The increasing demand for lightweight and cost-effective conductor materials in the electrical and automotive industries is leading to the substitution of copper with aluminum. However, challenges arise from the natural oxide layer of aluminum, which causes high contact resistances and therefore necessitates the use of copper as a conductor at the cable end. To join both materials, conventional laser-based joining processes are used due to their high flexibility and processing speeds. However, these processes promote the formation of brittle intermetallic phases, which reduce the strength and electrical conductivity of the joint. In contrast, indirect laser beam welding represents a novel process that generates only a thin fusion zone at the interface, thereby reducing the occurrence of intermetallic phases. In this context, the influences of different surface conditions of both joining partners on bond formation have not yet been systematically investigated. The present work therefore addresses both the characterization of these factors and the evaluation of targeted modification strategies to optimize the process and the joint properties. For this purpose, overlap spot welds of both sheet materials were carried out. Oxidic surface layers of aluminum act as diffusion barriers, but their effect can be reduced by suitable pretreatments of the copper surface. Nickel interlayers suppress the growth of intermetallic phases but act as a thermal barrier. Additional form-fit effects achieved by using laser-structured copper sheets, on the other hand, result in significantly higher strengths and improved electrical properties.