Abstract:
The present invention relates to a method for making a package structure having recession portion on the surface thereof. The method comprises: (a) providing a lead frame having a plurality of package units, each package unit having a plurality of leads and a die paddle; (b) providing an upper mold and a lower mold for clamping the lead frame, wherein the upper mold and the protruding block of the lower mold clamp the first portions of the leads so as to prevent molding compound bleeding to the upper surfaces of the first portions during mold filling operation, for improving the product yield; (c) injecting a molding compound between the upper mold and the lower mold, and forming a plurality of accommodation spaces; (d) attaching a plurality of chips onto the die paddles; (e) electrically connecting the chips to the first portions of the leads; (f) sealing the accommodation spaces; and (g) segregating the package units.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a package structure and fabricating method thereof, and more particularly to a package structure having at least one recession portion on the lower surface and a method of making the same.  
         [0003]     2. Description of the Related Art  
         [0004]     Referring to FIGS.  1  to  4 , the schematic sectional views of the method for making a quad flat no-lead package (QFN) with an opening are illustrated. First, referring to  FIG. 1 , a lead frame  10  is provided. The lead frame  10  includes a plurality of package units  11 , but only one single package unit  11  is illustrated hereinafter. The package unit  11  is comprises a plurality of leads  12  and a die paddle  13 , wherein the leads  12  surround the die paddle  13 , and the die paddle  13  has an upper surface  131  and a lower surface  132 . Each lead  12  has a first portion  121  and a second portion  122 , wherein the first portion  121  has an upper surface  1211  and a lower surface  1212 , and the second portion  122  has an upper surface  1221  and a lower surface  1222 . The upper surfaces  1211 ,  1221  constitute the upper surface of the lead  12 , and the lower surfaces  1212 ,  1222  constitute the lower surface of the lead  12 , wherein the upper surface  1211  of the first portion  121  is used for wire bonding. The first portion  121  is thinner than the second portion  122 , so as to form a step-like appearance.  
         [0005]     Then, referring to  FIG. 2 , an upper mold  21  and a lower mold  22  are provided for clamping the lead frame  10 . The upper mold  21  presses against the upper surfaces  1211  of the first portions  121  of the leads  12  and the upper surface  131  of the die paddle  13 . The lower mold  22  presses against the lower surfaces  1222  of the second portions  122  of the leads  12  and the lower surface  132  of the die paddle  13 . The upper mold  21  has a cavity  211 .  
         [0006]     Next, a molding compound is injected between the upper mold  21  and the lower mold  22 , to form a surrounding wall portion  23  and a lower cover portion  24 .  
         [0007]     Then, referring to  FIG. 3 , the upper mold  21  and the lower mold  22  are removed. The surrounding wall portion  23  is disposed on the upper surface  1211  of the first portion  121  of the lead  12 , and exposes the upper surface  131  of the die paddle  13  and the upper surface  1211  of the first portion  121  of the lead  12 . The die paddle  13  and the surrounding wall portion  23  form an accommodation space  14 . The lower cover portion  24  is disposed on the lower surface  1212  of the first portion  121  of the lead  12 .  
         [0008]     Afterwards, a chip  15  is provided. The chip  15  has an active surface  151  and a back surface  152 . The back surface  152  of the chip  15  is attached to the upper surface  131  of the die paddle  13  in the accommodation space  14  by using an adhesive layer  16 .  
         [0009]     Then, a plurality of wires  17  are used to electrically connect the active surface  151  of the chip  15  to the upper surface  1211  of the first portion  121  of the lead  12 .  
         [0010]     Referring to  FIG. 4 , a top cover  18  is provided for covering the surrounding wall portions  23  so as to seal the accommodation space  14 . If the chip  15  is an optical element, the top cover  18  is usually made of a transparent glass material. Finally, the lead frame  10  is partitioned to segregate the package units  11  thereon, i.e., to obtain a plurality of QFN packages  20 .  
         [0011]     The disadvantage of the conventional fabricating method is described as follows. The first portion  121  of the lead  12  is thinner than the second portion  122 , so after the upper mold  21  and the lower mold  22  clamp the lead frame  10  in  FIG. 2 , the first portion  121  becomes a free end. Therefore, after the molding compound is injected, a part of the molding compound enters the upper surface  1211  of the first portion  121  and the lower surface of the upper mold  21 , thus causing bleeding. As such, during continuous wire bonding operation, the wires  17  cannot be effectively connected to the upper surface  1211  of the first portion  121 , thereby causing a failure or product defect.  
