Abstract:
A printed board unit includes a printed board including lands thereon, a semiconductor device unit, and an attachment mechanism to attach the semiconductor device unit to the printed board. The semiconductor device unit includes a heat transfer member, a semiconductor device including first and second surfaces parallel to each other, the first surface having lands thereon, and a socket including contacts protruding from first and second surfaces of the socket, the first and second surfaces being parallel to each other. In the semiconductor device unit, the semiconductor device and the socket are attached to the heat transfer member so that the second surface of the semiconductor device opposes the heat transfer member. The lands of the semiconductor device are electrically connected to the lands of the printed board unit via the contacts of the socket.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to printed board units, and more particularly to a printed board unit which includes a large scale integration (LSI) package of a land grid array (LGA) type mounted on a printed board with an LGA socket interposed therebetween, and forms a server that is an information processing and communication facility. 
     A printed board unit forming a server is plugged into a motherboard in consideration of repairs in the event of a failure, and an LSI package is replaceably mounted on a printed board. 
     In the server, repairs are made with a printed board unit being removed from the server. During the repairs, the server operates with a reduced processing capacity compared with its normal state since the printed board unit is removed from the server. Therefore, it is desirable that the repairs should be made so quickly that a period for which the server operates with the reduced capacity compared with its normal state becomes as short as possible. 
     Further, like the above-described repairs, the additional installation of an LSI package on the printed board is also performed with a printed board unit being removed from the server. Therefore, it is also desirable that the additional installation of the LSI package should be quickly performed. 
     Moreover, it is desirable that the repairs should be made and the additional installation should be performed with the lowest possible costs. 
     2. Description of the Related Art 
     FIGS. 1 and 2 each show a conventional printed board unit  10 . The printed board unit  10  includes an LGA-type LSI package  20  mounted on a printed board  11  with an LGA socket  30  interposed therebetween. A stiffener  40  is provided on the lower surface of the printed board  11  with an insulating sheet  45  interposed therebetween, and a heat transfer plate  41  that doubles as a cooling fin is provided on the upper surface of the LSI package  20 . The printed board unit  10  further includes nuts  42 , which are tightened so that the heat transfer plate  41  presses the LSI package  20  onto the printed board  11  through a heat transfer sheet  46  by coiled springs  43 . Each of lands  21  of the LSI package  20  is electrically connected to a corresponding one of lands  12  formed on the printed board  11  via a corresponding one of contacts  31  of the LGA socket  30 . 
     The printed board unit  10  is mounted on a motherboard by being plugged thereinto and is incorporated into a server. 
     Here, a description will be given of repairs in the event of a failure of the LSI package  20 . 
     The repairs are made in the following procedure. In step  1 , the printed board unit  10  is removed outside from the server. In step  2 , at the site, the nuts  42  are loosened and removed, and the heat transfer plate  41  is pulled off the bolts  40   a  of the stiffener  40  so that the LSI package  20 , the LGA socket  30 , and the heat transfer plate  41  are apart from one another. In step  3 , the faulty LSI package  20  is replaced with a new LSI package. In step  4 , the LSI socket  30  is positioned on the printed board  11 . In step  5 , the new LSI package is positioned on the LSI socket  30 . In step  6 , the heat transfer plate  41  is combined with the stiffener  40  and the coiled springs  43  are fitted to the bolts  40   a  before the nuts  42  are tightened. In step  7 , the printed board unit  10  is inserted into the server. 
     Repairs are also made in the above-described procedure in the event of a failure of the LGA socket  30 . 
     Positioning the new LSI package on the LGA socket  30  requires accuracy, and is troublesome and relatively time-consuming. Therefore, the repairs of failures of the LSI package  20  and the LGA socket  30  are relatively time-consuming. 
     The additional installation of an LSI package also requires positioning the LSI package on an LGA socket, and therefore, is relatively time-consuming. 
     At some sites, dust attaches to the lands  21  of the LSI package  20  and the contacts  31  of the LGA socket  30  while the LSI package  20  and the LGA socket  30  are apart from each other so that the reliability of electrical connection between the LSI package  20  and the LGA socket  30  may be impaired. 
     In the event of a failure of an LSI package or an LGA socket, a new printed board unit may be fitted into the server after a printed board unit including the faulty LSI package or LGA socket is removed from the server, which method dispenses with the removal of the faulty LSI package or LGA socket. 
