Abstract:
A printed wiring board supports an electronic component thereon. The printed wiring board includes an opening which is recessed from a surface of the printed wiring board. The opening has a dimension which houses the electronic component therein. A plurality of pads is disposed on a bottom surface of the opening. The plurality of pads has a skew arrangement in a grid pattern with respect to inner edges of the opening.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based upon and claims the benefit of priority of Japanese Patent Application No. 2009-280822, filed on Dec. 10, 2009, the entire contents of which are incorporated herein by reference. 
       FIELD 
       [0002]    Embodiments discussed herein are related to a printed wiring board, and an electronic apparatus. 
       BACKGROUND 
       [0003]    As methods for fabricating a printed wiring board unit by mounting electronic components represented by large scale integration (LSI) on a printed wiring board, a flip chip method (for example, JP-A-8-222840) and a ball grid array (BGA) technique (for example, JP-A-9-162527) are known. In these techniques, electronic components are arranged in a state in which semi-sphere shaped or sphere shaped solder bumps are sandwiched between the electronic components and electrode pads on a printed wiring board, and then the solder bumps are melted to mount the electronic components on the printed wiring board. 
         [0004]    However, when deformation occurs in the printed wiring board on which the electronic components are soldered due to an external force or thermal expansion, there is a concern that the electronic components are detached when stress of the deformation concentrates on soldered portions. Therefore, for an electronic apparatus in which the printed wiring board unit where the electronic components are soldered is installed, a design robust enough to suppress deformation of the printed wiring board unit is required. Such a robust design can make it difficult to reduce size and weight of the electronic apparatus. 
       SUMMARY 
       [0005]    According to an embodiment of the invention, a printed wiring board for mounting an electronic component thereon is provided. The printed wiring board includes an opening which is recessed from a surface of the printed wiring board. The opening has a dimension which houses the electronic component therein. A plurality of pads is disposed on a bottom surface of the opening. The plurality of pads has a skew arrangement in a grid pattern with respect to inner edges of the opening. 
         [0006]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory, and are not restrictive of the invention. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0007]      FIG. 1  illustrates a personal computer corresponding to an example of an electronic apparatus of the present invention. 
           [0008]      FIG. 2  illustrates an internal structure of a main body of the personal computer in  FIG. 1 . 
           [0009]      FIGS. 3A and 3B  schematically illustrate a mounting position of an electronic component on a wiring board according to a first embodiment. 
           [0010]      FIG. 4  illustrates shapes and arrangement of electrode pads according to the first embodiment. 
           [0011]      FIGS. 5A and 5B  illustrate an electronic component placed on the electrode pads according to the first embodiment. 
           [0012]      FIG. 6  illustrates a positional relationship between the electrode pads and solder bumps according to the first embodiment. 
           [0013]      FIG. 7  illustrates a state after solder wets and moves. 
           [0014]      FIGS. 8A and 8B  illustrate a self-alignment of the electronic component according to the first embodiment. 
           [0015]      FIG. 9  illustrates that stresses on solder joints are alleviated. 
           [0016]      FIGS. 10A and 10B  illustrate an electronic component according to a second embodiment. 
           [0017]      FIGS. 11A and 11B  illustrate a state in which the electronic component according to the second embodiment is placed in an opening of a wiring board. 
           [0018]      FIGS. 12A and 12B  illustrate a self-alignment of the electronic component according to the second embodiment. 
           [0019]      FIGS. 13A and 13B  illustrate an electronic component according to a third embodiment. 
           [0020]      FIG. 14  illustrates a placement example of the electronic component according to the third embodiment. 
           [0021]      FIG. 15  illustrates a modified example of placement of the electronic component according to the third embodiment. 
           [0022]      FIG. 16  illustrates a self-alignment of the electronic component according to the third embodiment. 
           [0023]      FIGS. 17A and 17B  illustrate an opening according to a fourth embodiment. 
