A light source device includes an electronic component and a substrate. The electronic component includes first and second electrodes exposed at a lower surface. The first electrode includes first and second parts separated from each other by a separation region on the lower surface of the electronic component. The substrate includes a basal member and a first and second wiring layers disposed on an upper surface of the basal member. The electronic component is mounted to the substrate so that upper surfaces of the first and second wiring layers respectively face the first and second electrodes. The substrate includes a first region at a position overlapping the separation region as seen in a top view. Solder wettability of the substrate in the first region is lower than solder wettability of the substrate in at least regions of the first wiring layer facing the first and second parts of the first electrode.