High-Temperature Die Attachment Using Sn-Plated Zn Solder for Power Electronics

Pure Zn is a Pb-free die-attach material considered suitable for application in high-temperature electronics such as widebandgap semiconductor devices, as it has both the requisite electrical/thermal conductivity and an excellent thermal shock resistance. The high melting point of Zn (419.5 °C), however, means that die-attachment using pure Zn would require higher bonding temperatures (>430 °C), whereas a lower temperature is more desirable for mass production. This paper, therefore, presents a bonding method based on using Sn-plated Zn solder (Sn/Zn/Sn structure) to achieve a lower bonding temperature than pure Zn die attachment. The resulting shear strength of this bonding exceeds 25 MPa at 350 °C for 30 min, which is attributed to a uniform and complete Ni-Zn IMC (γ-Ni₅Zn₂₁) reaction layer. Furthermore, this bonding strength is retained beyond 25 MPa without serious degradation, even after thermal shock testing within a temperature range of -50 °C-300 °C; and thus, the Sn-plated Zn solder proposed has great potential as a die-attach material for high-temperature applications such as power devices.