131 Essential Guidelines for PCB Layout Design: Design Specifications for Improving Performance and Stability

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PCB Routing and Layout

PCB Routing and Layout Isolation Guidelines: Isolation of high- and low-current circuits, high- and low-voltage circuits, high- and low-frequency circuits, input and output circuits, and digital and analog circuits. The criterion for isolation is a difference of one order of magnitude. Isolation methods include: physical separation and ground isolation.

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PCB Routing and Layout

The crystal oscillator should be placed as close to the IC as possible, and the traces should be relatively wide.

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PCB Routing and Layout

Grounding the Crystal Oscillator Housing

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PCB Routing and Layout

When clock signals are routed through a connector, the pins on the connector should be surrounded by ground pins.

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PCB Routing and Layout

Provide separate power and ground paths for analog and digital circuits. Whenever possible, widen the power and ground traces for these two sections of the circuit or use separate power and ground planes to reduce the impedance of the power and ground loops and minimize any interference voltages that may occur in those loops.

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PCB Routing and Layout

For a standalone PCB, the analog ground and digital ground can be connected at a single point near the system ground. If the power supply voltages are the same, the power supplies for the analog and digital circuits should be connected at a single point at the power supply input. If the power supply voltages are different, connect a 1–2 nF capacitor in parallel near the two power supplies to provide a path for the signal return current between them.

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PCB Routing and Layout

If the PCB is plugged into the motherboard, the power supplies and grounds for the motherboard’s analog and digital circuits must also be separated; the analog ground and digital ground should be connected to the motherboard’s ground points, Power supplies should be connected at a single point near the system ground. If the supply voltages are the same, the power supplies for the analog and digital circuits should be connected at a single point at the power input. If the supply voltages are different, connect a 1–2 nF capacitor in parallel between the two power supplies near where they meet to provide a path for signal return current between them.

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PCB Routing and Layout

When high-speed, medium-speed, and low-speed digital circuits are used together, they should be assigned to different layout areas on the printed circuit board.

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PCB Routing and Layout

Low-level analog circuits and digital logic circuits should be separated as much as possible.

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PCB Routing and Layout

When designing multilayer printed circuit boards, the power plane should be located close to the ground plane and placed beneath it.

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PCB Routing and Layout

When designing multilayer printed circuit boards, the routing layers should be placed adjacent to a solid metal plane.

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PCB Routing and Layout

When designing multilayer printed circuit boards, separate digital and analog circuits; whenever possible, place them on different layers. If they must be placed on the same layer, remedial measures such as routing grooves, adding ground traces, or using physical barriers can be employed. Analog and digital ground planes and power supplies must be kept separate and must not be mixed.

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PCB Routing and Layout

Clock circuits and high-frequency circuits are the primary sources of interference and radiation; they must be housed separately and kept away from sensitive circuits.

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PCB Routing and Layout

Be aware of waveform distortion during long-distance transmission

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PCB Routing and Layout

The best way to reduce the loop area between the interference source and the sensitive circuit is to use twisted-pair and shielded cables, twisting the signal wires together with the ground wire (or current-carrying circuit) so that the distance between the signal and the ground wire (or current-carrying circuit) is as short as possible.

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PCB Routing and Layout

Increase the distance between the wires to minimize mutual inductance between the interference source and the affected line as much as possible.

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PCB Routing and Layout

If possible, route the lines from the interference source at a right angle (or close to a right angle) to the lines being affected; this can significantly reduce coupling between the two lines.

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PCB Routing and Layout

Increasing the distance between traces is the best way to reduce capacitive coupling.

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PCB Routing and Layout

Before beginning the actual cabling, the first step is to categorize the cables. The primary method of categorization is by power level, with cables grouped into several categories based on 30 dB increments in power level.

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PCB Routing and Layout

Wires of different categories should be bundled separately and laid apart from one another. Wires of adjacent categories may be grouped together after implementing measures such as shielding or twisting. The minimum distance between wire harnesses laid by category is 50–75 mm.

