Abstract:
An integrated circuit (“IC”) package mold includes an upper mold platen that defines an upper mold cavity for receiving an upper substrate having a die attach side with a plurality of dies mounted thereon and a non-attach side with no dies mounted thereon. The die attach side of the upper substrate faces upwardly. A lower mold platen defines a lower mold cavity for receiving a lower substrate having a die attach side with a plurality dies mounted thereon and a non-attach side with no dies mounted thereon. The die attach side of the lower substrate faces downwardly.

Description:
BACKGROUND 
       [0001]    Integrated circuits, also referred to as “IC&#39;s” or “semiconductor chips” or simply “chips,” are electronic circuits made by diffusion of trace elements into the surface of thin substrates of semiconductor material. Integrated circuits were first produced in the mid 20 th  Century. Because of their small size and relatively low production cost, integrated circuits are now used in most modern electronics. Semiconductor chips are typically mass produced in the form of a single wafer that contains a large number of identical integrated circuits. The wafer is cut (“singulated”) into a number of individual semiconductor chips referred to as “dies” or “dice.” 
         [0002]    Dies and sometimes other components such as passive devices are “packaged” to prevent damage to the dies and to facilitate attachment of the dies to circuit boards. Various packaging materials and processes have been used to package integrated circuit dies. One conventional packaging method involves mounting individual dies in a predetermined pattern on a substrate strip. The dies mounted on the substrate strip are then encapsulated in a plastic material, such as by a transfer molding process. Next, the encapsulated dies are singulated into individual integrated circuit packages by cutting the encapsulated die/substrate strip in accordance with the predetermined die mounting pattern. Typical cutting tools include saws and punches. Each integrated circuit package generally includes at least one die and the underlying portion of the substrate strip on which it was mounted. The underlying substrate strip is sometimes a leadframe to which the die is electrically connected. 
       SUMMARY 
       [0003]    An integrated circuit (“IC”) package mold assembly includes an upper mold platen defines an upper mold cavity for receiving an upper substrate having a die attach side with a plurality of dies mounted thereon and a non-attach side with no dies mounted thereon. The die attach side faces upwardly. A lower mold platen defines a lower mold cavity for receiving a lower substrate having a die attach side with a plurality dies mounted thereon and a non-attach side with no dies mounted thereon. The die attach side of the lower substrate faces downwardly. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]      FIG. 1  is a cross-sectional elevation view of a prior art mold assembly. 
           [0005]      FIG. 2  is a cross-sectional elevation view of an example embodiment of a mold assembly that includes a mold with a double cavity configuration. 
           [0006]      FIG. 3  is a cross-sectional elevation view of another example embodiment of a double cavity mold assembly. 
           [0007]      FIG. 4  is a detail isometric view of a portion of the double cavity mold assembly of  FIG. 3 . 
           [0008]      FIG. 5  is a cross-sectional elevation view of a portion of another example embodiment of a double cavity mold assembly. 
           [0009]      FIG. 6  is a flow chart that illustrates a method of making integrated circuit (“IC”) packages. 
       
    
    
     DETAILED DESCRIPTION 
       [0010]      FIG. 1  is a cross-sectional elevation view of a prior art mold assembly  10 . The mold assembly  10  includes a mold  11 , such as an injection mold, that has an upper mold platen  12  and a lower mold platen  14 . The upper mold platen  12  has a mold cavity  16  therein in fluid communication with a mold runner  18 . The mold assembly  10  also includes a leadframe sheet  22  that is positioned within the mold cavity  16 . The mold assembly  10  further includes a plurality of integrated circuit (IC) dies  24 ,  26 ,  28 , etc., which are attached to different portions  25 ,  27 ,  29 , etc., of the leadframe sheet  22 . Each of these portions  25 ,  27 ,  29  is associated with a separate IC package that will ultimately be formed by singulating (“dicing”) the leadframe sheet  22 . 
         [0011]    Each of the dies  24 ,  26 ,  28  is electrically connected to an associated leadframe portion  25 ,  27 ,  29  of the leadframe sheet  22 . In the assembly  10  of  FIG. 2  the dies are electrically connected to the leadframe sheet  22  by bond wires  30 . Each bond wire  30  has a first end  32  attached to an associated die, e.g., die  24 , and a second end  34  attached to the leadframe portion, e.g., portion  25 , on which the die is mounted. 
         [0012]    After insertion of the leadframe sheet  22  and attached wire bonded dies  24 , etc., the mold  10  is closed and the mold cavity  16  is filled with molten mold compound  40 . The mold compound  40  flows under pressure into the cavity  16  through the runner  18 , which is conventionally connected to a pressurized source of molten mold compound  40 . After the mold compound  40  has filled the cavity, curing of the mold compound commences, initially while the mold  10  is closed, and subsequently after it is has been opened and the entire assembly of leadframe sheet  22 , dies  24 , etc. and mold compound  40  has been removed. After removal from the mold  10 , the portion of the mold compound  40  that was in the runner  18  is removed from the portion of the mold compound covering the leadframe sheet  22 . The portion of the mold compound that was in the runner is scrapped as waste. This waste is typically around 40% of the total amount of mold compound injected in a molding operation. 
