Abstract:
In a semiconductor device, a semiconductor element is mounted on a package substrate, and a heat dissipating member is laid above the semiconductor element and the package thereby sealing the semiconductor element. Resin is filled into the space defined by the semiconductor element, the package substrate, and the heat dissipating member such that there are no gaps.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a semiconductor device and a method of manufacturing the semiconductor device.  
         [0003]     2. Description of the Related Art  
         [0004]     The recent semiconductor elements are more densely integrated than they used to be in the past. As a result, the recent semiconductor elements consume more power and release more heat than ever before. The released heat damages the semiconductor elements. Therefore, a heat dissipating member such as a heat spreader, a lid, or a heat sink is provided on a semiconductor device on which semiconductor elements are mounted. The heat dissipating member dissipates the heat released from the semiconductor elements to the outside to thereby projecting the semiconductor device from the heat.  
         [0005]     The heat dissipating member is directly mounted on a back surface of a semiconductor element, and is exposed to the upper surface of the semiconductor device. Therefore, the heat generated in the semiconductor element is directly transmitted to the heat dissipating member, and is dissipated to the outside air from the heat dissipating member. With this arrangement, the semiconductor element can be cooled efficiently.  
         [0006]     In this high-performance high-heat large scale integration (LSI) package, an LSI element and a heat dissipating member are connected together with a metal (solder), to increase heat transmission from the back surface of the LSI element to the heat dissipating member. For this metal connection, solder containing lead such as an Sn—Pb system (Sn—Pb, Sn—Pb—Ag), and solder containing no lead such Au—Sn, Au—Si, and Au—Ga are used.  
         [0007]     Japanese Patent Application Laid-open No. 2004-260138 discloses a first conventional semiconductor device having a semiconductor chip flip-chip connected to a mounting substrate. This configuration allows decreasing generation of a warp in the substrate, and suppressing destruction of solder bumps for connecting between the semiconductor chip and the substrate in a temperature cycle test, or occurrence of cracks in the substrate.  
         [0008]     According to the first conventional semiconductor device, the semiconductor substrate includes a semiconductor chip, a mounting substrate having this chip flip-chip connected to the substrate, a first filling section having an under-fill part and a fillet formed with a first resin, a reinforcing member, a first adhesive, a lid, and a second filling section formed with a second resin having a smaller coefficient of thermal expansion than that of the first resin.  
         [0009]     Japanese Patent Application Laid-open No. H6-61383 discloses a second conventional semiconductor device having a flip-chip element sealed into a ceramic package in a face down manner. Heat dissipation of the flip-chip is satisfactory, and the flip-chip element and a pad of the ceramic package are connected in high reliability.  
         [0010]     According to the second conventional semiconductor device, the flip-chip element is filled into the ceramic package, which has a recess opened at the top, in a face down manner. The recess is sealed with a metal lid. The semiconductor device has a buffer resin that is filled into between the flip-chip element and a bottom surface of the recess and surrounds the bumps, a heat-resistant resin that is filled in a lower part of the recess so that the upper surface of the flip-chip element is exposed, and solder that is filled into the recess so that the upper surface of the flip-chip element and the lower surface of the metal lid are closely adhered together and the solder is present between the flip-chip element and the metal lid.  
         [0011]     However, when the coefficient of thermal expansion of one constituent element is considerably different from that of other constituent element of an organic package substrate like in the conventional configuration, a warp can occur in the substrate due to residual stress of the connected parts, and a distortion or a cracking occurs in the junction of parts having mutually different physical properties. In other words, it is difficult to reliably maintain a stable connection state for a long time.  
         [0012]     In the first conventional semiconductor device, an air gap is present between the second filling section and the lid. Therefore, a distortion tends to occur at the boundary between the air gap and the parts due to the application of thermal stress. This air gap decreases radiation efficiency of semiconductor chips.  
         [0013]     In the second conventional semiconductor device, solder is present between the flip-chip element and the metal lid. Because the heat-resistant resin is not directly closely adhered to the metal lid, a distortion in the vertical direction of the metal lid due to the application of the thermal stress cannot be suppressed.  
       SUMMARY OF THE INVENTION  
       [0014]     It is an object of the present invention to at least solve the problems in the conventional technology.  
         [0015]     According to one aspect of the present invention, a semiconductor device includes a semiconductor element; a package substrate on which the semiconductor element is mounted; and a heat dissipating member that is connected to the semiconductor element and to the package substrate any of directly or via a reinforcing member while forming a space around the semiconductor element; and at least one opening that communicates to the space from outside. Moreover, resin is filled into the space via the opening such that the resin completely fills the space, and the resin is cured after filling.  
