Thermo-mechanical behavior of tin-lead and lead-free ceramic column grid array packages

High sensitivity moire interferometry is employed to characterize the thermo mechanical behavior of the lead (Pb)-free ceramic copper column grid array (CuCGA) package under accelerated thermal cycling and is compared with the conventional tin-lead (Sn-Pb) ceramic column grid array (CCGA).; In-situ thermal deformations of the highest DNP (distance to neutral point) copper column is measured for an initial isothermal loading of DeltaT= -75°C and subsequent accelerated thermal cycling of (-40°C)--(125°C). The deformed shape of the column and the distribution of inelastic strains are measured from the displacement fields. The dominant deformation mode is bending of the column due to thermal expansion mismatch between the module and the printed circuit board (PCB). The results are compared with those of tin-lead CCGA tested under similar conditions. Unlike tin-lead columns, where the failure occurs at the column near the top of the solder fillet and through the thickness of the column, in the CuCGA, the failure is found to occur first in the solder fillet at the solder/copper column interface and the crack propagates along the periphery of the copper column. The accumulated plastic deformation per cycle is larger in tin-lead columns compared to the copper columns. A deformation mechanism is provided to explain the nature of this failure.; Computational method---Non-linear, finite element analysis is also undertaken to assess the thermomechanical behavior of the Pb-free CuCGA in comparison to Sn-Pb CCGA by building a 3D, strip model of the CuCGA and CCGA and subjecting them to temperature excursions. Deformations and strains are noted and are used to verify the model with the experimental results.