Double tricrystal nucleation behavior in Pb-free BGA solder joints

• Autores: Jing Han, Fu Guo
• Localización: Microelectronics reliability, ISSN 0026-2714, Nº. 98, 2019, págs. 1-9
• Idioma: inglés
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• Resumen

  • The orientations of tin grains in a solder joint have a significant influence on its inhomogeneous deformation behavior under thermomechanical fatigue (TMF). In this paper, the tin orientations in as-solidified BGA joints were observed in detail by electron backscattering diffraction (EBSD). Double twinning of tin in the process of solidification was observed in the Sn-based solder joints. Although the morphologies of these twinned microstructures differed (beachball or intertwined), four orientations of tin grains, with each twin grain sharing a corporate [100] or [010] axis, were observed and analyzed in these systems. The results showed that the difference in orientation between the two groups of double tricrystals was in the range of 80° to 90°. The accurate misorientations were calculated to be 79.1°, 82.9° and 86.5°, corresponding to 57.2° and 62.8°. In a joint comprising 9 grains, there were 3 groups of double tricrystals. A joint comprising two grains, involving 55–65° tricrystal misorientations and a corporate [100] rotation axis, was practically a tricrystal. The joints exhibiting 4–9 grains with misorientations close to 60° (with a [100] or [010] axis) and 85° were composed of 1–3 groups of double tricrystals.