Abstract:
A semiconductor device has an insulating substrate, a semiconductor element which is mounted on the insulating substrate, a hollow casing which surrounds a peripheral edge of the insulating substrate to contain the semiconductor element therein, and a sealing material which is charged into the casing to seal the inside of the casing. The casing has protrusion portions each of which partially protrudes from an upper surface of the casing. Thus, it is possible to provide a semiconductor device in which poor external appearance or lowering of adhesion to a cover can be prevented even when a sealing material is injected up to the vicinity of an upper surface of a casing.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based on, and claims priority to, Japanese Patent Application No. 2014-001612, filed on Mar. 28, 2014, the contents of which are entirely incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a semiconductor device and a semiconductor device casing. 
         [0004]    2. Description of the Background Art 
         [0005]    A power semiconductor module in which one or two or more power semiconductor elements (semiconductor chips) are included in a casing and the inside of the casing is sealed with a sealing material has been known as a semiconductor device. Bonding wires etc. made of aluminum are used for these power semiconductor elements in order to electrically connect the semiconductor chips mounted on an insulating substrate to an electric circuit or terminals formed in the insulating substrate. 
         [0006]    The sealing material inside the casing is composed of an epoxy resin etc. and serves for protecting and insulating the semiconductor chips, the bonding wires, etc. which are received in the casing. To this end, in the power semiconductor module, the sealing material is charged into the casing to reach a height at which the bonding wires inside the casing can be sufficiently covered and insulated. On the other hand, there is a request for reduction of the size and thickness of the power semiconductor module, and it is desirable that the height of the casing is also made low as long as there is no problem. When the sealing material which is liquefied is injected into the casing, the sealing material is injected up to the vicinity of an upper surface of the casing so that the insulation property inside the casing can be achieved by the sealing material in balance with the reduction of the size and thickness. 
         [0007]    Since the sealing material is injected up to the vicinity of an upper edge of the casing, the sealing material may run onto the upper surface of the casing during the injection. In addition, the sealing material may run onto the upper surface of the casing during conveyance before the injected sealing material is solidified. 
         [0008]    The sealing material running on the upper surface of the casing may cause poor external appearance of the power semiconductor module. When the casing is covered with a cover and adhesively fixed to the cover, the sealing material running on the upper surface of the casing may lower the adhesion because the upper surface which is the bonded surface of the casing is not flat. 
         [0009]    Provision of a flange in an inner surface of the casing (JP-A-8-130291) or provision of a step portion in an inner surface of the casing (JP-A-4-354354) has been proposed for preventing the sealing material from running on the upper surface of the casing. 
         [0010]    However, the flange or the step portion provided in the inner surface of the casing is formed to face toward the inside of the casing so that the sealing material can be prevented from reaching the upper surface of the casing. Thus, the injection amount of the sealing material is limited up to a height where the flange or the step portion is formed. Therefore, the flange or the step portion cannot satisfactorily meet the request to inject the sealing material up to a position as close to the upper surface of the casing as possible in order to enhance the insulation property. Even when the sealing material can be injected up to the vicinity of the upper surface of the casing, it is difficult to prevent the sealing material from running on the upper surface of the casing. 
       SUMMARY OF THE INVENTION 
       [0011]    The invention is to favorably solve the problem of the aforementioned background-art semiconductor device. An object of the invention is to provide a semiconductor device and a semiconductor device casing in which poor external appearance and lowering of adhesion to a cover can be prevented even when a sealing material is injected up to the vicinity of an upper surface of a casing. 
         [0012]    A semiconductor device and a semiconductor device casing are provided as follows in order to achieve the aforementioned object. 
         [0013]    The semiconductor device according to the invention is provided with: an insulating substrate; a semiconductor element which is mounted on the insulating substrate; a hollow casing which surrounds a peripheral edge of the insulating substrate to contain the semiconductor element therein; and a sealing material which is charged into the casing to seal the inside of the casing. In the semiconductor device according to the invention, the casing has a protrusion portion which protrudes partially from an upper surface of the casing. 
