Abstract:
A method is proposed for fabricating a TFBGA (Thin &amp; Fine Ball-Grid Array) package with embedded heat spreader. Conventionally, since an individual TFBGA package is quite small in size, it would be highly difficult to incorporate an embedded heat spreader therein. As a solution to this problem, the proposed method utilizes a single substrate predefined with a plurality of package sites, and further utilizes a heat-spreader frame including an integrally-formed matrix of heat spreaders each corresponding to one of the package sites on the substrate. A batch of semiconductor chips are then mounted on the respective package sites on the substrate. During the encapsulation process, a single continuous encapsulation body is formed to encapsulate the entire heat-spreader frame and all the semiconductor chips. After ball implantation, a singulation process is performed to cut apart the encapsulation body into individual package units, each serving as the intended TFBGA package. In the foregoing process, since the entirety of the heat-spreader frame is relatively large in size as compared to the size of an individual TFBGA package, it can be easily handled, so that the embedding of a heat spreader in each package unit can be easily carried out.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to integrated circuit packaging technology, and more particularly, to a method of fabricating a TFBGA (Thin &amp; Fine Ball-Grid Array) package with embedded heat spreader.  
           [0003]    2. Description of Related Art  
           [0004]    BGA (Ball-Grid Array) is an advanced type of integrated circuit packaging technology which is characterized in the package configuration of a two-dimensional array of solder balls on the bottom surface of the substrate where the semiconductor chip is mounted. These solder balls allow the entire package body to be mechanically bonded and electrically coupled to a printed circuit board (PCB).  
           [0005]    TFBGA (Thin &amp; Fine Ball-Grid Array) is a downsized type of BGA technology that provides integrated circuit packages in very small sizes, which are customarily fabricated in batch from a single chip carrier, such as a substrate, predefined with a matrix of package sites, from each of which a single TFBGA package unit is fabricated. Conventionally, however, it would be highly difficult to incorporate an embedded heat spreader in each individual TFBGA package since each individual TFBGA package is quite small in size, typically from 5 mm×5 mm to 15 mm×15 mm (millimeter), and the separation between neighboring package sites on the substrate is only from 0.2 mm to 0.3 mm.  
           [0006]    Related patents include, for example, the U.S. Pat. No. 5,977,626 entitled “THERMALLY AND ELECTRICALLY ENHANCED PBGA PACKAGE”; the U.S. Pat. No. 5,216,278 entitled “SEMICONDUCTOR DEVICE HAVING A PAD ARRAY CARRIER PACKAGE”; and the U.S. Pat. No. 5,776,798 entitled “SEMICONDUCTOR PACKAGE AND METHOD THEREOF”; to name just a few.  
           [0007]    The U.S. Pat. No. 5,977,626 teaches the embedding of a heat spreader in a BGA package, while the U.S. Pat. No. 5,216,278 teaches the mounting of a heat spreader over the semiconductor chip to facilitate heat dissipation from the encapsulated chip. The U.S. Pat. No. 5,776,798 teaches a novel TFBGA package structure and fabrication thereof However, none of these patented technologies teach the embedding of a heat spreader in each TFBGA package. Therefore, there still exists a need in the semiconductor industry for a new integrated circuit packaging technology that can incorporate a heat spreader in a TFBGA package.  
         SUMMARY OF THE INVENTION  
         [0008]    It is therefore an objective of this invention to provide a new integrated circuit packaging technology that can provide each TFBGA package with an embedded heat spreader to facilitate heat dissipation from the encapsulated chip.  
           [0009]    In accordance with the foregoing and other objectives, the invention proposes a new method for fabricating a TFBGA package with embedded heat spreader. Broadly defined, the method of the invention comprises the following procedural steps: (1) preparing a substrate having a front surface and a back surface, and which is predefined with a plurality of package sites; (2) preparing a heat-spreader frame including an integrally-formed matrix of heat spreaders having a front surface and a back surface, each heat spreader corresponding to one of the predefined package sites on the substrate; (3) bonding and electrically-coupling a plurality of semiconductor chips to respective package sites on the front surface of the substrate; (4) assembling the heat-spreader frame to the substrate in such a manner that each heat spreader is positioned proximate to one of the semiconductor chips on the substrate; (5) performing an encapsulation process to form an encapsulation body which encapsulates the semiconductor chips and the heat-spreader frame; (6) performing a ball-implantation process to implant a plurality of solder balls on the back surface of the substrate; and (7) singulating through the encapsulation body to cut apart the plurality of package sites on the substrate into individual package units, each serving as the intended integrated circuit package.  