           [0024]      FIGS. 18A and 18B  illustrate a state in which an electronic component is placed in the opening according to the fourth embodiment. 
           [0025]      FIGS. 19A and 19B  illustrate a self-alignment of the electronic component according to the fourth embodiment. 
           [0026]      FIGS. 20A and 20B  illustrate a wall according to a fifth embodiment. 
           [0027]      FIG. 21  illustrates a state in which an electronic component is placed inside the wall according to the fifth embodiment. 
           [0028]      FIGS. 22A and 22B  illustrate a self-alignment of the electronic component according to the fifth embodiment. 
           [0029]      FIG. 23  illustrates that stresses on solder joints are alleviated according to the fifth embodiment. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0030]    Hereinafter, embodiments the present invention of a printed wiring board, a printed wiring board unit, and an electronic apparatus will be described with reference to the drawings. 
         [0031]      FIG. 1  illustrates a personal computer corresponding to an example of the electronic apparatus of the present invention. 
         [0032]    The personal computer  100  for mobile use shown in  FIG. 1  can include a main body  110  and a display portion  120  openable and closable relative to the main body  100  with a hinge. A display panel  121  is fitted into the inside portion of the display portion  120  which faces the main body when the display portion  120  is closed. The main body  110  has a structure in which a keyboard  112  and a touchpad  113  are mounted in an enclosure  111 . 
         [0033]      FIG. 2  illustrates an example of an internal structure of the main body of the personal computer in  FIG. 1 . 
         [0034]    As shown in  FIG. 2 , a printed circuit board unit  130  is mounted in the enclosure  111  of the main body  110 . Although the printed circuit board unit  130  is a unit in which various electronic components are mounted on the printed wiring board  131 , for convenience of description, electronic components, wiring, and the like other than one electronic component  132  are omitted from the figures. 
         [0035]    The wiring board  131  has an opening  133  recessed from the surface of the wiring board  131 . The opening  133  surrounds the bottom area recessed from the surface of the wiring board  131 . The electronic component  132 , having a package form of a rectangular plate shape, is mounted in the area surrounded by the opening  133 . Each of the four corners of the electronic component  132  comes into contact with the opening  133 , so that the electronic component  133  pushes the opening  133  in the direction to expand the opening  133 . 
         [0036]    In this embodiment, the opening  133  is recessed from the surface, so that the electronic component  132  is buried in the wiring board  131 . This contributes to thinning of the circuit board  130 , the main body  110 , and the personal computer  100 . 
         [0037]    Hereinafter, an example of a structure of the circuit board  130  around the electronic component  132  will be described in detail, and in addition, a mounting method of the electronic component  132  will be described. 
         [0038]      FIG. 3  schematically illustrates a mounting position of the electronic component on the wiring board according to the first embodiment. 
         [0039]    In  FIG. 3 , only a portion near the opening  133  of the wiring board  131  is shown.  FIG. 3A  illustrates a top view. On the other hand,  FIG. 3B  illustrates a side perspective view. 
         [0040]    As described above, the opening  133  is provided in the wiring board  131 . Electrode pads  134  are arranged in an area inside the opening  133 . In the arrangement of the electrode pads  134 , a row of electrode pads  134   a  located at the most front row in the top view of  FIG. 3A  are shown in the side perspective view of  FIG. 3B . The arrangement of the electrode pads  134  is a rectangular arrangement as a whole, and the area surrounded by the opening  133  is also rectangular in shape. However, the orientation of the rectangle of the arrangement is tilted from the orientation of the rectangle of the area. The tilt angle of the arrangement of the electrode pads  134  is preferred to be about 1 to 10 degrees. 
         [0041]    Here, the arrangement and structure of the electrode pads  134  will be described in further detail. 
         [0042]      FIG. 4  illustrates shapes and arrangement of electrode pads according to the first embodiment. 