         [0014]    The semiconductor device casing according to the invention serves as a hollow casing which surrounds a peripheral edge of an insulating substrate to contain a semiconductor element therein and which is filled with a sealing material, the casing including: a protrusion portion which protrudes partially from an upper surface of the casing. 
         [0015]    In the semiconductor device according to the invention, the protrusion portion is formed partially in the upper surface of the casing and the sealing material can be prevented from running on the protrusion portion even when the sealing material runs on the upper surface of the casing. Accordingly, poor external appearance can be prevented. In addition, flatness of the upper surface of the casing can be maintained so that adhesion when the upper surface of the casing and a cover are adhesively bonded to each other can be secured sufficiently. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a sectional view of a power semiconductor module according to an embodiment of the invention; 
           [0017]      FIG. 2  is a plan view of the power semiconductor module in  FIG. 1 ; 
           [0018]      FIG. 3  is a sectional view of the power semiconductor module in  FIG. 1 ; 
           [0019]      FIG. 4  is a partially enlarged plan view of the power semiconductor module in  FIG. 1 ; 
           [0020]      FIG. 5  is a sectional view of the power semiconductor module provided with a cover; 
           [0021]      FIG. 6  is a plan view of a modification of the power semiconductor module according to the embodiment of the invention; 
           [0022]      FIG. 7  is a plan view of another modification of the power semiconductor module according to the embodiment of the invention; 
           [0023]      FIG. 8  is a partially enlarged plan view of the power semiconductor module in  FIG. 6 ; 
           [0024]      FIG. 9  is a partially enlarged plan view of the power semiconductor module in  FIG. 7 ; 
           [0025]      FIG. 10  is a plan view of a power semiconductor module as a reference example; 
           [0026]      FIG. 11  is a sectional view of a power semiconductor module according to the background art; 
           [0027]      FIG. 12  is a sectional view of the power semiconductor module in  FIG. 11 ; and 
           [0028]      FIG. 13  is a partially enlarged plan view of the power semiconductor module in  FIG. 11 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0029]    A semiconductor device and a semiconductor device casing according to an embodiment of the invention will be described specifically with reference to the drawings. 
         [0030]      FIG. 1  shows a sectional view of a power semiconductor module as the semiconductor device according to the embodiment of the invention. In a power semiconductor module  1  shown in  FIG. 1 , a semiconductor chip  3  is mounted on an insulating substrate  2 . The insulating substrate  2  includes a metal substrate  2   a,  an insulating plate  2   b  provided on the metal substrate  2   a,  and metallic foil  2   c  provided on the insulating plate  2   b.  The insulating plate  2   b  is made of a ceramics material such as silicon nitride, alumina or aluminum nitride, or an organic insulating material such as an epoxy resin. Specifically, the metallic foil  2   c  is, for example, copper foil. The metallic foil  2   c  is selectively formed on the insulating plate  2   b.  Thus, an electrode formed on a lower surface of the semiconductor chip  3  or a circuit pattern connected to leads which will be described later can be formed. 
         [0031]    The semiconductor chip  3  is bonded on a wiring pattern made of the metallic foil  2   c,  for example, by solder  4  serving as a joining material so that the semiconductor chip  3  is electrically bonded to the wiring pattern. For example, the semiconductor chip  3  is a diode chip or a transistor chip. An IGBT chip, an MOSFET chip etc. can be used as the transistor chip. The kind of the semiconductor chip  3  is however not particularly limited. In addition, silicon carbide (SiC), gallium nitride (GaN) in addition to single crystal silicon can be used as a substrate of the semiconductor chip  3 . An example in which the semiconductor chip  3  serves as a diode chip is described in  FIG. 1 . Incidentally, although one semiconductor chip  3  mounted on the metallic foil  2   c  of one insulating substrate  2  is illustrated in  FIG. 1 , two or more semiconductor chips  3  may be mounted on the metallic foil  2   c  of one insulating substrate  2 . 
