Abstract:
A main object of the present invention is to provide a land grid array type semiconductor device which has been improved to provide greater positioning accuracy for an external electrode with respect to a mounting substrate. An external electrode is arranged in one surface of a substrate in area array. The external electrode includes an external electrode pad and an external electrode interconnection. The external electrode pad includes a first pad layer formed in a cylinder shape and a second pad layer formed to cover the surface of the first pad layer in a cone shape.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention generally relates to land grid array (LGA) type semiconductor devices and, more specifically to an LGA type semiconductor device which has been improved to provide greater positioning accuracy in mounting an electrode portion on a mounting substrate and greater bonding reliability with respect to the mounting substrate after the mounting. Further, the present invention relates to a method of mounting such an LGA type semiconductor device.  
           [0003]    2. Description of the Background Art  
           [0004]    [0004]FIG. 9 is a cross sectional view of a conventional LGA type semiconductor device, and FIG. 10 is a bottom view thereof.  
           [0005]    Referring to FIGS. 9 and 10, a semiconductor device  7  includes a substrate  2 . An external electrode  3  is provided on one surface of substrate  2 , and a sealing portion  1  for sealing a semiconductor element or the like is provided on the other surface of substrate  2  which is formed of a material such as a glass epoxy resin. An electrode interconnection made of copper or the like, is provided on the surface of and inside substrate  2 , forming an electrical and physical connection with the semiconductor element. As can be seen, external electrode  3  is exposed on the other surface of substrate  2  that is opposite sealing portion  1 . External electrode  3  is made of copper or the like which forms an electrical and physical connection with the mounting substrate.  
           [0006]    External electrode  3  includes an external electrode pad  4  which is cylindrical in shape and having a smooth surface, and an external electrode interconnection  6  extending from the inside to the outside of substrate  2  via a through hole  5 . External electrodes  3  are arranged on a grid, i.e., in area array on the side of substrate  2  that is opposite sealing portion  1 .  
           [0007]    Since external electrodes  3  are arranged on a grid in a plane, the structure has an advantage in manufacturing in that the greater number of electrodes can be provided per unit part area despite small pitches between electrodes.  
           [0008]    Now, the operation of the conventional LGA type semiconductor device will be described.  
           [0009]    Referring to FIG. 11, an operation of mounting semiconductor device  7  onto mounting substrate  8  will be described below. Mounting substrate  8  is formed of a material such as a glass epoxy resin. Although not shown, an electrode interconnection made of copper or the like is formed on the surface of mounting substrate  8 , which forms an electrical and physical connection with respect to semiconductor device  7 . Substrate external electrode  9  is exposed from the surface of mounting substrate  8  and made of copper or the like that forms an electrical and physical connection with respect to semiconductor substrate  7 . Substrate external electrodes  9  are provided on the surface of mounting substrate  8  and arranged in area array being opposite to external electrodes  3  of semiconductor device. A bonding medium  10  of a solder paste or the like is printed and applied onto substrate external electrode  9  by means of printing, dispensing or the like.  
           [0010]    The mounting operation of conventional semiconductor device  7  is as follows. Namely, bonding medium  10  is preliminarily printed and applied onto substrate external electrode  9  of mounting substrate  8 . In this state, semiconductor device  7  is mounted onto mounting substrate  8 . Next, external electrode pad  4  of semiconductor device  7  is pressed against bonding medium  10  for bonding. Further, mounting substrate  8  mounted with semiconductor device  7  is made to reflow at a temperature of at least the melting point of bonding medium  10 . Thus, bonding medium  10  melts to electrically and physically connect semiconductor device  7  and mounting substrate  8 .  
           [0011]    Having the above described structure, the conventional semiconductor device suffers from the following problem. Referring to FIG. 11, in mounting semiconductor device  7  onto mounting substrate  8 , external electrode pad  4  and bonding medium  10  fail to bond firmly due to a variation in supply amount of bonding medium  10 , a variation in mounting height caused by deflection of semiconductor device  7 , and so on. As a result, after reflowing, all or some of external electrode pads  4  fail to bond substrate external electrode  9 .  
         SUMMARY OF THE INVENTION  
         [0012]    The present invention is made to solve the aforementioned problem. An object of the present invention is to provide a land grid array (LGA) type semiconductor device which has been improved to provide greater positioning accuracy for a mounting substrate and semiconductor device in mounting a substrate.  
           [0013]    Another object of the present invention is to provide an LGA type semiconductor device which has been improved to provide greater bonding reliability for a mounting substrate and the mounted semiconductor device.  
