Mechanical behavior of high temperature interconnects and the superplasticity of high lead- content alloys.

摘要

Power electronics and applications with high ambient temperatures, such as deep well drilling for natural gas and oil exploration, requires interconnects in electronics survive temperatures in excess of 473K. This study examines the mechanical behavior and deformation mechanisms of Pb and Sn based alloys used in high temperature applications. In total, ten alloys were chosen based on their melting temperature and suitability as interconnects for high temperature flex packages. Characterization of the mechanical behavior was partitioned into three categories, time-independent elasticity/plasticity, time-dependent plasticity (creep), and superplasticity. Alloys with stable high temperature phases, namely 92.5Pb-5Sn-2.5Ag, 92.5Pb-5In-2.5Ag, and 93Pb-3Sn-2Ag-2In exhibited excellent strength through the entire temperature range. High mechanical strength was attributed to composite strengthening and grain boundary pinning in these alloys. 95Sn-5Sb was shown to be a viable alternative to Pb-based interconnects for applications up to 473K.;All compositions tested, except 85Pb-10Sb-5Sn, were found to follow power-law dislocation creep in the strain rate range of 10-9-10 -3 sec-1. A change in the controlling climb mechanism from pipe diffusion to lattice diffusion was observed around 0.7Tm. The enhancement in the self-diffusion of Pb was dependent on solute concentration and the specific solute atom in solution with Pb.;In the final portion of this study, the superplastic behavior of 85Pb-10Sb-5Sn, is reported for the first time, and a new phenomenological model for superplastic flow is proposed based on the deformed microstructure and mechanical characterization. 85Pb-10Sb-5Sn did not exhibit typical superplastic behavior in that very high homologous temperatures are required to experience superplastic elongations. A characteristic temperature (TGBS) was found, which differentiates superplastic from non-superplastic flow. The microstructure study revealed that localized viscous flow of regions between shearing interfaces, not sliding of individual or groups of grains is responsible for superplastic elongations.;This work fills a void in literature, providing a systematic study which fully characterizes the mechanical behavior of Pb and Sn based alloys used as interconnects in electronic packages subjected to temperatures in excess of 473K. Information garnered from this work can be used in future studies to develop alloys with superior high temperature properties.