Abstract:
The present invention provides a structure and a of stacked dice package and a process for forming the same, wherein an elastic adhesive layer applied on the first die covering all top surface of the first die and forming rims at the peripheral edges of the first die except the openings formed on the first contacting pads. With this shape of the elastic adhesive layer, the present invention can avoid micro crack happens in the die while performing wire bonding on the contacting pad of the die.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a structure for stacked package, and more particularly to a stack package with a releasing layer 
       DESCRIPTION OF THE PRIOR ART 
       [0002]    In the field of semiconductor devices, the device density is increased but the device dimension is reduced. The traditional package technique can&#39;t meet the demand of producing smaller chip with high density elements on the chip; therefore, new packaging or interconnecting techniques for such high density devices become demanding. 
         [0003]    Performing wire-bonding on a semiconductor package with stacked dice encounters many problems. Wire-bonding equipment induces significant force to the bonding pad on the die during wire-bonding; therefore, micro cracking in the die might happen. 
         [0004]    Some inventions have been proposed to solve the problem. U.S. Patent No. 2005/0035461 discloses a multiple stacked dice packaging structure with a n-shaped carrier cap; the n-shaped carrier is provided between the upper and the lower chip for ensuring coplanar when performing wire-bonding on the upper chip. Though the invention provides a cap for supporting the upper die, it needs large spacing which is inadequate for micro devices. 
         [0005]    Another solution proposed is adding an adhesive layer between the dice of a stacked dice to provide support for the upper die. U.S. Patent No. 2004/0251526 discloses a semiconductor package with stacked dice. An intermediate adhesive layer is applied between the upper die and the lower die. The adhesive layer provides support for the upper die while performing wire-bonding thereby reducing the incidence of die cracking; therefore, the invention discloses a structure and a method increase the yield of stacked packaging. The shortcoming of this invention is that the adhesive layer is injected by adhesive application equipment such as nozzle; unfortunately, the injection force is too strong to maintain bonding wire on the bonding point; i.e., the contacting point of wire binding on the pads may be damaged. As shown in  FIG. 1 , another shortcoming of injecting an adhesion layer includes that the adhesion layer can&#39;t cover the top surface of the pads thoroughly and the elastic particles in the adhesion layer can&#39;t spread evenly also. 
         [0006]    Therefore, the present invention provides a stacked structure with a releasing layer to solve the problem of micro cracking in the die. 
       SUMMARY OF THE INVENTION 
       [0007]    One advantage of the present invention is providing a method for coating an elastic adhesion material on a die and forming an opening on contacting pads before performing wire-bonding. 
         [0008]    Another advantage of the present invention is providing an upper chip without adhesive on its backside, 
         [0009]    Still another advantage of the present invention is providing a structure and a method without causing micro-cracking in the chip while performing wire-bonding. 
         [0010]    The present invention provides a structure of stacked dice package, comprising: a substrate with pluralities of pads; a first die with a first contacting pad attached on the substrate; a first wire electrically connected the pad and the first contacting pad; an elastic adhesive layer applied on the die, wherein the elastic adhesive layer covering all top surface of the first die and forming rims at the peripheral edges of the first die except the slots formed on the first contacting pads; a second die with a second contacting pad attached to the elastic adhesive layer; and a second wire electrically connected the pad and the second contacting pad and a layer of protection layer encapsulates the first die, the second die, the pads, the first wire and the second wire. 
         [0011]    The present invention provides a method for forming a stacked dice package comprising: providing a substrate with preformed pads; attaching a first die with a first contacting pad to the substrate, wherein an elastic adhesive layer is preformed on the first die; forming an opening in the elastic adhesive layer at the position of the first contacting pad, wherein the elastic adhesive layer covering all top surface of the first die and forming rims at the peripheral edges of the first die except the openings formed on the first contacting pads; wire-bonding the first contacting pad with the pad; attaching a second die with a second contacting pad to the elastic adhesive layer, wherein the second die attaching on the elastic layer without needing applying an adhesive on the backside of the second die and wire-bonding the second contacting pad with the pad. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  illustrates a prior art relating to a stacked dice packaging structure. 
           [0013]      FIG. 2  illustrates a cross-sectional view of stacked dice packaging structure according to the present invention. 
