What Are Creepage and Clearance?

Struggling with mysterious short circuits or failed safety tests? Electrical safety in your PCB design might be the culprit. These issues often trace back to overlooking two critical design parameters.

Creepage is the shortest path between two conductive parts along the surface of an insulating material. Clearance is the shortest distance between two conductive parts through the air. Both are vital for preventing electrical hazards.

Understanding creepage and clearance is not just about passing certification; it's about designing safe and reliable products. As a hardware engineer with nearly 20 years of experience, I've seen how crucial these distances are, especially in high-voltage applications or devices operating in challenging environments. Ignoring them can lead to product recalls, safety hazards, and significant redesign costs. Let's dive deeper into what these terms mean and why they matter so much in your PCB designs.

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What Is the Difference Between Creepage and Clearance?

Confused about whether you're measuring along a surface or through the air? You're not alone. Many engineers initially mix these up, but the distinction is critical for safety.

Clearance is the shortest distance in air between two conductors, like a direct flight. Creepage is the shortest path along the surface of an insulator between them, like a winding road.

Think of it this way: if you have two exposed copper traces on a PCB, clearance is the straight-line distance you'd measure if you could float a ruler directly between them. Creepage, however, means you have to trace the path an ant would walk along the PCB surface to get from one trace to the other. This path can be longer if there are grooves, slots, or barriers.

Key Distinctions at a Glance

To further clarify, here's a simple breakdown:

Feature	Clearance	Creepage
Medium	Through air	Along the surface of an insulator
Path Type	Shortest straight-line distance (3D)	Shortest path along surface (2D, contoured)
Primary Risk	Dielectric breakdown of air (arcing)	Surface tracking (current leakage)
Influenced by	Air pressure (altitude), transient voltage, humidity	Surface contamination (pollution), material CTI, humidity

In one of my early designs for an industrial controller, we had an issue with intermittent faults in a humid environment. The clearance was fine, but the creepage distance was insufficient for the material and pollution level, leading to surface tracking. We had to respin the board with added slots to increase the creepage path—a lesson learned the hard way. Understanding this fundamental difference is the first step to designing safe PCBs.

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Why Are Creepage and Clearance Important in PCBs?

Wondering if these safety distances are really that big a deal? Ignoring them can lead to arcing, tracking, and ultimately, product failure or even safety hazards like fire or shock.

Creepage and clearance are vital for preventing electrical arcing between conductors (clearance) and current leakage or tracking across insulator surfaces (creepage), ensuring product safety and long-term reliability.

These parameters are not just arbitrary numbers; they are fundamental to electrical safety.

Preventing Electrical Hazards

Clearance prevents dielectric breakdown of air, where a high voltage difference can cause an arc (a spark) to jump between two conductive parts. This is especially critical for high-voltage circuits, as arcing can cause immediate failure, component damage, or even fire.

Creepage, on the other hand, prevents tracking. Tracking is the slow formation of a conductive carbon path on the surface of an insulating material. This happens due to the prolonged effect of electrical stress in the presence of environmental contaminants (like dust and moisture). Imagine these contaminants accumulating on a PCB surface; over time, they can create a leakage path for current to flow where it shouldn't, leading to shorts or fires.

Consequences of Inadequate Distances

Issue	Primary Cause (Insufficient...)	Potential Consequences	Affected Products (Examples)
Arcing	Clearance	Short circuit, component destruction, fire, shock hazard	Power supplies, high-voltage circuits
Tracking	Creepage	Current leakage, insulation breakdown, fire, malfunction	Devices in humid/dusty environments
Safety Test Failure	Both	Product recall, redesign costs, loss of certification	All regulated electronic equipment
Reduced Reliability	Both	Intermittent faults, premature product failure, field returns	Consumer and industrial electronics

I recall a project involving a security system keypad designed for global markets. We had to be extremely careful with creepage and clearance to meet diverse international standards like IEC 62368-1¹. Failure to do so would mean no certification and no market access. These distances directly impact the safety against electric shock for the end-user and the reliability of the device.

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How Do You Measure Creepage Distance?

Unsure how to properly trace the path along an insulator's surface? Incorrect measurement can lead to designs that fail safety tests, even if you think you've allowed enough space.