           [0014]    Another object of the present invention is to provide a method of mounting such an LGA type semiconductor device.  
           [0015]    An LGA type semiconductor device according to one aspect of the present invention has external electrodes arranged in area array. The external electrode includes an external electrode pad and an external electrode interconnection extending from the inside to the outside of the substrate via a through hole. The external electrode pad includes a first pad layer formed in a cylinder or rectangular column shape, and a second pad layer provided to cover the surface of the first pad layer and formed in a cone or pyramid shape.  
           [0016]    According to one preferred embodiment of the present invention, the second pad layer has a recess in its surface.  
           [0017]    According to a more preferred embodiment of the present invention, the recess is a groove formed in a cone or pyramid shape.  
           [0018]    According to a more preferred embodiment of the present invention, the substrate further has on its one surface a dummy electrode having a shape different from the above mentioned external electrode pad and not electrically nor physically connected to the external electrode pad.  
           [0019]    According to a more preferred embodiment of the present invention, the dummy electrode includes a first layer formed in a cylinder or rectangular column shape, and a second layer provided to cover the surface of the first layer and formed in a cone or pyramid shape.  
           [0020]    In a method of mounting an LGA type semiconductor device according to a second aspect of the present invention, first of all, an LGA type semiconductor device is prepared including a substrate which has on its one surface external electrodes arranged in area array. The external electrode includes an external electrode pad and an external electrode interconnection extending from the inside to the outside of the substrate via a through hole. The external electrode pad includes a first pad layer formed in a cylinder or rectangular column shape, and a second pad layer provided to cover the surface of the first pad layer and formed in a cone or pyramid shape. A mounting substrate is prepared having a substrate external electrode and a bonding medium provided to cover the surface of the substrate external electrode. The second pad layer of the LGA type semiconductor device is pressed against the bonding medium of the mounting substrate to bond the LGA type semiconductor device to the mounting substrate. The mounting substrate mounted with the LGA type semiconductor device is annealed at a temperature of at least the melting point of the bonding medium.  
           [0021]    According to a preferred embodiment of the present invention, the second pad layer has in its surface a recess.  
           [0022]    According to a more preferred embodiment of the present invention, the recess is a groove formed in a cone or pyramid shape.  
           [0023]    The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]    [0024]FIG. 1 is a cross sectional view showing an LGA type semiconductor device according to a first embodiment of the present invention.  
         [0025]    [0025]FIG. 2 is a bottom view of the LGA type semiconductor device according to the first embodiment.  
         [0026]    [0026]FIG. 3 is a cross sectional view showing the LGA type semiconductor device according to the first embodiment mounted on a mounting substrate.  
         [0027]    [0027]FIG. 4 is a cross sectional view showing an LGA type semiconductor device according to a second embodiment.  
         [0028]    [0028]FIG. 5 is a cross sectional view showing the LGA type semiconductor device according to the second embodiment mounted on a mounting substrate.  
         [0029]    [0029]FIG. 6 is a cross sectional view showing an LGA type semiconductor device according to a third embodiment.  
         [0030]    [0030]FIG. 7 is a bottom view of the LGA type semiconductor device according to the third embodiment.  
         [0031]    [0031]FIG. 8 is a cross sectional view showing the LGA type semiconductor device according to the third embodiment mounted on a mounting substrate.  
         [0032]    [0032]FIG. 9 is a cross sectional view showing the conventional LGA type semiconductor device.  
         [0033]    [0033]FIG. 10 is a bottom view of the conventional LGA type semiconductor device.  
         [0034]    [0034]FIG. 11 is a cross sectional view showing the conventional LGA type semiconductor device mounted on the mounting substrate. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0035]    Now, the embodiments of the present invention will be described with reference to the drawings.  
         [0036]    First Embodiment  
         [0037]    [0037]FIG. 1 is a cross sectional view showing an LGA type semiconductor device according to the embodiment. FIG. 2 is a bottom view thereof when viewed from below. Note that the same portions as the above described prior art example are denoted by the same reference numerals, and the description thereof will not be repeated.  
         [0038]    Referring to FIGS. 1 and 2, a semiconductor device  15  is provided with a substrate  2 . An external electrode  11  is exposed on the surface of substrate  2  that is opposite a sealing portion  1 . External electrode  11  is used for providing an electrical and physical connection with the mounting substrate. External electrode  11  includes an external electrode pad  11   a , and an external electrode interconnection  6  extending from the inside to the outside of substrate  2  via a through hole  5 . External electrode pad  11   a  includes a first pad layer  12  in a cylinder shape, and a second pad layer  13  provided to cover the surface of first pad layer  12  and formed in a pyramid shape. First pad layer  12  is formed of a copper foil or a copper foil applied with a copper solder, having a thickness of 12-32 μm. Second pad layer  13  is formed of copper solder layers, having a height of 12-62 μm.  
