Abstract:
A package module is provided. The package module includes a substrate having a surface including a die region. A die is disposed in the die region of the surface on the substrate. A flexible heat spreader conformally covers the surface of the substrate and the die. The invention also discloses an electronic device with the package module.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to electronic package technology, and in particular, to a package module having a flexible heat spreader capable of reducing thermal stress and increasing heat dissipation. 
   2. Description of the Related Art 
   Demand for small, high performance portable electronic products such as mobile phones, portable computers, and the like have driven the industry to increase integration on semiconductor dice. Accordingly, the industry is achieving high integration by turning to 3D packaging by combining assembly technologies including wire bonding or flip chip to stack die packages to form a multi-package module (MPM). 
   MPM, a current assembly technology, integrates different dice functions, such as microprocessors or memory, logic, optic ICs, instead of placing individual packages onto a large printed circuit board (PCB). MPM, however, has a much higher power density than an individual single die package. Thus, thermal management is a key factor for successful development. 
   Conventional methods to combat the presence of heat during device operation typically include providing a heat spreader in thermal contact with IC chips in the package module.  FIG. 1  illustrates a conventional electronic device with an MPM. The electronic device comprises an MPM  100  comprising a substrate  12  and mounted on a PCB  101 . The upper and lower surfaces of the substrate  12  have dice  16  and  14  with different functions thereon, respectively, to create the MPM  100 . The lower surface of the substrate  12  comprises a plurality of bumps  10  thereon to correspondingly connect to the bonding pads  11  on the PCB  101  for electrical connection between the dice  16  and  14  and the PCB  101 . In the MPM  100 , heat generated from the die  16  can be dissipated by a heat spreading device. For example, a heat spreader  20  contacts the upper surface of the die  16  through an adhesion layer  17 . Moreover, a stiffener  18  is disposed on the substrate  12  and surrounds the die  16 . The heat spreader  20  and the substrate  12  are fixed by the stiffener  18  through adhesion layers  15  and  17 , in which the stiffener  18  serves as a hold for the heat spreader  20 . 
   In such an electronic device, the gap between the die  14  and the PCB  101  is too narrow, however, to dissipate the generated heat from the die  14 . Accordingly, low power chips are typically disposed on the lower surface of the substrate, thus hindering circuit design flexibility. Moreover, since the heat spreader  20  and the stiffener  18  typically comprise rigid materials, delamination of the heat spreader  20  and crack of the dice  16  may be occur due to the thermal stress generated from the thermal processes. Thus, device reliability is reduced. Additionally, MPMs with different sizes require stiffeners with different sizes, increasing manufacturing costs. 
   Accordingly, there is a need to develop a package module with an efficient heat spreader that does not suffer from the deficiencies found in the prior art. 
   BRIEF SUMMARY OF INVENTION 
   A detailed description is given in the following embodiments with reference to the accompanying drawings. 
   A package module and an electronic device are provided. An embodiment of a package module comprises a substrate having a surface comprising a die region. A die is disposed in the die region of the surface on the substrate. A flexible heat spreader conformally covers the surface of the substrate and the die. 
   An embodiment of an electronic device comprises a package module and a circuit board. The package module comprises a substrate having a first surface comprising a die region, and an opposing second surface. A plurality of solder balls is on the second surface of the substrate and arranged in an array. A die is disposed in the die region of the first surface on the substrate. A flexible heat spreader conformally covers the first surface of the substrate and the die. The circuit board has a plurality of bonding pads correspondingly bonded to the plurality of solder balls. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
     The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
       FIG. 1  is a cross-section of a conventional electronic device with a package module; 
       FIG. 2  is a cross-section of an embodiment of an electronic device with a package module according to the invention; 
       FIG. 3  is a top plan view of an embodiment of a package module according to the invention; 
       FIG. 4  is a bottom plan view of an embodiment of a package module according to the invention; 
       FIG. 5  is a bottom plan view of another embodiment of a package module according to the invention; 
       FIG. 6  is a cross-section of an embodiment of a flexible heat spreader according to the invention; 
       FIG. 7  is a cross-section of another embodiment of a flexible heat spreader according to the invention; 
       FIG. 8  is a cross-section of an embodiment of an electronic device with a package module according to the invention; and 
       FIG. 9  is a cross-section of another embodiment of an electronic device with a package module according to the invention. 
