Abstract:
A semiconductor device of the present invention includes a circuit board, a semiconductor element, a resin and a level display pad. On the circuit board substrate electrodes are provided. The semiconductor element is mounted on the circuit board via the substrate electrodes. The resin fills the gap between the semiconductor element and the circuit board. The level display pad is embedded in the resin and shows the distance from the surface of the circuit board.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to a face down type semiconductor device and a manufacturing process of the face down type semiconductor device, and more particularly to a face down type semiconductor device in which a semiconductor element can be easily replaced and a manufacturing process of such a face down type semiconductor device.  
         [0002]     In a face down type semiconductor device, when some defect is found in a semiconductor element after mounting the semiconductor element on the circuit board, the replacement of the semiconductor element might be demanded.  FIG. 4  is a flow diagram illustrating a method for replacing a semiconductor device in a conventional face down type semiconductor device. As shown in  FIG. 4 , a semiconductor element  1  is connected to a pad  21  on a circuit board  2  through a solder bump  3 . Moreover, in order to improve the reliability of the connectivity of the solder bump  3 , the gaps between the semiconductor element  1 , the circuit board  2 , and the solder bump  3  are filled with an underfill resin  4 . Hereinafter, a method for replacing the semiconductor element  1  is described.  
         [0003]     First of all, as shown in the step  1 ( a ) of  FIG. 4 , in order to remove the semiconductor element  1 , the face down type semiconductor device is heated up to temperature at which the solder bump  3  is melted and the semiconductor element  1  is taken out. Or, when the semiconductor element  1  does not need to be repaired, the semiconductor element  1  is scraped off by using a tool  7  such as an end mill, etc. as shown in the step  1 ( b ) of  FIG.4  , and the semiconductor element  1  is removed from the circuit board  2  (Japanese Unexamined Patent Publication No. 1999-186330).  
         [0004]     Next, a large part of the underfill resin  4  remaining on the circuit board  2  is removed by using a tool  7  such as an end mill, etc. (step  2 ). Next, the underfill resin  4 , which remains on the circuit board  2  because the underfill resin  4  cannot be completely removed in the step  2 , is cleaned by using a cotton swab  8  containing an organic solvent, etc. (step  3 ). In order to make the cleaning in step  3  easy, it is preferable to control the thickness of the remaining underfill resin  4  to be about 20 μm or less in step  2 .  
         [0005]     After the cleaning is completed, a new semiconductor element  1  is connected through the solder bump  3  on the circuit board  2  (steps  4  to  5 ). The gaps between the semiconductor element  1 , the circuit board  2 , and the solder bump  3 , are filled with the underfill resin  4 , and then the filled underfill resin  4  is heated and cured by the heating(step  6 ). According to the above-mentioned processes, the semiconductor element  1  is replaced by a new semiconductor element  1 .  
       SUMMARY OF THE INVENTION  
       [0006]     In the above-mentioned process for replacing the semiconductor element  1 , it is difficult to determine the thickness of the underfill resin  4  remaining on the circuit board  2 . This is because, as shown in  FIG. 5 , a worker removes the underfill resin  4  by using a tool  7  such as an end mill, etc. while making a visual observation. Therefore, a problem is that the work efficiency in the step of removing the underfill resin  4  becomes worse. Moreover, as shown in  FIG. 5  (S 3 ), since curvature or/and undulation of about  20  micro meter (μm) or less exist in the circuit board  2 , another problem is that the surface of the circuit board  2  is scraped off together with the underfill resin  4 .  
         [0007]     An object of the present invention is to provide a face down type semiconductor device in which a semiconductor element can be easily replaced and a manufacturing process thereof.  
