Abstract:
A semiconductor power module that can be downsized and is a malfunction-resistant is provided. In a semiconductor unit, a first circuit with a first semiconductor chip mounted on a first lead frame and a second circuit with a second semiconductor chip mounted on a second lead frame are sealed in a resin package. The first lead frame and the second lead frame are arranged to be overlapped. According to this arrangement, physical dimensions can be reduced as compared to a conventional semiconductor module in which no practical overlap exists. In addition, since the module is packaged using resin, the noise resistance of the semiconductor unit can be improved and malfunction can be still more reduced.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a structure of semiconductor power module. 
     2. Description of the Background Art 
     FIGS. 9A and 9B are diagrams showing a structure of conventional semiconductor module  90 . FIG. 9A shows a cross-sectional view of semiconductor module  90 . FIG. 9B is a top view of semiconductor module  90 . 
     Referring now to FIGS. 9A and 9B, the configuration of semiconductor module  90  is discussed. Semiconductor module  90  includes a main circuit formed by left-side lead frame  1  equipped with power element  2  and a control circuit formed by right-side lead frame  1  equipped with control element  3 . The main circuit is driven by the control circuit. Power element  2  is connected onto wiring formed by lead frame  1  by soldering. Control element  3  is also connected onto the wiring. Lead frame  1 , power element  2 , and control element  3  are electrically connected to one another by wire  4 . A semiconductor power module is formed by molding power element  2  and control element  3  of this kind of semiconductor module  90  with mold resin  5 . Part of lead frame  1  is exposed to the outside from mold resin  5 . This section is used as electrodes to electrically connect to the outside, that is, main circuit terminal and control circuit terminal. 
     As understood from FIG. 9A, left-side lead frame  1  that forms the main circuit and right-side lead frame  1  that forms the control circuit are arranged to be deviated in the vertical direction with respect to the mounted surfaces of power element  2  and control element  3 . The main circuit and lead frame  1  to which the main circuit is arranged are located on the same plane. Similarly, the control circuit and lead frame  1  to which the control circuit is arranged are located on the same plane. 
     Referring now to FIG. 9B, lead frame  1  of conventional semiconductor module  90  can be obtained by processing such as generally pressing a sheet of plate-form metal, and forms circuit wiring necessary for main circuit and control circuit, respectively. Wiring can be practically arranged on the same plane, since, as clear from the figure, all the wiring of lead frame  1  is formed without three-dimensionally intersecting one another,. 
     Because conventional semiconductor power modules have all the circuits composed with planate lead frames as well as practically and two-dimensionally in each circuit wiring of the main circuit and the control circuit, the physical dimensions must be upsized. This prevents downsizing semiconductor power modules, and consequently, it is unable to downsize the unit itself as well as to achieve large-scale integration. 
     In addition, since wiring inductance is increased by practically and two-dimensionally arranging circuit wiring, semiconductor module  90  may malfunction. Furthermore, because power element  2  of the main circuit section is allowed to radiate heat via lead frame  1  only, heat interferences occur between adjacent elements due to residual heat capacity of mold resin  5 . 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a semiconductor power module which can be downsized and which is malfunction-resistant. 
     A semiconductor unit according to the present invention includes the first circuit with the first semiconductor chip carried on the first lead frame and the second circuit with the second semiconductor chip carried on the second lead frame, which are sealed in a resin package. The first lead frame and the second lead frame are arranged to be overlapped. By arranging them overlapped, the physical dimensions of the unit can be reduced. 
     Another semiconductor unit according to the present invention includes the first circuit with the first three semiconductor chips carried on the first lead frame; the second circuit with the second three semiconductor chips, carried on the second lead frame, for controlling the corresponding first three semiconductor chips; the third circuit with third three semiconductor chips carried on the third lead frame; and the fourth circuit with fourth three semiconductor chips, carried on the fourth lead frame, for controlling the corresponding third three semiconductor chips, which are sealed in resin packages. Each of the first three semiconductor chips and each of the third three semiconductor chips are connected in series, respectively, and form a three-phase inverter as a switching element. The first lead frame and the third lead frame are arranged to be overlapped. Because lead frames of semiconductor chips connected in series which forms the three-phase inverter are arranged to be overlapped, the physical dimensions can be reduced. In addition, wiring inductance can be reduced. 