     The above-described method dispenses with the replacement of the faulty LSI package or LGA socket, thus realizing quick replacement of a faulty component. However, in order to realize this method, it is necessary to prepare a new printed board unit for replacement for each printed board unit, thus increasing the costs of spare components. 
     Similarly, in the case of the additional installation of an LSI package, it is necessary to prepare a new printed board unit for the additional installation, thus increasing the costs of spare components. 
     SUMMARY OF THE INVENTION 
     It is a general object of the present invention to provide a printed board unit in which the above-described disadvantages are eliminated. 
     A more specific object of the present invention is to provide a printed board unit which includes a semiconductor device unit as a replacement unit so as to be repaired and reproduced easily in a short time in the event of a failure only by replacing the semiconductor device unit. 
     The above objects of the present invention are achieved by a printed board unit including a printed board including lands thereon, a semiconductor device unit, and an attachment mechanism for attaching the semiconductor device unit to the printed board, wherein the semiconductor device unit includes: a heat transfer member; a semiconductor device including first and second surfaces parallel to each other, the first surface having lands thereon; and a socket including contacts protruding from first and second surfaces of the socket, the first and second surfaces being parallel to each other, wherein the semiconductor device and the socket are attached to the heat transfer member so that the second surface of the semiconductor device opposes the heat transfer member, and the lands of the semiconductor device are electrically connected to the lands of the printed board unit via the contacts of the socket. 
     According to the above-described printed board unit, the semiconductor device unit is a replacement unit. In the event of a failure of the semiconductor device, repairs are completed only by removing the semiconductor device unit including the faulty semiconductor device from the printed board unit and replacing the semiconductor device unit by a prepared new semiconductor device unit. Therefore, the positioning of the semiconductor device on the socket is unnecessary. Thus, the printed board unit is repaired in a shorter time than a conventional printed board unit, which requires a semiconductor device and a socket to be apart from each other for repair. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a sectional view of a conventional printed board unit; 
     FIG. 2 is an exploded view of the printed board unit of FIG. 1; 
     FIG. 3 is a perspective view of a printed board unit according to a first embodiment of the present invention; 
     FIG. 4 is an enlarged fragmentary sectional view of the printed board unit of FIG. 3 taken along the line IV—IV; 
     FIG. 5 is an exploded view of the printed board unit of FIG. 4; 
     FIGS. 6A and 6B are an exploded sectional view and an exploded perspective view of a semiconductor device unit shown in FIG. 3, respectively; 
     FIG. 7A is a bottom view of the semiconductor device unit shown in FIGS. 6A and 6B; 
     FIGS. 7B and 7C are sectional views of the semiconductor device unit of FIG. 7A taken along the lines B—B and C—C, respectively; 
     FIG. 8A is a bottom view of a variation of the semiconductor device unit; 
     FIG. 8B is a sectional view of the semiconductor device unit of FIG. 8A taken along the line B—B; 
     FIG. 9 is a perspective view of a printed board unit according to a second embodiment of the present invention; 
     FIG. 10 is an enlarged fragmentary sectional view of the printed board unit of FIG. 9 taken along the line X—X; 
     FIGS. 11 and 12 are an exploded perspective view and an exploded sectional view of the printed board unit of FIG. 10, respectively; and 
     FIGS. 13 and 14 are an exploded perspective view and an exploded sectional view of a semiconductor device unit shown in FIG. 9, respectively. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A description will now be given, with reference to the accompanying drawings, of embodiments of the present invention. 
     FIG. 3 is a diagram showing a printed board unit  100  according to a first embodiment of the present invention. FIG. 4 is an enlarged fragmentary sectional view of the printed board unit  100  taken along the line IV—IV. FIG. 5 is an exploded view of the printed board unit  100  of FIG.  4 . In the figures, elements corresponding to those of FIGS. 1 and 2 are referred to by the same numerals. 
     The printed board unit  100  includes a plurality of semiconductor device units  110  as replacement units arranged on the printed board  11 . 
     In each of parts on which the semiconductor device units  110  are mounted, the stiffener  40  is provided on the lower surface side of the printed board  11  with the insulating sheet  45  interposed therebetween, and the nuts are tightened on the four bolts  40   a  of the respective corner portions of the stiffener  40  so that each semiconductor device unit  110  is pressed onto the printed board  11  by the coiled springs. Each of the lands  21  of the LSI package  20  is electrically connected to the corresponding one of the lands  12  formed on the printed board  11  via the corresponding one of the contacts  31  of an LGA socket  30 A. 
