What are the FPC soft board mounting processes in SMT production?
In the SMT production line, the process of mounting SMD on flexible printed circuit boards (FPC) requires the development of miniaturization of electronic products, and a considerable part of the surface mount of consumer products, due to the assembly space, their SMDs are all mounted It is installed on the FPC soft board to complete the assembly of the whole machine. The surface mount of SMD on FPC has become one of the development trends of SMT technology. Regarding the process requirements and attention points of surface mount, the following Jingbang electronic technical operators will share with you a little bit.
1. Conventional SMD placement of FPC soft boards
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, small semi-automatic printing machines are used for printing, or manual printing can also be used, but the quality of manual printing is worse than that of semi-automatic printing.
2. Placement: Generally, manual placement can be used, and individual components with higher position accuracy can also be placed by manual placement machine.
3. Welding: Reflow welding is generally used, spot welding can also be used under special circumstances.
2. FPC soft board high-precision placement
Features: There must be a MARK mark for substrate positioning on the FPC, and the FPC itself must be flat. It is difficult to fix the FPC, and it is difficult to ensure consistency in mass production, and the equipment requirements are high. In addition, it is difficult to control the printing solder paste and mounting process.
The key process:
1. FPC soft board fixing: from printing and patching to reflow soldering, the whole process is fixed on the pallet. The pallet used requires a small thermal expansion coefficient. There are two fixing methods. When the mounting accuracy is QFP lead spacing above 0.65MM, use method A ; Use method B when the placement accuracy is less than 0.65MM for QFP lead spacing.
Method A: Set the pallet 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, be easy to peel off after reflow soldering, and there should be no adhesive residue on the FPC.
Method B: The pallet is customized, and its process requirements must be minimally deformed after multiple thermal shocks. There are T-shaped positioning pins on the pallet, and the height of the pins is slightly higher than that of the FPC.
2. Solder paste printing: Because the pallet is loaded with FPC, there is a high temperature resistant tape for positioning on the FPC soft board, so that the height is inconsistent with the pallet plane, so an elastic scraper must be used when printing. The composition of the solder paste has a greater impact on the printing effect, and a suitable solder paste must be selected. In addition, special treatment is required for the printing template of the B method.
3. Mounting equipment: First, the solder paste printing machine, the printing machine is best equipped with an optical positioning system, otherwise the welding quality will have a greater impact. Secondly, the FPC is fixed on the pallet, but there will always be some tiny gaps between the FPC and the pallet, which is the biggest difference from the PCB substrate. Therefore, the setting of equipment parameters will affect the printing effect, placement accuracy, and welding effect. Have a greater impact. Therefore, FPC placement requires strict process control.
The above is the editor of Jingbang Electronics sharing SMT chip processing FPC soft board mounting process knowledge, if you need more information, please inform us