Abstract:
A power module package structure is disclosed. The control circuits are fabricated on a circuit plate, instead of fabricating them directly on a main substrate. The fabrication cost is reduced because the size of the substrate is shrunk. Furthermore, the power chips are placed on a material with high thermal conductivity. The heat produced from the power chips can be transmitted quickly. Thus, the reliability of the power module package can be improved.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention generally relates to a kind of power module package structure. In particular, the present invention relates to a kind of power module package with characteristics of high heat dispersion efficiency and high integration.  
         [0003]     2. Description of the Prior Art  
         [0004]     Increasing device complexity but shrinking size is common trend of the electrical product. Therefore, in addition to the shrinking size of the electrical product, how to put the most of electrical elements and wire bonds into the semiconductor package of the electrical product is very important. However, lots of heat is produced by the package structure with the high integration of electrical elements and wire bonds, when the electrical products are working. Especially for the power module, the heat affects the life and performance of the electrical product. Therefore, it is an important subject to improve the heat dispersion of the package structure with high integration of electrical elements and wire bonds.  
         [0005]     Referring to  FIG. 1 , it is a cross-sectional diagram illustrating a conventional package structure of a power module. The package structure includes a high thermal conduction substrate  100 , which is made of a high polymer isolating layer and an aluminum foil layer. All circuits of the package structure (not shown in the diagram) are fabricated on the substrate  100 . The power element  110   a -the control element  110   b  and other elements  110   c  are disposed on the substrate  100 . A lead frame  121 - 122  is suspended above the substrate  100  and several wire bonds  111 - 112 - 113  are formed to electrically connect the elements  110   a - 110   b - 110   c  and the circuits on the substrate  100 . Then the elements and the circuits on the substrate  100  are encapsulated by package material, like resin, or molding but not the leads of lead frame  121 - 122 . The advantages of this power module package structure are simple and easy to manufacture. In this power module package structure, all elements  110   a - 110   b - 110   c  and all circuit are disposed on the substrate  100 , and therefore the density of the circuits can not to be increased. So this package structure needs a bigger substrate, and it&#39;s cost is higher because it&#39;s bigger substrate. The heat which is produced by the power element  110   a  is transmitted to the heat sink through the substrate. And the heat is transmitted from the power element to the substrate by the adhesive between the substrate and the power element. Therefore, even the substrate is made of a high thermal conduction material but the large number of the heat can be transpired immediately.  
         [0006]     Referring to  FIG. 2 , it is a cross-sectional diagram illustrating another conventional package structure of a power module. The power module package structure is similar to the package structure illustrated in  FIG. 1 . The structure also includes a high thermal conduction substrate  100 , which is made of a high polymer isolating layer and an aluminum foil layer, with all circuits on it. The power element  110   a -the control element  110   b  and other elements  110   c  are also disposed on the substrate  100 . A lead frame  121 - 122  is also suspended above the substrate  100  and several wire bonds  111 - 112 - 113  are also formed to electrically connect the elements  110   a - 110   b - 110   c  and the circuits on the substrate  100 . And the elements and the circuits on the substrate  100  are also encapsulated by package material, like resin, or molding but not the leads of lead frame  121 - 122 . The difference between the package structure illustrated in  FIG. 1  and  FIG. 2  is that there is a metal plate  200  connected to the rear of the substrate  100  in the structure illustrated in  FIG. 2 . The advantages of this power module package structure are simple and easy to manufacture. And another advantage is that lots of heat can be immediately transmit by the metal plate  200  because it&#39;s high thermal conduction. Although there are many advantages of this package structure in  FIG. 2 , but the density of the circuits still can not be increased because all circuits are fabricated on the substrate  100 . So the cost of the power module package still can be reduced.  
