Abstract:
A semiconductor device includes a memory module board mounting thereon a plurality of DRAM devices, and a mount board mounting thereon the memory module board via a combination of socket and plug. The socket formed on the mount board has a pair of heat radiation guide plates attached onto the side surfaces of the socket. The heat radiation plates have a thermal conductivity of 1 watt/meter·K. The surface of the mount board onto which the socket is attached is a conductive sheet having a thermal conductivity of 1 watt/meter·K.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a semiconductor device having a mount board in which a module board provided with one or a plurality of electronic components is mounted on a socket and, more particularly, to a technique of cooling the module board mounted on the mount board. 
   2. Description of the Related Art 
   In electronic devices such as a personal computer or a server, a conventional memory device such as a DRAM (Dynamic Random Access Memory) device is directly mounted on a motherboard (mount board). However, in up-to-date memory devices, a memory module board on which one or a plurality of memory devices are mounted on a printed circuit board is prepared separately from a mount board, and is mounted on the mount board by a socket provided on the surface of the mount board. 
   In a memory module board, the amount of heat generated in the memory devices increases in accordance with the development of a higher density of memory devices mounted and increase in the read/write speed thereof. 
   The increase in the amount of heat generated in a memory device has involved an excessive temperature rise in the memory module board. This causes a problem of operation errors and system down in the electronic devices. 
   To prevent operation errors and system down in the electronic devices and to ensure excellent operation characteristics of the electronic devices, temperature of the memory module board has to be prevented from excessively rising by efficiently diffusing the heat generated in the memory module board, to thereby suppress occurring of a thermal runway. Patent Publications JP-A-2004-079940 (FIG. 2), JP-A-2003-017634 (FIG. 1), and JP-A-2001-118984 (FIG. 1) describe that various heat radiation members are provided on the side surfaces of a memory module board, on which memory devices are provided, to radiate heat from the side surfaces of the memory module board, thereby suppressing the temperature rise thereof. 
   In the memory module boards used in recent years, the higher density and higher processing speed of the memory devices have considerably increased the mount of heat generated therein. Therefore, it is difficult to sufficiently suppress the temperature rise of the memory module board simply by radiating the heat from the side surfaces of the memory module board, and to ensure superior operating characteristics of electronic devices. 
   SUMMARY OF THE INVENTION 
   In view of the above situation, it is an object of the present invention to effectively suppress the temperature rise of a module board in a semiconductor device having a mount board on which the module board provided with electronic components such as memory devices is mounted on a socket, to ensure excellent operating characteristics of an electronic device including the semiconductor device. 
   The present invention provides, in a first aspect thereof, a semiconductor device including: a module board mounting thereon an electric component and having a plug at an edge of the module board; and a mount board having thereon a socket adapted to the plug on a surface portion of the mount board, for mounting thereon the module board via the plug, 
   wherein the socket includes a heat radiation guide plate in contact with a side surface of the socket. 
   The present invention provides, in a second aspect thereof, a semiconductor device including: a module board mounting thereon an electric component and having a plug at an edge of the module board; and a mount board having thereon a socket adapted to the plug on a surface portion of the mount board for mounting thereon the module board via the plug, 
   wherein the surface portion of the mount board has a thermal conductivity of 1 watt/meter·K or above. 
   According to the semiconductor device of the first aspect of the present invention, most of heat generated from the module board is radiated from the socket through the heat radiation guide plate in addition to conventional heat radiation paths, when the semiconductor device is supplied with electric power and the module board is operating. Therefore, in comparison with the conventional semiconductor devices, the heat generated in the module board is efficiently radiated therefrom, and temperature rise of the module board can be effectively suppressed. 
   According to the semiconductor device of the second aspect of the present invention, heat transferred to the surface portion of the mount board that the socket contacts quickly spreads in the in-plane directions of the mount board and is radiated to the mount board having a large heat capacity, when the semiconductor device is supplied with electric power and the module board is operating. This is because the surface portion of the mount board has a high thermal conductivity. Therefore, in comparison with the conventional semiconductor devices, the heat generated in the module board is efficiently radiated therefrom, and temperature rise of the module board can be effectively suppressed. 
