Differential thermal expansion in microelectronic systems

Abstract

Structures used in microelectronic systems, ranging in size from the individual device level to complete printed circuit boards, involve ceramic, metallic and polymeric materials in intimate physical contact. The different thermal expansion coefficients of these materials 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.This paper reviews this technologically important problem by taking examples from each of the "packaging levels" of microelectronic systems. 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.