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PCB Routing and Layout

When laying out resistors, the gain-control resistors and bias resistors (pull-up and pull-down) in amplifier, pull-up/pull-down, and regulated rectifier circuits should be placed as close as possible to the amplifier, active components, and their power supply and ground to minimize their decoupling effects (and improve transient response).

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PCB Routing and Layout

Place the bypass capacitor near the power supply input.

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PCB Routing and Layout

Decoupling capacitors should be placed at the power supply input, as close as possible to each IC.

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PCB Routing and Layout

Basic Characteristics of PCBs Impedance: Determined by the mass of the copper and the cross-sectional area. Specifically: 1 ounce = 0.49 milliohms per unit area Capacitance: C = EoErA/h, where Eo is the permittivity of free space, Er is the permittivity of the PCB substrate, A is the area through which the current flows, and h is trace spacing Inductance: Distributed evenly throughout the trace, approximately 1 nH/m For 1-ounce copper traces on a 0.25 mm (10 mil) thick FR4 substrate, located above the ground plane, a 0.5 mm wide, 20 mm long trace can produce an impedance of 9.8 milliohms, an inductance of 20 nH, and a coupling capacitance of 1.66 pF between the trace and ground.

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PCB Routing and Layout

Basic Guidelines for PCB Routing: Increase the spacing between traces to reduce crosstalk caused by capacitive coupling; route power and ground lines in parallel to optimize PCB capacitance; route sensitive high-frequency lines away from high-noise power lines; Widen power and ground traces to reduce their impedance;

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PCB Routing and Layout

Separation: Use physical separation to reduce coupling between different types of signal lines, especially between power lines and ground lines.

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PCB Routing and Layout

Local Decoupling: Decouple local power supplies and ICs by using high-capacity bypass capacitors between the power supply input and the PCB to filter low-frequency ripple and meet peak power requirements. Use decoupling capacitors between the power supply and ground of each IC, placing these capacitors as close to the pins as possible.

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PCB Routing and Layout

Trace Separation: Minimize crosstalk and noise coupling between adjacent traces on the same layer of the PCB. Apply the 3W standard to critical signal paths.

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PCB Routing and Layout

Protection and Bypass Circuits: Implement a two-sided ground protection measure for critical signals, and ensure that both ends of the protection circuit are grounded.

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PCB Routing and Layout

Single-layer PCB: Ground traces should be at least 1.5 mm wide, and changes in the width of jumpers and ground traces should be kept to a minimum.

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PCB Routing and Layout

Double-layer PCBs: Preferably use a ground grid or dot matrix layout, with a width of at least 1.5 mm. Alternatively, place the ground on one side and the signal and power traces on the other.

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PCB Routing and Layout

Protective Loop: Form a loop using the ground wire to enclose and isolate the protective logic.

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PCB Routing and Layout

PCB Capacitance: On multilayer boards, PCB capacitance arises from the thin insulating layers between the power plane and the ground plane. Its advantages include very high frequency response and low series inductance that is uniformly distributed across the entire surface or along the entire trace. It is equivalent to a decoupling capacitor uniformly distributed across the entire board.

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PCB Routing and Layout

High-speed and low-speed circuits: High-speed circuits should be routed close to the ground plane, while low-speed circuits should be routed close to the power plane. Copper fill for ground: Copper fill must ensure proper grounding.

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PCB Routing and Layout

The routing directions of adjacent layers should be orthogonal to each other, and different signal lines should not be routed in the same direction on adjacent layers to reduce unnecessary interlayer crosstalk; When this situation is difficult to avoid due to board structural limitations (such as certain backplanes), particularly at higher signal speeds, consider using ground planes to isolate each routing layer and using signal lines to isolate individual signal lines;

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PCB Routing and Layout

Wiring with one end left floating is not permitted, to avoid the “antenna effect.”

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PCB Routing and Layout

Impedance Matching Design Rules: The trace width within the same grid should remain consistent. Variations in trace width can cause non-uniformity in the characteristic impedance of the line, which can lead to reflections at high transmission speeds; this situation should be avoided during design. Under certain conditions, variations in trace width may be unavoidable; in such cases, the effective length of the inconsistent sections should be minimized as much as possible.

