Differential thermal expansion in microelectronic systems

The author examines the problem of differential thermal expansion in microelectronic systems by taking examples from each of the packaging levels of microelectronic systems. The different thermal expansion coefficients of different materials used in the structures of these systems cause stresses to be established in such structures if their temperature of operation differs from that of their fabrication in a nominally stress-free condition. Thermal cycling during normal operation can give rise to thermal fatigue at the various material interfaces, cause defect propagation, and lead to premature failure of the structures, either directly or through subsequent environmental degradation. The examples used include silicon oxidation and GaAs-on-silicon heteroepitaxy, ceramic or polymeric encapsulants of the fabricated structures, printed circuit boards (PCBs), and the solder connections used in mounting components on PCBs