Abstract:
A redistribution connecting structure for solder balls is disclosed. A substrate includes a plurality of bonding pads. A plurality of dielectric layers, a redistribution conductive layer between the dielectric layer, and a plurality of solder balls are formed on the substrate. The redistribution layer has a redistribution pad disposed adjacent to one of the bonding pads without electrical connection with the redistribution pad. One of the dielectric layers covering the redistribution conductive layer has an opening to partially expose the redistribution pad, in which the opening is approximately circular and has a cut-off portion so that the opening is adjacent to an opening of another of the dielectric layers exposing one of the bonding pads without overlapping. Accordingly, bonding area of the redistribution pad for a bonding pad under one of the solder balls can be expanded to reduce stress effect.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to a technique involving the connection of solder balls (i.e. solder bumps) for electronic devices, and more particularly, to a redistribution connecting structure for solder balls. 
   2. Description of the Prior Art 
   In the conventional art, solder balls are commonly disposed on the output terminal of electronic devices for connecting to other external devices. As the demand for product miniaturization increases, the position of solder balls must be rearranged and adjusted accordingly. As shown in  FIG. 1 , a conventional redistribution connecting structure  100  includes a substrate  110 , a first dielectric layer  120 , a redistribution conductive layer  130 , a second dielectric layer  140 , and a plurality of solder balls  150 . A plurality of bonding pads  111  is disposed on the substrate  110 , in which only one bonding pad is illustrated in the figure. The first dielectric layer  120  is disposed on the substrate  110  and exposes the bonding pad  111  through a plurality of openings. The redistribution conductive layer  130  is disposed on the first dielectric layer  120 . One end of the redistribution conductive layer  130  is processed to form a plurality of redistribution pads  131  for adjusting the position of the solder balls  150 . The second dielectric layer  140  is disposed on the first dielectric layer  120  and the redistribution conductive layer  130 . Preferably, the second dielectric layer  140  includes a plurality of circular openings  141  to proportionally expose a portion of the redistribution pads  131 . The solder balls  150  are disposed on the redistribution pads  131 . A plurality of ball bases  160  is disposed under the solder balls  150 , in which the ball bases  160  are connected to the redistribution pads  131  through the openings  141 , thereby establishing a connection for the solder balls  150 . 
   However, when the solder balls  150  are disposed too close to the bonding pads  111  having no electrical connection thereof, a stress will result and break the connection of the solder balls  150  and cause the solder balls to peel off. If the size of the opening  141  is reduced directly, the bonding area and the adhesive ability of the redistribution pads  131  and the ball bases  160  will decrease accordingly and result in the same problem. Currently, the position of the solder balls  150 , hence the position of the opening  141  of the second dielectric layer  140 , is formed away from the bonding pads  111  having no electrical connection thereof. This design ultimately limits the redistribution effect of the solder balls  150 . 
   SUMMARY OF THE INVENTION 
   It is an objective of the present invention to provide a redistribution connecting structure to solve the aforementioned problem. According to the preferred embodiment of the present invention, a redistribution conductive layer is disposed between a first dielectric layer and a second dielectric layer on a substrate. The first dielectric layer partially exposes a plurality of bonding pads formed on the substrate, and the second dielectric layer partially exposes a plurality of redistribution pads formed on the redistribution conductive layer. Preferably, when a solder ball is disposed adjacent to a bonding pad having no electrical connection thereof and an opening of the first dielectric layer that exposes the bonding pad is covered by the surface of the solder ball, a substantially circular opening having a cut-off portion of the second dielectric layer is formed. Specifically, the opening of the second dielectric layer is formed adjacent to but not overlapping the opening of the first dielectric layer, thereby increasing the bonding area between the ball base and the redistribution pad and reducing the overall stress. Ultimately, phenomenon such as breaking or peeling of solder balls can be prevented, thus increasing the yield of the product. 
   According to an embodiment of the present invention, the redistribution connecting structure for solder balls includes a substrate, a first dielectric layer, a redistribution conductive layer, a second dielectric layer, at least a solder ball, and a first bonding pad and a second bonding pad disposed on the substrate. The first dielectric layer is disposed on the substrate, in which the first dielectric layer includes a first opening and a second opening partially exposing the first bonding pad and the second bonding pad. The redistribution conductive layer is formed on the first dielectric layer. The redistribution conductive layer includes a first redistribution pad and a second redistribution pad, in which the first redistribution pad is electrically connected to the first bonding pad through the first opening, and the second redistribution pad is electrically connected to the second bonding pad through the second opening. The second dielectric layer is formed on the first dielectric layer and the redistribution conductive layer. The second dielectric layer includes a third opening and a fourth opening, in which the third opening partially exposes the first redistribution pad and the fourth opening partially exposes the second redistribution pad. The solder ball is disposed on the first redistribution pad. The area of the solder ball preferably covers the third opening and a portion of the second opening. The third opening is substantially circular and disposed adjacent to but not overlapping the second opening, in which the third opening further includes a cut-off portion. By using this design, the solder ball can be disposed above the electrically insulated second bonding pad, thus reducing the overall stress and the eliminating the need for having additional redistribution conductive layers. 
