Manufacturing method of redistribution layer

A manufacturing method of a redistribution layer comprising:

• a photosensitive layer forming step of forming a negative photosensitive material layer on a first main surface of a light-transmitting support substrate;
• a first exposure step of exposing the negative photosensitive material layer formed on the first main surface of the support substrate with light in a predetermined pattern;
• a second exposure step of exposing the negative photosensitive material layer formed on the first main surface of the support substrate with light over an entire surface of the negative photosensitive material layer from a side of a second main surface of the support substrate opposite to the first main surface;
• a development step of developing the negative photosensitive material layer exposed with light in the first exposure step and the second exposure step, and thereby forming a first insulating layer on the first main surface of the support substrate, the first insulating layer having a recessed pattern corresponding to the predetermined pattern on a second main surface of the first insulating layer, the second main surface of the first insulating layer being opposite to a first main surface of the first insulating layer opposing the first main surface of the support substrate;
• a first wiring layer forming step of forming, based on the recessed pattern, a first wiring layer on the second main surface of the first insulating layer;
• and
• a separation step of irradiating the first insulating layer with light to be absorbed by the first insulating layer from the side of the second main surface of the support substrate, and thereby separating, from the support substrate, the first insulating layer on which the first wiring layer is formed.