| 摘要 |
<p>A flexible printed circuit board having a polyimide film formed by a method wherein a polyimide precursor is directly applied on a metallic conductor foil, dried, heated and cured. The polyimide film comprises two or more laminated layers. The coefficient of thermal linear expansion of at least one polyimide layer except for the first polyimide layer in contact with the metallic conductor foil is larger than that of the first polyimide layer. Also, the thicknesses and curls of the laminated layers of the polyimide film satisfy the following equations: 3.0 < Qn-1 X tn < 50; tn-1 > tn, where tn is the thickness ( mu m) of the outermost polyimide layer (n-th layer), tn-1 is the thickness ( mu m) of from the first to the (n-1)-th layers, and Qn-1 is twice the value (cm) of the radius of curvature of the curl of the film of from the first to the (n-1)-th layers. This board does not curl just after the curing, and even after forming a circuit by etching.</p> |
