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A compliant and creep resistant sac al(ni) alloy - presentation
1. A Compliant and Creep
Resistant SAC-Al(Ni) Alloy
Dr. Benlih Huang, Dr. Hong-Sik Hwang,
and Dr. Ning-Cheng Lee
Indium Corporation of America
1
2. Background
• SAC solder with high Ag content needed for
thermal fatigue performance & for narrow pasty
range. IMC particles of Ag-Sn and Cu-Sn
responsible for the fatigue resistance.
• However, for high Ag SAC alloys, a greater
ductility is also desired for non-fragility.
• Addition of element which can reduce IMC
particles may improve the ductility.
2
3. Approaches
• Al reacts with both Ag and Cu, which
promises a reduction in the quantity of
Ag3Sn and Cu6Sn5, is a very capable
candidate.
• Adding Ni is reported to be beneficial, due
to its effect in suppressing the growth of
IMC scallop size and thickness on Cu.
3
4. Tests
• Tensile test
– The diameter and length of the cylinder central testing region is
0.125 inch and 2 inch, respectively.
– Crosshead speed - 0.2 inch/min.
– Yield strength, ultimate tensile strength, elongation at break, and
modulus determined.
– 5-15 specimen used for each alloy.
• SEM & EDX for microstructure
• DSC
– 10°C/min heating & cooling, between -40 & 260 °C
– 2nd heating run used for comparison
• Creep test
– Two specimen used for each combination of alloy and stress
condition.
4
5. Effect of alloy composition on yield strength
SAC(n)05-XY vs Yield Strength
SA C YS Ni0.88 A l0.96 A l0.6Ni0.04
A l0.48Ni0.04 A l0.05Ni2 A l0.19 A l2Ni0.02
A l0.15Ni0.01 A l0.2Ni0.012 A l0.3Ni0.018 A l0.15Ni0.05
A l0.073Ni0.05
7000
y = -63.742x 2 + 1059.8x + 2774.9
R2 = 0.9328
6000
5000 Yield strength increases
Yield Strength (psi)
with increasing Ag content
4000
3000
Addition of Al and Ni can
2000 result in a significantly
At Ag > 2%, Al 0.1-0.6% most reduced yield strength
1000 effective in reducing YS
High Ni also reduce YS
0
0 1 2 3 4 5
Ag % 5
6. Effect of Al addition on yield
strength of SAC(n)05-XY
Al % vs Yield Strength
(for SAC(n)05-XY, where n = 3.8-4)
7000
6000 YS of SAC405
& SAC305
Yield Strength (psi)
5000
4000 YS of SAC105 & 1505
3000 Note:
2000 All Ni ≤ 0.05%,- has no Ni
At Ag 3.8-4.0%, Ni ≤ 0.05%, Al reduces Al dominant in effect on
1000 YS most effectively at 0.1-0.6%. YS (w & w/o Ni, trends
comparable)
0
0 0.5 1 1.5 2 2.5
Al %
6
7. Effect of Ni addition on yield
strength of SAC(n)05-XY
Ni % vs Yield Strength
( for SAC(n)05-XY, where n = 3.8-4 )
6000
Addition of Ni results
in a slight decrease in
yield strength.
