Diffusion barrier characteristics and shear fracture behaviors of eutectic PbSn solder/electroless Co(W,P) samples

Abstract

Diffusion barrier characteristics, activation energy (E(a)) of IMC growth and bonding properties of amorphous and polycrystalline electroless Co(W,P) (termed as alpha-Co(W,P) and poly-Co(W,P)) to eutectic PbSn solder are presented. Intermetallic compound (IMC) spallation and an nano-crystalline P-rich layer were observed in PbSn/alpha-Co(W,P) samples subjected to liquid-state aging at 250 degrees C. In contrast, IMCs resided on the P-rich layer in PbSn/alpha-Co(W,P) samples subjected to solid-state aging at 150 degrees C. Thick IMCs neigh-boring to an amorphous W-rich layer was seen in PbSn/poly-Co(W,P) samples regardless of the aging type. alpha-Co(W,P) was found to be a sacrificial- plus stuffed-type barrier while poly-Co(W,P) is mainly a sacrificial-type barrier. The values of E(a)'s for PbSn/alpha-Co(W,P) and PbSn/poly-Co(W,P) systems were 338.6 and 167.5 kJ/mol, respectively. Shear test revealed the ductile mode dominates the failure in both alpha- and poly-Co(W,P) samples. Analytical results indicated the high P content in electroless layer might enhance the barrier capability but degrade the bonding strength. (C) 2011 Elsevier B.V. All rights reserved.