Abstract:
In an electronic circuit unit a concave portion housing a semiconductor component is provided on the rear surface of a circuit board and the disposed inside the concave portion in a state where the bottom portion of the semiconductor component is not protruded externally from the lower end of the concave portion. A different semiconductor component can be thermally compressed to the front surface side of the circuit board in a state where the lower end of the circuit board comes in contact with a jig and the circuit board is thus stably supported.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an electronic circuit unit suitable for an electronic apparatus such as a transceiver, etc.  
         [0003]     2. Description of the Related Art  
         [0004]     A conventional electronic circuit unit is described with reference to figures.  FIG. 7  is a cross-sectional view illustrating a part of the conventional electronic circuit unit,  FIG. 8  is a cross-sectional view illustrating an important part of the conventional electronic circuit unit,  FIG. 9  is an explanatory diagram illustrating a first process of assembling a semiconductor component in the conventional electronic circuit unit, and  FIG. 10  is an explanatory diagram illustrating a second process of assembling a semiconductor component in the conventional electronic circuit unit.  
         [0005]     Next, a structure of the conventional electronic circuit unit is described with reference to  FIG. 7 . A wiring pattern  52  having land portions  52   a  is provided on one surface (front surface) of a plate-shaped circuit board  51 .  
         [0006]     In a semiconductor component  53 , a plurality of electrodes  54  is provided on the lower surface thereof and metal bumps  55  are provided on the electrodes  54 . The electrodes  54  are connected to the land portions  52   a  through the metal bumps  55  heated and pressed (thermally compressed), so that the semiconductor component  53  is disposed on one surface of the circuit board  51 .  
         [0007]     Although not shown here, various electronic components are mounted on the one surface of the circuit board  51  and desired electrical circuits are formed in the circuit board  51 , thereby forming the conventional electronic circuit unit (for example, see Patent Document 1).  
         [0008]     The conventional electronic circuit unit in which the semiconductor component  53  is mounted on one surface of the circuit board  51  could not accomplish decrease in size of the electronic circuit unit. Therefore, in order to solve this problem, as shown in  FIG. 8 , the conventional electronic circuit unit could accomplish decrease in its size, by distributing and providing a plurality of semiconductor components  53   a  and  53   b  on both the front surface  51   a  and the rear surface  51   b  of the plate-shaped circuit board  51 .  
         [0009]     Next, an assembly method of the semiconductor components  53   a  and  53   b  in the electronic circuit unit is described. First, in a first process, as shown in  FIG. 9 , the rear surface  51   b  of the circuit board  51  is placed on the flat surface of a first jig  56 , and then metal bumps  55  provided on the electrodes  54  of the first semiconductor component  53   a  are placed on the land portions  52   a  provided on the front surface  51   a  of the circuit board  51 .  
         [0010]     Next, by pressing the first semiconductor component  53   a  with a second jig  57  in a state where the metal bumps  55  are heated, the metal bumps  55  are bonded to the land portions  52   a , and the electrodes  54  and the land portions  52   a  are thus connected to each other through the metal bumps  55 .  
         [0011]     Next, in a second process, as shown in  FIG. 10 , the circuit board  51  in which the first semiconductor component  53   a  has been completely assembled is reversed and the flat surface of the first semiconductor component  53   a  is placed on the first jig  56 .  
         [0012]     Next, the metal bumps  55  provided on the electrodes  54  of the second semiconductor component  53   b  are placed on the land portions  52   a  provided on the rear surface of the circuit board  51 . Thereafter, by pressing the second semiconductor component  53   b  with the second jig  57  in a state where the metal bumps  55  are heated, the metal bumps  55  are bonded to the land portions  52   a , and the electrodes  54  and the land portions  52   a  are thus connected to each other through the metal bumps  55 .  
         [0013]     In this way, the semiconductor components  53   a  and  53   b  are completely assembled onto both the front and rear surfaces of the circuit board  51 . However, in the second process shown in  FIG. 10 , since the first semiconductor component  53   a  is in contact with the first jig  56 , the circuit board  51  might be inclined when the second semiconductor component  53   b  is pressed, thereby making the support thereof unstable. Therefore, any variation might be caused in the attachment state of the metal bumps  55  of the second semiconductor component  53   b  to the land portions  52   a.    
