Abstract:
A semiconductor package with a heat spreader is described, including a first chip, a second chip, a heat spreader and a substrate. The first chip has an active surface over which the second chip is attached. The heat spreader is attached over the first chip. The first chip is bonded onto the substrate.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application claims the priority benefit of Taiwan application serial no. 92104001, filed Feb. 26, 2003.  
         BACKGROUND OF INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a multi-chip module (MCM) package with a heat spreader. More particularly, the present invention relates to a multi-chip module (MCM) package with a heat spreader efficient in heat dissipation.  
           [0004]    2. Description of the Related Art  
           [0005]    In the semiconductor industry, the manufacture of an IC product can be divided into two stages, including fabrication of bare IC chips and subsequent packaging processes. The bare IC chips are finished with sequential steps of wafer fabrication, circuit design, pattern transfer and wafer cutting. In the subsequent packaging processes, each bare chip is electrically connected to outer signal sources via bonding pads formed thereon, and then encapsulated with a molding material. The packaging processes are for protecting the bare chips from humidity, heat and noise from the environment, and for providing a medium of electrical connection between the bare chip and an outer circuit, such as a printed circuit board (PCB) or some package substrate.  
           [0006]    A bare chip is usually electrically connected to a package substrate via wires. As the integration of chips is continuously increased, the multi-chip module (MCM) package is considered to be a promising technique in the future. An MCM package includes a substrate and several chips bonded thereto, wherein the chips are electrically connected to each other via the circuit on the substrate to constitute a complete circuit structure.  
           [0007]    For example, dynamic random access memory (DRAM) chips and a central processing unit (CPU) can be bonded to a substrate to form an MCM package structure. Thus, the packaging density is increased so that less space is required, and signal delay between the chips is reduced. Therefore, MCM packages can satisfy the requirement of high performance, and are widely used in communication electronic products and portable electronic products.  
           [0008]    [0008]FIG. 1 illustrates a cross-sectional view of a conventional multi-chip module (MCM) package. The MCM package  100  includes a substrate  110 , two chips  130  and  150 , a molding material  170 , conductive lines  180  and  182 , and solder balls  184 . The substrate  110  has an upper surface  112 , a lower surface  122 , a die pad  114  and many contact pads  116  and  124  thereon, wherein the die pad  114  and the contact pads  116  are disposed on the upper surface  112  of the substrate  110 . The contact pads  116  are disposed around the die pad  114 , and the contact pads  124  are disposed on the lower surface  122  of the substrate  110 .  
           [0009]    The chip  130  has an active surface  132 , a back surface  142  opposite to the active surface  132 , and contact pads  134  and  136  surrounding the active surface  132  of the chip  130 , wherein the contact pads  134  surround the contact pads  136 . The chip  130  is adhered to the die pad  114  on the substrate  110  via an adhesive  144  on the surface  142 , and is electrically connected to the substrate  110  via wires  180  bonded thereto. One end of a wire  180  is bonded to a contact pad  134  on the chip  130 , and the other end is bonded to a contact pad  116  on the substrate  110 .  
           [0010]    The chip  150  has an active surface  152 , a back surface  162  opposite to the active surface  152 , and contact pads  154  surrounding the active surface  152 . The chip  150  is adhered to the central area of the active surface  132  of the chip  130  via an adhesive  164  on the back surface  162 , and is electrically connected to the chip  130  via wires  182  bonded thereto. One end of a wire  182  is bonded to a contact  154  on the chip  150 , and the other end is bonded to a contact  136  on the chip  130 .  
           [0011]    In addition, the chips  130  and  150 , the upper surface  112  of the substrate  110  and the wires  180  and  182  are encapsulated with a molding material  170 , and solder balls  184  are disposed on the contact pads  124  of the substrate  110 .  
           [0012]    As mentioned above, the chip  130  and the substrate  110  are electrically connected via wires  180 , and the two chips  130  and  150  are electrically connected via wires  182  in a conventional MCM package  100 . However, since the wires  180  and  182  are long and have small cross-sectional areas, the transmitted signals will decay rapidly, and will be delayed as well. Moreover, the parasitic LC effect will occur during the operation of a high-frequency circuit to cause signal reflection. Therefore, using wires ( 180 / 182 ) as a medium of signal transmission causes severe noise interference and worse electrical properties.  
           [0013]    Moreover, as the chips  130  and  150  are operated under high frequency, the temperatures thereof gradually raise because lots of heat is caused by dielectric loss. As the temperature exceeds the upper limit for normal operation of the chip, the inner circuit of the chip functions abnormally or even fails. The heat dissipation of a conventional MCM package  100  is simply achieved via the thermal conduction effect of the molding material  170  and the substrate  110 . Unfortunately, the thermal conduction coefficients of the two are so small that the heat from the chips  130  and  150  cannot be dissipated efficiently, and the chips easily function abnormally or even fail.  
         SUMMARY OF INVENTION  
         [0014]    In view of the forgoing, this invention provides an MCM package with a heat spreader to improve the efficiency of heat dissipation of the chips in the package.  