Yield Strength (psi)
4000
Note:
All Al ≤ 0.05% The extent of yield
Ni addition slightly reduces YS strength drop is about
2000 1/3 of Al addition
(6000 →4000)
0
0 0.5 1 1.5 2 2.5
Ni %
7
8. Effect of alloy composition on
tensile strength
SAC(n)05-XY vs Tensile Strength
SAC TS Ni0.88 Al0.96
Al0.6Ni0.04 Al0.48Ni0.04 Al0.05Ni2
Al0.19 Al2Ni0.02 Al0.15Ni0.01
Al0.2Ni0.012 Al0.3Ni0.018 Al0.15Ni0.05
Al0.073Ni0.05
10000
Tensile strength increases
with increasing Ag content
Tensile Strength (psi)
8000
The effect of Al and Ni
6000
addition not significant
4000
y = -45.527x2 + 988.47x + 4727.1
R2 = 0.8212
2000
Al & Ni not significant on TS
0
0 1 2 3 4 5
Ag %
8
9. Effect of alloy composition on
elongation at break
SAC(n)05-XY vs Elongation at Break
SAC Elongation Ni0.88
Al0.96 Al0.6Ni0.04
Al0.48Ni0.04 Al0.05Ni2
Al0.19 Al2Ni0.02
Al0.15Ni0.01 Al0.2Ni0.012
Al0.3Ni0.018 Al0.15Ni0.05
Al0.073Ni0.05 Linear (SAC Elongation)
25
Elongation at break is
Elongation at Break (%)
20 insensitive to Ag content
15
Adding Al or Ni does cause
10 a decrease in elongation at
break
5
Al & Ni reduce elongation at break
0
0 1 2 3 4 5
Ag %
9
10. Effect of alloy composition on modulus
SAC(n)05-XY vs Modulus
SA C M o dulus Ni0.88 A l0.96 A l0.6Ni0.04
A l0.48Ni0.04 A l0.05Ni2 A l0.19 A l2Ni0.02
A l0.15Ni0.01 A l0.2Ni0.012 A l0.3Ni0.018 A l0.15Ni0.05
A l0.073Ni0.05
3500
3000
Modulus increases with
2500
increasing Ag content
Addition of Al and Ni results
Modulus (ksi)
2000
in a slight decrease in
1500 y = -17.945x 2 + 291.13x + 1760.5
modulus
R2 = 0.8759
1000
500
Al slightly reduce modulus
0
0 1 2 3 4 5
Ag % 10
12. EDX graph on gray (top) and
dark (bottom) IMC particles of
Sn94.43Ag3.97Cu0.64Al0.96
The weight ratio of Ag to Al is
about 6:1, and the weight ratio
of Cu to Al is about 3:1 here.
Therefore, at Al content of
0.96%, most of the Ag and Cu in
this alloy
Sn94.43Ag3.97Cu0.64Al0.96
will be drained from the solder
matrix and be associated with
Al.
12
13. SEM micrograph of Sn94.49Ag3.99Cu0.64Ni0.88
200X 2000X
The gray needle was identified as Many bright Ag3Sn IMC particles in the
(Ni,Cu)3Sn4 form of micron-sized round particles or
short rods
13
14. Sn94.49Ag3.99Cu0.64Ni0.88
The weight ratio of Ni to Cu is about 2.3:1. With
Ni concentration being 0.88%, the Cu
entrapped in the (Ni,Cu)3Sn4 is estimated to be
about 0.4%. In other words, Cu will be highly
depleted by Ni-Cu-Sn IMC formation. As a
result, the SAC matrix composition here is
expected to be greatly skewed toward near-
eutectic Sn-Ag structure.
14
15. SEM micrograph of
Sn94.78Ag4.0Cu0.58Al0.6Ni0.04
1000X 5000X
The bright particles are Ag3Sn
IMC.
The large gray particle is Al9.4-Ag90.6, indicating the
extraordinary ability of Al to drain Ag from SAC matrix.
15
17. DSC thermographs (second run heating) of SAC387,
SAC+Al (Sn94.43Ag3.97Cu0.64Al0.96), and SAC+Ni
(Sn94.49Ag3.99Cu0.64Ni0.88)
Ag and Cu in this SAC+Al alloy mostly
drained from the solder matrix and be
associated with Al. Thus, instead of
forming near-ternary-eutectic SAC
composition, it very likely forms near-
SnAg eutectic and near-Sn-Cu eutectic
structures, as suggested by the two peaks
observed in DSC.
Cu is virtually depleted from SAC+Ni due
to the formation of (Ni,Cu)3Sn4.
