Comparison of thermo-mechanical behavior of lead-free copper and tin-lead column grid array packages

摘要

Thermo-mechanical behavior of the lead (Pb)-free ceramic copper column grid array (CuCGA) package under accelerated thermal cycling is characterized and 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 ΔT= -75 ℃ and subsequent accelerated thermal cycling of -40 ℃ to +125 ℃. 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.