           [0015]    It should be noted in advance that the use of the preposition “on” in this invention is not restricted to the cases where two objects contact with each other. For example, the expression “A is on B” means that A is disposed over and contacts with B, or that A is disposed over B without contact between them.  
           [0016]    The semiconductor package with a heat spreader of this invention includes a first chip, a second chip, a heat spreader and a substrate. The first chip has an active surface over which the second chip is attached. The heat spreader is attached over the first chip. The first chip is bonded onto the substrate.  
           [0017]    In a preferred embodiment of this invention, the substrate has an opening, which is passing through the substrate, for adapting the heat spreader and the second chip. Otherwise, the opening does not pass through the substrate, alternatively as a cavity, and the substrate has at least one thermo-via therein. The thermo-via passes through the substrate, and has one end exposed in the cavity of the substrate thermally connected with the heat spreader. In addition, the opening of the substrate may be filled with a filling material.  
           [0018]    Moreover, the heat spreader may be disposed on the active surface of the first chip, or on the back surface opposite to the active surface. The first chip can be bonded with the second chip, the substrate and the heat spreader through bumps, or the first and the second chips may be bonded to the substrate through wire bonding.  
           [0019]    It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0020]    The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.  
         [0021]    [0021]FIG. 1 illustrates a cross-sectional view of a conventional MCM package.  
         [0022]    [0022]FIG. 2 illustrates a cross-sectional view of an MCM package with a heat spreader according to a first embodiment of this invention.  
         [0023]    [0023]FIG. 3 illustrates an MCM package with a heat spreader mounted on a motherboard according to the first embodiment of this invention in a cross-sectional view.  
         [0024]    [0024]FIG. 4 illustrates a cross-sectional view of an MCM package with a heat spreader according to a second embodiment of this invention.  
         [0025]    [0025]FIG. 5 illustrates a cross-sectional of an MCM package with a heat spreader according to a third embodiment of this invention.  
         [0026]    [0026]FIG. 6 illustrates an MCM package with a heat spreader mounted on a motherboard according to a fourth embodiment of this invention in a cross-sectional view.  
         [0027]    [0027]FIG. 7 illustrates a cross-sectional view of an MCM package with a heat spreader according to a fifth embodiment of this invention. 
     
    
     DETAILED DESCRIPTION  
       [0028]    [0028]FIG. 2 illustrates a cross-sectional view of an MCM package with a heat spreader according to the first embodiment of this invention. The MCM package  200  includes a substrate  210 , two chips  230  and  250 , a heat spreader  270 , bumps  280 ,  282  and  284 , and solder balls  286 . The substrate  210  has an upper surface  212 , a lower surface  222 , an opening  214  therein, and contact pads  216  and  224  thereon. The opening  214  passes through the substrate  210 , the contact pads  216  are disposed on the upper surface  212  of the substrate  210  surrounding the opening  214 , and the contact pads  224  are disposed on the lower surface  222  of the substrate  210 . The solder balls  286  are disposed on and electrically connected to the contact pads  224  of the substrate  210 .  
         [0029]    The chip  230  has an active surface  232  with contact pads  234 ,  236  and  238  disposed thereon, wherein the contact pads  234  surround the active surface  232  and the contact pads  236  and  238 . The chip  230  is bonded to and electrically connected with the substrate  210  through bumps  280  that are disposed between the contact pads  234  of the chip  230  and the contact pads  216  of the substrate  210 .  
         [0030]    The chip  250  has an active surface  252  and contact pads  254  thereon, wherein the contact pads  254  are disposed on the active surface  252  and arranged in an array. The chip  250  is disposed on the active surface  232  of the chip  230  and disposed in the opening  214  of the substrate  210 , and is bonded to and electrically connected with the chip  230  through bumps  282 . The bumps  282  are disposed between the contact pads  236  of the chip  230  and the contact pads  254  of the chip  250 .  
         [0031]    The heat spreader  270  is disposed on the active surface  232  of the chip  230  and disposed in the opening  214  of the substrate  210 , and is bonded to the chip  230  through the bumps  284 , each of which connects a contact  238  of the chip  230  and the heat spreader  270 . The heat spreader  270  also can be a chip without electronic functions, dummy chip, which comprises a material such as silicon, and the bumps  284  have no signal transmission function. Moreover, the heat spreader  270  can be plated with gold to improve the adhesion between the heat spreader  270  and the chip  230 , and to improve the adhesion between the heat spreader  270  and the motherboard  300  (FIG. 3). In addition, the heat spreader also can be electrically connected to the ground contacts (not shown) of the chip  230  through ground bump, which is one of the bumps  284 .  
         [0032]    [0032]FIG. 3 illustrates an MCM package with a heat spreader mounted on a motherboard according to the first embodiment of this invention in a cross-sectional view. The MCM package  200  can be mounted on the motherboard  300  through solder balls  286  with a reflow step. The motherboard  300  has a surface  302  with contact pads  304 , a chip bonding area  306  and a heat spreader bonding area  308  disposed thereon, wherein the contacts  304  are located around the chip bonding area  306  and the heat spreader bonding area  308 . The solder balls  286  of the MCM package  200  are bonded to and electrically connected with the contact pads  304  of the motherboard  300 . A thermally conductive material  312  is applied to the chip bonding area  306  between the chip  250  and the motherboard  300  for rapidly conducting heat from the chip  250  to the motherboard  300 . In addition, a thermal conduction material  314  is applied to the heat spreader bonding area  308  between the heat spreader  270  and the motherboard  300  for rapidly conducting heat from the heat spreader  270  to the motherboard  300 .  
