Abstract: The characteristics and application of package case of X-band power amplifier were introduced. ALSi is selected as shell material.Gold plating layer has been widely used for its good weldability and corrosion resistance. However,the coating must be uniform,colourless,non-skinning and non-foaming. Therefore,the gold plating quality of ALSi shell material must be strictly controlled. The results show that the coating quality of ALSi shell material is greatly affected by the powder size. The morphology of the coating with powder size of 13. 19 μm and4. 64 μm was compared in the experiment. When the powder size is 13. 19 μm,the coating is obviously uneven,faults occur and the thickness is small,which makes it impossible to achieve practical coating. However,4. 64 μm powder is uniformly plated and has a moderate thickness.Secondly,with the same preparation powder size,the plating current density also has a certain impact on the quality of the coating. When the plating current density is 20 m A/cm²,a relatively uniform coating can be achieved,and the defects of the coating are less. When the current density is increased to 25 m A/cm²,the coating is obviously inhomogeneous and has more defects. The results show that the coating of ALSi shell material is continuous and complete when the powder material is prepared with 4. 64 μm powder at the plating current density of 20 m A/cm². The weldability test results meet the standard requirements of MIL-STD-883. The results of the studies provide a technical guarantee for the wide application of ALSi shell materials,and are of great significance for the development of microwave devices and components.