Why does SMT need to reflow the reflow carrier and the full process carrier?

The reason why PCB will bend and deform during reflow soldering is because the PCB used in our lead-free process is only Tg150, which means that the sheet will soften after the temperature exceeds 150 °C. The reflow soldering temperature of the lead-free process is as high as 250 °C, which means that today's PCBs will deform more or less as long as they pass through the reflow oven, and the thinner the PCB thickness, the softer deformation in the reflow oven. The more serious it is. Of course, there are other factors that may affect the plate bend, such as the uniformity of the copper foil on the board, whether there are heavy parts, the size of the board, the size and position of the plywood, etc. The temperature is the largest. Contributing factor, the carrier can be used to force the PCB to maintain its flatness when it passes through the furnace, reducing the bending deformation of the plate.