PCB News - Talking about SMT-PCB Design Principles

1. The layout of components on SMT-PCB

When the circuit board is placed on the conveyor belt of the reflow soldering furnace, the long axis of the components should be perpendicular to the transmission direction of the equipment, which can prevent the components from drifting or "tombstones" on the board during the soldering process.
The components on the PCB board should be evenly distributed, especially the high-power components should be dispersed to avoid local overheating on the PCB when the circuit is working, which will affect the reliability of the solder joints.

For double-sided mounting components, the larger components on both sides should be installed in a staggered position, otherwise the welding effect will be affected due to the increase of local heat capacity during the welding process.
Devices with pins on four sides, such as PLCC/QFP, cannot be placed on the wave soldering surface.
The long axis of the large SMT device installed on the wave soldering surface should be parallel to the direction of solder wave flow, which can reduce the solder bridging between the electrodes.
The large and small SMT components on the wave soldering surface should not be lined up in a straight line and should be staggered to prevent false soldering and missing soldering due to the "shadow" effect of the solder wave crest during soldering.
Two, the pad on the SMT-PCB

For SMT components on the wave soldering surface, the pads of larger components (such as transistors, sockets, etc.) should be appropriately enlarged. For example, the pads of SOT23 can be increased by 0.8-1mm to avoid the "shadow effect" of the components. The resulting empty weld.
The size of the pad should be determined according to the size of the component. The width of the pad is equal to or slightly larger than the width of the electrode of the component, and the welding effect is the best.
Between two interconnected components, avoid using a single large pad, because the solder on the large pad will connect the two components to the middle. The correct way is to separate the pads of the two components. The two pads are connected with a thinner wire. If the wires are required to pass a larger current, several wires can be connected in parallel, and the wires are covered with green oil.
There must be no through holes on or near the pads of SMT components. Otherwise, during the REFLOW process, the solder on the pads will flow along the through holes after melting, resulting in false soldering, less tin, or flow to the board. Causes a short circuit on the other side.

The above is an introduction to the principles of SMT-PCB design. Ipcb is also provided to PCB manufacturers and PCB manufacturing technology.