         [0032]    In addition, a capacitor chip  5  is connected to the wiring pattern made of the metallic foil  2   c  in  FIG. 1 . 
         [0033]    A casing  6  is attached to a peripheral edge of the insulating substrate  2  mounted with the semiconductor chip  3 . Specifically, the casing  6  has a hollow (frame-like) substantially rectangular parallelepiped shape and is made of an insulation resin such as a PPS resin. In the casing  6 , an upper end portion  6   a  is formed as an opening and a sealing material  10  can be injected into a hollow space inside the casing  6  from the upper end portion  6   a.  A lower end portion  6   b  of the casing  6  is bonded to the metal substrate  2   a  and the insulating plate  2   b  of the insulating substrate  2  by an insulation adhesive agent  7 . Due to the bonding using the insulation adhesive agent  7 , insulation property between the insulating substrate  2  and the casing  6  can be secured and a gap between the insulating substrate  2  and the casing  6  can be eliminated so that the sealing material  10  can be prevented from leaking out from the gap. 
         [0034]    The casing  6  has a step portion  6   da  protruding inward from a heightwise intermediate part of an inner surface  6   d . With the provision of the step portion  6   da , the thickness of the casing  6  in the step portion  6   da  is larger than the thickness of the casing  6  in the upper end portion  6   a  of the casing  6 , i.e. larger than the distance between the inner surface  6   d  and an outer surface  6   e  of the casing  6 . One ends of leads  8  each made of a copper plate are exposed in and attached to the step portion  6   da . The one ends of the leads  8  exposed in the step portion  6   da  of the inner surface  6   d  of the casing  6  are electrically connected to the metallic foil  2   c  of the insulating substrate  2  or the electrode of the semiconductor chip  3  by bonding wires  9 . 
         [0035]    The leads  8  and the casing  6  are molded integrally by insert molding. The leads  8  extend in the thickness direction of the casing  6  and the other end portions of the leads  8  appear on the outside from the outer surface  6   e  of the casing  6 . 
         [0036]    The internal space of the casing  6  is filled with the sealing material  10  for sealing members such as the semiconductor chip  3 . Examples of the sealing material  10  include a gel-like sealing material including silicon as a main component and a sealing material made of a thermosetting resin such as an epoxy resin. Of these examples of the sealing material  10 , the sealing material made of the thermosetting resin is preferred because it has high insulation property and high heat-resistance property. In the embodiment, the thermosetting resin, more specifically, the epoxy resin is used as the sealing material  10 . Of course, it is not intended to exclude the gel-like sealing material. The sealing material  10  which is liquefied but not solidified is injected into the internal space from the opening of the upper end portion  6   a  of the casing  6  and heated. Thus, the sealing material  10  is solidified to seal the semiconductor chip  3 , the bonding wires  9 , etc. 
         [0037]    In order to secure insulation property of the bonding wires  9 , the sealing material  10  is injected so that the injection amount of the sealing material  10  can reach a height at which the sealing material  10  can cover the bonding wires  9  sufficiently, specifically, a height at which the bonding wires  9  are covered by at least 1 mm. On the other hand, in order to reduce the size and the thickness, the casing  6  has a height which can be made low as long as the insulation property is not hindered. Therefore, the sealing material  10  is injected with a predetermined amount with which the height inside the casing  6  reaches the vicinity of an upper surface  6   c  of the casing  6 . 
         [0038]    The power semiconductor module  1  according to the embodiment has protrusion portions  6   f  provided partially in the upper surface  6   c  of the casing  6  in order to prevent poor external appearance even when the sealing material  10  runs on the upper surface  6   c  of the casing  6  due to the flowing of the sealing material during injection of the sealing material  10  or due to vibration during conveyance after the injection. 
         [0039]    The planar shape of each protrusion portion  6   f  will be described with reference to a plan view of  FIG. 2 . Incidentally, description of the semiconductor chip  3 , the capacitor chip  5 , the bonding wires  9  and the sealing material  10  is omitted in  FIG. 2  in order to make it easy to understand the invention. In the power semiconductor module  1  according to the embodiment, two protrusion portions  6   f  are formed in each corner portion of the casing  6  separately and respectively in positions adjacent to the corner portion along a longitudinal direction and a lateral direction of the casing. The casing  6  has four corner portions so that eight protrusion portions  6   f  in total are formed. 
