Wiring is intricate and constrained in the PCB design process. Even engineers with over ten years of experience often feel inadequate in their wiring skills, having encountered numerous issues that reveal the negative consequences of improper layouts. As a result, they may struggle with how to proceed. However, they possess a rational understanding that helps them navigate these challenges; despite any personal frustrations, their wiring often emerges as aesthetically pleasing and artistic.
Here are some valuable wiring tips and essentials:
Firstly, let’s provide a basic overview. PCB layers can be classified into single-layer, double-layer, and multi-layer designs. Single-layer PCBs are largely obsolete. Double-layer boards, commonly used in sound systems, serve as rough prototypes, while multi-layer boards, typically four layers or more, meet higher component density requirements. From a through-hole perspective, we can categorize them into through-holes, blind holes, and buried holes. A through-hole runs directly from the top to the bottom; a blind hole penetrates from either the top or bottom to a mid-layer but does not extend further, allowing for unobstructed access on other layers. A buried hole, on the other hand, connects mid-layers without being visible from the surface.
Before automatic wiring, it’s crucial to prepare wiring for high-demand interactive lines in advance. Input and output lines should not be adjacent or parallel to minimize reflection interference. If necessary, ground cables can provide isolation, and wiring on two adjacent layers should be perpendicular to each other to avoid parasitic coupling. The efficiency of automatic wiring relies on a well-organized layout. Wiring rules can be established beforehand, including the number of bends, through-holes, and steps. Typically, an exploratory wiring approach is undertaken first, quickly connecting short lines, followed by maze-like wiring. To optimize global wiring routes, lines can be disconnected and rerouted as needed, ultimately enhancing overall wiring effectiveness.
For layout design, one guideline is to keep digital and analog circuits as separate as possible, while another is to distance low-speed lines from high-speed ones. The fundamental principle involves segregating digital and analog grounding. Digital ground, which experiences high current spikes during switching, must not be mixed with analog ground, which remains stable. A recommended layout might resemble the one below.
1. Wiring precautions between power supply and ground wire:
(1) Incorporate decoupling capacitors between the power supply and ground wire. It’s essential to connect the power supply to the chip pin after the decoupling capacitor. The figure below illustrates several incorrect connection methods alongside a correct one—ensure you avoid common mistakes. Decoupling capacitors serve two main purposes: they supply the chip with instantaneous high current and mitigate power supply noise. The goal is to minimize power supply noise affecting the chip while also preventing chip-generated noise from impacting the power supply.
(2) Strive to widen both power supply and ground wires, with ground wires being wider than power lines. The hierarchy is: ground wire > power cord > signal lines.
(3) Consider using a large copper area as ground. Any unused sections of the printed board should be connected to ground for optimal use, or employ a multi-layer design where power and ground each occupy a distinct layer.
2. Handling mixed digital and analog circuits:
Modern PCBs often integrate both digital and analog circuits, necessitating careful routing to mitigate interference, particularly ground noise. Given the high frequency of digital circuits, sensitive analog components should be distanced from high-frequency signal lines. However, there should be only one external ground node for the PCB, necessitating careful internal processing of digital and analog circuit interactions. The grounds of digital and analog circuits remain separate within the board, only connecting at the interface (e.g., plugs) with a single connection point. Common ground on the PCB will depend on the system’s design.
3. Managing line corners:
Typically, line thickness changes at corners, which can lead to reflection issues. Corner design can affect line thickness; right angles are unfavorable, while 45-degree angles are preferable, and rounded corners are optimal but complicate PCB design. Generally, a 45-degree angle suffices for signals, with rounded corners reserved for particularly sensitive lines.
4. Design rule checks post-routing:
Regardless of the task, verification is essential upon completion. This process is akin to checking exam answers when time permits, ensuring high-quality PCB designs. Key inspection aspects include:
(1) Verifying reasonable distances between lines, component pads, through-holes, and ensuring production requirements are met.
(2) Assessing the appropriate widths of power and ground cables, ensuring they are tightly coupled (low wave impedance), and checking for space to widen ground cables within the PCB.
(3) Confirming protective measures for key signal lines, ensuring input and output lines are clearly separated.
(4) Ensuring independent ground wires for analog and digital circuits.
(5) Checking if any graphics (such as icons and notations) might cause signal shorts.
(6) Modifying any unsatisfactory lines.
(7) Verifying process line adherence on the PCB, ensuring resistance welding meets production requirements and that character marks are not pressed onto the device’s solder pad, which could compromise electric quality.
(8) Checking for reduced edge frames in multi-layer boards, as exposed copper foil on the power supply layer can lead to shorts.
In conclusion, these skills and methods are invaluable when designing PCBs. Beyond proficient tool use, a solid theoretical foundation and extensive practical experience are crucial for efficient PCB layout. A vital point is to exercise caution; whether wiring or layout, every step must be taken seriously. A small error can render the final product defective, making it difficult to trace the source of the problem. Thus, investing time in careful detail checks during the design process is far better than addressing errors later, which may require even more time. Ultimately, attention to detail is paramount in PCB design.