   These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates a cross-section of a redistribution connecting structure for solder balls according to the prior art. 
       FIG. 2A  illustrates a top-view of a redistribution connecting structure for solder balls according to the first embodiment of the present invention. 
       FIG. 2B  illustrates a cross-section of the redistribution connecting structure of  FIG. 2A  along the sectional line  2 B- 2 B. 
       FIGS. 3A ,  4 A, and  5 A illustrate a top-view of a redistribution connecting structure for solder balls during the fabrication process according to the first embodiment of the present invention. 
       FIGS. 3B ,  4 B, and  5 B illustrate a cross-section of a redistribution connecting structure for solder balls during the fabrication process according to the first embodiment of the present invention. 
       FIG. 6  illustrates a cross-section of a redistribution connecting structure for solder balls according to the second embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
     FIG. 2A  illustrates a top-view of a redistribution connecting structure  200  for solder balls (i.e. solder bumps) according to the first embodiment of the present invention.  FIG. 2B  illustrates a cross-section of the redistribution connecting structure  200  of  FIG. 2A  along the sectional line  2 B- 2 B. 
   As shown in  FIGS. 2A and 2B , the redistribution connecting structure  200  includes a substrate  210  having a plurality of bonding pads  211 , a first dielectric layer  220 , a redistribution conductive layer  230 , a second dielectric layer  240 , and a plurality of the solder balls  250 . The solder balls  250  include at least a first solder ball  251  and a second solder ball  252 , and the bonding pads  211  include a first bonding pad  211 A and a second bonding pad  211 B disposed on the substrate  210 . The redistribution conductive layer  230  is used to electrically connect the first solder balls  251  and the first bonding pad  211 A, and electrically connect the second solder ball  252  and the second bonding pad  211 B, as shown in  FIG. 2A  and  FIG. 4A . Preferably, the first solder ball  251  is disposed on the second bonding pad  211 B and the first redistribution pad  231 A of the redistribution conductive layer  230 , and the second bonding pad  211 B is electrically connected to the solder ball  251  without going through the redistribution conductive layer  230 . The substrate  210  of the present embodiment is preferably an integrated circuit die, a ceramic substrate, a plastic substrate, a printed circuit board, or a flexible circuit board. 
   Please refer to  FIG. 2B  and  FIGS. 3A and 3B . The first dielectric layer  220  is formed on the substrate  210 , in which the first dielectric layer  220  includes a plurality of openings  221  for exposing the surface of the bonding pads  211 . The openings  221  include a first opening  221 A and a second opening  221 B, in which the first opening  221 A partially exposes the first bonding pad  211 A and the second opening  221 B partially exposes the second bonding pad  211 B. In the present embodiment, the bonding pads  211 , including the first bonding pad  211 A and the second bonding pad  211 B, are formed in a shape of a rectangle or a square. The openings  221 , including the first opening  221 A and the second opening  221 B are formed in a shape of a circle. Preferably, the area of the openings  221  is smaller than the area of the bonding pads  211 , and the first dielectric layer  220  is composed of phosphosilicate glass, polyimide, or benzocyclobutene. 
   Please refer to  FIG. 2B  and  FIGS. 4A and 4B . As shown in  FIG. 2B  and  FIGS. 4A and 4B , the redistribution conductive layer  230  having a plurality of redistribution pads  231  is disposed above the first dielectric layer  220 , in which the redistribution conductive layer  230  is electrically connected to the corresponding bonding pads  211  through the opening  221  of the first dielectric layer  220 . The redistribution conductive layer  230  is preferably composed copper, aluminum, or other conductive metal. The redistribution pads  231  include a first redistribution pad  231 A disposed on the upper right corner of  FIG. 4A  and a second redistribution pad  231 B disposed on the upper corner of  FIG. 4A . The first redistribution pad  231 A is disposed adjacent to the second redistribution pad  211 B and electrically connected to the first bonding pad  211 A through the first opening  221 A, and the second redistribution pad  231 B is electrically connected to the second bonding pad  211 B. In the present embodiment, the first redistribution pad  231 A and the portion connecting the redistribution conductive layer  230  and the second bonding pad  211 B are located adjacent to each other and in the same level, thus resulting in a non-perfect circular shape. 
