Abstract:
A multiple die package includes a folded leadframe for interconnecting at least two die attached to another leadframe. In a synchronous voltage regulator the folded leadframe, which is formed from a single piece of material, connects the high side switching device with the low side switching device to provide a low resistance, low inductance connection between the two devices.

Description:
FIELD OF THE INVENTION 
     This invention relates packages with multiple semiconductor dice, and more particularly, to packages with multiple power semiconductor dice. 
     BACKGROUND OF THE INVENTION 
     The layout design of circuits which involve the interconnection of power semiconductor die, such as synchronous buck converters for example, involves consideration of the voltage and current losses associated interconnecting the power semiconductor die. Multiple power semiconductor packages offer the benefit of short interconnects between the power devices. However, placing the multiple devices into a form factor that is easily attached to a printed circuit (PC) board together with minimizing the length of the interconnections and maximizing the cross sectional area of the interconnections to reduce the resistance and inductance of the interconnections in a package that can be economically produced is a goal of the design of multiple power semiconductor chips. 
     SUMMARY OF THE INVENTION 
     The present invention comprises in one embodiment thereof a multiple die package includes a folded leadframe having two plates connected by a belt member with a surface of each of the plates having the largest area being parallel with each other, a second leadframe positioned between the plates, and first and second die, each attached to the second leadframe and to one of the plates. 
     In another form of the present invention a multiple die package for a synchronous voltage converter comprising a folded leadframe having two plates connected by a belt member with a surface of each of the plates having the largest area being parallel with each other, a second leadframe positioned between the plates, and a high side die and a low side die, each attached to the second leadframe and to one of the plates. 
     In still another form of the present invention a multiple die package for a synchronous voltage converter having a folded leadframe having two plates connected by a belt member, a surface of each of the plates having the largest area being parallel with each other, a second leadframe positioned between the plates, a high side die and a low side die, each attached to the second leadframe and to one of the plates, and a driver integrated circuit (IC) connected to the high side die and the low side die. 
     In yet another form of the present invention a method for forming a multiple die package comprising the steps of attaching a first and second die to opposite sides of a first leadframe, forming a folded leadframe having parallel plates joined by a belt, and placing the first leadframe between the plates and attaching the first and second die to the plates. 
     In another form of the present invention a method is provided for forming a multiple die package for a synchronous voltage converter including the steps of attaching a high side and low side die to opposite sides of a first leadframe, forming a folded leadframe having parallel plates joined by a belt, and placing the first leadframe between the plates and attaching the low side and high side die to the plates. 
     In still another form of the present invention a method is provided for forming a multiple die package for a synchronous voltage converter including the steps of attaching a high side and low side die to opposite sides of a first leadframe, forming a folded leadframe having parallel plates joined by a belt, placing the first leadframe between the plates and attaching the low side and high side die to the plates, and attaching an integrated circuit (IC) to the first leadframe, and wire bonding the IC to the first leadframe. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The aforementioned and other features, characteristics, advantages, and the invention in general will be better understood from the following more detailed description taken in conjunction with the accompanying drawings, in which: 
