Abstract:
A mold has two mold halves ( 6, 7 ). One of the mold halves ( 6 ) includes a contact section ( 8 ) which is adapted to contact a surface ( 5 ) of a semiconductor chip ( 1 ) mounted in the mold, in use.

Description:
FIELD OF THE INVENTION  
         [0001]    The invention relates to a mold, and especially, a mold for molding an encapsulating material around a semiconductor chip.  
         SUMMARY OF THE INVENTION  
         [0002]    In accordance with first aspect of the present invention, there is provided a mold comprising two mold halves, one of the mold halves comprising a contact section which is adapted to contact a surface of a semiconductor chip mounted in the mold, in use.  
           [0003]    In accordance with another aspect of the present invention, there is provided a method of molding material around a semiconductor chip, the method comprising mounting the semiconductor chip on a substrate, inserting the substrate and semiconductor chip into a mold, such that a contact section of the mold contacts a surface of the chip, molding the molding material around the semiconductor chip and the contact section to form a molded package, and subsequently removing the molded package from the mold.  
           [0004]    An advantage of the invention is that by providing a mold with a portion which contacts a surface of the semiconductor chip, it is possible to prevent molding material from covering the semiconductor chip where the portion of the mold contacts the semiconductor chip. This is especially useful where it is desirable to leave a surface of the semiconductor chip, or a portion of a surface, free of molding material.  
           [0005]    Preferably, the contact section of the mold, which is adapted to engage with the surface of the semiconductor chip, is in the form of a removable member which is mounted on one of the mold halves. Preferably, the removable member is mounted for movement relative to the mold half on which it is mounted.  
           [0006]    Preferably, the mold further comprises biasing means to bias the member into a mold cavity defined by the mold halves.  
           [0007]    In one example of the invention, the contact section comprises a compressible material, such as rubber or an elastomeric material.  
           [0008]    Typically, the surface of the contact section, which is adapted to contact the surface of a semiconductor chip is use, may be profiled to minimise seepage of molding material between the section of the mold and the surface of the semiconductor chip during molding.  
           [0009]    Typically, the surface of the chip contacted by the contact section may be an active surface or a non-active surface of the chip. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    Examples of a mold in accordance with the invention will now be described with reference to the accompanying drawings, in which:  
         [0011]    [0011]FIG. 1A is a cross-sectional view of a semiconductor chip mounted on a substrate;  
         [0012]    [0012]FIG. 1B is a cross-sectional view of a first example of a mold having an insert for molding an encapsulating material around the semiconductor chip and substrate shown in FIG. 1A;  
         [0013]    [0013]FIG. 2 is a cross-sectional view of a second example of a mold having an insert with a semiconductor chip and substrate located within the mold; and  
         [0014]    [0014]FIG. 3 is a cross-sectional view of a third example of a mold having an insert with a semiconductor chip and substrate shown located within the mold. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0015]    [0015]FIG. 1A shows a flip chip type semiconductor chip  1  which is electrically and physically connected to a substrate  2  by solder bumps  3  formed on bond pads (not shown) on the active surface of the chip  1 . The chip  1  and solder bumps  3  are connected to the substrate  2  using a conventional solder reflow process. It will be noted that the substrate  2  has two bent sections  4 . The bent sections  4  introduce flexibility to the substrate  2  so that if a force is applied to top surface  5  of the chip  1  the substrate  2  flexes at the bent sections  4  so that the force on the surface  5  moves the chip  1  downwards.  