   Please refer to  FIG. 2B  and  FIGS. 5A and 5B . As shown in  FIG. 2B  and  FIGS. 5A and 5B , the second dielectric layer  240  is disposed on the first dielectric layer  220  and the redistribution conductive layer  230 , in which the second dielectric layer  240  includes a plurality of openings  241  for exposing the redistribution pads  231 . In the present embodiment, the openings  241  include a third opening  241 A and a fourth opening  241 B, in which the third opening  241 A partially exposes the first redistribution pad  231 A and the fourth opening  241 B partially exposes the second redistribution pad  231 B. As shown in  FIGS. 2A and 2B , the solder balls  250  are disposed on the redistribution pads  231 , in which the first solder ball  251  is disposed on the first redistribution pad  231 A and the second solder ball  252  is disposed on the second redistribution pad  231 B. Preferably, the area  253  of the first solder ball  251  also covers the third opening  241 A and a portion of the second opening  221 B. Referring to  FIGS. 5A and 5B , since the third opening  241 A includes a substantially circular shape and a cut-off portion, the third opening  241 A is formed adjacent to the second opening  221 B but not overlapping the second opening  221 B. In the present embodiment, the edge of the cut-off portion of the third opening  241 A includes two straight lines for forming an included angle, thus resulting a substantially C-shaped third opening  241 A. Additionally, as shown in the right region or lower left side of  FIG. 5A , the edge of the cut-off portion of the openings  241  can be a straight line, thus forming a portion of the openings  241  into a substantially D shape. 
   As shown in  FIG. 2A , the distance d between the edge of the second opening  221 B and the center of the third opening  241 A is less than the radius r of the third opening  241 A. Hence, the third opening  241 A of the second dielectric layer  240  that located in a relatively upper level, is not affected by the position of the second opening  221 B of the first dielectric layer  220  that located in a relatively lower level, thereby providing adequate electrical barrier between the first redistribution pad  231 A and the adjacent second bonding pad  211 B and providing enough adhesion area for the first redistribution pad  231 A. 
   The first solder ball  251  can be disposed above different second bonding pads  211 B that are electrically insulated to each other, thus increasing the bonding area between the first redistribution pads  231 A and the ball base  260  positioned under the solder ball  251  and eliminating the need for forming additional layers for the redistribution conductive layer  230 . As shown in  FIG. 2B , the redistribution connecting structure  200  also includes at least a ball base  260 , in which the ball base  260  can be a conventional under bump metallurgy (UBM) structure composed of titanium/nickel-vanadium/copper, nickel/gold, nickel/copper, chromium/chromium-copper/copper. The ball base  260  is positioned on the redistribution pads  231  for connecting the solder balls  250 . Additionally, the ball base  260  is substantially circular and disposed on the second dielectric layer  240 , and the ball base  260  is connected to the first redistribution pad  231 A through the third opening  241 A. The ball base  260  is also extended to the top of the second opening  221 B for adjusting the position of the solder ball  251 , in which the area  253  of the solder ball covers the second opening  221 B and at least a portion of the second bonding pad  211 B. 
   The second embodiment of the present invention discloses another redistribution connecting structure for solder balls. As shown in  FIG. 6 , a redistribution connecting structure  300  for solder balls is provided. The redistribution connecting structure  300  includes at least a bonding pad  311  disposed on a substrate  310  of an integrated circuit chip. The substrate  310  includes a first dielectric layer  320  composed of phosphosilicate glass (PSG), silicon nitride, silicon dioxide, or polyimide thereon and an opening  321  for exposing the bonding pad  311 . A redistribution conductive layer  330  composed of copper, aluminum, alloy thereof, or other composite metals is formed on the first dielectric layer  320 . The redistribution conductive layer  330  includes at least a redistribution pad  331  disposed adjacent to the bonding pad  311  and electrically connected to the bonding pad  311  through the opening  321 . The size of the redistribution pad  341  is preferably larger than the bonding pad  311 . A second dielectric layer  340  (also refers to as a passivation layer) is disposed on the first dielectric layer  320  and the redistribution conductive layer  330 . The second dielectric layer  340  includes a non-circular opening  341  for exposing the redistribution pad  331 , in which the non-circular opening  341  is typically smaller than the redistribution pad  331 . Additionally, at least a substantially circular ball base  350  (also refers to as an UMB pad) is disposed on the second dielectric layer  340 , in which the ball base  350  is extended to the top of the opening  321  and connected to the redistribution pad  331  through the non-circular opening  341 . The ball base  350  is composed of a plurality of metal layers, including an adhesion layer, a barrier layer, and a wetting layer. The ball base  350  includes at least a solder ball  360  thereon. Referring to  FIG. 6 , the area  361  of the solder ball  360  covers the non-circular opening  341  and the opening  321  of the first dielectric layer  320 . The non-circular opening  341  includes a similar cut-off portion as described in the first embodiment, such that the non-circular opening  341  is adjacent but not overlapping the opening  321  of the first dielectric layer  320 . In other words, the redistribution conductive layer  330  of the redistribution connecting structure  300  includes a redistribution pad  331  disposed adjacent to the bonding pad  311 , such that the non-circular opening  341  of the second dielectric layer  340  that exposes the redistribution pad  331  can be used to increase the adhesion area of the ball base  350 . By using the second dielectric layer  340  to cover the top portion of the opening  321 , the thermal stress created with respect to the junction between the ball base  350  and the redistribution pad  331  is reduced significantly. Ultimately, the size and position of the ball barrier  350  can be adjusted accordingly, thereby preventing peeling or breakage of the solder ball  360  and increasing the yield of the product. 
   Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.