Component layout of PCB SMT DFM

I. Component layout of SMT/PCB

In PCB layout, component layout is a crucial step that directly affects the efficiency of wiring and the performance of circuits.

1. When the circuit board is placed on the conveyor belt of the reflow soldering furnace, the transmission direction of the equipment should be at a vertical angle to the long axis of the components, which can prevent the components from drifting or "tombstones" on the board during the reflow soldering process.

2. The components on the PCB 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.

3. For double-sided mounting components, the larger components on both sides should be installed in dispersed positions, otherwise the welding effect will be affected due to the increase of local heat capacity during the welding process.

4, PLCC/QFP and other components with pins on outsides cannot be placed on the wave soldering surface side.

5. The long axis of the large device mounted on the wave soldering surface should be parallel to the direction of solder wave flow, so as to reduce the solder bridging between the component leads.

6. 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 pseudo soldering and missing soldering caused by the "shadow" effect of the solder wave during soldering.

II. The pads on the SMT/PCB

The key points and common issues of solder pad design on SMT/PCB mainly include the shape, size, spacing, and matching with components of the solder pads.

1. 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 lengthened by 0.8-1mm, which can avoid the "shadow effect" due to component, which will result in empty welding.

2. 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, the welding effect is the best.

3. Between two interconnected components, avoid using a single large pad, because the solder on the large pad will drag the two components to the middle. The correct way is to separate the pads of the two components, Use a wire to connect between the two pads. If the wire is required to pass a larger current, several wires can be connected in parallel, and the wires are covered with soldermask.

4. There should be no through holes on or near the pads of SMT components, otherwise during the reflow process, after melting the solder on the pads will flow along the through holes, resulting in pseudo soldering, insufficient tin, or flow to the other side of the board and cause a short circuit.