         [0043]    Although  FIG. 4  illustrates the area in which the electrode pads  134  are arranged in the wiring board  131 ,  FIG. 4  illustrates a concept of the arrangement of the electrode pads  134 , so that the number of the electrode pads  134  shown in  FIG. 4  is different from that shown in  FIG. 3 . On the right side of  FIG. 4 , an enlarged view of a cross-sectional structure focused on a single electrode pad  134  is shown. 
         [0044]    The electrode pad  134  includes a circular-shaped pad main body  135  and a protruding portion  136  having a size smaller than the pad main body  135  and protruding to the outside of the circular-shape of the pad main body  135 . As a result, the planar shape of the electrode pad  134  is deviated with respect to the center of the electrode pad  134 . In the center of the pad main body  135 , a circular-shaped depression  137  recessed into the wiring board  131  is formed by a drill. The depression  137  is located at a deviated position with respect to the center of the electrode pad  134 . 
         [0045]    The orientations of the deviation of the shape of each electrode pad  134  are shown by rotation directions indicated by arrows in  FIG. 4 . The orientation of the protruding portion  136  is opposite to the rotation direction. As a result, when seeing the arrangement of the electrodes  134  as a whole, the orientations of the deviations of the shapes and the orientations of the protruding portions  136  are spirally directed. In other words, the orientations of the deviations of the shapes and the orientations of the protruding portions  136  form a spiral-shaped trajectory with respect to a pad at the center of the arrangement. 
         [0046]    Further, the position of the depression  137  in each electrode pad  134  is deviated in the rotation direction indicated by the arrow with respect to the center of the electrode pad  134 . As a result, when seeing the arrangement of the electrodes  134  as a whole, the orientations of the deviations of the depressions  137  with respect to the center of the electrode pad  134  are also spirally directed. 
         [0047]    Such plurality of electrode pads  134  correspond to an example of a plurality of pads arranged in a grid pattern according to the above-described embodiment. 
         [0048]    When mounting the electronic component  132  described above, the electronic component  132  is mounted on the electrode pads  134  arranged in the manner described above. 
         [0049]      FIG. 5  illustrates the electronic component placed on the electrode pads according to the first embodiment. 
         [0050]    In  FIG. 5 , to easily understand a positional relationship between the electronic component  132  and the electrode pads  134  or the like, a state is illustrated in which the portion hidden under the electronic component  132  is seen through the electronic component  132 .  FIG. 5A  illustrates a top view of the electronic component  132  and partially enlarged views of the electrode pads  134 , and  FIG. 5B  illustrates a side perspective view of the electronic component  132  and the electrode pads  134 . 
         [0051]    The electronic component  132  is placed on the electrode pads  134  so that the rectangular outer shape of the electronic component  132  is aligned almost squarely with the rectangular area surrounded by the opening  133 . Ball-shaped solder bumps  138 , each of which has a role of a connecting pin between the electronic component  132  and the electrode pad  134 , are attached on the bottom surface of the electronic component  132  (on the surface facing the electrode pads  134 ). Specifically, the ball grid array (BGA) technique is employed here. The orientation of the arrangement of the solder bumps  138  is also aligned with the rectangular outer shape of the electronic component  132 . 
         [0052]    On the other hand, as described above, the orientation of the arrangement of the electrode pads  134  is tilted or shifted from the rectangle of the area. As a result, the positions of the electrode pads  134  are shifted from the positions of the solder bumps  138 . The partially enlarged view shown above the top view of  FIG. 5A  illustrates that, in the upper right portion of the arrangement of the electrode pads  134 , the solder bumps  138  are shifted from the electrode pads  134  in the lower right direction. Also, the partially enlarged view shown below the top view of  FIG. 5A  illustrates that, in the lower left portion of the arrangement of the electrode pads  134 , the solder bumps  138  are shifted from the electrode pads  134  in the upper left direction. 
         [0053]    The positional relationship between the electrode pads  134  and the solder bumps  138  will be described in further detail. 
         [0054]      FIG. 6  illustrates an example of the positional relationship between the electrode pads and solder bumps according to the first embodiment. 
