Evolution of Transient Liquid-Phase Sintered Cu–Sn Skeleton Microstructure During Thermal Aging

Abstract

The evolution of the transient liquid-phase sintered (TLPS) Cu–Sn skeleton microstructure during thermal aging was evaluated to clarify the thermal reliability for die-attach applications. The Cu–Sn skeleton microstructure, which consists of Cu particles connected with Cu–Sn intermetallic compounds partially filled with polyimide resin, was obtained by the pressure-less TLP sintering process at 250 °C for 1 min using a novel Cu-solder-resin composite as a bonding material in a nitrogen atmosphere. Experimental results indicate that the TLPS joints were mainly composed of Cu, Cu6Sn5, and Cu3Sn in the as-bonded state, where submicron voids were observed at the interface between Cu3Sn and Cu particles. After thermal aging at 150, 175, and 200 °C for 1000 h, the Cu6Sn5 phase fully transformed into Cu3Sn except at the chip-side interface, where the number of the submicron voids appeared to increase. The averaged shear strengths were found to be 22.1 (reference), 22.8 (+3%), 24.0 (+9%), and 19.0 MPa (−14%) for the as-bonded state and specimens aged at 150, 175, and 200 °C for 1000 h, respectively. The TLPS joints maintained a shear strength over 19 MPa after thermal aging at 200 °C for 1000 h because of both the positive and negative impacts of the thermal aging, which include the transformation of Cu6Sn5 into Cu3Sn and the formation of submicron voids at the interface, respectively. These results indicate an excellent thermal reliability of the TLPS Cu–Sn skeleton microstructure.

Deformation Behavior of Transient Liquid-Phase Sintered Cu-Solder-Resin Microstructure for Die-Attach

“…These results suggest that the TLPS facilitates the reduction of the both Mises strain and stress macroscopically through thermal cycling. In an earlier study [34], we demonstrated the excellent thermal reliability of the TLPS joints after thermal aging at 200 • C for 1000 h through temperature storage tests, where IMC of the microstructure transformed from Cu 6 Sn 5 to Cu 3 Sn along with the formation of submicron voids at the interface between Cu and IMCs during the thermal aging. The IMC was treated as the Cu 6 Sn 5 in the simulations.…”

“…We have proposed an approach for the stiffness reduction of TLPS joints using a novel Cu-solder-resin composite for die-attach applications. We have already proven the feasibility of this approach [33] and demonstrated excellent thermal stability during thermal storage test at 200 • C for 1000 h [34]. The TLPS joint was composed of stiff Cu-Sn IMCs, ductile Cu, and soft resin, which were expected to reduce the apparent stiffness of the joint.…”

Recent Progress in Transient Liquid Phase and Wire Bonding Technologies for Power Electronics

“…Liu et al [88] used formic acid activation of the Sn-coated Cu particles for low-temperature die-attached applications. The joint shear strength was improved due to the formation of Cu3Sn IMCs with dispersions of Cu particles.…”

Joining Technology Innovations at the Macro, Micro, and Nano Levels

“…In the field of power electronics, the focus is directed at the development of novel materials for transient liquid phase bonding (TLP) and nanoparticle sintering routes. Rajendran et al [42] proposed an Sn-coated Cu-multiwalled CNT (MWCNT) composite (Sn-Cu-MWCNT) paste for Cu interconnections, and Tatsumi et al [43] developed a Cu-solder-resin composite paste for pressure-less die-attach technology for bonding Kovar chips onto Cu electrodes on Si 3 N 4 substrates. The Sn-Cu-MWCNT composite powder [42] was fabricated by subsequent electroless plating of Cu and Sn on a multi-walled carbon nanotube.…”

“…During the process, the Sn-Cu-MWCNT composite material transformed to MWCNT-Cu 3 Sn in the Cu joint zone. The Cu-solder-resin composite pastes developed by Tatsumi et al [43] allowed a TLP sintering (TLPS) process at a temperature of 250 • C without pressure application. The as-produced TLPS joints showed excellent thermal reliability (only 14% decrease in shear strength after thermal aging at 200 • C for 1000 h).…”