Combined effect of strain-rate and mode-ratio on the fracture of lead-free solder joints

Comparison of solder joint fracture behavior in Arcan and DCB specimens

“…Over the phase angle range 0-25°the change in the quasi-static J ci was statistically insignificant (t-test, 95% confidence), consistent with earlier quasi-static observations [6,7]. The increased effect of phase angle observed at the higher strain rate was attributed in [8] to the larger crack-tip plastic zone caused by the increased shear loading. Since the solder yield stress is a strong function of strain rate (see Table 1), a larger plastic zone under mixed-mode loading conditions suggests that fracture will be more sensitive to strain rate [8].…”

“…Copper-SAC305-copper solder joints were prepared using a time-above-liquidus (TAL) and cooling rate typical of surface mount manufacturing [3,[6][7][8][9][10][11][12]. C110 copper bars were cut and machined to the dimensions of Fig.…”

“…The J-integral is the predominant method to calculate the fracture energy for elastic-plastic fracture [29], and has been used extensively in the fracture analyses of layered materials (e.g. [6,8,12,[30][31][32][33]). For mixed-mode fracture of 2 mm solder joints, in particular, this method was validated in Ref.…”

“…[3,6,7] were found to mimic the fracture aspects of real BGA samples. These DCB specimens with 2 mm SAC305 solder joints (150 lm thick) were also used to measure the Nomenclature W phase angle (mode ratio) of loading U loading angle in Arcan specimen _ e strain rate K II mode II stress intensity factor K I mode I stress intensity factor K IC mode I critical stress intensity factor G Ic mode I critical strain energy release rate G ci elastic critical strain energy release rate for crack initiation G cs steady-state elastic critical strain energy release rate J strain energy release rate J ci critical strain energy release rate for crack initiation F force applied to the load jig F ti average fracture force applied to the load jig F 1 force acting on the upper adherend of DCB specimen F 2 force acting on the lower adherend of DCB specimen f I mode I geometrical factor in Arcan specimen f II mode II geometrical factor in Arcan specimen t solder joint thickness l solder joint length fracture energies at higher strain-rates (10-60 s À1 ) [8][9][10][11][12]. The values of J ci were in the range 200-1000 J/m 2 increasing with phase angles up to 40°at all strain rates.…”

“…[3,[6][7][8]12] that was shown to yield accurate results for relatively short solder joints. All processing parameters were held constant, and a consistent FEM approach was used to calculate the critical strain energy release rates and phase angles for both specimens.…”