   The present invention can be applied to a semiconductor device in which the electronic component is a memory device. Thermal runaway caused by an excessive tem rise in the memory device can thereby be prevented. In the present invention, the heat radiation guide plates or the surface portion, on which the memory module is mounted, preferably have a thermal conductivity of 50 W/m·K or higher. For example, iron, aluminum, copper or PGS can be used as the material having the thermal conductivity of 50 W/m·K or higher. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view showing the structure of a semiconductor device according to a first embodiment of the present invention; 
       FIG. 2  is a top plan view showing the semiconductor device in  FIG. 1  from which memory module boards are removed; 
       FIGS. 3A and 3B  are sectional views taken along the lines a-a and b-b in  FIG. 1 ; 
       FIG. 4A  is a perspective view showing the structure of a semiconductor device according to a first modification of the first embodiment, and 
       FIG. 4B  is a sectional view taken along the line b-b in  FIG. 4A ; 
       FIG. 5  is a top plan view showing the structure of a semiconductor device according to a second modification of the first embodiment; 
       FIG. 6  is a top plan view showing the structure of a semiconductor device according to a third modification of the first embodiment; 
       FIG. 7  is a top plan view showing the structure of a semiconductor device according to a fourth modification of the first embodiment; 
       FIGS. 8A and 8B  are sectional views showing a semiconductor device according to a second embodiment of the present invention, corresponding to  FIGS. 3A and 3B ; and 
       FIG. 9  is a sectional view showing the structure of a semiconductor device according to a modification example of the second embodiment. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Before describing the preferred embodiment of the present invention, the gist of the present invention will be described for a better understanding of the present invention. 
   The present inventor carried out a simulation, in which the thermal conduction paths are examined in a memory module board by thermal analysis, in order to find the structure for suppressing the temperature rise of a memory module board. As a result of the simulation, the following was found. The heat generated in the memory module board was radiated from the surface of the memory module board to the ambient air and simultaneously radiated through a socket toward the mount board. The amount of heat reached to the mount board was equal to about 45% of the whole heat radiation. Based on the result of this simulation, the present inventor derived an idea that the temperature rise of the memory module board can be effectively suppressed by efficiently radiating the heat toward the mount board from the memory module board. 
   The present inventor further discussed specifically the structure to efficiently radiate the heat from the memory module board to the mount board, and decided to provide a heat radiation guide plate which contacts each of the socket and the mount board. The memory module board is mounted on the socket via a plug. In this case, in addition to the conventional heat radiation paths, heat generated by the memory module board is transferred to the heat radiation guide plate from the combination of plug and socket, and further to the mount board therefrom. Thus, the heat is efficiently radiated from the memory module board. In addition, radiation of heat from the socket to the mount board was efficiently carried out by setting thermal conductivity of the heat radiation guide plate at higher than 1 W/m·K 
   Furthermore, the surface portion of the mount board that the socket or heat radiation guide plate contacts is configured by a heat radiation layer having a thermal conductivity of 1 W/m·K or higher, in place of the conventional layer having a thermal conductivity of less than 1 W/m·K. In this case, the heat transferred to the mount board through the combination of plug and socket or the heat radiation guide plate spreads quickly in the in-plane directions of the mount board through the heat radiation layer, and is radiated to the mount board having a larger thermal capacity through the heat radiation layer. Thus, the heat generated in the memory module board can be efficiently radiated to the mount board. 
   Alternatively, a similar advantage can be obtained by providing a heat radiation sheet having a thermal conductivity of 1 W/m·K or higher on the mount board, which is kept in contact with the socket or heat radiation guide plate. In particular, the heat can be radiated more efficiently from the memory module if the heat radiation guide plate, heat radiation layer, or heat radiation sheet is made of iron, aluminum, copper or a material having a thermal conductivity of 50 W/m·K or higher, such as PGS. 
   Now, the present invention will be described below in more detail with reference to the accompanying drawings, based on the embodiments of the present invention. 