         [0008]     According to one aspect of the present invention, a semiconductor device is provided which includes: a circuit board on which substrate electrodes. are provided, a semiconductor element mounted on the circuit board via the substrate electrodes, a resin which fills the gap between the semiconductor element and the circuit board and a level display pad which is embedded in the resin and shows the distance from the surface of the circuit board. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     Other features and advantages of the invention will be made more apparent by the following detailed description and the accompanying drawings, wherein:  
         [0010]      FIG. 1A  is a cross-section diagram of a face down type semiconductor device in the first embodiment of the present invention;  
         [0011]      FIG. 1B  is a diagram illustrating a at the line connecting A-A of  FIG. 1A  as seen from the upper surface;  
         [0012]      FIG. 2  is a flow diagram illustrating a manufacturing method of a face down type semiconductor device in the first embodiment of the present invention;  
         [0013]      FIG. 3  is a flow diagram illustrating a method for replacing a semiconductor element  1  in a face down type semiconductor device in the first embodiment of the present invention;  
         [0014]      FIG. 4  is a flow diagram illustrating a method for replacing a semiconductor element  1  in a face down type semiconductor device in the first embodiment of the present invention; and  
         [0015]      FIG. 5  is a flow diagram illustrating a process for scraping the underfill resin of a face down type semiconductor device in the prior art.  
         [0016]     In the drawings, the same reference numerals represent the same structural elements. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]     A first embodiment of the present invention will be described in detail below.  
         [0018]      FIG. 1A  is a cross-section diagram of a face down type semiconductor device in the first embodiment of the present invention and  FIG. 1B  is a diagram illustrating a at the line connecting A-A of  FIG. 1A  as seen from the upper surface. The semiconductor element  1  is mounted on the circuit board  2  by connecting the pad (circuit board electrode)  21  provided on the surface of the circuit board  2  to the solder bump  3  provided on the undersurface of the semiconductor element  1  (semiconductor chip)  1 . Moreover, in order to improve the reliability of the connectivity of the solder bump  3 , the gap between the semiconductor element  1  and the circuit board  2  is filled with the underfill resin  4  and sealed, thereby, embedding the solder bump  3  in the underfill resin  4 . The level display pad  5  is arranged at a plurality of positions including the edge part surrounding a plurality of pads  21  on the circuit board  2  and the space between the adjacent pads  21 . And the level display pad  5 , For instance, has a cylindrical shape consisting of a double layer of the first layer  5   a  and the second layer  5   b.    
         [0019]     The level display pad  5  can be provided, for instance, by forming a metallic layer  22  simultaneously while forming the pad  21  on the surface of the circuit board  2 ; forming the first layer  5   a  of the level display pad on the metallic layer  22  by plating after forming the pad  21 ; and the second layer  5   b  is formed on the first layer  5   a  by a printing technique. The level display-pad  5  is also sealed by the underfill resin  4  together with the semiconductor element  1 .  
         [0020]     Next, a manufacturing method of a face down type semiconductor device  6  in the first embodiment of the present invention will be described below.  
         [0021]      FIG. 2  is a flow diagram illustrating a manufacturing method of a face down type semiconductor device in the first embodiment of the present invention. First of all, when the pad  21  of the circuit board  2  is formed, the metallic layer  22  for the level display pad is formed simultaneously. The first layer  5   a  of the level display pad  5  is formed on the metallic layer  22  by plating, for instance, electroless nickel gold, etc. (step  1 ).  
         [0022]     Next, on the first layer  5   a  of the level display pad  5 , the second layer  5   b , which is formed with material which is easily removed by using an organic solvent, is formed. For instance, the second layer  5   b  of the level display pad  5  can be formed by silk printing, etc (step  2 ).  
         [0023]     Next, the solder bump  3  on the. undersurface of the semiconductor element  1  is overlapped with the pad  21  provided on the surface of the circuit board  2 , and then they are heated up to a temperature at which the solder bump  3  is melted, and the semiconductor element  1  is mounted on the circuit board  2  (step  3 ). The gap between the semiconductor element  1  and the circuit board  2  is filled with the underfill resin  4  and the underfill resin  4  is cured by heating and the face down type semiconductor device  6  is completed(step  4 ).  
         [0024]     Next, a manufacturing method and a method for replacing a semiconductor element  1  in a face down type semiconductor device in the first embodiment will be described below.  
