The relationship between trace width and current in PCB dizayn

This is a problem that has caused many people to have a headache. I found some information from the Internet and sorted it out as follows. We need to know that the thickness of copper foil is 0.5oz (about 18μm), 1oz (about 35μm), 2oz (about 70μm) copper, 3oz (about 105μm) and above.

1. Online forms

The load-bearing value listed in the table data is the maximum current load-bearing value at a normal temperature of 25 degrees. Therefore, various factors such as various environments, manufacturing processes, plate processes, and plate quality must be considered in the actual design. Therefore, the table is provided only as a reference value.

2. The current carrying capacity of copper foil of different thickness and width is shown in the following table:

Note: When using copper as a conductor to pass large currents, the current carrying capacity of the copper foil width should be derated by 50% with reference to the value in the table for selection consideration.

3. The relationship between copper foil thickness, trace width and current in PCB design

Need to know what is called temperature rise: the current heating effect is generated after the conductor is flowed. As time goes by, the temperature of the conductor surface continues to rise until it stabilizes. The stable condition is that the temperature difference before and after within 3 hours does not exceed 2°C. At this time, the measured temperature of the conductor surface is the final temperature of the conductor, and the unit of temperature is degree (°C). The part of the rising temperature that exceeds the temperature of the surrounding air (ambient temperature) is called temperature rise, and the unit of temperature rise is Kelvin (K). In some articles and test reports and test questions about temperature rise, the unit of temperature rise is often written as (℃), and it is inappropriate to use degrees (℃) to express temperature rise.

The PCB substrates usually used are FR-4 materials. The adhesion strength and working temperature of the copper foil are relatively high. Generally, the allowable temperature of the PCB is 260℃, but the actual PCB temperature should not exceed 150℃, because if it exceeds this temperature It is very close to the melting point of solder (183°C). At the same time, the allowable temperature of the on-board components should also be taken into consideration. Generally, civilian-grade ICs can only withstand a maximum of 70°C, industrial-grade ICs are 85°C, and military-grade ICs can only withstand a maximum of 125°C. Therefore, the temperature of the copper foil near the IC on the PCB with civilian ICs needs to be controlled at a lower level. Only high-power devices with higher temperature resistance (125℃～175℃) can be allowed to be higher. PCB temperature, but the effect of high PCB temperature on the heat dissipation of power devices also needs to be considered.