Abstract:
A semiconductor device with reinforced under-support structure and a method for fabricating the semiconductor device are provided, which can be used in the packaging of an MPBGA/TFBGA (Multi-Package Ball Grid Array &amp; Thin Fine-pitch Ball Grid Array) module to help reinforce the TFBGA under-support structure therein. The proposed chip-packaging method is characterized by the provision of large-area solder pads at the corners of a solder-pad array used for TFBGA attaching application, in order to form solder bumps of a large cross section and volume during reflow process to help reinforce the TFBGA under-package structure. This feature can reinforce the TFBGA under-package structure without having to use flip-chip underfill technology, and without having to use extra large type solder balls and arrange pads into different pitches as in the prior art.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to semiconductor packaging technology, and more particularly, to a semiconductor device with reinforced under-support structure and method of fabricating the same, which can be used in the fabrication of a semiconductor device, such as a MPBGA (Multi-Package Ball Grid Array) device having at least one TFBGA (Thin Fine-pitch Ball Grid Array) package to help reinforce the TFBGA package&#39;s under-support structure and thereby prevent the TFBGA package against stress damage, or can be used in the fabrication of a semiconductor device having a flip-chip structure to reinforce the flip-chip structure. 
   2. Description of Related Art 
   MPBGA (Multi-Package Ball Grid Array) is an advanced type of semiconductor device packaging technology, which can be used to pack two or more packages on one single substrate, so as to allow one single semiconductor device to offer a manifold level of functionality or data storage capacity. A graphic control unit, for instance, is typically designed in such a manner as to include a graphic control chip package together with one or more memory chip packages on the same substrate, so as to allow one semiconductor device to offer all the required graphic control functionality without having to be attached to external memory modules. 
     FIGS. 1A–1B  are schematic diagrams showing the architecture of a conventional MPBGA semiconductor device. As shown, this MPBGA semiconductor device is constructed on a substrate  100  for the packaging of three packages: a first package  110 , a second package  120 , and a third package  130 , wherein the first package  110  and the second package  120  are each, for example, a TFBGA (Thin Fine-pitch Ball Grid Array) type of memory chip package, while the third package  130  is for example a graphic control chip package. In this MPBGA semiconductor device, the first package  110  and the second package  120  are mounted on the substrate  100  by means of an array of solder bumps  111  ( FIG. 1B  only shows the under-support structure of the first package  110 ). By contrast, the third package  130  is electrically connected to the substrate  100  by means of bonding wires  131  and further encapsulated in a molded encapsulation body  132 . Finally, the MPBGA semi-conductor device is mounted by means of solder balls  140  (i.e., ball grid array) to an external printed circuit board  150 . 
   As the first package  110  and the second package  120  are bonded in position over the substrate  100 , however, a gap would be undesirably left between each TFBGA package ( FIG. 1B  only shows the first package  110 ) and its underlying surface, which, if not underfilled, would easily cause the under-support structure to suffer from fatigue cracking and electrical failure due to thermal stress when the entire semiconductor device is being subjected to high-temperature conditions. As a solution to this problem, it is an essential step in the fabrication process to fill an underfill material, such as epoxy resin, into the under-package gap to form an underfill layer  112  which, when hardened, can serve as a mechanical reinforcement for the under-support structure of the first package  110  to cope against thermal stress. 
   One drawback to the fabrication of the underfill layer  112 , however, is that it would require a highly complex process to achieve, which is quite laborious and time-consuming, making the overall packaging process quite cost-ineffective. 
   Related art includes, for example, the following patents:
         U.S. Pat. No. 6,020,633 “INTEGRATED CIRCUIT PACKAGED FOR RECEIVING ANOTHER INTEGRATED CIRCUIT”;   U.S. Pat. No. 5,381,307 “SELF-ALIGNING ELECTRICAL CONTACT ARRAY”; and   Japanese Patent JP 11111768 “MANUFACTURE OF SEMICONDUCTOR DEVICE”.       