     Still another semiconductor unit according to the present invention includes the first circuit carrying first two semiconductor chips on the first lead frame and the second circuit carrying the second semiconductor chip on the second lead frame, which are sealed inside a resin package. The first lead frame is bent inside the resin package to form an overlap and first two semiconductor chips are arranged opposite to each other. Because the lead frame is formed by bending, no wiring to lead frames is required and the number of wire bonding can be reduced, and consequently, reliability related to defective wire bonding can be improved. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other object and features of the present invention will become clear from the following description taken in conjunction with the preferred embodiments thereof with reference to the accompanying drawings, in which: 
     FIG. 1 is a top view of a two-dimensional configuration of a main circuit according to embodiment 1; 
     FIG. 2 is a top view of a two-dimensional configuration of a control circuit according to embodiment 1; 
     FIGS. 3A and 3B are a cross-sectional view and a top view of a semiconductor power module according to embodiment 1, respectively; 
     FIG. 4 is a top view of a two-dimensional configuration of a power module on the P side according to embodiment 2; 
     FIG. 5 is a top view of a two-dimensional configuration of a power module on the N side according to embodiment 2; 
     FIGS. 6A and 6B are a cross-sectional view and a top view of a semiconductor power module according to embodiment 2, respectively; 
     FIG. 7 is a cross-sectional view of semiconductor power module according to embodiment 3; 
     FIG. 8 is a cross-sectional view of semiconductor power module according to embodiment 4; and 
     FIGS. 9A and 9B are diagrams of a conventional semiconductor module. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings attached, preferred embodiments of the present invention will be described as follows. 
     (Embodiment 1) 
     In a semiconductor power module according to the present invention, a main circuit and a control circuit for controlling the operation of the main circuit are incorporated in one device. The main circuit contains a power element which is a semiconductor element for controlling electric power. In addition, the control circuit contains a control element which is a semiconductor element for controlling the operation of the main circuit. The semiconductor power module is primarily applied to devices for controlling motors, etc., such as inverter devices. 
     In embodiment 1, description will be made on semiconductor power module  30  (FIGS. 3A and 3B) in which a lead frame of main circuit  10  shown in FIG. 1 and a lead frame of control circuit  20  shown in FIG. 2 are overlapped, that is, laminated. Main circuit  10 , control circuit  20 , and semiconductor power module  30  will be described successively. Note that, in the drawings referred to as follows, reference characters are not assigned to all the elements. Components designated as reference characters are merely examples and similar components with no reference characters designated can be handled in the same manner. 
     FIG. 1 is a top view showing a two-dimensional configuration of main circuit  10 . Main circuit  10  includes lead frames  1   a ,  1   b , power element  2  mounted on lead frame  1   a , and wire  4   a  that connects power element  2  and lead frame  1   b . Lead frames  1   a  and  1   b  form wiring of main circuit  10 . Power element  2  is a semiconductor chip and is electrically connected on wiring formed by lead frame  1   a  by soldering. Power element  2  is, for example, an IGBT, and a flywheel diode. Main circuit  10  has a pattern formed by one frame. Consequently, it can be handled two-dimensionally. 
     FIG. 2 is a top view showing a two-dimensional configuration of control circuit  20 . Control circuit  20  includes lead frame  1   c , control element  3 , and wire  4   b . Lead frame  1   c  forms wiring of control circuit  20 . Control element  3  is also a semiconductor chip and is electrically connected to wiring formed by lead frame  1   c  by soldering. Control element  3  is an element for driving main circuit  10 . Since control circuit  20  has also a pattern formed by one frame, it can be handled two-dimensionally. 
     FIGS. 3A and 3B are diagrams showing semiconductor power module  30  constructed by laminating main circuit  10  and control circuit  20 . FIG. 3A is a cross-sectional view of semiconductor power module  30 . FIG. 3B is a top view of semiconductor power module  30 . 
