Abstract:
A BGA package includes a substrate, a chip, and a heat spreader. The spreader covers the chip, a bottom part of the spreader is mounted on an upper surface of the substrate by an adhesive. The spreader shields Electro Magnetic Interference to the chip. In addition, the substrate is made of a built-up PCB.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to an encapsulated BGA and more particularly to a flip chip package having a thermally conductive member encapsulated with the chip. 
     2. Description of the Related Art 
     Flip chip packages require a cover of some type over the silicone chip to protect it and to provide a larger flat surface for pick-and-place operations. However, any cover or encapsulant above the chip increases the thermal resistance path to an ambient environment and, hence, the operational temperature of the chip is increased. 
     U.S. Pat. No. 5,811,317, issued on Sep. 22, 1998 to Maheshwari et al., discloses a method for assembly of bare silicon die onto flexible or thin laminate substrates that minimizes substrate and die warpage induced after underfilled cure operations and at the same time reduces the cycle time for the assembly process. More specifically, an opposing layer of thermoset component is adhered to a balance plate (metal) or other material with an applicable coefficient of thermal expansion and modulus of elasticity on the top of the die. The offsetting layer of material causes the die to warp to the other side and as a result the two self opposing warpage effects neutralize themselves. Referring to FIG. 1, the flip chip package comprises a substrate  10 , a chip  11 , and a balance plate  12 . The chip  11  is sandwiched between the substrate  10  and the balance plate  12 . An underfill material  13  mounts the chip  11  to the substrate  10 , and an overfill material  14  mounts the balance plate  12  to the chip  11 . The drawback of the underfill material  13  is that after curing it is extremely rigid. Therefore, the balance plate  12  causes the chip  11  to warp to the other side and as a result the two self opposing warpage effects naturalize themselves. However, the balance plate  12  does not have the capability of heat conduction from the balance plate  12  to the substrate  10 . 
     U.S. Pat. No. 5,726,079, issued on Mar. 10, 1998 to Johnson, discloses a thermally conductive planar member in thermally conductive communication with a flip chip encapsulated within a dielectric material that surrounds portions of the thermally conductive planar member, the flip-chip, and a predefined portion of a substrate member. The flip chip package has pick-and-place capability without the thermal resistance disadvantage of capped chip packages. Referring to FIG. 2, the flip chip package comprises a substrate  20 , a chip  21  and a thermally conductive planar member  22 . The chip  21 , mounted on the substrate  20 , is connected to the planar member  22  by an adhesive  23  therebetween. An encapsulant  24  surrounds an ambient environment of the chip  21  and the planar member  22 . However, the planar member  22 , for heat dissipation, conducts little heat from the planar member  22 , and from the chip  21 , to solder bumps of the substrate  20 . 
     The present invention intends to provide a thermally enhanced BGA package which mitigates and overcomes the above problem. 
     SUMMARY OF THE INVENTION 
     The primary object of this invention is to provide a thermally enhanced BGA package, which comprises a heat spreader conducting heat from a top surface of a chip to the air as well as conducting heat from a bottom surface of the chip to the substrate. 
     The secondary object of this invention is to provide a thermally enhanced BGA package, which comprises a heat spreader shielding Electro Magnetic Interference (EMI) to a chip. 
     The other object of this invention is to provide a thermally enhanced BGA package, which comprises a heat spreader providing grounding effect on the substrate so as to reduce cross talk and characteristic impedance effects. 
     The other object of this invention is to provide a thermally enhanced BGA package, which comprises a heat spreader mitigating warpage effect. 
     In accordance with the present invention, a BGA package comprises a substrate, a chip, a pad and a heat spreader. The chip mounted on the substrate, which including the pad, is disposed in thermally conductive communication with the heat spreader that extends around the periphery of the pad. The heat spreader for heat dissipation conducts heat from the top surface of the chip to a heat dissipation member on the substrate, and to a pad. An encapsulant is exposed on the top of the spreader for heat convection. Therefore, heat on the top of the chip dissipates through conduction and convection at the same time. 
