PCBA Tech - Process requirements and precautions for SMT processing

The efficiency of SMT patch processing has many aspects. For example, if the overall production volume is constant and the number of SMT patch production lines is large, the production speed can also be increased. However, the operating costs are also increasing. Nowadays, the fierce competition in the electronics industry is unimaginable. In the case of the existing placement production line, it is fundamental to increase the placement rate and win customer satisfaction.

Features: The chip processing 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 during SMT processing: 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, and spot welding can also be used in special cases.

High-precision placement in SMT processing

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 FPC, and it is difficult to guarantee consistency in mass production, which requires high equipment. In addition, it is difficult to control the printing solder paste and placement process.

The key process: 1. FPC fixing: fixed on the pallet from the printing patch to the reflow soldering process. The pallet used requires a small coefficient of thermal expansion. There are two fixing methods, the placement accuracy is QFP lead spacing 0. The method is used when 65MM or more

A; when the placement accuracy is QFP lead pitch 0. 65MM or less

B; 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.

Solder paste printing: Because the pallet is loaded with FPC, there is a high temperature resistant tape for positioning on the FPC, 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 using method B.

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 have a greater impact on the printing effect, placement accuracy, and welding effect. Therefore, FPC placement requires strict process control.