Abstract:
A power module package is provided. The power module package includes a power circuit element, a control circuit element, a lead frame, a heat sink, and an epoxy molding compound (EMC). The control circuit element is connected to the power circuit and controls chips in the power circuit. The lead frame has external connecting means formed at the edges thereof, and a down set part, namely, formed between the external connecting means. The lead frame has a first surface to which the power circuit and the control circuit are attached, and a second surface used as a heat dissipating path, in particular, the power circuit is attached to the down set part. The heat sink which is closely attached to the down set part of the second surface of the lead frame by an adhesive. The EMC surrounds the power circuit, the control circuit, the lead frame and the heat sink, and exposes the external connecting means of the lead frame and a side of the heat sink.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a semiconductor package, and more particularly, to a power module package having improved heat dissipating capability. 
     2. Description of the Related Art 
     In general, in semiconductor packages, one or more semiconductor chips is or are mounted on a chip pad in a lead frame, encapsulated with an epoxy molding compound (EMC) to protect internal parts, and mounted on a printed circuit board (PCB). 
     However, as high speed, large scale and highly integrated electronic devices have been rapidly developed in recent times, techniques that allow for low cost, miniaturization, and lightweight manufacturing are also required for power devices which are applied to automobiles, industrial equipment and household electrical appliances. Further, the power devices require high reliability and good temperature characteristics. Thus, a power module package for mounting a plurality of semiconductor chips on a semiconductor package is commonly used. 
       FIG. 1  is a sectional view of a conventional power module package, which is disclosed in U.S. Pat. No. 5,703,399, published on May 15, 1996, titled “Semiconductor Power Module”. 
     Referring to  FIG. 1 , the power module package has a structure in which a plurality of semiconductor chips, including a power circuit  9  and a control circuit  8 , are mounted on a lead frame  3 . In the drawing, reference numerals  1 ,  2 , and  4   a  denote a heat sink, an epoxy molding compound (EMC) having a high heat conductivity, and a power circuit chip, respectively. Also, reference numerals  5   a ,  5   b ,  6   a ,  6   b , and  7  denote a control circuit chip, a resistance component, an aluminum wire, a gold wire, and an insulating EMC, respectively. 
     In the power module package having the above structure, the EMC  2  having high heat conductivity is used such that the heat sink  1  which is made of copper is slightly spaced apart from the lead frame  3 . Thus, the EMC  2  and the heat sink  1  dissipate heat, which is generated in the power circuit chip  4   a , to the outside of the power module package. However, the above-mentioned prior art has the following problems. 
     First, the EMC  2  is filled between the backside of the lead frame  3  and the heat sink  1  made of copper in order to maintain insulation properties, and thus there is a limitation in completely dissipating heat generated in the power circuit chip  4   a , to the outside of the power module package. Second, two EMCs having different characteristics are used in one power module package, and thus a process of manufacturing the power module package becomes complicated and it is difficult to perform the process of manufacturing the power module package automatically. Third, the heat sink  1  made of copper is used in the power module package, and a process of manufacturing the power module package is complicated, and thus a manufacturing cost is increased. 
     SUMMARY OF THE INVENTION 
     To solve the above problems, it is an object of the present invention to provide a power module package which more effectively dissipates heat generated in a power circuit chip and is simpler and cheaper to manufacture. 
     Accordingly, to achieve the above object, according to an embodiment of the present invention, there is provided a power module package. The power module package includes a power circuit, a control circuit which is connected to the power circuit and controls chips in the power circuit, a lead frame having external connecting means at the edges thereof, a down set part, namely, downwardly facing concave portion, formed between the external connecting means, a first surface to which the power circuit and the control circuit are attached, and a second surface used as a heat dissipating path, wherein the power circuit is attached to the down set part, a heat sink which is closely attached to the down set part of the second surface of the lead frame by an adhesive, and an epoxy molding compound (EMC) for surrounding the power circuit, the control circuit, the lead frame and the heat sink, and for exposing the external connecting means of the lead frame and a side of the heat sink. 
     It is preferable that the power circuit includes power circuit chips and an aluminum wire for connecting the power circuit chips to the lead frame, and the aluminum wire has the diameter of 250–500 μm. 
