Rapid fabrication of Cu/40-μm thick full Cu3Sn/Cu joints by applying pulsed high frequency electromagnetic field for high power electronics

Abstract With the application of wide bandgap semiconductors for high power electronics, the joints are inevitably faced with a trade-off between withstanding high temperature environments and remaining low bonding temperatures. In this study, a full Cu3Sn intermetallic compounds layer with thickness of 40 μm, which can survive at 679 °C, were obtained between Cu plates using pulsed High Frequency Electromagnetic Field (HFEF) within 10 min at ambient temperature. Output power and frequency of the HFEF was 6 kW and 530 kHz, respectively. In contrast to common Sn-based solder joints, the joints prepared through HFEF consisted predominately of Cu3Sn, because both the horizontal and vertical temperature gradients and the eddy currents within the joints strongly promoted the 3D diffusion of copper atoms. With increasing HFEF exposure time, the Cu3Sn changed from an irregular needle-like to smoothly scalloped or columnar morphology. The HFEF approach enabled Cu3Sn joints to achieve a superior shear strength (>56 MPa) and a greater stand-off height (>30 μm), which are useful to mitigate the coefficient of thermal expansion (CTE) mismatch problems; thereby yielding higher reliability. We envision that these full Cu3Sn joints prove useful in a wide range of applications in high-temperature and high-power electronics.