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Electroless Ni-Cu-P barrier between Si/Ti/Al pad and Sn-Pb flip-chip solder bumps

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2 Author(s)
Chun-Jen Chen ; Dept. of Mater. Sci. & Eng., Nat. Cheng Kung Univ., Tainan, Taiwan ; Lin, Kwang-Lung

This work investigates the barrier effect of the electroless Ni-Cu-P deposit between Al conductor and Sn-Pb solder bump, as well as the interfacial reaction with the Sn-Pb solder. For the Ni-Cu-P/63Sn-37Pb system, a (Ni, Cu)3Sn4 compound with three different morphologies: fine-grain, whisker, and polygon are formed at the Ni-Cu-P/63Sn-37Pb interface after reflow at 220°C for 15 s. These (Ni, Cu)3Sn4 crystals transform into polygon shape with smooth appearance during 150°C aging. For the Ni-Cu-P/95Pb-5Sn system, equiaxial (Ni, Cu)3Sn4 crystals are formed at the Ni-Cu-P/95Pb-5Sn interface after reflow at 350°C for 15 s, and they also transform into polygon shape during 150°C aging. In addition, the Ni-Cu-P deposit will crystallize to form Ni5 P2 during 350°C reflow. The growth of the (Ni, Cu)3 Sn4 compound by solid state reaction is a diffusion controlled process for both Ni-Cu-P/63Sn-37Pb and Ni-Cu-P/95Pb-5Sn systems. A 4 μm Ni-Cu-P deposit can provide adequate barrier function between an Al conductor and two Sn-Pb solders under 150°C aging for 1000 h

Published in:

Components and Packaging Technologies, IEEE Transactions on  (Volume:24 ,  Issue: 4 )