PURPOSE: To surely bond a semiconductor substrate, by dropping molten solder onto a substrate support under an inert or reducing atmosphere and then applying uniform pressure to the solder to promote the wetting of the substrate support with the molten solder.
CONSTITUTION: A substrate support 11a' plated with nickel on the surface is placed on the base board of an electric furnace and conveyed into the cover 2 of the furnace. The temperature of the substrate support is raised accorcing as the support is moved forth. The temperature of the support becomes maximum when it comes to the position 11d' of a molten solder dropping unit 6. At that time, molten solder 7 is dropped to make a spherical solder layer. A peripheral guide ring 12 is moved down toward the position 11e' of th substrate support and a piston 13 fitted in the ring is also moved down to thrust the solder layer for about 0.1W0.5sec. As a result, the solder is spread well on the plated nickel which is hard to be wetted. Therefore, a semiconductor substrate 10 is bonded well to the support.