         [0007]     Referring to  FIG. 3 , it is a cross-sectional diagram illustrating yet another conventional package structure of a power module. The package structure also includes a high thermal conduction substrate  100  which is made of a high polymer isolating layer and an aluminum foil layer. But the package structure in  FIG. 3  is different from the package structure in  FIG. 1  and in  FIG. 2 . In the power module illustrated in  FIG. 3 , all of the power element  110   a  and control element  110   b  are disposed on the lead frame by soldering or other method. The lead frame  121  and  122  are suspended above the substrate  100  but separated to each other without connecting. There are several wire bonds  111 - 112  and etc. formed by wire bonding to electrically connect the elements  110   a - 110   b , lead frame  121 - 122  and the circuits on it. And the elements and the circuits on the substrate  100  are encapsulated by package material, like resin, or molding but not the leads of lead frame  121 - 122 . The advantages of the power module package structure illustrated are simple and easy to manufacture. The density and accuracy of the circuits and package structure are limited because the circuits are fabricated on the lead frame. The heat produced by the power element  110   a  in power module is transmitted from the lead frame to substrate  110  through the packaging material. But the heat is not transmitted very well. It is because the heat is still transmitted from substrate to heat sink through the adhesive, and the adhesive is not a good thermal conductor.  
         [0008]     Therefore, it is an important subject that how to improve the density of the package structure and to cost down. And it is another subject that how to solve the question of bad thermal conduction caused by the power element and the package structure with high density.  
       SUMMARY OF THE INVENTION  
       [0009]     In view of foregoing mentioned problems, one object of the present invention is to provide a power module package structure with a stacking structure and a good path for heat transmitting. The stacking structure is formed by stacking the circuit plate on the lead frame. And all circuits in the power module package structure are fabricated on the circuit plate. Therefore, the package structure improves the heat transmitting and the density of the circuits caused by the package structure in prior art.  
         [0010]     Another object of the present invention is to provide a power module package structure with a circuit plate on which all circuit are fabricated thereon instead of on the substrate, as well as a stacking structure for increasing the density of the circuits and shrinking the size of the package. And the stacking structure is formed by stacking the circuit plate on part of the lead frame. Therefore, the size of the substrate is shrunk and the cost is reduced.  
         [0011]     Yet another object of the present invention is to provide a power module package structure in which the power elements are disposed on a high thermal conduction material on the substrate or disposed on a high thermal conduction substrate directly. The heat produced by the power elements is transmitted from high thermal conduction material to outside through the substrate, but not the package material with low thermal conduction. So the rate of thermal conduction of this power module package structure is better than the rate of thermal conduction of the conventional power module package structure. The power module package structure can bear the passing of the heat produced by the passing of lots of electric currents in short time because its high rate of thermal conduction. So the power module will not be broken down by the heat.  
         [0012]     Accordingly, one embodiment of the present invention provides a power module package structure with high density and high thermal condition. The package structure comprises a substrate with high thermal condition, and a lead frame is disposed on topside of the substrate. A circuit plate with all circuits of the power module is disposed on the part of the lead frame to form a stacking structure. There are one or several control elements disposed on the circuit plate. And several power elements are disposed on the high thermal conduction material like lead frame or metal block on the substrate, or are directly disposed on the substrate with high thermal conduction. There is a good heat transmitting path to be formed by both of the two ways. And several wire bonds are formed to connect to the circuit plate and the lead frame, the circuit plate and the power elements, the power elements and the lead frame. Part of the substrate-all elements-lead frame and circuit plate are encapsulated by a package material.  
