Manufacturing method of circuit substrate

A manufacturing method of a circuit substrate, comprising:

• providing a core layer, the core layer comprising a core dielectric layer, a first patterned circuit layer and a second patterned circuit layer, wherein the core dielectric layer has an upper surface and a lower surface opposite to each other, the first patterned circuit layer is disposed on the upper surface of the core dielectric layer, and the second patterned circuit layer is disposed on the lower surface of the core dielectric layer;
• forming an electroless plating nickel layer on the first patterned circuit layer and the second patterned circuit layer and covering the first patterned circuit layer and the second patterned circuit layer, wherein the electroless plating nickel layer has a first thickness, and the first thickness of the electroless plating nickel layer is between 1 micrometer and 10 micrometers;
• performing an etching process on the electroless plating nickel layer, so that the electroless plating nickel layer is thinned from the first thickness to a second thickness to form a thinned electroless plating nickel layer, wherein the second thickness of the thinned electroless plating nickel layer is between 0.01 micrometers and 0.9 micrometers;
• forming an electroless plating palladium layer on the thinned electroless plating nickel layer and covering the thinned electroless plating nickel layer;
• and
• forming a surface metal passivation layer on the electroless plating palladium layer and covering the electroless plating palladium layer.