Issue 46

N. Hiyoshi et alii, Frattura ed Integrità Strutturale, 46 (2018) 25-33; DOI: 10.3221/IGF-ESIS.46.03 30 this study as a new evaluation parameter. Crack propagation cycle was calculated as subtract the crack initiation cycle ( N i ) from the total number of cycles ( N ). Fig, 7 depicts crack propagation curves of the low-Ag solders, crack initiation cycle was replaced into a first cycle of the crack propagation cycle. The crack propagation of SnAgCu (colored in black) and SnAgCu+NiGe (colored in blue) seem to have a slower crack propagation rate than that of SnAgCu+Bi (colored in red) and SnAgCu+BiNiGe (colored in green). These results indicate that additive element Bi increase the crack propagation rate, but effect of additive elements Ni and Ge on the crack propagation rate are small. 0.5 1.0 1.5 2.0 2.5 10 -1 10 0 10 1 10 2 Fatigue life ratio N / N f Horizontal crack length 2 a , mm SAC107 Solders, 313K factor of 2  =0.3% SnAgCu SnAgCu+NiGe SnAgCu+Bi SnAgCu+BiNiGe  =0.4% Figure 6 : Crack length as a function of fatigue life ratio. 10000 20000 30000 0 2 4 6 Number of propagation cycle N p Horizontal crack length 2 a , mm SAC107 Solders, 313K SnAgCu 1 SnAgCu+NiGe SnAgCu+Bi SnAgCu+BiNiGe  =0.3%  =0.4% Figure 7 : Crack propagation curve of Sn-low-Ag-Cu solders at 313 K. Fig, 8 shows the number of crack propagation cycles which crack length reached to 5mm for comparing the crack propagation rate. SnAgCu and SnAgCu+NiGe have almost same crack propagation cycles for both 0.3% and 0.4% strain