Abstract:
Electronic devices and methods for fabricating electronic devices are described. One method includes providing a substrate and a die, and coupling the die to the substrate, wherein a gap remains between the die and the substrate. The method also includes placing an underfill material on the substrate and delivering at least part of the underfill material into the gap. The method also includes controlling the flow of the underfill material in the gap using magnetic force. Other embodiments are described and claimed.

Description:
RELATED ART 
       [0001]    In certain conventional electronic assembly manufacturing procedures, a die  10  and a substrate  12  are brought into electrical contact through solder bumps  14 . A reflow operation is carried out by heating to a temperature greater than the melting point of the solder, and a solder connection is made between the pads on the die  10  and pads on the substrate  12 . A material such as a polymer is then typically applied between the chip and substrate as an underfill encapsulant. 
         [0002]    As illustrated in  FIG. 1 , a dispenser  16  such as a needle is positioned adjacent to a die  10  coupled to a substrate  12  through solder bumps  14 . An underfill material  18  is dispensed on the substrate  12  next to the die attach area (the area that is covered by the die  10 ). The underfill material  18  may include a polymer, for example, an epoxy. With the application of heat, the underfill material  18  may be made to flow between the die  10  and substrate  12 , using capillary action. When formed from a polymer epoxy, the underfill material  18  may then be cured. The cured underfill material  18  surrounds the solder bumps  14  and protects the bumps and connection between the die  10  and substrate  12 , as well as support the die  10  on the substrate  12 . 
         [0003]      FIGS. 2(A)-2(D)  illustrate the flow of the underfill material  18  (cross-hatched in  FIGS. 2(A)-2(D) ) under the die  10 .  FIG. 2(A)  shows underfill material  18  adjacent to the die  10 .  FIGS. 2(B)-2(D)  show the progression of the underfill material  18  across the die attach area between the die  10  and substrate  12 , due to capillary forces.  FIG. 2(D)  illustrates the final position of the underfill material  18 , including the presence of a tongue region  11  and side spread regions  13 ,  15 ,  17  of underfill material  18  on the surface of the substrate  12 , to the sides of the die  10 . The tongue region  11  is larger than the side spread regions  13 ,  15 ,  17  because the tongue region  11  is on the side where the underfill material  18  was initially dispensed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]    Embodiments are described by way of example, with reference to the accompanying drawings, which are not drawn to scale, wherein: 
           [0005]      FIG. 1  illustrates a side view of a conventional processing operation in which an underfill material is dispensed on a substrate; 
           [0006]      FIGS. 2(A)-2(D)  illustrate the flow of underfill material into the die attach region between a die and a substrate due to capillary action, in accordance with certain conventional processing procedures; 
           [0007]      FIGS. 3(A)-3(D)  illustrate the flow of underfill material into the die attach region between a die and a substrate when applying a magnetic field to an underfill material including magnetic particles, in accordance with certain embodiments; 
           [0008]      FIGS. 4(A)-4(B)  illustrate views of an assembly in which the application of a magnetic field to an underfill material results in no tongue region or side spread regions being formed, in accordance with certain embodiments; 
           [0009]      FIG. 5(A)-5(B)  illustrate views of an assembly in which the application of a magnetic field to an underfill material results in a small and uniform in size tongue region and side spread regions being formed, in accordance with certain embodiments; 
           [0010]      FIG. 6  illustrates a flow chart of operations in a process for forming an assembly using an underfill material including magnetic particles and applying a magnetic field to the underfill material, in accordance with certain embodiments; and 
           [0011]      FIG. 7  illustrates an electronic system arrangement in which embodiments may find application. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    The presence of tongue and/or side spread regions as illustrated in  FIG. 2(D)  can lead to certain problems due to the large surface area that becomes covered with the underfill material. Such problems may include interactions between the underfill material and other structures, for example, when the substrate is small as in ultra small form factors, and when devices such as die side capacitors are mounted on the die side of the substrate. As a result, the underfill keep out zone on the substrate (the area where other structures are kept out due to the spread of the underfill material beyond the die attach area) may be undesirably large. 
         [0013]    Certain embodiments relate to the formation of electronic assemblies, in which the flow of underfill material outside of the die attach area is inhibited. Certain embodiments include electronic assemblies. Certain embodiments include methods for forming electronic assemblies. 