         [0040]    Functions and effects of the power semiconductor module  1  according to the embodiment will be described with reference to  FIG. 3  and  FIG. 4 .  FIG. 3  is a sectional view showing a situation when the sealing material  10  runs on the upper surface  6   c  of the casing  6 .  FIG. 4  is a planar partially schematic view showing the situation when the sealing material  10  runs on the upper surface  6   c  of the casing  6 . Even when the sealing material  10  runs on the upper surface  6   c  of the casing  6  during injection of the sealing material  10  or during conveyance before the injected sealing material  10  is solidified, the sealing material  10  goes around to side surfaces of the protrusion portions  6   f  but does not run on upper surfaces thereof. Accordingly, the external appearance of the power semiconductor module  1  according to the embodiment can be prevented from being poor. In addition, the working efficiency when the sealing material  10  is injected can be improved. 
         [0041]    Further, even when the sealing material  10  runs on the upper surface  6   c  of the casing  6 , the sealing material  10  can be prevented from running onto the protrusion portions  6   f . Accordingly, in the power semiconductor module  1  according to the embodiment, the adhesion when a cover  11  is adhesively fixed is not lowered, as shown in  FIG. 5  which is a perspective view when the cover  11  is attached. 
         [0042]    In the power semiconductor module  1  according to the embodiment, at least three protrusion portions  6   f  are required in order to be able to support the cover  11  flatly. Of course, when the dimension accuracy of the casing  6  and the accuracy of the height of each of the protrusion portions  6   f  are taken into consideration, the protrusion portions  6   f  are preferably provided adjacently to the corner portions and in the longitudinal direction and the lateral direction of the casing as shown in  FIG. 2 , in order to be able to surely support the cover  11 . 
         [0043]    In addition, it is desirable that each of the protrusion portions  6   f  is located in a position not interfering with a pressing tool when a bonding wire  9  is wire-bonded. 
         [0044]    The height of each protrusion portion  6   f  from the upper surface  6   c  of the casing  6  may be about 0.1 mm to about 1 mm which is high enough to prevent the sealing material  10  from running on the protrusion portion  6   f  even when the sealing material  10  runs on the upper surface. As a result of verification made by the present inventors, the thickness of the sealing material  10  in the upper surface  6   c  of the casing  6  was about 30 μm to about 80 μm when the sealing material  10  ran on the upper surface  6   c  of the casing  6 . Accordingly, it is possible to prevent the sealing material  10  from running on each protrusion portion  6   f  as long as the height of the protrusion portion  6   f  is not smaller than about 0.1 mm. On the other hand, when the height of each protrusion portion  6   f  exceeds about 1 mm, its contribution to reduction of the height of the casing  6  is dimmed. 
         [0045]    As shown in  FIG. 1 , the casing  6  has a shape in which the thickness of a lower portion below the step portion  6   da  is larger than the thickness of the upper end portion  6   a . Therefore, in the case where the casing  6  is molded by a mold and the temperature of the casing  6  is decreased to room temperature, the thermal contraction amount varies between the upper end portion  6   a  and the lower end portion  6   b  of the casing  6 . As a result, the casing  6  inevitably has a warped shape in which the longitudinal center becomes convex. Although depending on the dimensions of the casing, the warp amount in the center portion is larger by about 0.1 mm than that in longitudinal end portions of the casing. 
         [0046]    When such a warp of the casing  6  is taken into consideration, the protrusion portions  6   f  are preferably provided in the vicinities of the longitudinal end portions of the upper surface  6   c  of the casing  6  so that the cover  11  can be supported flatly on the casing  6  easily and the adhesion can be improved. 