         [0012]     Consequently, there is an existing need for a package structure and a package method to solve the above-mentioned problems.  
       SUMMARY OF THE INVENTION  
       [0013]     The objective of the present invention is to provide a package method, wherein a protruding block is added to the lower mold, and the upper mold and the protruding block respectively clamp the upper and lower surfaces of the first portion of the lead, thus preventing the molding compound from bleeding to the upper surface of the first portion, thereby improving the product yield.  
         [0014]     Another objective of the present invention is to provide a package method, including the following steps:  
         [0015]     (a) providing a lead frame, the lead frame having a plurality of package units, each package unit having a plurality of leads and a die paddle, wherein the leads surround the die paddle, each of the leads has an upper surface and a lower surface, and the die paddle has an upper surface and a lower surface;  
         [0016]     (b) providing an upper mold and a lower mold, for clamping the lead frame, wherein the upper mold presses against the upper surfaces of the leads and the upper surfaces of the die paddles, and the lower mold has at least one protruding block pressing against the lower surfaces of the leads;  
         [0017]     (c) injecting a molding compound between the upper mold and the lower mold, for forming a plurality of surrounding wall portions and a plurality of lower cover portions, wherein the surrounding wall portions are disposed on the upper surfaces of the leads and expose the upper surfaces of the die paddles and part of the upper surfaces of the leads, each die paddle and each surrounding wall portion form an accommodation space, and the lower cover portions are disposed on the lower surfaces of the leads;  
         [0018]     (d) attaching a plurality of chips on the die paddles in the accommodation spaces;  
         [0019]     (e) electrically connecting the chips to the upper surface of the leads;  
         [0020]     (f) sealing the accommodation spaces; and  
         [0021]     (g) segregating the package units.  
         [0022]     Yet another objective of the present invention is to provide a package structure having a recession portion on the surface. The package structure includes a lead frame, a molding compound, a chip, and a top cover. The lead frame has a plurality of leads and a die paddle. The leads surround the die paddle, and each of the leads has a first portion with an upper surface and a lower surface. The die paddle has an upper surface and a lower surface.  
         [0023]     The molding compound includes a surrounding wall portion and a lower cover portion. The surrounding wall portion is disposed on the upper surface of the first portion, and exposes the upper surface of the die paddle and the upper surface of the first portion. The die paddle and the surrounding wall portion form an accommodation space. The lower cover portion is disposed on the lower surface of the first portion, and has at least one recession portion exposing a part of the lower surface of the first portion. The chip is disposed on the die paddle in the accommodation space, and is electrically connected to the upper surface of the first portion via a plurality of wires. The top cover is disposed above the chip for sealing the accommodation space. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]     FIGS.  1  to  4  show the schematic sectional views of the method for making a conventional QFN package with an opening;  
         [0025]     FIGS.  5  to  11  show the schematic views of the method for making a package structure having a recession portion on the surface according to the first embodiment of the present invention;  
         [0026]      FIG. 12  shows the schematic cross-sectional view of the package structure according to the second embodiment of the present invention;  
         [0027]      FIG. 13  shows the bottom schematic perspective view of the package unit according to the second embodiment of the present invention;  
         [0028]      FIG. 14  shows the schematic cross-sectional view of the package structure according to the third embodiment of the present invention;  
         [0029]     FIGS.  15  to  18  show the schematic cross-sectional views of the method for making the package structure according to the third embodiment of the present invention;  
         [0030]      FIG. 19  shows the schematic cross-sectional view of the package structure according to the fourth embodiment of the present invention;  
         [0031]      FIG. 20  shows the schematic cross-sectional view of the package structure according to the fifth embodiment of the invention;  
         [0032]      FIG. 21  shows the schematic cross-sectional view of the package structure according to the sixth embodiment of the invention;  
         [0033]      FIG. 22  shows the schematic cross-sectional view of the package structure according to the seventh embodiment of the invention;  
         [0034]      FIG. 23  shows the schematic cross-sectional view of the package structure according to the eighth embodiment of the invention; and  
         [0035]      FIG. 24  shows the schematic cross-sectional view of the package structure according to the ninth embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0036]     Referring to FIGS.  5  to  11 , the schematic sectional views of the method for making a package structure having a recession portion on the surface according to the first embodiment of the present invention are illustrated. First, referring to  FIG. 5 , a lead frame  30  is provided. The lead frame  30  includes a plurality of package units  31 , but only one package unit  31  is illustrated hereinafter. The package unit  31  has a plurality of leads  32  and a die paddle  33 , with the leads  32  surrounding the die paddle  33 . The die paddle  33  has an upper surface  331  and a lower surface  332 . In the embodiment, the upper surface  331  of the die paddle  33  has a plurality of ribs (not shown), for increasing the force for holding the chip. Each lead  32  has a first portion  321  and a second portion  322 . The first portion  321  has an upper surface  3211  and a lower surface  3212 , and the second portion  322  has an upper surface  3221  and a lower surface  3222 . The upper surfaces  3211 ,  3221  constitute the upper surface of the lead  32 , and the lower surfaces  3212 ,  3222  constitute the lower surface of the lead  32 . The upper surface  3211  of the first portion  321  is used for wire bonding. The first portion  321  is thinner than the second portion  322 , so as to form a step-like appearance.  
