Lead-free particle reinforced
composite solders
Preliminary results
P.Unifantowicz, T.Rütti, J.Janczak-Rusch
Project goals
Synthesis of the composite solders based on
Sn-Ag-(Cu) alloy, with mechanical properties
superior to the noncomposite solders.
Characterization of the solders microstructures
Assesment of the impact of different processing
parameters, various types and volume fraction of
reinforcement particles on the microstructure.
Materials
Solder alloys:
Reinforcement particles:
Sn-3.5Ag
Cu
(3-7 m)
Ni (1-30m)
Ag3Sn IMC +Sn - eutectic
mixture
-Sn
Sn-3.8Ag-0.7Cu
-Sn
Ag3Sn +
Cu6Sn5 IMCs
+-Sn - eutectic
mixture
Ni-coated
glass spheres
(0.1-0.3 m)
Cu-coated
glass
(1-3 m)
Processing of composite solders
The mechanical mixing method was proven to be
successful in preparing metallic-particles reinforced
composite solders with uniform distribution of
reinforcement. The choice of using this method is
motivated by its simplicity and economic viability .
In the current experimental work the reinforcement particles
were added to the solder paste, containing solder metal
powder and flux. The mixture was blended in
atmospheric conditions, in a ceramic crucible for min. 15
minutes to assure uniform distribution of the particles.
Microstructures of the SnAgCu/Cup
composite solders
Sn-Ag-Cu
+4%
Cu (1-30 m)
Sn-Ag-Cu
+8%
Cu (1-30 m)
Sn-Ag
+4%
Cu (1-30 m)
Microstructures of the SnAgCu/Nip
composite solders
Sn-Ag-Cu
+ 8 % Ni
(3-7 m)
Sn-Ag-Cu
+ 8 % Ni
(0.1-0.3 m)
Sn-Ag-Cu
+ 0.4 % Ni
(0.1-0.3 m)
Sn-Ag-Cu
+ 4 % Ni
(0.1-0.3 m)
General findings
• Introducing of the compatible metallic particles into the eutectic
solder results in reaction with the Sn-rich matrix and formation of
intermetallic compounds.
• The copper particles, when added to the Sn-Ag eutectic under
critical amount, can dissolute and subsequently reprecipitate in the
matrix.
• Addition of 8% of submicron-Ni was found to give an excessive
amount of particles.
• The IMCs arround the particles were defined as Cu6Sn5 and Ni3Sn4.
• Thickness of this IMC layer depends from heating stage upon
melting and solidification process.
• A big heat input resulted in formation of large Cu6Sn5 rods and
coarsened Ag3Sn
…
The influence of particles addition on the
solders wettability
The contact angles were measured for solders reinforced with different
particles solidified on copper substrate. The results showed that:
• Addition of reinforcement particles caused an increase of contact
angle comparing to the noncomposite solders. By 10 wt.% of Cu
particles in Sn-Ag-Cu solder the difference was ~15°.
• Composite solders reinforced with the nickel particles had better
wetting characteristic with that the copper reinforced solders.
• When the partial vacuum was used, the contact angle decreased
significantly in comparison with the solders that solidified in
atmospheric pressure.