There are many different types of reflow soldering. A few of them have been listed below.

Infrared Reflow: In this method, the PCBA is passed under an infrared lamp. The distance between the lamp and the PCBA is 5cm/2in. The heat from the emitted radiation is used to melt the solder paste and subsequently used to form solder joint post solidification.

Infrared is the electromagnetic radiation located between microwave and visible light. 0.72 to 1.5 u is near-IR, 1.5 to 5.6 u is middle-IR and 5.6 to 1000 u is far-IR. The type of emitter used determines the wavelength of the IR used for reflow. Using IR for reflow allows greater control over the amount of penetrating energy exerted, which is very much required for an even temperature rise. Far-IR avoids shadowing effect and is not sensitive towards color. Using IR enhances heat-flow as it also heats the ambient air inside the oven. 

Vapour Phase Reflow: In this method, the reflow chamber is filled with an inert hydrocarbon vapour. The hydrocarbon is present in the chamber in liquid phase, but after heating it converts into vapour phase and this hot vapour at 250 degree Celsius is used to heat the solder paste, which on solidification forms solder joints. The equilibrium and maximum allowed temperature inside the oven is a function of the boiling point of the primary hydrocarbon used for the process. This means that the process is independent of the location and the configuration of the components on the PCB. No tombstoning or shadowing effect will be observed as long as sufficient soak time is allowed. This type is useful for a low volume and high mix type of PCB. The amount of flux which has to be used is moderate as this reflow occurs in an oxygen free environment, as all of it is expelled by the inert fluorocarbon vapour. 

Forced Convection Reflow: This method is similar to vapour phase reflow, which one major difference that instead of a hydrocarbon as the vapour used to heat the solder paste, this methods used hot air being blown perpendicular to the surface of the PCB to melt the solder paste.

As FPC manufacturer knows that, this method utilizes forced convection in the upper and lower part of the chamber. This method uses a perforated panel type heater with a plenum behind it. The heated air is sent over the PCB to melt the solder, it is then suctioned off by the ducts between the perforated panels. Higher end ovens use a perpendicular to the surface of the PCB gas flow technique t provide uniform heating of the PCB.

The disadvantages of this system is that it uses a large amount of gas to heat the PCB. Making the air oxygen free is also a cost additive challenge. This causes solder balling and lesser wetting problems compared to the IR-reflow method. 

In-line Conduction Reflow: This system employs a heated belt which to heat the PCB from the underside. The belt is made of a fiberglass impregnated with PTFE. All Teflon belts have carbon added to them to make them electrically conductive. This allows the belt to be externally grounded using a wiper brush. This system uses an IR heating element to heat the PCB from the top while using the belt to heat the PCB from the underside.