Undercut-free BLM process for Pb-free and Pb-reduced C4

Details Undercut-free BLM process for Pb-free and Pb-reduced C4 Undercut-free BLM process for Pb-free and Pb-reduced C4

2009-01-22

2010-11-02

Sarkar, Asok K (Department: 2891)

Active solid-state devices (e.g., transistors, solid-state diode

Combined with electrical contact or lead

Bump leads

C257SE23021, C257SE23068, C257SE21508, C438S613000

Reexamination Certificate

active

07825511

ABSTRACT:
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 is deposited above a metal pad layer. A top layer of the barrier layer metals (e.g., Cu) is patterned by CMP with a bottom conductive layer of the barrier metal stack removed by etching. The diffusion barrier and C4 solder bump 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.

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