MATERIALS TRANSACTIONS
Online ISSN : 1347-5320
Print ISSN : 1345-9678
ISSN-L : 1345-9678
Measurements and FEM Analyses of Strain Distribution in Small Sn Specimens with Few Crystal Grains
Takumi SasakiAtsushi YanaseDai OkumuraYoshiharu KariyaMasaaki KoganemaruToru Ikeda
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2019 Volume 60 Issue 6 Pages 868-875

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Abstract

Soldering is used to bond a semiconductor chip to a print circuit board (PCB). It is known that Sn, which is the base metal of Pb-free solder, shows remarkable crystal anisotropy. Clarifying the effect of Sn anisotropy on strain distribution is important for lifetime evaluation. The strain distribution in a micro specimen was measured under a tensile test by a digital image correlation method (DICM) with a microscope. Strain distributions were also analyzed by the finite element method with Hill’s anisotropic yield criterion and the crystal plasticity finite element analysis (CPFEA) with considering the critical resolves shear stress (CRSS) of each slip system. The deformation of the crystal structure of β-Sn depends on the size, number, and orientation of crystal grains. The CRSS was noticeably different for each slip system, and the yield stress varied with the orientation of crystal grains. Although the CPFEA without considering strain hardening was effective for predicting deformation within crystal grains, it is necessary to consider the strain hardening of crystals to predict the stress-strain curve of a micro specimen.

Fig. 10 Microphotographs taken by an optical microscope (top), distribution of equivalent strain measured by the DICM (middle), and calculated by the CPFEA (bottom) of seven specimens.15) Fullsize Image
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© 2019 The Japan Institute of Metals and Materials
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