Abstract:
A semiconductor package may include a first substrate, a second substrate facing the first substrate, a plurality of first electrical connections disposed between the first substrate and the second substrate, and a first material disposed between the first substrate and the second substrate. The plurality of first electrical connections may electrically couple the first substrate and the second substrate to each other. The first material may surround each of the plurality of first electrical connections, and a width of the first material proximal the first substrate may be smaller than a width of the first material proximal the second substrate.

Description:
This application is a divisional of U.S. patent application Ser. No. 13/604,333, entitled “Methods and Apparatus for Package on Package Structures,” filed on Sep. 5, 2012, which application is hereby incorporated herein by reference. 
    
    
     BACKGROUND 
     Improvements in the size, formation, density, and packaging of integrated circuits (“ICs”) have led the semiconductor industry to experience rapid growth. Improvements in integration density have led to decreased IC feature size, which allows more components to be integrated into a given area. 
     These integration improvements are essentially two-dimensional (“2D”) in nature, in that the volume occupied by the integrated components is essentially on the surface of a semiconductor wafer. Although dramatic improvement in lithography has resulted in considerable improvement in 2D IC formations, there are physical limits to density that can be achieved in two dimensions. One of these limits is the minimum size needed to make these components. Another is the increased design complexity for increased density 2D IC formations. 
     One attempt to increase circuit density is to stack two IC dies on top of each other to form what is referred to as a three-dimensional (“3D”) IC. In a typical 3D IC formation process, two dies are bonded together and electrical connections are formed between each die and contact pads on a substrate. For example, two dies may be bonded on top of each other with the lower die being coupled to a substrate. 
     Another 3D package which increases circuit density is referred to as a “Package-on-Package” (“PoP”) structure, wherein multiple dies coupled to respective substrates (e.g., an interposer) can be “stacked” on top of each other and coupled together. To form a PoP structure, a first die is electrically coupled to a first substrate to form a first circuit. The first circuit includes first connection points for connecting to a second circuit. The second circuit includes a second die and substrate having connection points on each side of the substrate. The first circuit is stacked and electrically coupled on top of the second circuit to form the PoP structure. The PoP structure can then be electrically coupled to a printed circuit board (“PCB”) or the like. 
     In this manner, PoP structures provide increased feature density for ICs which enables more functionality to be integrated into an IC package within a minimized surface area or “footprint” on a PCB. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present embodiments, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
         FIGS. 1-4  illustrate various intermediate stages of forming an embodiment; and 
         FIG. 5  illustrates a cross sectional view of a semiconductor formed according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The making and using of the embodiments of the present disclosure are discussed in detail below. It should be appreciated, however, that the present disclosure provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use the disclosed subject matter, and do not limit the scope of the different embodiments. 
     Referring first to  FIG. 1 , there is illustrated a cross-section view of a first substrate  130  in accordance with an embodiment. In an embodiment, the first substrate  130  may be a component of a package  100 , which may include, for example, one or more integrated circuit die(s)  120  mounted on the first substrate  130  via a first set of conductive connections  152 . The first set of conductive connections  152  may comprise, for example, lead free solder, eutectic lead, conductive pillars, combinations thereof, and/or the like. 
     In an embodiment, the integrated circuit die(s)  120  may also be connected to the first substrate  130  via a second set of conductive connections  154  coupled to each of a first set of conductive features  142 . The second set of conductive connections  154  may comprise, for example, capillary wire bonds, which may be formed of aluminum, copper, gold, or other wire bonding materials. The first set of conductive features  142  may be formed of aluminum, copper, gold or other like materials. In an embodiment, the second set of conductive connections  154  may, for example, be coupled to the first set of conductive features  142  using a thermocompression bond (“TCB”).  FIG. 1  illustrates electrical connections formed between the integrated circuit dies  120  (the second set of conductive connections  154 ) using wire bonding techniques for illustrative purposes only. Other embodiments may utilize other methods, such as flip-chip, ball grid arrays, through vias, and the like. 
     In various embodiments, the first substrate  130  may be, for example, a packaging substrate, a printed-circuit board, a high-density interconnect, or the like. Through vias (“TVs”) (not shown) may be used to provide electrical connections between each of the first integrated circuit die(s)  120  and each of a second set of conductive features  144  on an opposing surface of the first substrate  130 . The first substrate  130  may also include redistribution lines (“RDLs”) (not shown) within and/or on one or both surfaces of the first substrate  130  to allow for a different pin configuration as well as larger electrical connections. A first encapsulant or overmold  160  may also be formed over the components to protect the components from the environment and/or external contaminants. In various embodiments, the first encapsulant may include an epoxy, a SiO 2  filler, a hardener, an adhesion promoter, a catalyst, combinations thereof and the like. 
