Transcript Document
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
•
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 !
Liquidus projection of the Zn-Al-Mg system Ternary eutectic at ~ 343
C
The binary Bi – Ag phase diagram
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 K. Ishida / Ni Solder Joints” by Y. Takaku, I. Ohnima, Y. Yamada, Y. Yagi, I. Nakagawa, T. Atsumi,
The binary Bi – Ag phase diagram
The DSC heating curve of the eutectic Bi-Ag alloy
Solidification microstructure of the Bi-Ag eutectic alloy (BEI)
Solidification microstructure of the Bi-Ag hypo-eutectic alloy (BEI) Ag
solid Transient Liquid Phase (TLP) Bonding 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
solid Transient Liquid Phase (TLP) Bonding solid T = const liquid solid solid solid T = const Diffusion, Reaction solid solid product solid Any system wherein a liquid phase disappears by diffusion, reaction (amalgamation), volatilization, or other processes is a candidate for TLP bonding !
The effect of Ni additives in the Cu-substrate on the interfacial reaction with Sn
The binary Cu – Sn phase diagram
The binary Cu – Sn phase diagram 215
C
Diffusion zone morphology developed between Cu after reaction at 215
C in vacuum for 225 hrs and Sn
In the
-Cu
6
Sn
5
:
J Sn J Cu
D Sn D Cu
V Cu V Sn
1.6
Reaction zone developed between Sn and Cu 1at.% Ni alloy after annealing at 215
C for 400 hrs
pores !!!
Reaction zone developed between Sn and Cu 5at.% Ni alloy after annealing at 215
C for 400 hrs No pores !!!
No
-Cu 3 Sn was detected!
Isothermal sections through the Sn-Cu-Ni phase diagram P. Oberndorff, 2001 C.H. Lin, 2001 235
C 240
C
Reaction zone developed between Sn and Cu 5at.% Ni alloy after annealing at 215
C for 400 hrs No pores !!!
No
-Cu 3 Sn was detected!
Diffusion zone morphology developed between Cu after reaction at 215
C in vacuum for 225 hrs and Sn
In the
-Cu
6
Sn
5
:
J Sn J Cu
D Sn D Cu
V Cu V Sn
1.6
215
C; 1600 hrs; vacuum
The binary Cu – Sn phase diagram
Part of the Cu-Sn phase diagram in the vicinity of the
/ transition Simple Superlattice Long-Period Superlattice
215
C
phase ?
Cu5Ni Sn Cu5Ni Sn Ag Sn Cu5Ni 250
C 250
C Cu5Ni Cu5Ni (Cu,Ni) 6 Sn 5 Kirkendall plane (s) Cu5Ni (Cu,Ni) 6 Sn 5 (Cu,Ni) 6 Sn 5
Binary phase diagram Ni-Bi 250
C
250
C; 200 hrs; vacuum
250
C; 200 hrs; vacuum
Parabolic growth of the NiBi 3 intermetallic layers in the binary diffusion couples at 250
C k p = 5.2 x 10 -14 m 2 /s
50000 40000 30000 20000 10000 0 0 50 100 time (hr) 150 200 250
Knoop microhardness test on Ni-Bi and Cu-Sn systems Component Knoop hardness (kgf*mm -2 ) Ni NiBi 3 NiBi Cu Cu 3 Sn Cu 6 Sn 5 113.8
113.4
264.8
79.2
464.5
420.8
Ni Bi 280
C Ni Ni NiBi 3 Kirkendall plane (s)
250
C; 400 hrs; vacuum Kirkendall plane(s)
Ni Bi Ni Bi Ag Bi Ni 280
C 280
C Ni Ni NiBi 3 Kirkendall plane (s) NiBi 3 Ni NiBi 3
0.9
Liquidus surface 1 Ag 0.7
0.8
0.5
x( A g) 0.3
0.4
0.6
LIQUID 0.2
0.2
Ni x(Bi) x(Bi) FCC_A1 LIQUID BINI BI3NI Bi
0.9
250 C 1 Ag 0.7
0.8
0.5
x( A g) R 0.3
O M B 0.2
O _ A 7 + B I3 N I+ FC C _ A 1 0.2
0.4
0.6
Bi BI3NI+BINI+FCC_A1 x(Ni) x(Ni) FCC_A1+BINI+FCC_A1 Ni
0.9
268 C 0.7
0.5
x( A g) B I3 N I+ F C C _ A 1 + LI Q U ID 0.6
0.8
0.3
0.4
1 Ag 0.2
LIQUID+BI3NI 0.2
BI3NI+BINI+FCC_A1 Bi LIQUID+BI3NI+RHOMBO_A7 x(Ni) x(Ni) FCC_A1+FCC_A1+BINI Ni
268 C LIQUID+FCC_A1+BI3NI LIQUID LIQUID+BI3NI LIQUID +RHOMBO_A7 LIQUID+BI3NI+RHOMBO_A7 Bi x(Ni) x(Ni)
Concluding Remarks
• It is not possible to adjust and inexpensive elements (to increase above 260
C) liquidus temperature of any existing Sn-based solder alloys by simple alloying with environmentally friendly • Therefore, in the quest for (cost-effective) substitutes high-lead solders , attention has to be turned towards different base metals as well as the exploration of alternative joining techniques !
for • 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 !