Abstract:
There is provided a semiconductor device including (a) a package comprised of a base, a sidewall standing on the base at a periphery of the base, and a cover mounted over the sidewall, the base, sidewall and cover defining a closed adiabatic space in the package, (b) a first semiconductor chip mounted on the base in the close adiabatic space, and (c) a second semiconductor chip mounted on the cover. The semiconductor device makes it possible to prevent heat generated in an upper semiconductor chip from being transferred to a lower semiconductor chip, and more highly integrate semiconductor chips than a conventional one.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a semiconductor device and a method of fabricating the same, and more particularly to a semiconductor device capable of being integrated more highly than a conventional one and a method of fabricating such a semiconductor device. 
     2. Description of the Related Art 
     A conventional semiconductor device is generally designed to include a plurality of semiconductor chips two-dimensionally arranged on a substrate. FIG. 1 is a side view illustrating such a conventional semiconductor device. 
     The illustrated semiconductor device is comprised of a substrate  20  on which wirings are formed in a predetermined pattern, TAB (Tape Automated Bonding) tapes  25  on each of which a first LSI chip  40 A and a second LSI chip  40 B is mounted, respectively, bonding wires BW electrically connecting bonding pads of the first and second LSI chips  40 A and  40 B to electrically conductive leads of TAB tapes  25 , resin  26  covering the first and second LSI chips  40 A and  40 B and the bonding wires BW on the TAB tapes  25 , and solder balls  29  electrically connecting the TAB tapes  25  to the substrate  20 . 
     The above-mentioned conventional semiconductor device attempts to achieve higher integration by two-dimensionally arranging a plurality of LSI chips. However, since the substrate  20  has a limited size, it would be impossible to much increase the number of LSI chips to be arranged on the substrate  20 , resulting in difficulty in higher integration of LSI chips. 
     To solve this problem, Japanese Unexamined Patent Publications Nos. 10-84076, 8-32183 and 9-8220 have suggested a semiconductor device for achieving higher integration. 
     For instance, the semiconductor device suggested in Japanese Unexamined Patent Publication No. 10-84076 is designed to include a first package in which a first LSI chip is sealed, and a second package in which a second LSI chip is sealed and which is vertically stacked on the first package. The first and second LSI chips are electrically connected to a substrate through ball grid arrays (BGA) and electrically conductive leads of an auxiliary substrate. 
     However, the above-mentioned semiconductor device suggested in Japanese Unexamined Patent Publication No. 10-84076 is accompanied with the following problem. Since the above-mentioned semiconductor device is intended to be as small as possible in size, a gap between the first and second LSI chips is quite small. In addition, the gap is filled with resin. As a result, path through which heat generated in the second or upper LSI chip is radiated is not sufficiently ensured, resulting in that heat generated in the second or upper LSI chip is transferred to the first or lower LSI chip through the resin filling the gap therewith. The thus transferred heat prevents proper operation of the first or lower LSI chip. 
     SUMMARY OF THE INVENTION 
     In view of the above-mentioned problem of the conventional semiconductor device, it is an object of the present invention to provide a semiconductor device which is capable of preventing heat generated in an upper semiconductor chip from transferring to a lower semiconductor chip. 
     It is also an object of the present invention to provide a method of fabricating such a semiconductor device. 
     In one aspect of the present invention, there is provided a semiconductor device including (a) a package defining a closed adiabatic space therein, (b) a first semiconductor chip arranged in the closed adiabatic space, and (c) a second semiconductor chip mounted on the package. 
     There is further provided a semiconductor device including (a) a package comprised of a base, a sidewall standing on the base at a periphery of the base, and a cover mounted over the sidewall, the base, sidewall and cover defining a closed adiabatic space in the package, (b) a first semiconductor chip mounted on the base in the close adiabatic space, and (c) a second semiconductor chip mounted on the cover. 
     In accordance with the above-mentioned semiconductor device, semiconductor chips can be highly integrated by vertically arranging them, and in addition, the closed adiabatic space formed between the first and second semiconductor chips solves the problem that heat generated in the second semiconductor chip is transferred to the first semiconductor chip, ensuring proper operation of the first semiconductor chip. 
     In a preferred embodiment, each of the base and the cover is comprised of a printed wiring board. 
     In accordance with the embodiment, signals transmitted from the first and second semiconductor chips can be readily transmitted outside the package. 
