For electronic products, printed circuit board (PCB) design is an essential process that transforms an electrical schematic diagram into a functional product. The effectiveness of this design is closely linked to both the production process and the final product quality. For those who are new to electronic design, experience in this area is often limited. While they may have learned PCB design software, the boards they create frequently encounter various issues. Additionally, there is a lack of in-depth resources on this topic in many electronic publications.
PCB Layout:
The typical sequence for placing components on a PCB is as follows:
Start by positioning components in fixed locations that align with the product’s structural design, such as power connectors, indicator LEDs, switches, and other connectors. Once these components are placed, use the software’s LOCK function to secure them in place, ensuring that they won’t be accidentally moved during later stages of the design process.
1. **Placement of Components**:
Place special and large components on the circuit, such as heating elements, transformers, ICs, etc.
For small components, ensure that the distance between components and the edge of the board is minimized. Ideally, all components should be placed within 3mm from the edge or at least greater than the board’s thickness. This allows the assembly line to properly insert components during wave soldering in mass production and provides space for the guide groove to prevent defects at the edge due to shape processing. If it is necessary to exceed the 3mm limit due to too many components on the PCB, a 3mm auxiliary edge can be added to the board. The auxiliary edge should be V-shaped and can be broken by hand during production.
2. **Isolation Between High and Low Voltage Circuits**:
Many PCBs contain both high and low voltage circuits. The high-voltage components should be separated from the low-voltage components, with the isolation distance depending on the required withstand voltage. For instance, at 2000V, the gap should be at least 2mm, and this distance should increase proportionally for higher voltage requirements. For example, at 3000V, the separation should be more than 3.5mm. Additionally, to prevent electrical tracking, slots can be added between high and low voltage areas on the PCB.
3. **PCB Trace Routing**:
The layout of PCB traces should be as short as possible, particularly in high-frequency circuits. Traces should have rounded bends, as sharp angles or right-angle corners can negatively impact electrical performance, especially in high-frequency designs or high-density layouts. When routing traces across different layers, it is important to avoid parallel traces. Traces should be routed perpendicular, oblique, or bent to minimize parasitic coupling. If possible, avoid using the same trace for both input and output to prevent feedback; adding a ground trace between them can be beneficial.
4. **Trace Width**:
The trace width should be designed to meet both the electrical performance requirements and the production process. The minimum width is primarily determined by the current-carrying capacity, but should not be less than 0.2mm. For high-density and high-precision PCBs, trace widths and spacings can generally be 0.3mm. Trace width should also account for temperature rise under large currents. For example, when using 50μm copper foil, traces of 1-1.5mm width can carry up to 2A with minimal temperature rise. For the common ground trace, use the largest possible width—ideally, greater than 2-3mm. This is particularly important in circuits with microprocessors, as a thin ground trace can cause variations in ground potential, leading to unstable microprocessor timing signals and reduced noise margins. For traces between DIP package IC pins, use the 10-10 or 12-12 rule: For two traces between pins, use a pad diameter of 50 mils with 10 mil trace width and spacing; for one trace between pins, use a 64 mil pad with 12 mil width and spacing.
5. **Trace Pitch**:
The distance between adjacent traces must meet electrical safety standards, while also being wide enough to facilitate manufacturing. The minimum distance should be sufficient to handle the withstand voltage, which includes working voltage, fluctuating voltage, and peak voltage. If technical conditions allow for some metal residue between traces, the spacing can be reduced. Designers should consider the voltage and ensure that signal lines with high and low levels are as short as possible and spaced apart.
6. **Shielding and Grounding**:
The common ground trace should ideally be placed along the edge of the PCB, ensuring as much copper area as possible is used for grounding. This improves shielding effectiveness compared to using a long ground trace. Proper shielding also enhances transmission line characteristics, reduces distributed capacitance, and improves noise immunity. The common ground should form a loop or mesh to minimize ground potential differences, especially when there are numerous integrated circuits or power-hungry components. A looped ground reduces noise tolerance degradation. Additionally, the layout of ground and power supply traces should be as parallel as possible to the direction of data flow to enhance noise suppression. For multi-layer PCBs, use inner layers for ground and power planes, while routing signal traces on the inner and outer layers.
