edfas.org 19 ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 27 NO.2 VERIFICATION OF THE FAILURE CRITERION ON THE CORRODED ZONE SURFACE Additional salt spray tests were carried out to verify this failure criterion in the corroded zone. Some electronic assemblies have been submitted to salt spray test for 192 hr. The TTF determined by the shear force measurements is 180 hr (Fig. 7). However, for this exposure time, 50% of the solder joint area is corroded. So, it can be considered that the failure criterion for the corroded zone is correct. CONCLUSION The dynamics of corrosion on SAC305 solder joints subject to salt spray (5% NaCl) test were investigated in this study. The impact of salinity rate and the temperature were measured on the shear force and on the corroded surface of the solder joint. No electrical resistance variation was observed with and without corrosion. Thus, another parameter needs to be measured to quantify the impact of corrosion on the reliability of solder joints. The force necessary to shear the components and the corroded surface of the solder joint were chosen. The results show that the temperature accelerates the corrosion mechanism. Moreover, the salinity rate has a significant effect on the evolution of the corrosion. According to the SEM and EDX investigation of solder joints Fig. 3 Corroded solder joints. Table 2 Estimated values of TTF and percentage of corroded solder joint area T, °C Time, hr % solder joint corroded area 25 192 51 30 203 57 35 183 69 40 129 64 45 112 65 Fig. 4 Example estimation of the percentage of the corroded area of a solder joint at 25°C after 72 hr. Fig. 5 Percent of corroded solder joint area as a function of the exposure time at 5% NaCl. (a) (b) (c)
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