Can a 100A current flow through a PCB? Tips for setting up high current paths
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The current of a normal PCB design will not exceed 10 A, or even 5 A. Especially in home and consumer electronics, the continuous working current on the PCB usually does not exceed 2 A. However, I recently had to design power traces for my company's products, and the continuous current can reach about 80 A. Considering the instantaneous current and leaving a margin for the entire system, the continuous current of the power traces should be able to withstand more than 100 A.
So the question is, what kind of PCB can withstand a current of 100 A?
Method 1: Routing on PCB
To figure out the current capacity of PCB, we first start with the PCB structure. Take a double-layer PCB as an example. This circuit board is usually a three-layer structure: copper sheet, plate, and copper sheet. The copper sheet is the path for current and signal to pass through in the PCB. According to high school physics knowledge, we know that the resistance of an object is related to the material, cross-sectional area, and length. Since our current is running on the copper sheet, the resistivity is fixed. The cross-sectional area can be regarded as the thickness of the copper sheet, which is the copper thickness in the PCB processing options. Usually the copper thickness is expressed in OZ. The copper thickness of 1 OZ is converted to 35 um, 2 OZ is 70 um, and so on. Then it can be easily concluded that when a large current is to pass through the PCB, the wiring must be short and thick, and the thicker the copper thickness of the PCB, the better.
In practice, there is no strict standard for the length of wiring in engineering. In engineering, the three indicators of copper thickness/temperature rise/wire diameter are usually used to measure the current carrying capacity of PCB boards.
The following two tables can be used for reference:
From the table, we can know that for a 1 OZ copper thick circuit board, at a temperature rise of 10°, a 100 mil (2.5 mm) wide conductor can pass a current of 4.5 A. And as the width increases, the current carrying capacity of the PCB does not increase strictly linearly, but the increase gradually decreases, which is consistent with the actual situation in the project. If the temperature rise is increased, the current carrying capacity of the conductor can also be improved.
Through these two tables, we can get the following PCB wiring experience: increasing copper thickness, widening wire diameter, and improving PCB heat dissipation can enhance the current carrying capacity of PCB.
So if I want to run a current of 100 A, I can choose a copper thickness of 4 OZ, set the trace width to 15 mm, double-sided traces, and add a heat sink to reduce the temperature rise of the PCB and improve stability.
Method 2: Binding Post
In addition to routing on the PCB, you can also use wiring posts to route the wires.
Fix several terminals that can withstand 100 A on the PCB or product housing, such as surface mount nuts, PCB terminals, copper pillars, etc. Then use copper nose terminals to connect the wires that can withstand 100 A to the terminals. In this way, large currents can flow through the wires.
Method 3: Custom copper busbar
Even copper busbars can be customized. Using copper busbars to carry large currents is a common practice in industry. For example, transformers, server cabinets and other applications all use copper busbars to carry large currents.
Attached is the copper busbar current carrying capacity table:
Method 4: Special process
There are also some special PCB processes that may not be available in domestic manufacturers. Infineon Technologies has a PCB that uses a three-layer copper design. The top and bottom layers are signal wiring layers, and the middle layer is a 1.5 mm thick copper layer that is specifically used to lay out the power supply. This PCB can easily handle a small current of more than 100 A.
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