Low-Temperature Transient Liquid Phase Bonding Technology via Cu Porous-Sn58Bi Solid–Liquid System under Formic Acid Atmosphere

Abstract

This study proposes a low-temperature transient liquid phase bonding (TLPB) method using Sn58Bi/porous Cu/Sn58Bi to enable efficient power-device packaging at high temperatures. The bonding mechanism is attributed to the rapid reaction between porous Cu and Sn58Bi solder, leading to the formation of intermetallic compounds with high melting point at low temperatures. The present paper investigates the effects of bonding atmosphere, bonding time, and external pressure on the shear strength of metal joints. Under formic acid (FA) atmosphere, Cu6Sn5 forms at the porous Cu foil/Sn58Bi interface, and some of it transforms into Cu3Sn. External pressure significantly reduces the micropores and thickness of the joint interconnection layer, resulting in a ductile fracture failure mode. The metal joint obtained under a pressure of 10 MPa at 250 °C for 5 min exhibits outstanding bonding mechanical performance with a shear strength of 62.2 MPa.

Sn-58Bi/Cu porous joint formation under air condition without pressure

“…Under the same environmental conditions, the bonding temperature was 250°C, air environment, and no pressure. The shear strength at the joint was 12.90 MPa [3] . It is important to note that this result differs greatly from this study's finding.…”

“…Therefore, the reliability of soldering interconnection in SMD packaging of WBG devices has become a focus in the packaging field [1,2] . Recently, TLP has broad application prospects in many fields, and its significant advantages allow it to solve the problem of soldering interconnection [3] . TLP technology enhances the stability and reliability of WBG devices in high-temperature environments by improving their thermal conductivity [4] .…”