           [0010]    The foregoing method of the invention is characterized in the use of the heat-spreader frame including an integrally-formed matrix of heat spreaders. Since the entire heat-spreader frame is relatively large in size as compared to the size of an individual TFBGA package, it would be as a whole significantly easier to handle during the fabrication process than a single piece of heat spreader, making embedding of a single piece of heat spreader in each TFBGA package easy to implement. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0011]    The invention can be more fully understood by reading the following detailed description of the preferred embodiments, with reference made to the accompanying drawings, wherein:  
         [0012]    FIGS.  1 A- 1 F are schematic diagrams used to depict a first preferred embodiment of the method of the invention for TFBGA fabrication;  
         [0013]    FIGS.  2 A- 2 E are schematic diagrams used to depict a second preferred embodiment of the method of the invention for TFBGA fabrication;  
         [0014]    FIGS.  3 A- 3 C are schematic diagrams used to depict a third preferred embodiment of the method of the invention for TFBGA fabrication;  
         [0015]    FIGS.  4 A- 4 B are schematic diagrams used to depict a fourth preferred embodiment of the method of the invention for TFBGA fabrication;  
         [0016]    [0016]FIG. 5 is a schematic perspective view of a variety to the legged type of heat-spreader frame utilized by the invention;  
         [0017]    FIGS.  6 A- 6 C are schematic diagrams of another variety to the legged type of heat-spreader frame utilized by the invention;  
         [0018]    FIGS.  7 A- 7 C are schematic diagrams of still another variety to the legged type of heat-spreader frame utilized by the invention;  
         [0019]    FIGS.  8 A- 8 C are schematic diagrams of yet another variety to the legged type of heat-spreader frame utilized by the invention;  
         [0020]    FIGS.  9 A- 9 C are schematic diagrams of still yet another variety to the legged type of heat-spreader frame utilized by the invention; and  
         [0021]    FIGS.  10 A- 10 C are schematic diagrams of another additional variety to the legged type of heat-spreader frame utilized by the invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0022]    In accordance with the invention, preferred embodiments are disclosed in full details in the following with reference to the accompanying drawings.  
         [0023]    First Preferred Embodiment (FIGS.  1 A- 1 F)  
         [0024]    FIGS.  1 A- 1 F are schematic sectional diagrams used to depict the procedural steps involved in the first preferred embodiment of the method of the invention for fabricating a TFBGA package with embedded heat spreader. It is to be noted that, by the invention, each TFBGA package is fabricated in batch, and not individually, from a single chip carrier.  
         [0025]    Referring to FIG. 1A, by the method of the invention, the first step is to prepare a substrate  10  (or chip carrier), which can be a BT substrate, or an FR4 substrate, or a polyimide tape, and which is predefined with an array of package sites (in the example of FIG. 1A, a total of six (6) package sites, respectively designated by the reference numerals “ 11 ”, “ 12 ”, “ 13 ”, “ 14 ”, “ 15 ”, and “ 16 ”, are predefined; but it is to be noted that the number of package sites is an arbitrary design choice depending on the size of the substrate  10 ). Each of the package sites  11 ,  12 ,  13 ,  14 ,  15 ,  16  on the substrate  10  will be used as a base for the fabrication of a single unit of TFBGA package.  
         [0026]    Referring further to FIG. 1B, the next step is to prepare a heat-spreader frame  20  including an integrally-formed matrix of heat spreaders (in the example of FIG. 1B, the heat-spreader frame  20  includes a total of six (6) heat spreaders, respectively designated by the reference numerals “ 21 ”, “ 22 ”, “ 23 ”, “ 24 ”, “ 25 ”, and “ 26 ”, which are provided in conjunction with the respective package sites  11 ,  12 ,  13 ,  14 ,  15 ,  16  on the substrate  10 . It is to be noted that the number of heat spreaders on the heat-spreader frame  20  is an arbitrary design choice depending on the number of predefined package sites on the substrate  10 .  
         [0027]    The heat-spreader frame  20  can be a legged type or a non-legged type. In this first preferred embodiment, the heat-spreader frame  20  is a legged type having a plurality of legs  20   a  arranged on the peripheral edges thereof and bent down in perpendicular to the heat spreaders  21 ,  22 ,  23 ,  24 ,  25 ,  26  (the non-legged type is used in the second preferred embodiment, which will be described later in this specification).  
