Conventional SMD placement

Features: SMD processing accuracy requirements are not high, the number of components is small, the components are mainly based on resistors and capacitors, or there are individual shaped components.

Key process:

1. Solder paste printing: FPC is positioned on the printing pallet by external shape, generally printed by small semi-automatic printing machine, or manual printing, but the quality of manual printing is worse than that of semi-automatic printing.

2. Mounting in SMT processing: Generally, manual placement can be used, and individual components with higher positional accuracy can also be mounted by manual placement machine.

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

High-precision placement in SMT processing

Features: The FP mark should be used for the substrate positioning on the FPC, and the FPC itself should be flat. FPC is difficult to fix, consistency is difficult to ensure in mass production, and equipment requirements are high. In addition, printing solder paste and placement process control is difficult.

Key process: 1. FPC fixed: fixed from the printed patch to the reflow soldering on the pallet. The pallet used requires a small coefficient of thermal expansion. There are two kinds of fixing methods, and the mounting accuracy is the method when the QFP lead pitch is 0.65MM or more.

a. Mounting accuracy is used when the QFP lead pitch is 0.65MM or less.

b. Method: The pallet is placed on the positioning template. The FPC is fixed to 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, must be easily peeled off after reflow soldering, and there is no residual glue on the FPC.

Solder paste printing: Because the FPC is loaded on the pallet, the FPC has a high temperature resistant tape for positioning, so that the height is not consistent with the plane of the pallet, so an elastic scraper must be used for printing. The solder paste composition has a great influence on the printing effect, and a suitable solder paste must be selected. In addition, the printing template using the B method needs special treatment.

Mounting equipment: First, the solder paste printing machine, the printing machine preferably has an optical positioning system, otherwise the welding quality will have a greater impact. Secondly, the FPC is fixed on the pallet, but there is always a slight gap between the FPC and the pallet, which is the biggest difference from the PCB substrate. Therefore, the setting of the device parameters has a great influence on the printing effect, the mounting accuracy, and the welding effect. Therefore, FPC placement requires strict process control.