Wave soldering method using lead-free solder, apparatus therefor, and wave-soldered assembly

A wave soldering method using lead-free solder, for wave soldering a substrate with component parts mounted thereon from the upper side by using lead-free solder in a chamber filled with an inert gas atmosphere, said method comprising the steps of:

• conveying in said substrate through an inlet of said chamber;
• preheating the lower side of said substrate conveyed in in said conveying-in step at a preheating portion provided in said chamber;
• wave soldering said lower side of said substrate preheated in said preheating step and conveyed, by contact with a molten lead-free solder blowout at a wave soldering portion provided in said chamber;
• cooling said lower side of said substrate flow soldered with said lead-free solder in said wave soldering step and conveyed, by recirculating and cooling said inert gas atmosphere in said chamber and blowing the recirculated and cooled inert gas atmosphere to said lower side of said substrate at a blowing portion provided in proximity to or adjacently to said wave soldering portion in said chamber;
• and
• conveying out said substrate having said lower side cooled in said cooling step through an outlet of said chamber.