The Observation of Intermetallic Compound Microstructure Under Sn Whisker in Lead-free Finish

  • Yu, Chong-Hee (Honam Research Center, Electronics and Telecommunications Research Institute)
  • 발행 : 2009.06.30

초록

Sn whiskers can grow from the pure Sn and high Sn-based finish and cause the electrical shorts and failures. Even with the wealth of information on whiskers, we have neither the clear understanding of whisker growth nor methods for its prevention. In this study, the whisker grain roots which connected with intermetallic layer were analyzed by high-resolution transmission electron microscopy (HR-TEM). In the Sn-Cu plated leadframe (LF) that was stored at ambient condition for 540 days, filament-shaped whiskers were grown on the Sn-plated surface and ${\eta}'-Cu_6Sn_5$ precipitates were widely distributed along the grain boundaries at the Sn matrix. The measured of the lattice fringes at the ${\eta}'-Cu_6Sn_5$ was $4.71{\AA}$ at the coarse grain and $2.91{\AA}$ at the fine grain. The $Cu_3Sn$ which generates the tensile stresses was not observed. The formation of $Cu_6Sn_5$ precipitates and intermetallic layer were strongly related to whisker growth, but, the whisker growth tendency does not closely relate with the geometric morphology of irregularly grown intermetallic compound (lMC).

키워드

참고문헌

  1. K.N. Tu, and C,J.M. Li, "Spontaneous whisker growth on lead-free solder finishes", Mater. Sci. Eng. A, 409, 31-139, (2005).
  2. I. Sakamoto, "Whisker test methods of JEITA whisker growth mechanism for test methods", IEEE Trans. Elect. Packag. Manuf., 28, 10-16, (2005). https://doi.org/10.1109/TEPM.2005.847436
  3. K.N. Tu, Interdiffusion and reaction in bimetallic Cu-Sn thin films", Acta Metall., 21,347-354, (1973). https://doi.org/10.1016/0001-6160(73)90190-9
  4. K. Fujiwara, M. Ohtani, T. Isu and etal, "Interfacial reaction in bimetallic Sn/Cu thin films", Thin Solid Films, 70, 153-161, (1980).
  5. R. Chopra, M. Ohring and R.S. Oswald, "Low temperature compound formation in Cu/Sn thin film couples", Thin Solid Films, 94, 279-288, (1982). https://doi.org/10.1016/0040-6090(82)90490-4
  6. Boguslavsky and P. Bush, "Recrystallization principles applied to whisker growth in tin", In Proc. APEX Conf., Anaheim, (2003).
  7. G.T.T. Sheng, C.F. Hu, W.J. Choi, K.N. Tu, Y,Y, Bong, and Luu Nguyen, "Tin whiskers studied by focused ion beam imaging and transmission electron microscopy", J. Appl. Phys., 92, 64-69, (2002). https://doi.org/10.1063/1.1481202
  8. K.S. Kim, S.W. Han, and J.M. Yang, "Behavior of tin whisker formation and growth on lead-free solder plating", Thin Solid Films, 504, 350-354, (2006). https://doi.org/10.1016/j.tsf.2005.09.088
  9. N. Kuwano, Y. Jia, R. Tajima, S. Koga, S. Tsukanloto, and Y, Ohno, "Application of a focused ion beam mill to the characterisation of a microstructure in tin plating on a Fe 42wt% Ni substrate", J. Electron. Microsc., 53, 541-544, (2004). https://doi.org/10.1093/jmicro/dfh064
  10. T. Kakeshita, K. Shimizu, R. Kawanaka, and T. Hasegawa, "Grain size effect of electro-plated tin coatings on whisker growth", J. Mater. Sci., 17, 2560-2566, (1982). https://doi.org/10.1007/BF00543888
  11. B. Z. Lee, and D. N. Lee, "Spontaneous growth mechanism of tin whiskers", Acta Mater., 46, 3701-3714, (1998). https://doi.org/10.1016/S1359-6454(98)00045-7
  12. M. Dittes, P. Obemdorff: P. Crema, and V. Schroeder, "Tin whisker formation in thermal cycling conditions", IEEE, Singapore, (2003).
  13. K.-W. Moon, C.E. Johnson, M.E. Williams, O. Kongstein, C.A. Handwerker, and W.J. Boettinger, "Observed correlation of Sn oxide film to Sn whisker growth in Sn-Cu electrodeposit for Pb-free solders", J. Electron. Mater., 34, L.31-3, (2005). https://doi.org/10.1007/s11664-005-0274-3
  14. A.K. Larsson, L. Stenberg, and S. Lidin, "The Superstructure of Domain-Twinned $\eta'-Cu_{6}Sn_{5}$, Acta Cryst., 50, 636-643, (1994).
  15. C.W. Hwang, J.G Lee, K. Suganuma, and H. Mori, "Interfacial microstructure between Sn-3Ag-xBi Alloy and Cu Substrate with or without Electrolytic Ni Plating", J. Electron.Mater., 32, 52-62, (2003). https://doi.org/10.1007/s11664-003-0237-5