Abstract:
A cavity for receiving insertion of a plunger is designed so that the plunger may be withdrawn without permitting creation of a suction force sufficient to remove from the cavity a workpiece that the plunger carried into the cavity.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates generally to cooperation between a plunger and a receiving cavity and, more particularly, to avoiding creation of suction force upon plunger withdrawal. 
       BACKGROUND OF THE INVENTION 
       [0002]    In conventional integrated circuit (IC) manufacturing, a mold die is used to encapsulate the integrated circuit die in a mold compound (or other similar encapsulant), resulting in an encapsulated IC package. When the encapsulated IC package is removed from the mold die, one or more unwanted remnants of the mold compound typically remain attached to the package, and must be removed. A so-called gate corner slug is a known example of such an unwanted remnant. The gate corner slug is simply residual mold compound that accumulates at the point where the mold die gates the mold compound to the IC die for encapsulation.  FIGS. 1 and 2  illustrate a conventional apparatus for removing unwanted remnants such as the gate corner slug. The encapsulated IC package is placed on a die  21  shown in  FIGS. 1 and 2 , with the remnant overlying a cavity  22  in the die. The remnant is removed by inserting a reciprocating punch  23  into the die cavity  22  as shown in  FIG. 2 , and thereafter withdrawing the punch  23 . 
         [0003]      FIG. 3  diagrammatically illustrates the aforementioned remnant removal operation. At  31 , the punch  23  is inserted into the die cavity  22  to remove a remnant  32  from a lead frame  33  of an encapsulated IC package. As shown at  34 , when the punch  23  is withdrawn from the die cavity  22 , suction force  30  created by the withdrawal action may draw the remnant  32  (or at least a portion thereof) out of the die cavity  22 , where it may become a cause of damage to leads of the IC package. 
         [0004]    According to one conventional technique, the problem illustrated in  FIG. 3  may be avoided by increasing vacuum applied below the die  21  sufficiently to counteract the suction force created by punch withdrawal. Disadvantageously, however, the increased vacuum may contribute to damaging the encapsulated IC package while the package is positioned on the die  21 . 
         [0005]    It is desirable in view of the foregoing to provide for avoiding the aforementioned withdrawn remnant problem without risk of damage to the encapsulated IC package. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIGS. 1-4  illustrate structure, operation and problems associated with cooperable punch and die according to the prior art. 
           [0007]      FIGS. 5 and 6  illustrate structure of cooperable punch and die according to exemplary embodiments of the invention. 
           [0008]      FIG. 7  illustrates operations that may be performed according to exemplary embodiments of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0009]      FIG. 4  illustrates an example of the spatial relationship between a punch and cooperating die cavity of the type described above with respect to  FIGS. 1-3 . As shown in  FIG. 4 , an interior surface  41  of the die cavity  22  is in relatively close conformal relationship with the inserted punch  23 . With the surface  41  closely surrounding the inserted punch  23  as shown, the above-described suction force is created upon withdrawal of the punch  23 . Note that  FIG. 4  is a view from within the die cavity  22 , in the direction of punch withdrawal, and thus shows both the punch  23  and the undesired remnant  32  that the punch carries into the cavity. 
         [0010]      FIG. 5  is a view generally similar to that of  FIG. 4 , but illustrates a die  51  according to exemplary embodiments of the invention. The die  51  has provided therein a die cavity  53  whose interior surface is configured to provide additional air exhaust passages  52  within the die  51 . These added air exhaust passages  52  (not shown to scale for all embodiments) serve as auxiliary exhaust paths for pressurized air created by withdrawal of punch  23  from cavity  53 . Exhaustion of air through the passages  52  prevents punch withdrawal from creating a suction force sufficient to remove the remnant  32  from the cavity  53 . 
         [0011]    The interior surface of the die cavity  53  substantially surrounds the inserted punch  23  (in generally similar fashion to the interior die cavity surface  41  of  FIG. 4 ), facing generally transversely to the direction of punch insertion/withdrawal. The interior surface of die cavity  53  includes an inner surface portion  57  that faces the inserted punch  23  and generally conforms to the profile of the punch. The inner surface portion  57  is laterally spaced from the punch  23  by generally the same distance that separates the punch  23  from the interior surface  41  of the die cavity  22  in prior art  FIG. 4 . The interior surface of the die cavity  53  of  FIG. 5  further includes a plurality of sets of further surface portions. Each set of further surface portions defines a corresponding one of the air exhaust passages  52 . One such set of further surface portions is identified in detail with respect to the air exhaust passage  52  highlighted in  FIG. 5 . 
         [0012]    In particular, and as demonstrated by the example highlighted in  FIG. 5 , each air exhaust passage  52  is defined by an outer surface portion  55  and a corresponding pair of connecting surface portions  56 . The outer surface portion  55  faces the inserted punch  23 , but is located laterally further from the punch than the inner surface portion  57 . The connecting surface portions  56  face one another and extend laterally to connect the outer surface portion  55  to the inner surface portion  57 . Each of the connecting surface portions  56  joins the inner surface portion  57  to define an edge  58 . 
         [0013]    In some embodiments, the outer portions  55  and connecting surface portions  56  are generally planar surface portions. In some embodiments, all of the surface portions  55 - 57  are oriented to extend into the die  51  generally parallel to the insertion/withdrawal direction of the reciprocating punch  23 . In some embodiments, each outer surface portion  55  is oriented to be generally parallel to that part of the inner surface portion  57  to which it is connected by its corresponding pair of connecting surface portions  56 . In some embodiments, the connecting surface portions  56  are oriented generally parallel to one another, and perpendicularly relative to their corresponding outer surface portion  55 . 
         [0014]    In various embodiments, the pressure relief operation described above is realized by providing a die cavity having at least one air exhaust passage such as the examples  52  shown in  FIG. 5 . An air exhaust passage is provided by configuring the interior die cavity surface with an inner surface portion (such as the example  57  of  FIG. 5 ) and an outer surface portion (such as the example  55  in  FIG. 5 ) located further from the inserted punch  23  than the inner surface portion. Although the air exhaust passages  52  in the example of  FIG. 5  have generally planar surfaces and a generally rectangular cross-sectional profile, various other embodiments provide one or more air exhaust passage(s), with the passage(s) having various other surface configurations and various other cross-sectional profiles. 
         [0015]      FIG. 6  is a pictorial view of the above-described cooperating punch  23  and die  51  with air exhaust passages  52  according to exemplary embodiments of the invention. 
         [0016]    Various embodiments apply the above-described techniques with various types of reciprocating plungers that are received in cooperating cavities formed in various types of structures to prevent undesired withdrawal of various types of workpieces. 
         [0017]      FIG. 7  illustrates operations that may be performed according to exemplary embodiments of the invention. At  71 , a plunger is inserted into a cavity to move a workpiece into the cavity. At  73 , the plunger is withdrawn without permitting a withdrawal suction force sufficient to remove the workpiece from the cavity. 
         [0018]    Although exemplary embodiments of the invention have been described above in detail, this does not limit the scope of the invention, which can be practiced in a variety of embodiments.