         [0016]     According to another aspect of the present invention, a semiconductor device includes a semiconductor element enclosed between a package substrate and a heat dissipating member; and a layer of resin in a space between any one of the semiconductor element, the package substrate, and the heat dissipating member.  
         [0017]     According to still another aspect of the present invention, a method of manufacturing a semiconductor device includes mounting a semiconductor element on a package substrate; filling an underfill in between the package substrate and the semiconductor element, and curing the underfill; laying a heat dissipating member on the semiconductor element and the package substrate, thereby sealing the semiconductor element between the heat dissipating member and the package substrate; completely filling a space defined by the semiconductor element, the package substrate, and the heat dissipating member with a resin; and curing the resin filled in the space.  
         [0018]     The above and other objects, features, advantages and technical and industrial significance of this invention will be better understood by reading the following detailed description of presently preferred embodiments of the invention, when considered in connection with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]      FIG. 1  is a cross section of relevant parts of a semiconductor device according to an embodiment of the present invention;  
         [0020]      FIG. 2  is a perspective and cut view of the semiconductor device shown in  FIG. 1 ;  
         [0021]      FIG. 3  to  FIG. 8  are cross sections for explaining a method of manufacturing the semiconductor device shown in  FIG. 1 ;  
         [0022]      FIG. 9  is a cross section of relevant parts of a semiconductor device having a resin-filling slit on the heat dissipating member; and  
         [0023]      FIG. 10  is a cross section of relevant parts of a semiconductor device having a heat sink as the heat dissipating member.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]     Exemplary embodiments of the present invention will be explained in detail with reference to the accompanying drawings. Note that the invention is not limited by the embodiments.  
         [0025]      FIG. 1  is a cross section of relevant parts of a semiconductor device  10  according to an embodiment of the present invention.  FIG. 2  is a perspective cut view of the semiconductor device  10 . The semiconductor device  10  includes an LSI element  11 , which is a semiconductor element, a package substrate  12  on which the LSI element  11  is mounted, and a heat dissipating member  17  that is connected to the LSI element  11  with a metal. The heat dissipating member  17  is connected to the package substrate  12  via a frame-shaped stiffener (a reinforcing member)  15 . The heat dissipating member  17 , the stiffener  15 , and the package substrate  12  form a package space (a predetermined space)  23  around the LSI element  11 . Moreover, the heat dissipating member  17 , the stiffener  15 , and the package substrate  12  seal the LSI element  11 .  
         [0026]     An adhesive sheet  16  is used to fix the heat dissipating member  17  and the stiffener  15  to each other, and to fix the stiffener  15  and the package substrate  12  to each other. The LSI element  11  rests on plural bumps  13  formed on the package substrate  12 . An underfill  14  is filled in between the bumps  13 .  
         [0027]     Resin filling openings  20  from which a resin  19 , such as thermosetting resin, can be filled into the package space  23  are provided in the heat dissipating member  17 . The resin  19  is filled in such a manner that it completely fills the package space  23 . After filling, the resin  19  is cured. A lid is used as the heat dissipating member  17 .  
         [0028]     The package substrate  12  can be a flip chip ball grid array (FC-BGA), a flip chip land grid array (FC-LGA) package, or a flip chip pin grid array (FC-PGA) package. When the package substrate  12  is the FC-BGA, an organic substrate material can be used apart from a ceramic material containing any of Al 2 O 3 , AlN, and glass. For example, a glass ceramic substrate or an organic substrate having a thickness of 0.4 millimeter to 0.7 millimeter can be used as the package substrate  12 .  
         [0029]     The underfill  14  can be a material including a resin containing epoxy resin. It is preferable, but not necessary, that a coefficient of thermal expansion of the underfill  14  is about 1,500 ppm to 2,000 ppm, and is heat cured usually at about 150° C.  
         [0030]     Copper or stainless material having a coefficient of thermal expansion substantially equal to that of the package substrate  12  is used for the material of the stiffener  15 . A material made of epoxy resin is used for the adhesive sheet  16 .  
         [0031]     Copper or Al having satisfactory thermal conductivity, a composite material using copper or Al as a base, or a carbon composite material can be used for the material of the heat dissipating member  17 . In this embodiment, oxygen-free high conductivity copper is used. Solder containing In—Ag as a main component is used for the material of a metal connecting material  18 .  
         [0032]     The resin  19  has a coefficient of thermal conductivity (for example, 20 ppm to 40 ppm) that is different from that of the underfill  14 .  