   The U.S. Pat. No. 6,020,633 discloses a special type of MPBGA module structure. One drawback to this patent, however, is that it still utilizes under-fill technology to form an underfill layer for reinforcing the under-support structure of the TFBGA package on the substrate, so that it still has the above-mentioned drawbacks of the underfill method. 
   The U.S. Pat. No. 5,381,307 discloses the use of a specially-designed solder-pad array that includes large-size solder balls at the corners thereof to help align the package in position during reflow process, and can additionally help reinforce under-support structure. One drawback to this patent, however, is that it requires an increase in the number of pads on the substrate, thus undesirably making the overall layout design work more complex and laborious to implement. In addition, for TFBGA (Thin Fine-pitch Ball Grid Array) packages whose ball pitch thereof is below 0.75 mm, the provision of large-size solder balls at corners requires the solder balls to be laid at different ball pitches to prevent these solder balls to come in touch with each other and result in the bridging therebetween. 
   Japanese Patent JP 11111768 discloses a semiconductor device fabrication method that is characterized by the application of an adhesive agent at the corners to help reinforce under-support structure. One drawback to this solution, however, is that it requires a complex process to implement and is thus quite cost-ineffective. 
   There exists therefore a need for a new semiconductor device packaging technology that can help reinforce under-support structure without having to use underfill technology for the purpose of allowing the overall fabrication process to be more simplified and cost-effective to implement. 
   SUMMARY OF THE INVENTION 
   It is therefore an objective of this invention to provide a new semiconductor device and method that can help reinforce TFBGA under-support structure without having to use underfill technology for the purpose of allowing the overall fabrication process to be more simplified and cost-effective to implement than prior art. 
   It is another objective of this invention to provide a new semiconductor device and method that can help reinforce the TFBGA under-support structure without having to increase the number of pads on the substrate so as to allow the layout work more simplified than prior art, 
   The semiconductor device with reinforced under-support structure according to the invention comprises: a substrate, which is formed with at least one device mounting area having a solder-pad array therein; the solder-pad array having a plurality of solder pads, with corner-located solder pads being greater in area than those solder pads elsewhere; and at least one electronic component, which is mounted by means of solder joints on the solder-pad array to the device mounting area on the substrate. 
   The method according to the invention for fabricating a semiconductor device with reinforced under-support structure comprises the steps of preparing a substrate; wherein the substrate is formed with at least one device mounting area having a solder-pad array therein; wherein the solder-pad array is a polygonally-shaped solder-pad array having a plurality of first-type solder pads and a plurality of second-type solder pads, and wherein the first-type solder pads are positioned at the corners of the solder-pad array and are dimensioned to be greater in surface area than the second-type solder pads; pasting a solder material over the first-type solder pads and the second-type solder pads in the solder-pad array to thereby form a group of first-type solder bumps over the first-type solder pads and a group of second-type solder bumps over the second-type solder pads in the solder-pad array, and wherein the first-type solder bumps are greater in cross area and volume than the second-type solder bumps; and performing an SMT process to mount an electronic component onto the substrate by means of the first-type solder bumps and the second-type solder bumps. 
   The semiconductor packaging technology according to the invention is characterized by the provision of large-area solder pads at the corners of a solder-pad array, which can help to form solder bumps of a large cross section and volume during reflow process to thereby reinforce the TFBGA under-support structure. Compared to the prior art, the semiconductor device and method according to the invention can help reinforce the TFBGA under-support structure in an MPBGA semiconductor device without having to use under-fill technology, and therefore the invention allows the overall process to be more simplified and cost-effective to implement than prior art. Moreover, since the semiconductor device and method according to the invention can be implemented without having to increase the number of pads on substrate, it allows the layout work more simplified than prior art. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
     The invention can be more fully understood by reading the following detailed description of the preferred embodiments, with reference made to the accompanying drawings, wherein. 
