IWLPC (Wafer-Level Packaging) Conference Proceedings


Authors: Jui-Yun Tsai and Josef Gaida et al.
Company: Atotech Deutschland GmbH
Date Published: 9/17/2007   Conference: IWLPC (Wafer-Level Packaging)

Abstract: The metallurgical reactions between the Sn3.5Ag0.5Cu solder and two different UBM structures, Ni(P)/Au and Ni(P)/Pd/Au, were studied. Two kinds of Ni(P) layers, medium-P and high-P content, were selected. The reliability of the solder joints were characterized by ball shear test after multiple reflows. It was found that the reaction products at the interface were the same in the all systems after multiple reflows. However, the addition of Pd layer between Ni(P) and Au played strong effects on morphology of compounds and strength of joints as well. The morphology of the compounds were needle-shaped in the Ni(P)/Au system and were layer-shaped in the Ni(P)/Pd/Au system. The needle-shaped compounds became the weak points during the ball shear test. Therefore, the major fracture mode of ball shear test was between the roots of needle-shaped compounds and Ni(P)/Au UBMs. In the Ni(P)/Pd/Au system, the major fracture mode was inside the solder. The thickness of Ni3P in high-P content Ni(P) layer is thicker than that in medium-P content Ni(P) layer.

Keyords: Ni(P)¬/Pd/Au, Ni(P)/Au, Pb-free solder, flip-chip technology

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