Patent Publication Number: US-2009230543-A1

Title: Semiconductor package structure with heat sink

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a semiconductor package structure with a heat sink, particularly to a semiconductor package structure with a heat sink that is capable of solving the warpage issue of the package. 
     2. Description of the Prior Art 
     IC (integrated circuit) packaging belongs to the back-end stage of semiconductor device fabrication and includes wafer sawing, die attaching, wire bonding, molding, marking, and packaging. The main purpose of IC packaging is to saw the IC on a wafer processed with front-end processes into dies, attach the dies, bond the dies with wires, and package the IC. Recently, due to the highly integrated semiconductor chips, the accompanied heat generated increases accordingly. However, the trend of getting package structures thinner and smaller results in heat congested in the small-dimensional package structure and raise of heat flow density. 
     In order to increase heat dissipation efficiency in the package structures, multiple package structures with a heat sink have been developed, for example HSBGA (Heat Slug Ball Grid Array), which transfer heat to the outer space of the package structure by using a heat sink with high heat transfer coefficient. 
       FIG. 1  shows a conventional HSBGA package structure, which has a substrate  10  with a chip  20  set thereon and includes a heat sink  30  attached on the substrate by using an adhesive, and a package resin  40  covering the chip  20  and the heat sink  30 . As shown in the figure, the heat sink  30  includes an external portion  32  and an internal portion  34 , wherein the internal portion  34  is attached onto the substrate  10  and the external portion  32  is exposed to the package resin  40 . However, during the process of attaching the heat sink  30  to the substrate  10 , the heat sink  30  deviates from the predetermined position before curing due to vibration caused by the fabrication equipment or improper operation, and results in decrease of yield rate. 
     SUMMARY OF THE INVENTION 
     To solve the above-mentioned problem, one objective of the present invention is to provide a semiconductor package structure with a heat sink, which prevents the deviation of the heat sink during the attaching process and increases yield rate of the package. In addition, the semiconductor package structure improves the heat dissipation efficiency and reduces the warpage issue of the package after packaging by utilizing support portions of the heat sink. 
     To achieve the above-mentioned objective, a semiconductor package structure with a heat sink according to one embodiment of the present invention includes a substrate having a chip mounting area and a plurality of through holes surrounding the chip mounting area; a chip set on the chip mounting area and electrically connected to the substrate; a heat sink covering the chip, wherein the heat sink has a plurality of support portions extending from the upper surface to the lower surface of the substrate via those through holes; and a molding compound covering the chip, a portion of the substrate and the heat sink. 
     Other advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-section diagram showing a conventional HSBGA package structure. 
         FIG. 2  is a cross-section diagram showing a semiconductor package structure with a heat sink according to one embodiment of the present invention. 
         FIG. 3A  is a cross-section diagram showing a semiconductor package structure with a heat sink according to another embodiment of the present invention. 
         FIG. 3B  is a top view of  FIG. 3A  according to one embodiment. 
         FIG. 4A  is a cross-section diagram showing a semiconductor package structure with a heat sink according to yet another embodiment of the present invention. 
         FIG. 4B  is a cross-section diagram showing a semiconductor package structure with a heat sink having another protrusion according to one embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The following descriptions of specific embodiments of the present invention have been presented for purposes of illustrations and description and are not intended to be exclusive or to limit the invention to the precise forms disclosed 
     First of all, refer to  FIG. 2  which is a cross-section diagram showing a semiconductor package structure with a heat sink according to one embodiment of the present invention. As shown in the figure, a semiconductor package structure with a heat sink includes a substrate  110  having a chip mounting area (not shown) and a plurality of through holes  112  surrounding the chip mounting area. For example, the chip mounting area is a specific area of an upper surface  114  on the substrate  110 . A chip  120  is set on the chip mounting area and electrically connected to the substrate  110 . In the embodiment, the chip  120  is connected to the substrate  110  with a plurality of leads  150  as shown in the figure; it should be understood that the method for electrically connecting the chip  120  with the substrate  110  is not limited to wire bonding method, but other methods, e.g. flip chip method, may be practiced in the structure of the present invention. A heat sink  130  covers the chip  120 , wherein the heat sink  130  has a plurality of support portions  132  extending from the upper surface  114  to a lower surface  116  of the substrate  110  via those through holes  112 . A molding compound  140  covers the chip  120 , a portion of the substrate  110  and the heat sink  130 . 
