Patent Document

BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates in general to a metal bump. In particular, the present invention relates to a profile-design rule of a metal bump for reducing a diagonal distance between two adjacent metal bumps positioned at adjacent rows.  
           [0003]    2. Description of the Related Art  
           [0004]    The attachment of a bared die to a glass panel (called COG: chip on glass) is one advanced application for electrically connecting integrated circuits (ICs) achieving lighter weight, smaller size, lower cost and less power consumption demanded in various display products. The quality and reliability of the liquid crystal display (LCD) module depends on the way in which the driver IC is attached to the glass panel. Anisotropic conductive film (ACF) is the most popular material for attaching the chip to the glass panel. ACF is an adhesive film consisting of dispersed, microscopic, electrically conductive particles 3-15 μm in diameter and an insulating adhesive film 15-35 μm thick. Various kinds of conductive particles, such as carbon fiber, metal (Ni, solder), and metal (Ni/Au)-coated plastic balls have been proposed, and the uniformity of the conductive particles distribution is considered an influence on the electrical property and reliability of ACF. Also, various types of adhesive materials, such as thermoplastic, thermosetting, and mixed thermoplastic and thermosetting materials have been proposed. In general, ACF is classified into two types. One has conductive particles 5 μm in diameter covered with a very thin insulating layer, wherein the thin insulating layer is broken when the particles are deformed, the bared conductive particles serving as a bridge for electrically connecting the metal bump on the chip and the bonding pad on the glass panel. However, the breaking of the conductive particles during the fabricating process cannot be ensured; therefore, there is no guarantee of effective contact between the metal bump and the bonding pad. The other type of ACF is a double-layer type, which consists of one layer filled with conductive particles 3 μm in diameter and the other layer with no conductive particles, so that the functions of conduction and adhesion are separated. This can ensure the effective contact between the metal bump and the bonding pad. Nevertheless, when too many conductive particles exist in the space between two adjacent metal bumps, a lateral connection between the two adjacent metal bumps is easily formed, resulting in an electrical short.  
           [0005]    [0005]FIG. 1A to FIG. 1C are schematic cross-sectional diagrams of a method of connecting a chip  14  and a glass substrate  10  according to the prior art. The glass substrate  10  of the LCD module comprises a first area for disposing an array of thin film transistors (TFTs), a second area for disposing data IC chips or scan IC chips  14 , and a plurality of bonding pads  12  are formed on the second areas. The chip  14  has a plurality of metal pads  16  and a plurality of metal bumps  18 , wherein each metal bump  18  is patterned on each metal pad  16  and corresponds in position to each bonding pad  12 . In the prior method of connecting the chip  14  and the glass substrate  10 , as shown in FIG. 1A, an ACF  20  is attached to the surface of the glass substrate  10  to cover the bonding pad  12 . Then, the surface of the chip  14  is downwardly placed on the predetermined area of the glass substrate  10 , wherein each metal bump  18  corresponds to each bonding pad  12  of the glass substrate  10 . As shown in FIG. 1B, by means of the adhesion of the ACF  20  and the downwardly exerted pressure, the chip  14  is tightly attached to the glass substrate  10 . Next, a thermal process is performed to cure the ACF  20 . The conductive particles  22  sandwiched between the top of the metal bump  18  and the surface of the bonding pad  12  now serve as an electrically connecting bridge, as shown in FIG. 1C. However, the distribution of the conductive particles  22  cannot be controlled in processing, and thereby many conductive particles  22  that exist between adjacent metal bumps  18  may laterally connect with each other to cause electrical shorts.  
           [0006]    [0006]FIG. 2A shows a top view of the layout of the metal bumps  18  according to the prior art. For providing great output terminals and avoiding electrical shorts between metal bumps  18 , the metal bumps  18  are generally arranged in two rows. In each row, each metal bump  18  with a transverse width W 2  is spaced out a transverse distance W 1  apart from each other, and the tops of the metal bumps  18  are leveled off. For example, in a first row, a first metal bump  181  and a second metal bump  182  are adjacent and apart from the transverse distance W 1 . In a second row, a third metal bump  183  is disposed between the first metal bump  181  and the second bump  182 . Therefore, the three centers of the three bumps  181 ,  182 ,  183  respectively are arranged as a triangle. Notice that the transverse distance W 1  is equal to the transverse width W 2 , and a lengthwise distance L between the first row and the second row is smaller than the transverse distance W 1 . However, since the metal bump  18  is shaped into a square or rectangular profile, the shortest distance is found between a point A of the first metal bump  181  and a point B of the third metal bump  183 . A lateral connection between the first metal bump  181  and the third metal bump  183  is easily formed by the conductive particles to result in an electrical short. Similarly, a lateral connection is easily formed between a point C of the second metal bump  182  and a point D of the third metal bump  183 .  