         [0047]    In addition, when the warp of the casing  6  is taken into consideration, the height of each of the protrusion portions  6   f  provided in the vicinities of the longitudinal end portions of the upper surface  6   c  of the casing  6  is preferably made relatively larger than the height of each of the protrusion portions  6   f  provided near to the longitudinal center portion of the upper surface  6   c  of the casing  6  so that the cover  11  can be supported flatly on the casing  6  easily and the adhesion can be improved. 
         [0048]    When a not-shown flat plate is placed on the casing  6  in place of the cover  11 , the power semiconductor module  1  according to the embodiment can be used for mounting and laminating other components on the flat plate. When other components are mounted and laminated on the flat plate, high density mounting can be achieved. In the case where the flat plate is placed on the casing  6  in the background-art power semiconductor module, it is difficult to secure flatness of the flat plate and parallelism with the upper surface  6   c  of the casing  6  when the sealing material  10  runs on the upper surface  6   c  of the casing  6 . On the other hand, the power semiconductor module  1  according to the embodiment has an effect that flatness of the flat plate and parallelism with the upper surface  6   c  of the casing  6  can be secured because the flat plate is supported on the protrusion portions  6   f  even when the sealing material  10  runs on the upper surface  6   c  of the casing  6 . 
         [0049]    In addition, the power semiconductor module  1  in which the flat plate is placed on the casing  6  may be used for a structure in which a spring is provided above the flat plate and the metal substrate  2   a  of the power semiconductor module  1  is pressed against and fixed to radiation fins making contact with the metal substrate  2   a  by the urging force of the spring so that an excellent contact property can be secured between the metal substrate  2   a  and the radiation fins to thereby improve the heat radiation. Also in this case, the power semiconductor module  1  has an effect that flatness of the flat plate and parallelism with the upper surface  6   c  of the casing  6  can be secured. 
         [0050]    Modifications of the protrusion portions  6   f  of the casing  6  will be described with reference to the plan views of  FIG. 6  and  FIG. 7 . 
         [0051]    In a semiconductor device  21  according to the modification shown in  FIG. 6 , an upper surface  6   c  of a casing  6  is halved in the thickness direction so that a part on the side of an outer surface  6   e  whose height is larger than the height of a part on the side of an inner surface  6   d  can serve as a protrusion portion  6   g.  The protrusion portion  6   g  is not formed in a longitudinal center portion of the upper surface  6   c  of the casing  6 . Since the protrusion portion  6   g  is not formed in the longitudinal center portion of the upper surface  6   c  of the casing  6 , it becomes easy to support a cover  11  flatly against the aforementioned warp of the casing  6  so that the adhesion can be improved. 
         [0052]    In a semiconductor device  31  according to the modification shown in  FIG. 7 , protrusion portions  6   h  are formed substantially in the same positions in an upper surface  6   c  of a casing  6  as the protrusion portions  6   f  shown in  FIG. 2  but the thickness of each of the protrusion portions  6   h  is halved in the thickness direction. The protrusion portions  6   h  are formed on the side of an outer surface  6   e  of the casing  6 . 
         [0053]    The protrusion portion  6   g  shown in  FIG. 6  and the protrusion portions  6   h  shown in  FIG. 7  are different in protrusion shape from the protrusion portions  6   f  shown in  FIG. 2  but the height of each protrusion in the protrusion portion  6   g  and the protrusion portions  6   h  may be made equal to the height of each of the protrusion portions  6   f  shown in  FIG. 2 . In addition, when a warp of the casing  6  is taken into consideration, the protrusion portion  6   g  or the protrusion portions  6   h  provided in the vicinities of longitudinal end portions of the upper surface  6   c  of the casing  6  may be made relatively higher than the protrusion portion  6   g  or the protrusion portions  6   h  provided near to a longitudinal center portion of the upper surface  6   c  of the casing  6 . 
         [0054]    Functions and effects of the modification shown in  FIG. 6  will be described with reference to  FIG. 8 . Functions and effects of the modification shown in  FIG. 7  will be described with reference to  FIG. 9 .  FIG. 8  and  FIG. 9  are planar schematic views showing a situation when a sealing material  10  runs on the upper surface  6   c  of the casing  6  in the case of these modifications. 