         [0033]     A method of manufacturing the semiconductor device  10  is explained with reference to  FIG. 3  to  FIG. 8 .  FIG. 3  depicts a state in which the stiffener  15  adhered to the package substrate  12  with the adhesive sheet  16 .  FIG. 4  depicts a state in which the LSI element  11  and electronic components  22  are mounted on the package substrate  12 .  FIG. 5  depicts a state in which the underfill  14  filled, in the bumps  13  (not shown). The underfill  14  is cured in this state.  
         [0034]      FIG. 6  depicts a state in which the heat dissipating member  17  is soldered to the LSI element  11 .  FIG. 7  depicts a state in which the resin  19  is filled into the package space  23  through the resin filling openings  20 .  FIG. 8  depicts a state in which ball grid array (BGA) balls  21  are mounted on the package substrate  12 . Thus, the semiconductor device  10  becomes ready.  
         [0035]     Precisely, as shown in  FIG. 3 , first, the stiffener  15  is adhered to the package substrate  12  using the adhesive sheet  16 . This is a reinforcing member adhering step.  
         [0036]     The stiffener  15  is adhered to the package substrate  12  using the adhesive sheet  16  by applying a pressure of about 2 kg/cm 2 . To obtain a uniform adhesion thickness, glass fiber or inorganic filler is filled in the adhesive material.  
         [0037]     Thereafter, as shown in  FIG. 4 , the LSI element  11  is flip-chip mounted on the package substrate  12 . When the electronic components  22  such as a capacitor and a chip resistor need to be mounted on the surface on which the LSI element  11  is mounted, these electronic components  22  are also connected at the same time. This is a semiconductor element mounting step.  
         [0038]     When a solder material of an electrode is Sn—Ag, for example, the electrode is mounted at a peak temperature of a temperature profile of 235 to 245° C. At present, many packages employ a method that the electrode of the LSI element  11  is formed with Sn—Pb solder containing Pb by 90 percent or more, and the electrode is connected to the package substrate  12  with Sn- 37  Pb (eutectic crystal) that is soldered in advance. These packages are also soldered at a peak temperature usually at around 230° C.  
         [0039]     As shown in  FIG. 5 , after the LSI element  11  is mounted on the package substrate  12 , the underfill  14  is filled into between the bumps  13  on the surface of the flip-chip mounted circuit (see  FIG. 1 ), and the underfill  14  is cured. This is an underfill filling and curing step. This underfill  14  is cured at a temperature usually at around 150° C.  
         [0040]     As shown in  FIG. 6 , after the underfill  14  is filled and cured, the heat dissipating member  17  is connected to the LSI element  11  with the metal connecting material  18 . This is a heat dissipating member connecting step.  
         [0041]     To carry out the metal connection, the surface of the material of the heat dissipating member  17  needs to be metalized for the soldering. For example, Ni and Au are electrolytically plated on the surface of the oxygen-free copper material according to this embodiment to prevent wetness and oxidization. The Ni has a metal thickness of 3 micrometers, and Au has a metal thickness of 0.3 micrometer.  
         [0042]     The back surface of the FC-BGA package for connecting the heat dissipating member  17  at the LSI element  11  side is formed with a metal layer (metalized) in the wafer process in advance. This metal layer is Cu, Au, or the like. In this embodiment, Ti 5000 Å of adhered metal is formed, and Au is formed in the thickness of 0.3 micrometer on the Ti.  
         [0043]     As shown in  FIG. 7 , the resin  19  having a coefficient of thermal expansion substantially the same as that of the package substrate  12  is filled into the package space  23  sealed with the heat dissipating member  17 , from the resin filling opening  20 . The resin  19  is filled into the package space  23  completely so as not to have any gap in the package space. This is a resin filling step. By decreasing a difference between the coefficient of thermal expansion of the package substrate  12  and the coefficient of thermal expansion of the resin  19 , thermal stress can be decreased when it is applied.  
         [0044]     The resin  19  is cured usually at a temperature around 150° C. in the resin curing step.  
         [0045]     As shown in  FIG. 8 , after the resin  19  is cured, the BGA balls  21  are mounted on the package substrate  12  according to needs.  
         [0046]     For example, when the packaging solder for these parts is a low-melting point solder such as a general Sn- 37  Pb (eutectic crystal) solder, even a reflow temperature increases to around 250° C. corresponding to the Pb despite the reflow temperature of 230° C. or below, a thermal behavior of the package can be decreased. Therefore, the reflow temperature limit can be mitigated.  
         [0047]     As explained above,-the package space  23  is completely filled with the resin  19 , and the resin  19  is cured. As a result, the resin  19  firmly adheres to a part of the heat dissipating member  17 , a part of the metal connecting material  18 , the side surfaces of the semiconductor element  11 , an edge of the underfill  14 , and a part of the stiffener  15 .  