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PCB Routing and Layout

Prevent signal lines from forming self-loops between different layers, as self-loops can cause radiated interference.

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PCB Routing and Layout

Short-Circuit Rules: Keep wiring as short as possible, especially for critical signal lines such as clock lines; be sure to place the oscillator very close to the components.

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PCB Routing and Layout

Chamfering Rules: In PCB design, sharp angles and right angles should be avoided, as they create unnecessary radiation and result in poor manufacturability. The angle between any two lines should be greater than 135 degrees.

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PCB Routing and Layout

The wires connecting the filter capacitor pads to the connection plate should be 0.3 mm in diameter, and the interconnect length should be ≤1.27 mm.

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PCB Routing and Layout

Generally, the high-frequency section is placed at the interface to minimize the length of the wiring. It is also important to consider the separation of the ground planes for the high- and low-frequency sections; typically, the ground planes for the two sections are separated and then connected at a single point at the interface.

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PCB Routing and Layout

In areas with a high density of through-holes, care must be taken to avoid connecting cutouts in the power and ground planes, as this would segment the plane and compromise its integrity, thereby increasing the loop area of signal lines in the ground plane.

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PCB Routing and Layout

Guidelines for Avoiding Overlapping Power Planes: For PCBs with two or more layers, different power planes should not overlap spatially. This is primarily to reduce interference between different power sources, especially between those with significantly different voltages. Overlapping power planes must be avoided whenever possible; when this is unavoidable, consider inserting an intermediate ground layer.

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PCB Routing and Layout

3W Rule: To reduce crosstalk between lines, ensure that the spacing between them is sufficiently large. When the center-to-center distance between lines is at least three times the line width, the electric fields of 70% lines will not interfere with each other. To prevent interference between the electric fields of 98% lines, apply the 10W rule.

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PCB Routing and Layout

20H Rule: Using one H (the thickness of the dielectric between the power source and ground) as a unit, retracting by 20H will confine the electric field of the 70% within the grounded edge, while retracting by 1000H will confine the electric field of the 98% within the grounded edge.

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PCB Routing and Layout

The 5-5 Rule: A guideline for selecting the number of layers in a printed circuit board. If the clock frequency reaches 5 MHz or the pulse rise time is less than 5 ns, the PCB must be a multilayer board. If a two-layer board is used, it is best to designate one side of the board as a complete ground plane.

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PCB Routing and Layout

Mixed-Signal PCB Zoning Guidelines: 1. Divide the PCB into separate analog and digital sections; 2. Place A/D converters across both sections; 3. Do not split the ground plane; establish a unified ground plane beneath both the analog and digital sections of the board; 4. On all layers of the PCB, digital signals must be routed only in the digital section of the board, and analog signals must be routed only in the analog section of the board; 5. Separate the analog power supply from the digital power supply; 6. Tracing must not cross the gap between power supply planes; 7. Signal lines that must cross the gap between power supply planes must be routed on a layer adjacent to a large ground plane; 8. Analyze the actual paths and modes through which return ground currents flow;

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PCB Routing and Layout

Multilayer boards are an effective design measure for board-level EMC protection and are recommended as the preferred option.

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PCB Routing and Layout

Signal circuits and power supply circuits should each have their own independent ground wires, which ultimately connect to a single common ground; the two should not share a common ground wire.

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PCB Routing and Layout

The signal return path must use a separate, low-impedance grounding circuit; the chassis or structural framework must not be used as part of the circuit.

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PCB Routing and Layout

For equipment operating in the medium- and short-wave bands, when connected to ground, the ground wire length must be less than 1/4λ; if this requirement cannot be met, the ground wire length must not be an odd multiple of 1/4λ.

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PCB Routing and Layout

The ground wires for strong and weak signals must be routed separately and connected to the grounding grid at only one point each.