     FIG. 1  is a perspective view showing the structure of a semiconductor device according to a first embodiment of the present invention.  FIG. 2  is a top plan view showing the semiconductor device shown in  FIG. 1 , from which memory module boards are removed. The semiconductor device, generally designated by numeral  100 , has a mount board  10 , an elongate socket  20  provided on the mount board  10 , and memory module boards  30  mounted on the socket  20 . 
   The memory module board  30  is a card-like board having a rectangular shape. A plurality of memory devices  31  are provided on both surfaces of the memory module board  30 , and an elongate plug is provided on an edge portion of the memory module board  30 . The plug has a plurality of plug terminals arranged in a row on both sides of the memory module board  30  and near the edge of the memory module board  30 . The socket  20  has a plurality of socket terminals arranged in two rows and each corresponding to one of the plug terminals of the plug. 
   The mount board  10  is configured as a multilayer printed circuit board, and has a structure in which a plurality of insulating layers  11  of FR4 (flame Retardant Type 4) are layered one on another. The socket In an area underlying the socket  20  except for the center of the socket  20 , a heat radiation layer  13  made of copper is formed in place of the uppermost insulating layer  11   a . Copper heat radiation guide plates  40   a  and  40   b  are provided in contact with the surface of the heat radiation layer  13  and the side surfaces of the socket  20 . FR4 and copper have a heat conductivity of about 0.3 W/m·K and 385 W/m·K, respectively. 
     FIG. 3A  shows a part of a cross-section taken along the line a-a shown in  FIG. 1 . In the mount board  10 , interconnection patterns made of copper are formed between adjacent two insulating layers  11  and on top and bottom surfaces of the mount board  10 . A number of through-holes (not shown) each penetrating the mount board  10  and a number of via holes (not shown) each penetrating one or a plurality of insulating layers  11  are formed in the mount board  10 . Interconnection plugs are formed inside these through-holes and via holes, thereby connecting together different interconnection layers. 
   In the uppermost insulating layer  11   a , the area underlying the center of the socket  20  configures an interconnection area  12 . In the interconnection area  12 , a plurality of via holes each penetrating one or a plurality of insulating layers  11  including the uppermost insulating layer  11   a  are formed. A plurality of electrodes provided at the bottom of the socket  20  and extending from the respective socket terminals are connected to the interconnection plugs formed inside the via holes and through-holes. 
   The socket  20  has a U-shaped cross-section. A plurality of socket terminals  21  are provided on both inner side surfaces of the U-shaped socket  20 . On the memory module board  30 , a plurality of plug terminals (not shown) are formed on both side surfaces of the board at a lower portion thereof. These plug terminals are coupled to the socket terminals  21  of the socket by insertion of the plug into the socket  21 . The heat radiation guide plates  40   a  and  40   b  have a height substantially equal to the height of the socket  20 . A grease (not shown) is applied between side surfaces of the socket  20  and the heat radiation guide plates  40   a  and  40   b,  to tighten the contact between the side surfaces of the socket  20  and the heat radiation guide plates  40   a  and  40   b . Thus, efficiency of thermal conduction between the socket  20  and the heat radiation guide plates  40   a  and  40   b  is improved. 
     FIG. 3B  shows a longitudinal-section taken along the direction b-b shown in  FIG. 1  and  FIG. 3A  The heat radiation guide plates  40   a  and  40   b  have substantially the same dimensions as the side surface of the socket  20  in the lengthwise direction and in the height direction. The heat radiation guide plates  40   a  and  40   b  are provided adjacent to the socket  20 . The heat radiation layer  13  has such a planar shape that is large enough to encompass the whole bottom surface of the socket  20  and the heat radiation guide plates  40   a  and  40   b , and yet does not obstruct connection of the mount board  10 . 
   In manufacture of the semiconductor device  100 , at first, the heat radiation layer  13  made of copper is formed around the interconnection area  12  prior to formation of the uppermost insulating layer  11   a , during the process for forming the mount board  10 . After forming the uppermost insulating layer  11   a , the socket  20  is provided on the mount board  10 . Thereafter, the heat radiation guide plates  40   a  and  40   b  each are formed so as to contact a side surface of the socket  20  and the upper surface of the heat radiation layer  13 . 