         [0025]     When the pad  21  of the circuit board  2  is formed, the metallic layer  22 . for the level display pad  5  is formed simultaneously. The first layer  5   a  is formed on the metallic layer  22  by applying about a 20 μm thick nickel gold plating ( FIG. 2 , step  1 ). Next, the second layer  5   b  is formed by applying about a 50 μm thick white silk printing on the first layer  5   a  of the level display pad  5  ( FIG. 2 , step  2 ). The thicknesses of the first layer  5   a  and the second layer  5   b  are not limited to 20 μm and 50 μm, and they can be freely designed.  
         [0026]     Then, the solder bump  3  on the. undersurface of the semiconductor element  1  is overlapped with the pad  21  provided on the surface of the circuit board  2 , and then they are heated up to a temperature at which the solder bump  3  is melted, and the semiconductor element  1  is mounted on the circuit board  2  ( FIG.2 , step  3 ). The gap between the semiconductor element  1  and the circuit board  2  is filled with the underfill resin  4 , and the underfill resin  4  is cured by heating, the face down type semiconductor device  6  is completed ( FIG. 2 , step  4 ).  
         [0027]     A method for replacing the semiconductor element  1  of the face down type semiconductor device  6  obtained by the above-mentioned manufacturing method will be described below.  
         [0028]     Referring to  FIG. 3 , first of all, the face down type semiconductor device  6  is heated up to a temperature at which the solder bump  3  is melted, and the semiconductor element  1  is taken out. Or, when the semiconductor element  1  does not need to be repaired, the semiconductor element  1  may be removed away from the circuit board  2  by scraping off the semiconductor element  1  using a tool  7 . At this time, the level display pad  5  is sealed by the underfill resin  4  (step  1 ).  
         [0029]     Next, using the tool  7  such as an end mill, etc. the underfill resin  4  remaining on the circuit board  2  is removed while visually confirming the level display pad  5 . The second layer  5   b  is white and the first layer  5   a  is gold, so that the incision depth of the end mill can be set to be 50 μm in the step where a white color cannot be visually confirmed. Moreover, even if a white layer (the second layer  5   b ) appears, if the gold layer (the first layer  5   a ) cannot be visually confirmed, it can be easily judged that it is now in the step where the second layer  5   b  is being scraped, that is, where the underfill resin  4  of 20 μm or more remains.(step  2 ).  
         [0030]     At the step where the gold layer (the first layer  5   a ) can be visually confirmed, the removing operation by using a tool  7  such as an end mill, etc. is stopped (step  3 ). Since the underfill resin  4  of about 20 μm remains, the surface of the circuit board  2  is never scraped down even if curvature and undulations of 20 μm or less exist in the circuit board  2 .  
         [0031]     Next, the underfill resin  4  which cannot be removed by using a tool  7  such as an endmill, etc. and remains on the circuit board  2  is cleaned by using a cotton swab containing an organic solvent.  
         [0032]     The solder bump 3  on the undersurface of the semiconductor element  1  is overlapped on the circuit board  2  where cleaning is complete, and then they are heated up to a temperature where the solder bump  3  is melted, and the semiconductor element  1  is mounted on the circuit board  2 . The gap between the semiconductor element  1  and the circuit board  2  is filled with the underfill resin  4 , and the underfill resin  4  is cured by heating. According to the above-mentioned processes, the semiconductor element  1  of the face down type semiconductor device  6  can be replaced by the new semiconductor element  1 .  
         [0033]     According to a face down type semiconductor device  6  and a manufacturing method of a circuit board  2 , a worker can judge the remaining thickness of the underfill resin  4  by visually observing the level display pads  5  and can remove the underfill resin  4  efficiently by using a tool  7  such as an end mill, etc. without scraping the surface of the circuit board  2 . Therefore, a replacement of a semiconductor element  1  of a face down type semiconductor device  6  becomes easy.  
         [0034]     While this invention has been described in conjunction with the preferred embodiments described above, it will now be possible for those skilled in the art to put this invention. into practice in various other manners.