A system and method for eliminating undercut when forming a C4 solder bump for BLM (Ball Limiting Metallurgy) and improving the C4 pitch. In the process, a barrier layer metal stack (20') is deposited above a metal pad layer (19'). A top layer (22') of the barrier layer metals (e.g., Cu) is patterned by CMP with a bottom conductive layer (21 ') of the barrier metal stack (20') removed by etching. The diffusion barrier (40) and C4 solder bump (50) may be formed by electroless plating, in one embodiment, using a maskless technique, or by an electroplating techniques using a patterned mask. This allows the pitch of the C4 solder bumps to be reduced.