Interfacial reactions and mechanical properties of transient liquid-phase bonding joints in Cu/Sn/Ni(P) and Ni/Sn/(OSP)Cu structures for power modules

Abstract

Power modules are being increasingly used as essential parts in eco-friendly vehicles, and they are generally exposed to high temperatures during operation. To this end, electronic interconnection methods that can enhance durability and help withstand extreme environment are required. In this study, we investigated the properties of transient liquid-phase (TLP) bonding joints, which form various metal structures under different bonding conditions. For TLP bonding, Cu- or Ni-finished Si chips and Ni(P)-finished or organic solderability preservative (OSP)Cu-finished direct bond copper (DBC) substrates were used with Sn preforms. TLP bonding was employed for two types of structures: Cu-finished Si chip/Sn preform/Ni(P)-finished DBC substrate (Cu/Sn/Ni(P) structure) and Ni-finished Si chip/Sn preform/(OSP)Cu-finished DBC substrate (Ni/Sn/(OSP)Cu structure) with a bonding temperature of 300 °C applied for 10, 30, and 60 min under 1 MPa bonding pressure. After TLP bonding under these bonding conditions, interfacial reactions and compositions of intermetallic compounds (IMCs) were analyzed. To evaluate the mechanical properties of these joints, we conducted a low-speed die shear test. The shear strengths of these joints increased with bonding time, regardless of these joint bonding structures. The Ni content in (Cu, Ni)6Sn5 of the Cu/Sn/Ni(P) structure was found to be higher than that in the Ni/Sn/(OSP)Cu structure, which correlated with higher shear strength of joints in the Cu/Sn/Ni(P) structure than those in the Ni/Sn/(OSP)Cu structure.