Abstract:
A semiconductor chip with bumps formed therein comprises an active surface, a plurality of bonding pads, a passivation layer, a plurality of first UBMs (under bump metallurgy), a second UBM, a plurality of first bumps, and a plurality of second bumps. The bonding pads are disposed on the active surface of the semiconductor chip. The passivation layer covers the active surface of the semiconductor chip with the pads exposed out of the passivation layer. The first UMBs are individually disposed on the bonding pads. The second UMB is disposed on at least two of the bonding pads. The first bumps are disposed on the first UMBs. The second bumps are disposed on the second UBM.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of Invention  
         [0002]     This invention relates to a flip chip package. More particularly, the present invention is related to a flip chip package with solder bars formed therein.  
         [0003]     2. Related Art  
         [0004]     A well-known semiconductor package, such as a flip chip package is applicable to communication products, portable electronics products, and packages for high-frequency chips. Referring to  FIG. 1 , it discloses a conventional and well-know flip chip package  10 , which mainly comprises a chip  20  attached to a substrate  30  in a flip-chip bonding type. The chip  20  has an active surface  22  and a plurality of bonding pads  24  formed thereon. Besides, a plurality of bumps  26  electrically and mechanically connected to the contacts  32  of the substrate  30 . The bumps  26  are formed by conventional bumping process and C4 technology (Controlled Collapse Chip Connection). Furthermore, an underfill  28  is disposed between the chip  20  and the substrate  30  and encapsulates the bumps  26 . In this arrangement, the bonding pads  24  are utilized for signal transmitting, grounded to the substrate and to be noted that the bonding pads  24  are connected to the bumps  26  separately and substantially have the same size with each other.  
         [0005]     As mentioned above, the voltage regulator is provided as a DC to DC converter so as to provide the electronics system with a stable power supply. In apparatus with low power, such as notebooks, mobile phones, usually there is needed an efficient switch converter to manage power supply. However, a well-know and conventional switch converter is manufacture by the packages of small outline IC, small outline package and such packages usually have larger parasitic inductance and parasitic resistance. In addition, such packages can not dissipate the heat, arisen out of electronics systems with high power and high frequency devices formed therein, to external devices or the outside more quickly.  
         [0006]     Although the U.S. Pat. No. 6,229,220 and the TW. Pat 517370 disclose the method of keeping the bump height and the distance between the substrate and the chip from being collapsed by utilizing bumps with two different solder materials formed therein. However, such package still not provides a package with a better thermal and electrical performance.  
         [0007]     Therefore, providing another flip chip package to solve the mentioned-above disadvantages is the most important task in this invention.  
       SUMMARY OF THE INVENTION  
       [0008]     In view of the above-mentioned problems, this invention is to provide a flip chip package having an electrically conductive bar formed therein for enhancing the thermal and electrical performance.  
         [0009]     To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention specifically provides a flip chip package applicable to such high thermal and electrical performance. Therein, the flip chip package mainly comprises a chip, which has an active surface, a plurality of bonding pads, a passivation layer formed on the active surface and leaves the bonding pads exposed, a plurality of first under bump metallurgy layers, a second under bump metallurgy layer, a plurality of first bumps formed on the first under bump metallurgy layers and a second bump formed on the second under bump metallurgy layer. To be noted that the second under bump metallurgy layer is disposed on at least two of the bonding pads and a portion of the passivation layer between said two bonding pads and each said first under bump metallurgy layer is disposed on one of the corresponding bonding pads respectively. Namely, the second under bump metallurgy layer is extended from one bonding to another boning pad and located over the passivation layer located between the two bonding pads. In other words, the area of said each first under bump metallurgy layer is smaller than that of the second under bump metallurgy layer from a top view. Moreover, the second bump disposed on the second under bump metallurgy layer may form a bar, a ring, a rectangle and an ellipse. When the material of the second bump is made of solder, it becomes a solder bar.  
         [0010]     As mentioned above, the second under bump metallurgy layer has a large area and the second bump has a large size so that the second bump can be taken as ground bump to ground to a substrate. Hence, the electrical and thermal performance will increase and enhance.  
         [0011]     It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     The invention will become more fully understood from the detailed description given herein below illustrations only, and thus are not limitative of the present invention, and wherein:  
         [0013]      FIG. 1  is a cross-sectional view of a conventional flip chip package;  
         [0014]      FIG. 2  is a top view of a flip chip package according to the preferred embodiment of the present invention;  
         [0015]      FIG. 3  is a cross-sectional view of a flip chip package of  FIG. 2 ;  
         [0016]      FIG. 4  is a bottom view of a flip chip package of  FIG. 2 ;  
         [0017]      FIG. 5   a  and  FIG. 5   b  are cross-sectional views of solder bump and solder bar provided in the flip chip package of  FIG. 2 ; and  
         [0018]     FIGS.  6  to  11  are partially enlarged cross-sectional views showing the progression of steps for forming the flip chip package according to the preferred embodiment of this invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]     The flip chip package according to the preferred embodiments of this invention will be described herein below with reference to the accompanying drawings, wherein the same reference numbers are used in the drawings and the description to refer to the same or like parts.  
