Abstract: Failure analysis was carried out on the problem of low bonding strength of the cooling structure in electronic field after being brazed.By analyzing the fracture morphology of fracture samples,it was concluded that the welding process is the cause of the low bonding strength.For this problem,the grade brazing process was proposed to optimize the brazing process,and Al-Si-Mg-Cu filler metal was put forward as the secondary step filler metal. Microstructure and mechanical properties of joints by new brazing process were investigated. It was found that microstructure of joints by new brazing process bonded well. Shear strength of welded joints increased from 39 MPa to 52 MPa. Fracture mainly occurred in the brazing seam and the brazing filler metal wet the base metal well,which solved the problem of low bonding strength.