Facile Preparation of Self-Reducible Cu Nanoparticle Paste for Low Temperature Cu-Cu Bonding

Abstract

Cu nanoparticle (NP) paste is considered the next-generation die-attach material because of its cost-effectiveness and high conductivity and electro-migration resistance. However, the spontaneous oxidation of Cu NPs severely restrains the incorporation of Cu NP paste into practical applications. Herein, a novel self-reducible Cu NP paste was prepared and demonstrated for low-temperature Cu-Cu bonding. The Cu NP paste was composed of 62 wt.% ultra-small Cu NPs (6.5 nm) and 38 wt.% organic components [isopropanolamine (IPA) stabilizer and ethylene glycol]. The reducing and sintering mechanisms of Cu NP paste were proposed, and the effects of sintering temperature on the mechanical properties and microstructure evolutions of Cu-Cu joints were systematically investigated. Consequently, the reducibility of the IPA stabilizer was beneficial for eliminating the surface oxides and enhancing the sinterability of Cu NPs, and the robust and high-strength Cu-Cu joints (> 20 MPa) were achieved at low temperature of 200°C in Ar atmosphere. Furthermore, the microstructure observations reveal that the robust bonding is attributed to the remarkable metallurgical interconnection between the substrates and sintered Cu NP layer.