   

   DETAILED DESCRIPTION OF INVENTION 
   The following description is of the best-contemplated mode of carrying out the invention. This description is provided for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. The electronic device with a package module of the invention will be described in the following with reference to the accompanying drawings. 
     FIG. 2  illustrates an embodiment of an electronic device with a multi-package module according to the invention. The electronic device comprises a package module  200  and a circuit board  301 , such as a PCB. The package module  200  comprises a substrate  100  (e.g., package substrate or IC carrier), a plurality of solder balls  112 , dice  102  and  104 , and flexible heat spreaders  106  and  110 . In the embodiment, the substrate  100  may comprise plastic, ceramic, inorganic or organic material. Moreover, the substrate  100  has a first surface and a second surface. The first and second surfaces may be upper and lower surfaces  100   a  and  100   b , respectively. Here, the lower surface  100   b  represents a surface facing the surface of the circuit board  301  and the upper surface  100   a  represents the surface opposite to the lower surface  100   b . Referring to  FIGS. 3 and 4 , which are top and bottom plan views of the package module according to the invention, respectively, the upper surface  100   a  of the substrate  100  has a die region  101   a  and the lower surface  100   b  of the substrate  100  has a die region  101   b  and thermal channel regions  101   c . Typically, the die regions  101   a  and  101   b  are substantially at the center of the substrate  100 . Unlike the conventional package substrate, the lower surface  100   b  of the substrate  100  has thermal channel regions  101   c  outwardly extending to the edges or corners of the substrate  100  from the die region  101   b . For example, the thermal channel regions  101   c  outwardly extend to two opposing edges of the substrate  100 , respectively, from two opposing edges of the rectangular die region  101   b , as shown in  FIG. 4 . In another embodiment, the thermal channel regions  101   c  may outwardly extend to four corners of the substrate  100 , respectively, from four corners of the rectangular die region  101   b , as shown in  FIG. 5 . It will be apparent to those skilled in the art that the substrate  100  may comprise one or more thermal channel region(s) outwardly extending to the edge(s) or corner(s) of the substrate  100  from the edge(s) or corner(s) of the die region and it is understood that the invention is not limited to  FIGS. 4 and 5 . 
   Referring to  FIGS. 2 ,  3 ,  4 , and  5 , dice  102  and  104  with different functions may be respectively mounted in the die region  101   a  of the upper surface  100   a  and the die region  101   b  of the lower surface  100   b  of the substrate  100  by the same or different electronic packages. For example, dice  102  and  104  may respectively be mounted on the substrate  100  by flip chip or wire bonding. 
   The plurality of solder balls  112  is arranged in an array and located on the lower surface  100   b  of the substrate  100  except in the die region  101   b  and the thermal channel regions  101   c , to transmit signals to external circuits from the dice  102  and  104 . The interval between the bumps  112  is narrower than a width of the thermal channel region  101   c.    
   Flexible heat spreaders  106  and  110  are disposed on the upper and lower surfaces  100   a  and  100   b  of the substrate  100 , respectively. Unlike the conventional rigid heat spreader using the stiffener as a hold, the flexible heat spreader  106  conformally covers portions of the upper surface  100   a  of the substrate  100  and the die  102  in the die region  101   a , and the flexible heat spreader  110  conformally covers the thermal channel regions  101   c  of the lower surface  100   b  of the substrate  100  and the die  104  in the die region  101   b  without contacting the plurality of solder balls  112 . In the embodiment, the conformal heat spreader  106  may completely or partially cover the upper surface  100   a  of the substrate  100  and the surface of the die  102  in the die region  101   a . Moreover, the flexible heat spreaders  106  and  110  may outwardly extend from at least one edge of the substrate  100  and bond together. For example, the flexible heat spreaders  106  and  110  may outwardly extend from two opposing edges of the substrate  100  and bond together. 
