Characterization of recrystallization and microstructure evolution in lead-free solder joints using EBSD and 3D-XRD

Bite Zhou, Thomas R. Bieler, Tae Kyu Lee, Wenjun Liu

    Research output: Research - peer-reviewArticle

    • 14 Citations

    Abstract

    Development of vulnerable high-angle grain boundaries (and cracks) from low-angle boundaries during thermal cycling by means of continuous recrystallization was examined in fine-pitch ball grid array (BGA) packages with Sn-3.0Ag-0.5Cu (wt.%) (SAC305) lead-free solder joints. Electron backscatter diffraction (EBSD) and differential-aperture x-ray microscopy (DAXM or 3D-XRD) were used for surface and subsurface characterization. A large number of subgrain boundaries were observed in the parent orientation using both techniques. However, unlike studies of anisotropic deformation in noncubic metals at much lower homologous temperatures, no streaked diffraction peaks were observed in DAXM Laue patterns within each 1 μm3 voxel after thermal cycling, suggesting that geometrically necessary dislocations (GNDs) are effectively absorbed by the preexisting subgrain boundaries. Storage at room temperature (0.6T m) prior to DAXM measurement may also facilitate recovery processes to reduce local GND contents. Heterogeneous residual elastic strains were found near the interface between a precipitated Cu 6Sn5 particle and the Sn grain, as well as near particular subgrain boundaries in the parent orientation. Grain boundary migration associated with recrystallization resulted in regions without internal strains, subgrain boundaries, or orientation gradients. Development of new grain orientations by continuous recrystallization and subsequent primary recrystallization and grain growth occurred in the regions where the cracks developed. Orientation gradients and subgrain structure were observed within newly formed recrystallized grains that could be correlated with slip systems having high Schmid factors.

    LanguageEnglish (US)
    Pages319-331
    Number of pages13
    JournalJournal of Electronic Materials
    Volume42
    Issue number2
    DOIs
    StatePublished - 2013

    Profile

    Thermal cycling
    Electron diffraction
    Grain boundaries
    Cracks
    Microstructure
    Temperature
    Lead-free solders
    solders
    microstructure
    diffraction
    electrons
    Ball grid arrays
    Grain growth
    Crystal orientation
    Microscopic examination
    Diffraction
    Metals
    Recovery
    X rays
    cracks

    Keywords

    • EBSD
    • Lead-free solder
    • recrystallization
    • Sn crystal orientation
    • strain
    • synchrotron 3D-XRD

    ASJC Scopus subject areas

    • Electrical and Electronic Engineering
    • Electronic, Optical and Magnetic Materials
    • Condensed Matter Physics
    • Materials Chemistry

    Cite this

    Characterization of recrystallization and microstructure evolution in lead-free solder joints using EBSD and 3D-XRD. / Zhou, Bite; Bieler, Thomas R.; Lee, Tae Kyu; Liu, Wenjun.

    In: Journal of Electronic Materials, Vol. 42, No. 2, 2013, p. 319-331.

    Research output: Research - peer-reviewArticle

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    abstract = "Development of vulnerable high-angle grain boundaries (and cracks) from low-angle boundaries during thermal cycling by means of continuous recrystallization was examined in fine-pitch ball grid array (BGA) packages with Sn-3.0Ag-0.5Cu (wt.%) (SAC305) lead-free solder joints. Electron backscatter diffraction (EBSD) and differential-aperture x-ray microscopy (DAXM or 3D-XRD) were used for surface and subsurface characterization. A large number of subgrain boundaries were observed in the parent orientation using both techniques. However, unlike studies of anisotropic deformation in noncubic metals at much lower homologous temperatures, no streaked diffraction peaks were observed in DAXM Laue patterns within each 1 μm3 voxel after thermal cycling, suggesting that geometrically necessary dislocations (GNDs) are effectively absorbed by the preexisting subgrain boundaries. Storage at room temperature (0.6T m) prior to DAXM measurement may also facilitate recovery processes to reduce local GND contents. Heterogeneous residual elastic strains were found near the interface between a precipitated Cu 6Sn5 particle and the Sn grain, as well as near particular subgrain boundaries in the parent orientation. Grain boundary migration associated with recrystallization resulted in regions without internal strains, subgrain boundaries, or orientation gradients. Development of new grain orientations by continuous recrystallization and subsequent primary recrystallization and grain growth occurred in the regions where the cracks developed. Orientation gradients and subgrain structure were observed within newly formed recrystallized grains that could be correlated with slip systems having high Schmid factors.",
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