Patent Publication Number: US-2013248228-A1

Title: Flexible print circuit bonding structure of an electronic device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This Application claims priority of the People&#39;s Republic of China Patent Application No. 201210083461.0, filed on Mar. 22, 2012, the entirety of which is incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a flexible print circuit bonding structure of an electronic device, and in particular relates to a flexible print circuit bonding structure without metal contact. 
     2. Description of the Related Art 
     In general, metal traces are formed at an area outside an active area of an electronic device and electrically connected to electronic elements in the active area. In conventional electronic devices, the metal traces further extend to an outer bonding area of the electronic device to make a flexible print circuit (FPC) bonded with the metal traces through an anisotropic conductive film (ACF). Thus, an electrical signal provided from the flexible print circuit (FPC) is delivered to the electronic elements at the active area of the electronic device. 
     In the flexible print circuit bonding structure of conventional electronic devices, the anisotropic conductive film (ACF) directly contacts the metal traces. However, the bonding strength between the material of the metal traces and the material of the anisotropic conductive film (ACF) is not good. Therefore, the flexible print circuit (FPC) is easy delaminated from the metal traces. It causes the flexible print circuit bonding structures of conventional electronic devices to have issues of poor reliability. 
     In addition, a metal trace formed by a printing process has a greater thickness than that of a metal trace formed by other processes. When the metal traces formed by a printing process are bonded with a flexible print circuit (FPC) through an anisotropic conductive film (ACF), the metal traces are easy leveled due to the properties of the material of the metal traces. It causes a short issue occurring between the metal traces at the bonding area. Thus, it contributes to the flexible print circuit bonding structure of the conventional electronic devices having poor reliability. 
     BRIEF SUMMARY OF THE INVENTION 
     Therefore, the embodiments of the invention provide flexible print circuit bonding structures of an electronic device. The flexible print circuit bonding structures have no metal contact at a bonding area of the electronic device. In other words, metal traces formed at a tracing area of the electronic device do not extend to a bonding area of the electronic device. A flexible print circuit (FPC) is bonded with a transparent conductive layer at the bonding area through an anisotropic conductive film (ACF). Therefore, the reliability issue of the flexible print circuit bonding structures of the conventional electronic device caused by a poor bonding strength between the anisotropic conductive film (ACF) and metal contacts of the metal traces is overcome. 
     Moreover, according to the embodiments of the invention, the metal traces can be formed by a printing process and the above-mentioned reliability issue of the flexible print circuit bonding structures of the conventional electronic device is overcome. 
     According to an illustrative embodiment, flexible print circuit bonding structures of an electronic device is provided. The electronic device has a viewing area, a tracing area and a bonding area, wherein the tracing area is disposed between the viewing area and the bonding area. The flexible print circuit bonding structure comprises a substrate having a first surface and a second surface opposite to the first surface. A transparent conductive layer is disposed on the first surface of the substrate and extends from the tracing area to the bonding area. A metal trace layer is disposed on the transparent conductive layer at the tracing area, but does not extend to the bonding area. An anisotropic conductive film is disposed on the transparent conductive layer at the bonding area, wherein the anisotropic conductive film directly contacts the transparent conductive layer. Further, a flexible print circuit is bonded to the anisotropic conductive film. 
