The dissolution properties of Cu in molten Sn-Cu-Ni and Sn-Zn alloys were investigated and compared with those of Cu in SnAg -Cu alloys. In the Sn-Cu-Ni alloys with small amounts of Ni, the dissolution rate of Cu decreases with increasing Ni content when the Ni content is below 0.15 mass%. The dissolution rate is proportional to the difference between the saturated solute concentration in liquid (C s) and the solute concentration in liquid (C), (C s ϪC), which is estimated from the isothermal section of the Cu-Sn-Ni ternary phase diagram. In the Sn-Zn alloy, the Cu-Zn reaction layer forms at the solder/Cu interface. The layer prevents Cu dissolution and thus the dissolution rate of Cu is dramatically reduced.

The low cycle fatigue (LCF) behavior of as-cast Sn-0.7mass%Cu lead-free solder and compared with those of conventional Sn-37mass%Pb solder were investigated at strain rate 0.1%/s under various temperatures, R.T. (room temperature), 80 o C, 120 o C. In addition, the relationship between the surface feature in the LCF test and the fatigue life of these solders at R.T. were investigated. The fatigue life of Sn-0.7Cu decreased with increasing temperature. And the fatigue life of Sn-0.7mass%Cu was better than that of the Sn-37mass%Pb solder at R.T. and 80 o C. The surface deformation as fine meshes during the LCF test of Sn-0.7mass%Cu did not appear until 10% of fatigue life. Although over 10% of fatigue life, surface deformation that was caused by micro cracks and these link up occurred with increasing number of cycles.

No abstract

Two kinds of new Fe-Cr system alloy brazing filler, Fe-Cr-based and Fe-based, have been developed as a substitute for expensive Ni-based brazing filler in brazing of SUS304 stainless steel. Joint strength of the joints brazed with new filler were investigated and compared with the joint brazed with Ni-based brazing filler. The following results were obtained in the study. P-rich phases were formed because Ni in the new Fe-Cr system alloy diffused from the brazed layer to SUS304 stainless steel when joint clearance was 10 μm. When joint clearance was more than 50 μm, a finally-solidified region appeared in the brazed layer, at the same time, most of P segregated and was enriched in the finally-solidified region. It was proved that the volume fraction of P-rich phases in the finally-solidified region varied with the increase of joint clearance and joint strength decreases with the increase of the volume fraction of P-rich phases. Compared with Ni-based filler, joint strength of the joint brazed with Fe-based filler was almost equal when joint clearance was under 200 μm. On the other hand, joint strength of the joint brazed with Fe-Cr-based filler was slightly inferior regardless of joint clearance. Still, joint strength reached approximately 100 MPa. The result indicated that joint strength of the brazed joint with the Fe-Cr system alloy was strongly affected by the P addition. It is possible that promoting of joint strength can be brought by lower addition of P.

The low-cycle fatigue behavior and the relationship between the surface features in the low-cycle fatigue testing and the fatigue life of Sn-3.5Ag and Sn-0.7Cu lead-free solders were investigated at strain rate of 0.1%/s with a non-contact extensometer at room temperature ( 22 o C), 80 o C and 120 o C. In addition the fatigue life using the surface deformation of those solders were defined and estimated from the surface features of solders investigated by image processing and compared with Coffin-Manson type of fatigue behavior of solders. The fatigue life of Sn-3.5Ag solder was superior to that of Sn-0.7Cu solder under temperatures of 80 o C and 120 o C. The fatigue life defined from surface deformation indicated a close behavior to Coffin-Manson type of fatigue behavior in those solders. This method could identify the low-cycle fatigue life of solders from the surface deformation.