         [0039]    An antirust medium  14  is formed on the surface of second pad layer  13  for preventing the surface of second pad layer  13  from being oxidized. Antirust medium  14  also serves to promote bonding by the bonding medium in mounting the substrate. Antirust medium  14  is formed of a flux with a gold solder or nickel and gold solders.  
         [0040]    External electrodes  11  are arranged in area array on the side of substrate that is opposite sealing portion  1 . The arrangement method is not particularly limited. Although first pad layer  12  is illustrated as being cylindrical in shape in the above described embodiment, it may be in a rectangular column shape. Similarly, although second pad layer  13  is illustrated as being a cone, it may be a pyramid. Moreover, the side number of the rectangular column or pyramid is not particularly limited.  
         [0041]    Now, the operation will be described.  
         [0042]    [0042]FIG. 3 is a cross sectional view showing the LGA type semiconductor device of the first embodiment being mounted on the mounting substrate. Note that the same portions as the prior art example are denoted by the same reference numerals, and therefore the description thereof will not be repeated.  
         [0043]    In mounting semiconductor device  15  onto mounting substrate  8 , bonding medium  10  is preliminarily printed and applied onto substrate external electrode  9  of mounting substrate  8 . In this state, semiconductor device  15  is mounted onto mounting substrate  8 . At the time, external electrode pad  13  covered with antirust medium  10  is inserted to bonding medium  10  formed on substrate external electrode  9  for bonding. Further, mounting substrate  8  mounted with semiconductor device  15  is made to reflow at a temperature of at least the melting point of bonding medium  10 . Thus, bonding medium  10  melts to electrically and physically bond semiconductor device  15  and mounting substrate  8 .  
         [0044]    According to the embodiment of the present invention, if external electrode pad  13  of semiconductor device  15  is formed in a cone or pyramid shape, greater adhesion of external electrode pad  13  and bonding medium  10  is obtained in mounting semiconductor device  15  onto mounting substrate  8 . Thus, positioning accuracy of external electrode  11  of semiconductor device  15  and substrate external electrode  9  of mounting substrate  8  is enhanced. Further, bonding reliability of mounting substrate  8  and semiconductor device  15  is effectively enhanced.  
         [0045]    Second Embodiment  
         [0046]    [0046]FIG. 4 is a cross sectional view showing an LGA type semiconductor device of the second embodiment. Note that the same portions as the device of the first embodiment are denoted by the same reference numerals in FIG. 4, and the description thereof will not be repeated.  
         [0047]    Referring to FIG. 4, a groove  16  is formed in the surface of external electrode pad  13 . Groove  16  is in a cone or pyramid shape, internally extending. An antirust medium  14  is provided on the surface of external electrode pad  13 . Note that the position and number of grooves  16  are not particularly limited.  
         [0048]    Now, the operation will be described.  
         [0049]    [0049]FIG. 5 is a cross sectional view showing an LGA type semiconductor device of the second embodiment being mounted on a mounting substrate. Note that the same portions as the device of the first embodiment are denoted by the same reference numerals, and the description thereof will not be repeated.  
         [0050]    In mounting semiconductor device  17  onto mounting substrate  8 , a bonding medium  10  is preliminarily printed and applied onto substrate external electrode  9  of mounting substrate  8 . In this state, semiconductor device  17  is mounted on mounting substrate  8 . At the time, external electrode pad  13  covered with antirust medium  14  and provided in its surface groove  16  is inserted to bonding medium  10  on substrate external electrode  9  for bonding. Further, mounting substrate  8  mounted with semiconductor device  17  is made to reflow at a temperature of at least the melting point of bonding medium  10 . Thus, bonding medium  10  melts to electrically and physically bond semiconductor device  17  and mounting substrate  8 .  
         [0051]    According to the embodiment of the present invention, groove  16  in a cone or pyramid shape formed in the surface of external electrode pad  13  provides greater adhesion of external electrode pad  13  and bonding medium  10  in mounting semiconductor device  17  onto mounting substrate  8 . Thus, positioning accuracy of external electrode  11  of semiconductor device  17  and substrate external electrode  9  of mounting substrate  8  is enhanced. Further, bonding reliability of mounting substrate  8  and mounted semiconductor device  17  is enhanced.  