     A detailed description is given in the following embodiments with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
         FIG. 1  shows an illustrative top view of a portion of an electronic device containing a flexible print circuit bonding structure according to an embodiment of the invention; 
         FIG. 2  shows an illustrative cross section of a portion of an electronic device containing a flexible print circuit bonding structure along the cross section lines A-A′ and B-B′ of  FIG. 1  according to an embodiment of the invention; 
         FIG. 3  shows an illustrative top view of a portion of an electronic device containing a flexible print circuit bonding structure according to another embodiment of the invention; 
         FIG. 4  shows an illustrative cross section of a portion of an electronic device containing a flexible print circuit bonding structure along the cross section lines A-A′ and B-B′ of  FIG. 3  according to an embodiment of the invention; 
         FIG. 5  shows an illustrative top view of a portion of an electronic device containing a flexible print circuit bonding structure according to another embodiment of the invention; 
         FIG. 6  shows an illustrative cross section of a portion of an electronic device containing a flexible print circuit bonding structure along the cross section line C-C′ of  FIG. 5  according to an embodiment of the invention; 
         FIG. 7  shows an illustrative top view of a portion of an electronic device containing a flexible print circuit bonding structure according to another embodiment of the invention; and 
         FIG. 8  shows an illustrative cross section of a portion of an electronic device containing a flexible print circuit bonding structure along the cross section line D-D′ of  FIG. 7  according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
       FIG. 1  shows a top view of a portion of an electronic device  100  containing a flexible print circuit bonding structure according to an embodiment of the invention, and  FIG. 2  shows a cross section of a portion of the electronic device  100  containing the flexible print circuit bonding structure along the cross section lines A-A′ and B-B′ of  FIG. 1  according to an embodiment of the invention. In an embodiment, the electronic device  100  has a viewing area  100 A, a tracing area  100 B and a bonding area  100 C, wherein the tracing area  100 B is disposed between the viewing area  100 A and the bonding area  100 C. A plurality of touch sensing electrodes  104  and  112  is disposed at the viewing area  100 A, thus the viewing area  100 A is also referred to as an active area. In one embodiment, the touch sensing electrodes  104  may be a plurality of strip-shaped touch sensing electrodes extending along a first direction (for example an X-axis direction) and the touch sensing electrodes  112  may be a plurality of strip-shaped touch sensing electrodes extending along a second direction (for example a Y-axis direction). In other embodiments, the touch sensing electrodes  104  and  112  may have other shapes and other arrangements. 
     In the embodiment, the touch sensing electrodes  104  and  112  are formed from a first transparent conductive layer  105  and a second transparent conductive layer  113 , respectively. The first transparent conductive layer  105  is formed on a first surface  102 A of a substrate  102  and the second transparent conductive layer  113  is formed on a second surface  102 B of the substrate  102 . The materials of the first transparent conductive layer  105  and the second transparent conductive layer  113  may be indium tin oxide (ITO) or other transparent conductive materials. The substrate  102  may be a transparent glass substrate or plastic substrate. The first transparent conductive layer  105  and the second transparent conductive layer  113  are not only used to form the touch sensing electrodes  104  and  112  respectively at the viewing area  100 A, but they also extend to the tracing area  100 B and the bonding area  100 C to form a plurality of traces. 
     A metal trace layer  106  is formed on the first transparent conductive layer  105  at the tracing area  100 B, but does not extend to the bonding area  100 C. The metal trace layer  106  is electrically connected to the touch sensing electrodes  104  through the first transparent conductive layer  105  at the tracing area  100 B. In an embodiment, the metal trace layer  106  is formed by a printing process, such as a relief printing or a gravure printing technology or a transfer printing technology. The material of the metal trace layer  106  formed by a printing process is a printing metal conductive glue, for example a silver glue or a gold glue. The metal trace layer  106  formed by the printing process has a thickness of about 5 μm to about 15 μm. In another embodiment, the metal trace layer  106  can be formed by a sputtering process. The metal trace layer  106  formed by the sputtering process has a thickness of less than 1 μm. The material of the metal trace layer  106  formed by the sputtering process is for example Mo, Al, or a combination thereof. 
     A first anisotropic conductive film (ACF)  108  is directly bonded on a surface of the first transparent conductive layer  105  at the bonding area  100 C. A first flexible print circuit (FPC)  110  is bonded on the first anisotropic conductive film (ACF)  108 . Moreover, a second anisotropic conductive film (ACF)  114  is directly bonded on a surface of the second transparent conductive layer  113  at the bonding area  100 C. A second flexible print circuit (FPC)  116  is bonded under the second anisotropic conductive film (ACF)  114  to complete a flexible print circuit bonding structure of the embodiment. 
     Although the cross section of  FIG. 2  shows the first anisotropic conductive film (ACF)  108  aligned with the second anisotropic conductive film (ACF)  114 , and the first flexible print circuit (FPC)  110  aligned with the second flexible print circuit (FPC)  116 . However, actually, the first anisotropic conductive film (ACF)  108  is not aligned with the second anisotropic conductive film (ACF)  114 , and the first flexible print circuit (FPC)  110  is not aligned with the second flexible print circuit (FPC)  116 . The alignment shown in  FIG. 2  is produced by the first surface  102 A and the second surface  102 B of the substrate  102  respectively showing the cross section lines A-A′ and B-B′ of  FIG. 1 . 