         [0013]     According to foregoing package structure, the size of the substrate become smaller because the circuits are fabricated on the circuit plate in stead of on the substrate, and the stacking structure formed by the lead frame and the substrate. By this way, the size of the package structure can be shrunk effectively. The power elements are disposed on the high thermal conduction substrate or on the high thermal material on substrate to form a good thermal condition path. Therefore, the heat produced by the power elements is transmitted to outside or heat sink effectively and quickly. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:  
         [0015]      FIG. 1  to  FIG. 3  are cross-sectional diagrams illustrating three kinds of conventional power module package structure; and  
         [0016]      FIG. 4A  to  FIG. 4B  are cross-sectional diagrams illustrating a power module package structure in which circuit plate and all elements are disposed on the lead frame in accordance with another embodiment of the present invention;  
         [0017]      FIG. 5A  to  FIG. 5C  are cross-sectional diagrams illustrating a power module package structure with many kinds of the lead frame in accordance with another embodiment of the present invention;  
         [0018]      FIG. 6  is a cross-sectional diagram illustrating a power module package structure in which lead frame is disposed on the circuit plate in accordance with another embodiment of the present invention;  
         [0019]      FIG. 7  is a cross-sectional diagram illustrating a power module package structure in which power elements are disposed on the substrate in accordance with another embodiment of the present invention; and  
         [0020]      FIG. 8  is a cross-sectional diagram illustrating a power module package structure in which power elements are disposed on the high thermal conduction material in accordance with another embodiment of the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0021]     Referring to  FIG. 4A , it is a cross-sectional diagram illustrating a power module package structure in accordance with one embodiment of the present invention. The package structure includes a substrate  400  with high thermal conduction and good isolation. There are a topside  400   a  and a backside  400   b  opposite to the topside  400   a  on the substrate  400 . A lead frame  420  with several leads  421 - 422  and etc.(not show in the diagram) is disposed on the topside  400   a  of the substrate  400  by the second side  420   b  of the lead frame. A circuit plate  425  is disposed on the first side  420   a  of the lead frame  420  by connecting two of the ends of the circuit plate  425  with the first side  420   a.  A stacking structure is formed on the substrate  400  by this connecting. Therefore, the size of the substrate for package is effectively shrunk by this stacking structure. And the size of the package structure is also effectively shrunk by this stacking structure. Furthermore, one or a plurality of the second element  410   b  is disposed on the circuit plate  425 , and a plurality of first elements  410   a  are disposed on the first side  420   a  of the lead frame  420 . A plurality of wire bonds  411 - 412 - 413 - 414 - 415 - 416  are formed in order to connect each elements  410   a - 410   b  and the circuits of the circuit plate  425  and the lead frame  420  by wire bonding. Then part of the substrate-the elements-the circuit plate and lead frame are encapsulated by package material.  
         [0022]     In the foregoing package structure, all circuits are fabricated on the circuit plate  425  instead of on the substrate  400 , and a stacking structure is formed by the way of stacking the lead frame  420  and the circuit plate  425 . The occupied area of the substrate is shrunk by the stacking structure. So the size of the package structure is shrunk, too. And the substrate  400  of the present invention is an isolating material, for example a ceramic material, a metal-composite material, a single surface metal-composite material or a dual surface metal-composite material. The circuit plate of the present invention is also an isolating material, for example a glass fiber epoxy or a ceramic material.  
         [0023]     In the embodiment of the present invention, an adhesive material  417 , for example sliver epoxy, is be used to connect the circuit plate  425  with the lead frame  420  and the substrate  400  in order to form a stacking structure. In the other embodiments of the present invention, the circuit plate  425  can be directly connected with the lead frame  420  and the substrate  400  for forming a stacking structure by soldering.  
         [0024]     The first element  410   a  disclosed in the present invention is a power element which produces lots of heat when the power module is working. The power elements  410   a  are disposed on the lead frame  420  in order to form a good way to transmit heat. Therefore, the heat is transmitted to the substrate  400  and the outside heat sink quickly. Furthermore, a metal plate  430  is disposed on the backside  410   b  of the substrate  400 , like the structure illustrated in  FIG. 4B , for improving the rate and the ability of heat transmitting. The second element  410   b  is a control element which is used to control the power elements  410   a.  The control element  410   b  is disposed on the circuit plate  425 , and is connected with the circuits on the circuit plate  425  by wire. bonding. And the control element  410   b  is electrically connected with the power elements  410   a  by the wire bonds for controlling the power elements  410   a.    
         [0025]     Although in this embodiment, the two ends of the lead frame  420  turn upward, but not limit. The two ends of the lead frame can be on the same plane or respectively on different plane. Varity of structures of the lead frames are disclosed in following embodiments, but not limit. In the spirit of the present invention, the structure of the lead frame can be modified by the people who is familiar with this technique.  
