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The process of mounting SMD on a flexible circuit board (FPC) requires that when the miniaturization of electronic products develops, a considerable part of the surface mount of consumer products, due to the assembly space, the SMD is mounted on the FPC to complete the whole The assembly of the machine. The surface mounting of SMD on the FPC has become one of the development trends of SMT technology. The process requirements and points of attention for surface mounting are as follows.
Conventional SMD placement
Features: The placement accuracy is not high, the number of components is small, and the component varieties are mainly resistors and capacitors, or there are individual special-shaped components.
The key process:
1. Solder paste printing: FPC is positioned on a special pallet for printing by its appearance. Generally, it is printed by a small semi-automatic printing machine or manual printing, but the quality of manual printing is worse than that of semi-automatic printing.
2. Mounting: Generally, manual mounting can be used, and individual components with higher position accuracy can also be mounted by a manual placement machine.
3. Welding: The reflow welding process is generally used, and spot welding can also be used in special circumstances.
High-precision placement
Features: FPC flexible circuit boards must be marked with MARK for substrate positioning, and the FPC itself must be flat. FPC is difficult to fix, and consistency is difficult to ensure during mass production, and it has high requirements for equipment. In addition, it is difficult to control the printing solder paste and placement process.
The key process:
1. FPC flexible circuit board fixing: fixed on the pallet from the printing patch to the reflow soldering. The pallet used requires a small coefficient of thermal expansion. There are two fixing methods, and the mounting accuracy is the method when the QFP lead spacing is more than 0.65MM A; Method B is used when the placement accuracy is less than 0.65MM for QFP lead spacing.
Method A: The pallet is placed on the positioning template. The FPC is fixed on the pallet with a thin high-temperature resistant tape, and then the pallet is separated from the positioning template for printing. The high-temperature resistant tape should have a moderate viscosity, and it must be easy to peel off after reflow soldering, and There is no residual glue on the FPC.
Method B: The pallet is customized, and its process requirements must be minimally deformed after multiple thermal shocks. The pallet is equipped with a T-shaped positioning pin, and the height of the pin is slightly higher than that of the FPC.
2. Solder paste printing: Because the pallet is loaded with FPC, the FPC flexible circuit board has a high-temperature resistant tape for positioning, so that the height is inconsistent with the pallet plane, so you must choose an elastic squeegee when printing. The composition of the solder paste has a greater impact on the printing effect Large, you must choose a suitable solder paste. In addition, the printing template of the B method needs to be specially processed.