           [0014]      FIG. 3  illustrates a top view of a stacked dice packaging structure according to the present invention. 
           [0015]      FIG. 4  illustrates a stage of the process for manufacturing a stacked dice packaging structure according to the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0016]    The invention will now be described in greater detail with preferred embodiments of the invention and illustrations attached. Nevertheless, it should be recognized that the preferred embodiments of the invention is only for illustrating. Besides the preferred embodiment mentioned here, present invention can be practiced in a wide range of other embodiments besides those explicitly described, and the scope of the present invention is expressly not limited expect as specified in the accompanying claims. 
         [0017]    The present invention discloses a structure for making a stacked dice packaging structure with elastic adhesive layer. A photosensitive material is coated between the dice and pluralities of openings formed thereon for exposing contacting pads of a die before performing wire-bonding on contacting pads. 
         [0018]      FIG. 2  illustrates a cross-sectional view of a stacked dice packaging structure  1  in accordance with one embodiment of the present invention. As shown in the  FIG. 2 , the stacked dice packaging structure  1  includes a substrate  2  having pads, which is individually referred to as pad  3  and pad  4 , and an adhesive area  6  for placing a first die  7 . The substrate  2  is laminated and having an upper surface and a lower surface; wherein the upper surface means the surface on which a die placed. The pad  3  is located on the lower surface of the substrate  2  and a solder ball  14  is formed thereon. The pad  4  is located on the upper surface of the substrate  2  and keeps electrical connection with dice through wires; which is individually referred to as the first wire  5  and the second  6 . The material of the substrate includes organic epoxy type FR4, FR5, BT, PCB (print circuit board), alloy or metal. Alternatively, the substrate could be glass, ceramic or silicon. 
         [0019]    The first die  7  is disposed on the adhesive area  6  of the substrate  2  and fixed by an elastic adhesion layer  10 . the first contacting pads (Bonding pads)  8  are formed on the first die  7 ; i.e., As shown in  FIG. 3 , the first die  7  has a pluralities of contacting pads  8  located around the periphery of the top surface of the first die  7  for establishing electrical connection between pads  4  and the contacting pads  8 . The first wire  5  is made of varieties of metals, such as aluminum or gold. 
         [0020]      FIG. 3  shows a top view of the first die with a contacting pads  8  on which a first wires  5  bonds; wherein a layer of photo sensitive elastic material is covered on the top of the first die and a pluralities of slots  15  formed on the peripheral of the elastic adhesive layer  10  and extended to the edges of the die, that is, releasing layer for exposing the contacting pads  8  and receiving the bonding wires coupled between the first die and the substrate, i.e., the elastic adhesive layer  10  covers all to top surface of the first die  7  and forming a rim at the peripheral edge of the first die excepting the slots  15  formed on the pads  8 . 
         [0021]    The elastic adhesive layer  10  is a material with elongation rate higher than 20%. The preferably thickness of the elastic adhesive layer  10  is more than 20 μm. Preferably, the curing temperature of the elastic adhesive layer  10  is lower than 200° C. 
         [0022]    Referring back to  FIG. 2 , the second die  11  with the second contacting pads  12  is disposed on the elastic adhesive layer  10 ; wherein the contacting pads  12  keep electrical connection with the pads  4  through the second wire  6 . The contacting pad  12  and the second wire  6  are to be understand as being represented pluralities of contacting pads and wires; i.e., the second die  11  has pluralities of contacting pads  12  located around the periphery of the top surface of the second die  11  for keeping electrical contact between the second die  11  and the pads  4  through the second wire  6 . The second wire  6  is made of varieties of metals, such as aluminum or gold. In a preferred embodiment of the present invention, the thickness of the elastic adhesive layer  10  is thick enough to make the second die  11  far above the first wire  5  to prevent the second die  11  to contacting the first wire  5 . In a preferred embodiment of the present invention, the thickness of the elastic adhesive layer  10  is over the loop height of first wire  5 . In a preferred embodiment of the present invention, the second die  11  is placed on the elastic adhesive layer  10  without pre-formed tape on its back side. 
