Intermetallic compound growth between Sn-Cu-Cr lead-free solder and Cu substrate. (August 2019) - Bang, Junghwan
Abstract: The intermetallic compound (IMC) produced through an interfacial reaction between Sn-0.7wt.%Cu-0.2wt.%Cr (SC-Cr) solder and a Cu substrate was evaluated at 100 °C, 125 °C, and 150 °C for 1000 h and after ten reflows. The comparable study on the interfacial reaction for Sn-0.7wt.%Cu (SC07) and Sn-3.0wt.%Ag-0.5wt.%Cu (SAC) with a Cu substrate was also conducted. In the SC-Cr/Cu system, the Cr compounds that precipitated near the interface during thermal treatment effectively suppressed the growth of all IMCs including Cu3 Sn, resulting in a slow production of Kirkendall voids. The shear strength decreased as the thermal aging and number of multiple reflows increased. However, the SC-Cr/Cu system showed a superior bonding strength under high shear rate conditions compared with SAC/Cu and SC/Cu systems. The activation energies were determined to be 73.52 kJ/mol for the SAC305/Cu system, 57.31 kJ/mol for the SC07/Cu system, and 77.96 kJ/mol for the SC-Cr/Cu system. Highlights: The addition of Cr in the SnCu/Cu system effectively suppressed the growth of the interfacial IMC during diffusion based on the Cr phase precipitated near the Cu6 Sn5 grain. In the SC-Cr/Cu system, the growth of Cu3 Sn was suppressed during the thermal treatment, resulting in a slow production of Kirkendall voids. Ultimately, the results described above suggest that the addition of Cr in the SnCu/Cu system effectively suppresses the IMC growth as well as the formation of Kirkendall voids at the interface, resulting in excellent mechanical strength.