     Other objectives, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will now be described with reference to the accompanying drawings wherein; 
     FIG. 1 is a side view of a flip chip package in accordance with U.S. Pat. No. 5,811,317; 
     FIG. 2 is a side view of a flip chip package in accordance with U.S. Pat. No. 5,726,079; 
     FIG. 3 is a sectional view along line  3 — 3  in FIG. 4 of a BGA package in accordance with the first embodiment of the present invention; 
     FIG. 3 a  is a side view of a BGA package in accordance with the first embodiment of the present invention; 
     FIG. 4 is a top view of a BGA package in accordance with a second embodiment of the present invention; 
     FIG. 5 is a top view of a BGA package in accordance with the second embodiment of the present invention; 
     FIG. 6 is a sectional view, along line  6 — 6 , in FIG. 5 of a BGA package in accordance with the second embodiment of the present invention; 
     FIG. 7 is a sectional view of a BGA package in accordance with the third embodiment of the present invention; 
     FIG. 8 is a sectional view of a BGA package in accordance with the fourth embodiment of the present invention; 
     FIG. 9 is a sectional view of a BGA package in accordance with the fifth embodiment of the present invention; 
     FIG. 10 is a sectional view of a BGA package in accordance with the sixth embodiment of the present invention; and 
     FIG. 11 is a partial enlarged view of FIG. 10 in accordance with the sixth embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 3, a BGA package in accordance with the first embodiment comprises a substrate  30 , a pad  32 , a chip  33 , and a heat spreader  34 . The pad  32 , forming a mold gate, is mounted on an upper surface  31  of the substrate  30  to form a mold gate, thus the cured portion of an encapsulant material can be peeled from the mold gate of the upper surface  31  of the substrate  30 . The chip  33  mounted on the substrate  30 , which including the pad  32 , is in thermally conductive communication with the heat spreader  34  that extends around the periphery of the pad  32 . The encapsulating material is molded to form an encapsulant  38  on the substrate  30 , to seal the chip  33 . 
     Referring to FIGS. 3 and 4, the pad  32 , for heat dissipation, is made of metal material, and disposed around the corner of the chip  33 . The spreader  34  further comprises a plurality of holes A, through which the encapsulating material  39 , flows into the spreader  34  during molding. The chip  33  is disposed in thermally conductive communication (by an adhesive material) with the heat spreader  34 . A bottom part  35  of the spreader  34  comprises a plurality of protrusions  36  and extends around the periphery of the pad  32 . For heat dissipation, the bottom part  35  of the spreader  34 , is connected to the pad  32 , to which is connected a ground plate (not shown). After the encapsulating material is cured, a top part  37  of the spreader  34  is exposed on a top of the encapsulant  38 , so that some of the heat of the chip  33  is convected away from the top part  37  of the spreader  34  to the air. A sidewall  37   a  extends between the top part  37  and the bottom part  35  of the heat spreader  34 . Heat from the bottom part of the chip  33  is conducted to the upper surface  31  of the substrate  30  by solder bumps  33   a  and underfill  33   b . And heat from the top part of the chip  33  is conducted to an epoxy layer  39  of the encapsulant  38 , and to the top of the spreader  34 . For additional heat dissipation, some heat from the spreader  34  is convected from the top part  37  to the air and other heat is conducted from the bottom part  35  to the upper surface  31  of the substrate  30 , and to the pad  32 . It should be noted that heat from the bottom and top part of the chip  33  is being dissipated at the same time, so as to avoid deformation or warpage of the chip  33 , which may be caused by the difference in coefficient of expansion (CTE) from the bottom and top part of the chip  33 . 
     Referring to FIGS. 1,  2  and  3 , the spreader  34  of the present invention is compared with the balance plate  12  of U.S. Pat. No. 5,811,317 and the planar member  22  of U.S. Pat. No. 5,726,079. Some heat of the spreader  34  is convected to the air and at the same time other heat is conducted to the upper surface  31  of the substrate  30  and the pad  32 . But the balance plate  12  and the planar member  22  have no connection to the substrate  10 ,  20 , in that it is hard to conduct the heat of the balance plate  12  and heat of the planar member  22  to the substrate  10 ,  20 . 
     A plurality of protrusions  36  provided on the bottom part  35  of the heat spreader  34  are attached to the upper surface  31  of the substrate  30  such that the bottom part  35  of the heat spreader  34  and the upper surface  31  of the substrate  30  together define a plurality of gaps  36   a  which connect through the inside of the heat spreader  34  and allow the encapsulating material  39  to flow conveniently through the gaps  36   a  towards the inside of the heat spreader  34  for molding. 
     Referring to FIGS. 5 and 6, the BGA package in accordance with the second embodiment comprises a substrate  40 , a chip  42  and a heat spreader  43 . The spreader  43  covers the chip  42 , which is mounted on an upper surface  41  of the substrate  40 . A bottom part  44  of the spreader  43  further comprises a plurality of protrusions  45  attached to the upper surface  41  of the substrate  40  by an adhesive material. In that, the bottom part  44  and the upper surface  41  together define a gap through which the encapsulating material  48  flows into the spreader  43  during molding. The encapsulating material molded to form an encapsulating  47  on the substrate  40  to seal the chip  42 . After the encapsulating material is cured, a top part  46  of the spreader  43  is exposed on a top of the encapsulant  47 , in such way that some of the heat of the chip  42  dissipates in convectional way from the top part  46  of the spreader  43  to the air. Heat from the bottom part of the chip  42  is conducted to the upper surface  41  of the substrate  40  by solder bumps  42   a  and underfill  42   b . And heat from the top part of the chip  42  is conducted to an epoxy layer  48  of the encapsulant  47  and to the top of the spreader  43 . Then, for additional heat dissipation, some heat of the spreader  43  is convected from the top part  46  to the air, and the other heat is conducted from the bottom part  44  to the upper surface  41  of the substrate  40 . 