         [0014]     In order to remove the inclination of the circuit board  51 , it can be considered that a pressing portion for supporting the circuit board  51  is provided in the first jig  56 . However, in this case, there are various kinds of circuit boards  51  depending upon kinds of products and thus it is necessary to prepare a plurality of first jigs  56  corresponding to various kinds of circuit boards  51 , thereby causing increase in cost and deterioration in productivity.  
         [0015]     [Patent Document 1] Japanese Patent Application Laid-open No. 2001-60602  
         [0016]     In the conventional electronic circuit unit, since the first and second semiconductor components  53   a  and  53   b  are connected to the land portions  52   a  by thermal compression on both the front and rear surfaces of the plate-shaped circuit board  51 , the first semiconductor component  53   a  comes in contact with the first jig  56  during the second process of assembling the second semiconductor component  53   b , so that the circuit board  52  might be inclined when the second semiconductor component  53   b  is pressed and the support thereof becomes unstable. Therefore, any variation in the attachment state of the metal bumps  55  of the second semiconductor component  53   b  to the land portions  52   a  might be generated, thereby causing a problem that connection failure results from the metal bumps  55 .  
         [0017]     In order to remove the inclination of the circuit board  51 , it can be considered that a pressing portion for supporting the circuit board  51  is provided in the first jig  56 . However, in this case, there are various kinds of circuit boards  51  depending upon kinds of products and thus it is necessary to prepare a plurality of first jigs  56  corresponding to various kinds of circuit boards  51 , so that there is a problem that deterioration in productivity as well as increase in cost is caused.  
       SUMMARY OF THE INVENTION  
       [0018]     It is thus an object of the present invention to provide an electronic circuit unit which is excellent in productivity and is low in cost and which has reliable connection between electrodes and land portions.  
         [0019]     According to the first solving means of the present invention for achieving the above object, there is provided an electronic circuit unit comprising a circuit board formed by stacking a plurality of substrates, a wiring pattern having land portions provided on both the front and rear surfaces of the circuit board, and a semiconductor component disposed on both the front and rear surfaces of the circuit board and connected to the land portions through connection conductors by thermal compression, wherein a concave portion for housing the semiconductor component is provided on the rear surface of the circuit board and the semiconductor component is disposed inside the concave portion in a state where the bottom portion of the semiconductor component is not protruded externally from the lower end of the concave portion.  
         [0020]     According to the second solving means of the present invention, at least a pair of wall portions disposed to be opposite to each other with a gap therebetween may be provided on the rear surface of the circuit board, and the concave portion may be formed between the pair of wall portions.  
         [0021]     According to the third solving means of the present invention, a ring-shaped wall portion may be provided on the rear surface of the circuit board to surround the outer circumference of the concave portion.  
         [0022]     According to the fourth solving means of the present invention, the semiconductor component may be made of a flip chip.  
         [0023]     According to the fifth solving means of the present invention, the connection conductors may be made of metal bumps.  
         [0024]     The electronic circuit unit according to the present invention comprises a circuit board formed by stacking a plurality of substrates, a wiring pattern having land portions provided on both the front and rear surfaces of the circuit board, and a semiconductor component disposed on both the front and rear surfaces of the circuit board and connected to the land portions through connection conductors by thermal compression, wherein a concave portion for housing the semiconductor component is provided on the rear surface of the circuit board and the semiconductor component is disposed inside the concave portion in a state where the bottom portion of the semiconductor component is not protruded externally from the lower end of the concave portion.  
         [0025]     In this way, since the semiconductor component of the rear surface side is housed in the concave portion of the circuit board, a semiconductor component can be thermally compressed to the front surface side of the circuit board in a state where the lower end of the circuit board comes in contact with a jig and the circuit board is thus stably supported, so that the attachment state of the connection conductors at the side of the semiconductor component positioned on the front surface side of the circuit board to the land portions is good. Therefore, it is possible to obtain reliable attachment.  