         [0055]    In the same manner as  FIG. 4 ,  FIG. 6  illustrates the area where the above-described electrode pads  134  are arranged on the wiring board  131 . On the right side of  FIG. 6 , an enlarged view of a cross-sectional structure focused on a single electrode pad  134  is shown. 
         [0056]    Although omitted in the above description, more specifically, when the solder bump  138  is placed on the electrode pad  134 , solder printing  139  is performed on the electrode pad  134  and the solder bump  138  is placed on the solder printing  139 . 
         [0057]    As described above, the position of the solder bump  138  is shifted from the center of the electrode pad  134 , and the solder printing  139  is also printed in a position shifted in the same manner. More specifically, the shifted position is a position shifted toward the protruding portion  136  of the electrode pad  134 . 
         [0058]    After the electronic component  132  is placed on the electrode pads  134  in such a positional relationship, the solder bumps  138  and the solder printing  139  are heated along with the wiring board  131 , so that the solder bumps  138  and the solder printing  139  melt. When the solder bumps  138  and the solder printing  139  are melted by heat in this way, the solder moves to the pad main body  135  having a larger area by wetting of solder. 
         [0059]      FIG. 7  illustrates a state after the solder wets and moves. 
         [0060]    In the same manner as in  FIGS. 4 and 6 , in  FIG. 7 , the area where the above-described electrode pads  134  are arranged on the wiring board  131  is shown, and on the right side of the figure, an enlarged view of a cross-sectional structure focused on a single electrode pad  134  is shown. 
         [0061]    Solder  138 ′, which is the heat-melted solder of the solder bump  138  and the solder printing  139 , wets and moves to a larger area and flows into the depression  137 , so that the solder  138 ′ is strongly attracted to the pad main body  135 . Finally, the soldering is performed in a state where the center of the pad main body  135  and the center of the solder  138 ′ almost match each other. As a result, when seeing the solders  138 ′ as a whole, a rotational movement is generated in the direction indicated by arrows in  FIG. 7 . 
         [0062]    Although the movement of the solder caused by wetting is generated only when the solder before melting is shifted and placed on a circular pad, in this embodiment, the protruding portion  136  and the depression  137  are provided, so that the movement of the solder  138 ′ is reliably generated. 
         [0063]    When the solder  138 ′ wets and moves in this way, self-alignment of the electronic component  132  occurs along with the movement. 
         [0064]      FIG. 8  illustrates the self-alignment of the electronic component according to the first embodiment. 
         [0065]      FIG. 8A  illustrates a top view and  FIG. 8B  illustrates a side perspective view. 
         [0066]    As described above, the solder  138 ′ wets and moves. As a result, the position of the solder  138 ′ almost matches the position of the electrode pad  134 . When the solder wets and moves in this way, the electronic component  132  also rotates in the direction indicated by arrows in  FIG. 8  by the self-alignment. The rotated electronic component  132  is thus in a state where the four corners  132   a  are in contact with the opening  133 . When the corners  132   a  are in contact with the opening  133  in this way, as described below, stress concentration on the joints between the solder  138 ′ and the electrode pad  134  can be avoided. 
         [0067]      FIG. 9  illustrates that stresses on the solder joints are alleviated. 
         [0068]    Deformation may occur in the wiring board  131  because of an external force, temperature change, and the like applied to the thin personal computer  100 . When the deformation as shown in  FIG. 9  occurs in the wiring board  131 , stresses as shown by arrows in  FIG. 9  are generated by the deformation. In this embodiment, such stresses are transmitted to the corners  132   a  of the electronic component  132 , so that the stresses are received by the package itself of the electronic component  132 . Therefore, a case in which the stresses concentrate on the solder  138 ′ is avoided, so that the solder  138 ′ is not detached. 
         [0069]    In the first embodiment, outer circumferential pads in the grid pattern include a protruding portion in a width direction to form a spiral-shaped trajectory with respect to a centered pad in the grid pattern. 
