Flexible circuit board and method for producing same and bend structure of flexible circuit board

Abstract

Provided are a flexible circuit board with excellent bendability and durability against hard conditions particularly in a repeated bend portion having a small curvature radius, and a method of producing the same. The flexible circuit board includes a resin layer and a wiring formed of a metal foil and is used with a bend portion provided at at least one position of the wiring. The metal foil is made of a metal having a cubic crystal structure, and a cross section of the wiring cut in a thickness direction from a ridge line in the bend portion forms a principal orientation on any one of planes within a range of (20 1 0) to (1 20 0) in a rotation direction from (100) to (110) with [001] set as a zone axis. The wiring is formed so that the metal foil is made of a metal having a cubic crystal structure, and that the ridge line in the bend portion has an angle in a range of 2.9° to 87.1° relative to one of fundamental crystal axes <100> in a surface of the metal foil.

1 . A flexible circuit board comprising a resin layer and a wiring formed of a metal foil, to be used with a bend portion provided at least one position of the wiring,
 wherein the metal foil is made of a metal having a cubic crystal structure, and the metal foil comprises a copper foil,   wherein a cross section of the wiring cut in a thickness direction from a ridge line in the bend portion forms a principal orientation on any one of planes within a range of (510) to (150) in a rotation direction from (100) to (110) with [001] set as a zone axis, and   wherein I/I 0 ≧25 is satisfied between an intensity (I) of a (200) plane of the copper foil in the thickness direction, which is obtained by X-ray diffraction, and an intensity (I 0 ) of a (200) plane of a copper fine powder which is obtained by X-ray diffraction.   
     
     
         2 . The flexible circuit board according to  claim 1 , wherein the cross section of the wiring cut in the thickness direction from the ridge line in the bend portion is any one of planes located on a line segment joining a point indicating (510) with a point indicating (110) in a stereo triangle of a standard projection diagram of (100). 
     
     
         3 . The flexible circuit board according to  claim 1  or  2 ,
 wherein the metal foil is made of a metal having a face-centered cubic structure, 
 wherein the cubic crystal exhibits a preferred orientation in which an occupied area ratio of a region in which one of fundamental crystal axes <100> of a unit lattice of the face-centered cubic structure is located within an orientation difference of 10° relative to a thickness direction of the metal foil is equal to or larger than 50%, and exhibits a preferred orientation in which an occupied area ratio of a region in which another one of the fundamental crystal axes <100> of a unit lattice of the face-centered cubic structure is located within an orientation difference of 10° relative to a direction in a foil surface is equal to or larger than 50%, and 
 wherein a normal to the cross section of the wiring cut in the thickness direction of the metal foil from the ridge line in the bend portion has an angle in a range of 11.4° to 78.6° relative to a principal orientation of <100> in the foil surface. 
 
     
     
         4 . The flexible circuit board according to  claim 1 , wherein the metal foil comprises a rolled copper foil having a thickness in a range of 5 μm to 100 μm. 
     
     
         5 . The flexible circuit board according to  claim 1 , wherein the bend portion is formed with a repeated operation selected from the group consisting of sliding bending, fold bending, hinge bending, and slide bending. 
     
     
         6 . The flexible circuit board according  claim 1 , wherein the wiring is formed along a direction orthogonal to the ridge line in the bend portion. 
     
     
         7 . The flexible circuit board according to  claim 1 , wherein the resin layer comprises polyimide. 
     
     
         8 . An electronic device, which installs therein the flexible circuit board according to  claim 1 .