Experimental and Modeling of the Stress-Strain Behavior of a BGA Interconnect Due to Thermal Load

A plastic ball grid array component interconnect has been experimentally investigated and modeled on the basis of micropolar theory. The experimental results were analyzed, and the data also provided the verification for the micropolar interface model. Two different interconnect cross sections, namely, one near the component boundary and the other in the center region beneath the chip, have been measured. The effects of thermal cycling on the interconnect deformation have been considered. The deformation fields, due to the mismatch of the material properties of the constituents in the assembly system, have been observed by means of a multifunction macro-micro-moiré interferometer, whereby the displacement distributions have been obtained and analyzed for the different specimens. The interconnect layer is usually of smaller size as compared to the neighboring component, and there are even finer internal structures included in the interconnect. The scale difference makes conventional methods time consuming and of low efficiency. An interface model based on the micropolar theory has been developed, cf. Zhang, Y., and Larsson, R., 2007, "Interface Modelling of ACA Flip-Chip Interconnects Using Micropolar Theory and Discontinuous Approximation," Comput. Struct., 85, pp. 1500-1513, Larsson, R., and Zhang, Y., 2007, "Homogenization of Microsystem Interconnects Based on Micropolar Theory and Discontinuous Kinematics, " J. Mech. Phys. Solids, 55, pp. 819-841, aiming at predicting the interconnect behavior under thermal load, especially when there exist internal structures in the interface and the component/ structure sizes vary in a wide range. Numerical simulations, using the micropolar interface model, show a fairly good agreement between the experimental data and the numerical simulations