An electronic component is mounted on a substrate such as a circuit board by means of a soldering process such as reflow soldering. The circuit board has a thermal via hole therethrough to provide a heat dissipation path from the top surface to the bottom surface of the circuit board, for dissipating heat from the electronic component. To prevent molten solder from penetrating through the via hole during the soldering process, the via hole is sealed prior to the soldering process. The via hole is sealed from the bottom surface of the substrate by carrying out a screen printing process including at least two printing passes to print a sealing material into the open hole of the thermal via.