 . 
         [0037]    In  FIG. 3A , a carrier embodied as a Silicon (Si) fixture or silicon carrier  120  includes cavities  124 . The carrier  120  has a top surface  126 . The cavities  124  have a generally rectangular geometry with a top opening  126 , and an upwardly extending element  130  is positioned on a bottom surface  128  of the cavities  124 , as shown in  FIGS. 3A and 3B . 
         [0038]    The decal  104  is moved toward the carrier  120  in direction  60  as shown in  FIG. 3B , and positioned on the carrier  120  as shown in  FIG. 3C  to form feature cavities  140 . The feature cavities  140  are defined by the decal apertures  108  and the carrier cavities  124  of the decal  104  and the carrier  120 , respectively. 
         [0039]    Referring to  FIG. 3D , a metal element embodied as a metal ball  72  is positioned in the feature cavities  140 . The feature cavity  140  is filled with molten solder  76  as shown in  FIG. 3E . The solder may be injection molded. The molten solder  76  is cooled. The decal  104  is moved away from the carrier  120  in the direction  80  as shown in  FIG. 3F . Metal core solder contacts  150  are comprised of the solder  76  surrounding the metal ball  72 , which is held in the decal  104 . The metal core solder contacts  150  are partially exposed when the decal  104  is removed, specifically, a bottom portion  154  of the metal core solder contacts  150  are exposed, and have two legs  158 . The narrow opening side  118  of the aperture  108  of the decal  104 , as opposed to the wide side  116  of the aperture  108 , holds the solder contact  150  during the separation of the decal  104  from the carrier  120 . 
         [0040]    Referring to  FIG. 4A , the metal core solder contacts  150  are positioned on receiving elements  164  of a substrate, which may be embodied as an organic substrate  160 . The decal  104  is positioned over the organic substrate  160  as shown in  FIG. 4A . The metal core solder contacts  150  are aligned with the receiving element  164 . The receiving elements  164  may include a specified metallurgy for receiving the metal core solder contacts  150 , as shown in  FIG. 4B . The combined decal  104  and organic substrate  160 , as shown in  FIG. 4B  is heated, thereby reflowing the solder  76  of the solder contacts  150 , to arrive at the generally spherical shaped metal core solder contacts  152  shown in  FIG. 4C . 
         [0041]    Referring to  FIG. 4C , the decal  104  is removed, in direction  80 , after heating as above, from holding the metal core solder contacts  152  which exposes the metal core solder contacts  152  on the organic substrate  160 . 
         [0042]    Referring to  FIGS. 5A-7 , a method  200  and system according to another embodiment of the present invention for processing solder contacts includes a mask and a mold for selectively forming metal spheres. In  FIG. 5A , a film  202  includes holes  204  positioned over “V” shaped recesses  210  in a mold  208 . Other shapes may be used, for example, a “U” shape. The film  202  may be a polymer film, and the mold may be a comprised of, for example, silicon, glass, or ceramic. As shown in  FIG. 5B , the recesses  210  may be selectively covered by the film applied to the mold  208 , such that access to the recess  210  is denied. Other recesses  210  are available by being aligned with the holes  204  in the film  202 , as shown in  FIG. 5B . Referring to  FIG. 5C , metal balls  212  are positioned within the recesses  210  which are aligned with the holes  204  of the film  202  and not covered by the film  202 . After the film  202  is removed from the mold  208 , a second film  214  is applied to the mold  208  as shown in  FIG. 6 . The second film  214  has generally frustoconically shaped holes  216 , however, other geometries may be used. The second film  214  with holes  216  pass therethrough. The holes  216  are narrower at the top than at the bottom of the second film. The holes  216  are aligned with all the recesses  210  of the mold  208 , such that the metal balls  212  cannot be removed from the recesses  210 , but access to all the recess  210  is available. The cavities defined by the holes  216  and recesses  210  are filled with solder  220  (for example, using injection molding) to form a metal filled solder contact. The second film  214  may be removed and the mold  208  flipped to position the metal filled solder contact comprising the solder  220  and the metal balls  212 , onto a silicon wafer. 
         [0043]    Referring to  FIGS. 8A-8E , according to an illustrative embodiment of the present disclosure, a method  300  and system for processing metal cored solder contacts (bumps or structures) on an substrate embodied as a silicon wafer  304  having contact elements  306  on a top surface thereof, as shown in  FIG. 8A . The contact elements may be of a Ball Limiting Metallurgy (BLM). A polymer film  310  is positioned over the silicon wafer  304 . The film  310  includes apertures  314  therethrough. The apertures  314  are tapered from a top surface  316  of the film  310 , to a bottom surface  318  of the film  130  which defines the apertures  314  having a generally frustoconical shape. In the embodiment of the invention shown in  FIG. 8B , the film  310  has a narrower top portion of each of the apertures  314 , and a wider bottom portion of each of the apertures  314 , as defined by the geometry of the film  310 , and shown in  FIG. 8B . Instead of a decal, a dry film can be used and the dry film is pattered by using photolithography of laser drilling method to form  FIG. 8B , as is shown in an embodiment in  FIGS. 9A-9F . 
         [0044]    Referring to  FIG. 8C , a metal ball  72  is positioned within the aperture  314  on the contact element  306  of the combined silicon wafer  304  and film  310 . The aperture  314  is filled with molten solder  76  as shown in  FIG. 8D . The solder may be injection molded. The molten solder  76  is cooled. The film  310  is removed from the silicon wafer  304  as shown in  FIG. 8E . Metal core solder contacts  320  are comprised of the solder  76  surrounding the metal ball  72 . In the case of using dry film, the dry film can be removed by using a solvent. 
         [0045]    In an alternative embodiment, the same process  300  can be implemented using an organic substrate instead of a silicon wafer  304 . In another embodiment, multiple films, for example, two films, can be stacked on one on top of the other, with aligning apertures to form a cavity on top of contact elements  306  of an organic substrate. 
         [0046]    Referring to  FIGS. 9A-9F , a method  400  and system according to another embodiment of the invention for processing solder contacts includes patterning a dry film on a substrate. Like elements of the embodiment of the invention shown in  FIGS. 8A-8E  have the same reference numerals. A dry film  410  is laminated on the silicon wafer  304  having contact elements  306 , as shown in  FIG. 9B . The film  410  is patterned to form a patterned film  414 , for example, by photolithography or laser drilling. The patterned film  414  includes apertures  416  therethrough. The apertures  416  may be tapered as shown in  FIG. 9C , or be non-tapered, or formed having other geometrical configurations. 
         [0047]    Referring to  FIGS. 9D-9F , the process is similar to that shown in  FIGS. 8C-8E . In  FIG. 9F , the remaining dry film  410  may be removed by using a solvent.