         [0037]     Afterward, referring to  FIG. 6 , an upper mold  41  and a lower mold  42  are provided for clamping the lead frame  30 . The upper mold  41  presses against the upper surface  3211  of the first portion  321  of the lead  32  and the upper surface  331  of the die paddle  33 . The upper mold  41  has a cavity  411 . In the embodiment, the upper mold  41  further includes at least one pin  412  extending into the cavity  411 .  
         [0038]     The lower mold  42  presses against the lower surface  3222  of the second portion  322  of the lead  32  and the lower surface  332  of the die paddle  33 . Moreover, the lower mold  42  further includes at least one protruding block  421  pressing against the lower surface  3212  of the first portion  321  of the lead  32 . By using the protruding block  421  and the upper mold  41  to clamp the first portion  321  of the lead  32 , the molding compound can be prevented from bleeding to the upper surface  3211  of the first portion  321  during continuous mold filling operation.  
         [0039]     Then, a molding compound is injected between the upper mold  41  and the lower mold  42 , for forming a surrounding wall portion  43  and a lower cover portion  44 .  
         [0040]     Then, referring to  FIG. 7 , the upper mold  41  and the lower mold  42  are removed. The surrounding wall portion  43  is disposed on the upper surface  3211  of the first portion  321  of the lead  32 , and exposes the upper surface  331  of the die paddle  33  and part of the upper surface  3211  of the first portion  321  of the lead  32 . The die paddle  33  and the surrounding wall portion  43  form an accommodation space  34 . The surrounding wall portion  43  has at least one hole  431  formed by the pin  412 . The lower cover portion  44  is disposed on the lower surface  3212  of the first portion  321  of the lead  32 , and has at least one recession portion  441 . The recession portion  441  is formed by the protruding block  421 , and exposes a part of the lower surface  3212  of the first portion  321 . The top and the bottom schematic stereograms of the package unit  31  are shown respectively in  FIG. 8  and  FIG. 9 .  
         [0041]     After that, a chip  35  is provided. The chip  35  has an active surface  351  and a back surface  352 . The back surface  352  of the chip  35  is attached to the upper surface  331  of the die paddle  33  in the accommodation space  34  via an adhesive layer  36 .  
         [0042]     Then, a plurality of wires  37  are used to electrically connect the active surface  351  of the chip  35  to the upper surface  3211  of the first portion  321  of the lead  32 .  
         [0043]     Then, referring to  FIG. 10 , a gel  45  is injected into the accommodation space  34 . It should be noted that the step of injecting the gel  45  is not necessary in the invention, i.e., the gel  45  may not be injected according to the invention. Then, a top cover  38  is provided for covering the surrounding wall portion  43  so as to seal the accommodation space  34 . In the embodiment, the top cover  38  has at least one through hole  381 , for exhausting the compressed air inside the accommodation space  34  when the top cover  38  is put on. If the chip  35  is an optical element, the material of the top cover  38  usually can be a transparent glass material. If the chip  35  is not an optical element, the material of the top cover  38  can be ceramic, plastic, metal, or the like. In the embodiment, the gel  45  is injected at first and then the top cover  38  is put on. However, the gel  45  can also be injected via the through hole  381  after the top cover  38  is put on.  
