Multiscale modeling of the anisotropic transient creep response of heterogeneous single crystal SnAgCu solder

S. Mukherjee, B. Zhou, A. Dasgupta, T. R. Bieler

    Research output: Contribution to journalArticle

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    Abstract

    The lack of statistical homogeneity in functional SnAgCu (SAC) solder joints due to their coarse grained microstructure, in conjunction with the severe anisotropy exhibited by single crystal Sn, renders each joint unique in terms of mechanical behavior. A mechanistic multi-scale modeling framework is proposed in this study to predict the influence of composition and microstructure on the anisotropic transient creep response of single crystal SnAgCu (SAC) solder. Tier I consist of single-crystal eutectic Sn-Ag alloy, with nanoscale Ag3Sn particles embedded in a single-crystal Sn matrix. Tier II consists of single crystal SAC solder which is composed of Sn dendrites surrounded by the eutectic Sn-Ag phase of Tier I. The Tier I anisotropic transient creep model is based on dislocation mechanics. The Tier II model uses the results of Tier I as an input and is based on anisotropic composite micro-mechanics. In Tier I, creep deformation is governed by dislocation impediment and recovery at nanoscale Ag3Sn particles, with recovery being the rate controlling mechanism. Dislocation climb and dislocation detachment at the Ag3Sn particles are proposed to be the competing rate controlling recovery mechanisms. Line tension and mobility of dislocations in dominant slip systems of single crystal Sn are estimated based on the elastic crystal anisotropy of body centered tetragonal (BCT) Sn. The anisotropic transient creep rate of the eutectic Sn-Ag phase of Tier I is then modeled using above inputs and the evolving dislocation density calculated for dominant glide systems during the transient stage of creep. The dominant slip systems are determined based on the dislocation mobility and on the orientation angle between the crystal principal axes and the loading direction. The creep response of the eutectic phase (from Tier 1) is combined with the creep response of Sn lobes at Tier 2, using the anisotropic Mori-Tanaka homogenization theory, to obtain the transient creep response of a SAC305 single crystal along global specimen directions. This model has been calibrated using experimentally obtained transient creep response of a SAC305 single crystal specimen. The above multiscale calibrated model is then used to predict (i) the transient creep response of another SAC305 single crystal specimen and (ii) the effect of orientation (by changing one of the Euler angles) on the transient creep response of SAC305 single crystal. The grain orientation of above two SAC single crystal specimens (with respect to loading direction) were identified with orientation image mapping and then utilized in the model to estimate the resolved shear stress along the dominant slip directions. Parametric studies have also been conducted to predict the effects of the volume fraction, aspect ratio, and orientation of ellipsoidal Sn inclusions on the anisotropic transient creep response of SAC single crystals.

    Original languageEnglish (US)
    Pages (from-to)1-25
    Number of pages25
    JournalInternational Journal of Plasticity
    Volume78
    DOIs
    StatePublished - Mar 1 2016

    Profile

    Erythrocyte Inclusions
    Creep
    Genetic Engineering
    Anthralin
    Cardanolides
    Employee Grievances
    Soldering alloys
    Eutectics
    Muscle Contraction
    Recovery
    Automobiles
    Carcinoid Tumor
    Dislocations (crystals)
    Crystal orientation
    Microstructure
    Anisotropy
    Crystals
    Enzyme Reactivators
    Composite micromechanics
    Benzyl Compounds

    Keywords

    • A. Anisotropic material
    • A. Creep
    • A. Dislocations
    • A. Microstructures
    • SAC solder

    ASJC Scopus subject areas

    • Mechanical Engineering
    • Mechanics of Materials
    • Materials Science(all)

    Cite this

    Multiscale modeling of the anisotropic transient creep response of heterogeneous single crystal SnAgCu solder. / Mukherjee, S.; Zhou, B.; Dasgupta, A.; Bieler, T. R.

    In: International Journal of Plasticity, Vol. 78, 01.03.2016, p. 1-25.

    Research output: Contribution to journalArticle

    Mukherjee, S.; Zhou, B.; Dasgupta, A.; Bieler, T. R. / Multiscale modeling of the anisotropic transient creep response of heterogeneous single crystal SnAgCu solder.

    In: International Journal of Plasticity, Vol. 78, 01.03.2016, p. 1-25.

    Research output: Contribution to journalArticle

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    abstract = "The lack of statistical homogeneity in functional SnAgCu (SAC) solder joints due to their coarse grained microstructure, in conjunction with the severe anisotropy exhibited by single crystal Sn, renders each joint unique in terms of mechanical behavior. A mechanistic multi-scale modeling framework is proposed in this study to predict the influence of composition and microstructure on the anisotropic transient creep response of single crystal SnAgCu (SAC) solder. Tier I consist of single-crystal eutectic Sn-Ag alloy, with nanoscale Ag3Sn particles embedded in a single-crystal Sn matrix. Tier II consists of single crystal SAC solder which is composed of Sn dendrites surrounded by the eutectic Sn-Ag phase of Tier I. The Tier I anisotropic transient creep model is based on dislocation mechanics. The Tier II model uses the results of Tier I as an input and is based on anisotropic composite micro-mechanics. In Tier I, creep deformation is governed by dislocation impediment and recovery at nanoscale Ag3Sn particles, with recovery being the rate controlling mechanism. Dislocation climb and dislocation detachment at the Ag3Sn particles are proposed to be the competing rate controlling recovery mechanisms. Line tension and mobility of dislocations in dominant slip systems of single crystal Sn are estimated based on the elastic crystal anisotropy of body centered tetragonal (BCT) Sn. The anisotropic transient creep rate of the eutectic Sn-Ag phase of Tier I is then modeled using above inputs and the evolving dislocation density calculated for dominant glide systems during the transient stage of creep. The dominant slip systems are determined based on the dislocation mobility and on the orientation angle between the crystal principal axes and the loading direction. The creep response of the eutectic phase (from Tier 1) is combined with the creep response of Sn lobes at Tier 2, using the anisotropic Mori-Tanaka homogenization theory, to obtain the transient creep response of a SAC305 single crystal along global specimen directions. This model has been calibrated using experimentally obtained transient creep response of a SAC305 single crystal specimen. The above multiscale calibrated model is then used to predict (i) the transient creep response of another SAC305 single crystal specimen and (ii) the effect of orientation (by changing one of the Euler angles) on the transient creep response of SAC305 single crystal. The grain orientation of above two SAC single crystal specimens (with respect to loading direction) were identified with orientation image mapping and then utilized in the model to estimate the resolved shear stress along the dominant slip directions. Parametric studies have also been conducted to predict the effects of the volume fraction, aspect ratio, and orientation of ellipsoidal Sn inclusions on the anisotropic transient creep response of SAC single crystals.",
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