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A Study of Diffusion Barrier Characteristics of Electroless Co(W,P) Layers to Lead-free SnAgCu Solder

Published online by Cambridge University Press:  31 January 2011

Hung-Chun Pan  and
Tsung-Eong Hsieh
Hung-Chun Pan
Affiliation:
[email protected], National Chiao Tung University, Department of Materials Science and Engineering, Hsinchu, Taiwan, Province of China
Tsung-Eong Hsieh
Affiliation:
[email protected], National Chiao Tung University, Department of Materials Science and Engineering, Hsinchu, Taiwan, Province of China
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Abstract

Diffusion barrier characteristics of amorphous and polycrystalline electroless Co(W,P) layers (α-Co(W,P) and poly-Co(W,P)) to lead-free SnAgCu (SAC) solder were investigated via the liquid- and solid-state aging tests. In the sample containing α-Co(W,P) subjected to liquid-state aging at 250°C for 1 hr, the spallation of (Co,Cu)Sn3 intermetallic compound (IMC) into the solder and formation of a polycrystalline P-rich layer in between SAC and Co(W,P) were found. Further, the α-Co(W,P) transforms into polycrystalline structure embedded with tiny Co2P precipitates As to the sample containing α-Co(W,P) subjected to solid-state aging at 150°C up to 1000 hrs, a thick (Cu,Co)6Sn5 IMC resided in between SAC and Co(W,P) and the P-rich layer beneath IMCs was similarly seen. In the samples containing poly-Co(W,P) subjected to liquid-state aging, a mixture of (Co,Cu)Sn3 and (Co,Ag)Sn3 IMCs formed in between SAC and Co(W,P). An amorphous W-rich layer formed in between SAC and poly-Co(W,P). Similar interfacial morphology was observed in the samples subjected to the solid-state aging test. Analytical results indicated the electroless Co(W,P) is in essential a combined-type, i.e., sacrificial-type plus stuffed-type, diffusion barrier. However, the α-Co(W,P) is a better diffusion barrier for under bump metallurgy (UBM) applications in flip-chip (FC) bonding since it exhibits a lower Co consumption rate in comparison with poly-Co(W,P).

Keywords

amorphousbarrier layerdiffusion
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1156: Symposium D – Materials, Processes and Reliability for Advanced Interconnects for Micro-and Nanoelectronics–2009 , 2009 , 1156-D03-07
Copyright
Copyright © Materials Research Society 2009

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