To measure creepage, trace the shortest path along the surface of the insulating material between two conductive parts. This path follows the contours, including going into grooves and around barriers.

Measuring creepage requires careful attention to the surface profile. It's not a simple straight-line measurement if the surface isn't flat and unobstructed.

Accounting for Surface Features

Several surface features can influence the creepage path and its measurement, as detailed by standards like IEC 60664-1² (Insulation coordination for equipment within low-voltage systems - Part 1: Principles, requirements and tests):

Feature Type	Condition for Adding to Creepage Path	Measurement Rule (Simplified from IEC 60664-1)	Example Impact on Path
Groove/Slot	Width 'X' ≥ 1 mm, any depth	Measure along the contour of the groove/slot.	Adds twice the depth (if not through-slot)
Groove	Width 'X' < 1 mm	Limited by 'X'; if X ≥ depth 'Y', adds 'Y'.	May add less than its full contour
Rib	Height 'H' is significant (e.g., ≥ 2mm, width ≥ 1mm)	Measure along the contour of the rib.	Adds twice the height + top width
Uncemented Joint	Gap width 'X' < 1 mm	Shortest path across joint if gap < 1mm per side.	May shorten effective creepage distance

When I worked on a medical infusion pump, we had to be meticulous about creepage. These devices are used in potentially life-critical situations and often in environments where cleaning fluids (potential contaminants) are present. We used 3D models and physical measurements on prototypes to verify these distances, ensuring no conductive path could form over time. For instance, if a groove designed to increase creepage was too narrow (e.g., X < 1mm), its contribution to the path length was reduced according to the standard, potentially requiring us to make it wider or find alternative ways to meet the requirement.

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How Do You Measure Clearance Distance?

Think it's just a simple straight-line measurement? While seemingly straightforward, overlooking certain factors can lead to insufficient clearance and safety hazards like arcing.

Clearance distance is the shortest straight-line path through air between two conductive parts or between a conductive part and an earthed enclosure. It's measured "as the crow flies."

Measuring clearance is generally simpler than creepage because it's a direct spatial distance.

Key Measurement Points and Considerations

• Between Traces/Pads: The shortest air gap between any two exposed conductive elements.
• Component to Component/Trace: From a conductive part of one component to another, or to a trace/pad.
• High-Voltage to Chassis/Enclosure: Crucial for safety against shock if the enclosure is touchable.
• 3D Space: Clearance must be considered in all three dimensions, not just on the PCB surface. This includes parts on opposite sides of the board if there are openings.

According to IEC 62368-1, the minimum clearance depends on several factors, as illustrated below:

Factor Influencing Clearance	How it's Used in Standards (e.g., IEC 62368-1 Table 5)	Example Impact
Peak Working Voltage	Directly used for some calculations.	Higher peak voltage typically needs more clearance.
Required Impulse Withstand Voltage	Primary input for clearance tables. Determined by OVC and mains voltage.	A 2500V impulse needs more clearance than a 1500V impulse.
Pollution Degree	Can influence, but primarily for creepage. PD3 can demand larger clearances in some cases.	Less critical for clearance than for creepage.
Altitude	Correction factor applied to sea-level clearance value.	Higher altitude requires significantly more clearance.

For example, in the power supply section of the Tuxedo Keypad at Honeywell, we had to ensure adequate clearance between primary (mains connected) and secondary (low-voltage) circuits. For a peak working voltage of 300V in a Pollution Degree 2 environment, an impulse withstand voltage of 2500V might be required (based on Overvoltage Category II for a 230V system), translating to a clearance of around 1.5 mm to 2.0 mm from tables in IEC 62368-1 for basic insulation. Always measure the absolute shortest path.

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What Factors Affect Creepage and Clearance Requirements?

Is it just voltage, or are there other hidden influences on these crucial safety distances? Many factors come into play, and missing one can compromise your design's safety and compliance.

Key factors include working voltage, pollution degree of the environment, Comparative Tracking Index (CTI) of the PCB material, overvoltage category, and operating altitude.

Designing for appropriate creepage and clearance isn't a one-size-fits-all situation.