         [0070]    According to this feature, the solder reliably wets and moves from the protruding portion to the main body by the deviation of the shape of the pad. As a result, a spiral movement of the solder occurs reliably in the plurality of pads as a whole. Therefore, the electronic component reliably rotates by the self-alignment by normally placing the electronic component on the pads and performing soldering. By the rotation, a state can be reliably obtained in which the corner portions of the electronic component are in contact with inner edges of the opening or the wall. 
         [0071]    In the first embodiment, outer circumferential pads in the grid pattern include a depression provided in the thickness direction of the printed wiring board. 
         [0072]    According to this feature, the solder reliably wets and moves to the depression. As a result, the corner portions of the electronic component are in contact with inner edges of the opening or the wall. 
         [0073]    Although a circular depression is employed because of ease of work or the like in the first embodiment, the shape of the depression is not limited to a circular shape, but it can also be an elliptical shape, a polygonal shape, a groove shape, etc. 
         [0074]    Hereinafter, a second embodiment will be described. Please note that the same or similar elements as those of the first embodiment are given the same reference numerals and redundant description will be omitted. 
         [0075]    In the second embodiment, the shape of the electronic component is different from that of the first embodiment. 
         [0076]      FIGS. 10A and 10B  illustrate the electronic component according to the second embodiment. 
         [0077]      FIG. 10A  illustrates a top view and  FIG. 10B  illustrates a side view. 
         [0078]    The electronic component  140  according to the second embodiment has an octagonal outer shape as a whole, and portions that come into contact with the opening  133  are provided as flat portions  141 . The arrangement of the solder bumps  138  with respect to the electronic component  140  can be similar to that of the first embodiment. 
         [0079]    When the electronic component  140  is mounted on the wiring board  131 , in the same manner as in the first embodiment, the electronic component  140  is placed in an area surrounded by the opening  133 . 
         [0080]      FIG. 11  illustrates a state in which the electronic component according to the second embodiment is placed in the opening of the wiring board. 
         [0081]      FIG. 11A  illustrates a top view and  FIG. 11B  illustrates a side perspective view. 
         [0082]    The electronic component  140  is placed in the area surrounded by the opening  133  in a state in which the opening  133  and the flat portions  141  are detached from each other. When the solder is melted by heat, a self-alignment similar to that in the first embodiment occurs. 
         [0083]      FIG. 12  illustrates the self-alignment of the electronic component according to the second embodiment. 
         [0084]      FIG. 12A  illustrates a top view and  FIG. 12B  illustrates a side perspective view. 
         [0085]    In the second embodiment, as a result of the self-alignment of the electronic component  140 , the flat portions  141  are in flat contact with the opening  133 . When the flat portions  141  are in flat contact with the opening  133  in this way, the contact area increases. As a result, the stress received from the opening  133  is dispersed to the entire electronic component  140 , so that the stress concentration on the solder joints can be more reliably avoided. 
         [0086]    In the second embodiment, at least one of outer edges of the electronic component is in surface contact with an inner edge of either one of the opening or the wall. 
         [0087]    Next, a third embodiment will be described. In the third embodiment, the shape of the electronic component is different from that of the first embodiment. 
         [0088]      FIG. 13  illustrates the electronic component according to the third embodiment. 
         [0089]      FIG. 13A  illustrates a top view and  FIG. 13B  illustrates a side view. 
         [0090]    The electronic component  150  shown in  FIG. 13  includes a package section  152  in which an electronic circuit is enclosed and a plate member  151  additionally attached to the surface of the package section  152 . The package section  152  has a rectangular shape. On the other hand, the plate member  151  has an octagonal shape as a whole in the same manner as the electronic component  140  in the second embodiment, and portions that are in contact with the opening  133  in the plate member  151  are provided as flat portions  153 . When the electronic component  150  is mounted on the wiring board  131 , the electronic component  150  is also placed in an area surrounded by the opening  133 . An example of the placement of the electronic component  150  will be described below. 
