Microstructural Evolution of Transient Liquid Phase Sinter Joints in High Temperature Environmental Conditions

Abstract

Increasing power densities in electronic systems and their operation in harsh environments necessitate the development of packaging materials capable of withstanding extreme thermal conditions. Transient Liquid Phase Sintering (TLPS) has been demonstrated as a packaging technology with the potential to form reliable interconnects for electronic systems for these environments. During processing, the low melting point constituents of the TLPS system melt and diffuse with the higher melting temperature constituents. This mixture then isothermally solidifies into intermetallic compounds (IMCs) with an associated shift in melting point towards higher temperatures. Joints can be formed at low processing temperatures but possess high melting temperatures after process completion. The microstructural evolution during processing and subsequent exposure to high temperature conditions leads to changes in the microstructure of TLPS interconnects. Insight into the microstructural evolution of TLPS joint in high temperature conditions is required to ensure high temperature capability after processing and to guarantee reliable interconnection during the entire product life cycle. In this paper the microstructural evolution of TLPS interconnects based on the Cu-Sn material system during sintering and thermal aging is assessed. Cu-Sn TLPS joints were sintered for 2 and 30 minutes at 300°C and subsequently aged at 250°C for up to 100 hours. The microstructural evolution behavior of this material system is predicted analytically and compared to that of actual interconnects. The time to high temperature operation capability and the time to microstructural convergence are determined. These characteristics enable the future optimization of TLPS interconnect processes and will help to assess TLPS joint reliability.