We know that SMT manufacturing and PCB are closely related, and the two influence each other. Today, Sanjing mainly takes you to understand the design principles of PCB in SMT production.

The first is PCB pad design. When designing the pad, the size of the pad should be determined according to the size of the component. When the width of the pad is equal to or slightly larger than the electrode width of the component, the welding effect is the best.

The pads of larger SMT components (such as triodes, sockets, etc.) on the wave soldering interface should be appropriately enlarged to avoid void soldering.

Between two interconnected components, the pads of the two components should be separated, and a thinner wire should be used between the two pads to avoid using a single large pad, because the solder on the large pad will cause Connect the two components to the middle. If the wire is required to pass a larger current, several wires can be connected in parallel, and the wires are covered with green oil.

There should 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, and even flow to The other side of the board caused a short circuit.

The second is the layout of the components on the PCB. When the circuit board is placed on the conveyor belt of the reflow oven, the long axis of the component should be perpendicular to the transmission direction of the device, so as to prevent the drift or tombstone phenomenon of the component on the board during the soldering process.

The components on the PCB should be evenly distributed, especially the high-power components, to avoid local overheating and stress 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 installation process.

Components 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 cannot be lined up in a straight line, and the positions should be staggered, so as to prevent the formation of false soldering or missing soldering during soldering.

The above is about the design principles of PCB in SMT production, I hope it can be helpful to everyone!