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.
Highlights
The demand for high heat endurance bonding solutions is rising steadily because of generation power modules with wide bandgap semiconductor materials such as silicon carbide (SiC) [1,2]
The polyimide resin is chosen by a curing temperature close to the melting point of the solder and by the soft mechanical properties, whose yield strength is approximately 1 MPa, which was expected to deform while embedded within the microstructure of the Cu and intermetallic compounds (IMCs)
Ag3Sn, and Cu peaks are detected in the composite paste, while Cu6Sn5, Cu3Sn, as-bonded state.state
Summary
The demand for high heat endurance bonding solutions is rising steadily because of generation power modules with wide bandgap semiconductor materials such as silicon carbide (SiC) [1,2]. The SiC chips have lower power losses and higher switching speeds, even at elevated temperatures. These applications provide higher operation temperatures, which have recently exceeded 175 ◦ C or reached 200 ◦ C compared to the conventional 150 ◦ C. The bonding layers are exposed to high temperature operation atmospheres. High heat tolerance bonding technologies as alternatives to conventional Sn-based solders are in high demand. Sinter bonding using nano- or micro-particles is one of the most promising technologies and has been reported to provide outstanding thermal and electrical conductivity and
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