Abstract:
A method of flip-chip mounting can reliably and stably mount a semiconductor chip to a mounting substrate while avoiding problems such as damage to the semiconductor chip due to a difference in thermal expansion coefficients between the semiconductor chip and the mounting substrate. The method of flip-chip mounting a semiconductor chip supports a mounting substrate on a stage in a state where a resin material has been supplied onto a chip mounting surface of the mounting substrate and presses the semiconductor chip toward the mounting substrate using a pressure/heat applying head to bond the semiconductor chip to the mounting substrate and thermally harden the resin material. A concave part is provided in a support surface of the stage that supports the semiconductor chip, and the semiconductor chip is bonded to the mounting substrate by pressing the semiconductor chip toward the mounting substrate using the pressure/heat applying head in a state where the mounting substrate is bent toward the concave part.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a method of flip-chip mounting and in more detail to a method of flip-chip mounting that can avoid the problem of a semiconductor chip being damaged during bonding due to differences in thermal expansion coefficients between the semiconductor chip and a mounting substrate.  
         [0003]     2. Related Art  
         [0004]     Among methods of mounting a semiconductor chip on a mounting substrate as a flip-chip, as shown in  FIG. 5A , there is a method that connects a semiconductor chip  14  as a flip-chip after applying a resin material  12  in advance onto a semiconductor chip mounting region of a mounting substrate  10 .  FIG. 5B  shows a state where the semiconductor chip  14  is supported by a pressure/heat applying head  20 , is positioned with respect to the mounting substrate  10 , and is mounted on the mounting substrate  10  while pressure and heat are applied to the semiconductor chip  14 .  
         [0005]     When the resin material  12  is supplied onto the mounting substrate  10  in advance and the semiconductor chip  14  is connected as a flip-chip, as shown in  FIG. 5B , the mounting substrate  10  is supported on a stage  22  that has been heated to around 70 to 80° C., and mounting is carried out after the pressure/heat applying head  20  has been heated to the thermal hardening temperature or higher of the resin material  12  (around 200° C., for example). By merely heating the semiconductor chip  14  for around five seconds using the pressure/heat applying head  20 , bumps  14   a  of the semiconductor chip  14  are electrically connected to connection pads formed on the mounting substrate  10  and the resin material  12  that fills the gap between the semiconductor chip  14  and the mounting substrate  10  is thermally hardened.  
         [0000]     Patent Document 1  
         [0006]     Japanese Laid-Open Patent Publication No. 2000-138253  
         [0000]     Patent Document 2  
         [0007]     Japanese Laid-Open Patent Publication No. S57-176738  
         [0000]     Patent Document 3  
         [0008]     Japanese Laid-Open Patent Publication No. 2000-299330  
         [0000]     Patent Document 4  
         [0009]     Japanese Laid-Open Patent Publication No. 2000-323523  
         [0010]     However, since the thermal expansion coefficients of the semiconductor chip  14  and the mounting substrate  10  that is made of resin differ by a factor of around three, when the semiconductor chip  14  is flip-chip mounted, due to the large difference in thermal expansion between the semiconductor chip  14  and the mounting substrate  10 , after mounting, as shown in  FIG. 6 , the mounting substrate  10  becomes warped toward the semiconductor chip  14 .  
         [0011]     If mounting is carried out with the mounting substrate  10  in a warped state and the gap between the surfaces of the mounting substrate  10  and the semiconductor chip  14  becomes narrow in a central part of the chip mounting surface of the mounting substrate  10 , filler such as alumina or silica added to the resin material  12  to make the thermal expansion coefficient match that of the semiconductor chip  14  is compressed by the mounting substrate  10  and the semiconductor chip  14 , resulting in the problem of damage to the circuit surface of the semiconductor chip  14  and in wiring formed on the circuit surface becoming disconnected.  