Here are some valuable wiring tips and essentials:
Firstly, let’s provide a basic overview. PCB layers can be classified into single-layer, double-layer, and multi-layer designs. Single-layer PCBs are largely obsolete. Double-layer boards, commonly used in sound systems, serve as rough prototypes, while multi-layer boards, typically four layers or more, meet higher component density requirements. From a through-hole perspective, we can categorize them into through-holes, blind holes, and buried holes. A through-hole runs directly from the top to the bottom; a blind hole penetrates from either the top or bottom to a mid-layer but does not extend further, allowing for unobstructed access on other layers. A buried hole, on the other hand, connects mid-layers without being visible from the surface.
Before automatic wiring, it’s crucial to prepare wiring for high-demand interactive lines in advance. Input and output lines should not be adjacent or parallel to minimize reflection interference. If necessary, ground cables can provide isolation, and wiring on two adjacent layers should be perpendicular to each other to avoid parasitic coupling. The efficiency of automatic wiring relies on a well-organized layout. Wiring rules can be established beforehand, including the number of bends, through-holes, and steps. Typically, an exploratory wiring approach is undertaken first, quickly connecting short lines, followed by maze-like wiring. To optimize global wiring routes, lines can be disconnected and rerouted as needed, ultimately enhancing overall wiring effectiveness.
For layout design, one guideline is to keep digital and analog circuits as separate as possible, while another is to distance low-speed lines from high-speed ones. The fundamental principle involves segregating digital and analog grounding. Digital ground, which experiences high current spikes during switching, must not be mixed with analog ground, which remains stable. A recommended layout might resemble the one below.
1. Wiring precautions between power supply and ground wire:
(1) Incorporate decoupling capacitors between the power supply and ground wire. It’s essential to connect the power supply to the chip pin after the decoupling capacitor. The figure below illustrates several incorrect connection methods alongside a correct one—ensure you avoid common mistakes. Decoupling capacitors serve two main purposes: they supply the chip with instantaneous high current and mitigate power supply noise. The goal is to minimize power supply noise affecting the chip while also preventing chip-generated noise from impacting the power supply.
(2) Strive to widen both power supply and ground wires, with ground wires being wider than power lines. The hierarchy is: ground wire > power cord > signal lines.
(3) Consider using a large copper area as ground. Any unused sections of the printed board should be connected to ground for optimal use, or employ a multi-layer design where power and ground each occupy a distinct layer.
2. Handling mixed digital and analog circuits:
Modern PCBs often integrate both digital and analog circuits, necessitating careful routing to mitigate interference, particularly ground noise. Given the high frequency of digital circuits, sensitive analog components should be distanced from high-frequency signal lines. However, there should be only one external ground node for the PCB, necessitating careful internal processing of digital and analog circuit interactions. The grounds of digital and analog circuits remain separate within the board, only connecting at the interface (e.g., plugs) with a single connection point. Common ground on the PCB will depend on the system’s design.
3. Managing line corners:
Typically, line thickness changes at corners, which can lead to reflection issues. Corner design can affect line thickness; right angles are unfavorable, while 45-degree angles are preferable, and rounded corners are optimal but complicate PCB design. Generally, a 45-degree angle suffices for signals, with rounded corners reserved for particularly sensitive lines.
4. Design rule checks post-routing:
Regardless of the task, verification is essential upon completion. This process is akin to checking exam answers when time permits, ensuring high-quality PCB designs. Key inspection aspects include:
(1) Verifying reasonable distances between lines, component pads, through-holes, and ensuring production requirements are met.
(2) Assessing the appropriate widths of power and ground cables, ensuring they are tightly coupled (low wave impedance), and checking for space to widen ground cables within the PCB.
(3) Confirming protective measures for key signal lines, ensuring input and output lines are clearly separated.
(4) Ensuring independent ground wires for analog and digital circuits.
(5) Checking if any graphics (such as icons and notations) might cause signal shorts.
(6) Modifying any unsatisfactory lines.
(7) Verifying process line adherence on the PCB, ensuring resistance welding meets production requirements and that character marks are not pressed onto the device’s solder pad, which could compromise electric quality.
(8) Checking for reduced edge frames in multi-layer boards, as exposed copper foil on the power supply layer can lead to shorts.
In conclusion, these skills and methods are invaluable when designing PCBs. Beyond proficient tool use, a solid theoretical foundation and extensive practical experience are crucial for efficient PCB layout. A vital point is to exercise caution; whether wiring or layout, every step must be taken seriously. A small error can render the final product defective, making it difficult to trace the source of the problem. Thus, investing time in careful detail checks during the design process is far better than addressing errors later, which may require even more time. Ultimately, attention to detail is paramount in PCB design.