         FIGS. 1A ,  1 B,  1 C and  1 D are respective isometric, top, side, and isometric views of a folded leadframe stacked die package according to a first embodiment of the current invention with the encapsulating material shown in outline; 
         FIG. 2  is a cross sectional view taken along line  2 - 2  in  FIG. 1C ; 
         FIG. 3  is a cross sectional view taken along line  3 - 3  in  FIG. 1C ; 
         FIG. 4  is a cross sectional view taken along line  4 - 4  in  FIG. 1C ; 
         FIG. 5  is a schematic diagram of the interconnections of the die in the folded leadframe stacked die package shown in  FIG. 1A ; 
         FIGS. 6A ,  6 B,  6 C,  6 D,  6 E,  6 F,  6 G, and  6 H are isometric views showing the steps in forming the package shown in  FIG. 1A ; 
         FIG. 7  is an exploded view of the package shown in  FIG. 1A ; 
         FIGS. 8A ,  8 B,  8 C and  8 D are respective top, side, isometric, and isometric views of a folded leadframe stacked die package according to a second embodiment of the current invention with the encapsulating material shown in outline; 
         FIGS. 9A ,  9 B,  9 C,  9 D, and  9 E are isometric views showing the steps in forming the package shown in  FIG. 8A ; 
         FIG. 10  is an exploded view of the package shown in  FIG. 8A ; 
         FIGS. 11A ,  11 B, and  11 C are respective isometric, isometric, and side views of a folded leadframe stacked die package according to another embodiment of the current invention with the encapsulating material shown in outline; 
         FIGS. 12A ,  12 B, and  12 C are respective isometric, top, and side views of a folded leadframe stacked die package according to another embodiment of the current invention with the encapsulating material shown in outline; 
         FIG. 13  is a schematic diagram of the interconnections of the die in the folded leadframe stacked die package shown in  FIG. 12A ; 
         FIGS. 14A ,  14 B,  14 C,  14 D,  14 E, and  14 F are isometric views showing the steps in forming the package shown in  FIG. 12A ; 
         FIG. 15  is an exploded view of the package shown in  FIG. 12A ; 
         FIGS. 16A ,  16 B,  16 C and  16 D are respective top, side, isometric, and isometric views of a folded leadframe stacked die package according to another embodiment of the current invention with the encapsulating material shown in outline; 
         FIG. 17  is a schematic diagram of the interconnections of the die in the folded leadframe stacked die package shown in  FIG. 16A ; 
         FIGS. 18A ,  18 B,  18 C,  18 D,  18 E,  18 F, and  18 G are isometric views showing the steps in forming the package shown in  FIG. 16A ; 
         FIG. 19  is an exploded view of the package shown in  FIG. 16A ; 
         FIGS. 20A ,  20 B, and  20 C are respective top, side, and isometric views of a folded leadframe stacked die package according to another embodiment of the current invention with the encapsulating material shown in outline; 
         FIG. 21  is a schematic diagram of the interconnections of the die in the folded leadframe stacked die package shown in  FIG. 20A ; 
         FIGS. 22A ,  22 B,  22 C,  22 D,  22 E, and  22 F are isometric views showing the steps in forming the package shown in  FIG. 20A  according to an embodiment of the present invention; 
         FIGS. 23A ,  23 B,  23 C,  23 D,  23 E, and  23 F are isometric views showing the steps in forming the package shown in  FIG. 20A  according to an embodiment of the present invention; 
         FIG. 24  is an exploded view of the package shown in  FIG. 20A ; 
         FIGS. 25A ,  25 B, and  25 C are respective top, side, and isometric views of a folded leadframe stacked die package according to another embodiment of the current invention with the encapsulating material shown in outline; 
         FIG. 26  is a schematic diagram of the interconnections of the die in the folded leadframe stacked die package shown in  FIG. 25A ; 
         FIGS. 27A ,  27 B,  27 C,  27 D,  27 E, and  27 F are isometric views showing the steps in forming the package shown in  FIG. 25A  according to an embodiment of the present invention; 
         FIGS. 28A ,  28 B,  28 C,  28 D,  28 E, and  28 F are isometric views showing the steps in forming the package shown in  FIG. 25A  according to an embodiment of the present invention; 
         FIG. 29  is an exploded view of the package shown in  FIG. 25A . 
     