     It is also preferable that the control circuit includes control circuit chips and a gold wire for connecting the control circuit chips to the lead frame. 
     It is also preferable that the adhesive for attaching the lead frame to the heat sink is a high temperature tape, and the high temperature tape is formed of a material selected from the group consisting of alumina (Al 2 O 3 ), aluminum nitride (AIN), silicon oxide (SiO 2 ), and beryllium oxide (BeO), and the high temperature tape has a thickness of 10–20 μm. The high temperature tape can comprise particles including such thermally conductive materials embedded in a medium such as a polymer medium. 
     It is also preferable that the adhesive for attaching the lead frame to the heat sink is high temperature solder, and the high temperature solder is formed of a metal material selected from Pb/Sn, Sn/Ag, and Pb/Sn/Ag. 
     It is also preferable that the adhesive for attaching the lead frame to the heat sink is high thermal liquid epoxy, and the thickness of the high thermal liquid epoxy is 3–7 μm. 
     It is also preferable that the heat sink is made of plastic or ceramic, and the heat sink made of plastic or ceramic is formed of a material selected from the group consisting of alumina (Al 2 O 3 ), aluminum nitride (AIN), silicon oxide (SiO 2 ), and beryllium oxide (BeO), and the heat sink made of plastic or ceramic has a thickness of 1–3 mm. 
     In order to achieve the above object, according to another embodiment of the present invention, there is provided a power module package. The power module package includes a direct bonding copper (DBC) substrate, a power circuit which is attached to the DBC substrate, a lead frame which is connected to one end of the DBC substrate, a control circuit which is attached to the lead frame, a wire for electrically connecting the power circuit and the control circuit to the lead frame, and an epoxy molding compound (EMC) for exposing only the back side of the DBC substrate and part of the lead frame and completely sealing the other portions of the DBC substrate and the lead frame. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above objects and advantages of the present invention will become more apparent by describing in detail a preferred embodiment thereof with reference to the attached drawings in which: 
         FIG. 1  is a sectional view illustrating an example of a conventional power module package; 
         FIG. 2  is a sectional view of a power module package according to an embodiment of the present invention; 
         FIG. 3  is a sectional view of a power module package according to another embodiment of the present invention; 
         FIG. 4  is a sectional view of a power module package according to still another embodiment of the present invention; 
         FIG. 5  is a sectional view of the structure of a bottom mold die of a molding equipment used in a method for manufacturing the power module package according to the present invention; 
         FIG. 6  is a sectional view illustrating a sealing process of the method for manufacturing the power module package according to the present invention; and 
         FIGS. 7A through 7D  are sectional views illustrating the method for manufacturing the power module package according to another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
     The arrangement of a power circuit element and a control circuit element which will be described in this specification, and the structure of a lead frame and a heat sink are exemplified, however, this invention is not limited to only the specific shapes shown in drawings and is self-evident to a person skilled in the art. 
       FIG. 2  is a sectional view of a power module package according to an embodiment of the present invention. Referring to  FIG. 2 , the power module package  200  includes a lead frame  210 , a power circuit element  220 , a control circuit element  230 , a heat sink  250 , and an epoxy molding compound (EMC)  270 . The power circuit element  220  includes a power circuit chip  221  and an aluminum wire  222 . The aluminum wire  222  has a diameter of about 250–500 μm such that the aluminum wire  222  can withstand a high current rating. The control circuit element  230  includes a control circuit chip  231  and a gold wire  232 . The aluminum wire  222  and the gold wire  232  connect the power circuit chip  221  to the control circuit chip  231 . 
     The lead frame  210  has a first surface  211  onto which circuit elements are attached and a second surface  212  which is opposite to the first surface  211 , and a down set part  240 , namely, a downwardly facing concave portion, is formed in the middle of the lead frame  210 . The down set part  240  may be exactly placed in the center so that both sides thereof are symmetrical, but may be formed to be off to one side. The power circuit element  220  and the control circuit element  230  are attached to the first surface  211  of the lead frame  210 . In particular, the power circuit element  220 , which generates a large amount of heat, is attached to the first surface  211  of the down set part  240  of the lead frame  210 . 
