PURPOSE: To facilitate forming a high density circuit board by a method wherein a solder layer is provided on the contact part of an aluminum layer formed on an insulating board as a 1st conductor layer with a 2nd conductor layer, i.e. on a through-hole region, and heated and melted.

CONSTITUTION: After an aluminum layer 2 with required patterns is formed on the surface of an insulating board 1 as a 1st conductor layer by sputtering and photoetching, an insulator layer 3 with required patterns are formed by printing and baking. Then a 2nd conductor layer 4 which connects between the required wiring patterns of the aluminum layer electrically and whose main component is copper is formed by printing and baking. Further, after a solder layer 9 is provided on a through-hole part where the 1st conductor layer and the 2nd conductor layer are brought into contact with each other, the board is heated to a temperature of 200∼230°C to melt the solder. Therefore, even if an oxide film is not broken electrically, the electric contact at the through- hole part can be obtained and the application as a multilayer circuit board causes no problem.