Interface reaction between an electroless Ni–Co–P metallization and Sn–3.5Ag lead-free solder with improved joint reliability
Balaraju, J. N.
Date of Issue2014
School of Materials Science and Engineering
To address the reliability challenges brought by the accelerated reaction with the implementation of lead-free solders, an electrolessly plated Ni-Co-P alloy (3~4 wt.% P and 9~12 wt.% Co) was developed as the solder metallization in this study. Three compounds layers, (Ni,Co)3Sn4, (Ni,Co)3P and (Ni,Co)12P5 are formed at the reaction interface. Nano-sized voids are visible in the (Ni,Co)3P layer under TEM, but no large voids are found under SEM. This is an indication of effective diffusion barrier performance by the Ni-Co-P metallization than the binary Ni-P metallization. The influence of interfacial reaction on the solder joint reliability was reported through the evaluation of the tensile strength of micro solder joints. Upon aging at 180 C for 600 h, the tensile strength of Ni-Co-P/Sn-3.5Ag solder joint remains high, and the failure is caused by the bulk solder necking and collapse. As a comparison, the tensile strength of Ni-P/Sn-3.5Ag solder joint drops significantly after aging for 400 h at 180 C, and the fracture mode has shifted from ductile failure in the bulk solder to the brittle failure at the solder joint interface. The Ni-Co-P metallization, having a much slower consumption rate and improved resistance to joint strength degradation during long-term aging treatment, is a potential candidate for future microelectronic solder metallization materials.
DRNTU::Engineering::Materials::Electronic packaging materials
© 2014 Acta Materialia Inc. Published by Elsevier Ltd. This is the author created version of a work that has been peer reviewed and accepted for publication in Acta Materialia, published by Elsevier on behalf of Acta Materialia Inc. It incorporates referee’s comments but changes resulting from the publishing process, such as copyediting, structural formatting, may not be reflected in this document. The published version is available at: http://dx.doi.org/10.1016/j.actamat.2014.02.026.