    
    
     It will be appreciated that for purposes of clarity and where deemed appropriate, reference numerals have been repeated in the figures to indicate corresponding features. Also, the relative size of various objects in the drawings has in some cases been distorted to more clearly show the invention. 
     DETAILED DESCRIPTION 
     The present invention pertains to semiconductor packages with folded leadframes with multiple semiconductor devices. To facilitate the description of the invention, the semiconductor devices will be referred to as MOSFETs, although the present invention is not limited to such devices. 
     Turning now to the drawings,  FIGS. 1-4  are various views of a folded leadframe multiple die package  50  according to a first embodiment of the present invention. In the drawings an encapsulating material  52  is shown in outline. The folded leadframe package  50  has four leadframes  54 ,  56 ,  58 , and  60  and six MOSFETs  62 ,  64 ,  66 ,  68 ,  70 , and  72  connected together. The leadframe  56  includes six external leads  74 ,  76 ,  78 ,  80 ,  82 , and  84 , with only external leads  78  and  80  connected to the die attach portion of the leadframe  56 . 
     The leadframe  54  has a gate connection section  90  and a source connection section  92  which are attached to the respective gates and sources of the MOSFETs  62  and  64 . The gate and source connection sections  90 ,  92  have stepped down portions which are attachment to the external leads  82  and  84 , respectively. The leadframe  56  has a gate connection section  94  and a source connection section  96  which are attached to the respective gates and sources of the MOSFETs  66  and  68 . The gate and source connection sections  94 ,  96  extend to form the external leads  78 ,  80 , respectively. The leadframe  58  has a gate connection section  98  and a source connection section  100  which are attached to the respective gates and sources of the MOSFETs  70  and  72 . The gate and source connection sections  98 ,  100  have extend in the direction of the external leads  74 - 80 , and the external leads  76  and  74  have stepped down portions which are attached to the extended portions of the gate and source connections  98 ,  100 , respectively. 
     The leadframe  60  has four die bond sections  102 ,  104 ,  106 , and  108  and a metal tab section  110  which contains a mounting hole  112 . Each of the five sections are connected together by two thinner belts  114 . The five sections are connected to the drains of all MOSFETs. Since all the five sections are connected together, it is called common drain. The die bond section  102  is die bonded to the MOSFET  62 , the die bond section  104  is die bonded to the MOSFETs  64  and  66 , the die bond section  106  is die bonded to the MOSFETs  68  and  70 , and the die bond section  108  is die bonded to the MOSFET  72 . 
     The lead frames  54 ,  56 ,  58 , and the die bond sections of leadframe  60  have alignment holes  116  which are used to align the four leadframes during the assembly process of the folded leadframe package  50 . 
       FIG. 2  is a top cross section taken along line  2 - 2  in  FIG. 1C ,  FIG. 3  is a top cross section taken along line  3 - 3  in  FIG. 1C , and  FIG. 4  is a top cross section taken along line  4 - 4  in  FIG. 1C . 
       FIG. 5  is a schematic diagram of the folded leadframe package  50  when vertical MOSFETs are used for the MOSFETs  62 - 72 . The following table shows the correspondence between the package  50  reference numbers and the schematic reference numbers in  FIG. 5 : 
     
       
         
               
               
               
             
               
               
               
             
           
               
                   
                   
               
               
                   
                 Reference Nos. in the drawings 
                 Schematic Reference 
               
               
                   
                 for the Package 50 
                 Nos. in FIG. 5 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 60 
                 160 
               
               
                   
                 62 
                 162 
               
               
                   
                 64 
                 164 
               
               
                   
                 66 
                 166 
               
               
                   
                 68 
                 168 
               
               
                   
                 70 
                 170 
               
               
                   
                 72 
                 172 
               
               
                   
                 74 
                 174 
               
               
                   
                 76 
                 176 
               
               
                   
                 78 
                 178 
               
               
                   
                 80 
                 180 
               
               
                   
                 82 
                 182 
               
               
                   
                 84 
                 184 
               
               
                   
                 90 
                 190 
               
               
                   
                 92 
                 192 
               
               
                   
                 94 
                 194 
               
               
                   
                 96 
                 196 
               
               
                   
                 98 
                 198 
               
               
                   
                 100 
                 200 
               
               
                   
                   
               
             
          
         
       