If your have any questions about PCB ,please contact me info@wellcircuits.com
PCB Layout:
The typical sequence for placing components on a PCB is as follows:
Start by positioning components in fixed locations that align with the product’s structural design, such as power connectors, indicator LEDs, switches, and other connectors. Once these components are placed, use the software’s LOCK function to secure them in place, ensuring that they won’t be accidentally moved during later stages of the design process.
1. **Placement of Components**:
Place special and large components on the circuit, such as heating elements, transformers, ICs, etc.
For small components, ensure that the distance between components and the edge of the board is minimized. Ideally, all components should be placed within 3mm from the edge or at least greater than the board’s thickness. This allows the assembly line to properly insert components during wave soldering in mass production and provides space for the guide groove to prevent defects at the edge due to shape processing. If it is necessary to exceed the 3mm limit due to too many components on the PCB, a 3mm auxiliary edge can be added to the board. The auxiliary edge should be V-shaped and can be broken by hand during production.
2. **Isolation Between High and Low Voltage Circuits**:
Many PCBs contain both high and low voltage circuits. The high-voltage components should be separated from the low-voltage components, with the isolation distance depending on the required withstand voltage. For instance, at 2000V, the gap should be at least 2mm, and this distance should increase proportionally for higher voltage requirements. For example, at 3000V, the separation should be more than 3.5mm. Additionally, to prevent electrical tracking, slots can be added between high and low voltage areas on the PCB.
3. **PCB Trace Routing**:
The layout of PCB traces should be as short as possible, particularly in high-frequency circuits. Traces should have rounded bends, as sharp angles or right-angle corners can negatively impact electrical performance, especially in high-frequency designs or high-density layouts. When routing traces across different layers, it is important to avoid parallel traces. Traces should be routed perpendicular, oblique, or bent to minimize parasitic coupling. If possible, avoid using the same trace for both input and output to prevent feedback; adding a ground trace between them can be beneficial.
4. **Trace Width**:
The trace width should be designed to meet both the electrical performance requirements and the production process. The minimum width is primarily determined by the current-carrying capacity, but should not be less than 0.2mm. For high-density and high-precision PCBs, trace widths and spacings can generally be 0.3mm. Trace width should also account for temperature rise under large currents. For example, when using 50μm copper foil, traces of 1-1.5mm width can carry up to 2A with minimal temperature rise. For the common ground trace, use the largest possible width—ideally, greater than 2-3mm. This is particularly important in circuits with microprocessors, as a thin ground trace can cause variations in ground potential, leading to unstable microprocessor timing signals and reduced noise margins. For traces between DIP package IC pins, use the 10-10 or 12-12 rule: For two traces between pins, use a pad diameter of 50 mils with 10 mil trace width and spacing; for one trace between pins, use a 64 mil pad with 12 mil width and spacing.
5. **Trace Pitch**:
The distance between adjacent traces must meet electrical safety standards, while also being wide enough to facilitate manufacturing. The minimum distance should be sufficient to handle the withstand voltage, which includes working voltage, fluctuating voltage, and peak voltage. If technical conditions allow for some metal residue between traces, the spacing can be reduced. Designers should consider the voltage and ensure that signal lines with high and low levels are as short as possible and spaced apart.
6. **Shielding and Grounding**:
The common ground trace should ideally be placed along the edge of the PCB, ensuring as much copper area as possible is used for grounding. This improves shielding effectiveness compared to using a long ground trace. Proper shielding also enhances transmission line characteristics, reduces distributed capacitance, and improves noise immunity. The common ground should form a loop or mesh to minimize ground potential differences, especially when there are numerous integrated circuits or power-hungry components. A looped ground reduces noise tolerance degradation. Additionally, the layout of ground and power supply traces should be as parallel as possible to the direction of data flow to enhance noise suppression. For multi-layer PCBs, use inner layers for ground and power planes, while routing signal traces on the inner and outer layers.
If your have any questions about PCB ,please contact me info@wellcircuits.com
