Electrical Guidelines for PCB Design

Various factors determine the current-carrying capacity of a conductor, such as the material it is made of, its width, thickness, and the surrounding environment. Typically, this information is derived from tables and graphs provided by material and electronic component manufacturers.

⚡ Heat dissipation: When current flows through a conductor, it generates heat. The higher the current, the greater the heat produced. Excessive heat can cause damage or even fire, so it is essential to calculate how much heat the conductor can safely dissipate.

🧱 Base material: PCB materials have different thermal dissipation properties. For example, FR-4 (a standard PCB substrate) has different heat transfer characteristics compared to metal-core materials.

📏 Conductor width: Wider conductors have lower resistance and can carry higher currents with reduced heat loss.

🌡️ Temperature coefficient of resistance: As a conductor heats up, its resistance increases. This rise in resistance can limit the maximum current that can flow through it.

🔥 TG coefficient: The Glass Transition Temperature (TG) is a crucial factor in determining a PCB’s current-carrying capacity. It indicates the temperature at which the PCB material transitions from a rigid to a more elastic or glassy state. At elevated temperatures, the material softens, which can lead to deformation or even failure of the board.

1. Minimum Distances on Printed Circuit Boards

The following table provides only approximate values and does not guarantee accuracy. These values are valid for typical Central European conditions and for boards protected from environmental influences. In harsh environments (e.g., moisture, chemical pollution, high altitude, or high temperature), different values apply.

Voltage Between Conductors (V)	Min. Distance Without Solder Mask (mm)	Min. Distance Without Solder Mask (mil)	Min. Distance With Solder Mask (mm)	Min. Distance With Solder Mask (mil)
0–29.99 V	0.64	25	0.254	10
30–49.99 V	0.64	25	0.38	15
50–99.99 V	0.64	25	0.50	20
100–149.99 V	1.27	50	0.50	20
150–299.99 V	1.27	50	0.76	30
300–499.99 V	2.54	100	1.52	60
>499.99 V	0.05 mm/V	0.2 mil/V	0.003 mm/V	0.12 mil/V

After final assembly, solder joints and components can be additionally protected to improve insulation and safety.

2. Current-Carrying Capacity of PCB Traces

The following table provides only approximate reference values. In practice, the current-carrying capacity depends on many factors. Exact calculation is complex, and the provided information comes without warranty. The data applies to typical Central European conditions with protection from environmental effects.

Consider heat dissipation from the circuit board. The following values are valid for up to 30 °C ambient temperature. When a single layer is insufficient for the required current, use a through-hole PCB with traces on both sides connected by vias.

Trace Width (mm / mils)	Current Capacity at 17.5 µm / 0.5 oz (A)	Current Capacity at 35 µm / 1 oz (A)	Current Capacity at 70 µm / 2 oz (A)
0.2 mm / 8 mils	0.5	1.0	1.5
0.5 mm / 20 mils	1.2	2.0	3.2
1.0 mm / 40 mils	2.0	4.0	6.2
1.5 mm / 60 mils	3.0	5.0	8.1
2.0 mm / 80 mils	3.3	6.0	10.0
4.0 mm / 160 mils	6.0	10.0	16.0
6.0 mm / 240 mils	8.3	14.0	22.0
10.0 mm / 400 mils	12.0	21.0	Not applicable

A 3A current applied to a 60 mil-wide trace (35µm/1oz copper) will heat it by approximately 10 °C above room temperature.

3. Current-Carrying Capacity of Vias

Holes used for through-hole components are electrically reinforced by the component leads themselves, and therefore do not limit current capacity.

Drill Diameter (mm/mils)	Allowable Current (A)
0.4 mm / 16 mils	2.5
0.5 mm / 20 mils	3.0
0.6 mm / 24 mils	3.5
0.7 mm / 28 mils	4.0
0.8 mm / 32 mils	5.0