Method for increasing adhesion strength between a surface of copper or copper alloy and an organic layer

A method for increasing adhesion strength between a surface of copper or copper alloy and an organic layer, the method comprising in this order the steps:

• (i) providing a non-conductive substrate comprising on at least one side said surface, said surface having a total surface area of copper or copper alloy,
• (ii) contacting said substrate comprising said surface with an acidic aqueous non-etching protector solution comprising
• (ii-a) one or more than one amino azole,
• (ii-b) one or more than one organic acid and/or salts thereof,
• (ii-c) one or more than one peroxide in a total amount of 0.4 wt-% or less, based on the total weight of the protector solution, and
• (ii-d) one or more than one inorganic acid in a total amount of 0 to 0.01 wt %, based on the total weight of the protector solution,
• wherein during step (ii) the total surface area of said surface is not increased upon contacting with the protector solution, and
• wherein the protector solution is substantially free of chloride and fluoride ions.