         [0012]     When the bumps  14   a  are formed on the semiconductor chip  14  at wide intervals, it is possible to form large, high bumps  14   a , and therefore even if the mounting substrate  10  becomes warped during flip-chip bonding, the problem of the semiconductor chip  14  being damaged hardly occurs. However, with a product where the bumps  14   a  are disposed with a high density, the bumps  14   a  themselves become small and the height of the bumps  14   a  becomes lower (around 15 μm), and therefore there is the problem that the semiconductor chip  14  can be damaged even if the mounting substrate  10  only becomes slightly warped.  
       SUMMARY OF THE INVENTION  
       [0013]     The present invention was conceived to solve the problems described above, and it is an object of the present invention to provide a method of flip-chip mounting that can reliably and stably mount a semiconductor chip while avoiding problems such as damage to the semiconductor chip due to a difference in thermal expansion coefficients between the semiconductor chip and a mounting substrate when connecting the semiconductor chip as a flip-chip to the mounting substrate.  
         [0014]     To achieve the stated object, a method of flip-chip mounting a semiconductor chip according to the present invention supports a mounting substrate on a stage in a state where a resin material has been supplied onto a chip mounting surface of the mounting substrate and presses the semiconductor chip toward the mounting substrate using a pressure/heat applying head to bond the semiconductor chip to the mounting substrate and thermally harden the resin material, wherein a concave part is formed in a support surface of the stage that supports the semiconductor chip, and the semiconductor chip is bonded to the mounting substrate by pressing the semiconductor chip toward the mounting substrate using the pressure/heat applying head in a state where the mounting substrate is bent toward the concave part.  
         [0015]     A suction hole that is in communication with a base surface of the concave part may be provided in the stage, and when the semiconductor chip is bonded to the mounting substrate by the pressure/heat applying head, bonding may be carried out in a state where the mounting substrate is pulled by suction from the suction hole to forcibly bend the mounting substrate toward the concave part.  
         [0016]     Another method of flip-chip mounting a semiconductor chip supports a mounting substrate on a stage in a state where a resin material has been supplied onto a chip mounting surface of the mounting substrate and presses the semiconductor chip toward the mounting substrate using a pressure/heat applying head to bond the semiconductor chip to the mounting substrate and thermally harden the resin material, wherein a surface of the pressure/heat applying head on which the semiconductor chip is held by suction is formed as a concave surface, a suction hole that is in communication with the concave surface is provided, and when the semiconductor chip is bonded to the mounting substrate by the pressure/heat applying head, the semiconductor chip is pulled by suction from the suction hole to forcibly bend the semiconductor chip toward the concave surface.  
         [0017]     Yet another method of flip-chip mounting a semiconductor chip supports a mounting substrate on a stage in a state where a resin material has been supplied onto a chip mounting surface of the mounting substrate and presses the semiconductor chip toward the mounting substrate using a pressure/heat applying head to bond the semiconductor chip to the mounting substrate and thermally harden the resin material, wherein a spacer that supports the semiconductor chip at a distance from the mounting substrate is provided on the mounting substrate, and the mounting substrate and the semiconductor chip are bonded together so that the mounting substrate and the semiconductor chip are electrically connected and the mounting substrate and the semiconductor chip are separated by the spacer.  
         [0018]     Yet another method of flip-chip mounting a semiconductor chip supports a mounting substrate on a stage in a state where a resin material has been supplied onto a chip mounting surface of the mounting substrate and presses the semiconductor chip toward the mounting substrate using a pressure/heat applying head to bond the semiconductor chip to the mounting substrate and thermally harden the resin material, wherein a spacer that supports the semiconductor chip at a distance from the mounting substrate is provided on a bonding surface of the semiconductor chip, and the mounting substrate and the semiconductor chip are bonded together so that the mounting substrate and the semiconductor chip are electrically connected and the mounting substrate and the semiconductor chip are separated by the spacer.  
         [0019]     According to the method of flip-chip mounting according to the present invention, it is possible to flip-chip mount a semiconductor chip while solving the problem of a mounting substrate becoming bent during mounting due to a difference in thermal expansion coefficients between the semiconductor chip and the mounting substrate resulting in the semiconductor chip becoming damaged by filler included in a resin material, and therefore a drop in quality can be prevented. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]     The aforementioned and other objects and advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying drawings.  