         [0020]     As shown in  FIGS. 2, 3  and  4 , which illustrate a preferred embodiment of this invention. The flip chip package  100  mainly comprises a chip  120  flip-chip bonded to a substrate  130 . Said chip  120  has an active surface  122  and a plurality of bonding pads  124  formed on the active surface  122 . A plurality of bumps, including the solder bump  160  and the solder bar  162  as shown in  FIGS. 3 and 4 , are disposed over the bonding pads  124 . A plurality of under bump metallurgy layers  150  and  152  formed between the bumps and the chip  120 . To be more clearly, the under bump metallurgy layer  150  is substantially shaped into a circle and connected to the solder bump  160 . In addition, the under bump metallurgy layer  152  covers at least two bonding pads  124  by extending one of the two bonding pads  124  to the other of the two bonding pads  124 . Usually, there is a passivation layer  132 , as shown in  FIG. 5   a , formed over the active surface  122  and leaves the bonding pads  124  exposed. Accordingly, as mentioned above and the under bump metallurgy layer  152  may extend along the passivation layer  123  between the two bonding pads  124  as shown in  FIG. 5   a . On the basis, the bumps, such as the solder bar  162  is disposed over the two boning pads  124  and a portion of the passivation layer  132  between the two bonding pads  124 .  
         [0021]     As mentioned above, the chip  120  are electrically and mechanically connected to the substrate  130  through the under bump metallurgy layers  150  and  152 , and the bumps  160  and  162 . Moreover, in order to release the stress at the bumps  160  and  162 , there is further provided an underfill  128  disposed between the chip  120  and the substrate  130  for being utilized for releasing the stress to prevent the bumps  160  and  162  from being damaged.  
         [0022]     To be noted that the bonding pads  124  of the chip  120  can be transmitted the signals from the chip  120 , and grounded to the substrate  130  through the solder bar  162  so as to enhance the electrical and thermal performance. Because the under bump metallurgy layer  152  covering at least two bonding pads  124 , the area of the under bump metallurgy layer  152  is usually grounded to the substrate  130  or regarded as a power terminal for enhancing the electrical and thermal performance of the package. To be noted, as shown in  FIG. 4 , the solder bar  162  may be shaped into a rectangle with a curved edge, an ellipse, a ring and the solder bump  160  may be shaped into a circle. Namely, the first under bump metallurgy layer may be shaped into a circle; and the second under bump metallurgy layer may be shaped into a rectangle with a curved edge, an ellipse, a ring.  
         [0023]     Next, referring to  FIG. 5   a  again, it illustrates a chip  120  not attached to the substrate  130 . Usually, when the bumps are solder bumps  160  and a solder bar  162 , the bumps are eutectic bumps with a ratio of lead to tin being 37 to 63. When the bumps  160  and  162  are high-lead bumps, the ratio of the bumps  160  and  162  of tin to lead is 5 and 95. In addition, the bumps  160  and  162  usually comprise anther metals formed therein, such as In.  
         [0024]     Moreover, referring to  FIG. 5   b , it illustrates another embodiment showing the chip  120  is not attached to the substrate  130 . Specifically, the difference of this embodiment from that as shown above, the solder bumps  160  and the solder bar  162  both has a first solder material and a second solder material, with a high melting point than that of the first solder material, formed on the first solder material respectively so as to keep the solder bumps  160  and the solder bar  162  from being collapsed after the solder bumps  160  and the solder bar  162  are reflowed. Optionally, the melting point of the first solder material is higher than the second solder material at about 20° C. For example, the first solder material  146  has a solder composition with a ratio of tin to lead being 5 to 95 and the second solder material has a solder composition with a ratio of tin to lead being 63 to 37. Therein, the melting point of the second solder material is ranged between 200 and 250° C.; and the melting point of the first solder material is ranged between 320 and 360° C. On the basis, when the bumps are reflowed, the second solder material is reflowed to encapsulate the first solder material and have the first solder material secured to the second solder material.  
         [0025]     Moreover, the contacts on the substrate may have the same shape with that of the corresponding under bump metallurgy layers so as to have the bumps secured to the substrate well. In addition, the solder bar  162  has a larger size and area than that of the solder bump  160  so that the electrical performance and the thermal performance of the package  100  can be enhanced.  
         [0026]     Next, referring to FIGS.  6  to  12 , which illustrate the manufacture processes of the flip chip package as shown above. Again, referring to  FIG. 6 , the chip  120  has an active surface  122  and a plurality of bonding pads  124  formed thereon. Therein, a passivation layer  123  is disposed on the active surface  122  and leaves the bonding pads  124  exposed. Then, a metal layer  142 , usually called an under bump metallurgy layer, is formed over the active surface and the passivation layer. Therein, the metal layer  142  has three layers formed therein. An adhesion layer, an oxidation barrier and a wetting layer are formed from the side close to the active surface  122  to the other side far away from the active surface  122 .  
         [0027]     Next, referring to  FIG. 7 , a photo-resist layer  144  is formed and then a plurality of openings  170  and  172  formed in the photoresist layer  144  by lithography and development. Afterwards, as shown in  FIG. 8 , a first solder material is disposed in the openings  170  and  172 . Next, a second solder material  148  with a melting point lower than that of the first solder material  146  is disposed on the first solder material  146 . Therein, the first solder material  146  and the second solder material  148  can be formed by electroplating or screen-printing methods.  
         [0028]     Then, optionally, a reflow process is performed to have the first solder material  146  securely attached to the second solder material  148  and the first solder material  146  is secured to the chip  120 , when the first solder material  146  and the second solder material  148  is formed by screen-printing.  
         [0029]     Next, as shown in  FIG. 10 , the photo-resist layer  144  is then removed. Then, an etching process is performed to pattern the under bump metallurgy. Therein, the portion of the under bump metallurgy layer is not covered by the first solder material is removed. To be noted, if a reflow process is not performed to have the first solder material  146  and the second solder material  148  secured to each other, such reflow process can be performed after the patterned under bump metallurgy layer is formed.  
         [0030]     As mentioned above, if only one solder material is formed in the openings  170  and  172 , the photo-resist layer  144  can be removed in sequence of the step of forming solder material in the openings  170  and  172 .  
         [0031]     Although the invention has been described in considerable detail with reference to certain preferred embodiments, it will be appreciated and understood that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.