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Transient liquid phase bonding in the Cu-Sn system

Behnam Hosseinzaei (School of Engineering, Department of Metallurgy and Material, Ferdowsi University of Mashhad, Mashhad, Iran)
Ali Reza Kiani Rashid (School of Engineering, Department of Metallurgy and Material, Ferdowsi University of Mashhad, Mashhad, Iran)

Soldering & Surface Mount Technology

ISSN: 0954-0911

Article publication date: 7 August 2019

Issue publication date: 21 August 2019




This paper aims to study the features of microstructures and mechanical properties of the joints which were produced by transient liquid phase method. The difference between phases in bonding region identified through metallography pictures and applying hardness and shear strength tests.


The bonding process was carried out at a temperature of 300°C for time durations ranging from 15 to 120 min. The scanning electron microscopy equipped with energy dispersive spectroscopy system and optical microscopy were used to examine microstructural characteristics, and mechanical properties of the joints were studied by applying microhardness and shear tests. The shear tests were conducted by a shear fixture which was mounted on the tensile machine.


The intermetallic compounds of the Cu6Sn5 −η and the Cu3Sn-ε were formed simultaneously in the bonding interface. Although the η-phase, which exhibits scallop-shaped morphology, grows very quickly, upon completion of the isothermal solidification stage, it turns into the ε-phase. The hardness of the bonding interface is significantly higher than that of the substrate. The shear results show that once the bonding process is complete, brittle fracture occurs. Moreover, a greater decrease in strength was observed when the ε-phase is the only phase in the bonding region.


The hardness number of the η-phase is higher than that of the ε-phase. The hardness numbers of the η-phase and the ε-phase are 894 and 689 HV, respectively. The mean shear strength values of the samples that were bonded at 300 °C for 15, 60 and 120 min were 11.7, 9.5 and 5.4 MPa, respectively.



The authors thank Elizabeth Clark for editing and proofreading assistance. In addition, the authors would like to thank the heads of the advanced material lab, the metallographic lab and the heat treatment lab who were at their disposal for conducting the tests and preparing the samples in the process of doing the thesis. The authors would also like to pay sincere debt to whoever helped to make the progress of the MS thesis easier.


Hosseinzaei, B. and Kiani Rashid, A.R. (2019), "Transient liquid phase bonding in the Cu-Sn system", Soldering & Surface Mount Technology, Vol. 31 No. 4, pp. 221-226.



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