In PCB (printed circuit board) design, clearance refers to the minimum distance between different conductive objects on the circuit board, and its setting needs to comply with various requirements such as electrical performance, manufacturing process, and safety. The following are common gap requirements and related instructions in PCB design:
Table of Contents
1、 Electrical Clearance
Definition: The shortest spatial distance reserved between two conductors of different potentials to avoid breakdown or arc discharge.
Influencing factors:
-Working voltage: The higher the voltage, the larger the required gap (in accordance with international standards such as IEC 60664, UL 60950, etc.).
-Environmental conditions: Humidity and pollution levels (such as dust and salt spray) will reduce insulation strength, and gaps need to be increased.
-Material characteristics: The dielectric strength of the substrate material (such as the voltage resistance of FR-4).
Common electrical clearance standards (reference values)
| Working voltage (AC/DC) | Minimum electrical clearance (recommended value) | Application scenarios |
| ≤ 50V | 0.2~0.5mm | Low voltage digital circuits, consumer electronics |
| 50~250V | 1~3mm | Power circuit, industrial control |
| 250~1000V | 3~8mm | High voltage equipment, power electronics |
| >1000V | Calculated according to standard formula | High voltage power supply, power system |
Example:
-In a 220V AC power circuit, the gap between the live and neutral wires is usually ≥ 2mm, and the gap with the metal casing is ≥ 3mm.
-In the lithium battery protection board, the gap between the battery cell pins and the grounding copper foil should be ≥ 0.5mm to avoid short circuits.
2、 Creepage Distance
Definition: The shortest path distance between two conductors along the surface of an insulating material, used to prevent surface leakage or arc discharge.
Influencing factors:
-Pollution level (IEC standard):
-Level 1 (pollution-free): The creepage distance can be relatively small (such as 0.2mm).
-Level 3 (severe pollution, such as industrial environment): Need to increase the creepage distance (e.g. ≥ 8mm).
-Insulation material group: The lower the CTI (Relative Leakage Traceability Index) of the material, the higher the requirement for creepage distance.
Common creepage distance standards (reference values)
| Working voltage (AC RMS) | Pollution level 2 (general environment) | Pollution level 3 (harsh environment) |
| 50V | 0.8mm | 1.6mm |
| 250V | 3.2mm | 6.4mm |
| 1000V | 12.5mm | 25mm |
Application scenarios:
-In switch mode power supplies, the creepage distance between the primary and secondary circuits must be ≥ 6mm (in compliance with safety certification).
-The PCB of outdoor equipment needs to consider the effects of rainwater and salt spray, and the creepage distance is usually more than 50% greater than the electrical clearance.
3、 Gap between solder pads/vias
Definition: The minimum distance between adjacent pads, pads, and vias, taking into account both welding process and electrical safety.
requirement:
-Manual welding: Gap ≥ 0.3mm to avoid pad adhesion.
-Machine Welding (SMT):
-0402 packaging components: solder pad spacing ≥ 0.25mm;
-Package 0805 and above: Pad spacing ≥ 0.35mm.
-Via and solder pad: The distance between the edge of the via and the edge of the solder pad should be ≥ 0.2mm to avoid drilling and damaging the solder pad.
Example:
-When the pin spacing of QFP packaged chips is 0.5mm, the pad gap should be ≥ 0.25mm to prevent bridging.
-The via in the BGA pad area should be kept at a distance of ≥ 0.15mm from the pad to avoid short circuiting of the solder ball.
4、 Gap between wiring and components/frames
1. Wiring and component body
-Surface mount components (such as capacitors and resistors): The wiring and the edge of the component body should be ≥ 0.2mm to avoid affecting the wiring during component soldering.
-Plug in components (such as electrolytic capacitors and connectors): The wiring and pin hole edges should be ≥ 0.3mm to prevent wire compression during insertion.
2. Wiring and PCB frame
-General requirement: The distance between the wire and the edge of the board should be ≥ 0.5mm to prevent damage to the circuit when cutting the board.
-High voltage scenario: A “no laying zone” should be set up at the edge of the board, and the distance between the wiring and the board edge should be ≥ 2mm to avoid edge discharge.
5、 Gap between power layer and formation
Definition: The distance between the power plane (such as VCC) and the ground plane (GND) affects the interlayer capacitance and anti-interference ability.
requirement:
-Low voltage system (≤ 5V): interlayer spacing ≥ 0.1mm, current carrying capacity can be compensated by increasing copper foil thickness.
-High voltage system (such as 12V or above): The interlayer spacing should be ≥ 0.3mm to prevent interlayer breakdown.
-Attention: The smaller the gap between the power layer and the formation, the larger the interlayer parasitic capacitance, which helps to suppress power noise, but requires balancing processing costs (thin dielectric layer technology is difficult).
6、 Limitations of manufacturing processes on gaps
The processing capability of PCB factories directly affects the design of the minimum gap, and common limitations include:
-Minimum line width/spacing:
-Ordinary process: line width/line spacing ≥ 0.1mm (4mil);
-Precision technology (such as HDI board): can achieve below 0.05mm (2mil), but the cost significantly increases.
-Drilling accuracy: When the through-hole diameter is ≥ 0.3mm, the hole spacing should be ≥ 0.5mm; for small holes (≤ 0.2mm), the spacing should be ≥ 0.3mm to avoid hole wall collapse.
-Solder bridge width: The width of the solder mask layer between adjacent pads is ≥ 0.05mm to prevent solder leakage and short circuit between pads.
7、 Industry standards and certification requirements
PCBs from different fields need to follow specific gap specifications:
-Consumer electronics (such as mobile phones and computers): Follow the IPC-2221 standard, with a gap of ≥ 0.13mm (5ml), and prioritize miniaturization.
-Medical equipment: It must comply with the IEC 60601 standard, and the electrical clearance and creepage distance are usually more than 30% larger than ordinary products to ensure safety.
-Automotive electronics: Following the AEC-Q200 standard, the gap needs to adapt to vibration and temperature changes, usually ≥ 0.2mm, to prevent line breakage during long-term use.
-Aerospace: Implement MIL-P-55110 standard, with extremely strict clearance requirements (such as clearance ≥ 12mm under 1000V voltage), and pass the withstand voltage test.
8、 Practical suggestions for gap design
1. Prioritize referring to safety standards: Based on the product application scenario, consult corresponding standards such as UL, IEC, GB, etc. to avoid certification risks.
2. Reserved process margin: When designing the gap, it should be 50% larger than the minimum process capacity of the factory (such as the minimum line spacing of 0.1mm in the factory, which is designed to be 0.15mm), to reduce the production defect rate.
3. Partition isolation: Maintain a gap of ≥ 1mm between the high-voltage area, high current area, and low-voltage signal area, and isolate them with grounded copper foil to reduce interference.
4. With the help of design tools: using EDA software such as Altium and PADS, the rule checking function (DRC) automatically verifies whether the gap is compliant.
5. Simulation verification: Conduct electric field simulation on high-risk circuits (such as power supply and RF) to confirm whether the gap meets the breakdown voltage requirements.
Summarize
PCB gap design is a key link in balancing electrical performance, manufacturing costs, and safety. When designing, it is necessary to comprehensively consider voltage levels, environmental conditions, process capabilities, and industry standards, and avoid short circuits, leakage, interference, and other issues through reasonable spacing settings. At the same time, sufficient margin should be reserved for production and maintenance. It is recommended that beginners start with standard cases and gradually optimize their designs by combining them with factory process documents.
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