         [0013]    After the molded leadframe assembly has completed curing it is singulated along saw streets  36 ,  38 , etc., indicated by dashed lines in  FIG. 1 , into separate IC package units. 
         [0014]      FIG. 2  is a cross-sectional elevation view of an example embodiment of a mold assembly  110  that includes a mold  111  with a double cavity configuration. The mold  111  includes upper and lower mold platens  112 ,  114  having upper and lower mold cavities  116 ,  118 , respectively. A single mold runner  120  is in fluid communication with both mold cavities  116 ,  118 . 
         [0015]    The mold assembly  110  includes an upper substrate  122 , which may be a leadframe sheet substrate. Hereafter “leadframe sheet substrate” is referred to by the shorter phrase “leadframe sheet.” It is to be understood that substrates other than leadframe sheets may be used in the embodiments described in  FIGS. 2, 3 and 5 . 
         [0016]    The substrate  122  has a first end  124  and a second end  126  and has a die attach side  128  and an opposite or “non-attach side”  129 . A lower substrate  132 , which in this embodiment may be a leadframe sheet, has a first end  134  and a second end  136  and also includes a die attach side  138  and an opposite or non-attach side  139 . The upper substrate  122  and the lower substrate  132  each comprise a plurality of corresponding separate substrate portions  140  and  142 , respectively, which are vertically aligned. 
         [0017]    The mold assembly  110  also includes upper and lower substrate dies. The upper substrate dies  152  are mounted on the upper substrate portions  140  of the upper substrate  124  and are electrically connected thereto, as by upper bond wires  154 . Similarly lower substrate dies  162  are attached to the separate substrate portions  142  of the lower substrate  134  and are connected thereto by lower leadframe bond wires  164 . As illustrated in  FIG. 2 , a liner  170  may be used in some embodiments to separate the upper and lower substrates. In some embodiments when the respective substrates are, for example, nFBGA (New Fine Pitch Ball Grid Array packages) substrates or uBGA (Ultra FineLine Ball-Grid Array packages) substrates, rather than leadframe sheets, no liner is needed. The liner  170  engages the non-attach sides  129 ,  139  of the substrates  122 ,  132 . 
         [0018]    As further illustrated by  FIG. 2 , the mold assembly also includes heated mold compound  178  that is injected into the single mold runner and flows therethrough to fill both the upper and lower mold cavities  116 ,  118 . The mold compound  178  is initially allowed to cure within the mold cavities  116 ,  118 . Subsequently, the entire substrate/die/bond wire/mold compound assembly, including the mold compound  178  within the runner  120 , is removed from the mold  111 . The solidified mold compound  178  within the runner  120  is then removed and scrapped. Because there is a single runner  120  associated with both mold cavities  116 ,  118 , the scrap produced by this new process is substantially reduced as compared to the scrap produced in the conventional process illustrated in  FIG. 1 . 
         [0019]    Next the upper and lower molded substrates  122 , etc.,  132 , etc., are separated and the liner  170 , if used, is removed. Each substrate  122 , etc.,  132 , and associated dies and mold compound, etc., is then singulated by conventional methods to provide a plurality of separate IC packages. 
         [0020]      FIG. 3  is a cross-sectional elevation view of another example embodiment of a double-sided mold assembly  210  including a mold  211  that has upper and lower mold platens  212 ,  214  having upper and lower mold cavities  216 ,  218 , respectively. The mold  211  has a single runner  220 . The assembly  210  illustrated in  FIG. 3  is similar to that illustrated in  FIG. 2 , and similar structures therein are given the identical reference numerals as in  FIG. 2 , except that the reference numerals are 200 series rather than 100 series. The structures include: runner  220 , upper substrate  222  having a first and second ends  224 ,  226  and die attach side  228  and non-attach side  229  and upper leadframe portions  240 ; a lower substrate  232  with a first and second ends  234 ,  236  and with a die attach side  238  and non-attach side  139  and separate upper and lower substrate portions  240  and  242 ; upper dies  252 , which may be electrically connected to the upper substrate by bond wires  254 ; lower dies with bond wires  264 ; liner  270 ; and mold compound  278 . One difference in the assembly of  FIG. 3  is that upper and lower passive components  253 ,  255  (e.g., resistors, capacitors and/or inductors) are also operably mounted on each substrate portion  240  or  242  and electrically connected to the die(s) on the associated portion  240  or  242 . Another difference in the assembly of  FIG. 3  from that of  FIG. 2  is that holes  280  have been bored through the two substrates  222 ,  232  and liner sheet  270  after initially sandwiching the liner sheet  270  between the two substrates  222 ,  232  and before insertion of this substrate/liner assembly into the mold  210 . These holes  280  may be bored at each corner intersection of the substrates when they comprise leadframe sheets  222 ,  232 . Four separate leadframe portions are integrally connected. (The illustrated embodiment shows the holes located at corner intersections of the sheets  222 ,  232 , but the holes  280  may be provided at other locations. For example, if the binding feature is larger than corner space allows, several of the dies may be eliminated and the holes can be located on the leadframes, or other substrates, where the dies have been eliminated.) 
