Method of forming a solderable solder deposit on a contact pad

A method of forming a solderable solder deposit on a contact pad (B), comprising the steps of

• (i) providing an organic, non-conductive substrate (A) which exposes a first contact pad under a first opening in a first non-conductive resist layer (C), the first opening having a first maximum width, and at least a second contact pad under at least a second opening in the first non-conductive resist layer (C), the at least second opening having a second maximum width which is different from the first maximum width,
• (ii) depositing a conductive layer (G) inside (G″) and outside (G′) the first opening and the at least second opening such that an activated surface results, thereby forming an activated first opening and an activated at least second opening,
• (iii) electrolytically depositing nickel (D) or a nickel alloy (D) into the activated first opening and into the activated at least second opening such that a nickel or nickel alloy is deposited onto the activated surface,
• (iv) electrolytically depositing tin (E) or a tin alloy (E) onto the nickel or nickel alloy deposited in step (iii),
• with the proviso that the electrolytic deposition of steps (iii) or (iv) results in an entirely filled activated first opening and an entirely filled activated at least second opening,
• wherein the entirely filled activated first opening and the entirely filled activated at least second opening are completely filled with said nickel or nickel alloy, or in the entirely filled activated first opening and the entirely filled activated at least second opening the total volume of nickel or nickel alloy is higher than the total volume of tin and tin alloy, based on the total volume of the entirely filled activated first opening and the entirely filled activated at least second opening, and
• wherein the nickel or nickel alloy in step (iii) is deposited into the first opening and the at least second opening in a single step.