An electronic component unit manufacturing method includes: preparing a circuit board including a heat generating element mounted thereon and a bonding metal foil layer formed thereon, a heat transfer board including an insulative layer formed on one face thereof and a heat transfer metal foil layer formed on the insulative layer, and a heat sink; applying a cream solder to form a solder layer on the board bonding metal foil layer or the heat transfer metal foil layer; superimposing the bonding metal foil layer and the heat transfer metal foil layer with each other via the solder layer; re-melting the solder layer to solder the bonding metal foil layer and the heat transfer metal foil layer; and superimposing the other face of the heat transfer board with the heat sink to thereby assemble the circuit board with the heat sink via the heat transfer board.