FPC SMT process control

Normal SMD placement

Features: SMD processing accuracy requirements are not high, the number of components is small, the component varieties are mainly resistors and capacitors, or there are irregular shaped components.

Key process:
1. Solder Paste Printing: The FPC is positioned on a pallet, solde paste is usually printed on a small semi-automatic printer or manually printed, but the quality of manual printing is not as good as that of semi-automatic printing.
2. Components mounting: Generally, manual placement can be used, and individual components with higher positional accuracy can also be mounted by manual placement machine.
3. Welding: Reflow soldering process is generally used, and spot welding can also be used in special cases.

High-precision SMD placement

Features: There should be fiducial marks on FPC, and the FPC itself should be flat. FPC is difficult to fix, consistency is difficult to ensure in mass production, and requirements for printing and placement equipments are high. In addition, solder paste printing and placement process control is difficult.

Key process:
FPC fixing: During SMT process, FPC was fixed on the pallet from solder paste printing until passed reflow soldering. The pallet used requires a small coefficient of thermal expansion.
The pallet is placed on the positioning template. The FPC is fixed to the pallet with a thin high-temperature resistant tape, and then the pallet is taken off from the positioning template for printing. The high temperature resistant tape should have a moderate viscosity, must be easily peeled off after reflow soldering, and there is no residual glue on the FPC.

Solder paste printing: Because the FPC is loaded on the pallet and fixed with high temperature resistant tape for positioning, the height is not consistent with the plane of the pallet, so an elastic scraper must be used for printing paste.
The solder paste composition has a great influence on the printing effect, and a suitable solder paste must be selected.

Mounting equipment:

• Firstly, the solder paste printing machine preferably has an optical positioning system, otherwise the welding quality will have a greater impact.

• Secondly, the FPC is fixed on the pallet, but there is always a slight gap between the FPC and the pallet, this is the biggest difference from the Rigid PCB assembly. Therefore, the setting of the device parameters has a great influence on the printing effect, the mounting accuracy, and the welding effect. Therefore, FPC placement requires strict process control.