Abstract: Dip brazing is a brazing process suitable for common aluminium microwave assemblies. The base metal was the Chinese commercial aluminium alloy LF21 (similar to 3003). Brazing filler metals used were Al-11.5Si-1.5Mg and Al-7Si-1.5Mg. The parts were brazed at 605-615℃ (1121-1139°F)in a vacuum of 1×10^-5 Torr (1.3 mPa). Experiments showed that the oxide film of alumunum could not be removed during the vacuum brazing process, the molten brazing filler metal spread along the oxide/metal interface, with oxide film was lifted and floating on the surface of molten brazing filler metal. Thus during vacuum brazing of aluminium the capillary attraction was weak and the continuity of brazing joints was poor. In order to increase the capillary attraction and to obtain continuous fillet of brazing filler metal, local roughening of the surface of the parts to be brazed was performed, a technological cover was placed over the assemblies in vacuum container, and a certain amount of Mg-chips was put into the cover. Experimental results have proved the effectiveness of the new process:the wetting and spreading of brazing filler metal were very good, the flow distance and clearance fillability were raised up about 2 times; and the microwave assemblies having complicated configuration were brazed in one heat successfully, free from corrosion and distortion, so neither cleaning nor readjusting operation after brazing were needed.