     One of the primary features of the present invention lies in laminating to arrange main circuit  10  (FIG. 1) and control circuit  20  (FIG.  2 ). To describe the feature more specifically, semiconductor power module  30  is three-dimensionally arranged by superimposing a surface on which component(s) of control circuit  20  are formed (FIG. 2) (hereinafter called the “control circuit  20 -formed-surface”) over the surface on which component(s) of main circuit  10  (FIG. 1) are formed (hereinafter called the “main circuit  10 -formed-surface”). According to FIG. 3A, it can be understood that lead frame  1   a  of main circuit  10  and lead frame  1   b  of control circuit  20  are arranged to be overlapped. This means that power element  2  on the main circuit  10 -formed-surface and control element  3  on the control circuit  20 -formed-surface are arranged to be overlapped. By laminating to form main circuit  10  and control circuit  20 , the physical dimensions can be reduced, as shown in FIG. 3B, as compared to conventional semiconductor module  90  (FIG.  9 ( b )) with overlaps practically not existing. Note that the overlap is carried out on the lead frame and is not related to the circuit configuration. 
     Semiconductor power module  30  is obtained by molding laminated main circuit  10  and control circuit  20  by mold resin  5 . On the rear surface of lead frame  1   a  equipped with power element  2 , the thickness of mold resin  5  is B in FIG. 3A, whereas the thickness of mold resin on the rear surface of lead frame  1   c  equipped with control element  3  is C in FIG.  3 A. Increasing thickness of mold resin on the rear surface of lead frame  1   c  can improve noise resistance of semiconductor power module  30  and can still more reduce malfunction. 
     In order to secure electrical connection with the outside, part of lead frame  1   a  of main circuit  10  and part of lead frame  1   c  of control circuit  20  are extended to the outside of mold resin  5  and is bent at right angle upwards in the midway. Via these sections, semiconductor power module  30  is connected, for example, to an external power source and can control the amount of electric power supplied from the power source. 
     On the other hand, electrical connections inside semiconductor power module  30  can be secured between lead frame  1   b  of main circuit  10  and lead frame  1   c  of control circuit  20 . The contact surface is called parting surface A where lead frames  1   b  and  1   c  are exposed to the outside from mold resin  5 . Parting surface A is formed to align the surface of lead frame  1   c  to the surface of lead frame  1   b . Two-dimensionally aligning positions of lead frames  1   c  and  1   b  can simplify molding process of mold resin  5  as well as simplifying the construction of resin molds used. 
     Portions that can be connected from the viewpoint of circuit may be overlapped vertically and they may be connected electrically using wires. However, it is much easier to process and to achieve higher reliability when components of main circuit  10  and control circuit  20  are connected externally than when they are connected internally before sealing by mold resin  5 . Consequently, it is desirable to connect them after the mold resin  5  working process. 
     (Embodiment 2) 
     In embodiment 2, description will be made on a semiconductor power module having two power modules, each of which includes a main circuit and a control circuit for controlling the operation of the main circuit. More specifically, semiconductor power module  60  (FIGS. 6A and 6B) has power module  40  on P side, shown in FIG. 4, and power module  50  on N side, shown in FIG. 5, are overlapped (that is, laminated). 
     FIG. 4 is a top view showing a two-dimensional configuration of power module  40  on the P side. Power module  40  includes main circuit  10  (FIG. 1) and control circuit  20  (FIG. 2) explained in embodiment 1. That is, power module  40  includes lead frame  1   a , power element  2   a , and wire  4   a  that form the main circuit on the P side, and lead frame  1   c  and control element  3   a  that form the control circuit on the P side. Power element  2   a  and lead frame  1   c  are electrically connected by wire  4   a . Power module  40  has patterns formed on single frame. Consequently, it can be handled two-dimensionally. 
     FIG. 5 is a top view showing a two-dimensional configuration of power module  50  on the N side. Power module  50  also includes main circuit  10  (FIG. 1) and control circuit  20  (FIG. 2) described in embodiment 1. That is, power module  50  is equipped with lead frame  1   b , power element  2   b , and wire  4   b  that form the main circuit on the N side and lead frame  1   d  and control element  3   b  that form the control circuit on the N side. Power element  2   b  and lead frame  1   d  are electrically connected by wire  4   b . Since power module  50  has patterns also formed on single frame, it can be handled two-dimensionally. 