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PCB Routing and Layout

In general, equipment should have at least three separate ground lines: one for low-level circuits (known as the signal ground), one for relays, motors, and high-level circuits (known as the interference ground or noise ground); a third is the safety ground wire of the AC power supply, which must be connected to the equipment chassis ground when the equipment uses AC power; the chassis must be insulated from the power outlet, but both must be connected at a single point, and finally, all ground wires must be gathered at a single point and grounded. Circuit breakers should be grounded at a single point at the location of maximum current. When f 10 MHz, use multi-point grounding; when 1 MHz < f < 10 MHz, if the ground wire length is < 1/20λ, use single-point grounding; otherwise, use multi-point grounding.

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PCB Routing and Layout

Guidelines for Avoiding Ground Loops: Power cables should be routed parallel to ground wires.

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PCB Routing and Layout

The heat sink must be connected to the power ground, shield ground, or protective ground on the circuit board (preferably the shield ground or protective ground) to reduce radiated interference.

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PCB Routing and Layout

Separate digital ground from analog ground, and widen the ground trace

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PCB Routing and Layout

When using a mix of high, medium, and low speeds, pay attention to the different layout areas.

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PCB Routing and Layout

Dedicated neutral wire; the routing width of the power cord must be ≥1 mm

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PCB Routing and Layout

Keep the power and ground lines as close together as possible, and arrange the power and ground traces on the entire printed circuit board in a “well” pattern to ensure an even distribution of current.

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PCB Routing and Layout

Whenever possible, route the interference source lines at right angles to the lines subject to induction.

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PCB Routing and Layout

When classified by power rating, wires in different categories should be bundled separately, and the distance between separately laid wire harnesses should be 50–75 mm.

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PCB Routing and Layout

In applications with high performance requirements, the inner conductor must be fully enclosed in a 360° wrap, and a coaxial connector must be used to ensure the integrity of the electric field shielding.

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PCB Routing and Layout

Multilayer PCBs: The power plane and ground plane must be adjacent. High-speed signals should be routed close to the ground plane, while non-critical signals should be routed close to the power plane.

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PCB Routing and Layout

Power Supply: When a circuit requires multiple power supplies, isolate each power supply from the others by grounding them separately.

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PCB Routing and Layout

Vias: For high-speed signals, vias introduce inductance of 1–4 nH and capacitance of 0.3–0.8 pF. Therefore, vias in high-speed traces should be kept as small as possible. Ensure that the number of vias in parallel high-speed traces is consistent.

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PCB Routing and Layout

Stub Lines: Avoid using stub lines on high-frequency and sensitive signal lines.

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PCB Routing and Layout

Star-Configuration Signal Layout: Avoid using this for high-speed and sensitive signal lines

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PCB Routing and Layout

Radiating Signal Layout: Avoid using this layout for high-speed and sensitive circuits; maintain a consistent signal path width; and do not place vias too densely when crossing power and ground planes.

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PCB Routing and Layout

Ground Loop Area: Keeping the signal path and its ground return trace close together will help minimize ground loops.

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PCB Routing and Layout

Clock circuits are generally placed at the center of the PCB or in a well-grounded location, so that the clock is as close as possible to the microprocessor and the leads are kept as short as possible; at the same time, only the case of the quartz crystal oscillator should be grounded.

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PCB Routing and Layout

To further enhance the reliability of the clock circuit, the clock area can be isolated by using ground traces to enclose it, and the ground plane area beneath the crystal oscillator can be enlarged to prevent the routing of other signal lines through it;

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PCB Routing and Layout

The principles of component layout involve separating analog and digital circuit sections, high-speed and low-speed circuits, high-power and small-signal circuits, and noisy and non-noisy components. At the same time, component leads should be kept as short as possible to minimize mutual interference and coupling.

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PCB Routing and Layout

The circuit board is divided into zones based on function, with the ground lines of each zone connected in parallel and grounded at a single point. When there are multiple circuit units on the board, each unit should have an independent ground path, and all units should be connected to the common ground at a single point. Both single-sided and double-sided boards should use a single-point connection to the power supply and a single-point ground connection.