           [0007]    In addition, an electrical short is easily caused by an alignment error between the metal bump  18  and the bonding pad  12 . Please refer to FIG. 2B, which shows a top view of the metal bump  18  and the bonding pad  12  according to the prior art. In general, the profile of the bonding pad  12  is square or rectangular according to the profile of the metal bump  18 , and the surface area of the bonding pad  12  is larger than the top area of the metal bump  18 . Thereby, a tolerance limitation of an alignment error in COG technique depends on the shorted distance d between the first bonding pad  121  and the third bonding pad  123 . When the chip  14  is inaccurately attached to the glass substrate  10 , the up-left corner or the up-right corner of the third bonding pad  123  is easily contacted with the point A of the first metal bump  181  or the point C of the second metal bump  182 . Similarly, the down-right corner of the first bonding pad  121  or the down-left corner of the second bonding pad  122  is easily contacted with the point B or D of the third metal bump  183 .  
           [0008]    From the above-described disadvantages, the square or rectangular profile of the metal bump  18  reduces the diagonal distance between two adjacent metal bumps  18  positioned at adjacent rows. This causes electrical shorts and limits the tolerance of alignment error in COG technique, resulting in lowering quality and reliability of LCD modules.  
         SUMMARY OF THE INVENTION  
         [0009]    An object of the present invention is to provide a cylindrical bump to increase the diagonal distance between metal bumps positioned in adjacent rows.  
           [0010]    Another object of the present invention is to provide a polygonal bump to increase the diagonal distance between metal bumps positioned in adjacent rows.  
           [0011]    The metal bumps of the present invention include at least a first metal bump having at least one curved face, at least a second metal bump having at least one curved face, and at least a third metal bump having at least a first curved face and a second curved face. The three centers of the first metal bump, the second metal bump and the third metal bump are arranged as a triangle. The first curved face of the third metal bump is adjacent to the curved face of the first metal bump. The second curved face of the third metal bump is adjacent to the curved face of the second metal bump.  
           [0012]    Another embodiment of the present invention includes at least a first metal bump having at least one faceted face, at least a second metal bump having at least one faceted face, and at least a third metal bump having at least a first faceted face and a second faceted face. The three centers of the first metal bump, the second metal bump and the third metal bump are arranged as a triangle. The first faceted face of the third metal bump is adjacent to the faceted face of the first metal bump. The second faceted face of the third metal bump is adjacent to the faceted face of the second metal bump.  
           [0013]    It is an advantage of the present invention that these metal bumps avoid a lateral electrical connection, thus improving the tolerance limitation of alignment errors in COG technique.  
           [0014]    This and other objective of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiments which are illustrated in the various figures and drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    The present invention can be more fully understood by reading the subsequent detailed description in conjunction with the examples and references made to the accompanying drawings, wherein:  
         [0016]    [0016]FIG. 1A to FIG. 1C are schematic cross-sectional diagrams of a method of connecting the chip and the glass substrate according to the prior art.  
         [0017]    [0017]FIG. 2A shows a top view of the layout of the metal bumps according to the prior art.  
         [0018]    [0018]FIG. 2B shows a top view of the metal bump  18  and the bonding pad according to the prior art.  
         [0019]    [0019]FIGS. 3A to  3 E are top views of metal bumps according to the first embodiment of the present invention.  
         [0020]    [0020]FIGS. 4A to  4 E are top views of metal bumps according to the second embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0021]    A plurality of metal bumps is based on a corresponding plurality of metal pads on a chip. By means of COG technique and the adhesion of the ACF, the chip can be lowered and tightly attached to a plurality of bonding pads of a glass substrate. Therefore, the conductive particles of the ACF sandwiched between the top of the metal bump and the surface of the bonding pad serve as an electrically connecting bridge for electrically connecting the chip and the glass substrate. In order to avoid electrical shorts between adjacent metal bumps, the right-angled points of the square or rectangular profile are rounded or cut into curved faces or faceted faces, wherein the contact area of the metal bump should be kept at the maximum receivable range to maintain the demanded conductivity. This can increase the diagonal distance between adjacent metal bumps positioned at adjacent rows. Furthermore, a preferred arrangement in which three centers of three adjacent metal bumps positioned at two adjacent rows are arranged as an equilateral triangle can increase layout density of the metal bumps and is applied to a chip of smaller scale.  
         [0022]    [First Embodiment] 
         [0023]    [0023]FIGS. 3A to  3 E are top views of metal bumps according to the first embodiment of the present invention. A plurality of metal bumps  30  is arranged in two adjacent rows. In each row, each metal bump  30  with a transverse width W 2  is situated a transverse distance W 1  from all others, and the tops of the metal bumps  30  are leveled off. Notice that the transverse distance W 1  is equal to the transverse width W 2 , and a lengthwise distance L between the two adjacent rows is smaller than the transverse distance W 1 . In a first row, a first metal bump  301  and a second metal bump  302  are adjacent and apart from the transverse distance W 1 . In a second row, a third metal bump  303  is disposed between the first metal bump  301  and the second bump  302 . Therefore, the connection between the three centers of the three metal bumps  301 ,  302 ,  303  becomes a triangle.  