   In operation of the semiconductor device  100 , wherein electric power is supplied to the semiconductor device  100  to activate the memory module board  30 , most of the heat generated in the memory module board  30  is transferred to the heat radiation guide plates  40   a  and  40   b  through the socket  20 , in addition to the conventional heat radiation paths. The heat is then transferred to the heat radiation layer  13  from the heat radiation guide plates  40   a  and  40   b . Alternatively, the heat is directly transferred to the heat radiation layer  13  from the socket  20 . The heat transferred to the heat radiation layer  13  quickly spreads in the in-plane directions of the mount board  10 , and is thus quickly radiated toward the mount board  10  having a larger thermal capacity. Accordingly, in comparison with the conventional semiconductor device, the heat is efficiently radiated from the memory module board  30 , whereby temperature rise of the memory module board  30  can be effectively suppressed. 
   In the present embodiment, the heat radiation layer  13  is made of copper. However, the heat radiation layer  13  may be made of another material having a thermal conductivity of 1 W/m·K or higher. For example, the heat radiation layer  13  may preferably be made of a PGS (Pyrolytic Graphite Sheet). The PGS has a thermal conductivity of 600 to 800 W/m·K or so in the direction in which the crystal surface thereof extends, and a thermal conductivity of 15 W/m·K or so in the thickness direction of the crystal surface. Therefore, if the heat radiation layer  13  is made of PGS, the heat can be efficiently radiated by arranging the crystal surface of the PGS in parallel with the extending direction of the heat radiation layer  13 . 
   In addition, in the present embodiment, the heat radiation guide plates  40   a  and  40   b  are made of copper. However, the heat radiation guide plates  40   a  and  40   b  may be made of another material. As a preferable example, the heat radiation guide plates  40   a  and  40   b  may be made of aluminum having a thermal conductivity of 201 W/m·K, iron having a thermal conductivity of 80 W/m·K. Further, the heat radiation layer  13  or heat radiation guide plates  40   a  and  40   b  may be made of insulating material having a high thermal conductivity. Examples of the insulating material having a high thermal conductivity include silicon nitride, aluminum nitride, and the like. 
     FIG. 4A  is a perspective view showing the structure of a semiconductor device according to a first modification of the first embodiment.  FIG. 4B  shows a longitudinal-section taken along the line b-b shown in  FIG. 4A . In the semiconductor device  101 , heat radiation fins  41  are provided on a line extending from the longitudinal direction of the socket  20  and on the surface of the heat radiation layer  13 . That is, the heat radiation fins  41  are additionally provided in the structure of the semiconductor device  100  shown in  FIG. 1 . According to the semiconductor device  101  of the present modification, the heat radiation fins  41 , provided on the heat radiation layer  13 , assist radiation of the heat generated in the heat radiation layer  13  for the mount board  10  toward the ambient air. Accordingly, in comparison with the semiconductor device  100  shown in  FIG. 1 , the temperature rise of the memory module board  30  can be more effectively suppressed. A heat radiation fan may be additionally provided on the mount board  10 . 
   It is to be noted that, if the heat radiation layer  13  in the semiconductor device  100  shown in  FIG. 1  is made of a conductive material, interconnection patterns which contact the heat radiation layer  13  cannot be provided without involving a short-circuit failure. Therefore, the interconnection area  12  should have a broad area by providing the heat radiation layer  13  apart from the socket  20 , if complicated interconnections are to be provided in the interconnection area  12 .  FIGS. 5 to 7  show semiconductor devices in which the heat radiation layer  13  is provided apart from the socket  20 , according to second to fourth modifications of the first embodiment. 
