Method of building solder bumps

The invention is a method of forming a solder bump (17) on an under bump metallurgy (13) in which a contact pad (11) on a substrate material is partially covered by a passivation layer (12) upon the substrate material which is non-wettable by solder and in which the under bump metallurgy (13) covers the portions of the contact pad (11) which are not covered by the passivation layer (12) and in which the under bump metallurgy overlaps from the contact pad to cover portions of the passivation layer. The method comprises depositing a layer of solder soluble metal upon the under bump metallurgy so as to cover the under bump metallurgy with the solder soluble metal; coating the deposit of solder soluble metal with a layer of solidified solder while substantially avoiding complete dissolution of the solder soluble metal in the solder; and heating the solder until the layer of solder melts and the deposit of solder soluble metals substantially completely dissolves in the melted solder and the surface tension of the melted solder draws the solder and dissolved solder soluble metal away from the non-wettable passivation layer (12) and into a spheroid solder bump (17).