Design principles of PCB in SMT assembly

- Jan 18, 2019-

First, the layout of components on SMT-PCB

When the board is placed on the conveyor of the reflow soldering furnace, the long axis of the component should be perpendicular to the direction of the device's drive, which prevents drifting or "tap of" components on the board during soldering.

The components on the PCB should be evenly distributed. In particular, the high-power devices should be dispersed to avoid stress caused by local overheating on the PCB during operation, which affects the reliability of the solder joints.

For double-sided components, the larger-sized devices on both sides should be staggered to the mounting position. Otherwise, the welding effect will be affected by the increase of local heat capacity during the welding process.


Four-pin devices such as PLCC/QFP cannot be placed on the wave soldering surface.

The large SMT device mounted on the wave soldering surface has a long axis parallel to the direction in which the solder wave flows, which reduces solder bridging between the electrodes.

The large and small SMT components on the wave soldering surface should not be aligned in a straight line, and the position should be staggered to prevent soldering and soldering due to the "shadow" effect of the solder peak during soldering.

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