We investigated how adding Ni and Cu into Sn-6.4Sb-3.9Ag (mass%) lead-free solder affects its fatigue properties at high temperatures. The addition of Ni and Cu caused the formation of grains with high-angle grain boundaries and an increase in the number of grains. From the fatigue test, the solder with added Ni was confirmed to have superior fatigue properties at 175°C. The solder with added 0.4%Ni was confirmed to have the best fatigue properties. In contrast, in the solder with added Ni and Cu, the addition of 2.0%Cu in the solder degraded its fatigue properties at 175°C. From EBSD analysis, it was found that cracks grow at grain boundaries with dynamic continuous recrystallization in the solder with added Ni and 1.0%Cu. On the other hand, the fatigue damage in the solder with added 2.0%Cu was due to stress relaxation by dynamic recovery.

This paper reports on the development of a SiC power device packaging technology that extends the power-cycling lifetime to 300,000 cycles at temperatures above 200°C, which is the criterion for high-reliability applications. By mounting a buffer layer with an adjusted coefficient of thermal expansion (CTE) less than that of SiC, the creep-fatigue of the aluminum chip electrode is suppressed and lifetimes of 472,000 cycles at 65 to 200°C and 425,000 cycles at 65 to 225°C are achieved. In addition, the mechanism of the lifetime extension is discussed using cross-sectional structural observation, transient thermal resistance analysis, and stress-strain simulation utilizing the finite element method.

The recycling of solder materials, including those used for electronics mounting, will be increasingly desirable considering the demands of SDGs. There will also be greater diversification of anode composition in electrorefining. These tendencies will reduce the purity of anode materials. The electrorefining process is a key technology for recovering Sn from used materials. It has been reported that anode electrodes containing various impurity metals tend to be passivated easily. Anode passivation reduces refining purity. In this study, we evaluated the effect of Sn anode composition on passivation time in a sulfate bath under an electrorefining process. Some of the tin anode impurities considered are Bismuth and Antimony, though there are others. In this report we clarify that specific amounts of Bi in Sn-Sb material led to anti-passivation.

In this paper, the effective thermal conductivity of metallic conductors under flowing currents is evaluated.

The effective thermal conductivity is derived from the difference between the temperature rise in the direction of the current and that in the direction opposite to the current. The effective thermal conductivity is clarified to change with the direction of conduction current due to the Thomson effect.