         [0026]     Referring to the  FIG. 5A  is a cross-sectional diagram illustrating a power module package structure in accordance with another embodiment of the present invention. The package structure illustrated in  FIG. 5A  is similar to the package structure illustrated in  FIG. 4A . The difference between the two package structures illustrated in  FIG. 5A  and  FIG. 4A  is the structure of lead frame. In  FIG. 5A  all the ends of the lead frame  423   a  are on the same plane without sloping upward or down. In other words, they are straight. In the package structure illustrated in  FIG. 5B  is similar to the package structure illustrated in  FIG. 4A , and the ends of lead frame  423   b  can be on different plane. The ends of lead frame  423   b  illustrated in  FIG. 5B  is sloped downward and is different from the lead frame with sloping upward ends illustrated in  FIG. 4A . OR as illustrated in  FIG. 5C , the ends of the lead frame  423   c  are on different plane and one of ends is sloped upward and the others is sloped downward. Furthermore, there are much variation of the structure of the lead frame can be used in the present invention with the spirit of the present invention.  
         [0027]     Referring to the  FIG. 6 , it is a cross-sectional diagram illustrating a power module package structure in accordance with another embodiment of the present invention. The package structure includes a lead frame  420  having a first surface  420   a , a second surface  420   b  opposite to the first surface and a plurality of leads  421 - 422  and etc.(not showed in he diagram ); a substrate  400  with high thermal conduction and good isolation having a topside  400   a  and a backside  400   b  opposite to the topside  400   a  on the substrate  400 , and a circuit plate  425 . Part of the lead frame  420  is disposed on the circuit plate  425  in order to form a stacking structure by connecting the second surface  420   b  and the surface of circuit plate  425 . The other part of the lead frame is disposed on the substrate  400  by connecting the second surface  420   b  with the topside  400   a  of the substrate  400 . The stacking structure comprising the lead frame  420  and the circuit plate  425  is disposed on a metal plate. And the substrate  400  is disposed on the metal plate  430  by the connecting of the backside  400   b  and the metal plate  430 . One or a plurality of second elements  410   b  is disposed on the circuit plate  425 , and a plurality of first elements  410   a  are disposed on the circuit plate  425  respectively. The first elements are power elements, and the second elements are control elements. A plurality of wire bonds  411 - 412 - 413 - 414 - 415 - 416  are formed in order to connect each elements  410   a - 410   b  and the circuits of the circuit plate  425  and the lead frame  420  by wire bonding. Then part of the substrate-the elements-the circuit plate and lead frame are encapsulated by package material, but not the leads.  
         [0028]     In foregoing package structure, all circuits are fabricated on the circuit plate  425  instead of on the substrate  400 , and a stacking structure is formed by stacking the lead frame  420  and the substrate  400 . The occupied area of the substrate is shrunk by the stacking structure. So the size of the package structure is shrunk, too. The power elements  410   a  are disposed on the lead frame  420  and the heat is transmitted from the lead frame  420  through the substrate  400  and the metal plate  430  to outside environment or the heat sink quickly because of the high thermal conduction of the lead frame  420 . Furthermore, the ends of the lead frame  420  can be on the same plane or on different plane like the structure of lead frame  420  illustrated in  FIG. 5A  to  FIG. 5C .  
         [0029]     Referring to the  FIG. 7 , it is a cross-sectional diagram illustrating a power module package structure in accordance with another embodiment of the present invention. The package structure includes a lead frame  420  having a first surface  420   a , a second surface  420   b  opposite to the first surface and a plurality of leads  421 - 422  and etc.(not showed in he diagram ), and a circuit plate  425  is disposed on part of the first surface  420   a  of the lead frame  420  to form a stacking structure. In another embodiment, the stacking structure is formed by the way of connecting the circuit plate  425  and part of the second surface  420   b  of the lead frame  420 . A substrate  400  with high thermal conduction and good isolation having a topside  400   a  and a backside  400   b  opposite to the topside  400   a  on the substrate  400 . Part of the lead frame  420  is disposed on the substrate  400  by connecting the second surface  420   b  of the lead frame  420  and the topside  400   a  of the substrate  400 . One or a plurality of second elements  410   b  is disposed on the circuit plate  425 , and a plurality of first elements  410   a  are disposed on the circuit plate  425  respectively. The first elements are power elements, and the second elements are control elements. A plurality of wire bonds  411 - 412 - 413 - 414 - 415 - 416  are formed to connect each elements  410   a - 410   b  and the circuits of the circuit plate  425  and the lead frame  420  by wire bonding. Then part of the substrate-the elements-the circuit plate and lead frame are encapsulated by package material, but not the leads.  