         [0016]    [0016]FIG. 1B shows a mold which comprises an upper mold half  6  and a lower half  7 , which define a mold cavity  9 . An insert  8  may be inserted through an aperture in the upper mold half  6  so that surface  10  of the insert  8  enters the mold cavity  9 . The mold cavity  9  has a distance “d” between the upper surface of the upper mold half  6  and the lower surface of the lower mold half  7 . This dimension “d: is equal to the height “D” between the substrate  2  and the surface of the chip  1 , as shown in FIG. 1A. When the semiconductor chip  1  and substrate  2  are inserted into the mold and the upper mold half is closed onto the lower mold half  7 , the surface  10  of the insert  8  engages with the surface  5  of the chip  1  and as the mold halves  6 ,  7  are clamped shut, the force exerted by the insert  8  on the surface  5  causes the substrate  2  to flex at the bent sections  4  so that the semiconductor chip  1  is pushed downwards in the mold cavity  9  by the insert  8 . This downward force exerted by the insert  8  acts to generate a sealing pressure between the surface  10  and the surface  5  so that when molding material is injected into the mold cavity  9 , the molding material molds around the semiconductor chip  1 , the substrate  2  and solder bumps  3  but seepage of molding material between the surfaces  5 ,  10  is minimised. Hence, when the molded product is removed from the mold, the portion of the surface  5  which has been contacted by the surface  10  is free of molding material and so the portion of the surface  5  which has been contacted by the surface  10  is exposed.  
         [0017]    [0017]FIG. 2 shows a second example of a mold which comprises an upper mold half  15  and a lower mold half  16  which define a mold cavity  17 . An insert  19  may be inserted through an aperture in the upper mold half  15  so that a lower end  20  is located within the mold cavity  17 . The lower end  20  comprises a profiled edge  21  which extends along the outside of the lower end  20  and engages with a surface  26  of a semiconductor chip  22  located in the mold cavity  17 . A steel holder  18  encircles the insert  19  and provides a means to enable the insert  19  to be mounted on the mold.  
         [0018]    The semiconductor chip  22  is mounted on a substrate  23  (which may be metal or non-metal) by a layer of die attach epoxy  24 . Wire bonds  25  extend between bond pads (not shown) on the surface  26  of the chip  22  and electrical contact zones on the substrate  23 .  
         [0019]    The insert  19  is manufactured from a compressible material so that when the mold halves  15 ,  16  are closed, edge  21  of the insert compresses onto the surface  26  of the die  22  to minimise seepage of molding material between the surface  26  and the edge  21  with the section of the surface  26  located between the edges  21  is not covered by molding material.  
         [0020]    Therefore, when the chip  22  and substrate  23  are removed from the mold after a molding operation, the surface  26  covered by the insert  19  is free from molding material and is exposed.  
         [0021]    [0021]FIG. 3 shows a third example of a mold comprising mold halves  35 ,  36  which define a mold cavity  37 . The mold uses an insert  39  with a metal holder  38  which are similar to the insert  19  and holder  18  shown in FIG. 2. However, in this instance, a semiconductor chip  30  is mounted on a flat substrate  31  by a layer of die attach epoxy  32  and wire bonds  33  extend between bond pads (not shown) on surface  34  of the chip  30  and corresponding electrical contact areas on the substrate  31 . In this example, the substrate  31  (which may be metal or non-metal) lies on the lower surface of the lower mold half  35  so that when mold halves  35 ,  36  are closed, the insert  39  presses against the upper surface  34  of the chip  30  and the substrate  31  is pressed against the lower mold half  35 .  
         [0022]    Hence, when molding material is injected into the mold cavity  37  defined by the mold halves  35 ,  36 , the molding material is prevented from covering the surface  34  of the chip  30  by the edges  41  of the insert  39  and is prevented from covering the lower side of the substrate  31  by the fact that the lower side of the substrate  31  is pressed against the lower side of the lower mold half  35 .  
         [0023]    Hence, the invention has the advantage of permitting semiconductor chips to be encapsulated with a molding material while leaving a portion of a surface of the semiconductor chip free from molding material so that it is exposed. For example, it may be desirable to leave a surface of a semiconductor chip exposed for cooling reasons, or if the semiconductor chip forms a pressure or temperature sensor and the exposed part of the surface is the sensing portion of the chip.