In this paper the investigation of the internal convection heating in reflow soldering environment is discussed. Two measuring methods are presented; with these methods the internal convection coefficients (ICC) could be determined. In the first step the internal convection coefficient (ICC) was measured in the function of the distance from the circuit board (earned information from the z direction) under declared points of the reflow oven. This method is based on the comparing of the internal convection heat flux and the picked up heat mass by the measuring probes during the soldering. In the second step the homogeneity of the convection heating in the function of the nozzle lines (earned information from the x and y directions) is studied. This method is based on the comparing of the internal heat fluxes between the nozzle lines. From this information a 3D internal convection coefficient (ICC) map of the reflow oven was achieved. This 3D map is very important for the effective thermal modelling and the prediction of the reflow soldering profile.