Interfacial microstructure and hardness of nickel

Authors: Tama Fouzder Qingqian Li Y C Chan Daniel K Chan

Publish Date: 2014/06/27

Volume: 25, Issue: 9, Pages: 4012-4023

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Abstract

Sn–Ag–Cu composite solder has been prepared by adding Ni nanoparticles Interfacial reactions the morphology of the intermetallic compounds IMC that were formed the hardness between the solder joints and the plain Cu/immersion Agplated Cu pads depending on the number of the reflow cycles and the aging time have all been investigated A scallopshaped Cu6Sn5 IMC layer that adhered to the substrate surface was formed at the interfaces of the plain Sn–Ag–Cu solder joints during the early reflow cycles A very thin Cu3Sn IMC layer was found between the Cu6Sn5 IMC layer and the substrates after a lengthy reflow cycle and solidstate aging process However after adding Ni nanoparticles a scallopshaped Cu Ni–Sn IMC layer was clearly observed at both of the substrate surfaces without any Cu3Sn IMC layer formation Needleshaped Ag3Sn and sphereshaped Cu6Sn5 IMC particles were clearly observed in the βSn matrix in the solderball region of the plain Sn–Ag–Cu solder joints Additional fine Cu NiSn IMC particles were found to be homogeneously distributed in the βSn matrix of the solder joints containing the Ni nanoparticles The Sn–Ag–Cu–05Ni composite solder joints consistently displayed higher hardness values than the plain Sn–Ag–Cu solder joints for any specific number of reflow cycles–on both substrates–due to their wellcontrolled fine networktype microstructures and the homogeneous distribution of fine Cu Ni–Sn IMC particles which acted as secondphase strengthening mechanisms The hardness values of Sn–Ag–Cu and Sn–Ag–Cu–05Ni on the Cu substrates after one reflow cycle were about 151 and 166 Hv respectively–and about 122 and 144 Hv after sixteen reflow cycles respectively However the hardness values of the plain Sn–Ag–Cu solder joint and solder joint containing 05 wt Ni nanoparticles after one reflow cycle on the immersion Ag plated Cu substrates were about 177 and 187 Hv respectively and about 132 and 153 Hv after sixteen reflow cycles respectivelyThe authors would like to acknowledge the financial support provided by Chartermate Electronics Ltd Hong Kong City University of Hong Kong for the project 9041636 GRF grant from the Hong Kong Research Grants Council RGC ref No 100411 A study of nanostructured electronic interconnects–preparation characterization and integration RGC ref No 7004050 Nanoscale Solder Joint Assembly by Induced Dielectrophoretic Manipulation Preparation Characterization and Reliability for Nanoelectronic Packaging and the PhD studentship of CityU HK Prof Richard De La Rue is thanked for proof reading the manuscript The authors would like to thank Mr Chan Tit Wah for helping in DSC analysis

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