     A description will now be given of the semiconductor device unit  110 . 
     FIGS. 6A and 6B are an exploded sectional view and an exploded perspective view of the semiconductor device unit  110 , respectively. FIG. 7A is a bottom view of the semiconductor device unit  110 , and FIGS. 7B and 7C are sectional views of the semiconductor device unit  110  of FIG. 7A taken along the lines B—B and C—C, respectively. 
     As shown in FIGS. 5 and 7A through  7 C, each semiconductor device unit  110  includes a heat transfer plate  41 A as a base, the LSI package  20  bonded to the lower surface of the heat transfer plate  41 A with the heat transfer sheet  46  interposed therebetween, and an LGA socket  30 A supported on the lower side of the LSI package  20  by engaging pin members  111 . A cooling fin  112  may be attached to the upper surface of the heat transfer plate  41 A. 
     The heat transfer plate  41 A includes a shallow concave portion  41 A a  for positioning the LSI package  20  and a pair of holes  41 A b  and  41 A c  for positioning the LGA socket  30 A formed in a predetermined arrangement. The pair of the holes  41 A b  and  41 A c  are positioned around the ends of one diagonal  113  of the rectangular heat transfer plate  41 A. Holes  41 A d  and  41 A e  into which the engaging pin members  111  are fitted are formed around the ends of the other diagonal  114 . Through holes  41 A f  are formed in the respective corner portions of the heat transfer plate  41 A. 
     The LGA socket  30 A includes the contacts  31  which correspond to the respective lands  21  of the LSI package  20 . Positioning pins  32  and  33  are planted in a pair of diagonal corners of the LGA socket  30 . Step-like concave portions  34  and  35  into which flange portions  111   a  of the engaging pin members  111  are fitted are formed in the other pair of diagonal corners of the LGA socket  30 . 
     Each of the engaging pin members  111  has the flange portion  111   a  formed on its lower end and an engaging spring  111   b  of a reverse V-shape on its upper end. The holes  41 A d  and  41 A e  have hole portions  41 A d   1  and  41 A e   1  of larger diameters provided on their upper sides, respectively. The hole portions  41 A d   1  and  41 A e   1  include respective bottom portions  41 A d   2  and  41 A e   2 . 
     The printed board  11  has the numerous lands  12  and four through holes  13  formed on where the semiconductor device unit  110  is mounted. 
     The positions of the holes  41 A b  and  41 A c  correspond to those of the positioning pins  32  and  33 , respectively. The positions of the respective through holes  41 A f , the respective through holes  13 , and the respective bolts  40   a  correspond to one another. 
     Here, a further detailed description will be given of the semiconductor device unit  110 . 
     As shown in FIGS. 6A and 6B, and  7 A through  7 C, the LSI package is fitted into the shallow concave portion  41 A a  so as to be positioned with respect to the heat transfer plate  41 A. The positioning pins  32  and  33  are fitted into the respective holes  41 A b  and  41 A c  so that the LGA socket  30  is positioned with respect to the heat transfer plate  41 A. Thereby, the respective lands  21  of the LSI package  20  oppose the corresponding contacts  31  of the LGA socket  30 . 
     The engaging pin members  111  are fitted into the respective holes  41 A d  and  41 A e  so that the engaging springs  111   b  protrude through the holes  41 A d  and  41 A e  into the respective hole portions  41 A d   1  and  41 A e   1 , where the engaging springs  111   b  spread to engage the bottom portions  41 A d   2  and  41 A e   2  so as to be prevented from slipping off the hole portions  41 A d   1  and  41 A e   1 . The flange portions  111   a  of the engaging pin members  111  engage the step-like concave portions  34  and  35 , respectively, so that the LGA socket  30  is supported close to the LSI package  20 . The contacts  31  and the lands  21  oppose each other with a little space formed therebetween, or the contacts  31  may be in contact with the lands  21 . 
     The semiconductor device unit  110  having the above-described structure is positioned with respect to the printed board  11  with the respective bolts  40   a  penetrating through the through holes  13  to be fitted into the through holes  41 A f , so that the contacts  31  oppose the lands  12 . 