         [0024]    As shown in FIG. 3A, the first metal bump  301  has at least one curved face  32 , the second metal bump  302  has at least one curved face  34 , and the third metal bump  303  at least has a first curved face  36  and a second curved face  38 . The first curved face  36  of the third metal bump  303  is adjacent to the curved face  32  of the first metal bump  301 , and the second curved face  38  of the third metal bump  303  is adjacent to the curved face  34  of the second metal bump  302 .  
         [0025]    According to the profile-design rule, when the contact area of the metal bump  30  can be kept at a receivable range to maintain the demanded conductivity, the metal bumps  301 ,  302 ,  303  can present various profiles, such as the irregular profile shown in FIG. 3A, the elliptical profile shown in FIG. 3B, or the circular profile shown in FIG. 3C. The first advantage is that the smallest distance P 1  between the curved face  32  of the first metal bump  301  and the first curved face  36  of the third metal bump  303  is increased to avoid an electrical connection between the first metal bump  301  and the third metal bump  303 . Similarly, the smallest distance P 1  is increased to avoid an electrical connection between the second metal bump  302  and the third metal bump  303 .  
         [0026]    As shown in FIG. 3D, a top view of the metal bumps  30  corresponding in position to bonding pads  40 , the bonding pads  40  on a glass substrate present a circular profile depending on the circular profile of the metal bumps  30 . Within the smallest distance P 2  between the first bonding pad  401  and the third bonding pad  403 , the probable contact region is the circumference of the first metal bump  301  and the circumference of the third bonding pad  403 , as a point of tangency. Thus, the second advantage is that an electrical short is not likely to be caused between the first metal bump  301  and the third bonding pad  403  if the chip is inaccurately aligned to the glass substrate. This can improve the tolerance limitation of alignment error in COG technique. Similarly, an electrical short is not easily caused between the second metal bump  302  and the third bonding pad  403 .  
         [0027]    In accordance with the metal bumps  30  presenting a circular profile, there are other advantages. The fabricating method for the circular profile is simpler and improves the quality of the metal bumps  30 . Also, since gold bumps create the problem of an anisotropical variation at the right-angle point, the circular profile solves this problem. Furthermore, as shown in FIG. 3E, the three centers O 1 , O 2 , O 3  of the three metal bumps  301 ,  302 ,  303  can be arranged as an equilateral triangle to reduce the transverse distance between adjacent metal bumps  301 , 302  and the lengthwise distance between adjacent rows to a limitation. This can increase layout density of the metal bumps  30  and the size of the chip can be smaller to increase the amount of chips fabricated on a wafer.  
         [0028]    [Second Embodiment] 
         [0029]    Please refer to FIGS. 4A to  4 E, which are top views of metal bumps  50  according to the second embodiment of the present invention. A plurality of metal bumps  50  is arranged in two adjacent rows. In each row, each metal bump  50  with a transverse width W 2  is spaced out a transverse distance W 1  apart from each other, and the tops of the metal bumps  50  are leveled off. Notice that the transverse distance W 1  is equal to the transverse width W 2 , and a lengthwise distance L between the two adjacent rows is smaller than the transverse distance W 1 . In a first row, a first metal bump  501  and a second metal bump  502  are adjacent and separated by distance W 1 . In a second row, a third metal bump  503  is disposed between the first metal bump  501  and the second bump  502 . Therefore, the connection between the three centers of the three metal bumps  501 ,  502 ,  503  respectively forms a triangle.  
         [0030]    As shown in FIG. 4A, the first metal bump  501  has at least one faceted face  52 , the second metal bump  502  has at least one faceted face  54 , and the third metal bump  503  at least has a first faceted face  56  and a second faceted face  58 . The first faceted face  56  of the third metal bump  503  is adjacent to the faceted face  52  of the first metal bump  501 , and the second faceted face  58  of the third metal bump  503  is adjacent to the faceted face  54  of the second metal bump  502 .  
         [0031]    According to the profile-design rule, when the contact area of the metal bump  50  can be kept at a receivable range to maintain the demanded conductivity, the metal bumps  501 ,  502 ,  503  can present various profiles, such as the irregular profile shown in FIG. 4A, the rhombus profile shown in FIG. 4B, the equilateral pentagon profile shown in FIG. 4C, the equilateral hexagon profile shown in FIG. 4D, or the equilateral octagon profile shown in FIG. 4E. The first advantage is that the smallest distance P 3  between the faceted face  52  of the first metal bump  501  and the first faceted face  56  of the third metal bump  503  is increased to avoid an electrical connection between the first metal bump  501  and the third metal bump  503 . Similarly, the smallest distance P 3  is increased to avoid a electrical connection between the second metal bump  502  and the third metal bump  503 . The second advantage is that the diagonal distance between the bonding pads is also reduced, hence an electrical short is not easily caused between the metal bump  50  and the bonding pad if the chip is inaccurately aligned to the glass substrate. This can improve the tolerance limitation of alignment error in COG technique.  
         [0032]    Those skilled in the art will readily observe that numerous modifications and alterations of the device may be made while retaining the teaching of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.

Technology Category: 5