Spalling of Intermetallic Compounds during the Reaction between Lead-free Solders and Electroless Ni-P Metallization

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Intermetallic compound (IMC) spalling from electroless Ni-P film was investigated with lead-free solders (Sn-3.5 wt.% Ag and pure Sn) in terms of solder deposition methods (electroplating vs solder paste), P content in Ni-P layer (4.6, 9, and 13 wt.% P), and deposited solder thickness (120 and 200µm). The reaction of Ni-P with Sn3.5Ag paste easily led to IMC spalling after 2min reflow at 250°C while IMCs adhered to the Ni-P layer after 10min reflow for the reaction with electroplated Sn or Sn3.5Ag. It has shown that both solder composition and solder deposition method are important in determining IMC spalling from the Ni-P layer. The spalling increased with P content in the Ni-P layer as well as with solder volume. Ni3Sn4 intermetallics formed as a needleshaped morphology in the early stage and changed into a chunky shape. Needle-shaped compounds exhibited a higher propensity for spalling from the Ni-P layer than chunky shaped compounds because molten solder can easily penetrate into the interface between needle shaped IMCs and the P-rich layer.

By: Y. C. Sohn, Jin Yu, S. K. Kang, D. Y. Shih; T. Y. Lee

Published in: Journal of Materials Research, volume 19, (no 8), pages 2428-36 in 2004


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