Intermetallic compound growth between Sn-Cu-Cr lead-free solder and Cu substrate

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 degrees C, 125 degrees C, and 150 degrees 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 Cu3Sn, 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.