         [0014]      FIGS. 3(A)-3(D)  illustrate views of an electronic assembly during several stages of processing, in accordance with certain embodiments. More specifically,  FIGS. 3(A)-3(D)  illustrate the flow of underfill material  118  (cross-hatched in  FIGS. 3(A)-5(B) ) into a die attach region between a die  110  and a substrate  112  when applying a magnetic field to the underfill material  118 , as indicated by the arrow in  FIGS. 3(B)-3(D) . It should be appreciated that as illustrated in certain Figures herein, the underfill material  118  is observed through the die  110 . Die materials are not typically formed from transparent materials. However, to clearly indicate the position of the underfill material  118 , the die  110  appears to be transparent in certain Figures. 
         [0015]      FIG. 3(A)  shows the position of the underfill material  118  after it is dispensed on the substrate  112 , adjacent to one side of the die  110 . As illustrated in the blown-up portion of  FIG. 3(A) , the underfill material  118  includes particles  123  dispersed in an underfill matrix material  121 . The particles  123  may be formed from a variety of magnetic materials, including, but not limited to aluminum, platinum, magnesium, molybdenum, lithium, tantalum, and iron containing materials. One example of suitable magnetic particles includes Fe 2 O 3  particles. The magnetic particles may include a surface functionalization layer that is optimized to coat the particle with a layer that is electrically insulating in order to prevent the magnetic particles from causing the underfill material to become an electrically conductive medium. A specific example of suitable magnetic particles with a coating includes Fe 2 O 3  nanoparticles with alkyl surface functionalization. Other size particles (larger than nanoparticles) may also be used in various embodiments. Additional additives (for example, to inhibit particle agglomeration) may also be included in the underfill material  118 , if desired. 
         [0016]    The underfill matrix material  121  of the underfill material  118  may be any suitable material including, but not limited to, polymer epoxies. Suitable underfill matrix materials  121  may also include fillers therein, such as silica (SiO 2 ) filler and the like, and other additives as desired. Certain embodiments may include an underfill material such as an epoxy, containing up to 70 weight percent of particles, with the particles including both magnetic particles and filler particles, or with the particles only including magnetic particles. 
         [0017]      FIGS. 3(B)-3(C)  illustrate the progression of the underfill material  118  across the die attach region between the die  110  and substrate  112 , when subjected to a magnetic field in certain geometries, for example, in the direction of the arrow, and  FIG. 3(D)  showing the final position of the underfill material, including a substantially reduced tongue region  111  and smaller side spread regions  113 ,  115 ,  117 , when compared with conventional underfill processes. The magnetic field induces movement of the magnetic particles. As the particles move, they drag the underfill matrix fluid with them. By controlling the position and intensity of the magnetic field, the placement of the underfill may be carefully controlled. Precise control of the size and location of the tongue region  111  and side spread regions  113 ,  115 ,  117  may be accomplished through the use of magnetic force from one or more magnetic fields positioned to attract the magnetic particles in one or more directions to control the flow of the underfill material. This may be accomplished using at least one of a static magnetic field, a non-uniform magnetic field, and multiple magnetic fields at various locations. In addition, in certain embodiments, application of the magnetic field enables the underfill material to be positioned substantially faster than when using conventional methods for positioning the underfill material. 
         [0018]      FIGS. 4(A)-4(B)  illustrate an embodiment in which the application of magnetic force using one or more magnetic fields is controlled so that there is no tongue region and no side spread regions of underfill material extending outward from the die attach region.  FIG. 4(A)  illustrates a top view a die  110  coupled to a substrate  112  through a plurality of bump bonds  114 , with underfill material  118  positioned between the die  110  and substrate  112 . As seen in both the top view of  FIG. 4(A) , and the side view of  FIG. 4(B) , there is no underfill material  118  extending on the substrate  112  to the sides of the die  110 .  FIGS. 5(A)-5(B)  also illustrate top and side views of the die  110  coupled to the substrate  112  through bump bonds  114 , however, in this embodiment, the application of a magnetic field is controlled so that the underfill material, including the tongue  111  and side spread regions  113 ,  115 ,  117 , are substantially the same size. 
         [0019]    It should be appreciated that the magnetic field position may be controlled so that a desired amount of tongue and sidespread regions can be formed. For example, in certain applications, it may be useful to control the spread of the underfill material to a small, uniform distance outward from the die attach area, for protection. In one such example, the underfill material extends outward on the substrate from the die attach area a distance of no greater than 1 mm. In other applications it may be useful to further minimize or have no underfill spread on the substrate beyond the die attach area, or to provide for different amounts of underfill spread on different sides of the die attach area. 
