Patent Publication Number: US-2015069602-A1

Title: Chip-on-film device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a Divisional of and claims the priority benefit of U.S. patent application Ser. No. 13/659,932, filed on Oct. 25, 2012. The prior U.S. application Ser. No. 13/659,932 claims the priority benefits of U.S. provisional application Ser. No. 61/643,356, filed on May 7, 2012 and Taiwan application serial no. 101129796, filed on Aug. 16, 2012. The entirety of each of the above-mentioned patent applications is hereby incorporated by reference herein and made a part of this specification. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention is related to an integrated circuit (IC), and more specifically, to a chip-on-film (COF) device. 
     2. Description of Related Art 
     The COF device is to weld/package the IC onto a flexible circuit film. A metal bump is disposed on a corresponding Al pad in the IC. The metal bump is welded to the Al pad to facilitate the metal bump to be electrically connected to a core circuit. A back-end package process of the COF is by heating with high temperature in order to generate a eutectic reaction between the metal bump on the IC and a tinned metal on the flexible circuit film. 
     In order to coordinate with the back-end package process, the metal bump on the IC has to be big enough to be able to be welded on the tinned metal of the flexible circuit film easily. In a conventional IC layout of the COF device, an area of the Al pad is bigger than the metal bump, and the metal bump completely overlaps on the Al pad along a perpendicular direction of the IC. The Al pad of this conventional COF device occupies a large area of the IC and even affects a routing design of the metal interconnection (such as a supply wire, a ground wire or a data wire). 
     SUMMARY OF THE INVENTION 
     The invention provides a chip-on-film (COF) device that is capable of effectively reducing a pad area. 
     According to an aspect, a COF device is provided, including a flexible circuit film, a passivation layer, a first adhesive layer, a first pad, a second pad, a first metal interconnection, and a metal bump. The flexible circuit film includes at least a wire. The passivation layer includes at least a first hole. At least a part of the first adhesive layer is disposed in the first hole. The first pad is disposed under the passivation layer, and at least a part of the first pad is disposed under the first hole. The second pad is disposed under the passivation layer and on a first side of the first pad. At least a part of the first metal interconnection is disposed under the passivation layer, and disposed at the first side of the first pad, and disposed between the first pad and the second pad, wherein the first metal interconnection does not touch the first pad and the second pad. At least a part of the metal bump is disposed on the first adhesive layer, and the metal bump is electrically connected to the first pad via the first adhesive layer and welded on the at least one wire. The metal bump includes a first part, a second part and a third part. At least a part of the first part overlaps the first pad along a perpendicular direction of the COF device. The second part extends to an outside of the first pad along a first horizontal direction of the COF device and partially overlaps the first metal interconnection. At least part of the third part overlaps the second pad along the perpendicular direction of the COF device. 
     As described above, in the embodiments of the invention, the first part of the metal bump overlaps the first pad along the perpendicular direction of the COF device, and the second part of the metal bump overlaps the metal interconnection (such as a supply wire, a ground wire, a data wire, or other wires) outside the pad, and the third part of the metal bump overlaps the second pad along the perpendicular direction of the COF device. Therefore, the COF device is capable of effectively reducing the area of the pad to facilitate the routing design of the metal interconnection. 
     In order to make the aforementioned features and advantages of the invention more comprehensible, embodiments accompanying figures are described in details below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide further understanding and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments and, together with the description, serve to explain the principles of the invention. 
         FIG. 1  is a schematic top view of a COF device according to an embodiment of the invention. 
         FIG. 2  is a schematic cross-sectional view along the line A-A′ in  FIG. 1 , illustrating a COF device according to an embodiment of the invention. 
         FIG. 3  is a schematic cross-sectional view along the line A-A′ in  FIG. 1 , illustrating a COF device according to another embodiment of the invention. 
         FIGS. 4-7  are schematic views illustrating a layout of the disposition of the pad, the metal interconnections, and the metal bump illustrated in  FIG. 1  on an integrated circuit according to another embodiment of the invention. 
         FIG. 8  is a schematic top view of a COF device according to another embodiment of the invention. 