         [0091]      FIG. 14  illustrates the example of the placement of the electronic component according to the third embodiment. 
         [0092]    As the example of the placement of the electronic component, in the same manner as in the first embodiment and the second embodiment, the electronic component  150  is placed in an area surrounded by the opening  133  of the wiring board  131 . 
         [0093]      FIG. 15  illustrates a modified example of the placement of the electronic component according to the third embodiment. 
         [0094]    As the modified example of the placement of the electronic component, in an area surrounded by the opening  133  of the wiring board  131 , first, only the package  152  of the electronic component  150  is placed in the opening  133 . Thereafter, the plate member  151  is attached to the upper surface of the package  152 , so that the same state as that shown in  FIG. 14  appears. 
         [0095]    After the electronic component  150  is placed, when the solder is melted by heat, a self-alignment similar to those in the first embodiment and the second embodiment occurs. 
         [0096]      FIG. 16  is a side perspective view illustrating a result of the self-alignment according to the third embodiment. 
         [0097]    In the same manner as in the second embodiment, also in the third embodiment, as a result of the self-alignment of the electronic component  150 , the flat portions  153  are in flat contact with the opening  133 . Therefore, the contact areas are large, and thus the stress received from the opening  133  is dispersed to the entire package of the electronic component  150 . As a result, avoidance of the stress concentration on the solder joints is more reliable. In the case of the third embodiment, the stress is mainly applied to the plate member  151  of the electronic component  150 , so that the load of the package  152  is also alleviated. In the third embodiment, the electronic component can include a package portion and a plate member. The package portion encloses semiconductor devices such as ICs and LSIs therein. The plate member is a polygonal member attached to the package portion, and at least one side of the outer edges thereof is in surface contact with an inner edge of at least either one of the opening or the wall. 
         [0098]    Next, a fourth embodiment will be described. In the fourth embodiment, the shape of the inner edges of the opening is different from that of the first embodiment. 
         [0099]      FIG. 17  illustrates the shape of a wall according to the fourth embodiment. 
         [0100]      FIG. 17A  illustrates a top view and  FIG. 17B  illustrates a side perspective view. 
         [0101]    In the fourth embodiment, there is an opening  170 , the shape of which is different from the shape of the opening  133  which surrounds the rectangular area in the first embodiment, and in which portions that come into contact with the electronic component  132  when the self-alignment of the electronic component  132  is performed are provided and protrude to outside. 
         [0102]    In the same manner as in the first embodiment, the electronic component  132  is placed in an area surrounded by the opening  170 . 
         [0103]      FIG. 18  illustrates a state in which the electronic component is placed in the fourth embodiment. 
         [0104]      FIG. 18A  illustrates a top view and  FIG. 18B  illustrates a side perspective view. 
         [0105]    As shown in  FIGS. 18A and 18B , also in the fourth embodiment, the electronic component  132  is placed while the electronic component  132  is not in contact with the opening  170 . When the solder is melted by heat, a self-alignment similar to that in the first embodiment occurs. 
         [0106]      FIG. 19  illustrates a result of the self-alignment according to the fourth embodiment. 
         [0107]      FIG. 19A  illustrates a top view and  FIG. 19B  illustrates a side perspective view. 
         [0108]    In the fourth embodiment, as a result of the rotation of the self-alignment of the electronic component  132 , portions of the corners  132   a  of the electronic component  132  are received in a wide and flat area on concave portions  171  of the opening  170 . When the portions of the corners  132   a  are received in a wide and flat area on the concave portions  171  in this way, in the same manner as in the first embodiment and the second embodiment, the stress from the opening  170  is dispersed to the entire package of the electronic component  132 . In the fourth embodiment, at least one side of inner edges of either one of the opening or the wall includes an extension portion having a different degree of tilt with respect to an outer edge of the arrangement of the plurality of pads. 
