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: Contribution to journalArticle

  • 17 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
solders
Electron diffraction
Grain boundaries
Cracks
Ball grid arrays
microstructure
Microstructure
Grain growth
diffraction
Crystal orientation
Microscopic examination
electrons
Diffraction
Metals
Recovery
X rays
Temperature
cracks
grain boundaries

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: Contribution to journalArticle

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