Transient Liquid Phase Bonding as a Potential Substitute for Soldering with HighLead Alloys

1
Transient Liquid Phase Bonding as a Potential
Substitute for Soldering with High-Lead
Alloys A.A. Kodentsov Laboratory of Materials
and Interface Chemistry, Eindhoven University
of Technology,
The Netherlands
2

• 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 !

3
Liquidus projection of the Zn-Al-Mg system
Ternary eutectic at 343 ?C
4
The binary Bi Ag phase diagram
5
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

6
Transient Liquid Phase (TLP) Bonding
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 !
7
The effect of Ni additives in the Cu-substrate
on the interfacial reaction with Sn
8
The binary Cu Sn phase diagram
9
The binary Cu Sn phase diagram
215 ?C
10
Diffusion zone morphology developed between Cu
and Sn after reaction at 215 ?C in vacuum for 225
hrs
In the ?-Cu6Sn5
11
Reaction zone developed between Sn and Cu 1at.
Ni alloy after annealing at 215 ?C for 400 hrs
pores !!!
12
Reaction zone developed between Sn and Cu 5at.
Ni alloy after annealing at 215 ?C for 400 hrs
No ?-Cu3Sn was detected!
13
Isothermal sections through the Sn-Cu-Ni phase
diagram
P. Oberndorff, 2001
C.H. Lin, 2001
235 ?C
240 ?C
14
215 ?C 1600 hrs vacuum
15
The binary Cu Sn phase diagram
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Part of the Cu-Sn phase diagram in the vicinity
of the ? ? ?/ transition
Simple Superlattice
Long-Period Superlattice
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Cu5Ni
(Cu,Ni)6Sn5
250 ?C
Kirkendall plane (s)
Cu5Ni
Cu5Ni
Cu5Ni
Cu5Ni
250 ?C
Ag
Cu5Ni
18
Binary phase diagram Ni-Bi
250 ?C
19
250 ?C 200 hrs vacuum
20
250 ?C 200 hrs vacuum
21
Ni
NiBi3
280 ?C
Kirkendall plane (s)
Cu5Ni
Ni
Ni
Ni
280 ?C
Ag
Cu5Ni
Ni
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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 !

23
Diffusion zone morphology developed between Cu
and Sn after reaction at 215 ?C in vacuum for 225
hrs
24
Parabolic growth of the Cu-Sn intermetallic
layers in the binary diffusion couples at 215 ?C
1.58 x 10-16 m2/s
7.55 x 10-17 m2/s
25
Diffusion zone morphology developed between Cu
and Sn after reaction at 215 ?C in vacuum for 225
hrs
26
Determination of the ratio of intrinsic
diffusivities of species in line-compounds
27
Diffusion zone morphology developed between Cu
and Sn after reaction at 215 ?C in vacuum for 225
hrs
In the ?-Cu6Sn5
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The Cu3Ti type lattice (oP 8 ), the basic
structure of the long-period superstucture of the
?-Cu3Sn
The hexagonal analog of L12-structure of Cu3Au !
Ti
Cu
View down 010
29
The basic structure (oP 8 )
The hexagonal analog of the Cu3Au!

• Sn has 12 Cu NN
• Cu has 4 Sn and 8 Cu NN
• There are no Sn - Sn NN

c0
b0
a0

• In the Long-Period Superstructure of ?-Cu3Sn
  (oC80 ) antiphase shifts occur at every fifth
  period along the b0-axis

(a2a0 b10b0 cc0)
Projection onto (001) plane
30
The ordered Cu3Au rule
L12 - type structure (A3B)