     The heat sink  250  is attached to the second surface  212  of the down set part  240  of the lead frame  210  by a high temperature tape  260 , and a side of the heat sink  250  is completely exposed to the outside of the power module package  200 . As occasion demands, high temperature solder can be used instead of the high temperature tape. Preferably, the solder is formed of a metal material selected from Pb/Sn, Sn/Ag, and Pb/Sn/Ag. 
     The heat sink  250  has a thickness of about 1–3 mm and can be manufactured by using a material selected from the group consisting of alumina (Al 2 O 3 ), aluminum nitride (AIN), silicon oxide (SiO 2 ), and beryllium oxide (BeO). For example, a heat sink  250  made of ceramic can be manufactured by adding a material from the group consisting of alumina (Al 2 O 3 ), aluminum nitride (AIN), silicon oxide (SiO 2 ), and beryllium oxide (BeO) to a filling material including ceramic. Also, a heat sink  250  made of plastic can be manufactured by adding a material from the group consisting of alumina (Al 2 O 3 ), aluminum nitride (AIN), silicon oxide (SiO 2 ), and beryllium oxide (BeO) to a filling material including plastic. Meanwhile, if solder is used instead of the high temperature tape, metal is formed on a side of the heat sink  250  to be attached to the lead frame  210 . Similarly, the high temperature tape  260  can be manufactured by using a material from the group consisting of alumina (Al 2 O 3 ), aluminum nitride (AIN), silicon oxide (SiO 2 ), and beryllium oxide (BeO) and has a thickness of about 10–20 μm such that the lead frame  210  and the heat sink  250  are completely attached to each other. 
     According to the power module package having the above structure, the heat dissipating effect is increased because there is no space between the down set part  240  of the lead frame  210  and the heat sink  250 . 
       FIGS. 5 and 6  illustrate a method for manufacturing the power module package according to an embodiment of the present invention. Specifically,  FIG. 5  is a sectional view of the structure of a bottom mold die of a molding apparatus used in a method for manufacturing the power module package according to the present invention, and  FIG. 6  is a sectional view illustrating a sealing process of the method for manufacturing the power module package according to the present invention. 
     Referring to  FIGS. 2 ,  5  and  6 , first, the lead frame  210  having the down set part  240  formed in the middle thereof is prepared. The power circuit chip  221  and the control circuit chip  231  are attached to the first surface  211  of the lead frame  210  by performing a die attach process. The power circuit chip  221  is attached to part of the down set part  240  of the lead frame  210 . Next, a wire bonding process is performed, thereby properly connecting the power circuit chip  221  to the control circuit chip  231 . The gold wire  232  is used as a wire for the control circuit chip chip  231 , and the aluminum wire  222  is used as a wire for the power circuit chip  221 . Preferably, the aluminum wire  222  has a diameter of about 250–500 μm such that the aluminum wire  222  can withstand a high current rating. Bonding methods such as a wedge bonding method and a ball bonding method, are used in performing the wire bonding process. In order to perform the wire bonding process smoothly, it is preferable that the aluminum wire  232  is first bonded and then the gold wire  222  is bonded. 
     Next, the heat sink  250  is fixed in a groove  524  which is formed on a heat sink block  522  of the bottom mold die ( 520  of  FIG. 5 ). The heat sink  250  has a thickness of about 1–3 mm and can be manufactured by using a material selected from the group consisting of alumina (Al 2 O 3 ), aluminum nitride (AIN), silicon oxide (SiO 2 ), and beryllium oxide (BeO). For example, the heat sink made of ceramic can be manufactured by adding a material from the group consisting of alumina (Al 2 O 3 ), aluminum nitride (AIN), silicon oxide (SiO 2 ), and beryllium oxide (BeO) to a filling material including ceramic. Also, the heat sink  250  made of plastic can be manufactured by adding a material from the group consisting of alumina (Al 2 O 3 ), aluminum nitride (AIN), silicon oxide (SiO 2 ), and beryllium oxide (BeO) to a filling material including plastic. 
