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Failure analysis of lead-free solder joints for PBGA assemblies subjected to thermal cycling aging is reported. Experimental strain analysis using the digital image speckle analysis (DISA) method is capable of measuring the strain concentration at the corner of the solder joint where thermal fatigue cracks initiate and propagate. A micro-digital image speckle correlation system (Micro-DISC) was employed for micro-deformation and strain analysis. The Sn-3.8Ag-0.7Cu soldered assembly was subject to a temperature ramp from room temperature of 25 °C to 125 °C. The failure site agrees with the high strain locations measured by DISA.