   In the semiconductor device  102  shown in  FIG. 5 , the interconnection area  12  is provided to encompass the whole bottom surfaces of the socket  20  and the heat radiation guide plates  40   a  and  40   b . In the semiconductor device  103  shown in  FIG. 6 , a plurality of interconnection areas  12  are provided each to encompass the bottom surface of a corresponding socket  20  and a corresponding pair of heat radiation guide plates  40   a  and  40   b . In the semiconductor device  104  shown in  FIG. 7 , first heat radiation layers  13   a  to  13   c  are provided each between adjacent two of the socket  20 , second heat radiation layers  13   d  and  13   e  are respectively provided outside of the outermost socket  20 , and third heat radiation layers  13   f  and  13   g  are provided in the vicinity of the edges of the socket  20  arranged therein. The interconnection areas  12  are provided in the space between the heat radiation layers  13   a  to  13   g . This configuration provides a simpler structure for the interconnection circuit. 
   The heat radiation layers  13  having a high thermal conductivity and provided near the socket  20  in the semiconductor devices  102 ,  103 , and  104  shown in  FIGS. 5 to 7  effectively radiate the heat generated in the mount board  10  near the socket  20  in the in-plane directions of the mount board  10 . Thus, the temperature rise of the memory module board  30  can be effectively suppressed. 
     FIGS. 8A and 8B  show a cross-section and a longitudinal section, respectively, of a semiconductor device according to a second embodiment of the present invention.  FIG. 8A  shows the structure of the memory module similarly to  FIG. 3A , whereas  FIG. 8B  shows the structure of the memory module similarly to  FIG. 3B . In the semiconductor device  105 , the heat radiation layer  13  shown in  FIG. 1  is not formed, and the uppermost insulating layer  11   a  is formed over the entire surface of the mount board  10 . Heat radiation guide plates  40   a  and  40   b  are provided on the mount board  10 , which is in contact with the side surfaces of a socket  20 . 
   Heat radiation sheets  14  are provided on the mount board  10 , which is in contact with the side surfaces of the heat radiation guide plates  40   a  and  40   b . The semiconductor device  105  has a structure similar to the structure of the semiconductor device  100  shown in  FIG. 1  except for the features described above. 
   According to the semiconductor device  105  of the present embodiment, the heat radiation sheets  14  can be formed easily on the mount board  10 . Therefore, the semiconductor device  105  of the present embodiment can be more easily manufactured compared to the semiconductor device  100  of the first embodiment. In addition, the design choice of the circuit interconnections in the mount board  10  is increased since the heat radiation sheets  14  overlies an insulating layer  11   a . The heat radiation sheets  14  may be provided in contact with the side surfaces of the socket  20 , and heat radiation guide plates  40   a  and  40   b  may be provided on the heat radiation sheets  14 . 
     FIG. 9  shows a longitudinal-section of the memory module board in a semiconductor device according to a modification of the second embodiment, similarly to  FIG. 8B . The semiconductor device  106  of this modification corresponds to the structure of the semiconductor device  105  shown in  FIG. 8  provided with heat radiation fins  41  on the surfaces of the heat radiation sheets  14 . The heat radiation fins  41  are arranged on the line extended from the extending direction of the socket  20 . By using the mount board  106  in the present modification, the heat is effectively radiated from of the heat radiation sheets  14  or mount board  10  toward the ambient air through the fins  41 . Thus, in comparison with the semiconductor device  105  shown in  FIG. 8 , temperature rise of the memory module board  30  can be effectively suppressed. Additionally, a heat radiation fan may be provided on the mount board  10 . 
   In the embodiments described above, memory module boards have been described. However, temperature rise of a variety of module boards each provided with one or a plurality of other electronic components can be effectively suppressed by applying a structure similar to those described above. In another electronic component directly mounted on a mount board other than the module boards, the temperature rise of the electronic component can be also effectively suppressed by forming a heat radiation layer as described above or by providing heat radiation guide plates and/or heat radiation sheets. In this case, the heat radiation guide plates are provided in contact with each of the electronic component and the mount board. 
   The present invention has been described above based on preferred embodiments thereof. However, the semiconductor devices according to the present invention are not limited to the structures described in the embodiments. The scope of the present invention should be considered as including those semiconductor devices that would be derived by making various changes and modifications to the structures of the above embodiments.