Experimental In Situ Characterization and Creep Modeling of Tin-Based Solder Joints on Commercial Area Array Packages at -40 deg C, 23 deg C, and 125 deg C

The objective of this work was to experimentally determine the in situ creep behavior and constitutive model equations for a commercial area array package and printed wiring board assembly at -40, 23, and 125 deg C through shear loading. The chip is connected to the printed circuit board by means of solder joints made of 62%Sn-36%Pb-2%Ag alloy. It was shown that the creep rate of solder ball arrays could be investigated using a stress relaxation method. Under the shear relaxation mode, the creep strain increases with temperature and can be described by a power law model with coefficients determined by finite element modeling (FEM). An analytical model was developed to describe the stress relaxation of an array with an arbitrary number of solder balls by defining an equivalent solder ball shear area as a fitting parameter The resulting constitutive model is in excellent agreement with both FEM and experimental results at all test temperatures. A parametric study is conducted to investigate the creep response as a function of temperature for arrays consisting of a wide range of solder balls.