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PCB Routing and Layout

Signal lines should be as short and thick as possible, with protective ground connections on both ends. When signals need to be routed out, use flat cables and arrange them in an alternating “ground—signal—ground” pattern.

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PCB Routing and Layout

Place I/O interface circuits and power driver circuits as close to the edge of the printed circuit board as possible.

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PCB Routing and Layout

In addition to clock circuits, try to avoid routing traces near noise-sensitive devices and circuits as much as possible.

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PCB Routing and Layout

When a printed circuit board (PCB) includes high-speed data interfaces such as PCI and ISA, care must be taken to route the circuits on the board progressively according to signal frequency—that is, starting from the slot interface, route high-frequency circuits first, followed by medium-frequency circuits, and then low-frequency circuits—so that circuits prone to generating interference are kept away from the data interface.

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PCB Routing and Layout

Signal traces on printed circuit boards should be as short as possible; they should not exceed 625px in length, and the number of vias should be kept to a minimum.

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PCB Routing and Layout

When signal lines need to turn, use 45-degree or curved bends in the routing and avoid 90-degree bends to minimize reflections of high-frequency signals.

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PCB Routing and Layout

Avoid 90-degree bends when routing cables to reduce high-frequency noise emissions.

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PCB Routing and Layout

Pay attention to the crystal oscillator wiring. Place the crystal oscillator as close as possible to the microcontroller pins, isolate the clock area with a ground plane, and ground and secure the crystal oscillator package.

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PCB Routing and Layout

Divide the circuit board into appropriate zones, such as strong and weak signals, and digital and analog signals. Keep sources of interference (such as motors and relays) as far away as possible from sensitive components (such as microcontrollers).

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PCB Routing and Layout

Use ground lines to isolate the digital and analog sections; the digital ground and analog ground must be separated and ultimately connected to the power supply ground at a single point. The routing of A/D and D/A chips also follows this principle; manufacturers have already taken this requirement into account when assigning pin layouts for A/D and D/A chips.

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PCB Routing and Layout

The ground lines for microcontrollers and high-power devices should be grounded separately to minimize mutual interference. Place high-power devices as close to the edge of the circuit board as possible.

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PCB Routing and Layout

When wiring, minimize the area of the loop to reduce induced noise.

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PCB Routing and Layout

When wiring, use the thickest possible power and ground wires. In addition to reducing voltage drops, this is especially important for minimizing coupled noise.

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PCB Routing and Layout

ICs should be soldered directly onto the circuit board whenever possible; use IC sockets sparingly.

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PCB Routing and Layout

Reference points should generally be placed at the intersection of the left and bottom edge lines (or the intersection of their extensions) or at the first pad on the printed circuit board's plug-in component.

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PCB Routing and Layout

We recommend using a 25-mil grid for the layout.

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PCB Routing and Layout

Keep the total length of the connections as short as possible, and make the critical signal lines as short as possible.

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PCB Routing and Layout

Components of the same type should be aligned in the X or Y direction. Discrete components of the same type that have polarity should also be aligned in the X or Y direction whenever possible to facilitate production and debugging;

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PCB Routing and Layout

Components should be placed in a way that facilitates debugging and maintenance. Small components should not be placed next to large ones, and there should be sufficient space around components that require debugging. Heat-generating components should have sufficient space to facilitate heat dissipation. Thermosensitive components should be kept away from heat-generating components.

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PCB Routing and Layout

The distance between dual-in-line through-hole components must be >2 mm. The distance between a BGA and adjacent components must be >5 mm. The distance between small surface-mount components, such as resistors and capacitors, must be >0.7 mm. The distance between the outer edge of a surface-mount component’s pad and the outer edge of an adjacent through-hole component’s pad must be >2 mm. Through-hole components must not be placed within 5 mm of crimped components. Surface-mount components must not be placed within 5 mm of the solder side.

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PCB Routing and Layout

Decoupling capacitors for integrated circuits should be placed as close as possible to the chip’s power pins, with the principle being to place them as close as possible to the high-frequency signals. This ensures the shortest possible path between the power supply and ground.

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PCB Routing and Layout

Bypass capacitors should be evenly distributed around the integrated circuit.