     The lead frames, power elements, and control elements used for power modules  40 ,  50  are the same as those explained in embodiment 1. Consequently, their descriptions will be omitted. 
     FIGS. 6A and 6B shows semiconductor module  60  formed by laminating P-side power module  40  (FIG. 4) and N-side power module  50  (FIG.  5 ). FIG. 6A is a cross-sectional view of semiconductor power module  60 . FIG. 6B is a top view of semiconductor power module  60 . Semiconductor power module  60  can be obtained by molding laminated power module  40  (FIG. 4) and power module  50  (FIG. 5) by mold resin  5 . 
     Semiconductor power module  60  can be formed as, for example, a three-phase inverter circuit. As clear from FIG.  4  and FIG. 5, to each of the main circuits of P-side power module  40  and N-side power module  50 , three sets of power elements  2   a  and  2   b  are mounted. Power element  2   a  operates as a P-side switching semiconductor chip. Power element  2   b  operates as an N-side switching semiconductor chip. According to this arrangement, three sets of one P-side switching element  2   a  and one N-side switching element  2   b  required for a 3-phase inverter circuit can be obtained. Note that, switching element  2   a  and switching element  2   b  are connected in series but each pair is connected in parallel. 
     According to FIG. 6A, it is understood that P-side power module  40  (FIG. 4) and N-side power module  50  (FIG. 5) are arranged to be overlapped. Furthermore, the power element or the control element is arranged to be overlapped facing each other. In other words, the power element or the control element equipped to the lead frame is located to the inner side of the mold resin  5  than the lead frame, and the rear surface of the frame is arranged to face to the outside. By installing the power element, which is a heat generating source, to be divided vertically and securing the radiation passage separately, the radiation efficiency can be improved. Consequently, heat interference between adjoining elements can be reduced. In addition, by forming to laminate power module  40  and power module  50 , the physical dimensions can be reduced as shown in FIG.  6 B. 
     In order to secure electrical connection with outside devices, part of lead frame  1   a  of power module  40  and part of lead frame  1   b  of power module  50  are extended to the outside of mold resin  5  and are bent upwards at right angles in the midway. As clear from FIG. 6B, P-side lead frame  1   a  of the main circuit and N-side lead frame  1   b  are arranged to be adjacent to each other. According to this extremely simple configuration of simply specifying the external lead arrangement, wiring inductance can be reduced. This applies to lead frames  1   c  and  1   d . Via these sections, semiconductor power module  60  is connected to, for example, external power source and can control amount of electric power supplied from the power source. 
     On the other hand, electrical connection inside semiconductor power module  60  is secured between lead frame  1   a  of power module  40  and lead frame  1   b  of power module  50 . It is also secured between lead frame  1   c  of power module  40  and lead frame  1   d  of power module  50 . The connection surfaces are two parting surfaces A where lead frames  1   b  and  1   c  are exposed from mold resin  5  to the outside. Parting surface A is formed in such a manner that the surface of lead frame  1   a  is aligned to the surface of lead frame  1   b  and the surface of lead frame  1   c  is aligned to the surface of lead frame  1   d . By connecting the position of each lead frame on the P side and on the N side to be aligned two-dimensionally, the molding process of mold resin  5  can be simplified and the construction of resin molds used can also be simplified. 
     (Embodiment 3) 
     Embodiment 3 describes a semiconductor power module in which a two-dimensionally formed main circuit is bent into a U-letter form. 
     FIG. 7 is a cross-sectional view of semiconductor power module  70  according to embodiment 3. Semiconductor power module  70  has main circuit  72  and control circuit  74  molded with mold resin  5 . Main circuit  72  is formed by means of lead frame  1   a , to which power elements  2 - 1  and  2 - 2  are installed. Lead frame  1   a  is arranged to be bent in a U-letter form inside mold resin  5 . Power elements  2 - 1  and  2 - 2  are bent in the condition to be mounted to the inner surface of lead frame  1   a  and at the same time with the rear surface of lead frame  1   a  directed to the outside. This can be obtained by molding power elements with mold resin  5  in the bent condition. Note that two power elements  2 - 1 ,  2 - 2  are identified but main circuit  72  is practically same as main circuit  10  (FIG.  1 ). Consequently, specific description on main circuit  72  is omitted. 
