Abstract:
A ball grid array IC package and manufacturing method thereof comprise spherical conductive balls that are changed into a shape having an hourglass type feature. A semiconductor chip having a plurality of chip pads, a substrate having ball lands, hourglass type conductive balls electrically connected to the chip pads and to the ball lands, and an interval maintaining member maintaining a uniform interval between the semiconductor chip and substrate. The method includes a heat treatment that expands the interval maintaining member to provide a uniform width between the surface of the chip and the substrate so that the conductive balls change into the hourglass shape, after which removal of the heat treatment decreases the size of the interval maintaining member so that the physical separation between the surfaces is provided by the connecting members having the hourglass shapes.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates generally to a semiconductor or integrated circuit (IC) package and manufacturing method thereof, and more particularly, to a ball grid array package and manufacturing method thereof for providing an IC package in which leads comprising spherical conductive balls are changed into an hourglass type features.  
           [0003]    2. Description of the Related Art  
           [0004]    Generally, a ball grid array for an IC package uses conductive balls, such as solder balls and the like, which are arranged on a back surface of a substrate, to provide external leads. As a result, ball grid array packages provide a reduction in IC size, and further reduces the occurrence of lead deformation, unlike QFP (Quad Flat Package) packages.  
           [0005]    [0005]FIG. 1A illustrates a cross-sectional view of a ball grid array package according to a first embodiment of a conventional IC package, and FIG. 1B illustrates a cross-sectional view of a ball grid array package according to a second embodiment of a conventional IC package.  
           [0006]    Generally, ball grid array IC packages having the above-mentioned advantages are divided into two types, a vessel type having a ship feature shown in FIG. 1A, and an hourglass type having an hourglass feature shown in FIG. 1B, in accordance with conventional packages utilizing conductive balls  112  mounted on a substrate A ball grid array package manufactured as either a vessel or hourglass type undergoes a reliance test against heat at a temperature of 200 to 25° C.  
           [0007]    During the reliance test against heat at these temperatures, the conductive balls  114  of the vessel type ball grid package are metamorphosed from a spherical type into an elliptic type as shown in FIG. 1A. Stresses are generated from the interfaces among the conductive balls  114 , a print circuit board (PCB, hereinafter called substrate)  100  in contact with the conductive balls  114 , and the semiconductor chip  110 , which may result in formation of cracks in one or more of the contacting members.  
           [0008]    In order to overcome the manufacturing problems of vessel type packages, an hourglass type ball grid array package having an excellent joint reliance for a solder joint and an excellent thermal reliance has been proposed. Unfortunately, the hourglass type package needs an additional process of pulling up a semiconductor chip in vacuum, which requires using additional equipment so as to metamorphose a conductive ball into an hourglass type cylinder.  
         SUMMARY OF THE INVENTION  
         [0009]    Accordingly, the present invention is directed to a ball grid array IC package and manufacturing method thereof that substantially obviates one or more of the problems resulting from the limitations and disadvantages of the related art.  
           [0010]    One object of the present invention is to provide a ball grid array package allowing metamorphosis of a conductive ball into an hourglass feature with ease by maintaining a uniform interval between a semiconductor chip and a substrate.  
           [0011]    Another object of the present invention is to provide a method of manufacturing a ball grid array package allowing the metamorphosis of a conductive ball into an hourglass feature with ease by utilizing a member that provides a uniform interval between a semiconductor chip and a substrate.  
           [0012]    Additional features and advantages of the invention will be set forth in the following detailed description, and in part will be apparent from the description, or may be learned by practice of the invention as herein disclosed. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.  
           [0013]    To achieve these and other advantages, and in accordance with the purpose of the present invention as embodied and broadly described, ball grid array IC packages according to the present invention include a semiconductor chip having a plurality of chip pads, a substrate having ball lands, hourglass type conductive balls electrically connected to the chip pads and landed at the ball lands, respectively, and an interval maintaining member maintaining a uniform interval between the semiconductor chip and substrate.  
