Flexible multilayer wiring board and manufacture method thereof

A flexible multilayer wiring board including a plurality of circuit wirings stacked in layers via an insulating layer therebetween, said circuit wirings of the respective layers being interlayer-connected by via portions, wherein:

• first to N-th layer circuit wirings are stacked in layers via an insulating layer therebetween, N being an integer equal or greater than 2, the first layer circuit wiring is located on the outermost surface, and the circuit wirings of the respective insulating layers are interlayer-connected by via portions, wherein the via portions are located on the surface of the respective circuit wirings, and are not penetrating the respective circuit wiring and are projecting from the respective insulating layers so as to traverse the layer circuit wirings of the next insulating layers;
• the N-th layer circuit wiring is covered with an insulating layer on its side remote from the (N−1)th layer circuit wiring, and said N-th layer circuit wiring is connected to external connection terminals formed so as to penetrate said insulating layer and project from the surface of said insulating layer;
• and
• a line/space width in a highest density portion of each of said circuit wirings falls within the range of 5 μm/5 μm to 25 μm/25 μm.