     With the heat transfer plate  41  pressing the semiconductor device unit  110  onto the printed board  11  by the coiled springs  43 , the respective lands  21  of the LSI package  20  are electrically connected to the corresponding lands  12  formed on the printed board  11  via the corresponding contacts  31  of the LGA socket  30 A. 
     The printed board unit  100  having the above-described structure is mounted on a motherboard by being plugged thereinto and is incorporated into a server. 
     Here, a description will be given of repairs in the event of a failure of the LSI package  20 . 
     The repairs are made in the following procedure. In step  1 , the printed board unit  100  is removed outside from the server. In step  2 , at the site, after the nuts  42  are loosened and removed, the semiconductor device unit  110  is removed by being pulled up until the bolts  40   a  of the stiffener  40  are pulled out from the through holes  41 A f . In step  3 , a prepared new semiconductor device unit is fitted to the bolts  40   a  from the upper side of the printed board  11 , and the coiled springs  43  are fitted to the bolts  40   a  before the nuts  42  are tightened. In step  4 , the printed board unit  100  is inserted into the server. 
     Repairs are also made in the above-described procedure in the event of a failure of the LGA socket  30 A. 
     Therefore, according to this embodiment, a troublesome operation of positioning the LSI package  20  on the LGA socket  30 A is unnecessary, and repairs in the event of failures of the LSI package  20  and the LGA socket  30 A are made quickly to be completed in shorter times than in a case where the conventional printed board unit is employed. Consequently, a period for which the server operates with a reduced capacity compared with its normal state is shortened compared with the case where the conventional printed board unit is employed. 
     Further, at the sites of the above-described repairs, dust is prevented from being attached to the lands  21  of the LSI package  20  and the contacts  31  of the LGA socket  30 A. Therefore, the reliability of electrical connection between the LSI package  20  and the LGA socket  30 A after repair is prevented from being impaired. 
     Moreover, since it is a semiconductor device unit that is prepared for replacement in the event of a failure, the costs of spare components are low compared with a case where a printed board unit is prepared separately. 
     The removed semiconductor device unit  110  is sent to a factory, where the removed semiconductor device unit  110  is taken apart so that the faulty LSI package  20  and LGA socket  30 A are replaced with new ones, respectively. Then, the semiconductor device unit  110  is again assembled and reproduced. The reason why this reproduction is possible is that the semiconductor device unit  110  is structured so that the LSI package  20  and the LGA socket  30 A are removable from the heat transfer plate  41 A, respectively, and are detachable from each other. 
     The reproduction of the semiconductor device unit  110  is performed by means of a cylindrical jig  120  indicated by a double dot chain line in FIG.  7 B. The jig  120  is inserted into the hole portion  41 A e   1  to close the engaging spring  111   b  so that the engaging pin  110  is pulled out. The same operation is performed on the hole portion  41 A d   1 . Then, the faulty LSI package  20  and LGA socket  30 A are pulled apart from each other to be replaced with new ones. Thereafter, the semiconductor device unit  110  is again assembled and completed. The operation for this reproduction is performed with the capacity of the server being restored to its normal state. Therefore, the operation does not affect an operational condition of the server, and it does not especially matter if the operation takes time. 
     Here, a description will be given of the additional installation of an LSI package on the printed board  11 . 
     The printed board  11  has numerous lands and four through holes formed on a part on which the LSI package is to be additionally installed. 
     The additional installation of the LSI package is performed in the following procedure. In step  1 , the printed board unit  100  is removed outside from the server. In step  2 , at the site, the stiffener  40  is fitted to the printed board  11  from the lower side thereof, and a semiconductor device unit is fitted to the bolts  40   a  from the upper side of the printed board  11  before the coiled springs  43  are fitted to the bolts  40   a  and the nuts  42  are tightened. In step  3 , the printed board unit  100  is inserted into the server. 
     Therefore, an operation for the additional installation of the LSI package on the printed board  11  is performed quickly to be completed in a shorter time than in a case where the conventional printed board unit is employed. Consequently, a period for which the server operates with a reduced capacity compared with its normal state is shortened compared with the case where the conventional printed board unit is employed. 
     Since the part of the printed board  11  on which part the LSI package is to be additionally installed has only the numerous lands and the four through holes formed thereon, the production costs of the part are low. 
