Sacrificial seed layer process for forming c4 solder bumps

A method of forming a solder ball on a substrate comprising:

• starting with contacts exposed through an insulating layer and forming a base over the contacts, with the base having a top surface and being composed of at least one metal layer,
• forming a conductive metal layer with an upper surface over the base,
• forming a mask over the top surface of the conductive metal layer with C4 solder bump openings therethrough in the form of windows in the shape of C4 solder bump images down to the surface of the conductive metal layer above the contacts,
• etching away the exposed portions of the conductive metal layer below the C4 solder bump openings, thereby forming through holes, with sidewalls, in the conductive metal layer exposing C4 solder bump plating sites on the top surface of the base below the C4 solder bump openings with the conductive metal layer remaining intact on the periphery of the through holes at the C4 solder bump plating sites,
• plating solder onto the top surface of the base at the C4 solder bump plating sites filling the C4 solder bump openings by providing an electroplating current through the conductive metal layer and through the sidewalls thereof to plate the solder in the solder bump openings with the C4 solder bumps being in contact with the conductive metal layer on the periphery of the through holes by providing an electroplating current passing through the conductive metal layer and through the sidewalls thereof to plate the solder in the solder bump openings,
• depositing solder over the base to form C4 solder bumps filling the C4 solder bump plating sites within the C4 solder bump openings and through the sidewalls thereof to plate the solder in the solder bump openings,
• removing the mask, and
• then etching away the base aside from the C4 solder bumps thereby forming Ball Limiting Metallurgy (BLM) pads which are plated with the C4 solder bumps.

A method of forming a solder ball on a substrate comprising:

• starting with contacts exposed through an insulating layer and forming a base over the contacts, with the base having a top surface and being composed of at least one metal layer,
• forming a conductive metal layer with a upper surface over the base,
• forming a mask over the top surface of the conductive metal layer with C4 solder bump openings therethrough in the form of windows in the shape of C4 solder bump images down to the surface of the conductive metal layer above the contacts,
• etching away the exposed portions of the conductive metal layer below the C4 solder bump openings, thereby forming through holes, with sidewalls, in the conductive metal layer exposing C4 solder bump plating sites on the top surface of the base below the C4 solder bump openings with the conductive metal layer remaining intact on the periphery of the through holes at the C4 solder bump plating sites,
• depositing a barrier layer with a barrier surface over the top surface of the base,
• plating solder onto the barrier surface at the C4 solder bump plating sites filling the C4 solder bump openings by providing an electroplating current through the conductive metal layer and through the sidewalls thereof to plate the solder in the solder bump openings with the C4 solder bumps being in contact with the conductive metal layer on the periphery of the through holes by providing an electroplating current passing through the conductive metal layer and through the sidewalls thereof to plate the solder in the solder bump openings,
• depositing solder over the base to form C4 solder bumps filling the C4 solder bump plating sites within the C4 solder bump openings and through the sidewalls thereof to plate the solder in the solder bump openings,
• removing the mask, and
• then etching away the base aside from the C4 solder bumps thereby forming Ball Limiting Metallurgy (BLM) pads on which C4 solder bumps have been formed.