Patent Publication Number: US-2007103632-A1

Title: Liquid crystal display panel module and flexible printed circuit board thereof

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a liquid crystal display panel module and a flexible printed circuit board thereof, and in particular, to a flexible printed circuit board with a lead that is difficult to be broken when bending.  
      2. Description of the Related Art  
      In a chip-on-glass (COG) liquid crystal display panel module, a flexible printed circuit board is typically utilized to combine a glass substrate and a printed circuit board.  
       FIG. 1  depicts a conventional COG liquid crystal display panel module comprising a glass substrate  110 , a flexible printed circuit board  120 , and a printed circuit board  140 . Both the glass substrate  110  and the printed circuit board  140  are connected with the flexible printed circuit board  120  via an adhesive  130 .  
      As shown in  FIGS. 2   a  and  2   b , the flexible printed circuit board  120  comprises a base  121 , a plurality of leads  122 , and a passivation layer  123 . Since the flexible printed circuit board  120  requires smooth surfaces, the passivation layer  123  on the leads  122  is made of a polyimide (PI). Due to the hardness of polyimide, stress concentrates at an interface between the glass substrate  110  and the passivation layer  123 , as shown in portions A and B of  FIG. 1 . After repeat bending, the leads  122  on the flexible printed circuit board  120  are broken. Additionally, since the thickness of the passivation layer  123  is about 12 μm to 25 μm, a gap is formed between the edge of the glass substrate  110  and the passivation layer  123 . When foreign matter falls into the gap, the leads  122  may short circuit.  
      Thus, for the COG liquid crystal display panel module, it is important to prevent the leads on the flexible printed circuit board from breaking after repeated bending.  
      In U.S. Pat. No. 6,657,606, a flexible printed circuit board is provided to prevent leads thereon from breaking after repeated bending. Nevertheless, the flexible printed circuit board in U.S. Pat. No. 6,657,606 is applied to a chip-on-film (COF) liquid crystal display panel module, but not to the COG liquid crystal display panel module.  
     BRIEF SUMMARY OF THE INVENTION  
      Liquid crystal display panel modules are provided. An exemplary embodiment of a liquid crystal display panel module comprises a substrate and a flexible printed circuit board connected with the substrate. The flexible printed circuit board comprises a base, a lead, a passivation layer, and a first passivation layer. The lead is disposed on the base, and has a first end portion and a second end portion. The passivation layer covers the lead without covering the first end portion. The first insulation layer is disposed at an interface between the passivation layer and the first end portion to cover part of the passivation layer and part of the first end portion.  
      Furthermore, the liquid crystal display panel module comprises an adhesive disposed between the substrate and the flexible printed circuit board. The adhesive may be in contact with the first insulation layer. Alternatively, the adhesive may be disposed without contacting the first insulation layer. The adhesive comprises an anisotropic conductive film, a nonconductive film, an anisotropic conductive paste, or a nonconductive paste.  
      Additionally, the first insulation layer has a hardness lower than that of the passivation layer. The passivation layer comprises a polyimide. The first insulation layer comprises a resin, and the resin comprises a solder resist or a photo resist. The lead comprises electrolytically deposited copper or rolled annealed copper.  
      Moreover, the liquid crystal display panel module comprises a printed circuit board connected with the flexible printed circuit board. The flexible printed circuit board further comprises a second insulation layer disposed at an interface between the passivation layer and the second end portion to cover part of the passivation layer and part of the second end portion. An adhesive is disposed between the printed circuit board and the flexible printed circuit board.  
      Note that the liquid crystal display panel module is a chip-on-glass liquid crystal display panel module.  
      Flexible printed circuit boards are provided. An exemplary embodiment of a flexible printed circuit board comprises a base, a lead, a passivation layer, and a first passivation layer. The lead is disposed on the base, and has a first end portion and a second end portion. The passivation layer covers the lead without covering the first end portion. The first insulation layer is disposed at an interface between the passivation layer and the first end portion to cover part of the passivation layer and part of the first end portion.  
