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

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

Understanding of void formation in Cu/Sn-Sn/Cu system during transient liquid phase bonding process through diffusion modeling

Transient Liquid Phase (TPL) bounding of Sn foil sandwiched between two Cu foils involves, in the temperature range above the melting point of Sn (232 °C) and below 350 °C, the formation and the growth of two intermetallic compounds (IMCs) Cu6Sn5 and Cu3Sn and mostly unintended micro-pores. The present study aims to analyze the mechanism of void development during the soldering process through an experimental and modeling approach of diffusion-controlled IMC transformation. This modeling couples the diffusion process and the interface motion with the volume shrinkage induced by the difference of partial molar volumes of atoms between each phase. We also consider two types of inter-diffusion transports: (i) inter-diffusion based on the exchange of Cu and Sn atoms and (ii) inter-diffusion of Sn atoms with vacancies allowing Kirkendall void formation. The simulations of IMC growth performed correspond to a sequence of planar phase layers, where the distinctive scallop morphology of the Cu6Sn5 layer is described through an analytical function allowing to quantify the grain boundary diffusion pathway. We take into account of the volume diffusion mechanism for Cu3Sn intermetallic. For Cu6Sn5 intermetallic two mechanisms are considered, volume diffusion and grain boundary diffusion, limited by grain growth. The simulations of IMC growth kinetics, for different transport scenarios, are compared to the experimental evolving morphologies to determine the most likely mechanism of micro-void formation