         [0044]     Referring to  FIG. 11 , the partial enlarged schematic view of the surrounding wall portion of the molding compound according to the invention is illustrated. In the invention, a plurality of cutouts  432  is disposed in the surrounding wall portion  43  for preventing the gel  45  from suddenly bleeding out of the accommodation space  34 . The cutouts  432  are of a step-like appearance, for increasing the accommodation space of the gel  45 . When the liquid level of the gel  45  rises gradually, the gel  45  will enter the cutouts  432  at first, instead of bleeding out of the accommodation space  34  at once.  
         [0045]     Finally, the lead frame  30  is partitioned to segregate the package units  31  thereon, i.e., to obtain a plurality of package structures  40  according to the first embodiment.  
         [0046]     Referring to  FIG. 10  again, the schematic cross-sectional view of the package structure according to the first embodiment of the present invention is shown. The package structure  40  includes a lead frame  30 , a molding compound, a chip  35 , a gel  45 , and a top cover  38 .  
         [0047]     The lead frame  30  has a plurality of leads  32  and a die paddle  33 . The leads  32  surround the die paddle  33 , and the die paddle  33  has an upper surface  331  and a lower surface  332 . In the embodiment, the upper surface  331  of the die paddle  33  has a plurality of ribs (not shown), for increasing the force for holding the chip  35 . Each lead  32  has a first portion  321  and a second portion  322 . The first portion  321  has an upper surface  3211  and a lower surface  3212 , while the second portion  322  has an upper surface  3221  and a lower surface  3222 . The upper surfaces  3211 ,  3221  constitute the upper surface of the lead  32 , and the lower surfaces  3212 ,  3222  constitute the lower surface of the lead  32 . The upper surface  3211  of the first portion  321  is used for wire bonding. The first portion  321  is thinner than the second portion  322 , so as to form a step-like appearance. The thickness of the die paddle  33  is identical to that of the second portion  322 . The height of the upper surface  3211  of the first portion  321  of the lead is identical to that of the upper surface  331  of the die paddle  33 . The height of the lower surface  3222  of the second portion  322  of the lead is identical to that of the lower surface  332  of the die paddle  33 .  
         [0048]     The molding compound includes a surrounding wall portion  43  and a lower cover portion  44 . The surrounding wall portion  43  is disposed on the upper surface  3211  of the first portion  321 , and exposes the upper surface  331  of the die paddle  33  and the upper surface  3211  of the first portion  321 . The die paddle  33  and the surrounding wall portion  43  form an accommodation space  34 . Preferably, the surrounding wall portion  43  has at least one hole  431  for positioning. The lower cover portion  44  is disposed on the lower surface  3212  of the first portion  321 , and has at least one recession portion  441  exposing a part of the lower surface  3212  of the first portion  321 .  
         [0049]     The chip  35  has an active surface  351  and a back surface  352 . The back surface  352  of the chip  35  is attached to the upper surface  331  of the die paddle  33  in the accommodation space  34  via an adhesive layer  36 , and a plurality of wires  37  is used for electrically connecting the active surface  351  of the chip  35  to the upper surface  3211  of the first portion  321 .  
         [0050]     The gel  45  is disposed in the accommodation space  34 , for preventing the wires  37  from contacting each other and being oxidized. The gel  45  can just be coated on the active surface  351  of the chip  35  or injected in the accommodation space  34 . Preferably, the surrounding wall portion  43  is provided with a plurality of cutouts  432  (as shown in  FIG. 11 ) for preventing the gel  45  from suddenly bleeding out of the accommodation space  34 .  
         [0051]     The top cover  38  is disposed above the chip  35 , for sealing the accommodation space  34 . If the chip  35  is an optical element, the material of the top cover  38  usually can be a transparent glass material. If the chip  35  is not an optical element, the material of the top cover  38  can be ceramic, plastic, metal, or the like. In the embodiment, the top cover  38  has at least one through hole  381 , for exhausting the compressed air inside the accommodation space  34  when the top cover  38  is put on, or for injecting the gel  45 .  
         [0052]     Referring to  FIG. 12 , a schematic cross-sectional view of the package structure according to the second embodiment of the present invention is shown. The package structure  40 A includes a lead frame  30 , a molding compound (having a surrounding wall portion  43  and a lower cover portion  44 ), a chip  35 , a gel  45 , and a top cover  38 . The package structure  40 A is substantially the same as the package structure  40  of the first embodiment, but the pattern of the lead frame  30  is different. In the embodiment, the thickness of the die paddle  33  is the same as that of the first portion  321  of the lead  32 . The height of the upper surface  3211  of the first portion  321  of the lead  32  is identical to that of the upper surface  331  of the die paddle  33 . The height of the lower surface  332  of the die paddle  33  is identical to that of the lower surface  3212  of the first portion  321  of the lead  32 .  