         [0021]     In the drawings:  
         [0022]      FIG. 1  is a diagram useful in explaining a first embodiment of a method of flip-chip mounting according to the present invention;  
         [0023]      FIG. 2  is a diagram useful in explaining a second embodiment of a method of flip-chip mounting according to the present invention;  
         [0024]      FIG. 3  is a diagram useful in explaining a third embodiment of a method of flip-chip mounting according to the present invention;  
         [0025]      FIG. 4  is a diagram useful in explaining a fourth embodiment of a method of flip-chip mounting according to the present invention;  
         [0026]      FIG. 5  is a diagram useful in explaining a conventional method of flip-chip mounting; and  
         [0027]      FIG. 6  is a diagram showing a state where mounting is carried out in a state where a mounting substrate is warped. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     First Embodiment  
       [0028]      FIG. 1  shows a first embodiment of a method of flip-chip mounting according to the present invention. In the present embodiment, the resin material  12  is applied in advance onto a chip mounting surface of the mounting substrate  10  and the semiconductor chip  14  is positioned relative to and mounted upon the mounting substrate  10  while being held by suction on the pressure/heat applying head  20 .  
         [0029]     In the present embodiment, a concave part  24   a  is formed on a support surface of a stage  24  that supports the mounting substrate  10 , a suction hole  25  that is in communication with an inner base surface of the concave part  24   a  is provided in the stage  24 , and the suction hole  25  is connected to a vacuum suction apparatus (not shown). The concave part  24   a  is formed in a region that is within a region where the bumps  14   a  are formed on the semiconductor chip  14 .  
         [0030]     In the present embodiment, after the mounting substrate  10  has been set on the stage  24  and the resin material  12  has been supplied onto the chip mounting surface of the mounting substrate  10 , the vacuum suction apparatus is operated to pull the mounting substrate  10  by suction via the suction hole  25  and the semiconductor chip  14  held by suction on the pressure/heat applying head  20  is flip-chip mounted in a state where the mounting substrate  10  is downwardly convex, i.e., a state where a central part of the mounting substrate  10  is bent downward away from the semiconductor chip  14 .  
         [0031]     The pressure/heat applying head  20  is heated to around 200° C. The semiconductor chip  14  is held by suction on the pressure/heat applying head  20  and is pressed toward the mounting substrate  10  so that the bumps  14   a  of the semiconductor chip  14  are bonded to connection terminals provided on the mounting substrate  10  by soldering or the like. The resin material  12  held between the semiconductor chip  14  and the mounting substrate  10  fills the gap between the semiconductor chip  14  and the mounting substrate  10  and is thermally hardened. Since the stage  24  is formed as a flat surface at positions where the bumps  14   a  of the semiconductor chip  14  are formed, the pressing force acts reliably on the mounting substrate  10  and the semiconductor chip  14  so that electrical connections can be reliably produced between the bumps  14   a  and the connection terminals of the mounting substrate  10 .  
         [0032]     The resin material  12  seals and protects the bonded parts of the semiconductor chip  14  and the mounting substrate  10  from the outside. When the semiconductor chip  14  heats up and thermal stress acts between the semiconductor chip  14  and the mounting substrate  10 , the resin material  12  also acts so as to firmly hold the semiconductor chip  14  and the mounting substrate  10  together so that the electrical connections between the bumps  14   a  and the connection terminals do not become unreliable.  
         [0033]     In the method of flip-chip mounting according to the present embodiment, when the mounting substrate  10  is supported on the stage  22 , mounting is carried out with the mounting substrate  10  forcibly bent so as to be downwardly convex. By doing so, after mounting, even if the mounting substrate  10  deforms so as to become bent toward the semiconductor chip  14 , the gap between the mounting substrate  10  and the circuit surface of the semiconductor chip  14  is prevented from becoming excessively narrow. By keeping the gap between the semiconductor chip  14  and the chip mounting surface of the mounting substrate  10  at a predetermined distance or above, it is possible to avoid the problem of the circuit surface of the semiconductor chip  14  being damaged by the filler included in the resin material  12  after mounting.  