         [0028]    Referring further to FIG. 1C, in the next step, a die-bonding process is performed to mount a batch of semiconductor chips (only three are shown in the sectional view of FIG. 1C, which are designated by the reference numerals  31 ,  32 ,  33  respectively) respectively on the package sites  11 ,  12 ,  13  on the front surface  10   a  of the substrate  10  (note that only three of the six package sites  11 ,  12 ,  13 ,  14 ,  15 ,  16  shown in FIG. 1A are seen in the sectional view of FIG. 1C). Subsequently, a wire-bonding process is performed to electrically couple the semiconductor chips  31 ,  32 ,  33  to the substrate  10  by means of bonding wires  40 , such as gold wires.  
         [0029]    After that, the next step is to perform an encapsulation process using an encapsulation mold  50  having a downward-recessed cavity  50   a . First, the heat-spreader frame  20  is dropped in an upside-down manner into the cavity  50   a  of the encapsulation mold  50 , with its legs  20   a  pointing upwards; and next, the substrate  10 , together with the semiconductor chips  31 ,  32 ,  33  mounted thereon, is turned upside down (i.e., with the back surface  10   b  of the substrate  10  facing upwards) and then placed on the heat-spreader frame  20 , with the edge of its front surface  10   a  being adhered to the tips of the upward-pointing legs  20   a  of the heat-spreader frame  20 .  
         [0030]    Referring further to FIG. 1D, when the heat-spreader frame  20  and the substrate  10  are readily set in position in the cavity  50   a  of the encapsulation mold  50 , an encapsulating material, such as resin, is injected into the cavity  50   a  of the encapsulation mold  50  to form a single continuous encapsulation body  60  which encapsulates all the semiconductor chips  31 ,  32 ,  33  and the heat-spreader frame  20 .  
         [0031]    Referring further to FIG. 1E, as the encapsulation process is completed, the entire encapsulation body  60  is taken out of the encapsulation mold  50 . Next, a ball-implantation process is performed to implant a-plurality of solder balls  70  on the back surface  10   b  of the substrate  10 .  
         [0032]    Referring further to FIG. 1F, in the next step, a singulation process is performed to saw through the encapsulation body  60  (along the dashed lines shown in FIG. 1E that delimit the predefined package sites  11 ,  12 ,  13  on the substrate  10 ), so as to cut apart the entire package body into individual package units as indicated by the reference numerals “ 81 ”, “ 82 ”, and “ 83 ” in FIG. 1F. Each of the package units  81 ,  82 ,  83  includes one of the package sites  11 ,  12 ,  13 , one of the chips  31 ,  32 ,  33 , and one of the heat spreaders  21 ,  22 ,  23 . This completes the fabrication of a batch of TFBGA packages.  
         [0033]    In the foregoing method of the invention, since the entire heat-spreader frame  20  is relatively large in size as compared to the size of an individual TFBGA package, it would be as a whole significantly easier to handle during the fabrication process than a single piece of heat spreader, making embedding of a single piece of heat spreader in each TFBGA package easy to implement.  
         [0034]    Second Preferred Embodiment (FIGS.  2 A- 2 E)  
         [0035]    The second preferred embodiment of the method of the invention is described in the following with reference to FIGS.  2 A- 2 E. In FIGS.  2 A- 2 E, the same parts as the previous embodiment shown in FIGS.  1 A- 1 F are labeled with the same reference numerals.  
         [0036]    As shown in FIG. 2A, the second preferred embodiment differs from the previous one in that the heat-spreader frame  20  utilized here is a non-legged type (i.e., the legs  20   a  shown in FIG. 1B of the previous embodiment are here not provided). Except this, the heat-spreader frame  20  used here is substantially the same in shape as the previous embodiment, which also includes an integrally-formed matrix of heat spreaders  21 ,  22 ,  23 ,  24 ,  25 ,  26 . Beside the heat-spreader frame  20 , all the other constituent parts of the second preferred embodiment are identical in structure as the previous embodiment, so description thereof will not be repeated here.  
         [0037]    Referring next to FIG. 2B, during the encapsulation process, in order to prevent resin flash on the bottom surface of the heat-spreader frame  20 , a flash-masking structure  20   b  is formed over the bottom surface of the heat-spreader frame  20 . The flash-masking structure  20   b  can be, for example, a polyimide tape or an epoxy coating. The heat-spreader frame  20  and the substrate  10  are then placed set in the cavity  50   a  of the encapsulation mold  50  in the same manner as the previous embodiment (except in this case, the heat-spreader frame  20  has no legs to support the substrate  10 ).  
         [0038]    Referring further to FIG. 2C, when the heat-spreader frame  20  and the substrate  10  are readily set in position in the cavity  50   a  of the encapsulation mold  50 , an encapsulating material, such as resin, is injected into the cavity  50   a  of the encapsulation mold  50  to form a single continuous encapsulation body  60  which encapsulates all the semiconductor chips  31 ,  32 ,  33  and the heat-spreader frame  20 . During this process, however, part of the injected resin may be flashed onto the bottom surface of the flash-masking structure  20   b  that comes in touch with the bottom surface of the cavity  50   a.    
