Creep Behavior of Copper and Cu–0.3Cr–0.1Ag Alloy

The creep behavior of Cu–0.3Cr–0.1Ag alloy was investigated by the impression creep testing technique and compared with that of pure copper under constant punching stress in the range 80–550 MPa at temperatures in the range 688–855 K. The enhanced creep resistance of the Cr- and Ag-containing alloys was attributed to the distribution of Cr-rich phase in the copper matrix. Assuming a power-law relationship between the impression stress and velocity, the average stress exponents of 6.0–7.5 and 6.4–8.0 were obtained for pure Cu and CuCrAg, respectively. It was found that the average activation energies were 112.4 kJ mol−1 and 143.5 kJ mol−1 for the pure Cu and CuCrAg alloys, respectively. These activation energies are close to 138 kJ mol−1 for dislocation climb in Cu. This, together with the stress exponents of about 7, suggests that the operative creep mechanism is dislocation climb controlled by dislocation pipe diffusion.

Impression stress relaxation of Sn3.5Ag eutectic alloy

The reliability of microelectronic interconnections depends on hot deformation of solders. In this work, we studied the localized stress relaxation of Sn3.5Ag eutectic alloy using the impression testing in the temperature range of 393–488 K. By incorporating the effect of internal stress in the analysis, we obtained the strain rate-stress exponent of 6.59. The activation energy for the stress relaxation is in the range from 38.6 to 43.8 kJ/mol, which compares well with the estimated activation energy of dislocation pipe diffusion, 46 kJ/mol, in pure tin. This suggests that a single mechanism of dislocation climb limited by dislocation pipe diffusion might be the controlling mechanism for the localized stress relaxation of the Sn3.5Ag eutectic alloy.