         [0026]     Since stable support can be obtained from the circuit board itself, it is not necessary to prepare jigs corresponding to various kinds, so that it is possible to obtain an electronic circuit unit with reduced cost and enhanced productivity.  
         [0027]     Since at least a pair of wall portions disposed to be opposite to each other with a gap therebetween is provided on the rear surface of the circuit board and the concave portion is formed between the pair of wall portions, it is possible to obtain an electronic circuit unit having a simple structure and a large area of the rear surface side.  
         [0028]     since a ring-shaped wall portion is provided on the rear surface of the circuit board to surround the outer circumference of the concave portion, the support by the jig at the rear surface side of the circuit board can become more stable and reliable.  
         [0029]     Since the semiconductor component is made of a flip chip, the semiconductor component&#39;s cost is reduced and it is thus possible to obtain an electronic circuit unit with reduced cost.  
         [0030]     Since the connection conductors are made of metal bumps, the connection can be made reliably. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0031]      FIG. 1  is a perspective view illustrating an electronic circuit unit according to a first embodiment of the present invention;  
         [0032]      FIG. 2  is a perspective view illustrating the electronic circuit unit according to the first embodiment of the present invention as seen from the rear surface side;  
         [0033]      FIG. 3  is a cross-sectional view illustrating a main part of the electronic circuit unit according to the first embodiment of the present invention;  
         [0034]      FIG. 4  is an explanatory diagram illustrating a first process of assembling a semiconductor component in the electronic circuit unit according to the first embodiment of the present invention;  
         [0035]      FIG. 5  is an explanatory diagram illustrating a second process of assembling a semiconductor component in the electronic circuit unit according to the first embodiment of the present invention;  
         [0036]      FIG. 6  is a perspective view illustrating the electronic circuit unit according to a second embodiment of the present invention as seen from the rear surface side;  
         [0037]      FIG. 7  is a cross-sectional view illustrating a part of a conventional electronic circuit unit;  
         [0038]      FIG. 8  is a cross-sectional view illustrating a main part of the conventional electronic circuit unit;  
         [0039]      FIG. 9  is an explanatory diagram illustrating a first process of assembling a semiconductor component in the conventional electronic circuit unit; and  
         [0040]      FIG. 10  is an explanatory diagram illustrating a second process of assembling a semiconductor component in the conventional electronic circuit unit. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0041]     Hereinafter, an electronic circuit unit according to the present invention will be described with reference to the figures.  FIG. 1  is a perspective view illustrating an electronic circuit unit according to a first embodiment of the present invention,  FIG. 2  is a perspective view illustrating the electronic circuit unit according to the first embodiment of the present invention as seen from the rear surface side, and  FIG. 3  is a cross-sectional view illustrating a main part of the electronic circuit unit according to the first embodiment of the present invention.  
         [0042]      FIG. 4  is an explanatory diagram illustrating a first process of assembling a semiconductor component in the electronic circuit unit according to the first embodiment of the present invention,  FIG. 5  is an explanatory diagram illustrating a second process of assembling a semiconductor component in the electronic circuit unit according to the first embodiment of the present invention, and  FIG. 6  is a perspective view illustrating an electronic circuit unit according to a second embodiment of the present invention as seen from the rear surface side.  
         [0043]     Next, the structure of the electronic circuit unit according to the first embodiment of the present invention will be described with reference to FIGS.  1  to  3 . The circuit board  1  formed by stacking a plurality of substrates comprises a flat front surface (one surface)  1   a , a concave portion  1   c  provided at a rear surface side (the other surface)  1   b , and a ring-shaped wall portion  1   d  made of a part of the circuit board provided to surround the other circumference of the concave portion  1   c.    
         [0044]     A wiring pattern  2  is provided on the front surface  1   a  and the rear surface  1   b  of the circuit board  1  and in the intermediate layer therebetween, and the land portions  2   a  are provided in the wiring pattern  2  provided on the front surface  1   a  and the rear surface  1   b  of the circuit board  1 .  
         [0045]     First and second semiconductor components  3  and  4  made of a flip chip, etc. have a body portion  3   a ,  4   a  and a plurality of electrodes  3   b ,  4   b  provided on the lower surface of the body portion  3   a ,  4   a . Connection conductors  5  made of metal bumps, ball grid arrays, etc. are provided on the electrodes  3   b ,  4   b.    
