Today, fiber reinforced materials are present in a wide field of industrial applications. Short glass fiber reinforced composites are mainly used in automotive, aerospace and medical sectors. In recent years, endless fiber reinforced thermoplastics have gained importance as construction material, especially for lightweight assembly. There are different methods of joining thermoplastic materials such as vibration, resistance and induction welding. Another process is laser transmission welding, which can be characterized by its excellent reproducibility, high flexibility and potential for automation. Typically, laser transmission welding can be applied for joining unreinforced or glass fiber reinforced thermoplastic parts. This welding process was now adapted to heat conduction welding for joining thermoplastic CFRP to itself. The goal of these investigations was to determine the influence of the matrix material on the weld seam quality. The experiments were conducted with a carbon fiber fabric reinforced polyphenylene sulfide with natural matrix material as well as containing carbon black. In the first step, the temperature distribution at the upper joining member, where the heat generation occurred, was evaluated. The heat affected width was determined and correlated to the process temperatures in order to develop a process model. In a next step, lap shear samples were welded and tested. These results were then correlated with previous results.