         [0055]    As apparent from  FIG. 8  or  FIG. 9 , the thickness of the protrusion portion  6   g  or the protrusion portions  6   h  is thin and comparable to the thickness obtained by dividing the thickness of the upper surface  6   c  of the casing  6 . Accordingly, even when the sealing material  10  runs on the upper surface  6   c  of the casing  6  during injection of the sealing material  10  or during conveyance before the injected sealing material  10  is solidified, the sealing material  10  goes around to side surfaces of the protrusion portion  6   g  or the protrusion portions  6   h  but does not run on an upper surface or upper surfaces thereof. Accordingly, external appearance of the power semiconductor module  1  according to the embodiment can be prevented from being poor. In addition, the working efficiency when the sealing material  10  is injected can be improved. 
         [0056]    Further, the sealing material  10  can be prevented from running on the protrusion portion  6   g  or the protrusion portions  6   h  even when the sealing material  10  runs on the upper surface  6   c  of the casing  6 . Accordingly, the adhesion when the cover  11  is adhesively fixed can be prevented from being lowered. 
         [0057]    A reference example of a protrusion portion of a casing  6  will be described with reference to  FIG. 10  which is a plan view. 
         [0058]    A power semiconductor module  111  in the reference example shown in  FIG. 10  has a protrusion portion  106   g  similar to that in the modification shown in  FIG. 6 . The protrusion portion  106   g  is formed as follows. That is, the upper surface  6   c  of the casing  6  is halved in the thickness direction so that a part on the side of an outer surface  6   e  whose height is larger than the height of a part on the side of an inner surface  6   d  can serve as the protrusion portion  106   g.  The protrusion portion  106   g  is different from the protrusion portion  6   g  shown in  FIG. 6  in the point that the protrusion portion  106   g  is formed all over the periphery on the upper surface  6   c  of the casing  6 . The protrusion portion  106   g  in the reference example shown in  FIG. 10  can hardly support the cover  11  flatly against the casing  6  warped as described above and can achieve less improvement of the adhesion, in comparison with the modification shown in  FIG. 6 . 
         [0059]    A power semiconductor module  101  according to the background art will be described as a comparative example with reference to a sectional view shown in  FIG. 11 . In  FIG. 11 , incidentally, the same members as those in the power semiconductor module  1  shown in  FIG. 1  are referred to by the same numerals correspondingly and duplicate description thereof will be omitted below. 
         [0060]    The power semiconductor module  101  according to the background art shown in  FIG. 11  is different from the power semiconductor module  1  according to the embodiment of the invention shown in  FIG. 1  in the point that a casing  106  is attached to a peripheral edge of an insulating substrate  2  mounted with a semiconductor chip  3 . The casing  106  has the same configuration as the casing  6  of the power semiconductor module  1  according to the embodiment of the invention shown in  FIG. 1 , except that the casing  106  does not have the protrusion portions  6   f  formed in the casing  6 . 
         [0061]      FIG. 12  shows a sectional view of a situation in which a sealing material  10  injected into an internal space of the casing  106  of the semiconductor module  101  according to the background art runs on an upper surface of the casing  106 .  FIG. 13  shows a planar partial schematic view of  FIG. 12 . When the sealing material  10  runs on the upper surface of the casing  106  as shown in  FIGS. 12 and 13 , a cover  11  which is placed on the casing  106  cannot be supported flatly. Thus, the adhesion when the cover  11  is adhesively fixed is deteriorated and external appearance is poor. 
         [0062]    It will be apparent to one skilled in the art that the manner of making and using the claimed invention has been adequately disclosed in the above-written description of the exemplary embodiments taken together with the drawings. Furthermore, the foregoing description of the embodiments according to the invention is provided for illustration only, and not for limiting the invention as defined by the appended claims and their equivalents. 
         [0063]    It will be understood that the above description of the exemplary embodiments of the invention are susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.