Assembly of components on FPC flexible circuit boards is required. As the smart wearable industry becomes more and more popular, due to the limitation of assembly space, the surface mounting of SMD on FPC has become one of the development trends of SMT technology. However, FPCs are more difficult to assemble than PCBs because they are not as robust to assemble. Today, let us understand the difference between assembling flexible and rigid boards.
1. The soldering process is
like the PCB process, through the operation of the stencil and the solder paste printer, the solder paste is covered on the FPC and the flex-rigid board. But the surface of the FPC is not flat, so we need to use some fixtures or reinforcements to fix it. Usually we will paste reinforcement in the component area of FPC.
2. SMT components are placed
under the current trend of miniaturization of SMT components, small components will cause some problems during the reflow soldering process. If the FPC is small, elongation and wrinkling will not be a serious problem, allowing the SMT frame to be reduced or marker points to be increased. You may need flexibility after assembly if you don't want to stick the stiffeners to the bottom of the assembly. Therefore, SMT fixtures would be a good choice.
3. Reflow soldering process
Before reflow soldering, the FPC must be dried. This is an important difference between FPC and PCB assembly placement process. In addition to the dimensional instability of flexible materials, they are also relatively hygroscopic. They absorb water like a sponge. Reflow soldering must be stopped once the FPC has absorbed moisture. PCBs have the same problem, but with higher tolerances. FPC needs to be preheated and baked at a temperature of 225°-250°. This preheating and baking must be done quickly within 1 hour. If it is not baked in time, it will need to be stored in a dry or nitrogen storage room.