Abstract:
A semiconductor stacking structure and method of producing the same has a flexible substrate. A plurality of apertures is formed on the flexible substrate. The plurality of apertures may be formed in groups for coupling semiconductor devices to the flexible substrate. A plurality of traces is formed on the flexible substrate for coupling the plurality of apertures together. A first semiconductor device is coupled to a first side of the flexible substrate. A first adhesive layer is placed on a first side of the flexible substrate for coupling the first semiconductor device to the first side of the flexible substrate. A plurality of contacts is coupled to a second side of the flexible substrate. The contacts and the first adhesive layer liquefy and flow into designated apertures when heated to couple the contacts to the first semiconductor device.

Description:
FIELD OF THE INVENTION 
   This invention relates to semiconductor devices and, more specifically, to a stacking structure for semiconductor devices which uses a folded over flexible substrate and a method therefor. 
   BACKGROUND OF THE INVENTION 
   As electronic devices get smaller, the components within these devices must get smaller as well. Because of this, there has been an increased demand for the miniaturization of components and greater packaging density. Integrated Circuit (IC) package density is primarily limited by the area available for die mounting and the height of the package. One way of increasing the density is to stack multiple die or packages vertically in an IC package. Stacking multiple die or packages will maximize function and efficiency of the semiconductor package. 
   One method of stacking multiple die in an IC package is to use a folded over flexible substrate. In this method, a die and the other die are placed side by side on a flexible substrate. The flexible substrate is then folded over and the portion where the other die is placed covers the entire top surface of the die. In the case of more than two dies, the method is the same. 
   The above method is the current way of producing IC packages having multiple stacked die using a flexible substrate. However, there are several problems associated with using flexible substrates for producing IC packages having multiple stacked die. One problem is cost. Two metal layer flexible substrate tape is very expensive to use making certain packages cost prohibitive to the end user/client. Second, under current methods, connect density between dies is dramatically lower using a folded over substrate. 
   In order to provide high quality multi-chip stacked devices, the devices used for stacking must be either high yield FAB (i.e., memory devices) or known good die (KGD). Certain devices like ASIC and logic devices have a lower yield than devices like memory. Thus, these types of devices need to be screened if they are to be used in a multi-chip stacked device. A problem arises in that it is expensive to get a KGD prepared. Wafer component testing and burn-in testing is a very expensive process. However, testing of these types of devices is necessary in order to sort out potentially problematic chips and to prevent any quality and reliability issues. 
   Presently, there is a problem over the lack of known good die application into die stacking. If a logic or ASIC device is rejected after testing, the stack die coupled to these devices must be scraped. This is problematic to many end customers due to the cost of scraping good die which is stacked to a fail logic or ASIC device. 
   Therefore, a need existed to provide a device and method to overcome the above problems. 
   SUMMARY OF THE INVENTION 
   A semiconductor stacking structure and method of producing the same has a flexible substrate. A plurality of apertures is formed on the flexible substrate. The plurality of apertures may be formed in groups for coupling semiconductor devices to the flexible substrate. A plurality of traces is formed on the flexible substrate for coupling the plurality of apertures together. A first semiconductor device is coupled to a first side of the flexible substrate. A first adhesive layer or conductive paste is placed on a first side of the flexible substrate for coupling the first semiconductor device to the first side of the flexible substrate. A plurality of contacts is coupled to a second side of the flexible substrate. The contacts and the first adhesive layer liquefy and flow into designated apertures when heated to couple the contacts to the first semiconductor device. 
   The present invention is best understood by reference to the following detailed description when read in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an elevated perspective view of one embodiment of a flexible substrate used in a stacking structure of the present invention; 
       FIG. 2A  is an explodes view of one embodiment of a stacking structure of the present invention; 
       FIG. 2B  is an elevated perspective view of the first prepackaged device used in the stacking structure of the present invention; 
       FIG. 2C  is an elevated perspective view of the stacking structure depicted in  FIG. 2A ; 
       FIG. 3A  is an elevated perspective view of the stacking structure depicted in  FIG. 2B  with a second device stacked on top of the stacking structure; 
       FIG. 3B  is a close-up view of the connection between the second device and the stacking structure depicted in  FIG. 3A ; 
       FIG. 3C  is a close-up view of one embodiment of the connection between an electrical connector and the first device of the stacking structure depicted in  FIG. 3A ; 
       FIG. 3D  is a close-up view of another embodiment of the connection between an electrical connector and the first device of the stacking structure depicted in  FIG. 3A ; 
       FIG. 4A  is an exploded view of another embodiment of the stacking structure of the present invention; 
       FIG. 4B  is an elevated perspective view of the stacking structure depicted in  FIG. 4A ; 
       FIG. 4C  is a close-up view of the connection between the second device and the flexible substrate depicted in  FIG. 4B ; 
       FIG. 4D  is a close-up view of one embodiment of the connection between an electrical connector and the first device of the stacking structure depicted in  FIG. 4B ; and 
       FIG. 4E  is a close-up view of another embodiment of the connection between an electrical connector and the first device of the stacking structure depicted in FIG.  4 B. 