     A description will now be given of a variation of the semiconductor device unit  110 . 
     FIG. 8A is a bottom view of a semiconductor device unit  110 B, which is a variation of the semiconductor device unit  110 , and FIG. 8B is a sectional view of the semiconductor device unit  110 B of FIG. 8A taken along the line B—B. 
     The semiconductor device unit  110 B employs bent leaf spring members  121  instead of the engaging pins  111  shown in FIG.  7 B. Each of the leaf spring members  121  has a hook portion  121   a  of its one end engaged with a concave portion  30 B a  formed on each of the left and right sides of a LGA socket  30 B, and a hook portion  121   b  of the other end engaged with a corresponding one of groove portions  41 B g  formed in the upper surface of a heat transfer plate  41 B. Thereby, the LSI package  20  and the LGA socket  30 B are attached to the lower surface of the heat transfer plate  41 B. 
     A description will now be given of a second embodiment of the present invention. 
     FIG. 9 is a diagram showing a printed board unit  100 C according to the second embodiment of the present invention. FIG. 10 is an enlarged fragmentary sectional view of the printed board unit  100 C of FIG. 9 taken along the line X—X. FIGS. 11 and 12 are an exploded perspective view and an exploded sectional view of the printed board unit  100 C of FIG. 10, respectively. In the figures, elements corresponding to those of FIGS. 1 and 2 are referred to by the same numerals. 
     According to a structure of the printed board unit  100 C, each of semiconductor device units  110 C as replacement units mounted on a printed board  11 C includes a multi-chip module  130  and LGA sockets  30 C 1  and  30 C 2 . 
     A stiffener  40 C is provided on the lower surface side of the printed board  11 C with an insulating sheet  45 C interposed therebetween, and the nuts  42  are tightened on six bolts  40 C a  of the stiffener  40 C, so that a cooling fin  120 C presses the semiconductor device unit  110 C onto the printed board  11 C by the coiled springs  43 . Respective lands  131  of the multi-chip module  130  are electrically connected to the corresponding lands  12  formed on the printed board  11 C via corresponding contacts  31 C 1  and  31 C 2  of the LGA sockets  30 C 1  and  30 C 2 . 
     A guide frame  140  of a quadrilateral frame shape is attached to the upper surface of the printed board  11 C by screws  141  so as to enclose a part on which the semiconductor device unit  110  is mounted. The guide frame  140  serves to guide and position the semiconductor device unit  110  to be mounted. The screws  141  are screwed into the stiffener  40 C so that the guide frame  140  and the stiffener  40 C are fixed to each other with the printed board  11 C interposed therebetween. 
     A description will now be given of the semiconductor device unit  110 C. 
     FIGS. 13 and 14 are an exploded perspective view and an exploded sectional view of the semiconductor device unit  110 C, respectively. 
     As shown in FIGS. 12 through 14, the semiconductor device unit  110 C includes a heat transfer plate  150  as a base, the multi-chip module  130  bonded to the heat transfer plate  150  with a heat transfer sheet  46 C and insulating sheets  151  and  152  on the lower surface side of the heat transfer plate  150  interposed therebetween, the LGA sockets  30 C 1  and  30 C 2  on the lower surface side of the multi-chip module  130 , and a frame  153  of a quadrilateral frame shape and a support plate  154  of a quadrilateral shape each supporting the LGA sockets  30 C 1  and  30 C 2  to the heat transfer plate  150 . 
     The heat transfer plate  150  includes a shallow concave portion  150   a  for receiving an LSI chip  133  on its lower surface, holes  150   b  for fixing the frame  153 , holes  150   c  for fixing the support plate  154 , and holes  150   d  through which the bolts  40 C a  of the stiffener  40 C penetrate. 
     The multi-chip module  130  includes a multilayer substrate  132  having the numerous lands  131  on its lower surface, and a plurality of the bare LSI chips  133  mounted side by side in the center of the upper surface of the multilayer substrate  132 . The respected mounted LSI chips  133  are connected to the lands  131  by interconnection lines formed in the multilayer substrate  132 . The multilayer substrate  132  has formed therein positioning holes  134  for positioning the LGA sockets  30 C 1  and  30 C 2 , and holes  135  through which later-described bolts  154   b  penetrate. 