     Furthermore, in the embodiment, compared with a tracing distance from the touch sensing electrodes  104  to the bonding area  100 C used for traces, a tracing distance from the touch sensing electrodes  112  to the bonding area  100 C used for traces is shorter. Thus, there is no need to dispose a metal trace layer on the surface of the second transparent conductive layer  113  at the tracing area  100 B. 
       FIG. 3  shows a top view of a portion of an electronic device  100  containing a flexible print circuit bonding structure according to another embodiment of the invention, and  FIG. 4  shows a cross section of a portion of the electronic device  100  containing the flexible print circuit bonding structure along the cross section lines A-A′ and B-B′ of  FIG. 3  according to another embodiment of the invention. The difference between the embodiment of  FIGS. 1-2  and the embodiment of  FIGS. 3-4  is that the second anisotropic conductive film (ACF)  114  and the second flexible print circuit (FPC)  116  disposed on the second surface  102 B of the substrate  102  and the first anisotropic conductive film (ACF)  108  and the first flexible print circuit (FPC)  110  disposed on the first surface  102 A of the substrate  102  are located at the same side of the substrate  102 . Therefore, compared with the embodiment of  FIGS. 1-2 , the tracing distance from the touch sensing electrodes  112  to the bonding area  100 C used for traces of the embodiment of  FIGS. 3-4  is longer. It needs a second metal trace layer  118  to be disposed on the surface of the second transparent conductive layer  113  at the tracing area  100 B to reduce the resistance of the traces at the tracing area  100 B on the second surface  102 B of the substrate  102  and help the electrical conduction from the touch sensing electrodes  112  to the second anisotropic conductive film (ACF)  114  at the bonding area  100 C. 
       FIG. 5  shows a top view of a portion of an electronic device  100  containing a flexible print circuit bonding structure according to another embodiment of the invention, and  FIG. 6  shows a cross section of a portion of the electronic device  100  containing the flexible print circuit bonding structure along the cross section line C-C′ of  FIG. 5  according to an embodiment of the invention. In the embodiment, a plurality of touch sensing electrodes  120  is disposed at the viewing area  100 A. The touch sensing electrodes  120  include a plurality of rhombus-shaped touch sensing electrodes  120 X extending along a first direction (for example an X-axis direction) and the touch sensing electrodes  120 X are connected with each other. The touch sensing electrodes  120  further include a plurality of rhombus-shaped touch sensing electrodes  120 Y extending along a second direction (for example a Y-axis direction) and the touch sensing electrodes  120 Y are separated from each other. The touch sensing electrodes  120 Y are electrically connected with each other through a bridge structure  123 . The bridge structure  123  may be formed from ITO or a metal material. In other embodiments, the touch sensing electrodes  120  may have other shapes and other arrangements. 
     In the embodiment, the touch sensing electrodes  120  are formed from the same layer of a transparent conductive layer  121 . The transparent conductive layer  121  is formed on the substrate  102 . The material of the transparent conductive layer  121  may be ITO or another transparent conductive material. The substrate  102  may be a transparent glass substrate or plastic substrate. The transparent conductive layer  121  is not only used to form the touch sensing electrodes  120  at the viewing area  100 A, but also extends to the tracing area  100 B and the bonding area  100 C to form a plurality of traces. 
     A metal trace layer  122  is formed on the transparent conductive layer  121  at the tracing area  100 B, but does not extend to the bonding area  100 C. The metal trace layer  122  is electrically connected to the touch sensing electrodes  120  through the transparent conductive layer  121 . In an embodiment, the metal trace layer  122  is formed by a printing process. The material of the metal trace layer  122  formed by the printing process is a printing metal conductive glue, for example a silver glue or a gold glue. The metal trace layer  122  formed by the printing process has a thickness of about 5 μm to about 15 μm. In another embodiment, the metal trace layer  122  can be formed by a sputtering process. The metal trace layer  122  formed by the sputtering process has a thickness of less than 1 μm. The material of the metal trace layer  122  formed by the sputtering process is for example Mo, Al, or a combination thereof. An anisotropic conductive film (ACF)  124  is directly bonded on a surface of the transparent conductive layer  121  at the bonding area  100 C. Then, a flexible print circuit (FPC)  126  is bonded on the anisotropic conductive film (ACF)  124  to complete a flexible print circuit bonding structure of the embodiment. 