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PCB Routing and Layout

When laying out components, components that use the same power supply should be placed as close together as possible to facilitate future power supply segmentation.

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PCB Routing and Layout

The placement of reactive components used for impedance matching should be arranged appropriately based on their characteristics.

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PCB Routing and Layout

When placing capacitors and resistors for termination, it is important to clearly understand their intended use. For multi-load termination, the termination must be placed at the farthest end of the signal path.

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PCB Routing and Layout

When placing matching resistors, they should be placed close to the signal's drive end, typically no more than 500 mils away.

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PCB Routing and Layout

Adjust the characters so that none of them extend beyond the board edges. Ensure that the character information remains clearly visible after assembly, and that all characters are aligned in both the X and Y directions. The size of the characters and silk-screen printing must be consistent.

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PCB Routing and Layout

Prioritize Critical Signal Lines: Give priority to routing critical signals such as power, small-signal analog, high-speed signals, clock signals, and synchronization signals;

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PCB Routing and Layout

Rule of Minimum Loop Area: The loop area formed by a signal line and its return path should be as small as possible. The smaller the loop area, the less radiation is emitted, and the less external interference is received. In double-sided board design, after reserving sufficient space for the power supply, the remaining area should be filled with reference ground, and necessary vias should be added to effectively connect the signals on both sides. Ground isolation should be used as much as possible for critical signals. For designs operating at higher frequencies, special consideration must be given to signal loop issues on other planes; it is recommended to use multilayer boards.

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PCB Routing and Layout

Rule of Thumb for Ground Leads: Keep ground leads as short as possible and use thicker wires (especially in high-frequency circuits). For circuits operating at different voltage levels, do not use long common ground lines.

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PCB Routing and Layout

When connecting internal circuits to a metal enclosure, use a single-point ground to prevent discharge current from flowing through the internal circuits.

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PCB Routing and Layout

Components sensitive to electromagnetic interference must be shielded to isolate them from components or circuits that generate electromagnetic interference. If such circuits must run near these components, they should be routed at a 90° angle to them.

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PCB Routing and Layout

The wiring layer should be positioned adjacent to the solid metal plane. This arrangement is intended to create a flux cancellation effect.

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PCB Routing and Layout

Numerous loops are formed between ground points; the diameter of these loops (or the distance between ground points) should be less than 1/20 of the wavelength at the highest frequency.

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PCB Routing and Layout

On single-sided or double-sided printed circuit boards, the power and ground traces should be placed as close together as possible. The best approach is to route the power traces on one side of the board and the ground traces on the other side, with the two layers aligned vertically; this minimizes the power trace impedance.

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PCB Routing and Layout

Signal traces (especially high-frequency signals) should be kept as short as possible.

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PCB Routing and Layout

The distance between two conductors must comply with the provisions of electrical safety design codes, and the voltage difference must not exceed the breakdown voltage of the air or insulating medium between them; otherwise, an electric arc will be generated. Within a time span of 0.7 ns to 10 ns, the arc current can reach tens of amperes, and in some cases may even exceed 100 amperes. The arc will persist until the two conductors come into contact and short-circuit, or until the current drops to a level too low to sustain the arc. Examples of situations where spike arcs may occur include contact with a hand or a metal object; care must be taken to identify these during the design process.

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PCB Routing and Layout

Add a ground plane immediately adjacent to the double-sided board, and connect this ground plane to the ground point on the circuit at the shortest possible distance.

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PCB Routing and Layout

Ensure that each cable entry point is no more than 40 mm (1.6 inches) from the bottom of the chassis.

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PCB Routing and Layout

Connect both the connector housing and the metal switch housing to the chassis ground.

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PCB Routing and Layout

Place a wide conductive protective ring around the membrane keyboard, and connect the outer edge of the ring to the metal chassis—or at least to the metal chassis at the four corners. Do not connect this protective ring to the PCB ground.