         [0052]    Third Embodiment  
         [0053]    [0053]FIG. 6 is a cross sectional view showing an LGA type semiconductor device of the third embodiment, and FIG. 7 is a bottom view thereof when viewed from above. In the drawings, the same portions as the device of the above described embodiment are denoted by the same reference numerals, and the description thereof will not be repeated.  
         [0054]    Referring to FIGS. 6 and 7, a semiconductor device  22  is provided with a substrate  2 . A dummy electrode  18  is provided on the surface of substrate  2  on the side opposite sealing portion  1 . Dummy electrode  18  has a shape different from that of external electrode  11  and is not electrically nor physically connected to external electrode  11 .  
         [0055]    Dummy electrode  18  includes a first external electrode pad  19  and a second external electrode pad  20  formed to overlap with each other. Although first external electrode pad  19  is in a cylindrical shape in the present embodiment, it may be in a rectangular column shape. First external electrode pad  19  has a thickness of 12-32 μm. First external electrode pad  19  is formed of a copper foil or a copper foil with a copper solder. Second external electrode pad  20  is formed to cover the entire surface of first external electrode pad  19 . Although second external electrode pad  20  is in a cone shape in the present embodiment, it may be in a pyramid shape. Second external electrode pad  20  has a height of 12-62 μm. Second external electrode pad  20  is formed of layered copper solders. An antirust medium  21  is formed on second external electrode pad  20 . Antirust medium  21  is provided to prevent oxidation of the surface of external electrode pad  20  and to promote bonding of a bonding medium in mounting the substrate. Antirust medium  21  is formed of a flux with a gold solder or nickel gold solders. Although dummy electrode  18  is arranged on the side of substrate  2  that is opposite sealing portion  1 , the arrangement method and number are not particularly limited. In the present embodiment, the side number of the rectangular column and pyramid are not particularly limited.  
         [0056]    Now, the operation will be described.  
         [0057]    [0057]FIG. 8 is a cross sectional view showing an LGA type semiconductor device of the third embodiment mounted on a mounting substrate. In FIG. 8, the same portions as the above described embodiment are denoted by the same reference numerals, and the description thereof will not be repeated.  
         [0058]    Referring to FIG. 8, in mounting semiconductor device  22  onto mounting substrate  8 , a bonding medium  10  is preliminarily printed and applied onto a substrate external electrode  9  of mounting substrate  8 . In this state, semiconductor device  22  is mounted on mounting substrate  8 . At the time, an external electrode pad  13  (on the side of external electrode  11 ) covered with antirust medium  14  and an external electrode pad  20  (on the side of dummy electrode  18 ) covered with an antirust medium  21  are inserted to bonding medium  10  on substrate external electrode  9  for bonding. Further, mounting substrate  8  mounted with semiconductor device  22  is made to reflow at a temperature of at least the melting point of bonding medium  10 . Thus, bonding medium  10  melts to electrically and physically connect semiconductor device  22  and mounting substrate  8 .  
         [0059]    According to the embodiment of the present invention, in addition to external electrode pad  13  of external electrode  11 , external electrode pad  20  is formed on the side of dummy electrode  18 . Thus, external electrode pad  20  of dummy electrode  18  promotes bonding of external electrode  11  and bonding medium  10  in mounting semiconductor device  22  on mounting substrate  8 . As a result, adhesion of external electrode  11  and bonding medium  10  is enhanced, whereby positioning accuracy of external electrode  11  of semiconductor device  22  and substrate external electrode  9  of mounting substrate  8  increases. Further, bonding reliability of mounting substrate  8  and mounted semiconductor device  22  increases.  
         [0060]    Note that if the above described groove  16  is formed in one of, or both surfaces of external electrode pad  13  of external electrode  11  and external electrode pad  20  of dummy electrode  18 , a more favorable effect can be obtained.  
         [0061]    As in the foregoing, the LGA type semiconductor device according to the first aspect of the present invention provides enhanced positioning accuracy of the external electrode of the semiconductor device and the substrate external electrode of the mounting substrate. Further, bonding reliability of the mounting substrate and the mounted semiconductor device is enhanced.  
         [0062]    Further, the method of mounting the LGA type semiconductor device according to the second aspect of the present invention provides enhanced positioning accuracy of the external electrode of the semiconductor device and the substrate external electrode of the mounting substrate. In addition, bonding reliability of the mounting substrate and the mounted semiconductor device is enhanced.  
         [0063]    Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.