Abstract: This invention discloses a furnace in which hot gases are discharged from heaters to provide uniform heating to printed circuit boards commonly used in the electronic industry. Outside air is prevented from flowing into the furnace, so as to reduce and to stabilize the concentration of oxygen. The furnace 1 is designed with an air tunnel 2 to separate it into upper and lower sections which are fitted with hot air blow type heaters 5a, 5b. The hot air discharged from the heaters in the upper and lower sections flow in opposite directions to create a counter-flow of gases. Each individual heater can produce its own hot air circuit. They are designed with the blowing outlet and suction inlet in the same structure with the blowing outlet fitted with a redirectional flow plate 18 which directs the hot air to the suction inlet.

Abstract: A tunnel-type reflow furnace containing a preliminary heating zone and a main heating zone is disclosed. In the furnace, at least two pairs of infrared heaters are disposed on both the top and bottom of a tunnel providing a pathway for the transfer of an article to be heated, and the infrared heaters are of a gas blowing type. In a preferred embodiment, a gas-blowing nozzle that is freely adjustable in the direction of gas blowing is provided between infrared heaters on both the top and bottom of the tunnel. This furnace allows the heating profile to be easily changed in accordance with a specific use. It is also capable of efficient and uniform heating of a printed circuit board even if it carries many components at high density. As a result, the furnace ensures reliable soldering of the circuit board.