Abstract: A solder reflow convection furnace employing flux collection and heating to minimize flux and solvent build up and gas densification to reduce input gas flow is disclosed. As solder melts in the furnace, an effluent of vaporized flux is driven off and can condense on cooler components. To minimize such condensation, the gas is directed through a cooling system in which the flux condenses, and the cooled, cleaned gas is directed into the furnace's product cooling section. In another embodiment, in which the gas in the furnace is recirculated, a cooling coil is located upstream of the recirculating gas mover to heat the primary gas. The vaporized flux condenses on the cooling coil, which can be readily removed and replaced. In another aspect of the invention, when the furnace employs a gas amplifier, the recirculating gas is cooled prior to reentry into the heating chamber, which increases its density and removes flux by condensation.

Abstract: A convection furnace using a shimmed gas amplifier to provide a flow of gas over a heating element is disclosed. The heating element is mounted in a substantially leak proof, pressurizable heating chamber. A gas amplifier in an upper plate of the chamber draws gas from a surrounding plenum into the heating chamber at a high flow rate. The pressure in the chamber increases from the input of pressurized gas and the heating of gas flowing over the heating element. The gas amplifier is provided with a toothed spacing shim which creates a stronger flow into the chamber. The stronger flow is capable of resisting the back pressure on the flow from the high pressure in the chamber. The heated gas passes through a plurality of orifices in a lower plate of the chamber to impinge on product traveling below the heating chamber on a conveyor and is recirculated via the plenum to the gas amplifier. The heat transfer rate in the chamber may be controlled by controlling the input flow rate to the gas amplifier.