     On the other hand, control circuit  74  is formed by the use of lead frame  1   c , to which control element  3  is installed. Control circuit  74  is practically the same as control circuit  20  (FIG.  2 ). Consequently, specific description on control circuit  74  is omitted. 
     Electrical connections inside semiconductor power module  70 , that is, electrical connections between main circuit  72  and control circuit  74  are secured by wire  4 . Wire  4  is connected to lead frame  1   c  via a clearance between patterns of lead frame  1   a  or bypassed to avoid an edge section of lead frame  1   a . Needless to say, molding by mold resin  5  is carried out after wire  4  is installed. 
     Since inside semiconductor power module  70 , one piece of lead frame  1   a  is arranged to be bent inside mold resin  5 , the physical dimensions can be reduced and wiring inductance can be reduced. By installing the power element, which is a heat generating source, to be divided vertically and securing the radiation passage separately, the radiation efficiency can be improved. Consequently, heat interference between adjoining elements can be reduced. In addition, since the number of wire bonding can be reduced, reliability related to wire bonding failure can be improved. 
     Further, on the rear surface of lead frame  1   a  to which power element  2  is mounted, the thickness of mold resin  5  is B in FIG. 7, whereas on the mold resin thickness on the rear surface of lead frame  1   c  to which control element  3  is mounted is C in FIG.  7 . By increasing mold resin on the rear surface of lead frame  1   c , noise resistance of semiconductor power module  70  can be improved and malfunction can be further more reduced. 
     (Embodiment 4) 
     In semiconductor module  60  shown in FIG. 6A, lead frame  1   a  on one side is arranged separately from lead frame  1   c . In addition, lead frame  1   b  on the other side is also arranged separately from lead frame  1   d.    
     In embodiment 4, lead frames  1   a  and  1   c  on one side are brought in contact to each other and in addition lead frames  1   b  and  1   d  on the other side are also arranged to be in contact to each other. The contact is made by physical connections. By the way, electrical connections may be secured, and if it is not necessary, they may be brought into contact in the insulated condition. 
     FIG. 8 is a cross-sectional view of semiconductor power module  80  according to embodiment 4. As described above, the difference between semiconductor power module  80  and semiconductor power module  60  (FIG. 6A) lies in the configuration and positional relationship of lead frames  1   a ,  1   b ,  1   c , and  1   d . Thus, only the difference is described hereinafter. Because each component of semiconductor power module  80  is the same as that of semiconductor power module  60 , the description on them is omitted. As is the case described referring to FIG. 6, the 3-phase inverter can also be formed by semiconductor power module  80 . 
     In semiconductor power module  80 , some of lead frame  1   c  and  1   d  are extended more than those of semiconductor power module  60 . They are arranged with the extended surface of lead frame  1   c  overlapped to the outside surface of lead frame  1   a . In the same manner, they are arranged with the extended surface of lead frame  1   d  overlapped to the outside surface of lead frame  1   b . Overlapping lead frame  1   a  of power element  2   a  to lead frame  1   c  of control element  3   a  and overlapping lead frame  1   b  of power element  2   b  to lead frame  1   d  of control element  3   b  enables heat generated in the main circuit or the control circuit to be radiated from the control circuit or the main circuit, and the heat radiation efficiency can be improved. It is needless to say that effects by semiconductor power module  60  can be obtained as they are. 
     The description on embodiments of the present invention has been made. In the description and drawings referred to in the above, the semiconductor power module is a package, the whole of which is molded with resin except part of lead frames. However, the back surface of the lead frame to which a heat generating source of power element, control element, etc. may be exposed from the package. Because with this configuration, heat can be released directly to the atmosphere, the heat radiation efficiency can be improved. 
     It will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.