That is, the board is placed in an oven, and the temperature raised until the solder melts. The temperature is then reduced and the board removed. Vapor-phase reflow soldering is currently the most popular and consistent method. It uses a liquid fluorinert compound for the heat-transfer medium. Dwell time in the chamber is generally on the order of 15-30 seconds, depending on the mass and density of the board.
Temperature control is important.
The two leading and safest SMD reflow soldering methods are infrared and vapor-phase. Infrared reflow uses air for the transfer medium, and is actually a mixture of infrared heating and convection oven technologies. The heating is generated by infrared lamps or panels, and the air circulated with a blower to prevent stratification. Because the medium is dry air rather than moist vapor, it takes longer to heat the board to reflow temperature. On the other hand, the method produces less thermal stress on the board.