     In an embodiment, the second set of conductive features  144  may have formed thereon a third set of conductive connections  156  in electrical contact with the second set of conductive features  144 . The third set of conductive connections  156  may comprise, for example, lead free solder, eutectic lead, conductive pillars, combinations thereof, and/or the like. In another embodiment, a flux (not shown) may be applied to the surface of each of the second set of conductive features  144 , which may be in contact with each of the corresponding third set of conductive connections  156 . The flux may be applied, for example, during an operation in which the surface of the first substrate  130  may be dipped or coated in the flux. The flux may help clean the surface of the second set of conductive features  144  thereby aiding in the formation of the electrical contact between each of the second set of conductive features  144  and each of the corresponding the third set of conductive connections  156 . 
     Referring now to  FIG. 2(A) , an epoxy flux  200  may be applied to the third set of conductive connections  156 . In various embodiments, the epoxy flux  200  may comprise, for example, a polymer, epoxy, flux, and/or the like or any combination thereof. Exemplary epoxy fluxes that may be used with embodiments of the present disclosure are manufactured by Henkel® or the Indium Corporation®. 
     In an embodiment, as illustrated in  FIG. 2(A) , the first package  100  may be dipped in the epoxy flux  200  to cover an exposed surface of the third set of conductive connections  156 . As shown in  FIG. 2(A) , the third set of conductive connections  156  may have a full height H as measured from a surface of the second set of conductive features  144 . In an embodiment, the epoxy flux  200  may be applied to the surface of each of the third set of conductive connections  156  to between about one-half and less than the full height H of each of the third set of conductive connections  156 . 
     Although  FIG. 2(A)  illustrates dipping the package  100  in the epoxy flux  200 , the epoxy flux  200  may be applied to the third set of conductive connections  156  through other methods, such as, for example, spraying or brushing the epoxy flux  200  on the third set of conductive connections  156  to between about one-half and less than the full height H of each of the third set of conductive connections. In an embodiment, the epoxy flux  200  may be applied, in an individual manner to each of the third set of conductive connections  156  through an injection or other similar means to apply the epoxy flux  200  to the surface of the third set of conductive connections  156 . 
       FIG. 2(B)  illustrates the epoxy flux  200  as applied to the surface of each of the third set of conductive connections  156  following a desired application method, as discussed above. As illustrated, the epoxy flux  200  may be applied to the surface of the third set of conductive connections  156  to between about one-half and less than the full height H of each of the third set of conductive connections to a cover height H COVER . Applying the epoxy flux  200  to the cover H COVER  within the range of between about one-half and less than the full height H of each of the third set of conductive connections  156  may prevent bridging between the third set of conductive connections  156  during subsequent reflow of the connections, which is described in further detail below. Application of the epoxy flux  200  to the third set of conductive connections  156  outside this range may not prevent bridging during reflow. 
     Referring now to  FIG. 3 , the package  100  may be electrically coupled to a second substrate  310 . In an embodiment, the second substrate  310  may be a component of a package  300 , which may include, for example, one or more IC die(s) (not shown) mounted thereon. The one or more IC die(s) may be mounted on the second substrate  310  using conductive connections (not shown) which may comprise, for example, lead free solder, eutectic lead, conductive pillars, capillary wire bonds, combinations thereof, and/or the like. The conductive connections may be coupled to conductive features (also not shown), which may provide electrical contact between the one or more IC dies and the second substrate  310 . The conductive connections and features may be formed of aluminum, copper, gold, combinations thereof, or the like. 
     Further formed on the surfaces of the second substrate  310  may be a third set of conductive features  312 , which may be formed on the same side as the one or more IC die(s), and a fourth set of conductive features  314 , which may be formed on an opposing surface of the second substrate  310 . In an embodiment, the third set of conductive features  312  may have formed thereon a fourth set of conductive connections  322 , which may comprise lead free solder, eutectic lead, conductive pillars, combinations thereof, and/or the like. In an embodiment, the fourth set of conductive features  314  may have formed thereon a fifth set of conductive connections  324 , which may comprise lead free solder, eutectic lead, conductive pillars, combinations thereof, and/or the like. 
     In various embodiments, the second substrate  310  may be, for example, a packaging substrate, a printed-circuit board, a high-density interconnect, or the like. Through vias (not shown) may be used to provide electrical connections between the IC die(s) and the fourth set of conductive features  314  on the opposing surface of the second substrate  310 . The second substrate  310  may also include RDLs (not shown) within and/or on one or both surfaces of the second substrate  310  to allow for a different pin configuration as well as larger electrical connections. A second encapsulant or overmold  330  may also be formed over the components to protect the components from the environment and external contaminants. 
     During manufacture, the second encapsulant  330  may first be applied to fully cover (not shown) the fourth set of conductive connections  322 . The second encapsulant  330  may then be removed to expose a surface  322   a  of each of the fourth set of conductive connections  322 . Removal of the second encapsulant  330  may be performed using a saw, laser, grinding, or other similar singulation process to expose the surface  322   a  of each of the fourth set of conductive connections  322 . Following removal of the second encapsulant  330 , the surfaces  322   a  of each of the fourth set of conductive connections  322  may be at an approximately equal height along a horizontal plane parallel to the surface of the second substrate  310 . 