      A detailed description is given in the following embodiments with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:  
       FIG. 1  is a schematic view of a conventional chip-on-glass liquid crystal display panel module;  
       FIG. 2   a  is a schematic view of a flexible printed circuit board in  FIG. 1 ;  
       FIG. 2   b  is another schematic view of the flexible printed circuit board in  FIG. 1 ;  
       FIG. 3  is a schematic view of an embodiment of a liquid crystal display panel module;  
       FIG. 4   a  is a schematic view of a flexible printed circuit board in  FIG. 3 ;  
       FIG. 4   b  is another schematic view of the flexible printed circuit board in  FIG. 3 ;  
       FIG. 5  is a schematic view of another embodiment of a liquid crystal display panel module; and  
       FIG. 6  is a schematic view of a variant embodiment of a flexible printed circuit board. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Referring to  FIG. 3 , an embodiment of a liquid crystal display panel module  1  comprises a glass substrate  10 , a flexible printed circuit board  20 , and a printed circuit board  40 . Both the glass substrate  10  and the printed circuit board  40  are connected with the flexible printed circuit board  20  via an adhesive  30 .  
      Referring to  FIGS. 4   a  and  4   b , the flexible printed circuit board  20  comprises a base  21 , a plurality of leads  22 , a passivation layer  23 , a first passivation layer  24 , and a second insulation layer  25 . Each lead  22  is disposed on the base  21 , and has a first end portion  22   a  and a second end portion  22   b . The passivation layer  23  covers the leads  22  without covering the first end portion  22   a  and the second end portion  22   b . The passivation layer  23  may be made of a polyimide.  
      The first insulation layer  24  is disposed at an interface between the passivation layer  23  and the first end portion  22   a  to cover part of the passivation layer  23  and part of the first end portion  22   a . Similarly, the second insulation layer  25  is disposed at an interface between the passivation layer  23  and the second end portion  22   b  to cover part of the passivation layer  23  and part of the second end portion  22   b . Note that the hardness of the first and second insulation layers  24  and  25  is lower than that of the passivation layer  23 . Additionally, the first and second insulation layers  24  and  25  are made of a resin that may be a solder resist or a photo resist.  
      Referring to  FIG. 3 , the adhesive  30  is disposed between the substrate  10  and the flexible printed circuit board  20  to connect the flexible printed circuit board  20  with the substrate  10 . Also, the adhesive  30  is disposed between the printed circuit board  40  and the flexible printed circuit board  20  to connect the printed circuit board  40  with the flexible printed circuit board  20 . The adhesive  30  may be an anisotropic conductive film (ACF), a nonconductive film (NCF), an anisotropic conductive paste (ACP), or a nonconductive paste (NCP).  
      Note that the adhesive  30  is disposed without contacting with the first and second insulation layers  24  and  25  in  FIG. 3 ; however, it is not limited to this. For example, as shown in  FIG. 5 , an adhesive  30 ′ is in contact with a first insulation layer  24 ′ in a liquid crystal display module  1 ′. Thus, foreign matter cannot contact the exposed leads causing short circuits. Furthermore, although only the first insulation layer  24 ′ is shown in  FIG. 5 , the second insulation layer can be disposed so as to not contact the adhesive based on requirements.  
      Additionally, although the insulation layers are disposed at both end portions of the leads in  FIG. 3 , they are not limited to this. Based on requirements, only one insulation layer can be disposed on the leads. Furthermore, the structure of the flexible printed circuit board is not limited to that shown in  FIG. 4   a . For example, as shown in  FIG. 6 , an adhesive layer  26  may be disposed between a base  21 ′ and a passivation layer  22 ′ in a flexible printed circuit board  20 ″. Note that the liquid crystal display panel module is a chip-on-glass liquid crystal display panel module.  
      As previously described, the insulation layer with lower hardness is disposed at the interface between the leads and the passivation layer to prevent the leads around the edge of the flexible printed circuit board from breaking after repeated bending. Thus, the insulation layer can enhance the flexibility and endurance of the leads without affecting the flatness of the flexible printed circuit board. As a result, since the flexibility and endurance are enhanced, the lead material is not limited to rolled annealed copper, and may be made with lower cost electrolytically deposited copper.  
      While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To 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.