Fourth: Wiring
Wiring is the most crucial process in PCB design, as it directly impacts the performance of the PCB board. In PCB design, wiring is typically divided into three main aspects.
Firstly, layout is essential for a successful PCB design. Without proper connections and with wires flying everywhere, the board will be considered subpar, and it can be said that the design has not even begun.
Secondly, achieving satisfactory electrical performance is crucial to determine the qualification of a printed circuit board. After laying out the components, careful adjustment of the wiring is necessary to achieve optimal electrical performance.
Lastly, aesthetics play a significant role in wiring. Even if the wiring is functional and meets electrical performance requirements, if it appears messy and colorful at first glance, it will still be perceived as substandard. This can lead to difficulties during testing and maintenance. Neat and orderly wiring, without unnecessary crossings, is essential. These principles should be followed while also ensuring the functionality of the electrical components and meeting specific requirements.
When it comes to wiring, the following principles should be kept in mind:
1. Prioritize wiring the power and ground wires first to ensure the electrical performance of the circuit board. Whenever possible, widen the power and ground wires, with the ground wire being wider than the power wire. The relationship should be ground wire > power wire > signal wire.
2. Wire high-demand lines, such as high-frequency lines, first. Avoid parallel edges at the input and output ends to prevent reflection interference. If necessary, add ground isolation. Wiring on adjacent layers should be perpendicular to each other to avoid parasitic coupling.
3. Ground the oscillator’s shell and keep the clock line as short as possible. Avoid extensive routing of the clock line. Increase the ground area under the clock oscillation circuit and high-speed logic circuit section to minimize the surrounding electric field.
4. Use 45-degree polyline wiring whenever possible to reduce the radiation of high-frequency signals. Avoid using 90-degree polylines. Highly demanding lines should also utilize double-curved lines.
5. Avoid forming loops on any signal line. If unavoidable, keep the loop as small as possible and minimize the number of signal line vias.
6. Keep key lines as short and thick as possible with protective ground on both sides.
7. When transmitting sensitive signals and noisy field band signals through flat cables, follow a “ground wire-signal-ground wire” pattern.
8. Reserve test points for key signals to facilitate production and maintenance testing.
9. After completing the schematic diagram wiring, optimize the wiring. Once network inspection and DRC check are correct, fill the unwired area with ground wire and use a large copper layer as ground. Unused areas on the printed board should be connected to ground. Alternatively, consider using a multilayer board with each layer dedicated to power and ground lines.
Line:
In general, the signal line width should be 0.3mm (12mil), and the power line width should be 0.77mm (30mil) or 1.27mm (50mil). When wiring density is high, consider using two lines between IC pins, with a width of 0.254mm (10mil) and a spacing of at least 0.254mm (10mil). In special cases with dense device pins, adjust the line width and spacing accordingly.
Pad:
Pads (PAD) and transition holes (VIA) should have a disk diameter 0.6mm larger than the hole diameter. Depending on the component type, use appropriate disk/hole sizes. Component mounting apertures on the PCB should be slightly larger than the component pin size.
Via:
Typically 1.27mm/0.7mm (50mil/28mil), but can be reduced in high-density scenarios while maintaining a minimum size of 1.0mm/0.6mm (40mil/24mil).
Pitch requirements for pads, lines, and vias:
PAD and VIA: ≥ 0.3mm (12mil)
PAD and PAD: ≥ 0.3mm (12mil)
PAD and TRACK: ≥ 0.3mm (12mil)
TRACK and TRACK: ≥ 0.3mm (12mil)
For higher density:
PAD and VIA: ≥ 0.254mm (10mil)
PAD and PAD: ≥ 0.254mm (10mil)
PAD and TRACK: ≥ 0.254mm (10mil)
TRACK and TRACK: ≥ 0.254mm (10mil)
Wiring is the most crucial process in PCB design, as it directly impacts the performance of the PCB board. In PCB design, wiring is typically divided into three main aspects.
Firstly, layout is essential for a successful PCB design. Without proper connections and with wires flying everywhere, the board will be considered subpar, and it can be said that the design has not even begun.
Secondly, achieving satisfactory electrical performance is crucial to determine the qualification of a printed circuit board. After laying out the components, careful adjustment of the wiring is necessary to achieve optimal electrical performance.
Lastly, aesthetics play a significant role in wiring. Even if the wiring is functional and meets electrical performance requirements, if it appears messy and colorful at first glance, it will still be perceived as substandard. This can lead to difficulties during testing and maintenance. Neat and orderly wiring, without unnecessary crossings, is essential. These principles should be followed while also ensuring the functionality of the electrical components and meeting specific requirements.
When it comes to wiring, the following principles should be kept in mind:
1. Prioritize wiring the power and ground wires first to ensure the electrical performance of the circuit board. Whenever possible, widen the power and ground wires, with the ground wire being wider than the power wire. The relationship should be ground wire > power wire > signal wire.
2. Wire high-demand lines, such as high-frequency lines, first. Avoid parallel edges at the input and output ends to prevent reflection interference. If necessary, add ground isolation. Wiring on adjacent layers should be perpendicular to each other to avoid parasitic coupling.
3. Ground the oscillator’s shell and keep the clock line as short as possible. Avoid extensive routing of the clock line. Increase the ground area under the clock oscillation circuit and high-speed logic circuit section to minimize the surrounding electric field.
4. Use 45-degree polyline wiring whenever possible to reduce the radiation of high-frequency signals. Avoid using 90-degree polylines. Highly demanding lines should also utilize double-curved lines.
5. Avoid forming loops on any signal line. If unavoidable, keep the loop as small as possible and minimize the number of signal line vias.
6. Keep key lines as short and thick as possible with protective ground on both sides.
7. When transmitting sensitive signals and noisy field band signals through flat cables, follow a “ground wire-signal-ground wire” pattern.
8. Reserve test points for key signals to facilitate production and maintenance testing.
9. After completing the schematic diagram wiring, optimize the wiring. Once network inspection and DRC check are correct, fill the unwired area with ground wire and use a large copper layer as ground. Unused areas on the printed board should be connected to ground. Alternatively, consider using a multilayer board with each layer dedicated to power and ground lines.
Line:
In general, the signal line width should be 0.3mm (12mil), and the power line width should be 0.77mm (30mil) or 1.27mm (50mil). When wiring density is high, consider using two lines between IC pins, with a width of 0.254mm (10mil) and a spacing of at least 0.254mm (10mil). In special cases with dense device pins, adjust the line width and spacing accordingly.
Pad:
Pads (PAD) and transition holes (VIA) should have a disk diameter 0.6mm larger than the hole diameter. Depending on the component type, use appropriate disk/hole sizes. Component mounting apertures on the PCB should be slightly larger than the component pin size.
Via:
Typically 1.27mm/0.7mm (50mil/28mil), but can be reduced in high-density scenarios while maintaining a minimum size of 1.0mm/0.6mm (40mil/24mil).
Pitch requirements for pads, lines, and vias:
PAD and VIA: ≥ 0.3mm (12mil)
PAD and PAD: ≥ 0.3mm (12mil)
PAD and TRACK: ≥ 0.3mm (12mil)
TRACK and TRACK: ≥ 0.3mm (12mil)
For higher density:
PAD and VIA: ≥ 0.254mm (10mil)
PAD and PAD: ≥ 0.254mm (10mil)
PAD and TRACK: ≥ 0.254mm (10mil)
TRACK and TRACK: ≥ 0.254mm (10mil)