       FIG. 7  shows a top view of a portion of an electronic device  100  containing a flexible print circuit bonding structure according to another embodiment of the invention, and  FIG. 8  shows a cross section of a portion of the electronic device  100  containing the flexible print circuit bonding structure along the cross section line D-D′ of  FIG. 7  according to an embodiment of the invention. In the embodiment, the electronic device  100  has a viewing area  100 A, a first tracing area  100 BR and a second tracing area  100 BL respectively disposed on the right side and left side of the viewing area  100 A, and a first bonding area  100 CR and a second bonding area  100 CL respectively disposed on the right side of the first tracing area  100 BR and the left side of the second tracing area  100 BL. 
     In the embodiment, a plurality of touch sensing electrodes  130  is disposed at the viewing area  100 A. The touch sensing electrodes  130  include a plurality of strip-shaped touch sensing electrodes  130 R extending along a first direction (for example an X-axis direction) and the touch sensing electrodes  130 R have a width gradually increasing along the first direction. The touch sensing electrodes  130  further include a plurality of strip-shaped touch sensing electrodes  130 L extending along the first direction (for example an X-axis direction) and the touch sensing electrodes  130 L have a width gradually decreasing along the first direction. The touch sensing electrodes  130  are formed from the same layer of a transparent conductive layer  131 . The transparent conductive layer  131  is formed on the substrate  102 . The material of the transparent conductive layer  131  may be ITO or another transparent conductive material. The substrate  102  may be a transparent glass substrate or a plastic substrate. The transparent conductive layer  131  is not only used to form the touch sensing electrodes  130  at the viewing area  100 A, but it also extends to the first tracing area  100 BR, the second tracing area  100 BL, the first bonding area  100 CR and the second bonding area  100 CL to form a plurality of traces. 
     A first metal trace layer  132 R is formed on the transparent conductive layer  131  at the first tracing area  100 BR, but does not extend to the first bonding area  100 CR. The first metal trace layer  132 R is electrically connected to the touch sensing electrodes  130 R through the transparent conductive layer  131 . A second metal trace layer  132 L is formed on the transparent conductive layer  131  at the second tracing area  100 BL, but does not extend to the second bonding area  100 CL. The second metal trace layer  132 L is electrically connected to the touch sensing electrodes  130 L through the transparent conductive layer  131 . 
     In an embodiment, the first metal trace layer  132 R and the second metal trace layer  132 L are formed by a printing process. The materials of the first metal trace layer  132 R and the second metal trace layer  132 L are a printing metal conductive glue, for example a silver glue or a gold glue. The first metal trace layer  132 R and the second metal trace layer  132 L formed by the printing process have a thickness of about 5 μm to about 15 μm. In another embodiment, the first metal trace layer  132 R and the second metal trace layer  132 L may be formed by a sputtering process. The first metal trace layer  132 R and the second metal trace layer  132 L formed by the sputtering process have a thickness of less than 1 μm. The materials of the first metal trace layer  132 R and the second metal trace layer  132 L formed by the sputtering process are for example Mo, Al, or a combination thereof. 
     A first anisotropic conductive film (ACF)  134 R is directly bonded on a surface of the transparent conductive layer  131  at the first bonding area  100 CR. Then, a first flexible print circuit (FPC)  136 R is bonded on the first anisotropic conductive film (ACF)  134 R. Furthermore, a second anisotropic conductive film (ACF)  134 L is directly bonded on a surface of the transparent conductive layer  131  at the second bonding area  100 CL. Then, a second flexible print circuit (FPC)  136 L is bonded on the second anisotropic conductive film (ACF)  134 L to complete a flexible print circuit bonding structure of the embodiment. 
     According to the flexible print circuit bonding structures of an electronic device provided from the embodiments of the invention, the metal trace layer electrically connecting to the electronic elements (such as the touch sensing electrodes) at the viewing area is only disposed at the tracing area, but does not extend to the bonding area. Therefore, the anisotropic conductive film (ACF) used for bonding with the flexible print circuit (FPC) directly contacts the transparent conductive layer at the bonding area. Compared with the conventional flexible print circuit bonding structures of electronic devices, the flexible print circuit bonding structures of the embodiments of the invention can prevent the flexible print circuit (FPC) from delaminating. Thus, the reliability of the flexible print circuit bonding structures of an electronic device is enhanced. 
     Moreover, compared with the conventional flexible print circuit bonding structures of electronic devices, the flexible print circuit bonding structures of the embodiments of the invention are more suitable for the metal trace layer fabricated by a printing process. Thus, the material and the fabrication cost of the metal trace layer is reduced. 
     While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.