Breakdown of Influencing Factors

Factor	Primarily Affects	Description	Typical Impact on Distance Required	Standard Reference (Example)
Working Voltage	Both	RMS or DC voltage continuously present. Peak voltage also critical for clearance.	Higher voltage → Larger distance	IEC 60664-1, IEC 62368-1
Pollution Degree (PD)	Creepage (mainly)	Environmental contamination level (dust, moisture).	Higher PD → Larger distance	IEC 60664-1
Material CTI	Creepage	Insulating material's resistance to tracking.	Lower CTI → Larger distance	IEC 60112, IEC 60664-1
Overvoltage Category (OVC)	Clearance	Expected transient overvoltages from the mains supply (e.g., due to lightning or switching).	Higher OVC → Larger distance	IEC 60664-1
Altitude	Clearance	Operating height above sea level, affecting air's dielectric strength.	Higher altitude → Larger distance	IEC 60664-1 (Table A.2)
Insulation Type	Both	Basic, Supplementary, Reinforced, Double. Each has different requirements.	Higher safety level → Larger distance	Product safety standards
Frequency	Clearance	For frequencies >30 kHz, clearance requirements may need adjustment.	Higher frequency → May need more	IEC 60664-4

During the development of an aerospace sensor module, altitude was a major consideration. We had to apply correction factors of over 1.4x to our sea-level clearance calculations. For creepage, the choice of a high CTI (Material Group I) laminate was crucial due to the compact design, even in a relatively controlled internal environment (PD2).

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What Is Pollution Degree in Creepage and Clearance?

Think your office environment is clean enough to ignore pollution? Even seemingly clean environments can have contaminants that affect PCB reliability over time if not accounted for in safety distances.

Pollution Degree quantifies the amount and type of environmental contaminants (dust, moisture) that can reduce insulation effectiveness. It directly impacts required creepage distances.

Pollution Degree (PD) is a critical concept defined in standards like IEC 60664-1. It classifies the expected environmental conditions.

Understanding Pollution Degree Levels (IEC 60664-1)

Pollution Degree	Description	Typical Environment Examples	Main Consequence for Design
PD1	No pollution or only dry, non-conductive pollution. Pollution has no influence.	Sealed enclosures, potted assemblies, clean rooms.	Smallest creepage distances allowed.
PD2	Only non-conductive pollution occurs. Occasional temporary conductivity by condensation.	Office, laboratory, typical home environments.	Standard creepage distances for many products.
PD3	Conductive pollution, or dry non-conductive pollution that becomes conductive by condensation.	Industrial areas, workshops, garages, some outdoor locations (sheltered).	Significantly larger creepage distances.
PD4	Persistent conductivity occurs (e.g., conductive dust, rain, snow, salt spray).	Exposed outdoor equipment, harsh industrial settings.	Largest creepage; often requires special measures like potting or robust enclosures.

My work with photonic computing chips often involved designs for very controlled, clean environments where the core optical components were sealed, effectively creating a local PD1 environment. In contrast, the Tuxedo Keypad, intended for general indoor use, was designed for PD2. For an industrial motor controller I encountered earlier in my career, it had to meet PD3 due to the factory floor environment, which meant much larger spacing or careful use of conformal coating.

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What Is CTI (Comparative Tracking Index) and How Does It Relate to Creepage?

Ever wondered why some PCB materials are better at preventing surface breakdown? The CTI value of your laminate is a crucial factor, directly influencing the minimum creepage distance needed.

CTI measures an insulating material's resistance to tracking. A higher CTI means better resistance, allowing for smaller creepage distances for a given voltage and pollution degree.

The Comparative Tracking Index (CTI) is a figure, in volts, that indicates an insulating material's resistance to surface tracking. The test method is defined in IEC 60112. Materials are then grouped based on their CTI values.

Material Groups Based on CTI (IEC 60664-1)

Material Group	CTI Value Range (Volts)	Typical Materials	Relative Creepage Distance Required (for same Voltage & PD)
I	CTI ≥ 600	Specialized laminates (e.g., some polyimides, ceramics), glass	Smallest
II	400 ≤ CTI < 600	Better FR-4 variants, some engineering plastics	Smaller
IIIa	175 ≤ CTI < 400	Standard FR-4, many common plastics	Larger
IIIb	100 ≤ CTI < 175	Lower-grade phenolics, some basic plastics	Largest

Standard FR-4 PCB laminate often falls into Material Group IIIa. When designing a compact power module where board space was at a premium, I specifically sourced an FR-4 variant with a certified CTI of 600V (Material Group I). This allowed us to meet the creepage requirements with significantly smaller conductor spacing than if we had used a standard IIIa material, saving valuable PCB real estate. The cost of the material was higher, but it was a necessary trade-off for miniaturization.

