Abstract: It was found that 21 pieces of 100 aluminum alloy antenna assemblies failed due to solder spreading out. The antenna assemblies were brazed with 5 layers of 3A21 raw material sheets in vacuum. The surface roughness, grain microstructure, precipitated phase, solder microstructure and Vickers hardness of the antennas and raw material sheets were compared, and the heat treatment comparison experiment was carried out to analyze several factors which affect the brazing quality of the antennas. It was confirmed that one of the main factors affecting the spread degree of solder on the sheet surface was surface roughness. Failed antenna raw material sheets had larger grain size and lower hardness. Such failure did not occur again after strictly controlling the heat treatment temperature below recrystallization temperature and the grain size of raw material sheets.