     The LGA sockets  30 C 1  and  30 C 2  each have a rectangular shape, and include the contacts  31 C 1  and  31 C 2 , respectively, which penetrate therethrough to correspond to the respective lands  131  of the multi-chip module  130 . The LGA sockets  30 C 1  and  30 C 2  further include positioning pins  155 . The positioning pins  155  are plated in the respective LGA sockets  30 C 1  and  30 C 2  so as to protrude upward and downward therefrom. Each of the positioning pins  155  includes an upward protruding portion  155   a  and a downward protruding portion  155   b . The LGA socket  30 C 1  includes, along one longitudinal side thereof, a step-like concave portion  30 C 1   a  for engaging a corresponding inside holding portion  153   a  of the frame  153 , and, along the other longitudinal side thereof, a step-like concave portion  30 C 1   b  for engaging a corresponding concave portion  154   a  formed on each side of the support plate  154 . Similarly, the LGA socket  30 C 2  includes step-like concave portions  30 C 2   a  and  30 C 2   b  corresponding to the step-like concave portions  30 C 1   a  and  30 C 1   b  of the LGA socket  30 C 1 , respectively. 
     Bolts  153   b  are planted in the frame  153  so as to protrude upward therefrom, and holes  153   c  through which the bolts  40 C a  of the stiffener  40 C penetrate are formed in the frame  153 . The bolts  154   b  are planted in the support plate  154  so as to protrude upward therefrom. 
     As shown in FIG. 12, the printed board  11 C has the numerous lands  12  formed on the part on which the semiconductor device unit  110 C is mounted, and the six through holes  13  formed in correspondence to the bolts  40 C a  of the stiffener  40 C. The printed board  11 C further has through holes  160  formed in correspondence to the downward protruding portions  155   b  of the positioning pins  155  of the LGA sockets  30 C 1  and  30 C 2 . 
     Here, a further detailed description will be given of the semiconductor device unit  110 C. 
     The semiconductor device unit  110 C has a structure shown in FIGS. 12 through 14. The multi-chip module  130  is fixed to the lower surface of the heat transfer plate  150 . The LSI chip  133  is received by the shallow concave portion  150   a  to be bonded thereto with the heat transfer sheet  46 C interposed therebetween. The insulating sheets  151  and  152  are interposed between the multilayer substrate  132  and the heat transfer plate  150 . The frame  153  is attached to the heat transfer plate  150  with nuts  156  being screwed on the bolts  153   b  inserted into the holes  150   b  of the heat transfer plate  150 . The support plate  154  is attached to the heat transfer plate  150  with nuts  157  being screwed on the bolts  154   b  inserted into the holes  150   c  of the heat transfer plate  150 . The LGA sockets  30 C 1  and  30 C 2  have the respective step-like concave portions  30 C 1   a  and  30 C 2   a  supported by the holding portions  153   a  of the frame  153 , and the respective step-like concave portions  30 C 1   b  and  30 C 2   b  supported by the holding portions  154   a  of the support plate  154 . The LGA sockets  30 C 1  and  30 C 2  are positioned with respect to the multi-chip module  130  with the upward protruding portions  155   a  being fitted into the positioning holes  134  of the multi-chip module  130  so that the upper ends of the respective contacts  31 C 1  and  31 C 2  oppose the corresponding lands  131  of the multi-chip module  130 . The holes  153   c  of the frame  153  correspond to the holes  150   d  of the heat transfer plate  150 . 
     As shown in FIG. 12, the semiconductor device unit  110 C having the above-described structure and the cooling fin  120 C are fixed on the printed board  11 C. The semiconductor device unit  110 C is fitted inside the guide frame  140  with the bolts  40 C a  of the stiffener  40  being fitted into the holes  153   c  and  153   d , and is positioned on the printed board  11 C with the downward protruding portions  155   b  being inserted into the through holes  160 . The contacts  31 C 1  and  31 C 2  oppose the lands  131 . The bolts  40 C a  are fitted into through holes  120 C a  of the cooling fin  120 C, and have the nuts  42  tightened thereon. The cooling fin  120 C presses the semiconductor device unit  110 C onto the printed board  11 C by resilient force of the coiled springs  43 . The respective lands  131  of the multi-chip module  130  are electrically connected to the lands  12  formed on the printed board  11 C via the corresponding contacts  31 C 1  and  31 C 2  of the LGA sockets  30 C 1  and  30 C 2 . 
