Integrated Modeling of C4 Interconnects

An extensive methodology for the numerical modeling of C4 interconnects in flip chip organic packages is presented, with particular emphasis on the variability introduced by the manufacturing process. A number of different analytical and experimental techniques are used to develop a complete mechanical model of the interconnect, in order to infer the characteristics of various packaging options with respect to the reliability of C4 interconnects. A fully parametric "macroscopic" finite element model of the entire module (laminate, underfill, chip, lid structure) is first constructed, and is used to define boundary conditions for "microscopic" models of the interconnects. A flexible software system that allows the complete parameterization of the module (in terms of its topology, scales, and material properties) is described. The geometry of the interconnect is calculated parametrically from first principles using a model of the solder joint in fluid phase, taking into account various properties of the interconnect such as the solder volume, the pad diameters, the relative position of the pads, etc. Data validating this fluid model on BGA and on C4 solder balls are also presented. Finally, the variability inherent to manufacturing flip chip packages is emulated by sampling some of the model parameters from random distributions (examples of such parameters include laminate warpage and solder joint volume, and their influence on global package properties, such as the underfilled gap between laminate and chip). Illustrative examples of applying this methodology for problem solving in a manufacturing environment are also presented.