         FIG. 9  is a schematic cross-sectional view along the line B-B′ in  FIG. 8 , illustrating a COF device according to an embodiment of the invention. 
         FIG. 10  is a schematic top view of a COF device according to yet another embodiment of the invention. 
         FIG. 11  is a schematic cross-sectional view along the line C-C′ in  FIG. 10 , illustrating a COF device according to an embodiment of the invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
       FIG. 1  is a schematic top view of a chip-on-film (COF) device  100  according to an embodiment of the invention.  FIG. 2  is a schematic cross-sectional view along the line A-A′ in  FIG. 1 , illustrating the COF device  100  according to an embodiment of the invention. Referring to  FIGS. 1 and 2 , the COF device  100  includes a flexible circuit film  110  and an integrated circuit  120 . The flexible circuit film  110  includes a film  111  and at least a wire  112 . The wire  112  with a conductive material is disposed on a surface of the film  111 . 
     A substrate  130  of the integrated circuit  120  illustrated in  FIG. 2  is only schematically presented. In fact, there may be various kinds of electrical elements, doped regions, metal layers, insulating layers, polysilicon layers, contact plugs, via plugs and/or other integrated circuit components inside, above, or under the substrate  130 . The integrated circuit  120  further includes a metal bump  121 , an adhesive layer  122 , a passivation layer  123 , a pad  124 , and at least a metal interconnection (such as  126  and  127  illustrated in  FIGS. 1 and 2 ). 
     The passivation layer  123  is disposed on the substrate  130  of the integrated circuit  120 . The passivation layer  123  includes a hole  125 . The pad  124  is disposed under the passivation layer  123  and on the substrate  130 . As illustrated in  FIGS. 1 and 2 , at least a part of the pad  124  is disposed under the hole  125 . The pad  124  may be an aluminum pad, a gold pad, or other conductive materials. At least a part of each of the metal interconnections  126  and  127  is disposed under the passivation layer  123  and on a side of the pad  124 . Neither of the metal interconnections  126  and  127  touches the pad  124 . The metal interconnections  126  and  127  are the supply wire, ground wire, data wire, control wire, floating metal, or other wires of the integrated circuit  120  respectively. 
     The adhesive layer  122  is disposed on the passivation layer  123 . A part of the adhesive layer  122  is disposed in the hole  125 . At least a part of the metal bump  121  is disposed on the adhesive layer  122 , and the metal bump  121  is electrically connected to the pad  124  via the adhesive layer  122 . The metal bump  121  may be a gold bump or other metallic material. The adhesive layer  122  may be a titanium tungsten layer, which is the adhesive layer  122  formed by a titanium layer and a tungsten layer, or the adhesive layer  122  formed by a titanium-tungsten alloy. In other embodiments, a material for the adhesive layer  122  may be other conductive materials used as a welding medium between the metal bump  121  and the pad  124 . In some embodiments, based on the collocation of the materials of the metal bump  121  and the pad  124 , both of the metal bump  121  and the pad  124  have an excellent adhesion; therefore, the adhesive layer  122  may be omitted, and the metal bump  121  and the pad  124  may be bonded directly. 
     An area ratio of the hole  125  and the metal bump  121  may be 40% to 50% on a perpendicular direction Z of the COF device  100 . In the present embodiment, the area ratio of the hole  124  and the metal bump may be set at 20% to 40%. 
     For example, on the perpendicular direction Z of the COF device  100 , a shorter side of the hole  125  (such as the side marked with e in  FIG. 1 ) is greater than 12 μm, and a longer side (such as the side marked with f in  FIG. 1 ) is greater than 35 μm. 
     A distance b from an edge of the hole  125  to an edge of the metal bump  121  is greater than 3 μm. If the value of b is too small, an eutectic alloy might be formed by the Al in the pad  124  and the Au in the metal bump and cause a defect. A distance a from an edge of a first part  121 A of the metal bump  121  to an edge of the pad  124  is greater than 3 μm. If the value of a is too small, an alignment error might occur in a manufacturing process. Therefore, when a size of the metal bump  121  is designed, a size of the pad  124  and a size of the hole  125  need to be put into consideration at the same time. 