           [0014]    In another embodiment, a method of manufacturing ball grid array IC packages according to the present invention includes the steps of providing a semiconductor chip having a plurality of chip pads, attaching spherical conductive balls and an expansive interval maintaining member on the chip pads, mounting the conductive balls on the ball lands, and expanding a volume of the interval maintaining member by carrying out thermal treatment on the resultant so as to change the spherical conductive balls into shapes including hourglass features.  
           [0015]    In a further embodiment, a method of manufacturing ball grid array IC packages according to the present invention includes the steps of providing a semiconductor chip having a plurality of chip pads, forming spherical conductive balls on the chip pads, forming ball lands and an expansive interval maintaining member on a substrate, mounting the conductive balls on the ball lands, and expanding a volume of the interval maintaining member by carrying out thermal treatment on the resultant structure so as to change the spherical conductive balls into shapes having hourglass features.  
           [0016]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as described and as claimed herein. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. In the drawings:  
         [0018]    [0018]FIG. 1A illustrates a cross-sectional view of a ball grid array IC package according to a first conventional embodiment found in the related art;  
         [0019]    [0019]FIG. 1B illustrates a cross-sectional view of a ball grid array package according to a second conventional embodiment found in the related art;  
         [0020]    [0020]FIG. 2 illustrates a cross-sectional view of a ball grid array package according to a first embodiment of the present invention;  
         [0021]    [0021]FIGS. 3A to  3 D illustrate cross-sectional views showing the steps for manufacturing a ball grid array IC package according to a first embodiment of the present invention;  
         [0022]    [0022]FIG. 4 illustrates a perspective view of a semiconductor chip having chip pads at a central part thereof according to a first embodiment of the present invent ion;  
         [0023]    [0023]FIG. 5A and FIG. 5B illustrate the process steps of manufacturing a spherical polymer ball;  
         [0024]    [0024]FIG. 6 illustrates a perspective view of a semiconductor chip having chip pads at a circumference thereof;  
         [0025]    [0025]FIG. 7 illustrates a cross-sectional view taken approximately along a line VII-VII extending through the semiconductor chip of FIG. 6;  
         [0026]    [0026]FIG. 8 illustrates an exploded perspective view of a ball grid array IC package according to a second embodiment of the present invention;  
         [0027]    [0027]FIG. 9 illustrates an exploded perspective view of a ball grid array IC package according to a third embodiment of the present invention;  
         [0028]    [0028]FIG. 10 illustrates a cross-sectional view of an assembled ball grid array IC package according to the third embodiment of the present invention; and  
         [0029]    [0029]FIG. 11 illustrates an exploded perspective view of a ball grid array IC package according to a fourth embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0030]    Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Where possible, the same reference numerals will be used to illustrate like elements throughout the several embodiments of the specification.  
         [0031]    FIGS.  2  to  7  illustrate a ball grid array IC package and manufacturing method thereof according to a first embodiment of the present invention. FIG. 2 illustrates a cross-sectional view of a ball grid array IC package according to a first embodiment of the present invention. FIGS. 3A to  3 D illustrate cross-sectional views of manufacturing a ball grid array IC package according to a first embodiment of the present invention. FIG. 4 illustrates a perspective view of a semiconductor chip having chip pads at a central part thereof according to a first embodiment of the present invention, and FIGS. 5A and 5B illustrate a process of manufacturing a spherical polymer ball.  
         [0032]    [0032]FIG. 6 illustrates a perspective view of a semiconductor chip having chip pads at a circumference thereof according to a first embodiment of the present invention and FIG. 7 illustrates a cross-sectional view taken approximately along the line VII-VII of FIG. 6.  
