Circuit board and preparation method thereof

A preparation method of a circuit board, comprising:

• forming a seed layer on a surface of a substrate;
• forming a dry film which is patterned on a surface of the seed layer away from the substrate;
• forming a first copper layer which is patterned on a portion of the seed layer not covered by the dry film;
• removing the dry film and removing a portion of the seed layer not covered by the first copper layer;
• and
• forming a second copper layer by electroplating on the surface of the substrate through a conductive lead;
• wherein forming the second copper layer comprises adjusting an acid-to-copper ratio of an electroplating solution suitable for electroplating the second copper layer, a type of additives in the electroplating solution, and a content of additives in the electroplating solution as required, so that copper crystal grains nucleate and grow along a vertical lattice of the first copper layer as much as possible, and a thickness of the second copper layer along a thickness direction of the substrate is greater than a thickness of the second copper layer along a direction perpendicular to the thickness direction of the substrate;
• the second copper layer encloses the seed layer and the first copper layer to form a plurality of traces spaced apart from each other, each of the plurality of traces comprises the seed layer, the first copper layer and the second copper layer, and a ratio of a thickness of each of the plurality of traces to a pitch between any two adjacent ones of the plurality of traces is greater than 1.