     The first substrate  130  may be electrically coupled to the second substrate  310 , thereby creating a Package-on-Package structure  400 , as illustrated in  FIG. 4 .  FIG. 4  illustrates a bonding step in accordance with an embodiment wherein the third set of conductive connections  156  (having the epoxy flux  200  applied to the surface of each connection) may be brought into contact with the fourth set of conductive connections  322  of the second substrate  310 . Each of the corresponding third and fourth conductive connections  156 ,  322  of the first and second substrates  130 ,  310  may be bonded using a reflow process. In various embodiments, the reflow process may include induction reflow, RTP, IR, and the like. 
     Given that the surfaces  322   a  of each of the fourth set of conductive connections  322  of the second substrate  310  may be at an approximately equal height following removal of the second encapsulant  330 , the epoxy flux  200  may inhibit or prohibit electrical bridging or shorting between the conductive connections of the substrates  130 ,  310  during reflow. Such electrical bridging or shorting may otherwise occur in the absence of the epoxy flux  200  being applied to the third set of conductive connections  156  to the cover height H COVER . Further, electrical bridging or shorting may occur if the coverage of the epoxy flux  200  is outside the range of between about one-half and less than the full height H of each of the third set of conductive connections  156 . 
     In an embodiment, the second set of conductive features  144  on the first substrate  130  and the third and fourth sets of conductive features  312 ,  314  on the second substrate  310  may be arranged in a ball grid array (“BGA”) arrangement. In various embodiments, the pitch of third and fourth sets of conductive features may vary in a range from approximately 200 μm to approximately 500 μm. 
       FIG. 5  illustrates a combined fifth set of conductive connections  510  formed between the second and third conductive features  144 ,  312  of the corresponding first and second substrates  130 ,  310  following the reflow of third and fourth conductive connections  156 ,  322  of  FIG. 4 . Following reflow of a material which may include, for example, an epoxy flux mixture, the flux may evaporate, which may leave epoxy  520  formed between the fifth set conductive connections  510 . In an embodiment, wherein a polymer and flux may be used, there may be left polymer formed between the fifth set of conductive connections  510 . 
     It should be noted that the shape of the fifth set of conductive connections  510  as illustrated in  FIG. 5  is arbitrary and may change depending on various factors including, but not limited to, distance between the first and second substrates  130 ,  310 , the time period that the reflow may be performed, the type of reflow process, and/or the types/material composition of third and fourth conductive connections  156 ,  322  formed on the second and third conductive features  144 ,  312  of the first and second substrates  130 ,  310 . 
     Following reflow of the third and fourth conductive connections  156 ,  322  of the corresponding first and second substrates  130 ,  310  to form the fifth set of conductive connections  510 , other normal processes may be used to complete the package  400 . In an illustrative example, the second substrate  310  may be electrically coupled to yet another substrate, such as a PCB, a high density interconnect, a silicon substrate, an organic substrate, a ceramic substrate, a dielectric substrate, a laminate substrate, another semiconductor package, or the like. Further, a third encapsulant or overmold  520  may be formed between the first substrate  130  and the second encapsulant  330  to protect the substrate from the environment and external contaminants. 
     In an embodiment a device is provided. The device comprises a first substrate having a first surface, a second substrate having a first surface covered by a first encapsulant, a plurality of first electrical connections electrically coupling the first substrate to the second substrate, and a first material positioned between each of the first electrical connections, wherein the material is separated from the first surface of the first substrate. 
     In another embodiment, a method is provided. The method comprises providing a first substrate having a first plurality of electrical connections formed thereon; applying a first material to the first plurality of electrical connections to between about one-half and less than a full height of each of the first plurality of electrical connections; providing a second substrate having a second plurality of electrical connections formed thereon; contacting the first plurality of electrical connections of the first substrate to the second plurality of electrical connections of the second substrate; and performing a reflow process to form a third plurality of electrical connections between the first substrate and the second substrate, wherein the first material is positioned between each of the third plurality of electrical connections. 
     In another embodiment, another method is provided. The method comprises providing a first substrate; forming a first plurality of electrical connections on a first plurality of electrical features of the first substrate; applying a first material to the first plurality of electrical connections to between about one-half and less than a full height of each of the first plurality of electrical connections; providing a second substrate; forming a second plurality of electrical connections on a second plurality of electrical features of the second substrate; covering the second plurality of electrical connections with a first encapsulant; removing the first encapsulant from a surface of each of the second plurality of electrical connections; contacting the first plurality of electrical connections of the first substrate to the second plurality of electrical connections of the second substrate; and performing a reflow process to form a third plurality of electrical connections between the first substrate and the second substrate, wherein the first material is positioned between each of the third plurality of electrical connections. 
     It should be understood that the above description provides a general description of embodiments and that embodiments may include numerous other features. For example, embodiments may include under bump metallization layers, passivation layers, molding compounds, additional dies and/or substrates, and the like. Additionally, the structure, placement, and positioning of the first IC die(s)  120  are provided for illustrative purposes only, and accordingly, other embodiments may utilize different structures, placements, and positions. 
     Although the present embodiments and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the disclosure as defined by the appended claims. For example, it will be readily understood by those skilled in the art that the structures and ordering of steps as described above may be varied while remaining within the scope of the present disclosure. 
     Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present disclosure. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.