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Effect of Au-Sn IMCs’ formation and morphologies on shear properties of laser reflowed micro-solder joints

Wei Liu (State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, Harbin, China AND School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh, United Kingdom)
Rong An (Key Laboratory of Micro-systems and Micro-structures Manufacturing, Ministry of Education, Harbin Institute of Technology, Harbin, China)
Chunqing Wang (State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, Harbin, China AND Key Laboratory of Micro-systems and Micro-structures Manufacturing, Ministry of Education, Harbin Institute of Technology, Harbin, China)
Yanhong Tian (State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, Harbin, China)

Soldering & Surface Mount Technology

ISSN: 0954-0911

Article publication date: 2 February 2015

Abstract

Purpose

The purpose of this paper is to investigate the effect of typical morphologies of Au-Sn IMCs (intermetallic compounds) at the interfaces of solder and pads on shear properties of laser reflowed micro-solder joints.

Design/methodology/approach

Sn-2.0Ag-0.75Cu-3.0Bi (SnAgCuBi) solder balls (120 μm in diameter), pads with 0.1, 0.5, 0.9 or 4.0 μm thickness of Au surface finish, and different laser input energies were utilized to fabricate micro-solder joints with Au-Sn IMCs having different typical morphologies. The joints were performed by a shear test through a DAGE bond test system. Fracture surfaces of the joints were analyzed by scanning electron microscopy and energy-dispersive X-ray spectrometry to identify fracture modes and locations.

Findings

Morphologies of Au-Sn IMCs would affect shear properties of the joints remarkably. When needle-like AuSn4 IMCs formed at the interfaces of solder and pads, almost entire surfaces presented the manner of ductile fracture. Moreover, shear forces of this kind of solder joints were higher than those of joints without Au-Sn IMCs or with a nearly continuous/continuous Au-Sn IMCs layer. The reason was that the shear performance of the solder joints with needle-like AuSn4 IMCs was enhanced by an interlocking effect between solder and needle-like AuSn4 IMCs. As a nearly continuous or continuous Au-Sn IMCs layer formed, the fracture surfaces presented more character of brittle than ductile fracture. However, if an Au layer still remained under Au-Sn IMCs, the shear performance of the joints would be enhanced.

Originality/value

The results in this study can be used to optimize microstructures and shear properties of laser reflowed micro-solder joints.

Keywords

Citation

Liu, W., An, R., Wang, C. and Tian, Y. (2015), "Effect of Au-Sn IMCs’ formation and morphologies on shear properties of laser reflowed micro-solder joints", Soldering & Surface Mount Technology, Vol. 27 No. 1, pp. 45-51. https://doi.org/10.1108/SSMT-07-2014-0016

Publisher

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Emerald Group Publishing Limited

Copyright © 2015, Emerald Group Publishing Limited