         [0033]    Referring again to FIG. 2, a ball grid array IC package according to a first embodiment of the present invention is constructed with a semiconductor chip  210  having a plurality of chip pads  212 , hourglass type conductive balls  215  electrically connected to the chip pads  212 , a substrate  200  having ball lands  204  on which the conductive balls  215  are mounted, polymer balls  230  formed on the semiconductor chip  210  for maintaining a uniform interval between the semiconductor chip  210  and substrate  200  to make the conductive balls  215  hourglass type, and an adhesive layer  232  disposed between the semiconductor chip  210  and the polymer balls  230 .  
         [0034]    When the chip pads  212  are arranged at a central part of the semiconductor chip  210 , as shown in FIG. 4, the polymer balls  230  are arranged at a peripheral part of the semiconductor chip  210 , where the chip pads  212  are not disposed. On the other hand, when the chip pads  212  are arranged at the peripheral part of the semiconductor chip  210 , as shown in FIG. 6, the polymer balls  230  are arranged at the central part of the semiconductor chip  210 , where the chip pads  212  are not disposed.  
         [0035]    In a method of manufacturing the ball grid array IC package according to the first embodiment of the present invention, shown in FIG. 3A, spherical conductive balls  214  are formed on chip pads  212  of a semiconductor chip  210 . Preferably, the conductive balls  214  are solder balls having a spherical shape.  
         [0036]    Polymer balls  230  are attached to the semiconductor chip  210  using an adhesive layer  232 . The adhesive layer  232  may comprise an adhesive tape, an adhesive agent or other appropriate adhesive member.  
         [0037]    The polymer balls  230  shown in FIG. 7 are attached to the semiconductor chip  210  by the adhesive layer  232  and a tape  234  or the like, and are thereby sealed and isolated completely from the outer atmosphere. The polymer balls  230  preferably are formed of an epoxy based resin or a polyimide based resin.  
         [0038]    In FIGS. 3A to  3 D, the chip pads  212  and the conductive balls  214  are arranged at the central part of the semiconductor chip  210 , while the polymer balls  230  are arranged at the peripheral part of the semiconductor chip  210 . Conversely, the chip pads  212  and the conductive balls  214  may be arranged at the peripheral part of the semiconductor chip  210 , while the polymer balls  230  are arranged at the central part of the semiconductor chip  210 , as shown in FIG. 6.  
         [0039]    As shown in FIG. 5A and FIG. 7, the respective polymer balls  230 ) are charged with one of air, gas, water, oil or like material  250  using an injector  240 , such as a piston or the like, whereby the volume of the respective polymer balls  230  are expanded, as shown in FIG. 5B. Alternatively, the polymer balls  230  may be charged with any material having expansion/contraction properties, depending on a temperature expansion variance instead of the above-described air, gas, water, and oil.  
         [0040]    Referring now to FIGS. 3A to  3 D, a metal has been deposited on the substrate  200 . Ball lands  204  are provided by etching the metal so as to provide portions of the metal, corresponding to the chip pads  212 , on the semiconductor chip  210 . The conductive balls  214  are then disposed on the ball lands  204  of the substrate  200 .  
         [0041]    Referring now to FIG. 3B, a thermal treatment is carried out on the above resultant structure using an infrared lamp, shown as arrows  220 . In this case, the thermal treatment is preferably carried out at a temperature of between 200 to 250° C., and more preferably, at a temperature of about 235° C.  
         [0042]    As a result of the thermal treatment, the volume of each of the polymer balls  230  charged with one of air, gas, water, oil or the like is expanded, whereby the polymer balls  230  come into contact with the substrate  200 . Such contact applies a predetermined pressure to the substrate  200 .  
         [0043]    Consequently, a uniform interval between the semiconductor chip  210  and substrate  200  is obtained. he expanded polymer balls  230  maintain a predetermined interval between the semiconductor chip  210  and the substrate  200 .  
         [0044]    Referring now to FIG. 3C, the conductive balls  215  are reflowed by the thermal treatment so as to be metamorphosed into shapes having hourglass features.  