         [0048]     Because the corresponding parts are restricted by the resin  19 , stress can be decreased, and thermal stress due to a secondary connection (the mounting of the BGA balls  21 ) can be applied by many times. Consequently, a warp in the package substrate  12  and a distortion at a junction between the parts having different physical properties can be corrected, thereby dispersing and decreasing stress applied to a junction between the parts.  
         [0049]     Furthermore, a reduction in the reliability of semiconductor device  10  due to a mismatch between the coefficient of thermal expansion of the heat dissipating member  17  and the coefficient of thermal expansion of the LSI element  11  can be suppressed. Therefore, Cu or Al having satisfactory thermal conductivity can be used for the material of the heat dissipating member  17 , thereby further improving heat dissipation.  
         [0050]     The resin  19  is filled into the package space  23  without a gap, and the resin  19  is also closely adhered to a part of the metal connecting material  18  without a gap. Therefore, thermal resistance decreases substantially from that according to the conventional technique, thereby improving heat dissipation efficiency. Consequently, the metal connecting material  18  having high thermal conductivity corresponding to high heat dissipation of the LSI element  11  can be provided.  
         [0051]     Because the resin filling openings  20  are provided on the side surfaces of the heat dissipating member  17 , the following effects can be obtained. Usually, on the side surfaces of the heat dissipating member  17  provided with the resin filling openings  20 , other constituent elements are not provided. Therefore, even when the thermosetting resin  19  slightly overflowed from the resin filling openings  20  is not removed, this resin does not interfere with the manufacturing of the semiconductor device  10 . Consequently, a step of removing the surplus resin is not necessary, which further simplifies the manufacturing process.  
         [0052]     The resin filling openings  20  can be provided on side surfaces of the stiffener  15  instead of the side surfaces of the heat dissipating member  17 . Alternatively, the resin filling openings  20  can be provided on both the side surfaces of the heat dissipating member  21  and the stiffener  15 . In these cases, effects similar to the above can be also obtained.  
         [0053]     The resin filling opening  20  can be provided as a slit  20   a  as shown in  FIG. 9 . In this case, effects similar to the above can be also obtained. In this example, a heat spreader is used for the heat dissipating member  17 .  
         [0054]     The heat dissipating member  17  explained above is a lid. However, a heat sink can be used instead of the lid, as shown in  FIG. 10 . In this case, effects similar to the above can be also obtained.  
         [0055]     The stiffener  15  can be omitted. In other words, the heat dissipating member  17  can be directly connected to the package substrate  12 .  
         [0056]     The adhesive sheet  16  used for connecting the stiffener  15  can be used according needs, and other adhering unit can be also used.  
         [0057]     According to the present invention, a space around the semiconductor device is completely filled with a resin. Therefore, stress can be decreased, and thermal stress due to a secondary connection can be applied by many times. Accordingly, a warp in the package substrate and a distortion in a junction between the parts having different physical properties can be corrected, thereby dispersing and decreasing stress applied to each junction. The resin can be filled into the space without a gap, and is also closely adhered to a part of the heat dissipating member without a gap. As a result, thermal resistance can be substantially decreased from that according to the conventional technique, thereby improving heat dissipation efficiency. Consequently, the invention can solve problems due to high heat generation in a semiconductor element.  
         [0058]     According to the present invention, by decreasing a difference between the coefficient of thermal expansion of the package substrate and the coefficient of thermal expansion of the thermosetting resin, stress applied to the soldered part of the semiconductor element can be decreased.  
         [0059]     According to the present invention, usually, other constituent elements are not provided on the side surfaces on which the resin filling openings are provided. Therefore, even though the thermosetting resin slightly overflowed from the resin filling openings is not removed, this resin does not become interference in the manufacturing of the semiconductor device. Consequently, a step of removing surplus resin is not necessary, which further simplifies the manufacturing process.  
         [0060]     According to the present invention, even when a general heat dissipating member is used, heat dissipation efficiency can be improved. Consequently, the invention can solve problems due to high heat generation in a semiconductor element.  
         [0061]     According to the present invention, it is possible to provide a method of manufacturing a semiconductor device capable of suppressing the occurrence of a warp in a substrate due to the application of a thermal stress during a manufacturing of the semiconductor device and a distortion at a junction between parts having different physical properties, capable of dispersing and decreasing stress applied to a junction between the parts, and capable of decreasing problems due to high heat generation in a semiconductor element.  
         [0062]     Although the invention has been described with respect to a specific embodiment for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art that fairly fall within the basic teaching herein set forth.