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What Are the Common Standards for Creepage and Clearance?

Feeling lost in a sea of safety regulations? Knowing which standards apply to your product is the first step towards compliant and safe design, guiding your creepage and clearance calculations.

Key international standards include IEC 62368-1 (AV/ICT equipment), IEC 60950-1 (older ITE), IEC 60664-1 (insulation coordination), and IEC 60601-1 (medical electrical equipment). IPC-2221B also provides generic guidance.

Navigating safety standards is critical. Here's an overview:

Overview of Key Standards and Their Relevance

Standard	Full Title / Main Focus	Primary Application Domain	Key Relevance for Creepage/Clearance
IEC 62368-1	Audio/video, information and communication technology equipment – Part 1: Safety requirements	Modern electronics (computers, AV, telecom, office machines)	Current primary standard for most new designs; uses hazard-based principles (HBSE).
IEC 60950-1	Information technology equipment – Safety – Part 1: General requirements	Older ITE (being replaced by IEC 62368-1 but still used for existing products)	Prescriptive rules; many concepts are foundational.
IEC 60664 Series	Insulation coordination for equipment within low-voltage systems (multiple parts)	Fundamental, cross-product; referenced by many other standards	Defines PD, CTI, OVC; provides base tables for distances. Part 3 covers coating/potting. Part 4 covers high frequency.
IEC 60601-13	Medical electrical equipment – Part 1: General requirements for basic safety and essential performance	Medical devices (diagnostic, therapeutic, monitoring)	Very stringent requirements; defines Means of Patient/Operator Protection (MOPP/MOOP).
IPC-2221B	Generic Standard on Printed Board Design	General PCB design practices (not a safety compliance standard)	Provides industry guidelines, e.g., conductor spacing tables based on voltage, useful for non-agency designs.
UL Standards (e.g., UL 62368-1)	Various standards published by Underwriters Laboratories	North American market access (often harmonized with IEC)	National deviations and specific requirements for US/Canada.

My experience with medical infusion pumps at Smiths Medical, for instance, relied heavily on IEC 60601-1. The creepage and clearance distances for MOPP were significantly larger than for general ITE, directly impacting PCB size and layout. For the Tuxedo Keypad at Honeywell, IEC 60950-1 (and later IEC 62368-1) was central.

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How Does Voltage Level Affect Required Creepage and Clearance?

Is a few extra volts really going to change your layout significantly? Yes, voltage is a primary driver, and the relationship isn't always linear, especially when considering safety margins and standards.

Higher operating or transient voltages require proportionally larger creepage and clearance distances to prevent arcing, tracking, and ensure safety. This relationship is detailed in safety standard tables.

The working voltage and potential transient overvoltages are fundamental.

Voltage Types and Their Impact

Voltage Aspect	Relevance To	How It Influences Distance Requirements (General Principle)	Example Standard Reference
RMS Working Voltage	Creepage	Higher continuous voltage stress increases risk of tracking.	IEC 60664-1, Table F.4
DC Working Voltage	Creepage	Similar to RMS, higher voltage means more stress.	IEC 60664-1, Table F.4
Peak Working Voltage	Clearance	Higher peak can initiate dielectric breakdown of air.	IEC 60664-1, Table F.2
Required Impulse Withstand Voltage	Clearance	Dictates ability to survive transient overvoltages (e.g., from lightning).	IEC 60664-1, Table F.2 (derived from OVC)

Here's an illustrative (simplified) example of how distances might change based on IEC 62368-1 (Basic Insulation, PD2, Material Group IIIa for creepage):

Parameter	Scenario 1 Example	Scenario 2 Example
Impulse Withstand Voltage	1500V (e.g., 120V OVC II)	4000V (e.g., 400V OVC III)
Resulting Min. Clearance	~0.8 mm	~3.0 mm
RMS Working Voltage	100V	400V
Resulting Min. Creepage	~1.0 mm	~4.0 mm

Note: These are illustrative. Actual values must be determined from current standards for the specific application. During the design of a power distribution unit for industrial automation that handled 480V AC (OVC III), the required clearance was around 5.5mm and creepage around 8.0mm for basic insulation. This was a huge jump from the <1mm requirements for low voltage logic on the same board.

