Effect Of Underfill On Flip-Chip Solder Bumps: An Experimental Study By Microscopic Moiré Interferometry

Thermo-mechanical deformations of flip-chip interconnections on an organic substrate are investigated by microscopic moiré interferometry. A detailed experimental procedure for microscopic moiré experiments is described and the effect of specimen preparation is discussed. Two identical packages, one with and the other without underfill, are investigated. They are subjected to a uniform thermal loading and thermally induced displacement fields are documented by microscopic moiré interferometry. The ultra-high displacement measurement sensitivity and the microscopic spatial resolution of the method allow a detailed analysis of solder bumps. The normal and shear strains (averaged along the vertical centerlines) at each solder bump are calculated from the displacement fields. The experimental results confirms the effect of underfill on the solder bump strains; the average shear strains are reduced by an order of magnitude and the average normal strains in the direction perpendicular to the chip thickness becomes compressive.