         [0034]     In a method of flip-chip mounting that forcibly bends the mounting substrate  10  by pulling the mounting substrate  10  by suction from the concave part  24   a  side of the stage  24 , by controlling the vacuum suction force, the amount by which the mounting substrate  10  bends can be adjusted, and therefore it is possible to control the gap between the mounting substrate  10  and the semiconductor chip  14  after mounting in accordance with the product. It is effective to adjust the amount by which the mounting substrate  10  bends since the size, thickness, and material of the mounting substrate  10  differ from product to product.  
         [0035]     Note that in the method of flip-chip mounting where the concave part  24   a  is provided in the stage  24 , it is also possible to mount the semiconductor chip  14  as a flip-chip with the mounting substrate  10  set on the stage  24  but without pulling the mounting substrate  10  by suction from the suction hole  25  to forcibly bend the mounting substrate  10 .  
         [0036]     That is, after the resin material  12  has been supplied onto the mounting substrate  10 , when the semiconductor chip  14  held by suction on the pressure/heat applying head  20  is pressed toward the mounting substrate  10 , the mounting substrate  10  bends toward the concave part  24   a  via the resin material  12 . This method is effective in cases where the semiconductor chip  14  will not be damaged by the filler included in the resin material  12  even if the mounting substrate  10  is not greatly bent during flip-chip mounting, since the construction of the apparatus can be simplified.  
       Second Embodiment  
       [0037]      FIG. 2  shows a second embodiment of a method of flip-chip mounting according to the present invention. The method of flip-chip mounting according to the present embodiment is characterized by using a stage  22  where the support surface that supports the mounting substrate  10  is formed as a flat surface and using a pressure/heat applying head  26  where a concave surface  26   a  that allows the semiconductor chip  14  to bend away from the chip mounting surface of the mounting substrate  10  is provided on a surface on which the semiconductor chip  14  is held and a suction hole  27  is provided so as to be in communication with a center position of the concave surface  26   a . The suction hole  27  is also in communication with a vacuum suction apparatus (not shown).  
         [0038]      FIG. 2  shows a state where, after the mounting substrate  10  has been set on the stage  22  and the resin material  12  has been supplied onto the chip mounting surface of the mounting substrate  10 , the semiconductor chip  14  is held by suction on the pressure/heat applying head  26 , and the semiconductor chip  14  is heated while being pressed onto the mounting substrate  10  so as to be flip-chip mounted. By pulling the semiconductor chip  14  by suction from the suction hole  27  provided in the pressure/heat applying head  26 , the semiconductor chip  14  is flip-chip mounted in a state where the semiconductor chip  14  is upwardly convex as shown in  FIG. 2 , i.e., where a central part of the semiconductor chip  14  is bent in a direction away from the mounting substrate  10 .  
         [0039]     The resin material  12  held between the mounting substrate  10  and the semiconductor chip  14  is heated by the pressure/heat applying head  26 , fills the gap between the semiconductor chip  14  and the mounting substrate  10 , and thermally hardens.  
         [0040]     In the method of flip-chip mounting according to the present embodiment, since the semiconductor chip  14  is mounted in a state where the semiconductor chip  14  is bent so as to be upwardly convex, it is possible to mount the semiconductor chip  14  while preventing the gap between the semiconductor chip  14  and the mounting substrate  10  from becoming excessively narrow after mounting. By doing so, it is possible to avoid the problem of the circuit surface of the semiconductor chip  14  becoming damaged by the filler included in the resin material  12 . Note that the filler included in the resin material  12  is mixed in so as to constitute around 30 to 40% by weight, and therefore is a large proportion of the resin material  12 .  