     
       FIGS. 6A-6H  show the various steps in assembling the folded leadframe package  50  according to an embodiment of the present invention.  FIG. 6A  shows a subassembly with MOSFETs  62  and  64  attached to the leadframe  54 ,  FIG. 6B  shows another subassembly with MOSFETs  66  and  68  attached to the leadframe  56 , and  FIG. 6C  shows another subassembly with MOSFETs  70  and  72  attached to the leadframe  58 . These three subassemblies are formed into another subassembly shown in  FIG. 6D .  FIG. 6E  shows the leadframe  60  prior to being folded, and  FIG. 6F  shows the leadframe  60  after it has been folded. The subassembly shown in  FIG. 6D  is inserted into the folded leadframe  60  and the MOSFETs  62 - 72  are die bonded to the plates  102 - 108  of the folded leadframe  60  to form the folded leadframe package  50  prior to encapsulation as shown in  FIG. 6G . After encapsulation the completed folded leadframe package  50  is shown in  FIG. 6H . The folded leadframe  60  is an integral unit meaning that it is formed from a single piece of material. 
       FIG. 7  is an exploded view of the folded leadframe package  50 . 
       FIGS. 8A ,  8 B,  8 C, and  8 D are top ( FIG. 8A ), side ( FIG. 8B ), and isometric ( FIGS. 8C and 8D ) views of a folded leadframe multiple die package  200  according to a second embodiment of the present invention. In the drawings an encapsulating material  202  is shown in outline. The folded leadframe package  200  has two leadframes  204  and  206  and two MOSFETs  208  and  210  connected together. The leadframe  204  includes three external leads  212 ,  214 , and  216 , with external lead  212  connected to a section of the die attach portion  218  of the lead frame  204  connected to the sources of the MOSFETs  208  and  210 , and the external lead  216  connected to a section of the die attach portion  218  of the lead frame  204  connected to the gates of the MOSFETs  208  and  210 . The leadframe  204  also has a metal tab connector  222  which has a mounting hole  224  formed therein. The metal tab  222  is encapsulated by the encapsulating compound  202  with holes in the encapsulating compound aligned with the mounting hole  224 . The leadframe  206  has two die bond sections  226  and  228 , both of which have stepped tabs  230  and  232 , respectively, which attach to the external lead  214  connected to the common drain of MOSFETs  208  and  210 .. The two die bond sections  226 ,  228  are connected together by two thinner belts  234 . The die bond section  226  is die bonded to the MOSFET  208 , the die bond section  228  is die bonded to the MOSFET  210 . 
     The die attach portion of the lead frame  204  and the die bond sections of leadframe  206  have alignment holes  236  which are used to align the two leadframes during the assembly process of the folded leadframe package  200 . 
       FIGS. 9A-9D  show the various steps in assembling the folded leadframe package  50  according to an embodiment of the present invention.  FIG. 9A  shows a subassembly with MOSFETs  208  and  210  attached to the leadframe  204 .  FIG. 9B  shows the leadframe  206  prior to being folded, and  FIG. 9C  shows the folded leadframe  206 . The subassembly shown in  FIG. 9A  is inserted into the folded leadframe  206 , the plates  226 ,  228  of the folded leadframe  206  are die attached to the MOSFETs  208 , 210 , and the tabs  230 ,  232  of the folded leadframe  206  are attached to the external lead  214  of the subassembly shown in  FIG. 9A  to form the folded leadframe package  200  prior to encapsulation shown in  FIG. 9D . After encapsulation the completed folded leadframe package  200  is shown in  FIG. 9E . 
       FIG. 10  is an exploded view of the folded leadframe package  200 . 
       FIGS. 11A ,  11 B and  11 (C) are two isometric views ( 11 A and  11 B) and a side view ( 11 C) of a variation of the embodiment of the present invention shown in  FIGS. 9A-9D . In  FIGS. 11A-11C  two double bonded ceramic (DBC) plates  238  have been attached to the outer surfaces of the die bonding sections  226 ,  228  and their outer surfaces are exposed (i.e., not encapsulated) to provide improved heat transfer from the two MOSFETs  208 ,  210  to the outside of the folded leadframe package  200 . 
       FIGS. 12A ,  12 B, and  12 C are respective top, side, and isometric views of a folded leadframe multiple die package  300  according to another embodiment of the present invention. In the drawings an encapsulating material  302  is shown in outline. The folded leadframe package  300  has two leadframes  304  and  306 , a gate clip  308 , and two MOSFETs  310  and  312  connected together in a manner to form a synchronous voltage regulator. The leadframe  304  has a die bond section  314 , a source attach section  316 , and a gate attachment section  318 , and also includes four external leads  320 ,  322 ,  324 , and  326 . The external lead  320  is isolated from the other sections of the leadframe  304 , the external lead  322  is connected to the die bond section  314  of the leadframe  304 , the external lead  324  is connected to the source attach section  316  of the leadframe  304 , and the external lead  326  is connected to the gate attachment section  318  of the leadframe  304 . The leadframe  306  is a folded leadframe with a source attach plate  328 , a die bond plate  330 , and a thinner belt  332  connected between the two plates  328 ,  330 . The die bond section  314  of the leadframe  304  is die bonded to the MOSFET  310  and the die bond plate  330  of the leadframe  306  is die bonded to the MOSFET  312 . The die attach section  316  of the leadframe  304  is attached to the source of the MOSFET  312  and the die attach plate  328  of the leadframe  306  is attached to the source of the MOSFET  310 . 
     The outside surface of the die bond plate  330  is exposed and thereby enhances the heat dissipation generated by the MOSFETs  310  and  312 . The exposed surface of the die bond plate  330  allows a connection to be made to the common node of the drain of the MOSFET  312  and the source of the MOSFET  310  rather than through an external lead. 
     As shown in  FIGS. 14A-14F  the source attach plate  328  and the die bond plate  330  of the lead frame  306  and the die attach section  314  of the leadframe  304  have alignment holes  334  which are used to align the two leadframes during the assembly process of the folded leadframe package  300 . 
       FIG. 13  is a schematic diagram of the synchronous voltage regulator contained in the folded leadframe package  300  when vertical MOSFETs are used for the MOSFETs  310 ,  312 . The following table shows the correspondence between the leadframe drawings reference numbers and the schematic reference numbers: 
     
