Common Pitfalls for Beginners: Safety Clearance Issues in PCB Design

December 8, 2025

Beginners in PCB design often encounter various pitfalls, such as common clearance issues: spacing between traces, spacing between pads, and more. This article discusses safety clearance issues in PCB design.

Electrical Safety Spacing

1.Spacing Between Wires

This spacing depends on the manufacturing capabilities of the PCB manufacturer. It is recommended to maintain a spacing of at least 4 mil between traces. The minimum spacing refers to the distance between traces, as well as between traces and pads. From a manufacturing perspective, larger clearances are preferable whenever possible. A typical spacing of 10 mil is commonly used.

2.Pad Hole Diameter and Pad Width

According to PCB manufacturers, for mechanical drilling, the minimum pad hole diameter should not be less than 0.2 mm. For laser drilling, the recommended minimum is 4 mil. The tolerance for hole diameters varies slightly depending on the material but is generally controlled within 0.05 mm. The minimum pad width should not be less than 0.2 mm.

3.Spacing Between Pads

Based on PCB manufacturers' capabilities, it is recommended to maintain a spacing of at least 0.2 mm between pads.

4.Spacing Between Copper and Board Edge

The spacing between charged copper and the PCB edge should preferably be no less than 0.3 mm. For large-area copper pours, an inward offset from the board edge is typically required, usually set to 20 mil.

Non-electrical Safety Spacing

1.Character Width, Height, and Spacing

For silkscreen characters, standard values such as 5/30 mil or 6/36 mil are typically used. If the text is too small, it may become blurred during printing.

2.Silkscreen-to-Pad Distance

Silkscreen must not overlap pads, as this would prevent solder from adhering to the silkscreen area during soldering, affecting component placement. Manufacturers generally require an 8 mil spacing. In cases where PCB space is extremely limited, a 4 mil spacing may be acceptable. If silkscreen accidentally overlaps a pad, manufacturers will automatically remove the silkscreen from the pad to ensure proper soldering.

3.Mechanical 3D Height and Horizontal Spacing

During component placement, conflicts in horizontal and vertical spacing with other mechanical structures must be considered. Designers should account for spacing between components and between the finished PCB and the product casing to ensure compatibility in spatial structure and allocate sufficient safety clearances.

Partial Safety Distance Rules

1.High-Voltage Network Spacing Requirements

For -48V power input ports, the creepage distance and electrical clearance between the -48V power and other circuits (except PGND) must exceed 2.0 mm. The creepage distance and electrical clearance between PGND and other circuits must also exceed 2.0 mm.

2.Recommended PCB Manufacturing Trace Width/Spacing

Recommended: 6 mil/6 mil.
Minimum usable: 4 mil/5 mil.
Extreme minimum: 4 mil/4 mil.

3.Solder Mask Bridge

The solder mask bridge should be at least 2 mil (except for densely packed SMD components like QFP packages) to avoid solder bridging during manufacturing.

Recommended Hole Rule Settings

For ICT test vias (pad size 32 mil), the spacing between pins, test pins, test vias, and through-hole pins must not be less than the following:

Test Point Spacing Requirements

a) Center-to-center spacing between two test points (d):Preferred: 85 mil; Acceptable: 70 mil; Avoid: 50 mil.

b) Test point to via spacing (d):Preferred: 20 mil; Minimum: 12 mil.

c) Test point to solder-side component pad edge spacing (d):Preferred: 20 mil; Minimum: 12 mil.For wave-soldered boards: Preferred: 40 mil; Minimum: 25 mil.

d) Test point to solder-side trace spacing (d):Preferred: 20 mil; Minimum: 12 mil.

e) Test point to PCB edge spacing (d):Minimum: 125 mil (only required for sealed-ring fixtures).

f) Test point to locating hole spacing (d):Preferred: 200 mil; Minimum: 125 mil (to facilitate positioning post installation).

Spacing for Through-Hole Pins to Other Pins

The spacing between through-hole pins, SMD pins, and test pins must not be less than the specified values and must also comply with SMD component layout requirements, through-hole component layout requirements, and press-fit component layout requirements.