         [0039]    Referring further to FIG. 2D, as the encapsulation process is completed, the entire encapsulation body  60  is taken out of the encapsulation mold  50 . From the encapsulation process, however, a small amount of flashed resin  20   c  might be left over the exposed surface of the flash-masking structure  20   b  over the heat-spreader frame  20 .  
         [0040]    Referring further to FIG. 2E, in the next step, the flash-masking structure  20   b , together with the flashed resin  20   c  thereon, are removed by using a special solvent or other suitable etching means. This allows no flashed resin to be left over the exposed surface of the heat-spreader frame  20 . If the flash-masking structure  20   b  were not provided, the flashed resin  20   c  would be left directly over the exposed surface of the heat-spreader frame  20 , which would then be very difficult to remove.  
         [0041]    The subsequent steps of ball implantation and singulation are all the same as the previous embodiment, so description thereof will not be repeated.  
         [0042]    The foregoing method of the invention allows the embedding of a flash-free heat spreader in each TFBGA package.  
         [0043]    Third Preferred Embodiment (FIGS.  3 A- 3 C)  
         [0044]    The third preferred embodiment of the method of the invention is disclosed in the following with reference to FIGS.  3 A- 3 C. In FIGS.  3 A- 3 C, the same parts as the previous embodiments are labeled with the same reference numerals.  
         [0045]    This embodiment is largely the same as the first embodiment except that the substrate  10  needs not be turned upside down during the encapsulation process. Details are described below.  
         [0046]    Referring first to FIG. 3A, as the substrate  10  is readily mounted with the semiconductor chips  31 ,  32 ,  33 , the tips of the legs  20   a  of the heat-spreader frame  20  are adhered by means of an adhesive agent (not shown) onto the front surface  10   a  of the substrate  10 .  
         [0047]    Referring further to FIG. 3B, the next step is to perform an encapsulation process, in which the substrate  10  together with the semiconductor chips  31 ,  32 ,  33  mounted thereon are placed in an encapsulation mold  51  having a bottom-side upward-recessed cavity  51   a , without being turned upside down as in the case of the first embodiment, for the purpose of forming an encapsulation body  60  which encapsulates all the semiconductor chips  31 ,  32 ,  33  and the heat-spreader frame  20 .  
         [0048]    Referring further to FIG. 3C, as the encapsulation process is completed, the entire encapsulation body  60  is taken out of the encapsulation mold  51 . Next, a ball-implantation process is performed to implant a plurality of solder balls  70  on the back surface  10   b  of the substrate  10 . After this, a singulation process is performed to saw through the encapsulation body  60  along the dashed lines shown in FIG. 3C that delimit the predefined package sites  11 ,  12 ,  13  on the substrate  10 . The subsequent steps are all the same as the first embodiment, so description thereof will not be repeated herein.  
         [0049]    Fourth Preferred Embodiment (FIGS.  4 A- 4 B)  
         [0050]    The fourth preferred embodiment of the method of the invention is disclosed in the following with reference to FIGS.  4 A- 4 B. In FIGS.  4 A- 4 B, the same parts as the previous embodiments are labeled with the same reference numerals.  
         [0051]    Referring to FIG. 4A, this embodiment differs from the previous ones only in that the semiconductor chips  31 ,  32 ,  33  are electrically coupled to the substrate  10  through the flip-chip technology by means of solder bumps  41  instead of the wire-bonding technology utilized in the previous embodiments. FIG. 4B shows a singulated TFBGA package unit. Beside the use of the flip-chip technology, all the other process steps are the same as the previous embodiments, so description thereof will not be repeated herein.  
         [0052]    Various Other Modifications to the Legged Type of Heat-Spreader Frame  
         [0053]    Beside the design shown in FIG. 1B, the legged type of heat-spreader frame can have various other modifications, as respectively shown in FIG. 5, FIGS.  6 A- 6 C, FIGS.  7 A- 7 C, FIGS.  8 A- 8 C, FIGS.  9 A- 9 C, and FIGS.  10 A- 10 C. In these figures, similar parts are labeled with the same reference numerals.  
         [0054]    [0054]FIG. 5 is a schematic perspective view of a variety to the legged type of heat-spreader frame  20  utilized by the invention. As shown, in this embodiment, the heat spreaders  21 ,  22 ,  23 ,  24 ,  25 ,  26  are integrally formed into a flat piece having a plurality of legs  20   a  around the edge thereof.  