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How Does Altitude Affect Clearance Distances?

Designing for a mountaintop observatory or an avionics system? If your product operates at high altitudes, standard sea-level clearance values might not be safe due to thinner air.

At higher altitudes, air density decreases, reducing its dielectric strength. Therefore, clearance distances must be increased by a correction factor to maintain the same level of insulation.

Air's insulating capability degrades as it thins.

Applying Altitude Correction Factor⁴s (IEC 60664-1, Table A.2)

The sea-level clearance value (valid up to 2000m) is multiplied by these factors:

Altitude (meters)	Altitude (feet, approx.)	Correction Factor	Example: 3.0mm Sea-Level Clearance becomes:
≤ 2000	≤ 6560	1.00	3.00 mm
3000	9840	1.14	3.42 mm
4000	13120	1.29	3.87 mm
5000	16400	1.48	4.44 mm
6000	19685	1.70	5.10 mm
7000	22965	1.95	5.85 mm
8000	26245	2.20	6.60 mm
10000	32800	2.72	8.16 mm

I remember working on an avionics sensor system for a high-altitude drone. The operating altitude was specified up to 30,000 feet (around 9144 meters). We had to apply a correction factor of approximately 2.5 (interpolated from the table) to all external clearances, which significantly impacted connector choices and enclosure design. Creepage distances are generally not affected by altitude.

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What Are Typical Creepage and Clearance Values for Mains Voltage?

Dealing with 120V or 230V AC and unsure about safe spacing? While specific values vary, general guidelines from standards offer a starting point for these common voltages.

For 230V AC mains, Pollution Degree 2, Material Group IIIa (e.g., FR-4), typical basic insulation clearance might be ~2.0-2.5mm (based on 2500V impulse), and creepage ~2.5mm. For 120V AC, these may be slightly less.

Let's illustrate with examples based on IEC 62368-1 for equipment connected to a mains supply.

Example Scenario: 230V AC Mains (Basic Insulation)

Parameter	Assumption / Value (IEC 62368-1)	Resulting Value (Illustrative)
Nominal Voltage	230V AC RMS	-
Overvoltage Category (OVC)	II (pluggable equipment)	-> Impulse Withstand 2500V
Pollution Degree (PD)	2 (home/office)	-
Min. Clearance Required	Based on 2500V Impulse, PD2 (Table 5 / F.2 IEC 60664-1)	2.0 mm
Material Group (CTI)	IIIa (standard FR-4, 175 ≤ CTI < 400V)	-
Min. Creepage Required	Based on 230V RMS, PD2, Mat Grp IIIa (Table 6 / F.4 IEC 60664-1)	2.5 mm

Example Scenario: 120V AC Mains (Basic Insulation)

Parameter	Assumption / Value (IEC 62368-1)	Resulting Value (Illustrative)
Nominal Voltage	120V AC RMS	-
Overvoltage Category (OVC)	II	-> Impulse Withstand 1500V
Pollution Degree (PD)	2	-
Min. Clearance Required	Based on 1500V Impulse, PD2 (Table 5 / F.2 IEC 60664-1)	0.8 mm
Material Group (CTI)	IIIa	-
Min. Creepage Required	Based on 120V RMS, PD2, Mat Grp IIIa (Table 6 / F.4 IEC 60664-1)	1.25 mm (or 1.6mm if voltage band considered >125V)

These values are simplified examples. Always consult current standards. During my time at Honeywell, designing the Tuxedo Keypad which used an external mains adapter, we still had to ensure these internal spacings were met for any primary-side components within the adapter itself, and for any connections from the adapter input to internal circuitry if it wasn't fully isolated to SELV (Safety Extra Low Voltage).

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Can Conformal Coating Reduce Creepage Requirements?