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                 Reference Nos. in the drawings 
                 Schematic Reference 
               
               
                   
                 for the Package 300 
                 Nos. in FIG. 13 
               
               
                   
                   
               
             
             
               
                   
                 306 
                 406 
               
               
                   
                 308 
                 408 
               
               
                   
                 310 
                 410 
               
               
                   
                 312 
                 412 
               
               
                   
                 314 
                 414 
               
               
                   
                 316 
                 416 
               
               
                   
                 318 
                 418 
               
               
                   
                 320 
                 420 
               
               
                   
                 322 
                 422 
               
               
                   
                 324 
                 424 
               
               
                   
                 326 
                 426 
               
               
                   
                 330 
                 430 
               
               
                   
                   
               
             
          
         
       
     
       FIGS. 14A-14F  show the various steps in assembling the folded leadframe package  300  according to an embodiment of the present invention.  FIG. 14A  shows a subassembly with MOSFET  310  die bonded to the die bond section  314 , and MOSFET  312  attached to the source attach section  316  and the gate attachment section  318  of the leadframe  304 .  FIG. 14B  shows the subassembly of  FIG. 14A  with the gate clip  308  attached.  FIG. 14C  shows the leadframe  306  prior to being folded, and  FIG. 14D  shows the leadframe  306  after it has been folded. The subassembly shown in  FIG. 14B  is inserted into the folded leadframe  306  and the source of MOSFET  310  is attached to plate  328  of the folded leadframe  306 , and the MOSFET  312  is die bonded to the plate  330  to form the folded leadframe package  300  prior to encapsulation as shown in  FIG. 14E . After encapsulation the completed folded leadframe package  300  is shown in  FIG. 14F . 
       FIG. 15  is an exploded view of the folded leadframe package  300 . 
       FIGS. 16A ,  16 B,  16 C, and  16 D are respective top ( FIG. 16A ), side ( FIG. 16B ), and isometric ( FIGS. 16C and 16D ) views of a folded leadframe multiple die package  500  according to another embodiment of the present invention. In the drawings an encapsulating material  502  is shown in outline. The folded leadframe package  500  has two leadframes  504  and  506 , a double bonded ceramic (DBC) plate  508 , and two MOSFETs  510  and  512  connected together in a manner to also form a synchronous voltage regulator. The leadframe  504  has a source attach section  514 , and a gate attach section  516 , and also includes two external leads  520  and  522 . The external lead  520  is connected to, and in the same plane as, the gate attach section  516 , and the external lead  522  is connected to, and in the same plane as, the source die attach section  514 . 
     The leadframe  506  is a folded leadframe with the source attach plate  528 , a die bond plate  530 , and a thinner belt  532  connected between the two plates  528 ,  530  such that the two plates  528 ,  530  can be folded into two parallel, stacked plates. The leadframe  506  also includes a gate attach section  518  and two external leads  524  and  526 . The external lead  524  is in the same plane as the external leads  520  and  522  in the areas in which the external leads are not encapsulated, but is stepped up in the encapsulated region of the folded leadframe multiple die package  500  where it is connected to the source attach plate  528  of leadframe  506 , and the external lead  526  and is connected to the gate attach section  518 . 
     The source attach section  514  of the leadframe  504  is attached to the source of the MOSFET  510  and the gate attach section  516  is attached to the gate of the MOSFET  510 . The gate attach section  518  of the leadframe  506  is attached to the gate of the MOSFET  512 . The source attach plate  528  of the leadframe  506  is attached to the source of the MOSFET  512 , and the die bond plate  530  is die bonded to the MOSFET  510 . As best shown in  FIGS. 18-19 , the BDC plate  508  is attached between the top of the source attach section  514  of the leadframe  504  and bottom of the source attach plate  528  of the leadframe  506  to electrically isolate the two leadframes. 
     The outside (drain) of the MOSFET  512  and the outside of the die bond plate  530  are exposed and thereby enhance the heat dissipation generated by the MOSFETs  510  and  512 . The outside of the MOSFET  512  allows a connection to be made to the drain of the MOSFET  512  rather than through an external lead. 
     The die attach plate  528  and the die bond plate  530  of the lead frame  506 , and the source attach section  514 , and the two gate attach sections  516  and  518  of the leadframe  504  have alignment holes  534  which are used to align the two leadframes during the assembly process of the folded leadframe package  500 . 
       FIG. 17  is a schematic diagram of the synchronous voltage regulator contained in the folded leadframe package  500  when vertical MOSFETs are used for the MOSFETs  510 ,  512 . The following table shows the correspondence between the leadframe drawings reference numbers and the schematic reference numbers: 
     