         [0055]    FIGS.  6 A- 6 C are schematic diagrams of another variety to the legged type of heat-spreader frame  20  utilized by the invention; wherein FIG. 6A shows a top view of this heat-spreader frame  20 ; FIG. 6B shows a side view of the same; and FIG. 6C shows a sin-singulated TFBGA package unit with an embedded heat spreader  21  cutting apart from the heat-spreader frame  20  shown in FIGS.  6 A- 6 B. This heat-spreader frame  20  is characterized in that the heat spreaders  21 ,  22 ,  23 ,  24 ,  25 ,  26  are flatly shaped both in front surface and in back surface.  
         [0056]    FIGS.  7 A- 7 C are schematic diagrams of still another variety to the legged type of heat-spreader frame  20  utilized by the invention; wherein FIG. 7A shows a bottom view of this heat-spreader frame  20 ; FIG. 7B shows a side view of the same; and FIG. 7C shows a singulated TFBGA package unit with an embedded heat spreader  21  cutting apart from the heat-spreader frame  20  shown in FIGS.  7 A- 7 B. This heat-spreader frame  20  is characterized in that the heat spreaders  21 ,  22 ,  23 ,  24 ,  25 ,  26  are flatly shaped in front surface, and are each formed with a protruded block  20   d  in the back surface. As shown in FIG. 7C, the provision of the protruded block  20   d  can help reduce the heat path from the semiconductor chip  31  to the heat spreader  21 , so that the heat-dissipation efficiency can be increased.  
         [0057]    FIGS.  8 A- 8 C are schematic diagrams of still yet another variety to the legged type of heat-spreader frame  20  utilized by the invention; wherein FIG. 8A shows a bottom view of this heat-spreader frame  20 ; FIG. 8B shows a side view of the same; and FIG. 8C shows a singulated TFBGA package unit with an embedded heat spreader  21  cutting apart from the heat-spreader frame  20  shown in FIGS.  8 A- 8 B. This heat-spreader frame  20  is characterized in that the heat spreaders  21 ,  22 ,  23 ,  24 ,  25 ,  26  are flatly shaped in front surface, and are each formed with a plurality of dimples  20   e  in back surface. As shown in FIG. 8C, the provision of these dimples  20   e  can help increase the contact area between the heat spreader  21  and the encapsulation body  60 , thus further strengthening the bonding between the heat spreader  21  and the encapsulation body  60 .  
         [0058]    FIGS.  9 A- 9 C are schematic diagrams of yet another variety to the legged type of heat-spreader frame  20  utilized by the invention; wherein FIG. 9A shows a bottom view of this heat-spreader frame  20 ; FIG. 9B shows a side view of the same; and FIG. 9C shows a singulated TFBGA package unit with an embedded heat spreader  21  cutting apart from the heat-spreader frame  20  shown in FIGS.  9 A- 9 B. This heat-spreader frame  20  is characterized in that the heat spreaders  21 ,  22 ,  23 ,  24 ,  25 ,  26  are flatly shaped in front surface, and are each formed with a plurality of crosswise and lengthwise interleaved grooves  20   f  in back surface. As shown in FIG. 9C, the provision of these grooves  20   f  can help increase the contact area between the heat spreader  21  and the encapsulation body  60 , thus further strengthening the bonding between the heat spreader  21  and the encapsulation body  60 .  
         [0059]    FIGS.  10 A- 10 C are schematic diagrams of another additional variety to the legged type of heat-spreader frame  20  utilized by the invention; wherein FIG. 10A shows a top view of this heat-spreader frame  20 ; FIG. 10B shows a side view of the same; and FIG. 10C shows a singulated TFBGA package unit with an embedded heat spreader  21  cutting apart from the heat-spreader frame  20  shown in FIGS.  10 A- 10 B. This heat-spreader frame  20  is characterized in that the heat spreaders  21 ,  22 ,  23 ,  24 ,  25 ,  26  are each formed with a protruded block  20   g  in front surface and a plurality of through holes  20   h  around each protruded block  20   g . As shown in FIG. 10C, the provision of the protruded block  20   g  can help reduce the heat path from the semiconductor chip  31  to the heat spreader  21 , while the through holes  20   h  can act as bolting means that can help secure the heat spreader  21  firmly to the encapsulation body  60 , so that the heat spreader  21  would hardly break away from the encapsulation body  60 .  
         [0060]    The invention has been described using exemplary preferred embodiments. However, it is to be understood that the scope of the invention is not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements. The scope of the claims, therefore, should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.