Hoping to shrink your board by using conformal coating? While it helps, it's not a magic bullet and its effectiveness depends on proper application and qualification.

Yes, a properly applied conformal coating of suitable type and thickness can reduce creepage requirements by effectively improving the local pollution degree around conductors, often to Pollution Degree 1.

Conformal coating provides a dielectric barrier. IEC 60664-3 guides its use.

Impact of Conformal Coating

Aspect	Effect of Proper Conformal Coating	Standard Reference
Local Pollution Degree	Can improve to PD1, even if ambient is PD2 or PD3.	IEC 60664-3
Creepage Distance	Can be reduced based on PD1 values for the given voltage/CTI.	IEC 60664-1 Tables
Clearance Distance	Generally not reducible by coating (it's an air gap).	-
Type of Protection (IEC 60664-3)	Type A (General), Type B (Humidity), Type C (Harsh Environment)	IEC 60664-3

Key Considerations for Using Conformal Coating

Consideration	Importance
Coating Material	Acrylic, urethane, silicone, epoxy, parylene. Choice depends on environment, temp, flexibility, repairability.
Application	Must be uniform, good adhesion, no bubbles/pinholes/cracks, complete coverage (especially sharp edges).
Qualification	Often requires testing (e.g., dielectric strength, adhesion, thermal cycling) to prove effectiveness.
Thickness	Must meet minimum specified thickness for the coating type and desired protection level.
Masking	Connectors, test points, and some components may need to be masked before coating.

In a project involving an outdoor sensor unit exposed to humidity and salt fog (PD3/PD4 conditions), we used a specialized silicone conformal coating. This allowed us to meet stringent creepage requirements in a compact design. The coating process itself was a critical, highly controlled manufacturing step, including specific curing profiles and 100% inspection for coverage and defects.

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How Do Slots and Barriers Affect Creepage Distance?

Need to increase surface insulation without making your PCB bigger? Slots and barriers are common techniques to extend the creepage path effectively within a limited area.

Slots (cutouts) and insulating barriers force the creepage path to follow a longer route along the insulator surface, effectively increasing the creepage distance between conductors without increasing their direct separation.

These features are vital for compact, safe designs.

Using Slots (Cutouts)

Slots are openings milled through the PCB.

• Path Extension: Force creepage around the slot.
• Effectiveness (IEC 60664-1):

Slot Width (X)	Impact on Creepage Calculation (Simplified)
X ≥ 1.0 mm	Path measured fully along contour of slot ends.
X < 1.0 mm	Contribution to path may be limited or discounted.
Slot bridges two lands	The creepage path is now the sum of two air clearances across the slot plus the path around the slot's ends on the PCB.

Using Barriers (Ribs)

Barriers are raised insulating ridges on the PCB surface.

• Path Extension: Force creepage up, over, and down the barrier.
• Effectiveness (IEC 60664-1):

Barrier Feature	Condition for Adding to Creepage Path
Height (H)	Typically ≥ 2 mm (varies by standard/application)
Width (W)	Often ≥ 1 mm for stability and effectiveness
Profile	Shape influences exact path length calculation.

I’ve often used slots under optocouplers to separate primary and secondary circuits. For a high-density power supply, we molded insulating barriers directly into the plastic casing, which then pressed against the PCB, creating defined creepage paths between high-voltage sections. The key is that the barrier must be of the same or better CTI material as the PCB and form a tight seal with the PCB surface if it's a separate part.

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What Tools Are Used to Calculate or Check Creepage and Clearance?

Manually checking every critical net can be tedious and error-prone. Fortunately, modern EDA tools and specialized calculators can help automate and verify these vital safety distances.

EDA software (e.g., Altium Designer, Cadence Allegro) often has built-in DRCs for creepage/clearance. Specialized tools like Saturn PCB Toolkit and online calculators also exist for specific standard-based calculations.

Various tools can assist in this critical task.