         [0109]    Next, a fifth embodiment will be described. In the fifth embodiment, a wall is provided instead of the opening as compared to that of the first embodiment. 
         [0110]      FIG. 20  illustrates the structure of the wall according to the fifth embodiment. 
         [0111]      FIG. 20A  illustrates a top view and  FIG. 20B  illustrates a side perspective view. 
         [0112]    In the fifth embodiment, a wall  180  is provided to project from the surface of the wiring board  131 . Such a wall  180  is suitable for a case in which the thickness of the wiring board  131  is small and it is not easy to provide an opening recessed from the surface as in the first to the fourth embodiments. The electronic component  132  is placed in an area surrounded by the wall  180 . 
         [0113]      FIG. 21  illustrates the placement of the electronic component according to the fifth embodiment. 
         [0114]      FIG. 21A  illustrates a top view and partially enlarged views and  FIG. 21B  illustrates a side perspective view. 
         [0115]    In the fifth embodiment, the electronic component  132  is placed in a surface area of the wiring board  131  surrounded by the wall  180  projecting from the surface of the wiring board  131 . At this time, the positional relationship between the electrode pads  134  and the solder bumps  138  is similar to that in the first embodiment. After the electronic component  132  is placed in this way, the solder bumps  138  are heated along with the wiring board  131 , and the solder bumps  138  are melted. When the solder bumps  138  are melted, a self-alignment occurs in the same manner as in the first embodiment. 
         [0116]      FIG. 22  illustrates a result of the self-alignment according to the fifth embodiment. 
         [0117]      FIG. 22A  illustrates a top view and  FIG. 22B  illustrates a side perspective view. 
         [0118]    Also in the fifth embodiment, the electronic component  132  rotates by the self-alignment in the direction indicated by arrows shown in  FIG. 22A . As a result of the rotation, portions of the corners  132   a  of the electronic component  132  come into contact with the inner surface of the wall  180 . Also, when the portions of the corners  132   a  of the electronic component  132  are in contact with the inner surface of the wall  180  projecting from the surface of the wiring board  131 , a case in which the stress accompanying the deformation of the wiring board  131  concentrates on a soldered portion is avoided. 
         [0119]      FIG. 23  illustrates that the stress concentration on the solder joints is avoided also in the fifth embodiment. 
         [0120]    When the deformation as shown in  FIG. 23  occurs in the wiring board  131  in the fifth embodiment, stresses as shown by arrows in  FIG. 23  are applied to the wall  180 . The stresses are transferred from the wall  180  to the portions of the corners  132   a  of the electronic component  132 . Then, the stresses transferred to the portions of the corners  132   a  are received by the package itself of the electronic component  132 . Therefore, also in the fifth embodiment, a case in which the stresses concentrate on the solder  138 ′ is avoided, so that the solder  138 ′ is not detached. 
         [0121]    In the fifth embodiment, the shape of the inner surface of the wall  180  and the shape of the electronic component  132  are similar to those in the first embodiment. However, even when the wall is used instead of the opening, the same shapes of the electronic component as those in the second embodiment and the third embodiment can be used. Also, even when the wall is used, the same shape of inner edge as that the fourth embodiment can be used. 
         [0122]    Although, in the first to the fifth embodiments described above, a typical rectangular shape is mainly described as the shape of the electronic component, as the shape of the electronic component of the above-described embodiment, a triangular shape, a pentagonal shape, a hexagonal shape, an octagonal shape, and so forth may be used in addition to the rectangular shape. 
         [0123]    In the first to the fifth embodiments, soldering of the BGA method is described as a specific example of soldering, as soldering for fixing the electronic component of the above-described embodiment on the board main body, the flip-chip method may also be employed. 
         [0124]    All examples and conditional language recited herein are intended for pedagogical objects to aid the reader in understanding the invention and the concepts contributed by the inventors to further the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the invention have been described in detail, it will be understood by those of ordinary skill in the relevant art that various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention as set forth in the claims.