Thermomechanical fatigue failures are an important class of failures in microelectronic inter- connect structures. Thermomechanical stresses arise from differences in the coefficients of thermal expansion of the various materials comprising a microelectronics circuit. Polymer dielectrics and ad- hesives have larger coefficients of expansion than metal conductors. Dielectrics and adhesives may also exhibit large anisotropy in the coefficient of expansion, producing significant thermomechanical stresses in vias or other metal interconnect structures. During ambient thermal cycling or operational power dis- sipation, cyclic stresses are induced, which cause fatigue failures. The basic elements of thermomechani- cal fatigue behavior of microelectronic interconnect structures. such as lines and vias, are presented in this paper. In addition, a case study illustrating many of the concepts is presented for a complex 3-D interconnect.
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