Effects of grain orientation and grain size on etching behaviors of high-strength and high-conductivity Cu alloy

Etching is a precise chemical material reduction processing method that can get small and precise components with specific size and pattern. In etching of the high-precision lead frames, microstructure of the Cu alloy plate has become an important factor that affects the etching rate, size accuracy and surface roughness of the etched products. In this study, the CuCrSn alloy samples with different grain size were etched by aqua regia and then comprehensively characterized to reveal the effects of grain orientation and grain size on the etching behavior. The results show that the etching morphologies and rates of the Cu alloy grains are significantly different and dominated by the grain orientation, and etching of the grains with their surface nearly parallel to the {100} crystal planes are the lowest, meanwhile the roughness of these etched surfaces is the lowest. After the etching, the grain surfaces show very fine stepped structures composed of two or more {100} crystal planes along which the Cu atoms dissolve. The priority corrosion is prone to occur at the grain boundaries (GBs), and the etching around the GBs is more significant when the grains are finer. With the increase in grain size, the etching at the GBs become less apparent, and the difference in etching rates between different grains increases, results in height difference and an increase in roughness of the etched surfaces.