         [0021]      FIG. 4  is a detail isometric view illustrating a portion of structure located around the holes  280  shown in  FIG. 3 . This structure includes a rectangular frame structure  284 . The rectangular frame structure laterally connects first, second, third and fourth upper leadframe portions  286 ,  288 ,  290 ,  292 , respectively, of the upper leadframe sheet  222 . The lower leadframe sheet  232  has an identical configuration (not shown) lying directly below that of sheet  222 . The hole  280  passes through the center of this rectangular frame portion  284  and an aligned portion  282  of the liner  270 . 
         [0022]    With reference to  FIG. 3 , the holes  280  through the assembled sheets  222 ,  270 ,  232  provide a path for molten mold compound  278 . The mold compound  278  that flows through the holes  280  forms a connecting structure that holds the two sheets  222 ,  232  together and in alignment during curing, including the curing phase that takes place after removal of the molded leadframe/die/bond wire structure from the mold  211 . The holes  280  may also help to provide pressure equalization between the upper and lower mold cavities  216  and  218  as molten mold compound flows into these cavities. The corner frame structure  284  and the mold compound  278  passing through the holes  280  are bored or cut out and removed after curing to allow the leadframe sheets  222 ,  232  to be separated and subsequently singulated. In another embodiment, the corner structure remains intact until singulation and the two connected molded leadframe sheets  222 ,  232  and liner  270  are all singulated simultaneously with deeper singulation cuts. The upper and lower IC package pairs, thus formed, are then separated. In this case, singulation removes the corner structure and connecting mold compound structure. 
         [0023]    The prior art structure, as shown by  FIG. 1 , has a metal leadframe sheet  22  on one side of the assembly, and epoxy encapsulant compound  40  on the other side. Due to a mismatch in thermal expansion of these two materials, when the assembly is ejected from the mold  11  and cools down from a high mold temperature, the encapsulated leadframe sheet  22  tends to warp. Such warping makes the prior art leadframe sheet  22  difficult to work with and, in some cases, is so severe that the molded leadframe sheet  22  must be scrapped. In the assembly of  FIG. 3 , the connecting structure formed by the mold compound  278  after it solidifies in holes  280 , combined with the symmetry of the two substrates, prevents warping of the substrates  222 ,  232 . 
         [0024]      FIG. 5  is a cross-sectional elevation view of a portion of another example embodiment of a double-sided mold assembly  310 . The mold assembly  310  includes a mold  311  that comprises upper and lower mold platens  312 ,  314  having upper and lower mold cavities  316 ,  318 , respectively. The mold  311  may be identical to the mold  211  illustrated in  FIG. 3 , except that upper projections  317  and lower projections  319  extends from the upper and lower mold platens, like symmetrical stalactites and stalagmites, to form a clamping assembly that sandwiches and holds upper and lower leadframes/substrates  322 ,  332  therebetween. These projections  317 ,  319  may be provided by ribs that are integrally formed with the respective upper and lower mold platens  312 ,  314  or may be provided by pins inserted through the walls of the mold platens or may be formed by other means. The projections may engage the leadframes/substrates  322 ,  332  at the boundaries of adjacent substrate portions, such that any irregularities in the mold compound layer formed by the projections  317 ,  319  is trimmed off during subsequent singulation. 
         [0025]    This clamping assembly  317 ,  319  vertically supports the leadframes  322 ,  332 , counteracting a tendency of the leadframes to droop under their own weight prior to the inflow of mold compound (not shown in  FIG. 5 ). 
         [0026]    As used herein terms such as up, down, above, under, vertical, horizontal, etc., are used in a relative sense to explain the physical relationship between various structures shown in the drawings, rather than in an absolute sense indicating an orientation of objects within a gravitational field. 
         [0027]      FIG. 6  is a flow chart that illustrates a method of making integrated circuit (“IC”) packages. The method includes, as shown at  601 , placing first and second IC package substrates having a plurality of individual portions associated with individual IC packages in non-attach side facing, mirror image relationship. The method also includes, as shown at  602 , placing the first and second substrates in a mold having upper and lower cavities with the first substrate positioned in an upper mold platen cavity and the second substrate positioned in a lower mold platen cavity that is in fluid communication with the upper mold platen cavity. As shown at  603 , the method further includes filling the upper and lower mold cavities with molten mold compound. 
         [0028]    Certain specific embodiments of double cavity mold assemblies and methods of use thereof have been expressly described in detail herein to aid those reading this disclosure to understand the inventive concepts involved. Alternative embodiments of such mold assemblies and methods will occur to those skilled in the art after reading this disclosure. It is intended that the language of the appended claims be broadly construed to cover such alternative embodiments, except as limited by the prior art.