Assembling components on FPC flexible circuit boards requires that as the smart wearable industry becomes more and more popular, due to the limitation of assembly space, 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 strong to assemble. Today, let us understand the difference between assembling flex and rigid boards
1. Welding process
Like the PCB process, through the operation of stencil and welding printer, the welding is covered on the FPC and the rigid-flex board. But the surface of FPC is not flat, so we need to use some fixtures or reinforcements to fix it. Usually we will paste the reinforcement in the component area of the FPC.
2. SMT component placement
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, stretching and wrinkles will not be a serious problem, so that the SMT frame can be reduced or the marking point can be increased. You may need flexibility after assembly if you don't want to glue the ribs to the bottom of the assembly. Therefore, an SMT jig 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 component placement process. In addition to the dimensional instability of flexible materials, they are also relatively hygroscopic. They absorb water like a sponge. Once the FPC has absorbed moisture, the reflow soldering must be stopped. 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.