     According to this embodiment, since the upward and downward protruding portions  155   a  and  155   b  of the same positioning pin  155  are employed for positioning, the positions of the lands  131  of the multi-chip module  130 , the positions of the contacts  31 C 1  and  31 C 2  of the LGA sockets  30 C 1  and  30 C 2 , and the positions of the lands  12  of the printed board  11 C are matched with accuracy. 
     The printed board unit  100 C having the above-described structure is mounted on a mother board by being plugged thereinto, and is incorporated into a server. 
     Here, a description will be given of repairs in the event of a failure of the multi-chip module  130 . 
     The repairs are made in the following procedure. In step  1 , the printed board unit  100 C is removed outside from the server. In step  2 , at the site, after the nuts  42  are loosened and removed, the cooling fin  120 C and the semiconductor device unit  110 C are pulled out from the bolts  40 C a  of the stiffener  40 C to be removed. In step  3 , a prepared new semiconductor device unit and the cooling fin  120 C are fitted to the bolts  40 C a  from the upper side of the printed board  11 C, and the coiled springs  43  are fitted to the bolts  40 C a  before the nuts  42  are tightened. In step  4 , the printed board unit  100 C is inserted into the server. 
     Repairs are also made in the above-described procedure in the event of a failure of the LGA sockets  30 C 1  or  30 C 2 . 
     Therefore, repairs in the event of failures of the multi-chip module  130  and the LGA socket  30 C 1  or  30 C 2  are made quickly to be completed in shorter times than in a case where the conventional printed board unit is employed. Consequently, a period for which the server operates with a reduced capacity compared with its normal state is shortened compared with the case where the conventional printed board unit is employed. 
     Further, at the sites of the above-described repairs, dust is prevented from being attached to the lands  131  of the multi-chip module  130  and the contacts  31 C 1  or  31 C 2  of the LGA socket  30 C 1  or  30 C 2 . Therefore, the reliability of electrical connection between the multi-chip module  130  and the LGA socket  30 C 1  or  30 C 2  after repair is prevented from being impaired. 
     Moreover, since it is a semiconductor device unit that is prepared for replacement in the event of a failure, the costs of spare components are low compared with a case where a printed board unit is prepared separately. 
     The removed semiconductor device unit  110 C is sent to a factory, where the removed semiconductor device unit  110  is taken apart by loosening and removing the nuts  156  and  157  so that the faulty multi-chip module  130  and LGA socket  30 C 1  or  30 C 2  are replaced with new ones, respectively. Then, the semiconductor device unit  110 C is again assembled and reproduced. 
     Here, a description will be given of the additional installation of a multi-chip module on the printed board  11 C. 
     The printed board  11 C has numerous lands and six through holes formed on a part on which the multi-chip module is to be additionally installed. 
     The additional installation of the multi-chip module is performed in the following procedure. In step  1 , the printed board unit  100 C is removed outside from the server. In step  2 , at the site, the stiffener  40 C is fitted to the printed board  11 C from the lower side thereof, and the guide frame  140  is placed on the upper surface of the printed board  11  to be fixed thereto by the screws  141 . In step  3 , a semiconductor device unit and the cooling fin  120 C are fitted to the bolts  40 C a  before the coiled springs  43  are fitted to the bolts  40 C a  and the nuts  42  are tightened. In step  4 , the printed board unit  100 C is inserted into the server. 
     Therefore, an operation for the additional installation of the multi-chip module on the printed board  11 C is performed quickly to be completed in a shorter time than in a case where the conventional printed board unit is employed. Consequently, a period for which the server operates with a reduced capacity compared with its normal state is shortened compared with the case in which the conventional printed board unit is employed. 
     Further, since it is a semiconductor device unit that is prepared for additional installment, the costs of spare components are low compared with a case where a printed board unit is prepared separately. 
     Moreover, since the part of the printed board  11 C on which part the multi-chip module is to be additionally installed has only the numerous lands and the six through holes formed thereon, the production costs of the part are low. 
     The present invention is not limited to the specifically disclosed embodiments, but variations and modifications may be made without departing from the scope of the present invention. 
     The present application is based on Japanese priority application No. 2000-291143 filed on Sep. 25, 2000, the entire contents of which are hereby incorporated by reference.