   In the embodiment, each of the flexible heat spreaders  106  and  110  may comprise a flexible thermally conductive layer  105  and an underlying adhesion layer  103 , as shown in  FIG. 6 . The flexible thermally conductive layer  105  may comprise a metal, such as copper, with a thickness less than 30 μm or a carbon tube prepreg material. An additional protective layer  105   a  comprising, for example, nickel or anode oxide material is formed on the surface of the flexible thermally conductive layer  105  opposite to the adhesion layer  103  while using copper for the flexible thermally conductive layer  105 . That is, the protective layer  105   a  is separated from the adhesion layer  103  by the flexible thermally conductive layer  105 . The adhesion layer  103  interposed between the flexible thermally conductive layer  105  and the substrate  100  may comprise B-stage resin, polyimide (PI), or other adhesion materials known in the art and be employed to bond the flexible thermally conductive layer  105  onto the substrate  100  and the dice  102  and  104 . In particular, the use of the flexible B-stage resin is more sufficient for conformally covering the substrate  100  by the flexible thermally conductive layer  105 . Additionally, the flexible thermally conductive layer  105  has a substantially flat surface, such that the adhesion layer  103  can separate the dice  102  and  104  from the flexible thermally conductive layer  105 . In another embodiment, however, the surface of the flexible thermally conductive layer  105  has a plurality of convex patterns  105   b  to form a rough surface, as shown in  FIG. 7 . When the flexible heat spreaders  106  and  110  are bonded to the substrate  100  by pressure, the plurality of convex patterns  105   b  of the flexible thermally conductive layer  105  may pass through the adhesion layer  103  so as to directly contact the first and second dice  102  and  104 , thereby further increasing heat dissipation. 
   The circuit board  301  has a plurality of bonding pads  302  thereon, correspondingly bonded to the plurality of solder balls  112 , thereby electronically connecting the circuit board  301  and the dice  102  and  104 . Typically, the circuit board  301  comprises at least one or more metal layers and at least one or more insulating layers, in which the metal layer may serve as a signal layer, a power layer, and/or a grounding layer. In order to simplify the diagram, a flat substrate is depicted. Additionally, the circuit board  301  may comprise a thermal dissipation device (not shown) thereon, and one end of the flexible heat spreader  106  or  110  may be bonded to the thermal dissipation device of the circuit board  301 , thereby increasing heat dissipation of the electronic device. Hereinafter, to simplify the diagram, only an exemplary embodiment of one end of the flexible heat spreader  106  bonded to the circuit board  301  is depicted. 
   Additionally, in the embodiments, the package module  200  may be a multi-package module (MPM) with dice  102  and  104 . In some embodiments, a package device  114  may be disposed between the substrate  100  and the flexible heat spreader  106  of the package module  200 . The package device  114  is bonded to the substrate  100  through the bumps  115 , thereby forming a package on package (POP) module, as shown in  FIG. 8 . 
   Additionally, although an exemplary embodiment of a multi-package module  200  comprising dice  102  and  104  and the corresponding flexible heat spreaders  106  and  110  is depicted, it will be apparent to those skilled in the art that the multi-package module  200  may comprise a single chip  102  and the corresponding flexible heat spreader  106  only (not shown). In this case, the package device  114  may be disposed between the substrate  100  and the flexible heat spreader  106  of the package module  200  to form a POP module, as shown in  FIG. 9 . 
   According to these embodiments, since heat generated from the die  104  on the lower surface  100   b  of the substrate  200  can be dissipated by the heat spreader  110 , the die  104  can be a high power die, such as a central processing unit (CPU) die, in circuit design. That is, circuit design is more flexible. Moreover, since the thermal stress generated from the thermal processes can be reduced by the flexible heat spreaders  106  and  110 , delamination of the heat spreader and crack of the dice can be prevented, thereby increasing device reliability. Additionally, since the utilization of the flexible heat spreaders  106  and  110  does not need the additional stiffener for fixing and holding the heat spreaders  106  and  110 , manufacturing costs can be reduced. 
   While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.