Cu@Sn Core-Shell Structure Powder Preform for High-Temperature Applications Based on Transient Liquid Phase Bonding

This paper presents a novel die-attach material for high-temperature applications based on transient liquid phase (TLP) bonding. Cu particles are electroless plated with Sn to achieve Cu@Sn structure, and the fabricated Cu@Sn particles are compressed into preforms for die attachment. This material can be reflowed at a low temperature (<260 degrees C) due to the low melting temperature of the outer Sn layer. However, after reflow soldering, the resulting interconnections can withstand a high temperature of at least 415 degrees C, with the entire outer Sn layer transforming into Cu-Sn intermetallic compounds (IMCs) with high remelting temperatures. The formed bondlines exhibit good electrical and thermal conductivity due to the low porosity and the embedded Cu particles in the interconnections. A large shear strength at 400 degrees C can be achieved with the high-remelting Cu-Sn IMCs in the interconnections. Furthermore, the interconnections also exhibit excellent reliability under thermal shock cycling from -55 to 200 degrees C. The I-V curve and breakdown voltages of the novel preform-bonded IGBTs are measured to examine the interconnection quality compared with those of Cu-Sn TLP-bonded IGBTs. This die-attach material is suitable for power devices operating under high temperatures or other harsh environments.