     Next, after the wire bonding process, the lead frame  210  is placed in a molding apparatus. Here, the heat sink  250  has already been fixed in the groove  524  of the bottom mold die  520 . Subsequently, the high temperature tape  260  is melted such that the heat sink  250  is completely attached to the second surface  212  of the down set part  240  of the lead frame  210 . Here, the temperature and pressure for melting the high temperature tape  260  are about 160–220° C. and about 30 kg/cm 2 , respectively. The high temperature tape  260  can be manufactured by using a material selected from the group consisting of alumina (Al 2 O 3 ), aluminum nitride (AIN), silicon oxide (SiO 2 ), and beryllium oxide (BeO) and has a thickness of about 10–20 μm. 
     Next, a top mold die  510  is lowered, and the EMC  270  is flowed into an EMC apparatus through a gate  530 . The EMC  270  is changed into a liquid by heat and pressure. Thus, the EMC  270  flows in a direction indicated by the arrows and fills the inside of a mold  500  uniformly. A transfer molding equipment including a plurality of gates and runners is used as the molding equipment, and preferably, the temperature for a sealing process is about 160–170° C. 
     Next, the lead frame after the sealing process, that is, the power module package  500 , is unloaded from the molding apparatus, then the heat sink  250  is completely attached to the second surface  212  of the down set part  240  of the lead frame  210  by using the high temperature tape  260 . Subsequently, subsequent processes such as a trim process and a forming process are performed. 
       FIG. 3  is a sectional view of a power module package according to another embodiment of the present invention. Referring to  FIG. 3 , the power module package  300  includes a lead frame  310 , a power device  320 , a control device  330 , a heat sink  350 , and an epoxy molding compound (EMC)  370 . The power device  320  includes a power circuit chip  321  and an aluminum wire  322 . The control device includes a control circuit chip  330  and a gold wire (not shown). The lead frame  310  has a thickness of about 0.5–1.0 mm and includes a down set part  340  that is formed in the middle of the lead frame  310 . The power device  320  and the control device  330  are attached to one surface of the lead frame  310 . In particular, the power device  320 , which generates a large amount of heat, is attached to the down set part  340  of the lead frame  310 . 
     The heat sink  350  is attached to the opposite surface of the down set part  340  of the lead frame  310  using high thermal liquid epoxy  360 , and a side of the heat sink  350  is completely exposed to the outside of the power module package  300 . The high thermal liquid epoxy  360  can be made by adding a filling material including a material from the group consisting of alumina (Al 2 O 3 ), aluminum nitride (AIN), silicon oxide (SiO 2 ), and beryllium oxide (BeO) to epoxy. The thickness of the high thermal liquid epoxy  360  is about 3–7 μm and represents thermal resistance less than about 1.5° C./W, and thus has improved thermal conductivity in comparison with a conventional power module package in which epoxy molding compounds are used. 
       FIGS. 7A through 7D  are sectional views illustrating the method for manufacturing the power module package according to another embodiment of the present invention. First, referring to  FIG. 7A , the lead frame  310  having a thickness of about 0.5–1.0 mm is prepared. The power circuit chip  321  and the control circuit chip  330  are attached to the surface of the lead frame  310  by performing a die attach process. The power circuit chip  321  is attached to part of the down set part  340  of the lead frame  310 . The die attach process may be performed using solder or silver (Ag) epoxy as an adhesive. In a case where the die attach process is performed using solder as an adhesive, the temperature and pressure for the die attach process is about 350–380° C. and about 3–5 kg/cm 2 , respectively, and the die attach process is performed in a hydrogen atmosphere. In a case where the die attach process is performed using Ag epoxy as an adhesive, the die attach process is performed at the room temperature and pressure under about 1–2 kg/cm 2 . 
     Next, referring to  FIG. 7B , the high thermal liquid epoxy  360  is attached to the upper surface of the heat sink  350  made of ceramic having a thickness of about 1–3 mm. The high thermal liquid epoxy  360  can be made by adding a filling material including a material from the group consisting of alumina (Al 2 O 3 ), aluminum nitride (AIN), silicon oxide (SiO 2 ), and beryllium oxide (BeO) to epoxy. 
     Next, referring to  FIG. 7C , the heat sink  350  made of ceramic is attached to the lead frame  310  onto which the power circuit chip  321  is attached, using the high thermal liquid epoxy  360  as an adhesive. The attach process is performed at a temperature of about 150–180 ° C. and pressure under about 0.5–1.0 kg/cm 2  for about 3–5 minutes. 
