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On Pb-free (solder) Interconnections for High-Temperature Applications A.A. Kodentsov

On Pb-free (solder) Interconnections for High-Temperature Applications A.A. Kodentsov Laboratory of Materials and Interface Chemistry, Eindhoven University of Technology, The Netherlands. Cross-sectional view of flip-chip package.

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On Pb-free (solder) Interconnections for High-Temperature Applications A.A. Kodentsov

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  1. On Pb-free (solder) Interconnections for High-Temperature Applications A.A. Kodentsov Laboratory of Materials and Interface Chemistry, Eindhoven University of Technology, The Netherlands

  2. Cross-sectional view of flip-chip package

  3. There is still no obvious (cost-effective) replacement for high-lead, high melting ( 260 - 320 C) solder alloys • It is not possible to adjust (to increase above 260 C) liquidus temperature of any existing Sn-based solder alloys by simple alloying with environmentally friendly and inexpensive elements • Therefore, in the quest for (cost-effective) replacements of the high-lead solders, attention has to be turned towards different base metals as well as the exploration of alternative joining techniques !

  4. Liquidus projection of the Zn-Al-Mg system Ternary eutectic at ~ 343 C

  5. The binary Bi – Ag phase diagram

  6. TMS 2008 Annual Meeting, New Orleans March 9-13, 2008 “Interfacial behaviour between Bi-Ag Solders and the Ni -substrates” (Hsin-Yi Chuang and Jenn-Ming Song) “Interfacial Reaction and Thermal Fatigue of Zn-4wt.%Al-1wt.% Cu/Ni Solder Joints” by Y. Takaku, I. Ohnima, Y. Yamada, Y. Yagi, I. Nakagawa, T. Atsumi, K. Ishida

  7. The binary Bi – Ag phase diagram

  8. The DSC heating curve of the eutectic Bi-Ag alloy

  9. Solidification microstructure of the Bi-Ag eutectic alloy (BEI)

  10. Ag Solidification microstructure of the Bi-Ag hypo-eutectic alloy (BEI)

  11. Transient Liquid Phase (TLP) Bonding solid solid interlayer(s) solid • The interlayers are designed to form a thin or partial layer of a transient liquid phase (TLP) to facilitate bonding via a brazing-like process in which the liquid disappears isothermally • In contrast to conventional brazing, the liquid disappears, and a higher melting point phase is formed at the bonding temperature

  12. Transient Liquid Phase (TLP) Bonding solid solid solid solid product T= const liquid solid solid solid T= const Diffusion, Reaction solid Any system wherein a liquid phase disappears by diffusion, reaction (amalgamation), volatilization, or other processes is a candidate for TLP bonding !

  13. The effect of Ni additives in the Cu-substrate on the interfacial reaction with Sn

  14. The binary Cu – Sn phase diagram

  15. The binary Cu – Sn phase diagram 215 C

  16. Diffusion zone morphology developed between Cu and Sn after reaction at 215 C in vacuum for 225 hrs In the -Cu6Sn5:

  17. Reaction zone developed between Sn and Cu 1at.% Ni alloy after annealing at 215 C for 400 hrs pores !!!

  18. Reaction zone developed between Sn and Cu 5at.% Ni alloy after annealing at 215 C for 400 hrs No pores !!! No -Cu3Sn was detected!

  19. Isothermal sections through the Sn-Cu-Ni phase diagram P. Oberndorff, 2001 C.H. Lin, 2001 235 C 240 C

  20. Reaction zone developed between Sn and Cu 5at.% Ni alloy after annealing at 215 C for 400 hrs No pores !!! No -Cu3Sn was detected!

  21. Diffusion zone morphology developed between Cu and Sn after reaction at 215 C in vacuum for 225 hrs In the -Cu6Sn5:

  22. 215 C; 1600 hrs; vacuum

  23. The binary Cu – Sn phase diagram

  24. Part of the Cu-Sn phase diagram in the vicinity of the   / transition Simple Superlattice Long-Period Superlattice

  25. -phase? 215 C

  26. Cu5Ni Sn Cu5Ni (Cu,Ni)6Sn5 Sn Sn (Cu,Ni)6Sn5 Cu5Ni Cu5Ni (Cu,Ni)6Sn5 250 C Kirkendall plane (s) Cu5Ni Cu5Ni Cu5Ni Cu5Ni 250 C Ag Cu5Ni Cu5Ni

  27. Binary phase diagram Ni-Bi 250 C

  28. 250 C; 200 hrs; vacuum

  29. 250 C; 200 hrs; vacuum

  30. Parabolic growth of the NiBi3 intermetallic layers in the binary diffusion couples at 250 C kp= 5.2 x 10-14 m2/s

  31. Component Knoop hardness (kgf*mm-2) Ni 113.8 NiBi3 113.4 NiBi 264.8 Cu 79.2 Cu3Sn 464.5 Cu6Sn5 420.8 Knoop microhardness test on Ni-Bi and Cu-Sn systems

  32. Ni Bi Ni NiBi3 280 C Kirkendall plane (s) Cu5Ni Ni Ni

  33. 250 C; 400 hrs; vacuum Kirkendall plane(s)

  34. Ni Bi Ni NiBi3 Bi Bi NiBi3 Ni Ni NiBi3 280 C Kirkendall plane (s) Cu5Ni Ni Ni Ni 280 C Ag Cu5Ni Ni

  35. Concluding Remarks • It is not possible to adjust (to increase above 260 C) liquidus temperature of any existing Sn-based solder alloys by simple alloying with environmentally friendly and inexpensive elements • Therefore, in the quest for (cost-effective) substitutes for high-lead solders, attention has to be turned towards different base metals as well as the exploration of alternative joining techniques ! • Through the judicious selection of Sn- or Bi-based interlayer between under bump metallization and substrate pad, (cost-effective) Transient Liquid Phase (TLP) Bonding can be achieved at ~ 250-280 C, and the resulting joints are capable of service at elevated temperatures ! • The TLP Bonding should be taken into further consideration as substitute for the high-lead soldering !

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