         [0023]    As shown in  FIG. 2 , protection layer  13  encapsulates the first dice  7 , the second die  11 , the pads  4 , the first wire  5  and the second wire  6  to protect them from outside interference, for example, moisture. In one embodiment of the present invention, materials for the protective layer  13  comprise organic compound, liquid compound, and silicone rubber. In another embodiment of the invention, the protection layer  13  preferably has suitable coefficient of thermal expansion to reduce the effects caused by the difference in the thermal coefficient of expansion between the protection layer and the other elements of stacked dice packaging structure. In one embodiment of the invention, the material of the protection layer can be thermoplastics, epoxy. 
         [0024]    The process of present invention for manufacturing a stacked dice packaging structure includes providing a wafer with an elastic adhesive layer  10  spin coated on its surface. Then, the wafer is diced into UV tape form or blue tape form; therefore the elastic adhesive layer covering all top surface of said first die and forming rims at the peripheral edges of the first die, A pick and place fine alignment system is used to re-distribute the known good dies, that is, the first die  7  illustrated in  FIG. 2 , on the substrate  2  with the first contacting pads, which is individually referred to as the pad  3  and the pad  4 , and a layer of adhesion  6  is preformed thereon to bond the back side of the first die  7  for forming the structure  1  illustrated in  FIG. 4 . As shown in  FIG. 3 , the elastic adhesive layer  10  covers all top surface of first die  7 . In a preferred embodiment of the present invention, the applied thickness of the elastic adhesive layer  10  should be thick enough to position the other die, that is, the second die  11  shown in  FIG. 2 , far above the first wire  5  to prevent the second die  11  to contact the first wire  5 . 
         [0025]    Next, as shown in  FIG. 3 , lithography is performed on the elastic adhesive layer  10  for forming openings  15  on the contacting pads  8 ; openings  15  can be any kind of format that allow the first wire  5  to be wire bonded the first contacting pads  8  and pads  4  of substrate; in the preferred embodiment of the present invention, the openings  15  are rectangular. Pluralities of openings  15  formed on the peripheral of the elastic adhesive layer  10  for exposing the first contacting pads  8 , i.e., the elastic adhesive layer  10  covers all to top surface of first die and forming a rim at the peripheral edge of the first die except the openings  15  formed on the first contacting pads  8 . 
         [0026]    Next, as shown in  FIG. 4 , wire-bonding the contacting pads  8  of the first die  7  with pads  4  on the substrate  2  by the first wires  5  to establish electrical connection between the first die  7  and the pads  4 . In one embodiment of the invention, wire-bonding is performed by conventional technique such as ultrasonic bonding, compression bonding, soldering. 
         [0027]    Then pick and place fine alignment system (die bonder) is used again to stack the other known good dies, that is, the second die  11  shown in  FIG. 2 , on the elastic adhesive layer  10  by attaching for forming a stacked structure of dice; wherein, the second die  11  has pluralities of contacting pads  12  on its top surface; i.e., the second die  11  has pluralities of contacting pads  12  located around the periphery of the top surface of the second die  11 . In a preferred embodiment of the present invention, the die  11  is placed on the elastic adhesive layer  10  without needing applying a layer of adhesive on its back side. 
         [0028]    Referring to  FIG. 2 , after the second die  10  is placed on the elastic adhesive layer  10 , pluralities of wires represent by the second wire  5  wire-bonding the contacting pads  12  with pluralities of pads  4 ; wherein, the elastic layer  10  is stable enough for ensuring coplanar of dice when performing wire-bonding on the upper chip and thick enough for preventing the first die  7  and the second die  11  from colliding with each other while performing wire-bonding. In one embodiment of the invention, wire-bonding is performed by conventional technique such as ultrasonic bonding, compression bonding, soldering. 
         [0029]    After the second die  11  bonded on the adhesion layer  10 , curing the elastic adhesion layer  10  for fixing the shape of the elastic layer. After the dice the substrate is molded by the molding compound, the stacked dice packaging structure is finished. In one embodiment of the present invention, molding is performed by applying a protection layer on the first die  7 , second die  11 , pluralities of wires represent by the second wire  5  and the first wire  6 , a pluralities of pads represent by pad  4  to encapsulating them. 
         [0030]    Although preferred embodiments of the present invention have been described, it will be understood by those skilled in the art that the present invention should not be limited to the described preferred embodiments. Rather, various changes and modifications can be made within the spirit and scope of the present invention, as defined by the following claims.