       FIG. 5  is a front view of another embodiment of the stacking structure of the present invention. 
       FIG. 6  is a front view of another embodiment of the stacking structure of the present invention. 
       FIG. 7  is a front view of another embodiment of the stacking structure of the present invention. 
   

   Common reference numerals are used throughout the drawings and detailed description to indicate like elements. 
   DETAILED DESCRIPTION 
   Referring to  FIG. 1 , a flexible substrate  10  is shown. The flexible substrate  10  is used in the stacking structure of the present invention. The flexible substrate  10  is used to electrically couple two or more devices together in a stacked structure. The flexible substrate  10  may be a flex tape such as a polyamide or the like. The flexible substrate  10  will have one or more metal layers which are used for electrical connections. However, this is just one type of flexible substrate  10 . The above references should not be seen as to limit the scope of the present invention. 
   The flexible substrate  10  will have a plurality of apertures  12 . The apertures  12  are used to couple a device to the flexible substrate  10 . The apertures  12  may be formed on the flexible substrate  10  in groups. Each of the groups is used to couple a specific device to the flexible substrate  10 . For example, as may be seen in  FIG. 1 , a first group  14  of apertures  12  is formed on one end of the flexible substrate  10 . A second group  16  of apertures  12  is formed on a second end of the flexible substrate  10 . Additional groups of apertures  12  may be formed on the flexible substrate  10 . The number of groups is generally based on the number of devices that will be coupled to the flexible substrate  10 . The apertures  12  are coupled to one another by a plurality of traces  18 . The traces  18  will allow different devices on the flexible substrate  10  to be coupled to one another. 
   Referring now to  FIGS. 2A-2C , one embodiment of a stacking structure for semiconductor devices  100  (hereinafter stacking structure  100 ) is shown. The stacking structure  100  has a device  20  which is coupled to the flexible substrate  16 . The device  20  is a fully encapsulated package which has a semiconductor die  22 . The semiconductor die  22  may be any type of device. For example, the semiconductor die  22  may be a memory device, a logic device, an ASIC device, and other like elements. It should be noted that the listing of the above types of semiconductor dies  22  is given as an example and should not be seen as to limit the scope of the present invention. 
   The stacking structure  100  may be a lead type of device, a Ball Grid Array (BGA) type of device, or a Land Grid Array (LGA) type of device In the embodiment depicted in  FIG. 1A , the stacking structure  100  is a BGA type of package. However, this should not be seen as to limit the scope of the present invention. 
   The device  20  is coupled to the flexible substrate  16 . As stated above, the apertures  12  are used to couple different devices  20  to the flexible substrate. The apertures  12  may be formed completely through the flexible substrate. Alternatively, a bond pad  24  may be positioned over the apertures  12 . The bond pad  24  is generally a metal such as copper, nickel, gold plate and the like. The apertures  12  and location and use of the bond pads  24  are based on design choice. The use of bond pads  24  is based on design choice and the type of device to be coupled to the flexible substrate  10 . 
   The device  20  is coupled to one side of the flexible substrate  16 . A solder paste layer  26  may be applied to couple the device  20  to the flexible substrate  16 . Electrical contacts  28  are positioned on an opposite side of the flexible substrate  16 . The stacking structure  100  will then go through a reflow process. The reflow process will liquefy the solder paste layer  26  and the electrical contacts  28 . The liquefied solder paste layer  26  and electrical contacts  28  will merge together in the apertures  12  thereby coupling the device  20  to the electrical contacts  28 . 
   Referring now to  FIG. 2C , the flexible substrate  16  is then folded over and coupled to a top surface of the device  20  to form the stacking structure  100 . An adhesive layer  30  is used to couple the flexible substrate  16  to the top surface of the device  20 . An adhesive film, paste or the like may be used as the adhesive layer  30 . The listing of the above should not be seen as to limit the scope of the present invention. 
