Controlling Interfacial Exchanges in Liquid Phase Bonding Enables Formation of Strong and Reliable Cu-Sn Soldering for High-Power and Temperature Applications

Developing solder joints capable of withstanding high power density, high temperature, and significant thermomechanical stress is essential to further develop electronic device performances. This study demonstrates an effective route of producing dense, robust, and reliable high-temperature Cu-Sn soldering by modifying the interfacial exchange during a transient liquid phase bonding (TLP) process. Our approach thus relies on altering internal phenomena (diffusion and transport of reactive species) rather than classical external TLP bonding parameters (e.g., time, temperature, and pressure). By adding a Cu3Sn-coated layer between Cu and Sn before the TLP process, fast dissolution of Cu in liquid Sn is achieved, altering undesired Cu6Sn5 scallop grain impingement and promoting their uniform growth within the liquid. A bonding and pore formation mechanism of the solder with or without the Cu3Sn-coated layer is proposed based on experimental and theoretical analysis. The developed TLP joint possesses a shear stress resistance of more than 80 MPa with a thermal cycle endurance superior to 1200 (-45-180 °C), making it highly reliable compared to a classical solder joint with shear and thermal cycling resistances of 45 and 500 MPa, respectively. The developed approaches thus provide an easy, affordable, and scalable method of producing a high-temperature and durable Cu-Sn joint for high-power module applications.