PCB Tech - Flexible rigid PCB: SMT mounting method for double-sided circuit boards

Flexible rigid PCB: SMT mounting method for double-sided circuit boards

With the increasing integration of circuit boards, 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 Flex rigid PCB, so it is necessary to use the A side and B side of the circuit board.

After mounting components on the A side of the Flex rigid board, the components on the B side need to be reprinted. Then side A and side B will be reversed at this time. Now the top one will flip to the bottom, and the bottom one will flip to the top. This flip is only the first step. The more troublesome thing is that SMT reflow soldering must be performed again, because some components, especially BGA, are very harsh on soldering temperature.

If the solder paste is heated and melted during the second reflow soldering, and the bottom surface (the first side) has a heavier part, the device may fall or shift due to its own weight and the melting of the solder paste. The quality is abnormal, so the PCB process For one processing in the control, we will choose to solder heavier components before reflow soldering during the second soldering.

In addition, when there are many BGA and IC components on a circuit board, because some peeling and reflow problems must be eliminated, important components will be placed on the second side as parts, so that they can only be reflowed once. This is good. For other components with fine pins, for the precision required for alignment, if the device can be mounted on the first side with DFM allowed, then it will be more effective than mounting on the second side.

The control accuracy is better. Because when the PCB circuit board is in the first reflow oven, under the influence of high temperature soldering, there will be bending and deformation that are invisible to the naked eye but affect the soldering of some tiny pins. At the same time, the problem is that small deviations will be caused during solder paste printing, and the amount of secondary solder paste is difficult to control

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