Controlling Interfacial Reactions and Intermetallic Compound Growth at the Interface of a Lead-free Solder Joint with Layer-by-Layer Transferred Graphene.

The immoderate growth of intermetallic compounds (IMCs) formed at the interface of a solder metal and the substrate during soldering can degrade the mechanical properties and reliability of a solder joint in electronic packaging. Therefore, it is critical to control IMC growth at the solder joints between the solder and the substrate. In this study, we investigated the control of interfacial reactions and IMC growth by the layer-by-layer transfer of graphene during the reflow process at the interface between Sn-3.0Ag-0.5Cu (in wt %) lead-free solder and Cu. As the number of graphene layers transferred onto the surface of the Cu substrate increased, the thickness of the total IMC (Cu6Sn5 and Cu3Sn) layer decreased. After 10 repetitions of the reflow process for 50 s above 217 °C, the melting temperature of Sn-3.0Ag-0.5Cu, with a peak temperature of 250 °C, the increase in thickness of the total IMC layer at the interface with multiple layers of graphene was decreased by more than 20% compared to that at the interface of bare Cu without graphene. Furthermore, the average diameter of the Cu6Sn5 scallops at the interface with multiple layers of graphene was smaller than that at the interface without graphene. Despite 10 repetitions of the reflow process, the growth of Cu3Sn at the interface with multiple layers of graphene was suppressed by more than 20% compared with that at the interface without graphene. The multiple layers of graphene at the interface between the solder metal and the Cu substrate hindered the diffusion of Cu atoms from the Cu substrate and suppressed the reactions between Cu and Sn in the solder. Thus, the multiple layers of graphene transferred at the interface between dissimilar metals can control the interfacial reaction and IMC growth occurring at the joining interface.