       FIG. 1A  (PRIOR ART) is a schematic diagram showing the top view of a conventional MPBGA semiconductor device; 
       FIG. 1B  (PRIOR ART) is a schematic diagram showing a sectional view of the MPBGA semiconductor device of  FIG. 1B ; 
       FIG. 2A  a schematic diagram showing the top view of a substrate utilized by the semiconductor device and method of the invention, 
       FIG. 2B  a schematic sectional diagram showing the semiconductor device of the invention, 
       FIG. 3A  a schematic diagram showing a top view of a MPBGA semiconductor device that utilizes the packaging structure of the invention, 
       FIG. 3B  a schematic diagram showing a sectional view of the MPBGA semiconductor device that utilizes the packaging structure of the invention and 
       FIGS. 4A–4C  are schematic diagrams showing various other embodiments of the semiconductor device and method according to the invention. 
   

   DESCRIPTION OF PREFERRED EMBODIMENTS 
   Referring to  FIG. 2A  and  FIG. 2B , the semiconductor device with reinforced under-support structure according to the invention comprises a substrate  200  and at least one electronic component  220 , wherein the substrate  200  is formed with at least one device mounting area  201  on one surface thereof and a solder-pad array  211  formed within the device mounting area  201 , while the electronic component  220  is provided with a plurality of solder bumps  221  for mechanically bonding and electrically coupling the electronic component  220  to the substrate  200 . 
   The solder-pad array  211  formed within the device mounting area  201  on the substrate  200  is composed of a plurality of first-type solder pads  211   a  and a plurality of second-type solder pads  211   b , wherein the first-type solder pads  211   a  are arranged on the corners of the solder-pad array  211 , and which are greater in area than the second-type solder pads  211   b . Moreover, the solder-pad array  211  is implanted with a solder-bump array  230 , which is composed of a plurality of first-type solder bumps  230   a  and a plurality of second-type solder bumps  230   b ; wherein the first-type solder bumps  230   a  are greater in area than the second-type solder bumps  230   b ; and wherein the first-type solder bumps  230   a  are implanted respectively on the first-type solder pads  211   a , while the second-type solder bumps  230   b  are implanted respectively on the second-type solder pads  211   b . 
   Note that  FIGS. 2A–2B  are simplified schematic diagrams to show only those parts related to the invention; and the shown parts are not drawn to actual scale, size, and number, which can be arbitrary design choices in the actual implementation of the invention. 
     FIGS. 4A–4C  are schematic diagrams showing(, various other embodiments of the aforementioned solder-pad array  211  in actual implementation of the invention; wherein  FIG. 4A  shows an example of an solder-pad array  400  having four large-area first-type solder pads  401  at each corner (only one corner is shown);  FIG. 4B  shows an example of the solder-pad array  500  having six large-area first-type solder pads  501  at each corner (only one corner is shown); and  FIG. 4C  shows an example of an solder-pad array  600  having nine large-area first-type solder pads  601  at each corner (only one corner is shown). Various other embodiments are still possible. Fundamentally, the number of size of the solder pads are not limited to these preferred embodiments, and the key point of the invention is that the corner-located solder pads should be greater in area than those solder pads that are located elsewhere. 
   As shown in  FIG. 2B , the electronic component  220  can be, for example, a BGA package or a flip-chip package, and which is solder-jointed by means of the solder-pad array  211  through solder balls or bumps to the first-type solder bumps  230   a  and the second-type solder bumps  230   b  to thereby be mechanically bonded and electrically connected to the substrate  200 . 
   The method for fabricating a semiconductor device according to the invention is described below. 
   In the method according to the invention, the first step is to prepare a substrate  200  which is formed with at least one device mounting area  201  on one surface thereof and a solder-pad array  211  formed within the device mounting area  201 , and wherein the solder-pad array  211  is composed of a plurality of first-type solder pads  211   a  and a plurality of second-type solder-pads  211   b , wherein the first-type solder pads  211   a  are arranged on the corners of the solder-pad array  211 , and which are greater in area than the second-type solder pads  211   b.    
