Reliability of Flip Chip Applications with Ceramic and Organic Chip Carriers

摘要

The paper deals with four primary failure mechanisms, namely thermomechanical fatigue, electromigration, thermomigration, and cyclic creep, listed in order of severity in terms of their effect on the reliability of flip-chip solder joints as well as second-level packaging interconnections. It is basically a tutorial review of the mechanisms and the reliability-models, developed semi-empirically over the years, based on experimental data obtained under accelerated conditions and on the physics of the mechanisms. The models apply to any solder joint and chip carrier combination, however each solder/chip carrier system is characterized by different parameters which depend on the process, materials, and design, reflecting the solder and package properties. While fatigue and creep depend on the package materials and structure, electromigration and thermomigration are practically independent of the chip carrier and other package components, thus the models and characteristic parameters applying to these two mechanisms are valid for ceramic, glass ceramic, and organic chip carriers, and the characteristic parameters vary only for different solders, i.e., activation energy, current-density exponent. Besides temperature which affects all given mechanisms, the number of cycles or the time-to-failure depend on C4 shear strain and cycle frequency (fatigue), current density (electromigration), thermal gradient (thermomigration), and load, shear-strain and frequency (creep).There are other factors that influence fatigue, such as chip underfill, hermeticity, and temperature mini-cycles which are not part of this paper but which are mentioned in the text with respect to their relative effect on fatigue.