     Next, referring to  FIG. 7D , an aluminum wire bonding process or gold wire bonding process is performed, thereby electrically connecting the power circuit chip  321  to the lead frame  310 , the power circuit chips  321  to each other and the control circuit chip  330  to the lead frame  310 . Wires  322  including gold wires and aluminum wires. The gold wire is used as a wire for the control circuit chip  330 , and aluminum wires are used as wire for the power circuit chips  321 . The aluminum wire bonding process is performed by wedge bonding, and the gold wire bonding process is performed by ball bonding. 
     Next, as shown in  FIG. 3 , an encapsulation process is performed such that only the lower surface of the heat sink  350  made of ceramic and the end part of the lead frame  310  are exposed by the EMC  370 , and then, general trim and forming processes are performed. 
       FIG. 4  is a sectional view of a power module package according to still another embodiment of the present invention. The power module package according to the present embodiment is different from the power module packages according to the previous embodiments in which a heat sink is used, in that a direct bonding copper (DBC) substrate is used in the power module package according to the present embodiment. 
     Referring to  FIG. 4 , the power module package  400  includes a lead frame  410 , a power device  420 , a control device  430 , a DBC substrate  450 , and an epoxy molding compound (EMC)  470 . The power device  420  includes a power circuit chip  421  and an aluminum wire  422 . The control device includes a control circuit chip  430  and a gold wire (not shown). The DBC substrate  450  is comprised of central ceramic  451 , an upper copper layer  452  attached to the upper surface of the ceramic  451 , and a lower copper layer  453  attached to the lower surface of the ceramic  451 . The power circuit chip  421  is attached to the surface of the upper copper layer  452  of the DBC substrate  450 . The lead frame  410  is connected to the upper copper layer  452  of the DBC substrate  450 . The control circuit chip  430  is attached to the lead frame  410 . 
     A DBC substrate having higher thermal conductivity is used in the power module package  400 , and thus the power module package  400  has improved heat dissipating capability. 
     In order to manufacture the power module package  400 , first, the lead frame  410  is attached to the DBC substrate  450 . The attach process may be performed using an adhesive such as solder or thermal tape, or by welding using a laser or spot, or by thermal compression using silver (Ag) or Ag/Sn plating. Next, the power circuit chip  421  and the control circuit chip  430  are attached to the lead frame  410 . The die attach process may be performed using solder and Ag epoxy. The solder is used to attach the power circuit chip  421  to the lead frame  410 , and in this case, the die attach process is performed at a temperature of about 330–360° C. The Ag epoxy is used to attach the control circuit chip  430  to the lead frame  410 , and in this case, the die attach process is performed at the room temperature. Next, the power circuit chip  421  and the control circuit chip  430  are electrically connected to the lead frame  410  by performing a wire bonding process. An aluminum wire is used as a wire for the power circuit chip  421 , and a gold wire is used as a wire for the control circuit chip  430 . Next, an encapsulation process is performed using the EMC  470 , and then, general trim and forming processes are performed. 
     As described above, the power module package and the method for manufacturing the same according the present invention have the following effects. 
     First, since the heat sink is directly attached to the back side of the down set part of the lead frame by using the high temperature tape, heat which is generated during operation of the power module package can be effectively dissipated, thereby increasing the reliability of the power module package. As an example, when the structure and material of the heat sink of the power module package are changed like those in the prevention invention, RΘ jc , as the thermal resistance of the conventional power module package was measured to be 0.19° C./Watt. On the other hand, RΘ jc  of the power module package according to the present invention was measured to be 0.15° C./Watt, and as a result, the heat dissipating capability is improved by 20–30%. For reference, RΘ jc  is an index representing a difference in temperature from the PN junction of the power circuit chip  121  to a case, as a mold line. Similarly, RΘ jc , was measured to be 0.15° C./Watt even in a case where the high thermal liquid epoxy instead of the high temperature tape is used. 
     Second, since the sealing process for the power module package is performed at a time by using the EMC having the same heat conductivity, it is advantageous to simplify and automatize processes. 
     Third, the power module package is manufactured by using the heat sink (not metal) at a low cost and the processes are simplified, thereby reducing the manufacturing cost of the power module package. 
     While this invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.