     In a preferred embodiment, the cover is comprised of a metal plate. 
     In accordance with the embodiment, it would be possible to enhance heat-radiation characteristic of the second semiconductor chip mounted on the cover. 
     In a preferred embodiment, when the base is formed therein with a first wiring terminal appearing at an upper surface of the base, and the sidewall is formed therein with a second wiring terminal appearing at a lower surface of the sidewall, the semiconductor device further includes a solder ball located between the base and the sidewall, the first and second wiring terminals being electrically connected to each other through the solder ball. 
     In accordance with the embodiment, it would be possible to surely electrically connect the base to the sidewall. 
     In a preferred embodiment, when the sidewall is formed therein with a wiring terminal appearing at an upper surface of the sidewall, the semiconductor device further includes a bonding wire through which the second semiconductor chip is electrically connected to the wiring terminal. The bonding wire may be covered with resin on the cover. 
     In a preferred embodiment, when the base is formed therein with a wiring terminal appearing at an upper surface of the base, the semiconductor device further includes a bonding wire through which the first semiconductor chip is electrically connected to the wiring terminal. The bonding wire may be bent in the closed adiabatic space. 
     In another aspect of the present invention, there is provided a semiconductor device including (a) a plurality of packages vertically stacked one on another, each of the packages defining a closed adiabatic space therein, and (b) a plurality of semiconductor chips each arranged in the closed adiabatic space of each of the packages. 
     There is further provided a semiconductor device including (a) a plurality of packages vertically stacked one on another, each of the packages being comprised of a base, a sidewall standing on the base at a periphery of the base, and a cover mounted over the sidewall, the base, sidewall and cover defining a closed adiabatic space in each of the packages, and (b) a plurality of semiconductor chips each arranged in the closed adiabatic space of each of the packages. 
     In a preferred embodiment, when the base is formed therein with a first wiring terminal appearing at an upper surface of the base, and the sidewall is formed therein with a second wiring terminal appearing at a lower surface of the sidewall, the semiconductor device further includes solder balls each located between the base and the sidewall, the first and second wiring terminals being electrically connected to each other through each of the solder balls. 
     In a preferred embodiment, when the sidewall is formed therein with a wiring terminal appearing at an upper surface of the sidewall, the semiconductor device further includes bonding wires through each of which a semiconductor chip mounted on a package which the sidewall partially constitutes is electrically connected to the wiring terminal. 
     In a preferred embodiment, when the base is formed therein with a wiring terminal appearing at an upper surface of the base, the semiconductor device further includes a bonding wire through which a semiconductor chip mounted in a package which the base partially constitutes is electrically connected to the wiring terminal. 
     In another aspect of the present invention, there is provided a method of fabricating a semiconductor device, including the steps of (a) mounting a first semiconductor chip on a first substrate, (b) mounting a sidewall on the first semiconductor chip so that the first semiconductor chip is located within an opening formed through the sidewall, (c) mounting a cover over the sidewall so that a space defined by the first semiconductor substrate, the sidewall and the cover is a closed adiabatic space, (d) mounting a second semiconductor chip on the cover. 
     The step (b) may be carried out prior to the step (a). As an alternative, the steps (a) and (b) may be concurrently carried out. 
     There is further provided a method of fabricating a semiconductor device, including the steps of (a) mounting a first semiconductor chip on a first substrate, (b) mounting a sidewall on the first semiconductor chip so that the first semiconductor chip is located within an opening formed through the sidewall, (c) mounting a second substrate over the sidewall so that a space defined by the first semiconductor substrate, the sidewall and the second substrate is a closed adiabatic space, (d) mounting a second semiconductor chip on the second substrate, and (e) repeating the steps (b) to (d) desired number of times. 
     The above and other objects and advantageous features of the present invention will be made apparent from the following description made with reference to the accompanying drawings, in which like reference characters designate the same or similar parts throughout the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of a conventional semiconductor device mounted on a substrate. 
     FIG. 2 is a cross-sectional view of a semiconductor device in accordance with the first embodiment. 
     FIG. 3 is a cross-sectional view of the semiconductor device illustrated in FIG. 2, mounted on a substrate. 
     FIG. 4 is an exploded perspective view of the semiconductor device illustrated in FIG.  2 . 
     FIG. 5 is a cross-sectional view of the embodiment of FIG. 2 further illustrating aspects relating to the electrical interconnection of lower and upper multi-layered wiring boards of the device. 
