Deformation Mechanism of Two-Phase Solder Column Interconnections Under Highly Accelerated Thermal Cycling Condition: An Experimental Study

Abstract

Thermomechanical behavior of solder interconnections of a ceramic column grid array package assembly is characterized by high sensitivity moiré interferometry. The in situ thermal deformations of the most distant column from the axis-of-symmetry are documented for (a) an initial isothermal loading of ΔT = −60° and (2) subsequent accelerated thermal cycles of (20°C)−(125°C)−(−40°C)−(20°C). The deformed shape of the column obtained from the displacement fields clearly delineates the effect of the eutectic solder fillet on the column deformation accumulated during accelerated thermal cycling. A deformation mechanism is suggested to explain the results, which is confirmed by the results from the actual accelerated thermal cycle test of the same assembly. The distributions of inelastic strains accumulated during thermal cycles are determined along the sides of the column. The results emphasize the importance of the solder fillet height for optimum reliability. The effect of specimen preparation required for the moiré experiment on the column deformation is also discussed to validate the experimental data.