         [0033]    In the above-mentioned MCM package  200 , for example, the chips  230  and  250  are a central processing unit (CPU) and a memory chip, respectively. As the chip  230  is operated under high frequency and generates lots of heat because of dielectric loss, the heat can be rapidly conducted to the environment through the bumps  284 , the heat spreader  270  and the thermally conductive material  314 , as well as through the bumps  282 , the chip  250  and the thermally conductive material  312 . Therefore, the MCM package  200  of this invention is quite efficient in heat dissipation.  
         [0034]    Nevertheless, this invention is not restricted to apply to the aforementioned cases. FIG. 4 illustrates a cross-sectional view of an MCM package with a heat spreader according to the second embodiment of this invention. The constituents having been mentioned in the first embodiment are labeled with the same reference numbers, and the descriptions thereof are omitted here. In this embodiment, the MCM package  202  further includes a filling material  320  that is filled into the opening  214  of the substrate  210  and between the two chips  230  and  250 , between the chip  230  and the heat spreader  270  and between the chip  230  and the substrate  210  using a method such as a dispensing method. The filling material  320  is for encapsulating the chip  250 , the heat spreader  270  and the bumps  280 ,  282  and  284 .  
         [0035]    [0035]FIG. 5 illustrates a cross-sectional view of a MCM package with a heat spreader according to the third embodiment of this invention. The constituents that have been mentioned in the first and the second embodiments are labeled with the same reference numbers, and the descriptions thereof are omitted here. In this embodiment, the MCM package  204  further includes a molding material  322 , which may be filled into a mold cavity (not shown) of a mold (not shown) to encapsulate the upper surface  212  of the substrate  210  and the sidewalls  244  of the filling material  320  and the chip  230 . The back surface  242  of the chip  230  is adhered to a surface of the mold cavity, so that the back surface  242  is exposed after the mold is released.  
         [0036]    Though the opening passes through the substrate in the embodiments described above, the corresponding structure of this invention is not restricted thereto. FIG. 6 illustrates an MCM package with a heat spreader mounted on a motherboard according to the fourth embodiment of this invention in a cross-sectional view. The constituents having been mentioned in the first embodiments are labeled with the same reference numbers, and the descriptions thereof are omitted here. Referring to FIG. 6, the substrate  410  has a cavity  414  thereon with a bottom surface  416 , and many thermo-vias  418  passing through the substrate  410 . One end of each thermo-via  418  is exposed at the bottom surface  416  of the cavity  414  on the substrate  410 , and the other end is connected with a solder ball  486 , while the substrate  410  is bonded to the motherboard  500  through the solder balls  486 . A thermally conductive material  512  is applied between the chip  250  and the bottom surface  416  of the cavity  414 , so that heat can be rapidly conducted from the chip  250  to the substrate  410 , and then from the substrate  410  to the motherboard  500  through the thermo-vias  418  and the solder balls  486 . In addition, a thermally conductive material  514  is applied between the heat spreader  270  and the bottom surface  416  of the substrate  410 , so that heat can be rapidly conducted from the heat spreader  270  to the substrate  410 , and then from the substrate  410  to the motherboard  500  through the thermo-vias  418  and the solder balls  486 . Besides, the heat spreader  270  also can be electrically connected to the ground contacts (not shown) of the chip  230  through ground bump, which is one of the bumps  284 . Furthermore, the substrate further comprises a ground-vias and the heat spreader is electrically connected to the ground-vias. The MCM package  400  further comprises a filling material  520  that is filled into the cavity  414  on the substrate  410  and between the two chips  230  and  250 , between the chip  230  and the heat spreader  270  and between the chip  230  and the substrate  410  using a method such as a dispensing method. The filling material  520  is for encapsulating the chip  250 , the heat spreader  270  and the bumps  280 ,  282  and  284 .  
         [0037]    Moreover, though the first chip is bonded with the heat spreader through bumps, this invention is not restricted to adopt such a design. As shown in FIG. 7, which illustrates a cross-sectional view of an MCM package with a heat spreader according to the fifth embodiment of this invention, the first chip  230  may be bonded with the heat spreader  270  with a thermally conductive adhesive  289 . The other constituents that have been mentioned in the first embodiment are labeled with the same reference numbers, and the descriptions thereof are omitted here.  
         [0038]    Furthermore, the first chip is not restricted to bond with only one second chip or only one heat spreader, and can be bonded with multi second chips or multi heat spreaders.  
         [0039]    As mentioned above, in the MCM package with a heat spreader of this invention, the active surface of the first chip is disposed with a heat spreader in addition to a second chip. Therefore, the heat generated from the first chip can be rapidly conducted to the environment, and heat dissipation of the MCM package is highly efficient.  
         [0040]    It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention covers modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.