         [0020]      FIG. 6  is a flow chart showing a number of operations in accordance with certain embodiments. Box  200  is providing an underfill mixture including magnetic particles in an electrically insulating material such as a polymer epoxy. The magnetic particles may include a surface coating thereon, to inhibit electrical shorting through the underfill mixture. Box  202  is dispensing the underfill mixture onto a substrate adjacent to the gap between a first body such as a die and a second body such as a package substrate. Box  204  is applying a magnetic force using one or more magnetic fields to control the flow of the underfill material in and through the gap between the die and substrate. The one or more magnetic fields may also be utilized to control the extent to which some of the underfill material flows outside of the gap between the die and the substrate, for example, to minimize the size of the tongue region and the side spread regions. Where a material such as a polymer epoxy is used as the underfill material, Box  206  is curing the polymer epoxy. Various modifications to the above operations may be made, with certain operations being optional. 
         [0021]    Assemblies including a substrate and die joined together as described in embodiment above may find application in a variety of electronic components.  FIG. 7  schematically illustrates one example of an electronic system environment in which aspects of described embodiments may be embodied. Other embodiments need not include all of the features specified in  FIG. 7 , and may include alternative features not specified in  FIG. 7 . 
         [0022]    The system  301  of  FIG. 7  may include at least one central processing unit (CPU)  303 . The CPU  303 , also referred to as a microprocessor, may be a die which is attached to an integrated circuit package substrate  305 , which is then coupled to a printed circuit board  307 , which in this embodiment, may be a motherboard. The CPU  303  on the package substrate  305  is an example of an electronic device assembly that may be formed in accordance with embodiments such as described above. A variety of other system components, including, but not limited to memory and other components discussed below, may also include die and substrate structures formed in accordance with the embodiments described above. 
         [0023]    The system  301  may further include memory  309  and one or more controllers  311   a ,  311   b  . . .  311   n , which are also disposed on the motherboard  307 . Such controllers  311   a ,  311   b  . . .  311   n  may include, but are not limited to, video controllers, audio controllers, memory controllers, and the like. The motherboard  307  may be a single layer or multi-layered board which has a plurality of conductive lines that provide communication between the circuits in the package  305  and other components mounted to the board  307 . Alternatively, one or more of the CPU  303 , memory  309  and controllers  311   a ,  311   b  . . .  311   n  may be disposed on other cards such as daughter cards or expansion cards. The CPU  303 , memory  309  and controllers  311   a ,  311   b  . . .  311   n  may each be seated in individual sockets or may be connected directly to a printed circuit board. A display  315  may also be included. 
         [0024]    Any suitable operating system and various applications execute on the CPU  303  and reside in the memory  309 . The content residing in memory  309  may be cached in accordance with known caching techniques. Programs and data in memory  309  may be swapped into storage  313  as part of memory management operations. The system  301  may comprise any suitable computing device, including, but not limited to, a mainframe, server, personal computer, workstation, laptop, handheld computer, handheld gaming device, handheld entertainment device (for example, MP3 (moving picture experts group layer-3 audio) player), PDA (personal digital assistant) telephony device (wireless or wired), network appliance, virtualization device, storage controller, network controller, router, etc. 
         [0025]    The controllers  311   a ,  311   b  . . .  311   n  may include one or more of a system controller, peripheral controller, memory controller, hub controller, I/O (input/output) bus controller, video controller, network controller, storage controller, communications controller, etc. For example, a storage controller can control the reading of data from and the writing of data to the storage  313  in accordance with a storage protocol layer. The storage protocol of the layer may be any of a number of known storage protocols. Data being written to or read from the storage  313  may be cached in accordance with known caching techniques. A network controller can include one or more protocol layers to send and receive network packets to and from remote devices over a network  317 . The network  317  may comprise a Local Area Network (LAN), the Internet, a Wide Area Network (WAN), Storage Area Network (SAN), etc. Embodiments may be configured to transmit and receive data over a wireless network or connection. In certain embodiments, the network controller and various protocol layers may employ the Ethernet protocol over unshielded twisted pair cable, token ring protocol, Fibre Channel protocol, etc., or any other suitable network communication protocol. 
         [0026]    While certain exemplary embodiments have been described above and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative and not restrictive, and that embodiments are not restricted to the specific constructions and arrangements shown and described since modifications may occur to those having ordinary skill in the art.