Abstract:The furnace brazing of Cu/LF21 by using different solder thickness of BAlSiMg is studied. The results show that the solder layer is so thin that the liquid phase produced by eutectic reaction cannot fill the entire weld completely while the more brittle phase CuAl2 and AlCu produced in the brazing seam zone can lead to coming along the micro-cracks in the cooling process of the weld so that both of them can lead to reducing joint strength of solder joints. Therefore, to obtain the ideal joint, the brittle phases in weld must be a non-continuous distribution or the dispersion state of existence.