Pad surface finish for high routing density substrate of BGA...

Details Pad surface finish for high routing density substrate of BGA... Pad surface finish for high routing density substrate of BGA...

2006-12-12

2006-12-12

Vu, Hung (Department: 2811)

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

Combined with electrical contact or lead

Bump leads

C257S748000, C257S762000, C257S778000, C257S779000, C257S780000

Reexamination Certificate

active

07148569

ABSTRACT:
The present invention is directed to a new bonding pad structure that includes a copper pad and a pad surface finish comprising multiple layers of solder. The multiple layers of solder include at least a layer of eutectic solder (or a layer of pure-Sn solder) covering the copper pad and a layer of high-Pb solder covering the layer of eutectic solder (or the layer of pure-Sn solder). Since the layer of high-Pb solder is significantly thicker than the eutectic solder layer (or the layer of pure-Sn solder), there is insufficient tin supply in the eutectic solder (or the layer of pure-Sn solder) for forming a thick Cu/Sn intermetallic layer on the copper pad. Instead, a thin Cu/Sn intermetallic layer is formed on the copper pad and there is less likelihood of forming a crack in the thin Cu/Sn intermetallic layer.

REFERENCES:
patent: 6326088 (2001-12-01), Mayer et al.
patent: 2004/0046264 (2004-03-01), Ho et al.

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