     Following the above description, in one embodiment, the semiconductor package structure further includes a plurality of bumps  160  arranged on the lower surface  116  of the substrate  110  and electrically connecting the semiconductor package structure to other external devices. Further, the support portions  132  on the heat sink  130  may have a stripe shape and be inserted into the through holes  112  on the substrate  110  with ease. In one embodiment, the number of the through holes  112  on the substrate  110  exceeds the number of the support portions  132  on the heat sink  130 . That is, in case of the number of the through holes  112  equaling to the number of the support portions  132 , after the support portions  132  having a strip shape pass through the through holes  112 , the molding compound  140  used for molding passes through the through holes  112  and covers the support portions  132  protruding from the substrate  110 ; otherwise, in case of the number of the through holes  112  exceeding the number of the support portions  132 , some of the molding compound  140  may flow through the through holes  112  directly to form the support bumps which may prevent the disintegration caused by non-uniform applied force while the semiconductor package structure is packaged into other external devices or warpage occurred during the molding compound cures. 
     Next referring to  FIG. 3A , in another preferred embodiment, a window  118  (as shown in  FIG. 3B ) is further configured at the chip mounting area on the substrate  110  for the need of window-type semiconductor package. As shown in the figure, a plurality of leads  152  pass through the windows  118  and electrically connect the chip  120  with the lower surface  116  of the substrate  110 . In addition, in order to shrink the thickness of the package and enhance the heat dissipation rate, the heat sink  130  may directly attach to the chip  120  by using a thermally conductive dielectric adhesive, and the attaching also assists the positioning of the heat sink  130 . In another embodiment, the heat sink  130  partially emerges from the molding compound  140 . Furthermore, refer to  FIG. 3B  which is a possible top view of  FIG. 3A . It should be understood that the position and shape of the through holes  112  is not limited thereon. 
     Following the above description, referring to  FIG. 4A , in one embodiment, the semiconductor package structure further includes at least one protrusion  134  protruding from the support portion  132 , wherein the protrusion  134  may form an angle, e.g. an acute angle, an obtuse angle, or a right angle (as shown in the figure), with the support portion  132  to increase the conjunction and friction force between the molding compound  140  and the heat sink  130  to prevent the possible disintegration of the heat sink  130 . The protrusion  134  has no shape limitation: for example, the structure of the protrusion  134  of a semiconductor package structure according to another embodiment is depicted in  FIG. 4B , but the shape of the protrusion  134  is not thus limited. In yet another embodiment, a coarse surface is formed at the contact surface between the heat sink  130  and the molding compound  140  by surface processing to increase the friction force between the molding compound  140  and the heat sink  130  thereafter. 
     According to the above descriptions, one characteristic of the present invention is to utilize support portions of the heat sink which pass through the substrate to increase the heat dissipation area and improve the warpage issues occurred during or after the packaging process, wherein the shape and number of the support portions is not limited. Besides, the support portions protrudes from the lower surface of the substrate, and the support portions of the heat sink covered with the molding compound after packaging may also provide support for the package structure. The semiconductor package structure with a heat sink of the present invention may reduce the disintegration problem of the package possibly occurred when the package is packaged into external devices. In addition, the support portions of the heat sink may further include a protrusion or a coarse surface formed at the contact surface between the molding compound and the heat sink to increase the conjunction strength between the molding compound and the heat sink. Besides, the protrusion has no shape and size limit so that the manufacturing process of the package is more flexible. 
     To sum up the foregoing descriptions, the present invention provides a semiconductor package structure with a heat sink, which prevents the deviation of the heat sink during the attaching process and increase yield rate of the package. In addition, the semiconductor package structure improves the heat dissipation efficiency and reduces the warpage issue of the package after packaging by utilizing the support portions of the heat sink. 
     While the invention is susceptible to various modifications and alternative forms, a specific example thereof has been shown in the drawings and is herein described in detail. It should be understood, however, that the invention is not to be limited to the particular form disclosed, but to the contrary, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the appended claims.