Experimental evaluation of solder joint thermal strain in a CSP using digital speckle correlation

Thermomechanical strain was directly measured using a computer image processing technique in an area encompassing the solder-copper interface near the corner of an outermost solder ball in a chip scale package (CSP). Due to the ultra-high spatial resolution of the technique, the shear strain concentration was revealed and quantified over the area with linear dimensions in terms of microns. Discussions are given on the significance of the measurement for identifying the root cause for solder joint failure, and on the application prospects for the technique as an experimental tool in emerging areas of research where microscopic strain measurement is needed