Isothermal solid-state aging of Pb-5Sn solder bump on Ni/Cu/Ti under bump metallization

Abstract

Isothermal solid-state aging of the Pb-5Sn solder bump on the Ni/Cu/Ti under bump metallization was investigated. Only a layered (Ni,Cu)(3)Sn-4 phase was formed at the solder/Ni interface aged at 160 degrees C. The (Ni,Cu)(3)Sn-4 layer attached closely to the Ni layer after 4320 h of aging. Another (Ni,Cu)(3)Sn-2 phase was formed when the aging temperature was raised to 300 degrees C. The (Ni2Cu)(3)Sn-2 phase did not form as a continuous layer along the interface but grew discontinuously in the Ni layer. After aging at 300 degrees C for 360 h, the majority of the (Ni,Cu)(3)Sn-4 phase detached from the interface. Pb was found to penetrate the detached (Ni,Cu)(3)Sn-4 phase and filled the gap between the detached (Ni,Cu)(3)Sn-4 phase and the attached (Ni,Cu)(3)Sn-2 phase. Based on microstructural analyses, the causes for the detachment of the (Ni,Cu)(3)Sn-4 phase and the Pb penetration were discussed. (c) 2006 Elsevier B.V. All rights reserved.