NEPCON West - Fiberoptic Expo Conference Proceedings


THERMAL AGING CHARACTERIZATION OF OSP METAL FINISHING FOR FLIP CHIP PACKAGING WITH FOUR LAYER LAMINATE SUBSTRATE

Authors: Mike C. Loo and Lily Zhao
Company: Philips Semiconductors
Date Published: 12/3/2002   Conference: NEPCON West - Fiberoptic Expo


Abstract: Flip chip package with four layer laminate substrate is used for mid I/O range flip chip (300 to 1000I/O) that require less demanding electrical performance. Since the device is not for high performance application, cost reduction for the package becomes critical. To reduce the cost, instead of having gold/nickel plating, the copper pads on the substrate are coated with an organic solderable preservative (OSP) finish to prevent oxidation. Without the nickel as the diffusion barrier, the copper will form a copper/tin intermetallic after ball attach with eutectic lead tin solder.

During high temperature storage, the intermetallic will grow and may result in poor ball adhesion. During the study, it is found that the copper plating quality, especially for the high density four layer substrate, can influence this intermetallic growth behavior. In this paper, first, the configuration of the flip chip package with four layer laminate substrate will be presented. Second, the effect of storage temperature, time, and copper plating quality on the intermetallic microstructure and ball adhesion will be discussed.

Key words: four layer flip chip BGA, OSP, high temperature storage, copper plating, intermetallic.



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