     The metal bump  121  includes the first part  121 A and a second part  121 B. At least a part of the first part  121 A along the perpendicular direction Z of the COF device  100  overlaps the pad  124 . The second part  121 B extends to an outside of the pad  124  along a horizontal direction Y of the COF device  100 , and at least part of the second part  121 B overlaps the metal interconnections  126  and  127 . This may be a Bump on Active (BOA) design. The passivation layer  123  is disposed between the metal bump  121  and the metal interconnections  126  and  127 . For example, a width c of each of the metal interconnections  126  and  127  is 0.1 μm to 40 μm. A distance d from an edge of the metal interconnection  126  to an edge of the pad  124  is greater than 0.1 μm, and a height difference caused by the metal interconnections can be prevented from being too far apart. 
     In a back-end package process of the COF device  100 , a high temperature, for example, is applied to heat up the metal bump  121  on the integrated circuit  120  and the wire  112  on the flexible circuit film  110  to generate a eutectic reaction in order for the metal bump  121  to be welded to the wire  112 . In the present embodiment, a hardness of the metal bump  121  is 25-100 Hv, 40-70 Hv, or 40-50 Hv. When the COF device  100  is compressed with the integrated circuit  120 , if the hardness of the material used for the metal bump  121  is too high (higher than 70 Hv, for example), a crazing issue may occur on the wire  112  and/or the metal bump  121  and affect a reliability. If the hardness of the material used for the metal bump  121  is too low (lower than 40 Hv, for example), then skew of a lead angle due to a bad compression may easily be caused when the COF device  100  is compressed with the integrated circuit  120 . 
     A surface roughness of the metal bump  121  is 0.05-2 μm or 0.8-1.2 μm. The surface roughness may be controlled through a manufacturing process of disposing the metal bump. When the COF device  100  is compressed with the integrated circuit  120 , the surface roughness being too high (higher than 2 μm, for example) may cause a poor contact between the metal bump  121  and the wire  112 . The surface roughness being too small (smaller than 0.05 μm, for example) may cause the metal bump  121  to slip to an outer region of the wire  112 . 
     As described above, since the first part  121 A of the metal bump  121  overlaps the pad  124  along the perpendicular direction Z of the COF device  100 , and the second part  121 B of the metal bump  121  overlaps the metal interconnections (such as  126  and/or  127 ) outside the pad  124 , the COF device  100  is capable of effectively reducing the area of the pad  124  to facilitate the a routing design of the metal interconnections. 
       FIG. 3  is a schematic cross-sectional view along the line A-A′ in  FIG. 1 , illustrating a COF device  100  according to another embodiment of the invention. For the embodiment illustrated in  FIG. 3 , a relevant description of  FIG. 2  may be referred to. The embodiment of  FIG. 3  further includes at least a metal layer  128 , which is different from the embodiment of  FIG. 2 . The metal layer  128  is disposed under the pad  124 , and the metal layer  128  is electrically connected to the pad  124 . As illustrated in the embodiment of  FIG. 3 , the metal interconnections  126  and  127  are disposed next to the metal layer  128 . The metal interconnection  126 , the metal interconnection  127 , and the metal layer  128  belong to a same layer. A distance (such as the distance marked with g in  FIG. 3 ) between the metal interconnections and the metal bump needs to be smaller than  100  um in order to prevent an issue of the metal bump  121  being tilted due to an uneven stress during the compression of the IC. The metal interconnection  126 , the metal interconnection  127 , and the metal layer  128  may belong to different layers in other embodiments. 
       FIG. 4  is a schematic view illustrating a layout of the disposition of the pad, the metal interconnections, and the metal bump illustrated in  FIG. 1  on the integrated circuit  120  according to an embodiment of the invention. For pad structures  410 ,  420 ,  430 , and  440  of the integrated circuit  120  illustrated in  FIG. 4 , a relevant description of 
       FIG. 1  may be referred to. As illustrated in the embodiment of  FIG. 1 , the pad structures  410 - 440  each includes a BOA (Bump on Active) structure (i.e. the bump is on top of an active region). The pad structures  410 - 440  are divided into two rows. One of the rows near an edge  401  of the integrated circuit  120  includes the pad structures  410  and  420 . The other row near a center  402  of the integrated circuit  120  includes the pad structures  430  and  440 . In the embodiment as illustrated in  FIG. 4 , part of all of the BOA structures of the pad structures  410 - 440  faces a direction of the center  402  of the integrated circuit  120 . 