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                 Reference Nos. in the drawings 
                 Schematic Reference 
               
               
                   
                 for the Package 500 
                 Nos. in FIG. 17 
               
               
                   
                   
               
             
             
               
                   
                 506 
                 606 
               
               
                   
                 510 
                 610 
               
               
                   
                 512 
                 612 
               
               
                   
                 516 
                 616 
               
               
                   
                 518 
                 618 
               
               
                   
                 520 
                 620 
               
               
                   
                 522 
                 622 
               
               
                   
                 524 
                 624 
               
               
                   
                 526 
                 626 
               
               
                   
                 528 
                 628 
               
               
                   
                 530 
                 630 
               
               
                   
                   
               
             
          
         
       
     
       FIGS. 18A-18G  show the various steps in assembling the folded leadframe package  500  according to an embodiment of the present invention.  FIG. 18A  shows a subassembly with MOSFET  510  attached to the source attach section  514  and the gate attachment section  516  of the leadframe  504 .  FIG. 18B  shows the subassembly of  FIG. 18A  with the BDC plate  508  attached to the sections of the leadframe  504 .  FIG. 18C  shows the leadframe  506  prior to being folded and MOSFET  512 . The source of the MOSFET  512  attached to the plate  528 , and the gate of the MOSFET  512  is attached to the gate attach section  518 .  FIG. 18D  shows the leadframe  306  and the MOSFET  512  of  FIG. 18C  joined with the subassembly of  FIG. 18B  with plate the DBC plate  508  bonded to the plate  528  of the leadframe  506 .  FIG. 18E  shows the leadframe  506  partially folded, and  FIG. 18F  shows the leadframe  206  after it has been fully folded to form the folded leadframe package  500  prior to encapsulation. After encapsulation the completed folded leadframe package  500  is shown in  FIG. 18G . 
       FIG. 19  is an exploded view of the folded leadframe package  500 . 
       FIGS. 20A ,  20 B, and  20 C are respective top, side, and isometric views of a folded leadframe multiple die package  700  according to another embodiment of the present invention. In the drawings an encapsulating material  702  is shown in outline. The folded leadframe package  700  has two leadframes  704  and  706 , an integrated circuit (IC)  708 , and two MOSFETs  710  and  712  connected together in a manner to form a synchronous voltage regulator with an integral MOSFET driver IC  708 . The leadframe  704  has a die bond section  714 , a source attach section  718 , a gate attach section  720 , a gate clip  722 . The leadframe  704  also includes seven external leads  724 ,  726 ,  728 ,  730 ,  732 ,  734 , and  736 . The external lead  724  is connected to the die bond section  714 , and the external lead  726  is connected to the gate clip  722 . The external leads  726 - 734  are not attached to any other elements in the folded leadframe package  700 , but are connected by wire bonds  738  to the IC  708 . The external lead  734  is connected to the gate attach section  720 , and the external lead  736  is connected to the source attach section  718 . 
     The leadframe  706  is a folded leadframe with the source attach plate  740 , a die bond plate  742 , and a thinner belt  744  connected between the two plates  740 ,  742  such that the two plates  740 ,  742  can be folded into a two parallel plates. The die bond section  714  of the leadframe  704  is die bonded to the MOSFET  710  and the IC  708 . The source attach section  718  attached to the source of the MOSFET  712 , and the gate attach section  720  is attached to the gate of the MOSFET  712 . The source attach plate  740  of the leadframe  706  is attached to the source of the MOSFET  710 , and the die bond plate  742  is die bonded to the MOSFET  712 . The gate clip  722  is attached to the gate of the MOSFET  710  and the external lead  726 . The source of the MOSFET  712  is electrically connected to the IC  708  by a set of wire bonds  746  which may range in number from  2  to  4  in different embodiments of the present invention. 
     The outside surface of the die bond plate  742  is exposed and thereby enhances the heat dissipation generated by the MOSFET  712 . 
     The die attach plate  740  of leadframe  706  and the die bond section  714  of the leadframe  704  each have an alignment hole  748  which are used to align the two leadframes during the assembly process of the folded leadframe package  700 . 
       FIG. 21  is a schematic diagram of the synchronous voltage regulator contained in the folded leadframe package  700  when vertical MOSFETs are used for the MOSFETs  710 ,  712 . The following table shows the correspondence between the leadframe drawings reference numbers and the schematic reference numbers: 
     