         [0053]     Furthermore, in the embodiment, the lower cover portion  44  covers the lower surface  332  of the die paddle  33 , and the lower cover portion  44  further includes at least one hole  442  exposing a part of the lower surface  332  of the die paddle  33 . The hole  442  is formed by adding a pin (not shown) to the lower mold  42 . When the upper and lower molds  41 ,  42  clamp the lead frame  30 , the pin presses against the lower surface  332  of the die paddle  33 , and forms the hole  442  after the mold filling operation, as shown in  FIG. 13 .  
         [0054]     Referring to  FIG. 14 , a schematic sectional view of the package structure according to the third embodiment of the present invention is shown. The package structure  40 B includes a lead frame  30 , a molding compound (having a surrounding wall portion  43  and a lower cover portion  44 ), a chip  35 , a gel  45 , and a top cover  38 . The package structure  40 B is substantially the same as the package structure  40  of the first embodiment, but the pattern of the lead frame  30  is different. In the embodiment, the lead frame  30  does not have the die paddle, and the leads  32  are arranged circularly. Each of the leads  32  has a first portion  321  and a second portion  322 .  
         [0055]     The molding compound includes the surrounding wall portion  43  and the lower cover portion  44 . The surrounding wall portion  43  is disposed on the upper surface  3211  of the first portion  321  of the lead  32 , and exposes the upper surface  3211  of the first portion  321  of the lead  32 . Preferably, the surrounding wall portion  43  also has a hole  431 . The lower cover portion  44  is disposed on the lower surface  3212  of the first portion  321  of the lead  32 , and has an upper surface  443  and a recession portion  441 . The lower cover portion  44  and the surrounding wall portion  43  form an accommodation space  34 . The recession portion  441  exposes the lower surface  3212  of the first portion  321  of the lead  32 . Preferably, the lower cover portion  44  also has a hole  442 .  
         [0056]     The chip  35  is provided with an active surface  351  and a back surface  352 . The back surface  352  of the chip  35  is attached to the upper surface  443  of the lower cover portion  44  in the accommodation space  34  via an adhesive layer  36 , and the active surface  351  of the chip  35  is eclectically connected to the upper surface  3211  of the first portion  321  via a plurality of wires  37 . The top cover  38  is disposed above the chip  35 , for sealing the accommodation space  34 .  
         [0057]     Referring to FIGS.  15  to  18 , a method for fabricating the package structure according to the third embodiment of the present invention is illustrated. The fabricating method of the package structure  40 B is described as follows. First, referring to  FIG. 15 , a lead frame  30  is provided. The lead frame  30  has a plurality of package units  31 , and each package unit  31  has a plurality of leads  32  arranged circularly. Each of the leads  32  has a first portion  321  and a second portion  322 . The first portion  321  has an upper surface  3211  and a lower surface  3212 , and the second portion  322  has an upper surface  3221  and a lower surface  3222 . The upper surfaces  3211 ,  3221  form the upper surface of the lead  32 , and the lower surfaces  3212 ,  3222  form the lower surface of the lead  32 , wherein the upper surface  3211  of the first portion  321  is used for wire bonding.  
         [0058]     After that, referring to  FIG. 16 , an upper mold  41  and a lower mold  42  are provided for clamping the lead frame  30 . The upper mold  41  presses against the upper surface  3211  of the first portion  321  of the lead  32 . The lower mold  42  has at least one protruding block  421  and a pin  422 . The protruding block  421  presses against the lower surface  3212  of the first portion  321  of the lead  32 , and the pin  422  presses against the upper mold  41  to form the hole  442 . Then, a molding compound is injected between the upper mold  41  and the lower mold  42 , for forming the surrounding wall portions  43  and the lower cover portions  44 . After the upper mold  41  and the lower mold  42  are removed, the surrounding wall portions  43  are disposed on the upper surfaces  3211  of the first portions  321  of the leads  32 , and expose part of the upper surfaces  3211  of the first portions  321  of the leads  32 . The lower cover portions  44  are disposed on the lower surfaces  3212  of the first portions  321  of the leads  32 , and each of them has an upper surface  443 . The lower cover portion  44  and each surrounding wall portion  43  form an accommodation space  34 .  
