Wet chemical etching of copper foil. (35 μm thick) at the base of the photoresist cavity (100 μm deep) was investigated experimentally in two geometries (width:depth of 1:1 and 5:1), two acidic cupric chloride solutions, and various flow rates in the range of Péclet number between 107 and 2930. Anisotropic etch profiles were obtained for all conditions investigated. In a etching solution, results indicated that a salt film precipitated on the entire surface and the etch rate was controlled by the rate of convective mass transfer of product removal. The etch rate was highly nonuniform (anisotropic) owing to the presence of local microhydrodynamic flow patterns within the cavity which influenced the local mass‐transfer rate. In a etching solution it was concluded, based on the observations of surface roughness, that the film precipitated only in the corners of a 5:1 (width:depth) cavity, whereas the rest of the surface dissolved film‐free. Moreover, the dependence of etch rate on fluid velocity was weak. For the same solution and 1:1 cavities, dissolution proceeded under conditions of film precipitation on the entire surface.