     Referring to FIG. 7, the BGA package in accordance with the third embodiment comprises a substrate  50 , a chip  52  and a heat spreader  53 . The spreader  53  covers the chip  52 , which is mounted on an upper surface  51  of the substrate  50 . A bottom part  54  of the spreader  53  further comprises a plurality of protrusions  55  attached to the upper surface  51  of the substrate  50  by an adhesive material. In that, the bottom part  54  and the upper surface  51  together define a gap through which the encapsulating material flow into the spreader  53 , during molding. The encapsulating material is molded to form an encapsulating  57  on the substrate  50  to seal the chip  52 . After the encapsulating material is cured, a top part  56  of the spreader  53  is exposed on a top of the encapsulant  57 , in that some of heat of the chip  52  is dissipated in a convectional way from the top part  56  of the spreader  53  to the air. Heat from the bottom part of the chip  52  is conducted to the upper surface  51  of the substrate  50  by solder bumps  52   a  and underfill  52   b . And heat from the top part of the chip  52  is conducted through an adhesive layer  52   c  to the top of the spreader  53 . Then, for added heat dissipation, some heat of the spreader  53  is convected from the top part  56  to the air, and other heat is conducted from the bottom part  54  to the upper surface  51  of the substrate  50 . 
     Referring to FIG. 8, the BGA package in accordance with the fourth embodiment comprises a substrate  60 , a chip  62  and a heat spreader  63 . The spreader  63  covers the chip  62 , which is mounted on an upper surface  61  of the substrate  60 . A bottom part  64  of the spreader  63  further comprises a plurality of protrusions  65  attached to the upper surface  61  of the substrate  60  by an adhesive material. In that, the bottom part  64  and the upper surface  61  together define a gap through which the encapsulating material  68  flows into the spreader  63  during molding. The encapsulating material is molded to form an encapsulant  66  on the substrate  60  to seal the chip  62 . Heat from the bottom part of the chip  62  is conducted to the upper surface  61  of the substrate  60 , by solder bumps  62   a  and underfill  62   b . And heat from the top part of the chip  62  is conducted to an epoxy layer  67  of the encapsulant  66  and the top of the spreader  63 . Then, for heat dissipating, heat of the spreader  63  is conducted from the bottom part  64  to the upper surface  61  of the substrate  60 . 
     Referring to FIG. 9, the BGA package in accordance with the fifth embodiment comprises a substrate  70 , a chip  72  and a heat spreader  73 . The spreader  73  covers the chip  72 , which is mounted on an upper surface  71  of the substrate  70 . A bottom part  74  of the spreader  73  further comprises a plurality of protrusions  75  attached to the upper surface  71  of the substrate  70  by an adhesive material. In that, the bottom part  74  and the upper surface  71  together define a gap through which the encapsulating material flows into the spreader  73  during molding. The encapsulating material is molded to form an encapsulant  76  on the substrate  70  to seal the chip  72 . Heat from the bottom part of the chip  72  is conducted to the upper surface  71  of the substrate  70  by solder bumps  72   a  and underfill  72   b . And heat from the top part of the chip  72  is conducted through an adhesive layer  72   c  to the top of the spreader  73 . Then, for added heat dissipation, heat from the spreader  73  is conducted from the bottom part  74  to the upper surface  71  of the substrate  70 . 
     Referring to FIG. 10, the BGA package in accordance with the sixth embodiment, comprises a substrate  80 , a chip  83  and a heat spreader  84 . The substrate  80  further comprises a metal layer  82  which provides an enhanced structure so as to avoid the substrate  80  bending under strain. For heat dissipation, heat of the chip  83  is conducted through an adhesive layer  83   a  and the spreader  84  to the substrate  80 . 
     Referring to FIG. 11, the substrate  80  comprises the metal layer  82 , two BT (Bismaleimide Triazine Resin) layers  82   a , two routine layers  82   b , and two films  82   c . The metal layer  82  is sandwiched between the two BT layers, and the routine layers formed on the BT layers, and the films  82   c  formed on the routine layers. 
     Although the invention has been described in detail with reference to its presently preferred embodiments, it will be understood by one of ordinary skill in the art that various modifications can be made without departing from the spirit and the scope of the invention, as set forth in the appended claims.