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                 Reference Nos. in the drawings 
                 Schematic Reference 
               
               
                   
                 for the Package 700 
                 Nos. in FIG. 21 
               
               
                   
                   
               
             
             
               
                   
                 706 
                 806 
               
               
                   
                 708 
                 808 
               
               
                   
                 710 
                 810 
               
               
                   
                 712 
                 812 
               
               
                   
                 714 
                 814 
               
               
                   
                 718 
                 818 
               
               
                   
                 720 
                 820 
               
               
                   
                 722 
                 822 
               
               
                   
                 724 
                 824 
               
               
                   
                 726 
                 826 
               
               
                   
                 728 
                 828 
               
               
                   
                 730 
                 830 
               
               
                   
                 732 
                 832 
               
               
                   
                 734 
                 834 
               
               
                   
                 736 
                 836 
               
               
                   
                 742 
                 842 
               
               
                   
                   
               
             
          
         
       
     
       FIGS. 22A-22F  and  FIGS. 23A-23F  show two alternate methods of assembling the folded leadframe package  700 .  FIG. 22A  shows a subassembly with the IC  708  die bonded to the die bond section  714  of the leadframe  704 .  FIG. 22B  shows the subassembly of  FIG. 22A  with the wire bonds attached to the IC  708  and the leadframe  704 .  FIG. 22C  shows the subassembly of  FIG. 22B  with the MOSFET  710  die bonded to the die bond section  714 , and the MOSFET  712  attached to the source attach section  718  and the gate attach section  720  of the leadframe  704 .  FIG. 22D  shows the subassembly of  FIG. 22C  with the gate clip  722  attached.  FIG. 22E  shows the subassembly of  FIG. 22D  with the folded leadframe  706  attached to the source of the MOSFET  710  and die bonded to the MOSFET  712  to form the folded leadframe package  700  prior to encapsulation. After encapsulation the completed folded leadframe package  700  is shown in  FIG. 22F . 
     In the second alternate method of assembly  FIGS. 23A and 23B  are the same as  FIGS. 22A and 22B .  FIG. 23C  shows the unfolded leadframe  706  with source of the MOSFET  710  attached to the plate  740 , and the MOSFET  712  die bonded to the plate  742 .  FIG. 23D  shows the subassemblies of  FIGS. 23B and 23C  joined with the MOSFET  710  die bonded to the die bond section  714  of the leadframe  704 , and the source attach section  718  and the gate attach section  720  attached to the MOSFET  712 .  FIG. 23E  shows the subassembly of  FIG. 23D  with the gate clip  722  attached to form the folded leadframe package  700  prior to encapsulation. After encapsulation the completed folded leadframe package  700  is shown in  FIG. 23F . 
       FIG. 24  is an exploded view of the folded leadframe package  700 . 
       FIGS. 25A ,  25 B, and  25 C are respective top, side, and isometric views of a folded leadframe multiple die package  900  according to another embodiment of the present invention. In the drawings an encapsulating material  902  is shown in outline. The folded leadframe package  900  has two leadframes  904  and  906 , an IC  908 , and two MOSFETs  910  and  912  connected together in a manner to form a synchronous voltage regulator with an integral MOSFET driver IC  908 . The leadframe  904  has a die bond only section  914 , a combination source attach and die bond section  916 , and a gate attach sections  918  and a gate clip  920 . The leadframe  904  also includes seven external leads  922 ,  924 ,  926 ,  928 ,  930 ,  932 , and  934 . The external lead  922  is connected to the die bond only section  914 , and the external lead  924  is attached to the gate clip  920 . The external leads  926 - 930  are not attached to any other elements in the folded leadframe package  900 , but are connected by wire bonds  936  to the IC  908 . The external lead  932  is connected to the combination source attach and die bond section  916 , and the external lead  934  is connected to the gate attach sections  918 . 
     The leadframe  906  is a folded leadframe with a source attach plate  938 , a die bond plate  940 , and a thinner belt  942  connected between the two plates  938 ,  940  such that the two plates  938 ,  940  can be folded into a two parallel plates. The die bond only section  914  of the leadframe  904  is die bonded to the MOSFET  910 . The combination source attach and die bond section  916  is attached to the source of the MOSFET  912  and die bonded to the IC  908 . The gate attach section  918  is attached to the gate of the MOSFET  912 . The source attach plate  938  of the leadframe  706  is attached to the source of the MOSFET  910 , and the die bond plate  940  is die bonded to the MOSFET  912 . The gate clip  920  is attached to the gate of the MOSFET  910  and the external lead  924 . The source of the MOSFET  912  is electrically connected to the IC  908  by a set of wire bonds  946  which may range in number from 2 to 4 in different embodiments of the present invention. 
     The outside surface of the die bond plate  940  is exposed and thereby enhances the heat dissipation generated by the MOSFET  912 . 
     The die attach plate  938  of the leadframe  906  and the die bond only section  914  of the leadframe  904  each have an alignment hole  944  which are used to align the two leadframes during the assembly process of the folded leadframe package  900 . 
       FIG. 26  is a schematic diagram of the synchronous voltage regulator contained in the folded leadframe package  900  when vertical MOSFETs are used for the MOSFETs  910 ,  912 . The following table shows the correspondence between the leadframe drawings reference numbers and the schematic reference numbers: 
     