     FIG. 6 is a cross-sectional view of a semiconductor device in accordance with a second embodiment comprising three LSI chips. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 2 illustrates a semiconductor device in accordance with the preferred embodiment of the present invention. 
     The semiconductor device  10  is comprised of a package, a lower LSI chip  11  enclosed in the package, an upper LSI chip  12  mounted on the package, resin  17  deposited on the package to thereby cover the upper LSI chip  12  therewith, and a plurality of solder balls  19  arranged at a bottom of the package. 
     The package is comprised of a base  15  on which the lower LSI chip  11  is mounted, a frame-shaped sidewall  16   a  standing on the base  15  at a periphery of the base  15  and having an inner space in which the lower LSI chip  11  is surrounded, and a rectangular cover  13  mounted over the sidewall  16   a  and entirely covering the inner space of the sidewall  16   a  therewith. 
     The base  15  is comprised of a lower multi-layered wiring board, the sidewall  16   a  is comprised of a frame-shaped upper multi-layered wiring board. 
     The base or lower multi-layered wiring board  15  is centrally formed at a surface thereof with a rectangular recess  15   a  into which the lower LSI chip  11  is to be fit. A plurality of the solder balls  19  are arranged in a matrix on a lower surface of the base  15  for outwardly directing signals transmitted from the lower and upper LSI chips  11  and  12 . 
     The base or lower multi-layered wiring board  15  is composed of plastic and is formed therein with a plurality of electrically conductive first and second leads  14   a  and  14   a . The first leads  14   a  are located closer to the recess  15   a  than the second leads  14   b , and have opposite ends both appearing at upper and lower surfaces of the base  15 . The second leads  14   b  are located remoter from the recess  15   a  than the first leads  14   a , and have opposite ends both appearing at upper and lower surfaces of the base  15 . Each one of the first and second leads  14   a  and  14   b  is electrically connected to an associated solder ball  19  at a lower surface of the base  15 . 
     The lower LSI chip  11  fit into the recess  15   a  is electrically connected at bonding pads thereof (not illustrated) to the associated first leads  14   a  through bonding wires BWa. 
     The upper multi-layered wiring board  16  is composed of plastic, and is in the form of a rectangular frame. The upper multi-layered wiring board  16  is formed therein with a plurality of electrically conductive third leads  18 . The third leads  18  have opposite ends both appearing at upper and lower surfaces of the upper multi-layered wiring board  16 . 
     The lower multi-layered wiring board  15 , the upper multi-layered wiring board  16  and the cover  13  cooperate with one another to define a closed adiabatic space  16   b . The sidewall  16   a  is formed at an upper inner edge with a stepped portion  16   c  at which the cover  13  is supported. 
     As illustrated, for example, in FIG. 5, third leads  18  and the second leads  14   b  are electrically connected to each other through solder balls  19   a , for instance. The lower multi-layered wiring board  15  can be electrically readily connected to the upper multi-layered wiring board  16  through the use of such solder balls. wiring board  15  by arranging the solder balls therebetween. Such a gap is filled with resin. 
     The first to third leads  14   a ,  14   b  and  18  are composed of electrically conductive material such as copper (Cu) or gold (Au), and are formed by filling such electrically conductive material in through-holes vertically formed through the lower and upper multi-layered wiring boards  15  and  16 . 
     The cover  13  is composed of electrically conductive material such as metal. The upper LSI chip  12  is mounted centrally on the cover  13 . Since the upper LSI chip  12  is mounted on such electrically conductive material, for instance, metal, it is possible to facilitate radiation of heat generated in the upper LSI chip  12 . 
     The upper LSI chip  12  is electrically connected at bonding pads thereof (not illustrated) to the associated third wiring leads  18  through bonding pads BWb. The upper LSI chip  12  and the bonding wires BWb are both covered in the resin  17  molded on the cover  13 . 
     FIG. 3 illustrates that the semiconductor device  10  illustrated in FIG. 2 is mounted on a substrate. The semiconductor device  10  is mounted on and electrically connected to a substrate  20  on which wirings are formed in a predetermined pattern. Though not illustrated, other semiconductor devices each having the same structure as that of the semiconductor device  10  are arranged also on the substrate  20  to thereby achieve higher integration of semiconductor devices. 