   Referring to  FIG. 3A , a second device  32  is coupled to the stacking structure  100 . The second device  32  is generally a prepackaged device. The second device  32  is generally a different type of prepackaged device than that of the first device  20 . To couple the second device  32  to the stacking structure  100 , contacts  34  on the second device  32  will engage the bond pads  24  on the flexible substrate  10 . This will allow the second device  32  to be electrically coupled to the first device  12 . 
   Referring to  FIG. 3B , a close-up view of the connection between the second device  32  and the flexible substrate  10  is shown. The contact  34  of the second device  32  is coupled to a bond pad  38  on a substrate  36 . This will allow for an electrical connection between a die of the second device and the contact  34 . Each of the contacts  34  of the second device  32  will be position within a corresponding aperture  12 . Each contact  34  will be coupled to a bond pad  24 . Each bond pad  24  is coupled to the flexible substrate  10 . This will allow the second device  32  to be electrically coupled to the first device  20 . 
   Referring now to  FIG. 3C , a close-up view of the connections between the second device  32  and the flexible substrate  10  and the connection between the first device  12  and the flexible substrate  10 . In this embodiment, the connections between the second device  32  and the flexible substrate  10  is the same as that described above. Each of the contacts  34  of the second device  32  will be position within a corresponding aperture  12 . Each contact  34  will be coupled to a bond pad  24  which is further coupled to the flexible substrate  10 . This will allow the second device  32  to be electrically coupled to the first device  20 . For the connection between the first device  20  and the flexible substrate  10 , the aperture  12  is formed completely through the flexible substrate  10 . The electrical contacts  28  are positioned on an opposite side of the flexible substrate  16 . During a reflow process, the electrical contacts  28  attached to the prepackaged device  20 , which in this embodiment are solder balls, will liquefy. The liquefied solder balls will become electrical contacts  28  in the apertures after getting down through via holes of tape substrate  10  with ball pad center holed  13  thereby coupling the first device to the electrical contacts  28  automatically. 
   Referring now to  FIG. 3E , a close-up view of the connections between the second device  32  and the flexible substrate  10  and the connection between the first device  12  and the flexible substrate  10 . In this embodiment, the connections between the second device  32  and the flexible substrate  10  is the same as that described above. Each of the contacts  34  of the second device  32  will be position within a corresponding aperture  12 . Each contact  34  will be coupled to a bond pad  24  which is further coupled to the flexible substrate  10 . This will allow the second device  32  to be electrically coupled to the first device  20 . For the connection between the first device  20  and the flexible substrate  10 , a bond pad  24  is positioned across the aperture  12 . Contacts  40  on the first device  20  are electrically coupled to the bond pad  24 . The electrical contacts  28  are then electrically coupled to the bond pad  24  thereby coupling the first device  20  to the electrical contacts  28 . 
   Referring to  FIG. 4A , another embodiment of a stacking structure  200  is shown. In this embodiment, the flexible substrate  10  is similar to the flexible substrate  10  disclosed above. The flexible substrate  10  will have a plurality of apertures  12 . The apertures  12  may be formed on the flexible substrate  10  in groups. Each of the groups is used to couple a specific device to the flexible substrate  10 . Some of the apertures  12  may have bond pads  24  coupled thereto. Alternatively, bond pads  24  may be directly coupled to the flexible substrate  10 . The use of bond pads  24  is based on design choice and the type of device to be coupled to the flexible substrate  10 . The apertures  12  and the bond pads  24  are coupled to one another by a plurality of traces  18 . The traces  18  will allow different devices on the flexible substrate  10  to be coupled to one another. In the embodiment depicted in  FIG. 4A , the flexible substrate  10  has a group of apertures  12  with bond pads  24  coupled thereto on one side and a group of bond pads  24  coupled to the flexible substrate  10  on an opposite side. The group of apertures  12  with bond pads  24  and the bond pads located opposite are coupled together with traces  18 . 
   In the embodiment depicted in  FIG. 4A , a first device  20  and a second device  32  are coupled to the flexible substrate  10 . The first device  20  and the second device  32  can be coupled to the flexible substrate  10  in a variety of different manners. 
