Fused filament fabrication as an additive manufacturing process is characterized by the flexible and cost-effective production of complex components predestining this production method to manufacture on top of existing structures. In this manner, a novel approach is to combine production processes with additive manufacturing to extend functions such as subsequent mounts or repair of existing parts. In order to use the full potential of this concept, comprehensive investigations are necessary to understand the failure mechanisms and its impact on the macroscopic material behavior. A key factor is the interface between the existing substrate and the newly deposited layers, since its mechanical behavior determines the use of the finished hybrid part. Within this contribution, the interlaminar fusion bonding is investigated by means of compression shear tests. Furthermore, X-ray computed tomography is utilized to study the microscopic structure of the fusion bonding before and after testing. This study refers to polycarbonate (PC) as filament printed on top and three different substrates: neat PC filament, neat PC sheet and glass-fiber reinforced PC sheet. The investigations make the influence of fibers in the semi-finished part and different chamber temperatures during the printing process a subject of discussion. The results reveal two classes of failure types and show a clear dependency of the shear strength on the chamber temperature and material combination of the specimen. Thus, this work provides a valuable contribution to the design of future additively manufactured components.