Comparison of Tool Types

Tool Type	Examples	Key Functionality	Pros	Cons
EDA Software	Altium Designer, Cadence Allegro/OrCAD, Siemens EDA PADS/Xpedition, KiCad	Integrated DRC for clearance and (sometimes basic) creepage. 3D clearance checks.	Integrated with design, automated, can handle complex geometries.	Creepage rule setup can be limited/complex. 3D accuracy depends on models.
Specialized Calculators	Saturn PCB Toolkit, various online tools	Implement tables/formulas from standards (IEC 60950-1, IEC 62368-1, IPC-2221).	Quick estimations, good for understanding standard rules, often free.	Not integrated, rely on manual input, may not cover all scenarios/revisions.
Gerber Viewers with Measurement	Gerbv, ViewMate, GC-Prevue	Manual measurement on final manufacturing data (Gerber/ODB++).	Verifies final output, good for sanity checks.	Manual, time-consuming for full check, 2D only unless advanced.
Physical Measurement Tools	Calipers, microscope with reticle, feeler gauges	Measurement on actual prototypes or products.	Verifies actual built product, accounts for manufacturing variations.	Destructive (if cross-sectioning), slow, needs physical sample.
Field Solvers / Simulators	COMSOL, Ansys Maxwell (for advanced cases)	Simulate electric fields to analyze breakdown voltage.	Highly accurate for complex geometries/materials.	Complex, expensive, specialized expertise needed, overkill for most PCBs.

I heavily rely on Altium's DRC, setting up detailed constraint classes and rules. For instance, creating different clearance rules for SELV nets versus primary mains nets. However, for complex creepage paths involving slots or barriers, a manual check against the standard's calculation rules is often still needed, or I use a specialized calculator for a baseline. Physical measurement on first articles is a must for critical safety spacings.

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What Are Some Common Creepage and Clearance Mistakes in Design?

Think your design is safe because the EDA tool shows no errors? Subtle mistakes in applying creepage and clearance rules can still slip through, leading to compliance failures or field issues.

Common errors include: misinterpreting pollution degree, ignoring CTI, insufficient clearance under components, forgetting altitude effects, incorrect rule setup in EDA tools, and relying solely on minimum standard values without safety margins.

Over my years, I've seen several recurring mistakes:

Environmental and Material Misjudgments

• Optimistic Pollution Degree: Assuming PD1 or PD2 for a product that will see harsher, PD3 conditions without adequate sealing or coating.
• Unknown or Incorrect CTI: Not verifying the CTI of the specified PCB laminate. Using a generic FR-4 CTI value (e.g., assuming 175V) when it could be lower (e.g., 100V) or if a higher CTI material was intended but not properly specified for purchasing.
• Ignoring Altitude: Forgetting altitude correction for clearance if a product might be deployed in mountainous regions or avionics.

Dimensional and Layout Oversights

• Hidden Clearances: Overlooking clearance under components (e.g., between underside of an IC and traces passing beneath it) or 3D clearances (e.g., a tall capacitor to a chassis lid).
• Component Placement: Placing high-voltage and low-voltage components too close without considering their terminal spacing or body dimensions. For example, the clearance between the pins of a relay coil (low voltage) and its contacts (high voltage).
• Board Edge Neglect: Insufficient clearance between live traces and the PCB edge, especially if that edge is near conductive mounting hardware or an enclosure.
• Insufficient Slot Width/Depth: Making slots too narrow (<1mm) or grooves too shallow to be fully effective per standards.

Process, Tooling, and Documentation Errors

• Flawed EDA Rules: Incorrectly configured design rules in EDA tools, or rules not covering all necessary net-to-net or net-to-object interactions.
• Coating Assumptions: Relying on conformal coating to solve all creepage issues without a controlled process, proper material selection, or qualification.
• No Safety Margin: Designing to the absolute minimum values from standards. Manufacturing tolerances, assembly variations, or unexpected environmental stresses can erode these minimums. I always add at least a 10-25% margin depending on criticality.
• Documentation Gaps: Failing to document specific creepage/clearance requirements on assembly drawings or fabrication notes, especially if special features like barriers or specific CTI materials are needed.

I once debugged a field failure in an industrial controller where intermittent resets occurred in humid conditions. The design met calculated creepage for PD2, but the actual site was closer to PD3. A small design change adding wider slots and specifying a conformal coat resolved it, but it was a costly field fix.

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Conclusion

Creepage and clearance are fundamental for safe, reliable PCBs. Understanding these distances, the many factors influencing them, and relevant international standards is absolutely essential for every hardware engineer.

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