What are the precautions for SMT production?

1. Conventional SMD mounting

Features: There are few SMD components, and the precision requirements for SMD processing are not high. The component varieties are mainly resistors and capacitors, or there are individual

SMT process:

1. Solder paste printing: Printing is done by a small semi-automatic printer, or manual printing is also possible, but the quality of manual printing is worse than that of automatic printing.

2. Mounting in SMT processing: Generally, manual mounting can be used, and individual components with higher position accuracy can also be mounted by manual SMT machines.

3. Welding: Generally, a reflow soldering process is used, and spot welding can also be used in special cases.

2. High-precision mounting in SMT processing

Features: There must be a MARK mark on the FPC 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 the equipment requirements are high. In addition, it is difficult to control the printing solder paste and mounting process.

Key process: 1. FPC fixing: Fixed on the pallet from printing the patch to reflow soldering. The pallet used requires a small thermal expansion coefficient. There are two fixing methods, and the mounting accuracy is 0 for the QFP lead spacing. The above method A is used; the mounting accuracy is 0 for the QFP lead spacing. The following method B is used; Method A: The pallet is put 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 moderate viscosity, must be easy to peel off after reflow soldering, and there should be no residual adhesive on the FPC.

Solder paste printing: Because the FPC is loaded on the pallet, there is a high-temperature-resistant tape for positioning on the FPC, which makes the height inconsistent with the pallet plane, so an elastic scraper must be used for printing. The composition of the solder paste has a great influence on the printing effect, and a suitable solder paste must be selected. In addition, the printing template using method B needs to be specially treated.

Mounting equipment: First, the solder paste printer, the printer is preferably equipped with an optical positioning system, otherwise the welding quality will be greatly affected. 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 have a great impact on the printing effect, mounting accuracy, and welding effect. Therefore, the mounting of FPC requires strict process control.

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