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Influence of thermal cycling on shear strength of
Cu Sn3.5AgIn Cu joints with various content
of indium   Pavol Šeboa, Peter Švecb,
Dušan Janickovicb, Pavol Štefánika   a
Institute of Materials and Machine Mechanics,
SAS, Racianska 75, 831 02 Bratislava, Slovakia b
Institute of Physics, SAS, Dúbravská cesta 9, 845
11 Bratislava, Slovakia
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• Subject of study
• Published results
• Aim of this contribution
• Conclusions

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COST 531 Lead-free solder materials From many
material combinations for study of low
temperature lead-free solder we chose on the base
of literature data Sn-Ag based alloys
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Subject of study

• To characterize the effect of indium addition in
  lead-free Sn 3.5 Ag solder on its
• phase transition temperature,
• wetting of copper substrate
• shear strength of copper joints.

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Published results
Part of the results were presented at the COST
531 meetings in Lausanne and Genoa Most of the
results were published in Kovove Mater. 43 (2005)
202-209
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Differential scanning calorimetry
?Hm, ?Hf , Txm, Txf are for enthalpy changes
and onset temperatures of melting and freezing of
relevant solders, respectively
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Indium concentration dependence of contact angle
of solders on Cu substrate for various
temperatures
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Shear strength of Cu-solder-Cu joints
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Cu-solder-CuCF composite joint
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Shear strenght of Cu-solder-CuCF composite joint
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Conclusions

• Indium decreases the onset temperature and
  etnhalpy changes of melting and freezing
• Wetting angle between copper substrate and
  SnAgIn solder decreases with increasing amount
  of In and wetting temperature and time
• Joint strength moderately decreases with
  increasing joining temperature and the amount of
  In. Failure of joints occures in solder.
• Joint stregth of Cu-CF composite is lower than
  that of Cu-Cu due to poor adhesion between Cu and
  CF layer where the failure is occured.

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• The aim of this paper is
•     to recognize the microstructure changes in
  Sn-3,5Ag solders and joints of Cu-Cu
•  to identified the intermetallic compounds in the
  Cu solder Cu pad interfaces
• to determine the effect of thermal cycling on the
  degradation in residual shear strength of Cu
  Sn-3.5Ag-In Cu joints
• with various amount of indium.

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Materials Solders Lead-free solder alloys
contained 0 (1) 6.5(2) and 9(3) mass
In    Produced in bulk form (for wetting
experiments) and by rapid quenching in the ribbon
form 5 mm wide and 0.05mm thick (for
Cu-solder-Cu joints)   Substrates Cu plates
prior to placing with solder into the holder and
furnace were daubed with rosin moderately
activated flux.
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Joints Joints-four for each set of
cycling-were prepared at 280C and 1800 s in the
air atmosphere  One specimen was used for
microstructure study, three for shear strength
measurement   Cycling Cycling was done in air
atmosphere in the temperature interval RT
150C  Number of cycles 100 200 500 and
1000. Also in interval RT-180C 500 cycles
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• Investigation (of solders, joints, interface in
  joint) 
• Microstructure light and scanning electron
  microscopy (SEM), energy disperse X-ray analyzer
  (EDAX),
• X-ray diffraction (CuK? radiation)
•   Influence of thermal treatment on solders
• Resistometry planar furnace with 4 probes
  method
•  Shear strength Zwick testing machine, push-off
  method

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Results Microstructure of original solders
Solder Sn-3.5Ag
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Solder Sn-3.5Ag-6.5 In
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Solder Sn-3.5Ag-9In
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In 0
In 6.5
In 9
X-ray phase analyssis of Sn-3.5Ag solders with In
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Temperatuture dependence of the resistance of the
Sn-3.5Ag solder with In
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All three solders heated In0 up to 180
C In6.5 up to 160 C In9 up to 180
C and quenched X-ray diffraction No change
in phase composition SEM coarsening of
microstructure in In6.5 and In9
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Shear strengths of the Cu-solder-Cu joints
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Cu6Sn5
Cu6Sn5 between Cu-Sn3.5Ag solder after uncyceld
(a) and 1000 cycles (b) RT 150 C
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Cu6Sn5
Cu6Sn5 between Cu-Sn3.5Ag6.5In solder after
uncyceld (a) and 1000 cycles (b) RT 150 C
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Shear strengths of the Cu-solder-Cu joints
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Shear strength of Cu-solder-Cu joints for
100,200,500 and 1000 cycles (including shear
strength of no cycled joints).  Joints with
solder (1) Shear strength decreases with
increasing amount of cycles. This decrease
reflects the increase of Cu6Sn5 phase
thickness.  Joints with solder (2) Shear
strength increases with increasing the number of
cycles and thickness of Cu6Sn5 layer
decreases.  Joints with solder (3) Shear
strength increases except for 1000 cycles (where
shear strength is on the level of no cycled
joint). The thickness of Cu6Sn5 layer decreases
with increasing the number of cycles except for
1000 cycles where InSn4 phase arises instead of
In4Ag9.  One can suppose that this phase retards
the dissolution of copper from Cu6Sn5 phase.The
higher is the thickness of Cu6Sn5 layer the
lower is the shear strength of the joint. The
In4Ag9 phase seems to enhance the dissolution of
copper from Cu6Sn5 phase into the SnAg solder.
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In 0 1000 cycles
In 6.5 1000 cycles
In 9 1000 cycles
In 9 uncycled
X-ray phase analyssis of joints with Sn-3.5Ag
solder and In
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• Conclusion
• Sn-3.5Ag-In(06.59 mass.) solders consist of Sn
  and Ag3Sn In4Ag9 and In4Ag9 and InSn4,
  respectively.
• In all joints before and after thermal cycling in
  the temperature interval RT-150C as well as
  RT-180C at the interface between copper
  substrate and the solder Cu6Sn5 phase is formed.
• For the joints made with indium-free solder the
  thickness of this phase is growing with
  increasing the number of cycles and the shear
  strength of these joints is decreasing.
• For the joints made with In containing solders
  the thickness of this phase (Cu6Sn5) is
  decreasing with increasing the number of cycles
  and the shear strength of these joints is
  increasing.
• Contents of phases in joints made with Sn-3.5Ag
  and Sn-3.5Ag-6.5 mass In is equal before and
  after cycling
• For joint with Sn-3.5Ag-9In solder after 1000
  cycles InSn4 phase is formed instead of In4Ag9
  phase.