   Referring to  FIG. 4B , once the first device  20  and the second device  32  are coupled to the flexible substrate  10 , the flexible substrate  10  is folded over. An adhesive layer  42  is applied to the top surface of the devices  20  and  32  to couple the top surfaces of devices  20  and  32  together. The stacking structure  200  may further have electrical contacts  28 . The electrical contacts  28  are generally coupled to the first device  20  in a similar manner as disclosed above. The electrical contacts  28  are inserted into the aperture  12 . The electrical contacts  28  will come in contact with the corresponding bond pad  24  forming an electrical contact between the first device  20  and the electrical contacts. The stacking structure  200  depicted in  FIGS. 4A and 4B  is best used where heat dissipation is not an issue. 
   Referring to  FIG. 4C , a close-up view of the connection between the second device  32  and the flexible substrate  10  is shown. The contact  34  of the second device  32  is coupled to a bond pad  38  on a substrate  36 . This will allow for an electrical connection between a die of the second device and the contact  34 . Each contact  34  will be coupled to a bond pad  24  coupled to the flexible substrate  10 . This will allow the second device  32  to be electrically coupled to the first device  20 . 
   Referring now to  FIG. 4D , a close-up view of the connections between the second device  32  and the flexible substrate  10  and the connection between the first device  12  and the flexible substrate  10 . In this embodiment, the connections between the second device  32  and the flexible substrate  10  are as follows. Each contact  34  is coupled to a bond pad  24  which is further coupled to the flexible substrate  10 . This will allow the second device  32  to be electrically coupled to the first device  20 . For the connection between the first device  20  and the flexible substrate  10 , the aperture  12  is formed completely through the flexible substrate  10 . The electrical contacts  28  are positioned on an opposite side of the flexible substrate  16  from the first device  20 . During a reflow process, the solder paste layer  26  and the electrical contacts  28  will liquefy. The liquefied solder paste layer  26  and electrical contacts  28  will merge together in the apertures  12  thereby coupling the first device  20  to the electrical contacts  28 . 
   Referring now to  FIG. 4E , a close-up view of the connections between the second device  32  and the flexible substrate  10  and the connection between the first device  12  and the flexible substrate  10 . In this embodiment, the connections between the second device  32  and the flexible substrate  10  is the same as that described above. Each contact  34  is coupled to a bond pad  24  which is further coupled to the flexible substrate  10 . This will allow the second device  32  to be electrically coupled to the first device  20 . For the connection between the first device  20  and the flexible substrate  10 , a bond pad  24  is positioned across the aperture  12 . Contacts  40  on the first device  20  are electrically coupled to the bond pad  24 . The electrical contacts  28  are then electrically coupled to the bond pad  24  thereby coupling the first device  20  to the electrical contacts  28 . 
   Referring to  FIG. 5 , another embodiment of the stacking structure  300  is shown. The stacking structure  300  is very similar to that shown in  FIGS. 3A-3D . The main difference is that in  FIG. 5  any additional package is stacked on top of the second device  32 . The third device  50  is generally a prepackaged device. The third device  50  may be coupled to the flexible substrate  10  in a plurality of different manners. Different combinations of apertures  12  and bond pads  24  in combination or by themselves may be used. In the embodiment depicted in  FIG. 5 , to couple the third device  50  to the stacking structure  300 , additional bond pads  24  are coupled to the flexible substrate  10  in a manner similar to that described above. Contacts  52  on the third device  50  will engage the bond pads  24  on the flexible substrate  10 . This will allow the third device  50  to be electrically coupled to the first device  20  and the second device  32 . It should be noted that additional packages may be coupled to the stacking structure  300  without departing from the spirit and scope of the present invention. 
   Referring to  FIG. 6 , another embodiment of a stacking structure  400  is shown. The stacking structure  400  is similar to that shown in  FIGS. 3A-3D . The main difference is that the second device  32  is a flip chip  32 A. The flip chip  32 A has contacts  34  coupled to bond pads  24  on the flexible substrate  10 . In this embodiment, there is no under filling of the flip chip  32 A. 
   Referring to  FIG. 7 , another embodiment of a stacking structure  500  is shown. The stacking structure  500  is similar to that shown in FIG.  6 . The main difference is that there is under filling of the flip chip  32 A. 
   This disclosure provides exemplary embodiments of the present invention. The scope of the present invention is not limited by these exemplary embodiments. Numerous variations, whether explicitly provided for by the specification or implied by the specification, such as variations in structure, dimension, type of material and manufacturing process may be implemented by one of skill in the art in view of this disclosure.