         [0041]     When air is evacuated to pull the semiconductor chip  14  from the suction hole  27  provided in the pressure/heat applying head  26 , by controlling the vacuum suction force of the vacuum suction apparatus, mounting can be carried out with the amount of bending of the semiconductor chip  14  being suitably controlled. In the same way as when mounting is carried out with the mounting substrate  10  in a bent state in the first embodiment, when mounting is carried out with the semiconductor chip  14  in a bent state, by slightly bending the semiconductor chip  14  by only a slight amount, it is possible to control the gap between the semiconductor chip  14  and the chip mounting surface of the mounting substrate  10  to an extent where the circuit surface of the semiconductor chip  14  is not damaged.  
       Third Embodiment  
       [0042]      FIG. 3  shows a third embodiment of a method of flip-chip mounting according to the present invention. The method of flip-chip mounting according to the present embodiment is characterized by providing a spacer  11 , which supports the semiconductor chip  14  at a distance from the mounting substrate  10 , in advance on a chip mounting surface of the mounting substrate  10  and mounting the semiconductor chip  14  with the spacer  11  between the mounting substrate  10  and the semiconductor chip  14 .  
         [0043]     As shown in  FIG. 3 , a spacer  11  is formed using a resist in advance on the chip mounting surface of the mounting substrate  10  and after the resin material  12  has been supplied onto the chip mounting surface of the mounting substrate  10 , the semiconductor chip  14  is mounted on the mounting substrate  10  using the pressure/heat applying head  20 . By setting the thickness of the spacer  11  at a thickness where the semiconductor chip  14  is supported at a distance from the mounting substrate  10  without bonding of the connected parts of the semiconductor chip  14  and the mounting substrate  10  being obstructed and without the circuit surface of the semiconductor chip  14  being damaged, when the semiconductor chip  14  is flip-chip mounted on the mounting substrate  10 , mounting can be carried out without the filler included in the resin material  12  damaging the semiconductor chip  14 .  
         [0044]     The spacer  11  is formed in a predetermined pattern by applying a resist or using a resist material formed as a film. When forming the spacer  11 , it is possible to form the spacer  11  at a position that does not adversely affect the semiconductor chip  14  during mounting. By using a photosensitive resist material, the spacer  11  can be formed in a desired pattern.  
       Fourth Embodiment  
       [0045]      FIG. 4  shows a fourth embodiment of a method of flip-chip mounting according to the present invention. The method of flip-chip mounting according to the present embodiment is characterized by forming a spacer  13  on the circuit surface of the semiconductor chip  14 , that is, a surface that faces the mounting substrate  10  when mounting is carried out, instead of forming the spacer  11  on the mounting substrate  10 .  
         [0046]     As the method of forming the spacer  13  on the circuit surface of the semiconductor chip  14 , it is possible to use a method that applies a resin (an adhesive) on the circuit surface of the semiconductor chip  14  and then hardens the resin to produce the spacer  13 . In the manufacturing process of the semiconductor chip  14 , it is judged whether the characteristics of individually formed semiconductor chips are defective or non-defective at the semiconductor wafer-stage and marking is carried out to indicate whether the individual semiconductor chips are defective or non-defective. When marking is carried out to indicate whether the individual semiconductor chips are defective or non-defective, instead of marking, it is possible to apply the resin that forms the spacer  13  described above, with the actual spacer  13  being formed in a later process. This method is efficient in that the marking of the semiconductor chips and the formation of the spacers  13  can be carried out simultaneously.  
         [0047]     In the same way as the spacer  11  of the third embodiment, the protruding height of the spacer  13  is set so that a predetermined gap is kept between the semiconductor chip  14  and the mounting substrate  10  without obstructing the operation that electrically connects the semiconductor chip  14  to the mounting substrate  10 . In the present embodiment also, the spacer  13  is formed at a position on the circuit surface of the semiconductor chip  14  that does not adversely affect the semiconductor chip  14  after mounting.  
         [0048]     In this way, by flip-chip mounting with a spacer  13  provided on the surface of the semiconductor chip  14  that faces the mounting substrate  10 , it is possible to reliably mount the semiconductor chip  14  on the mounting substrate  10  without damaging the semiconductor chip  14 .