         [0045]    Then, the infrared lamp (not shown) is turned off, as shown in FIG. 3D, whereby the polymer balls  230  contract because of a decrease in their volume as a result of the temperature drop.  
         [0046]    After the hourglass type conductive balls  215  have been fabricated, the removal of the contact polymer balls  230  is optional.  
         [0047]    [0047]FIG. 8 illustrates an exploded perspective view of a ball grid array IC package according to a second embodiment of the present invention.  
         [0048]    Referring to FIG. 8, a ball grid array IC package according to a second embodiment of the present invention is constructed with a semiconductor chip  310  having a plurality of chip pads (not shown), conductive balls  314  (shown in phantom) electrically connected to the chip pads, a substrate  300  having ball lands  304  on which conductive balls  314  are mounted, polymer balls  330 , formed on those portions of the substrate  300  where the ball lands  304  are not formed, for maintaining a uniform interval between the semiconductor chip  310  and the substrate  300  so as to change the shape of the conductive balls  314  to ones having an hourglass type, and an adhesive layer  332  disposed between the substrate  300  and the polymer balls  330 .  
         [0049]    A method of manufacturing a ball grid array IC package according to the second embodiment of the present invention is almost the same as the first embodiment of the present invention except for polymer balls  330  being formed on a substrate  300 .  
         [0050]    The method of manufacturing a ball grid array package according to the second embodiment of the present invention is explained briefly as follows.  
         [0051]    First, the spherical conductive balls  314  are attached to the chip pads (not shown) of the semiconductor chip  310 . Polymer balls  330 , as shown in FIG. 8, are then attached to those portions of the substrate  300  where ball lands  304  are not formed by inserting the adhesive layer  332  at a peripheral part.  
         [0052]    Subsequently, the respective polymer balls  330  are charged with one of air, gas, water, oil or the like. The conductive balls  314  are then mounted on the ball lands  304  of the substrate  300 .  
         [0053]    Subsequently, thermal treatment is carried out on the above resultant structure. Maintaining a uniform interval between the semiconductor chip  310  and substrate  300  is achieved by the expansion of the polymer balls  330  to provide a uniform distance between the surfaces of the chip  310  and the substrate  300 . The conductive balls  314  are reflowed by the thermal treatment so as to be metamorphosed into shapes having the hourglass features.  
         [0054]    After the hourglass type conductive balls have been fabricated, the removal of the contact polymer balls  330  is optional, and alternatively, they are allowed to reduce their volume and size to be less than the height of the conductive members having the hourglass features.  
         [0055]    Accordingly, in the first and second embodiments of the present invention, the spherical conductive balls are metamorphosed into shapes having the hourglass features using polymer balls having expansion/contraction properties depending on temperature variance by maintaining a uniform interval between the semiconductor chip and substrate.  
         [0056]    [0056]FIG. 9 illustrates an exploded perspective view of a ball grid array IC package according to a third embodiment of the present invention, and FIG. 10 illustrates a cross-sectional view of a ball grid array IC package according to the third embodiment of the present invention.  
         [0057]    Referring to FIG. 9, a ball grid array IC package according to a third embodiment of the present invention is constructed with a semiconductor chip  410  having a plurality of chip pads (not shown), conductive balls  414  (shown in phantom) electrically connected to the chip pads, a substrate  400  having ball lands  404  on which the conductive balls  414  are later mounted, a jig  434  attached to a peripheral part of the substrate  400  where the ball lands  404  are not formed, polymer balls  430  formed on the jig  434  for maintaining a uniform interval between the semiconductor chip  410  and the substrate  400  so as to make the conductive balls  414  have shapes of the hourglass type, and an adhesive layer  432  disposed between the semiconductor chip  410  and the polymer balls  430 .  