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                 Reference Nos. in the drawings 
                 Schematic Reference 
               
               
                   
                 for the Package 900 
                 Nos. in FIG. 26 
               
               
                   
                   
               
             
             
               
                   
                 906 
                 1006 
               
               
                   
                 908 
                 1008 
               
               
                   
                 910 
                 1010 
               
               
                   
                 912 
                 1012 
               
               
                   
                 914 
                 1014 
               
               
                   
                 918 
                 1018 
               
               
                   
                 920 
                 1020 
               
               
                   
                 922 
                 1022 
               
               
                   
                 924 
                 1024 
               
               
                   
                 926 
                 1026 
               
               
                   
                 928 
                 1028 
               
               
                   
                 930 
                 1030 
               
               
                   
                 932 
                 1032 
               
               
                   
                 934 
                 1034 
               
               
                   
                 940 
                 1040 
               
               
                   
                   
               
             
          
         
       
     
       FIGS. 27A-27F  and  FIGS. 28A-28F  show two alternate methods of assembling the folded leadframe package  900 .  FIG. 27A  shows a subassembly with the IC  908  die bonded to the combination source attach and die bond section  916  of the leadframe  904 .  FIG. 27B  shows the subassembly of  FIG. 27A  with the wire bonds attached to the IC  708  and the leadframe  904 .  FIG. 27C  shows the subassembly of  FIG. 27B  with the MOSFET  910  die bonded to the die bond only section  914 , and the MOSFET  912  attached to the source attach section  916  and the gate attach section  918  of the leadframe  904 .  FIG. 27D  shows the subassembly of  FIG. 27C  with the folded leadframe  906  attached to the source of the MOSFET  710  and die bonded to the MOSFET  912 .  FIG. 27E  shows the subassembly of  FIG. 27D  with the gate clip  920  attached to form the folded leadframe package  900  prior to encapsulation. After encapsulation the completed folded leadframe package  900  is shown in  FIG. 27F . 
     In the second alternate method of assembly  FIGS. 28A and 28B  are the same as  FIGS. 27A and 27B .  FIG. 28C  shows the unfolded leadframe  906  with source of the MOSFET  910  attached to the plate  938 , and the MOSFET  912  die bonded to the plate  940 .  FIG. 28D  shows the subassemblies of  FIGS. 28B and 28C  joined with the MOSFET  910  die bonded to the die bond only section  914  of the leadframe  904 , and the source attach section  916  and the gate attach section  918  attached to the MOSFET  912 .  FIG. 28E  shows the subassembly of  FIG. 28D  with the gate clip  920  attached to form the folded leadframe package  900  prior to encapsulation. After encapsulation the completed folded leadframe package  900  is shown in  FIG. 28F . 
       FIG. 29  is an exploded view of the folded leadframe package  900 . 
     While the invention has been described with reference to particular embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the scope of the invention. 
     Therefore, it is intended that the invention not be limited to the particular embodiments disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope and spirit of the appended claims.