         [0046]     At the front surface side  1   a  of the circuit board  1 , the electrodes  3   b  of the plural first semiconductors  3  are connected to the land portions  2   a  through the connection conductors  5  to be heated and pressed (thermally compressed). At the rear surface side  1   b  of the circuit board  1 , at least one second semiconductor component  4  is housed in the concave portion  1   c , and the electrodes  4   b  of the second semiconductor component  4  are connected to the land portions  2   a  through the connection conductors  5  to be heated and pressed (thermally compressed).  
         [0047]     At this time, the bottom portion (bottom portion of the body portion  4   a ) of the second semiconductor component  4  housed in the concave portion  1   c  is not externally protruded from the lower end of the concave portion  1   c , that is, the bottom portion is not downwardly protruded from the lower end of the wall portion  1   d.    
         [0048]     The land portions  2   a  positioned on the front and rear surfaces  1   a  and  1   b  of the circuit board  1  are mounted with various electronic components  6  including capacitors or resistors of a chip shape, etc, and desired electrical circuits are formed on the circuit board  1 , thereby forming the electronic circuit unit according to the present invention.  
         [0049]     A method of assembling the first and second semiconductor components  3  and  4  in the electronic circuit unit will be now described with reference to  FIGS. 4 and 5 . First, in a first process, as shown in  FIG. 4 , the front surface  1   a  of the circuit board  1  is placed on the flat surface of a first jig  7  and the connection conductors  5  provided on the electrodes  4   b  of the second semiconductor component  4  are placed on the land portions  2   a  provided on the rear surface  1   b  of the circuit board  1 .  
         [0050]     Next, by pressing the body portion  4   a  of the second semiconductor component  4  with a second jig  8  in a state where the connection conductors  5  are heated, the connection conductors  5  are bonded to the land portions  2   a , and the electrodes  4   b  and the land portions  2   a  are connected to each other through the connection conductors  5 .  
         [0051]     Next, in a second process, as shown in  FIG. 5 , the circuit board  1  in which the second semiconductor component  4  has been completely assembled is reversed and the bottom portion of the wall portion  1   d  of the circuit board  1  is placed on the first jig  7 .  
         [0052]     Next, the connection conductors  5  provided on the electrodes  3   b  of the first semiconductor component  3  are placed on the land portions  2   a  provided on the front surface  1   a  of the circuit board  1 . Thereafter, by pressing the body portion  3   a  of the first semiconductor component  3  with the second jig  8  in a state where the connection components  5  are heated, the connection conductors  5  are bonded to the land portions  2   a , and the electrodes  3   b  and the land portions  2   a  are connected to each other through the connection conductors  5 .  
         [0053]     In this way, the assembly of the first and second semiconductor components  3  and  4  onto both the front and rear surfaces of the circuit board  1  is completed. However, in the first process shown in  FIG. 4  and the second process shown in  FIG. 5  of the assembly process, the front surface  1   a  of the circuit board  1  or the lower end of the wall portion  1   d  serves as a support at the time of thermal compression, so that the first and second semiconductor components  3  and  4  can be reliably bonded.  
         [0054]     Therefore, it is not necessary to prepare a plurality of first jigs  7  corresponding to various kinds of circuit boards  1 , so that it is possible to obtain an electronic circuit unit with reduced cost and enhanced productivity.  
         [0055]     An electronic circuit unit according to a second embodiment of the present invention is shown in  FIG. 6 . In the second embodiment, at least a pair of wall portions  1   d  provided to be opposite to each other with a gap therebetween is provided on the rear surface  1   b  of the circuit board  1 , thereby forming the concave portion  1   c  between the pair of wall portions  1   d.    
         [0056]     Since the remaining structure is similar to that of the first embodiment, the same elements are denoted by the same reference numerals and descriptions thereof will be omitted.  
         [0057]     In the second embodiment, the first and second semiconductor components  3  and  4  can be also assembled using the same method as assembling the first and second semiconductor components  3  and  4  in the first embodiment.