         [0058]    A method of manufacturing a ball grid array IC package according to the third embodiment of the present invention is shown in FIGS. 9 and 10. First, the conductive balls are formed on the chips pads of the semiconductor chip  410 . After a metal has been deposited on the substrate  400  by known sputtering methods, ball lands  404  are provided by etching the metal so as to leave portions of the metal corresponding to the chip pads on the surface of substrate  400 . A jig  434  is attached to a peripheral part of the substrate  400  where the ball lands  404  are not formed. In this case, the polymer balls  430  are arranged on the jig  434 .  
         [0059]    The adhesive layer  432  is disposed between the polymer balls  430  and the jig  434  so as to strengthen the adhesive power of the polymer ball attachment. Moreover, the polymer balls  430  are charged with any material having expansion/contraction properties depending on a temperature variance, for example, air, gas, water, oil or the like.  
         [0060]    After the conductive balls  414  have come into contact with the ball lands  404 , thermal treatment is carried out on the above resultant structure using an infrared lamp (not shown). As a result of the thermal treatment, the volume of each of the polymer balls  430  is expanded, whereby a uniform interval between the semiconductor chip  410  and substrate  400  is obtained. The conductive balls  414  are reflowed by the thermal treatment so as to be metamorphosed into connections having the hourglass features. Moreover, the jig  434  is detachable so as to be reused after the thermal treatment.  
         [0061]    [0061]FIG. 11 illustrates an exploded perspective view of a ball grid array IC package according to a fourth embodiment of the present invention. Referring to FIG. 11, a ball grid array IC package according to a fourth embodiment of the present invention is constructed with a semiconductor chip  510  having a plurality of chip pads (not shown), conductive balls  514  (shown in phantom) electrically connected to the chip pads, a substrate  500  having ball lands  504  on which the conductive balls  514  are later mounted, a jig  534  attached to a peripheral part of the substrate  500  where the ball lands  504  are not formed, and bimetals  530  formed on the jig  534  for maintaining a uniform interval between the semiconductor chip  510  and the substrate  500  so as to change the shape of the conductive balls  514  into on of having the hourglass type.  
         [0062]    Each of the bimetals  530  is constructed comprising plural thin metal pieces, each having different heat expansion coefficients, the bimetals  530  being bent in accordance with a temperature variance.  
         [0063]    A method of manufacturing a ball grid array IC package according to the fourth embodiment of the present invention is essentially the same of the third embodiment of the present invention. First, the conductive balls  514  are attached to the chips pads of the semiconductor chip  510 . The ball lands  504  are formed on the substrate  500 .  
         [0064]    Subsequently, as shown in FIG. 11, the jig  534 , on which the bimetals  530  are formed, is attached to a peripheral part of the substrate  500 . An adhesive layer may be disposed between the substrate  500  and the jig  534  so as to strengthen the adhesiveness power between the substrate and the bimetals  530 .  
         [0065]    After the conductive balls  514  have been made to come into contact with the ball lands  504 , thermal treatment, is carried out on the above resultant structure using an infrared lamp (not shown). As a result of the thermal treatment, the bimetals  530  are expanded. In this case, the spherical conductive balls  514  are extended by the vertical expansion of the bimetals  530  to the extent of the interval between the semiconductor chip  510  and substrate  500  SO as to change the connection into a shape having the hourglass features. Moreover, the jig  534  is detachable so as to be reused after the thermal treatment.  
         [0066]    As mentioned in the above description of the present invention, an interval maintaining member is formed on a substrate or a semiconductor chip so as to secure a uniform interval between the semiconductor substrate and the semiconductor chip. Thus, the present invention is capable of extending the length of the respective conductive balls to the extent of the interval so as to manufacture an hourglass type IC package with greater precision and efficiency.  
         [0067]    Moreover, the present invention does not require equipment for pulling upward a semiconductor chip in vacuum to provide an hourglass type conductive ball.  
         [0068]    The foregoing embodiments are merely exemplary and are not to be construed as limiting the present invention. The present teachings can be readily applied to other types of similar or dissimilar apparatus. The description of the present invention is intended to be illustrative, and not to limit the scope of the following claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art from an understanding of the invention as described and illustrated.