Process requirements and precautions for SMT chip​ processing

Process requirements and precautions for SMT chip processing

1、 Conventional SMD mounting

Features: The chip processing accuracy is not high, the number of components is small, and the component varieties are mainly resistance and capacitance, or there are single special-shaped components.

Key process:

1。 Solder paste printing: FPC is positioned on the special printing pallet based on the appearance. Generally, small semi-automatic printers are used for printing, and manual printing can also be used, but the quality of manual printing is worse than that of semi-automatic printing.

2。 SMT mounting in processing: Generally, it can be mounted by craft, and the single component with higher azimuth accuracy can also be mounted by manual mounting machine.

3。 Welding: Reflow welding is generally used, and spot welding can also be used in special cases.

2、 High precision mounting in SMT chip processing

Features: The FPC shall have MARK symbol for substrate positioning, and the FPC itself shall be flat. It is difficult to fix FPC, and it is difficult to ensure the consistency during mass production, so the demand for equipment is high. It is difficult to control other printing solder paste and mounting skills.

Key process: 1. FPC fixation: fixed on the pallet from printing to reflow soldering. The supporting plate used requires a small coefficient of thermal expansion. There are two fixing methods, and the mounting accuracy is QFP lead distance 0. Method for above 65MM

A； The mounting accuracy is QFP lead distance 0. For use below 65MM

B； Method A: The supporting plate is sleeved on the positioning template. FPC is fixed on the pallet with thin high temperature resistant adhesive tape, and then the pallet and positioning template are printed separately. High temperature resistant tape shall have moderate viscosity, be easy to peel after reflow welding, and have no residual adhesive on FPC.

Solder paste printing: FPC is loaded on the pallet, and there is high temperature resistant tape for positioning on the FPC, which makes the height inconsistent with the pallet plane, so it is necessary to use an elastic scraper when printing. The composition of solder paste has a great influence on the printing effect, so it is necessary to select the appropriate solder paste. Other printing templates using method B need special treatment.

Mounting equipment: the top one. Solder paste printer. The printer should be equipped with an optical positioning system, otherwise the welding quality will be greatly affected. Secondly, FPC is fixed on the pallet, but there are always some small gaps between FPC and pallet, which is the biggest difference with PCB substrate. Therefore, the setting of equipment parameters will have a great impact on the printing effect, mounting accuracy and welding effect. Therefore, FPC mounting demands strict process control.