Creepage and Clearance Standards for High-Voltage PCBs

If a high voltage develops between exposed metal on a PCB, electrostatic discharge can occur if the charge exceeds the threshold for dielectric breakdown. This material failure damages components and, in extreme cases, causes board conflagration. Creepage and clearance limits between exposed metal on your PCB are codified in critical industry standards for observation during design and manufacturing. These standards are industry-agnostic, but different standards are broadly application-specific.

When VSE produces a run of PCBs, one of its goals is to comply with standards on creepage and clearance; VSE confirms these distances in design data to ensure adherence during DFM checks. It’s challenging to determine creepage and clearance distances between traces and components on a PCB by the naked eye; various PCB design tools help prevent violations with design rule checklists.

Creepage and Clearance Comparison
Creepage	Clearance
Surface distance between two conductor edges Creepage will always be at least as great as the clearance	Air gap (think as the crow flies) is the distance between two conductor edges Clearance will always be, at most, as great as the creepage

Creepage and Clearance on a PCB

These two terms are closely related and refer to two ways to measure the distance between conductive elements on the surface of a PCB.

There are two ways to measure the distance between two conductors on a board:

• Creepage is the distance along the board’s surface.
• Clearance is the distance in air between two conductors (AKA air gap).

If this needs additional clarification, take a look at the diagram below. This image shows a side view of a PCB with a surface contour between two copper conductors. Creepage is shown in red and follows the surface of the board.

The diagram above suggests that the creepage distance is always larger than the clearance distance, but this is not always true. Consider components with hanging conductive elements/heat sinks where creepage and clearance distances become less distinguishable. In the case below, where two decawatt (DPAK) package components have heat sinks hanging over the pads, the clearance distance uses the overhanging metal edge of the DPAK components.

When laying out components, orientation, spacing, and any overhanging conductors must be considered to ensure observation of creepage or clearance limits. Simply rearranging or shifting components can provide enough clearance between exposed metals for safety standard compliance. In other instances where creepage rule violations occur while clearance is satisfied, one option is to place a notch that passes through the entire circuit board between components. A knowledgeable CM can recommend the best design changes for your board during a DFM check.

Creepage and Clearance in High-Voltage PCB Design

High-voltage PCBs (typically > 60 VDC/30 VAC) face unique creepage and clearance challenges. As voltage increases, so does the risk of dielectric breakdown, arcing, insulation failure, and even conductive anodic filamentation (CAF). Environmental factors like humidity, dust, altitude, pollution, and material CTI directly impact these risks. As a result, manufacturers must apply voltage-based formulas or IPC/IEC tables to set minimum distances. For example, IPC‑2221 (discussed below) raises external conductor spacing from ~0.6 mm at 50 V to ~2.5 mm at 300 V.

The interplay of clearance (air gap) and creepage (surface distance) becomes critical: clearance is the shortest line-of-sight gap, while creepage tracks the insulation surface. Failing to meet either path exposes the board to tracking, flashover, CAF, and sudden failure, especially under combined high voltage and contamination. Intentionally routing with slots, barriers, or conformal coatings can increase creepage without redesigning component layouts.

Important Creepage and Clearance Standards

Several important standards define clearance and creepage distances in a PCB. The best-known standards are IPC-2221, IPC-9592B, UL-61010-1, and UL-60950-1 (second edition). These standards list different creepage and clearance design rules for products in various applications and operating environments. While reproducing every rule in these standards is beyond the scope of this article, designers should con­sult the creepage and clearance limits relevant to their application.

IPC-2221 and IPC-9592B

IPC2221A is a more general standard that specifies creepage and clearance distances. However, the creepage and clearance rules subdivide into different application areas. The limits described in IPC2221 differ by DC or peak AC voltage level, substrate material, etc. Limits for internal and coated or uncoated conductors on external layers are also of consideration. IPC-9592B is more specific in that it defines trace clearance and creepage requirements in power conversion devices running above 100 V.

UL-61010-1

This set of standards specifies safety and design requirements for electrical testing equipment, laboratory equipment, and industrial process control equipment. It excludes several products in different application areas. A complete list of excluded application areas and the relevant UL standards is in Section 1.1.2 of the UL-61010-1 standards.

UL-60950-1

This particular standard essentially replicates the IEC-60950-1 standard for information technology products. This standard specifies high- and low-voltage equipment safety standards, including creepage and clearance distances on a PCB. It is broad enough to cover everything from office to telecommunications equipment.

Component Placement and DFM Risks

Component placement on high-voltage PCBs influences electrical performance, manufacturability, and regulatory compliance. Once mounted, components like DPAKs with exposed pads or overhanging heat sinks can significantly reduce creepage and clearance distances, triggering automatic DFM violations during template checks. For example, a tightly spaced high-voltage MOSFET and its adjacent capacitor may meet clearance on paper but violate creepage when a heatsink hangs over the trace.

Further, tight clearances at board edges elevate the risk of arcing during depanelization. In particular, surface tracking worsens with residual flux and environmental contamination. This requirement is crucial in industrial or humid environments (pollution degree ≥ 2), where moisture-laden dust forms conductive films on board surfaces. Software flags help detect these scenarios, but the layout engineer must preemptively isolate high-voltage clusters, align components to reduce overlap and allocate space for notches, grooves, or barriers. These steps minimize iterative layout cycles, tooling delays, and manufacturing feedback loops.

Best practices include:

• Reserve ≥ 3× component width between high-voltage nets, board edges, or low-voltage zones.
• Orient components to avoid overlapping creepage paths when assembled.
• Deconflict high- and low-voltage regions across layers via silkscreen zones and assembly flags.
• Use board features (slots, notches, grooves) to separate conductive features without compromising routing.

Embedding Creepage and Clearance Rules to Smooth Manufacturing

Embedding creepage and clearance requirements into your PCB can streamline manufacturing and compliance outcomes. Modern ECAD tools allow rule creation tied to IPC‑2221, IPC‑9592, UL/IEC standards, and environmental factors like pollution degree, CTI, and altitude. When high-voltage nets cross a specified threshold (e.g., > 60 VDC), automated checks immediately flag spacing violations, eliminating surprises after board fab.

Adding physical board features such as slots, ribs, or groove barriers at the layout stage significantly raises effective creepage distances at a minimal cost. Slots are the most cost-effective and easy to implement, while notches or grooves can add clearance and simplify flight-test qualification. Conformal coatings, chosen for high CTI and moisture resistance, serve as virtual creepage guards and reduce the danger of circuit tracking in industrial or outdoor settings.

Early compliance with spacing rules also lights the path for smoother factory documentation: net classes, silkscreen instructions, and assembly notes become compliance tools rather than post-hoc corrections. This methodology lowers failure rates during high-voltage testing (e.g., hipot, tracking tests) and accelerates UL or CE certification. According to industry sources, rule-based design can cut production delays by up to 30%, reduce rework costs, and deliver compliant assemblies “first time, every time.”

The Value of a Knowledgeable Partner

Given the list of rules related to PCB creepage and clearance and the complexity they can place on DFM checks, it helps to partner with an experienced CM. Your CM can be a significant asset in ensuring high yield, quality, and safe operation of your new product. If you are looking for a CM that prides itself on its care and attention to detail to ensure that each PCB assembly is built to the highest standards, look no further than VSE. Contact us today to learn more about partnering with us for your next project.