         [0059]     Next referring to  FIG. 17 , the chip  35  is attached to the upper surface  443  of the lower cover portions  44  in the accommodation space  34 . Then, a plurality of wires  37  is formed to electrically connect the chip  35  to the upper surface  3212  of the first portion  321  of the lead  32 .  
         [0060]     Then, referring to  FIG. 18 , the top cover  38  is used to seal the accommodation space  34 . Finally, the lead frame  30  is partitioned to segregate the package units  31  thereon, i.e., to obtain a plurality of package structures  40 B.  
         [0061]     Referring to  FIG. 19 , a schematic cross-sectional view of the package structure according to the fourth embodiment of the present invention. The package structure  50  includes a lead frame  30 , a molding compound (having a surrounding wall portion  43  and a lower cover portion  44 ), a chip  35 , a gel  45 , and a top cover  38 . The package structure  50  is substantially the same as the package structure  40  of the first embodiment, but the pattern of the lead frame  30  is different. In the embodiment, the leads  32  are of a uniform thickness, while the lower surface  3212  of the first portion  321  of the lead  32  is higher than the lower surface  3222  of the second portion  322 , thus forming a bent appearance. The thickness of the die paddle  33  is identical to that of the first portion  321  of the lead  32 . The upper surface  331  of the die paddle  33  is of the same height as the upper surface  3211  of the first portion  321  of the lead  32 .  
         [0062]     Referring to  FIG. 20 , a schematic sectional view of the package structure according to the fifth embodiment of the present invention is shown. The package structure  50 A of the present embodiment is substantially the same as the package structure  40 A of the second embodiment, but the pattern of the lead frame  30  is different. In the embodiment, the leads  32  are of a uniform thickness, and the lower surface  3212  of the first portion  321  of the lead  32  is higher than the lower surface  3222  of the second portion  322 , so as to form a bent appearance. The die paddle  33  is thinner than the first portion  321  of the lead  32 . The upper surface  331  of the die paddle  33  is of the same height as the upper surface  3211  of the first portion  321  of the lead  32 .  
         [0063]     Referring to  FIG. 21 , a schematic cross-sectional view of the package structure according to the sixth embodiment is shown. The package structure  50 B of the present embodiment is substantially the same as the package structure  40 B of the third embodiment, but the pattern of the lead frame  30  is different. In the embodiment, the leads  32  are of a uniform thickness, and the lower surface  3212  of the first portion  321  of the lead  32  is higher than the lower surface  3222  of the second portion  322 , so as to form a bent appearance.  
         [0064]     Referring to  FIG. 22 , a schematic cross-sectional view of the package structure according to the seventh embodiment of the present invention is shown. The package structure  60  of the embodiment is substantially the same as the package structure  50  of the fourth embodiment, but the pattern of the lead frame  30  is different. In the embodiment, the lower surface  332  of the die paddle  33  is of the same height as the lower surface  3222  of the second portion  322  of the lead  32 .  
         [0065]     Referring to  FIG. 23 , a schematic cross-sectional view of the package structure according to the eighth embodiment of the present invention. The package structure  60 A of the embodiment is substantially the same as the package structure  50 A of the fifth embodiment, but the pattern of the lead frame  30  is different. In the embodiment, the die paddle  33  is thinner than the first portion  321  of the lead  32 . The upper surface  331  of the die paddle  33  is lower than the upper surface  3211  of the first portion  321  of the lead  32 . And the lower surface  332  of the die paddle  33  is higher than the lower surface  3222  of the second portion  322  of the lead  32 .  
         [0066]     Referring to  FIG. 24 , a schematic cross-sectional view of the package structure according to the ninth embodiment of the present invention. The package structure  60 B of the embodiment is substantially the same as the package structure  5 OB of the sixth embodiment, but the pattern of the lead frame  30  is different. In the embodiment, the upper surface  443  of the lower cover portion  44  is lower than the upper surface  3211  of the first portion  321  of the lead  32 .  
         [0067]     While several embodiments of the present invention have been illustrated and described, various modifications and improvements can be made by those skilled in the art. The embodiments of the present invention are therefore described in an illustrative but not restrictive sense. It is intended that the present invention may not be limited to the particular forms as illustrated, and that all modifications which maintain the spirit and scope of the present invention are within the scope as defined in the appended claims.