       FIG. 5  is a schematic view illustrating a layout of the disposition of the pad, the metal interconnections, and the metal bump illustrated in  FIG. 1  on the integrated circuit  120  according to another embodiment of the invention. For pad structures  510 ,  520 ,  530 , and  540  of the integrated circuit  120  illustrated in  FIG. 5 , a relevant description of  FIG. 1  may be referred to. As illustrated in the embodiment of  FIG. 1 , the pad structures  510 - 540  each has a BOA structure. The pad structures  510 - 540  are divided into two rows. One of the rows near the edge  401  of the integrated circuit  120  includes the pad structures  510  and  520 . The other row near the center  402  of the integrated circuit  120  includes the pad structures  530  and  540 . In the embodiment as illustrated in  FIG. 5 , all of the BOA structures of the pad structures  510  and  520  on an outer row face a direction of the center  402  of the integrated circuit  120 . All of the BOA structures of the pad structures  530  and  540  on an inner row face a direction of the edge  401  of the integrated circuit  120 . 
       FIG. 6  is a schematic view illustrating a layout of the disposition of the pad, the metal interconnections, and the metal bump illustrated in  FIG. 1  on the integrated circuit  120  according to yet another embodiment of the invention. For pad structures  610 ,  620 ,  630 , and  640  of the integrated circuit  120  illustrated in  FIG. 6 , a relevant description of  FIG. 1  may be referred to. As illustrated in the embodiment of  FIG. 1 , the pad structures  610 - 640  each has a BOA structure. The pad structures  610 - 640  are divided into two rows. One of the rows near the edge  401  of the integrated circuit  120  includes the pad structures  610  and  620 . The other row near the center  402  of the integrated circuit  120  includes the pad structures  630  and  640 . In the embodiment as illustrated in  FIG. 6 , all of the BOA structures of the pad structures  610  and  620  on an outer row face a direction of the edge  401  of the integrated circuit  120 . All of the BOA structures of the pad structures  630  and  640  on an inner row face a direction of the center  402  of the integrated circuit  120 . 
       FIG. 7  is a schematic view illustrating a layout of the disposition of the pad, the metal interconnections, and the metal bump illustrated in  FIG. 1  on the integrated circuit  120  according to yet another embodiment of the invention. For pad structures  710 ,  720 ,  730 , and  740  of the integrated circuit  120  illustrated in  FIG. 7 , a relevant description of  FIG. 1  may be referred to. As illustrated in the embodiment of  FIG. 1 , the pad structures  710 - 740  each has a BOA structure. The pad structures  710 - 740  are divided into two rows. One of the rows near the edge  401  of the integrated circuit  120  includes the pad structures  710  and  720 . The other row near the center  402  of the integrated circuit  120  includes the pad structures  730  and  740 . In the embodiment as illustrated in  FIG. 7 , all of the BOA structures of the pad structures  710 - 740  face a direction of the edge  401  of the integrated circuit  120 . 
     As described above, whether the BOA structures of the pad structures are disposed on the edge direction of the integrated circuit  120  or disposed on the center direction of the integrated circuit  120  may be determined according to a design requirement/specification of an actual product. For example, based on a consideration of preventing the metal bump from being deformed due to an external impact during a production process, a position and a direction of where the metal bump is placed on the integrated circuit and the corresponding position of an opening of the pad may all be adjusted correspondingly. In addition, a flatness of a part of the pad may be improved by a grinding process. 
       FIG. 8  is a schematic top view of a COF device  800  according to another embodiment of the invention. For the embodiment illustrated in  FIG. 8 , a relevant description of  FIG. 1  may be referred to.  FIG. 9  is a schematic cross-sectional view along the line B-B′ in  FIG. 8 , illustrating the COF device  800  according to an embodiment of the invention. Referring to  FIGS. 8 and 9 , the COF device  800  includes a flexible circuit film  110  and an integrated circuit  820 . The flexible circuit film  110  includes a film  111  and at least a wire  112 . The wire  112  with a conductive material is disposed on a surface of the film  111 . 