     FIG. 4 is an exploded perspective view of the semiconductor device  10  illustrated in FIG.  2 . Hereinbelow is explained a method of fabricating the semiconductor device  10 , with reference to FIG.  4 . 
     First, the lower LSI chip  11  is fit into the recess  15   a  formed at a surface of the lower multi-layered wiring board  15 . Then, the lower LSI chip  11  is electrically connected at bonding pads BP thereof to the first leads  14   a  of the lower multi-layered wiring board  15  through the bonding wires BWa. 
     Then, the upper multi-layered wiring board  16  is mounted on the lower multi-layered wiring board  15  with the lower LSI chip  11  being located in the space  16   b , and the third leads  18  are electrically connected to the second leads  14   b  through solder balls (not illustrated). 
     Then, a gap formed between the sidewall  16   a  and the lower multi-layered wiring board  15  is filled with resin, which is then cured. 
     It should be noted that the step of fitting the lower LSI chip  11  into the recess  15   a  of the lower multi-layered wiring board  15  may be carried out before or after the step of fixing the upper multi-layered wiring board  16  on the lower multi-layered wiring board  15 . 
     Then, the cover  13  is fit in the stepped portion  16   c  of the upper multi-layered wiring board  16 , and is caused to electrically connect to ground terminals (not illustrated) formed on the upper multi-layered wiring board  16 . Thus, the sidewall  16   a , the lower multi-layered wiring board  15  and the cover  13  define the closed adiabatic space  16   b  in which the bonding wires BWa electrically connecting the lower LSI chip  11  to the first leads  14   a  are sufficiently accommodated, even if the bonding wires BWa are bent. 
     Then, the upper LSI chip  12  is fixed on the cover  13  at a center of the cover  13 , and is electrically connected at bonding pads BP thereof to the third leads  18  of the upper multi-layered wiring board  16 . 
     Then, the resin  17  is deposited on the cover  13  so that the resin  17  entirely covers the cover  13 , the upper multi-layered wiring board  16 , the upper LSI chip  12  and the bonding wires BWb therewith, and is cured in a trapezoidal form. Thus, the upper LSI chip  12  and the bonding wires BWb are sealed in the resin  17 . 
     Thus, there is completed the semiconductor device  10  in which the lower LSI chip  11  is accommodated in the package and the upper LSI chip  12  is mounted on the package. 
     In accordance with the above-mentioned embodiment, the lower and upper LSI chips  11  and  12  are vertically arranged. Thus, the semiconductor device in accordance with the above-mentioned embodiment could have an area equal to about a half of an area of a semiconductor device in which two LSI chips are two-dimensionally arranged. As a result, it is possible to reduce an area occupied by the semiconductor device  10  on the substrate  20 , ensuring higher integration of semiconductor devices. 
     In addition, the closed adiabatic space  16   b  prevents heat generated in the upper LSI chip  12  from being transferred to the lower LSI chip  11 , ensuring proper operation of the lower LSI chip  11 . 
     Though the semiconductor device  10  in accordance with the above-mentioned embodiment is designed to include two LSI chips  11  and  12  vertically arranged, it should be noted that the semiconductor device  10  may be designed to include three or more LSI chips vertically arranged, in which case, a plurality of the packages each defined by the lower multi-layered wiring board  15 , the upper multi-layered wiring board  16  and the cover  13  are vertically stacked. As illustrated in FIG. 6, in such a semiconductor device, a cover  13   a  in a first package may constitute a portion of a base  15   b  of a second package located immediately above the first package. Intermediate LSI chip  11   a  may be electrically interconnected to solder balls  19  via circuit paths in bases  15   a, b  and sidewalls  16   a . Uppermost LSI chip  12  may be interconnected to solder balls  19  via circuit paths in sidewalls  16   c , bases  15   a, b  and sidewalls  16   a . The solder balls  19  are arranged only on a lower surface of a lower multi-layered wiring board  15   a  located lowermost, and the resin  117  is deposited only on a cover of a package located uppermost. 
     While the present invention has been described in connection with certain preferred embodiments, it is to be understood that the subject matter encompassed by way of the present invention is not to be limited to those specific embodiments. On the contrary, it is intended for the subject matter of the invention to include all alternatives, modifications and equivalents as can be included within the spirit and scope of the following claims. 
     The entire disclosure of Japanese Patent Application No. 11-73689 filed on Mar. 18, 1999 including specification, claims, drawings and summary is incorporated herein by reference in its entirety.