As circuit boards produced by FPC manufacturer become more integrated, double-sided mounting circuit boards will be widely used in the future. Terminal products are getting smaller, smarter, and more integrated. Components with various functions are stacked on a PCB circuit board, so it is necessary to use both sides A and B of the circuit board.

After the components are mounted on the A side of the circuit board, the components on the B side need to be printed again. Then at this time, side A and side B will be reversed. The top one will now be flipped to the bottom, and the bottom one will be flipped to the top. This flip is only the first step. What is more troublesome is that SMT reflow soldering must be performed again, because some components, especially BGA, are very harsh for soldering temperature. If the solder paste is heated and melted during the second reflow soldering and there are heavier parts on the bottom surface (the first side), at this time, the device may fall or shift due to its own weight and the melting of the solder paste. The quality is abnormal, so in the process control of PCBA processing, we will choose to solder the heavier components before reflow soldering during the second soldering.

In addition, as FPC manufacturer know that， when there are many BGA and IC components on a circuit board, because some dropouts and solder reflow problems must be eliminated, important components will be placed on the second side to make parts, so that it can only be reflowed once. it is good. For other components with fine pins, for the fineness of the alignment requirements, if this device can be mounted on the first side when DFM allows, then it will be more effective than mounting on the second side. The precision control is better. Because when the PCB circuit board is in the first reflow oven, under the influence of high temperature soldering, bending and deformation that are invisible to the naked eye but affect the soldering of some tiny pins will occur. At the same time, the problem is that it will cause a small offset in the solder paste printing, and the amount of the second solder paste is difficult to control

Of course, some components are not involved in the selection of side A and side B because of the influence of the manufacturing process. So how to better optimize the quality of welding is actually to choose a step that has the least impact on the process and the quality can be optimized.