17 Interconnect Quality and Reliability of 3D Packaging
569
17.6.4 Concluding Remarks
The TM effect of traditional interconnects has been summarized, including eutectic
Pb-Sn solder joint, and Pb-free flip chip solder joint. From the previous studies of flip
chip solder joints, we can conclude that a temperature gradient of 1000 °C/cm will
cause Pb to diffuse from hot end to cold end with Q* to be −25.3 kJ/mole, and it causes
Sn to diffuse from cold end to hot end with Q* to be +1.36 kJ/mole. The materials
driven away by thermal gradient will form void and cause reliability issue. The study
of TM of new interconnect structures in 3D IC, such as microbumps and TSVs, is
still on-going. At present, microbump is found to be more resistant to TM because of
its lower bump height (higher back stress), and stronger bonding in IMC. However,
the asymmetrical IMC growth will occur inside microbumps under a temperature
gradient. The study of TM in TSV is few. We can only conclude from precious study
of pure Cu that 5 °C difference for a 10 μm long TSV will induce TM. Finally,
the use of Si interposer will cause new TM issue due to thermal crosstalk between
the horizontal dies. It is a new reliability issue due to heterogeneous integration of
various chips on a common interposer of good thermal conduction.
Acknowledgements The editors would like to thank Indranath Dutta from Washington State
University and Tae-Kyu Lee from Portland State University for their critical review of this chapter.
References
1. K.N. Tu, Reliability challenges in 3D IC packaging technology. Microelectron. Reliab. 51(3),
517–523 (2011)
2. Y. Wang, I.M. De Rosa, K.N. Tu, Size effect on ductile-to-brittle transition in Cu-solder-Cu
micro-joints, in 2015 Proceedings of 65th Electronic Components and Technology Conference
(2015), pp. 632–639
3. S.F. Choudhury, L. Ladani, Grain growth orientation and anisotropy in Cu 6 Sn 5 intermetallic:
nanoindentation and electron backscatter diffraction analysis. J. Electron. Mater. 43(4), 996–
1004 (2014)
4. K. Sakuma, K. Sueoka, S. Kohara, K. Matsumoto, H. Noma, T. Aoki, Y. Oyama, H. Nishiwaki,
P.S. Andry, C.K. Tsang, J.U. Knickerbocker, Y. Orii, IMC bonding for 3D interconnection, in
2010 Proceedings of 60th Electronic Components and Technology Conference (2010), pp. 864–
871
5. J.F. Li, P. Agyakwa, C.M. Johnson, Interfacial reaction in Cu/Sn/Cu system during the transient
liquid phase soldering process. Acta Mater. 59(3), 1198–1211 (2011)
6. H.Y. Chuang, T.L. Yang, M.S. Kuo, Y.J. Chen, J.J. Yu, C.C. Li, C.R. Kao, Critical concerns in
soldering reactions arising from space confinement in 3-D IC packages. IEEE Trans. Device
Mater. Reliab. 12(2), 233–240 (2012)
7. S.J. Wang, L.H. Hsu, N.K. Wang, C.E. Ho, EBSD investigation of Cu–Sn IMC microstructural
evolution in Cu/Sn–Ag/Cu microbumps during isothermal annealing. J. Electron. Mater. 43(1),
219–228 (2014)
8. K. Zeng, R. Stierman, T.C. Chiu, D. Edwards, K. Ano, K.N. Tu, Kirkendall void formation in
eutectic SnPb solder joints on bare Cu and its effect on joint reliability. J. Appl. Phys. 97(2),
24508 (2005)
569
17.6.4 Concluding Remarks
The TM effect of traditional interconnects has been summarized, including eutectic
Pb-Sn solder joint, and Pb-free flip chip solder joint. From the previous studies of flip
chip solder joints, we can conclude that a temperature gradient of 1000 °C/cm will
cause Pb to diffuse from hot end to cold end with Q* to be −25.3 kJ/mole, and it causes
Sn to diffuse from cold end to hot end with Q* to be +1.36 kJ/mole. The materials
driven away by thermal gradient will form void and cause reliability issue. The study
of TM of new interconnect structures in 3D IC, such as microbumps and TSVs, is
still on-going. At present, microbump is found to be more resistant to TM because of
its lower bump height (higher back stress), and stronger bonding in IMC. However,
the asymmetrical IMC growth will occur inside microbumps under a temperature
gradient. The study of TM in TSV is few. We can only conclude from precious study
of pure Cu that 5 °C difference for a 10 μm long TSV will induce TM. Finally,
the use of Si interposer will cause new TM issue due to thermal crosstalk between
the horizontal dies. It is a new reliability issue due to heterogeneous integration of
various chips on a common interposer of good thermal conduction.
Acknowledgements The editors would like to thank Indranath Dutta from Washington State
University and Tae-Kyu Lee from Portland State University for their critical review of this chapter.
References
1. K.N. Tu, Reliability challenges in 3D IC packaging technology. Microelectron. Reliab. 51(3),
517–523 (2011)
2. Y. Wang, I.M. De Rosa, K.N. Tu, Size effect on ductile-to-brittle transition in Cu-solder-Cu
micro-joints, in 2015 Proceedings of 65th Electronic Components and Technology Conference
(2015), pp. 632–639
3. S.F. Choudhury, L. Ladani, Grain growth orientation and anisotropy in Cu 6 Sn 5 intermetallic:
nanoindentation and electron backscatter diffraction analysis. J. Electron. Mater. 43(4), 996–
1004 (2014)
4. K. Sakuma, K. Sueoka, S. Kohara, K. Matsumoto, H. Noma, T. Aoki, Y. Oyama, H. Nishiwaki,
P.S. Andry, C.K. Tsang, J.U. Knickerbocker, Y. Orii, IMC bonding for 3D interconnection, in
2010 Proceedings of 60th Electronic Components and Technology Conference (2010), pp. 864–
871
5. J.F. Li, P. Agyakwa, C.M. Johnson, Interfacial reaction in Cu/Sn/Cu system during the transient
liquid phase soldering process. Acta Mater. 59(3), 1198–1211 (2011)
6. H.Y. Chuang, T.L. Yang, M.S. Kuo, Y.J. Chen, J.J. Yu, C.C. Li, C.R. Kao, Critical concerns in
soldering reactions arising from space confinement in 3-D IC packages. IEEE Trans. Device
Mater. Reliab. 12(2), 233–240 (2012)
7. S.J. Wang, L.H. Hsu, N.K. Wang, C.E. Ho, EBSD investigation of Cu–Sn IMC microstructural
evolution in Cu/Sn–Ag/Cu microbumps during isothermal annealing. J. Electron. Mater. 43(1),
219–228 (2014)
8. K. Zeng, R. Stierman, T.C. Chiu, D. Edwards, K. Ano, K.N. Tu, Kirkendall void formation in
eutectic SnPb solder joints on bare Cu and its effect on joint reliability. J. Appl. Phys. 97(2),
24508 (2005)