The invention discloses a preparation method of a multi-layer flexible printed circuit. The preparation method of the multi-layer flexible printed circuit comprises the following steps: providing flexible base materials of a first surface and a second surface which are arranged back to back; setting a first circuit layer on the first surface; setting a first insulating medium layer on the first circuit layer;
processing and forming a number of through-holes on the first insulating medium layer;
coating a conductive
slurry or ink on the insulating medium layer, and making a part of the conductive
slurry or ink flow into the through-holes and contact with the first circuit layer; then solidifying the conductive
slurry or ink to form a second conductive layer on the insulating medium layer and form a conductive filler which can at least connect the first and second circuit
layers electrically in the through-holes; and repeating the above operations until more than two insulating
layers and more than three circuit
layers are formed. The preparation method of the multi-layer flexible printed circuit is simple and easy to implement, has the advantages of good
controllability, low cost and
friendly environment, and benefits large-scale implementation; and the obtained printed circuit has super thin and soft characteristics.