     A substrate  830  of the integrated circuit  820  illustrated in  FIG. 9  is only schematically presented. In fact, there may be various kinds of electrical elements, doped regions, metal layers, insulating layers, polysilicon layers, contact plugs, via plugs and/or other integrated circuit components inside, above, or under the substrate  830 . The integrated circuit  820  further includes a metal bump  821 , an adhesive layer  822 , a passivation layer  823 , a pad  824 , and at least a metal interconnection (such as  921 ,  922 ,  923 , and  924  illustrated in  FIGS. 8 and 9 ). For the metal bump  821 , the adhesive layer  822 , the passivation layer  823 , the pad  824 , the first metal interconnections  921  and  922 , and the second metal interconnections  923  and  924  illustrated in  FIGS. 8 and 9 , a relevant description of the metal bump  121 , the adhesive layer  122 , the passivation layer  123 , the pad  124 , and the metal interconnections  126  and  127  illustrated in  FIGS. 1-3  may be referred to, respectively. 
     The passivation layer  823  is disposed on the substrate  830  of the integrated circuit  820 . The passivation layer  823  includes a hole  825 . The pad  824  is disposed under the passivation layer  823  and on the substrate  830 . As illustrated in  FIGS. 8 and 9 , at least a part of the pad  824  is disposed under the hole  825 . A metal layer  910  is disposed under the pad  824 , and the metal layer  910  is electrically connected to the pad  824 . The metal interconnections  921 - 924  and the metal layer  910  belong to a same layer. At least a part of the first metal interconnections  921  and  922  is disposed under the metal bump  821  and on a first side of the pad  824  (the metal layer  910 ). The second metal interconnections  923  and  924  are disposed under the passivation layer  823  and on a second side of the pad  824  (the metal layer  910 ). None of the metal interconnections  921 - 924  touches the pad  824 . 
     The metal bump  821  includes a first part  821 A, a second part  821 B, and a third part  821 C. At least a part of the first part  821 A along the perpendicular direction Z of the COF device  800  overlaps the pad  824 . The second part  821 B extends to an outside of the pad  824  along a first horizontal direction Y of the COF device  800 , and at least part of the second part  821 B overlaps the first metal interconnections  921  and  922 . The third part  821  C extends to the outside of the pad  824  along a second horizontal direction -Y of the COF device  800 , and at least a part of the third part  821 C overlaps the second metal interconnections  923  and  924  along the perpendicular direction Z of the COF device  800 . 
     Even though the second metal interconnections  923  and  924  are illustrated to be disposed on a bottom side of  FIG. 8 , the invention is not limited thereto. In other embodiments, the second metal interconnections may be disposed on other sides of the pad  824 , such as the left side or the right side of  FIG. 8 . Corresponding to a disposition of the second interconnections, the third part  821 C of the metal bump  821  may extend to the outside of the pad  824  along another horizontal direction (such as X direction or -X direction) of the COF device  800 . 
       FIG. 10  is a schematic top view of a COF device  1000  according to yet another embodiment of the invention. For the embodiment illustrated in  FIG. 10 , a relevant description of  FIG. 1  may be referred to.  FIG. 11  is a schematic cross-sectional view along the line C-C′ in  FIG. 10 , illustrating the COF device  1000  according to an embodiment of the invention. Referring to  FIGS. 10 and 11 , the COF device  1000  includes a flexible circuit film  110  and an integrated circuit  1020 . The flexible circuit film  110  includes a film  111  and at least a wire  112 . The wire  112  with a conductive material is disposed on a surface of the film  111 . 