• The nearest neighbour (NN) arrangement of A-atoms

• The nearest neighbour arrangement of B-atoms

31
Reaction zone developed between Sn and Cu after
annealing at 215 ?C for 400 hrs
markers !!!
32
Reaction zone developed between Sn and Cu after
annealing at 215 ?C for 400 hrs
33
Reaction zone developed between Sn and Cu 1at.
Ni alloy after annealing at 215 ?C for 400 hrs
pores !!!
34
Reaction zone developed between Sn and Cu 5at.
Ni alloy after annealing at 215 ?C for 400 hrs
No ?-Cu3Sn was detected!
35
Isothermal sections through the Sn-Cu-Ni phase
diagram
P. Oberndorff, 2001
C.H. Lin, 2001
235 ?C
240 ?C
36
Reaction zone developed between Sn and Cu 1at.
Ni alloy after annealing at 215 ?C for 400 hrs
37
Isothermal section through the Sn-Cu-Ni phase
diagram at 235 ?C. (P. Oberndorff, Ph. D.
Thesis, Eindhoven University of Technology, The
Netherlands, 2001)
Cu 1at. Ni
38
Isothermal section through the Sn-Cu-Ni phase
diagram at 240 ?C. (C.H. Lin, Master Thesis,
National Tsing-Hua University, Republic of China,
2001)
Cu 1at. Ni
39
Reaction zone developed between Sn and Cu 5at.
Ni alloy after annealing at 215 ?C for 400 hrs
40
Isothermal section through the Sn-Cu-Ni phase
diagram at 235 ?C. (P. Oberndorff, Ph. D.
Thesis, Eindhoven University of Technology, The
Netherlands, 2001)
Cu 5at. Ni
41
Isothermal section through the Sn-Cu-Ni phase
diagram at 240 ?C. (C.H. Lin, Master Thesis,
National Tsing-Hua University, Republic of China,
2001)
Cu 5at. Ni
42
Diffusion zone morphology developed between Cu
and Sn after reaction at 215 ?C in vacuum for 225
hrs
In the ?-Cu6Sn5
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215 ?C 1600 hrs vacuum
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The binary Cu Sn phase diagram
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The NiAs- type lattice the basic structure of the
?-Cu6Sn5
hP 4
tetrahedral hole
octahedral hole
trigonal hole
46
Pictorial view of the NiAs (hP4 ) structure
Ni
As
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Pictorial view of the NiAs (hP4 ) structure

• Ni has 6 As NN

A
C

• As is surrounded by 6 Ni

A
B
A
C

• The As octahedra share faces normal to the c-axis

A
B
A

• The Ni-atoms are direct neighbours along 001
  direction

48

• The composition Cu6Sn5 is achieved by adding
  additional Cu-atoms in one tenth of the
  tetrahedral interstices in the hexagonal
  Sn-sublattice

Cu
Sn
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1. Ordering of the excess Cu -atoms in the
tetrahedral interstices results in the ?/-
Long-Period Superlattice
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2. The excess Cu-atoms occupy the tetrahedral
interstices at random
Sn
Type A
Type B

• An arrangement of the unit cells along the
  three principle axes in the sequence ABABAABABA
  results in the supercell of the ?/-phase

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215 ?C
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Binary phase diagram Ni-Bi
250 ?C
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250? C 400 hrs vacuum
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250? C 400 hrs vacuum
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Reaction zone developed between Sn and Cu 5at.
Ni alloy after annealing at 215 ?C for 400 hrs
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The reaction zone developed in the incremental
couple based on Cu and ?-Cu6Sn5 (215 ?C 225 hrs)
Unstable Kirkendall plane ?
61
The Cu3Ti type lattice (oP 8 ), the basic
structure of the long-period superstucture of the
?-Cu3Sn
The hexagonal analog of L12-structure of Cu3Au !
Ti
Cu
View down 010
62
The basic structure (oP 8 )
The hexagonal analog of the Cu3Au!

• Sn has 12 Cu NN
• Cu has 4 Sn and 8 Cu NN
• There are no Sn - Sn NN

c0
b0
a0

• In the Long-Period Superstructure of ?-Cu3Sn
  (oC80 ) antiphase shifts occur at every fifth
  period along the b0-axis

(a2a0 b10b0 cc0)
Projection onto (001) plane