1. Lead-free particle reinforced composite solders Preliminary results P.Unifantowicz, T.Rütti, J.Janczak-Rusch

2. 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.

3. Materials Solder alloys: Sn-3.5Ag Sn-3.8Ag-0.7Cu Reinforcement particles: Cu Ni (1-30  m) (3-7  m) Ni-coated Cu-coated glass spheresglass (0.1-0.3  m) (1-3  m) Ag 3 Sn + Cu 6 Sn 5 IMCs +  -Sn - eutectic mixture  -Sn Ag 3 Sn IMC +  - Sn - eutectic mixture  -Sn

4. 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.

5. Microstructures of the SnAgCu/Cu p composite solders Sn-Ag-Cu + 4 % Cu (1-30  m) Sn-Ag + 4 % Cu (1-30  m) Sn-Ag-Cu + 8 % Cu (1-30  m)

6. Microstructures of the SnAgCu/Ni p composite solders Sn-Ag-Cu + 8 % Ni (3-7  m) Sn-Ag-Cu + 0.4 % Ni (0.1-0.3  m) Sn-Ag-Cu + 8 % Ni (0.1-0.3  m) Sn-Ag-Cu + 4 % Ni (0.1-0.3  m)

7. 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 Cu 6 Sn 5 and Ni 3 Sn 4. Thickness of this IMC layer depends from heating stage upon melting and solidification process. A big heat input resulted in formation of large Cu 6 Sn 5 rods and coarsened Ag 3 Sn …

8. 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.