Effect of Ca element on oxygen content, wetting and spreading properties of Au–Ga filler metal

Abstract

To meet the low oxygen content requirement on filler metals used in high reliable vacuum brazing of power device, Ca was doped into the Au–Ga filler metal, and the effects of Ca on the oxygen content, the wetting and spreading properties of the filler metal were investigated. The results reveal that Ca can effectively decrease the oxygen content in the Au-Ga-Ca filler metal, and the wettability and spreadability of the Au-Ga-Ca filler metal on the Cu substrate were significantly improved. With 0.004 wt % of Ca addition, the oxygen content in the filler metal decreased to 0.0032 wt % and the spreading area increased to a peak value of74.6 mm2. Proper amount of Ca addition can also effectively restrain the growth of intermetallic compounds (IMC) layer at the vacuum brazed filler metal/Cu interface and improve the shear strength of the joints. For the Cu/Au-Ga-0.004Ca/Cu joints vacuum brazed at 480 °C and a vacuum degree of 5 × 10−3 mbar, the IMC/filler metal interface is flat and the IMC layer is uniform in thickness, and shear strength of the joint was 48.3 MPa, 49.5% higher than the Cu/Au–Ga/Cu joint. It is demonstrated that the Au-Ga-0.004Ca filler metal has the best combination property, and high ratio of brazed area can be obtained with Au-Ga-0.004Ca filler metal at a proper vacuum degree in brazing of real components.