   In the next step, a solder substance is pasted onto the first-type solder pads  211   a  and the second-type solder pads  211   b  to thereby form a solder-bump array  230  thereon, which is composed of a plurality of first-type solder bumps  230   a  and a plurality of second-type solder bumps  230   b ; wherein the first-type solder bumps  230   a  are greater in area than the second-type solder bumps  230   b.    
   In the next step, an electronic component  220  is mechanically bonded and electrically connected to the substrate  200  by means of bonding the solder bumps  221  to the first-type solder bumps  230   a  and the second-type solder bumps  230   b.    
   Referring to  FIG. 3A  and  FIG. 3B , in the following preferred embodiments, the semiconductor device and method of the invention is utilized in the fabrication of a MPBGA (Multi-Package Ball Grid Array) semiconductor device with the purpose of reinforcing the TFBGA (Thin Fine-pitch Ball Grid Array) package&#39;s under-support structure therein. However, broadly speaking, the invention can also be used to reinforce a flip chip&#39;s under-support structure for the flip chip to be more robust to cope against thermal stress. 
   As shown, the substrate  300  is used to mount two packages: a first package  310  and a second package  320 ; wherein the first package  310  is, for example, a TFBGA memory chip package, while the second package  320  is for example a graphic control chip package. Moreover, the first package  310  can be either a WB-TFBGA (Wire-Bonded TFBGA) package, or a FC-TFBGA (Flip-Chip TFBGA) package. To mount these two packages  310 ,  320 , the substrate  300  is provided with a first device mounting area  301  and a second device mounting area  302 . Further, the first device mounting area  301  and the second device mounting area,  302  are each provided with a polygonally-shaped solder-pad array, such as a rectangularly-shaped solder-pad array  311 . 
   The invention is characterized by arranging the solder-pad array  311  into a subgroup of large-area first-type solder pads  311   a  and a subgroup of small-area second-type solder pads  311   b , wherein the large-area first-type solder pads  311   a  are positioned at the four corners of the solder-pad array  311 . 
   As shown in  FIG. 3B , during package-mounting process, the two packages  310 ,  320  are mounted respectively over the first mounting area  301  and the second mounting area  302  on the substrate  300 . The first package  310  is mounted onto the first mounting area  301  by, for example, a first step of pasting a solder material through the use of, for example, stencil-printing technology, over the solder-pad array  311  to thereby form a plurality of first-type solder bumps (not shown) over the first-type solder pads  311   a  in the solder-pad array  311  and meanwhile a plurality of second-type solder bumps (not shown) over the second-type solder pads  311   b  in the solder-pad array  311 . Since the first-type solder pads  311   a  are greater in surface area than the second-type solder pads  311   b , the resulted first-type solder bumps are greater in cross area and volume than the second-type solder bumps. 
   In the next step, a SMT (Surface-Mount Technology) is performed to mount the first package  310  over the first mounting area  301 ; and then a reflow process is performed to reflow the first-type solder bumps to form solder joint  341  for mechanically bonding and electrically connecting the first package  310  to the substrate  300 . 
   On the other hand, the second package  320  is mounted in the same manner as prior art, i.e., electrically connected to the substrate  300  by means of bonding wires  321 , such as gold wires, to the second device mounting area  302 . Description thereof will not be further detailed herein. 
   It is known that the weakest points on TFBGA under-support structure in an MPBGA semiconductor device are at the four corners of the TFBGA under-support structure. For this sake, the invention is specifically intended for forming large-size solder joints  341  at the four corners of the TFBGA package  310  to provide reinforced under-support structure for the TFBGA package  310 . Compared to the prior art, the semiconductor device and method according to the invention can help reinforce the TFBGA under-support structure in an MPBGA semiconductor device without having to use flip-clip underfill technology, and therefore the invention allows the overall process to be more simplified and cost-effective to implement than prior art. Moreover, since the semiconductor device and method of the invention can be implemented without having to increase the number of pads on substrate, it allows the layout work more simplified than prior art. The invention is therefore more advantageous to use than the prior art. 
   The invention has been described using exemplary preferred embodiments. However, it is to be understood that the scope of the invention is not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements. The scope of the claims, therefore, should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.