Consequently the copper-striped matrix
becomes near-eutectic SnAg structure.
17
18. DSC thermographs (second run heating) of SAC405 and
SAC405+Al(Ni) alloys, including Sn95.2Ag4Cu0.64Al0.19,
Sn94.78Ag4.0Cu0.58Al0.6Ni0.04, and Sn94.43Ag3.97Cu0.64Al0.96
increase in Al content
will drain more Ag
and Cu from the SAC
system. This in turn
causes a shift of
SAC405 from near
ternary eutectic
composition towards
combination of
eutectic SnAg and
eutectic SnCu.
18
19. Liquidus temperature of SAC+Al(Ni) alloys
as a function of Al content
Liquidus vs Al %
228
Liquidus Temp (deg C)
226
At Al content greater than 0.6%,
224 the liquidus temperature
increases more rapidly with
222 continued increase in Al content
220
218
0 0.3 0.6 0.9 1.2
Al w t %
19
20. DSC thermographs (second run heating) of SAC105, SAC1505, and
SAC405+Al+Ni alloys, including Sn95.3Ag3.92Cu0.62Al0.15Ni0.05 and
Sn94.78Ag4.0Cu0.58Al0.6Ni0.04
Compared with SAC105
and SAC1505, the
SAC405+Al+Ni alloys
exhibit both a lower liquidus
temperature and a narrower
pasty range.
20
21. Effect of alloy on steady creep rate
Steady Creep Rate vs Stress
SA C 105 SA C1505
The yield strength of both
SnA g3.92Cu0.62A l0.15Ni0.05 SnA g4.0Cu0.58A l0.6Ni0.04
SAC405+Al+Ni alloys is much lower
SA C305 SA C405
than SAC405 & 305, and is similar to
that of SAC105 and SAC1505
1.E-04
SAC305
However, both SAC405+Al+Ni alloys
1.E-05 exhibit a steady creep rate lower than
Steady Creep Rate (1/sec)
SAC105 that of SAC105 and SAC1505,
1.E-06 comparable with SAC305, and are
SAC+Al0.6Ni0.04 higher than SAC405.
SAC1505
1.E-07
SAC405
Thus, new alloy exhibit SAC305 creep
rate but SAC105 softness.
1.E-08
SAC+Al0.15Ni0.05
1.E-09
10 20 30 40
Stress (MPa)
21
22. Discussion
• Softening attributed to
– Large no. of small hard Ag3Sn converted into small
no. of large soft non-stoichiometric Ag-Al IMC
particles
– Reduction in Cu6Sn5 particles due to formation of
non-stoichiometric Al-Cu and large (Ni,Cu)3Sn4 IMC
particles
• Creep rate
– Non-stoichiometric IMC particle or large particle,
although less effective in increasing yield strength,
are considered still harder than Sn, therefore are
expected to provide resistance in creep.
22
23. Conclusion
• Addition of Al into SAC alloys reduces the number of hard Ag3Sn
and Cu6Sn5 IMC particles, and forms larger, softer non-
stoichiometric AlAg and AlCu particles. This results in a significant
reduction in yield strength, and also causes some moderate
increase in creep rate.
• For high Ag SAC alloys, adding Al 0.1-0.6% to SAC alloys is most
effective in softening, and brings the yield strength down to the level
of SAC105 and SAC1505, while the creep rate is still maintained at
SAC305 level.
• Addition of Ni results in formation of large (Ni,Cu)3Sn4 IMC particles
and loss of Cu6Sn5 particles. This also causes softening of SAC
alloys, although to a less extent than that of Al addition.
• For SAC+Al+Ni alloys, the pasty range and liquidus temperature
°
are about 4°C less than that of SAC105 or SAC1505 if the added
quantity is less than about 0.6%.
• Thus, new alloys exhibit SAC305 creep rate, SAC105 softness, &
lower mp than SAC105.
23