         [0030]     In this embodiment, all circuits are fabricated on the circuit plate  425  instead of on the substrate  400 , and a stacking structure is formed by stacking the lead frame  420  and the substrate  400 . The occupied area of the substrate is shrunk by the stacking structure. So the size of the package structure is shrunk, too. The power elements  410   a  are directly disposed on the substrate  400  and the heat is transmitted from the substrate  400  to outside environment or the heat sink quickly because of the high thermal conduction of the substrate  400 . Furthermore, the ends of the lead frame  420  can be on the same plane or on different plane like the structure of lead frame  420  illustrated in  FIG. 5A  to  FIG. 5C .  
         [0031]     Referring to the  FIG. 8 , it is a cross-sectional diagram illustrating a power module package structure in accordance with another embodiment of the present invention. The package structure includes a substrate  400  with high thermal conduction and good isolation having a topside  400   a  and a backside  400   b  opposite to the topside  400   a  on the substrate  400 . A lead frame  420  having a plurality of leads  421 - 422  is disposed on the substrate  400  by connecting the second surface  420   b  of the lead frame  420  and the frant side  400   a  of the substrate  400 . Furthermore, a plurality of high thermal conduction block  424  are disposed on the topside  400   a  of the substrate  400 . One end of the circuit plate  425  is disposed on the first surface  420   a  of the lead frame  420  in order to form a stacking structure. And another end of the circuit plate  425  is connected with the high thermal conduction block  424  which is most near the circuit plate  425 . Therefore, the occupied area of the substrate is shrunk by the stacking structure, and the size of the package structure is shrunk, too. A plurality of control elements are disposed on the circuit plate  425 , and a plurality of power elements on the high thermal conduction block  424  respectively. A plurality of wire bonds  411 - 412 - 413 - 414 - 415 - 416  are formed to connect each elements  410   a - 410   b  and the circuits of the circuit plate  425  and the lead frame  420  by wire bonding. Furthermore, a metal plate  430  is connected with the backside  400   b  of the substrate  400 . But in another embodiment, the metal plate  430  is not necessary. Then part of the substrate-the elements-the circuit plate and lead frame are encapsulated by package material, but not the leads.  
         [0032]     In the foregoing package structure illustrated in  FIG. 8 , the substrate  400  and the circuit plate  425  are as the same as the substrate and the circuit plate illustrated in other diagrams. A stacking structure formed by the circuit plate  425  and the lead frame  420  is disposed on the substrate  400 . The occupied area of the substrate is shrunk, and the size of the package structure is shrunk because of the stacking structure.  
         [0033]     The power elements are disposed on the high thermal conduction block  424  which are disposed on the substrate  400 , and the substrate  400  is connected with the metal plate  430 . An efficient way of heat transmitting is formed by this structure. Lots of heat is transmitted from the high thermal conduction block through the substrate  400  and the metal plate  430  to outside environment or heat sink. Therefore, the package structure of the present invention can bear lots of heat which is produced by the passing of lots of the electric current in short time. The high thermal conduction block  424  is a metal block.  
         [0034]     In other embodiment, the control elements  410   b  can be electrical connected with the circuit plate  425  without the wire bonds. The circuit plate  425  and the lead frame  420  are electrical connected to each other by using the adhesive  417  instead of the wire bonds, for example sliver adhesive. Furthermore, the ends of the lead frame  420  can be on the same plane or on different plane like the structure of lead frame  420  illustrated in  FIG. 5A  to  FIG. 5C .  
         [0035]     The foregoing embodiments are the prefer embodiments but not limit. In the spirit of the present invention, the package structure can be modified and implemented, and the variations are still part of the present invention. Therefore, the scope of the present invention is defined by the claims.