Circuit assembly and electrical junction box

A circuit assembly comprising:

• a substrate that is provided with a thermally conductive portion that has thermal conductivity and passes through the substrate in the plate-thickness direction thereof, and that includes an electrically conductive path;
• a semiconductor package that is mounted to the substrate and includes a chip, a resin portion that covers the chip, a first lead portion that is connected to the chip and is exposed on the substrate side of the resin portion, and a second lead portion that is connected to the chip and is exposed to the side opposite to the substrate side of the resin portion;
• a heat dissipating member that is arranged facing the side opposite to the semiconductor package with respect to the substrate and is connected to the thermally conductive portion in such a way as to conduct heat;
• and
• an electrically conductive member that connects the second lead portion and the thermally conductive portion.