     A substrate  1030  of the integrated circuit  1020  illustrated in  FIG. 11  is only schematically presented. In fact, there may be various kinds of electrical elements, doped regions, metal layers, insulating layers, polysilicon layers, contact plugs, via plugs and/or other integrated circuit components inside, above, or under the substrate  1030 . The integrated circuit  1020  further includes a metal bump  1021 , a first adhesive layer  1022 , a passivation layer  1023 , a first pad  1024 , a metal interconnection  1026 , a metal interconnection  1027 , a second adhesive layer  1122 , and a second pad  1029 . For the metal bump  1021 , the first adhesive layer  1022 , the passivation layer  1023 , the first pad  1024 , the metal interconnection  1026 , the metal interconnection  1027 , the second adhesive layer  1122 , and the second pad  1029  illustrated in  FIGS. 10 and 11 , a relevant description of the metal bump  121 , the adhesive layer  122 , the passivation layer  123 , the pad  124 , and the metal interconnections  126  and  127  illustrated in  FIGS. 1-3  may be referred to respectively. 
     The passivation layer  1023  is disposed on the substrate  1030  of the integrated circuit  1020 . The passivation layer  1023  includes a first hole  1025  and a second hole  1028 . The first pad  1024  and the second pad  1029  are disposed under the passivation layer  1023  and on the substrate  1030 . As illustrated in  FIGS. 10 and 11 , at least a part of the first pad  1024  is disposed under the first hole  1025 , and at least part of the second pad  1029  is disposed under the second hole  1028 . A first metal layer  1110  is disposed under the first pad  1024 , and the first metal layer  1110  is electrically connected to the first pad  1024 . A second metal layer  1120  is disposed under the second pad  1029 , and the second metal layer  1120  is electrically connected to the second pad  1029 . The metal interconnections  1026 - 1027 , the first metal layer  1110 , and the second metal layer  1120  belong to a same layer. At least a part of the metal interconnections  1026  and  1027  is disposed under the metal bump  1021  and positioned between the first pad  1024  (the first metal layer  1110 ) and the second pad  1029  (the second metal layer  1120 ). The metal interconnections  1026  and  1027  are disposed under the passivation layer  1023 . Neither of the metal interconnections  1026  and  1027  touches the pads  1024  and  1029 . 
     The metal bump  1021  includes a first part  1021 A, a second part  1021 B, and a third part  1021 C. At least a part of the first part  1021 A along the perpendicular direction Z of the COF device  1000  overlaps the first pad  1024 . The second part  1021 B extends to an outside of the first pad  1024  along a horizontal direction Y of the COF device  1000 , and at least part of the second part  1021 B overlaps the metal interconnections  1026  and  1027 . The third part  1021 C extends to the outside of the first pad  1024  along the horizontal direction Y of the COF device  1000 , and at least a part of the third part  1021 C overlaps the second pad  1029  along the perpendicular direction Z of the COF device  1000 . 
     The first adhesive layer  1022  and the second adhesive layer  1122  may be titanium tungsten layers or other conductive layers. The first adhesive layer  1022  and the second adhesive layer  1122  are disposed on the passivation layer  1023 . A part of the first adhesive layer  1022  is disposed in the first hole  1025 . A part of the second adhesive layer  1122  is disposed in the second hole  1028 . At least a part of the metal bump  1021  is disposed on the first adhesive layer  1022 , and the metal bump  1021  is electrically connected to the first pad  1024  via the first adhesive layer  1022 . At least another part of the metal bump  1021  is disposed on the second adhesive layer  1122 , and the metal bump  1021  is electrically connected to the second pad  1029  via the second adhesive layer  1122 . 
     As described above, in the embodiments of the invention, the first part of the metal bump overlaps the pad along the perpendicular direction of the COF device, and the second part of the metal bump overlaps the metal interconnection (such as a supply wire, a ground wire, a data wire, or other wires) outside the pad. Moreover, the metal bump may overlap the metal interconnections and form a Bump on Active (BOA) structure. Therefore, the COF device in the embodiments of the invention is capable of effectively reducing the area of the pad to facilitate the routing design of the metal interconnections. 
     Although the invention has been described with reference to the above embodiments, they are not intended to limit the invention. It is apparent to one of ordinary skill in the art that modifications to the described embodiments may be made without departing from the spirit of the invention. Accordingly, the scope of the invention will be defined by the attached claims and not by the above detailed descriptions.