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PCB Routing and Layout

Use multilayer PCBs: Compared to double-sided PCBs, ground planes, power planes, and tightly spaced signal-to-ground traces can reduce common-mode impedance and inductive coupling to between 1/10 and 1/100 of that found in double-sided PCBs. Whenever possible, position each signal layer adjacent to a power plane or ground plane.

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PCB Routing and Layout

For high-density PCBs that have components on both the top and bottom surfaces, very short trace lengths, and extensive ground fills, internal layers can be used. Most of the signal traces, as well as the power and ground planes, are located on the internal layers, thereby functioning similarly to a Faraday cage.

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PCB Routing and Layout

Place all connectors on one side of the circuit board whenever possible.

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PCB Routing and Layout

On all PCB layers directly beneath the connectors leading out of the chassis (which are susceptible to direct ESD strikes), place a wide chassis ground or a polygonal ground fill, and connect them together with vias spaced approximately 13 mm apart.

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PCB Routing and Layout

When assembling a PCB, do not apply any solder to the mounting hole pads on the top or bottom layers. Use screws with built-in washers to ensure tight contact between the PCB and the metal chassis, shielding layer, or ground plane.

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PCB Routing and Layout

On each layer, an identical “isolation zone” must be established between the chassis ground and the circuit ground; if possible, maintain a spacing of 0.64 mm (0.025 inches).

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PCB Routing and Layout

Set up a ground ring around the circuit to prevent ESD interference: 1. Place a ground ring around the entire perimeter of the circuit board; 2. The width of the ground ring on all layers must be >2.5 mm (0.1 inch); 3. Connect the ground ring with vias every 13 mm (0.5 inch); 4. Connect the ground ring to the common ground of the multilayer circuit; 5. For double-sided boards mounted in a metal enclosure or shielded device, connect the ground ring to the circuit’s common ground; 6. For unshielded double-sided circuits, connect the ground ring to the enclosure ground; Do not apply solder mask to the ground ring so that it can act as an ESD discharge path; include at least one 0.5 mm wide (0.020 inch) gap at some location on the ground ring (on all layers) to prevent the formation of large ground loops; 7. If the circuit board will not be placed inside a metal enclosure or shielding device, do not apply solder mask to the top and bottom layer ground traces on the board, so that they can serve as discharge paths for ESD arcs.

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PCB Routing and Layout

In areas that could be directly struck by ESD, a ground trace must be routed near each signal line.

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PCB Routing and Layout

Circuits susceptible to ESD should be placed in the center of the PCB to minimize the likelihood of being touched.

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PCB Routing and Layout

When the length of a signal line exceeds 300 mm (12 inches), be sure to route a ground wire parallel to it.

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PCB Routing and Layout

Connection guidelines for mounting holes: They may be connected to the circuit’s common ground or isolated from it. 1. When a metal bracket must be used in conjunction with a metal shield or chassis, a 0Ω resistor must be used to establish the connection. 2. Determine the size of the mounting holes to ensure reliable installation of metal or plastic brackets. Use large pads on both the top and bottom layers of the mounting holes; do not apply solder mask to the bottom-layer pads, and ensure that the bottom-layer pads are not soldered using the wave soldering process.

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PCB Routing and Layout

Shielded and unshielded signal lines must not be arranged in parallel.

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PCB Routing and Layout

Routing guidelines for reset, interrupt, and control signal lines: 1. Use high-frequency filtering; 2. Route them away from input and output circuits; 3. Route them away from the edges of the circuit board.

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PCB Routing and Layout

The circuit boards inside the chassis are not installed in the openings or along the internal seams.

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PCB Routing and Layout

Place the circuit boards that are most sensitive to static electricity in the center, where they are less likely to be touched by hand; place the components that are sensitive to static electricity in the center of the circuit boards, where they are less likely to be touched by hand.

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PCB Routing and Layout

Guidelines for bonding two metal blocks: 1. Solid bonding strips are preferable to braided bonding strips; 2. The bonding area must be free of moisture and standing water; 3. Use multiple conductors to connect the ground planes or ground grids of all circuit boards inside the chassis; 4. Ensure that the width of the bonding points and washers is greater than 5 mm.